Complete Denture Prosthetics

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Complete Denture ProstheticsThird EditionD.J. Neill DFC, MDS, FDSRCS(Eng)Emeritus Professor of Prosthetic Dentistry, University of London

R.I. Nairn MSc, SDS, FDSRCS(Eng)Department of Prosthetic Dentistry, United Medical and Dental Schools of Guy's and St Thomas's Hospitals,London

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First published 1990

© Butterworth-Heinemann Ltd, 1990

British Library Cataloguing in Publication Data

Neill, D.J. (Derrick James) 1922-Complete denture prosthetics.-3rd. ed.1. Prosthetic dentistry. Laboratory techniquesI. Title II. Nairn, R.I (Robert Ian) 1929617.69028

ISBN 0-7236-2063-6

Library of Congress Cataloging-in-Publication Data

Neill,D.J.Complete denture prosthetics / D.J. Neill, R.I. Nairn. -- 3rd ed.

p. cm.Includes bibliographical references.ISBN 0-7236-2063-6:1. Complete dentures. I. Nairn, R.I. II. Title.[DNLM: 1. Denture, Complete. WU 530 NA411c]

RK656.N42 1990617.6'92--dc20DNLM/DLCfor Library of Congress 90-12184

CIP

Typeset by Scribe Design, Gillingham, KentPrinted in Great Britain at the University Press, Cambridge

Preface to third edition

Despite the passage of time we see no reason to alterthe principles enunciated in the first edition. Thetechniques which we have used to illustrate theapplication of these principles are not immutable,and may be modified as advances in materialsscience provide us with alternatives. We have,however, made a number of revisions of the text.

Associated topicsFollowing the clinical and laboratory techniquesdescribed in Part I, we have provided in Part IIinformation on a number of associated topics whicharise from the consideration of the principles andtechniques of complete denture construction. Muchof this is new material.

The coverage is by no means meant to becomprehensive, but to give a summary outline

covering the most important principles of the topics.It is hoped that they will give the reader someunderstanding which he can use as a basis for furtherstudy.

We have included here a critique of the osseointe-grated implant procedures to provide the readerwith a brief insight into this interesting developmentin the field of denture prosthetics.

As practitioners and technicians may be facedwith the treatment of patients suffering from serumhepatitis and HIV, advice is included on the stepswhich should be taken to protect the operator andtechnician from contamination.

Reviewers of earlier editions have suggested thatwe should include a reading list to augment thefootnotes found in the text, and so we have prepareda bibliography which has been inserted at the end ofthe book.

iii

Preface to the first edition

Prosthetic Dentistry is concerned with the applica-tion of the physical and biological sciences and theacquisition of manual skills. We cannot stress toostrongly the importance of understanding thereasons underlying the choice of materials andtechniques, and it has been our intention to rational-ize the procedures described. These are, of course,other techniques which may be equally effectiveand, providing the student has a clear idea of theobjective in view, an understanding of the functionsand structure of the tissues of the oral cavity, andknowledge of the properties of the materials whichhe is using, he should be in a position to use hismanual skills to the optimum. Knowing 'how'without knowing 'why' limits the dentist to slavishlycopying methods which may be inappropriate to theneeds of the particular case.

The present text was developed from notesprepared for our students and we are grateful tomany of our colleagues who in the course of usingthese notes in the clinic have made useful sugges-tions for their amendment. We would like toacknowledge our indebtedness to those distin-guished teachers who have moulded our thoughts

and encouraged our interest in this subject, includ-ing the late Professor H.B. Fenn, Mr John Lee, andthe late Dr Carla. Boucher. We are most gratefulto our technicians, Messrs John Cragg and JohnGlaysher, without whose skilled assistance we couldnot have illustrated this book. They have offeredmuch valuable criticism throughout.

Our thanks are due to Professor W.J. Tulley andMr A.C. Campbell for permission to use illustra-tions from their book A Manual of Practical Ortho-dontics and thanks to Mr John Lee for allowing usto reproduce certain illustrations from Dental Aes-thetics, both published by John Wright and Sons Ltdof Bristol, our own publishers, to whom we extendour thanks for their helpful collaboration.

We would also like to thank Mr R. Wilson, whoprepared most of the line diagrams, and the staffsof the Photographic Departments of Guy's HospitalDental School and the Royal Dental Hospital fortheir assistance. Finally we wish to express ourappreciation to our secretaries for their painstakingpreparation of the manuscripts.

D.J.N.R.I.N.

v

Contents

Preface iii

Preface to the first edition v

Introduction 3

Clinical stage 1 5History and examination 5

Clinical stage 2 6Construction of the denture base: introduction to

the principles of retention 6Primary impressions 7

Laboratory procedures 1 22Constructing casts from the primary

impressions 22Construction of special trays 23

Clinical stage 2 (continued) 27Secondary impressions 27

Laboratory procedures 2 42Preparing the secondary casts 42Modifying the upper cast to provide an arbitrary

post-dam 42Acrylic baseplates 43The wax patterns 44Constructing the mounting easts 47Constructing wax occlusion rims 47Composite occlusions rims 47

Clinical stage 3 49Checking the permanent baseJaw relationships 52Establishing jaw relationships with permanent

bases 54Protrusive recordThe facebow recordSelection of teeth

49

6263

65

Laboratory procedure 3 70Adding the post-dam to the upper denture

base 70Mounting the baseplates and occlusion rims 71Selecting posterior teeth 71Setting the teeth 73Clinical stage 4 80The trial dentures 80

Laboratory procedures 4 91Setting the condylar track angles 91Developing the lateral and protrusive

occlusions 91Contouring and finishing the wax surfaces 97Processing dentures 98

Clinical stage 5 101Inserting the completed dentures 101Instructions to patients regarding the use of the

dentures 104Advice to patients on proper care of dentures 104Denture cleansers 104

Laboratory procedures 5 107Remounting 107Reforming centric, lateral and protrusive

occlusions 107

Clinical stage 6 111Adjustment of dentures 111

Diagnosis 117The loose denture 117The denture which causes pain 117

Factors influencing the prognosis of the completedenture treatment 119

Rebasing complete dentures 123

vii

Denture copying 126Laboratory procedure 126Clinical procedure 128

Relief areas 132

Resilient linings 134

Implants 136

Preprosthetic surgery 139

Cross infection 142

Overdentures 143

Tissue conditioners

Further reading

Index 149

146147

viii

Part IClinical and laboratory techniques

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Introduction

We are not normally conscious of our teeth,although we realize that they enable us to enjoy ourfood and to speak clearly, and that they make acontribution for better or for worse to our appear-ance.

When someone loses all his teeth (becomesedentulous), he also loses some of the ability toperform certain activities - eating, speaking, facialexpression - and his appearance is impaired. Hisappearance is impaired not only by the loss of theteeth themselves but also because of the loss ofsupport for the facial tissues lying over them. Whenthe teeth are lost, some of the bone supporting themresorbs. The artificial substitutes - completedentures - must not only replace the lost teeth andlost supporting bone and soft tissue, but also restorethe impaired functions and appearance.

If this is to be done efficiently it is necessary tounderstand what is involved in the following func-tions:

Eating:

Opening the mouth.Inserting the food.Controlling the position of the food.Chewing.Swallowing.

Speaking:

Opening the mouth.Movements of the soft palate.

Movements of the tongue against the teeth orpalate.

Movements of the lips against the teeth or eachother.

Facial expression:

Contractions of the circumoral and facial muscleswhich move the soft tissues surrounding them.

Movements of the tongue.

Appearance:

The appearance of the face is due to the nature(e.g. colour and consistency) of the soft tissuesthemselves (skin, connective tissue, muscles), theform of their bony support, and the form and colourof the eyes, teeth, hair etc.

It is apparent that the complete dentures mustfunction within an active muscular environment. Ifthey are to be efficient in restoring the impairedfunctions they must not move about nor must theyimpede the muscular activities involved in thesefunctions. However, the restoration of function andappearance is only one half of the problem; theother half is to ensure that the dentures have noharmful effects on the remaining tissues.

To gain a sound understanding and some insightinto the construction of complete dentures it isimportant never to lose sight of these end objectivesand to relate all the procedures to them.

3

Clinical stage 1

History and examination

The patient you are about to treat mayor may nothave worn dentures. In all probability if he hasdentures they are now unsatisfactory. You will wantto know why this is so. In order to find out you willlisten to his complaints and will examine thedentures and his mouth. From this you will form anopinion as to the cause of his difficulty - thisconstitutes the diagnosis. The patient may not havehad any dentures, but it is still necessary to examinehis mouth to be sure that no abnormality or problemexists. You will now be in a position to forecast thelikelihood of a successful outcome to prosthetictreatment - this is the prognosis.

You will not be able to make a diagnosis orprognosis until you are familiar with what consti-tutes a correctly made denture, what is a normalmouth, and what is the nature of any abnormalitieswhich can occur, and so further consideration of thissubject will be deferred. It is dealt with in Part IIunder the main heading of 'Diagnosis'.

Tissue conditioning

If your examination of the mouth reveals that thestate of the oral tissues is unsatisfactory for support-ing dentures, some preliminary mouth preparationmay be necessary. Lyttle has shown that the wearingof ill-fitting dentures for some time causes somedeformation of the soft tissues. If the dentures arewithheld from the patient for 48-72 hours this tissuetrauma recovers. As most patients would be unwill-ing to accede to such a course, temporary liningmaterials known as 'tissue conditioners' have beendevised to allow the tissue recovery to occur whilst

Figure 1 Complete upper denture which has been relinedwith tissue conditioner.

the dentures continue to be worn (Figure 1). Thesematerials consist of a polymer powder mixed with acombination of methyl alcohol with an aromaticester. After an initial set these materials remainplastic for up to 3-4 days, so therefore soft tissuewhich has been distorted may recover. Where excesspressure is being applied the tissue conditioner willbe displaced and the fitting surface of the denturebase will show through. The area of excessivepressure thus revealed can be reduced. The tissueconditioning procedure may need to be repeated atintervals of 3 or 4 days. (Further information aboutthese materials is provided in Part II - AssociatedTopics.)

Sometimes the oral mucosa is more severelyaffected by some general or local disorder which willneed further investigation and treatment beforeproceeding with the construction of new dentures.Such a condition is denture-related stomatitis (see p.122).

5

Clinical stage 2

Construction of the denture base:introduction to the principles ofretention

In the Introduction it was concluded that if thecomplete denture is to aid the restoration ofimpaired functions then it must not move about.The first means of preventing movement is theconstruction of a denture base which is retentive. Aretentive denture base cannot easily be displacedfrom the underlying tissues. The forces which keepit in place are known as the 'forces of retention'.

When a denture moves away from the underlyingmucosa the increasing volume beneath tends to befilled by the flow of air and saliva from theperiphery. Anything which impedes the flowincreases retention. The surface tension between thefluid film and both the denture and mucous mem-brane offers resistance to the flow, as does theviscosity of the intervening fluid.

When the soft tissues at the denture border havebeen elastically displaced during impression takingand thus during the seating they will recoil tomaintain contact with the denture if it is subject toa displacing force.

To utilize these forces a denture base needs to beaccurately adapted to the mucous membrane, tocover the maximum available area, and to establishan effective seal with the tissues at the border. Thesoft tissues at the border of the denture supportingarea should be slightly deformed so that a seal iseffected between these tissues and the dentureborder, and this seal must be maintained during allfunctions. These tissues behave in an elastic mannerand should not be deformed so much that they willtend to displace the denture or become sore. The

6

denture must not restrict those movements of theoral musculature which will occur during normalactivities.

If the denture base is fully extended to developretention, then it will also cover the greatest area ofunderlying bone and the denture will be providedwith the optimum support.

Whilst the bone varies in its shape, the soft tissuesoverlying it vary in amount and consistency. Someof the tissues will be easily deformed (e.g. thosearound the border) and others will virtually beundisplaceable (e.g. those over the midline of thepalate). Also, impression materials which are fluidwhen introduced into the mouth will displace thesoft tissues less than materials whose viscosities arehigh. It should be noted that the success with whicha border seal can be developed is dependent uponthe nature of the border tissues - if they are readilydisplaceable it will be good and if not so it will bepoor. A proper understanding of the structure of theoral tissues, together with a knowledge of thephysical properties of the impression materialsavailable, is therefore essential.

To produce the denture base we make impress-ions using a variety of different materials. It isdifficult to produce the exact degree of base exten-sion or border-tissue displacement in one impress-ion. Two stages of impression making will be used- primary impressions and secondary impressions.

In a primary impression the object is to recordcertain landmarks. Excessive displacement of someof the border tissues is acceptable. However, if adenture were made from such an impression repro-ducing its whole area, it would either be displacedduring function or produce soreness of the bordertissues. In making the secondary impression a moreprecise degree of border-tissue displacement isobtained.

Primary impressions

Objectives1. To obtain an impression of the whole of the

denture-supporting area of each jaw.2. To record the full extent of the sulcus.3. To obtain an impression in which certain

landmarks on the edentulous jaws are recorded.

By achieving these objectives a model can beobtained upon which a correctly designed tray maybe constructed in order to make the secondaryimpression.

It cannot be emphasized too much that the wholesuccess of making a retentive denture base dependson achieving an adequate primary impression fulfill-ing all the required criteria. It is not possible tomake corrections at the second impression stagewhich will compensate for deficiencies in the prim-ary impression. To think so is bound to lead tofrustration and failure.

Furthermore, only impression compound has thecorrect properties of consistency and ability to bemanipulated which are necessary in a primaryimpression material. On their own, less viscousmaterials, such as alginate, are quite unsuitable.

Instruments and materials (Figure 2)1. Edentulous impression trays.2. Stanley knife (No. 99E).3. Water bath (composition heater).

Primary impressions 7

4. Impression compound.5. Bowl for hot water.6. Plastic bowl and spatula.7. Low-fusing compound.8. Clean apron to protect the patient's clothing.9. Clean head-rest cover and paper square for

the bracket table.10. Mirror and probe.11. Patient's record card.12. Mouthwash.13. Indelible pencil.14. Alginate impression material and water mea-

sure.15. Denture bowl.

Procedure

Before the patient's arrival1. Check that the composition heater is loaded

with material and that the water temperature iscorrect (60°C) (Figure 3)

2. Sterilize the impression trays and other instru-ments.

3. Change the head-rest cover.4. Obtain a new paper towel for the bracket table.5. Fill a clean tumbler with warm mouthwash.6. Fill a denture bowl with cold water.

On arrival of the patient1. Seat the patient and adjust the chair - the

patient should be seated upright with the head in

Figure 2 Instruments and materials needed for primary impressions.

8 Clinical stage 2

Figure 3 The water bath is at a temperature of 60°C.

Figure 4 The patient correctly seated in the chair.

Figure SA The patient's head is inadequately supported because the head-restis too low and too far back. B The head is displaced because the head-rest istoo high and too far forward

line with the body. The back- and head-rests shouldbe adjusted to give support (Figures 4,5 ).

2. Protect the patient's clothing with an apron.3. Adjust the height of the chair. When taking the

lower impression the patient's mouth should be ona level with the operator's shoulder. When takingthe upper impression the patient's mouth should beon a level with the operator's elbow and the chairmay be tilted back a little.

4. Position of the operator. For the lower impress-ion the operator should be in front of the patient

and on the right side. For the upper impression theoperator should be to the right and a little behindthe patient. (Figures 6-8).

Selection of the trayWhen the patient already possesses dentures theymay provide a valuable guide to tray selection, butif none is available it may be useful in choosing atray to use callipers to measure the arch width. In

Figure 6 The position of the patient and the operator forthe lower impression.


Figure 7 The position of the patient and the operator forthe upper impression.

B

Figure SA The chair is too low. The operator taking the lower impression must bend into anuncomfortable posture. B The chair is too high. The operator taking an upper impressionwill be unable to see what he is doing and he will be uncomfortable.

the case of the lower tray, measurement is made byplacing the tips of the callipers on the lingual aspectsof the ridges on the left and right sides just belowthe retromolar pads (Figure 9A). This measurementmust be compared with the measurement betweenthe lingual flanges of the tray (Figure 9B).

In the upper jaw the tips of the callipers areplaced in the buccal vestibule in the tuberosityregions and this distance is compared with the widthof the tray flanges in the corresponding area (Figure10). Care should be taken to ensure that the trays

are long enough to cover the retromolar pads or thehamular notches.

Insertion of an impression tray into the mouthUntil the student has learnt to manipulate an emptyimpression tray into the mouth he should notattempt to take an impression. The width of theaperture through which an impression tray must beinserted into the mouth is frequently little more than

10 Clinical stage 2

A B

Figure 9A Callipers are used to measure the distancebetween the lingual surfaces of the retromolar pads.

A

Figure lOA Callipers are used to measure the distancebetween the buccal surfaces of the maxillary tuberosities.

half the width of the tray. It is therefore necessaryto rotate each tray into place.

In the case of the lower tray, the tray should beheld with the handle pointing to the patient's leftwith the whole tray at right-angles to the positionwhich it will finally occupy. Introduce the left sideof the tray into the mouth and then, whilst the trayis rotated in a clockwise direction, retract the rightside of the angle of the mouth to allow the right sideof the tray to enter (Figure 11).

The upper tray should be held with the handlepointing to the patient's right. With the first finger

B Selecting a lower tray by comparing this measurementwith the distance between the lingual flanges.

B

B Selecting an upper tray by comparing this measurementwith the distance between the buccal flanges.

of the left hand retract the upper lip, whilst with theright hand rotate the impression tray into themouth. The right side enters first and as the trayrotates the outside of the right flange exerts tensionagainst the corner of the mouth (Figure 12).

Check the selected tray in the mouth

Lower tray1. Insert the tray into the mouth and position it

with the heels covering the retromolar pads (Figures11 and 13).

A

B

cFigure llA The first stage of inserting the lower tray intothe mouth. B The second stage of inserting the lower trayinto the mouth. C The tray in position over the lowerridge.

2. Lower the tray anteriorly and observe theadaption of the tray to the alveolar ridge of the jaw.

Upper tray1. Insert the tray into the mouth and raise the

back edge so that the heels rest in the hamularnotches (Figures 12C and 14).

2. Lift the front of the tray and observe theadaptation of the tray to the arch.

Primary impressions II

A

B

CFigure 12A The first stage of inserting the upper tray intothe mouth. B The second stage of inserting the upper trayinto the mouth. C The tray is correctly positioned belowthe upper jaw.

3. Ensure that the patient has half closed hismouth from the wide-open position when checkingthe tray - this reduces tension in the cheek tissues.

Manipulation of compound1. Soften the composition in hot water at 60°C.

Knead it until the mass is of uniform consistency.Do not soften in boiling water as this will leach outsome of the volatile constituents and will alter theproperties.

12 Clinical stage 2

A BFigure 13A The hamular notches are marked on the cast. B The desirable relationship between the lower tray and theretromolar pads is seen here.

.•

A B

Figure 14 The desirable relationship between the upper tray and the hamular notches is illustrated on a cast.

Further information concerning the properties ofthis material will be found by reading the followingreferences: Anderson (1976), and Craig (1976).

2. Remove the required quantity of compoundfrom the water-bath and knead it between thefingers to obtain a uniform consistency (Figure 15).

3. Replace the compound in the water-bath for afew seconds to reheat.

4. Remove it from the water-bath and prepare itfor loading into the impression tray.

Lower impression

Load the tray1. Knead the compound into a rope 1.5 cm in

diameter and long enough to reach around the tray.

A

13

B

Figure lSA A mixture of compositions, being kneaded together. B The material is now of uniform colour andconsistency.

A B

D

Figure 16A For the lower tray the compound is moulded into a rope constricted in the middle. B Warming the lower tray.e The softened composition is placed in the tray. D The composition has been adapted to the ridge form. Note the bulkin the posterior lingual area.

14 Clinical stage 2

Constrict the middle third of the roll of compounduntil its diameter is 1 ern (Figure 16A).

2. Warm the inner surface of the tray in a bunsenflame (Figure 16B).

3. Place the compound in the tray (Figure 16C).4. Adapt the compound to the tray, grooving it

with a finger to receive the crest of the alveolarridge. In the front of the tray the compound shouldbe deeper on the lingual aspect than on thelabiobuccal by 3 mm. At the back this shouldincrease to 6 mm. Care must be taken to preventwrinkles forming on the surface of the compound.Moulding of the compound should always com-mence at the midline, the excess material beingpushed towards the lingual, labiobuccal, and distalaspects.

5. Invert the tray and pass it quickly beneath astream of cold water. This ensures that the tray willnot burn the patient's lips.

6. Flame the compound surface by passing itquickly through a bunsen flame two or three times.This softens the upper layers of the compound andtherefore ensures accurate reproduction of thetissue surface.

7. Temper the flamed surface of the compound byimmersing the whole of the loaded tray in a bowl ofhot water. This ensures that the mucous membranewill not be burned by a tacky hot surface.

Record the impression1. Work from in front of the patient.2. Rotate the loaded tray into the mouth (Figure

17A).3. Instruct the patient to slightly close the mouth

and raise the tongue (Figure 17B).4. Centre the tray and stretch the cheeks to ensure

that they are not trapped beneath the loaded tray.5. Instruct the patient to relax the tongue. Seat

the tray firmly downwards. Retract the lip adequ-ately to ensure proper seating of the anterior part ofthe tray.

6. Place the thumb of the right hand beneath thepatient's chin and the first and second fingersrespectively on top of the tray in the right and leftpremolar regions, and apply gentle force. At thesame time get the patient to thrust the tongueforward.

7. Keep the tray stationary whilst the compoundcools. The setting of the compound may be acceler-ated by syringing with cold water. Use a salivaejector to remove the water.

Remove the impression1. Instruct the patient to partially close the mouth.2. Displace the cheeks to break the air seal at the

border of the impression.

A

B

cFigure 17A The loaded lower tray has been rotated intothe mouth and is positioned over the alveolar ridge. Notethat the lower lip has been retracted. B The patient hasraised his tongue before the tray is seated. C The lowertray has been seated and is being held in place while thepatient protrudes the tongue.

3. Grip the handle of the tray firmly between thethumb and first and second fingers of the right hand,and apply an upward and backward force on thetray.

Check the impressionNecessary landmarks are (Figures 18,19):A. External oblique ridges - to be covered.B. Mylohyoid ridges - to be covered.Extension to vestibular reflection - to be com-

plete.C. and D. Lingual, labial, and buccal fraena - to

be recorded.E. Retromolar pads - to be covered.F. Extension into the post-mylohyoid fossa - to

be complete.There should be no wrinkles on the impression

surface. The tray flange should not show throughthe compound. -

Common faults1. Too much material at the front of the tray. The

excess flows into the floor of the mouth, distortingthe lingual sulcus and restricting tongue movement(Figure 20).

2. Inadequate extension into the posterior lingualarea (Figure 21) due to:

a. Tongue not lifted above the lingual flange ofthe tray and thus preventing flow of material intothe posterior lingual area.

Figure 18 The composition lower impression


D

Figure 19 Landmarks on the lower impression. A Thegroove formed by the external oblique ridge. B Thedepression produced by the contracted mylohyoid muscle.C The notch caused by the lingual fraenum. D The notchescaused by the labial and buccal fraena. E The depressionproduced by the retromolar pad. F The eminence causedby the extension of the material into the post-mylohyoidfossa.

Figure 20 Lower composition impression showing excessmaterial in anterior lingual area.

Figure 21 Lower composition showing inadequateextension into the lingual pouch area.

16 Clinical stage 2

b. Insufficient impression compound.c. Material incorrectly formed in the tray.d. Underextended tray.3. Inadequate extension into the labial sulcus due

to the lip being too tight. The patient did not closethe jaws and the lip was not pulled forward whenthe impression was seated.

4. Cheek trapped in impression. The impressionwas seated without stretching the cheeks asidebefore positioning the tray.

Corrective alginate wash To obtain greater surfacedetails and to record the effect of the contractedmylohyoid muscle, the initial compound impressionis used as a tray to record a further impression in analginate material. Prior to this certain modificationsare made.

Excess compound will have flowed onto the outersurface of the tray. In the case of the lowerimpression excess material accumulates above theheel of the tray, on the anterolingual surface, andin the buccal vestibular region. After the impressionmaterials have been cooled by immersion in coldwater, the surplus composition should be removedwith a Stanley knife (Figure 22). If deficiencies existthese should be made good by the addition of low-fusing compound. This is provided in the form of astick, the end of which is heated in a flame to softenthe compound, which is then traced onto theimpression wherever it is deficient (Figure 23).

After the new compound has been added thewhole impression is dipped into hot water and thenreseated in the patient's mouth.

Now any undercuts in the impression are cutaway, and the compound is also cut away from thelingual surface of the lower impression in the areacorresponding to the position of the mylohyoidmuscle (Figures 24, 25). This hollowing out of theimpression should extend to a depth of 2-3 mm.When the impressions have been modified in thisway their inner surfaces should be coated with anadhesive solution.

Preparing the alginate impression material Algin-ate impression materials are known as 'irreversiblehydrocolloids'. You should familiarize yourself withtheir setting mechanism and physical properties.

1. Place the lid on the tin of alginate and shakewell to ensure that the powder is not condensedbefore measuring. (This is important because thewater/powder ratio is being determined by volumeand not by weight). If the powder is tightly packed,too thick a mix will result. If sachets of constantweight are used a standard water/powder ratio isautomatically achieved.

2. Scoop out one measure of alginate powder andlevel it off by passing a flat, dry instrument acrossthe top of the scoop. Place the measured quantity

Figure 22 Trimming overextension of lower compositionimpression.

Figure 23 Adding low-fusing compound to a deficientlingual border.

Figure 24 A hollow is cut in the lingual surface of theimpression to accommodate the contraction of themylohoid muscle.

Figure 2S The trimming of the impression is complete.

of alginate in a dry mixing bowl. If sachets are beingused place one in the bowl.

3. Measure the appropriate quantity of water inthe measuring cylinder provided (the water shouldbe at a temperature of 21°C). For the purposes ofthe wash impression, a more fluid consistency of theimpression material is sometimes considered desir-able and the amount of water can be increased.

Note: This alteration in water/powder ratio is onlypermissible because for this purpose a low viscosityis more important than dimensional accuracy orstrength. It is not being used to record undercutareas or to produce a model of great accuracy, as isthe case when impressions are being taken of thepartially edentulous mouth.

4. Pour the water into the bowl and note the time.Mix the powder and water together with a flat metalspatula; slowly at first to incorporate the powderinto the water and then vigorously until a paste ofuniform consistency has been obtained. Mixing ofthe alginate should be complete in 45 seconds.

5. Apply the alginate paste evenly to the surfaceof the composition impression, paying particularattention to the lingual area so that there is sufficientmaterial in the mylohyoid groove area (Figure 26).

Record the impressionScat the loaded tray in the patient's mouth, in asimilar manner to that already described. Have the


Figure 26 The composition has been coated with alginateimpression material.

A

B

Figure 27 The alginate wash in the compositionimpression.

18 Clinical stage 2

patient thrust the tongue firmly forward to ensurethat the mylohyoid muscle will be contracted. Thetongue must be kept forward until the material isset.

Remove from the mouth and check, applying thecriteria used for the composition impression (Figure27).

Upper impression

Load the tray1. Knead the compound into a ball, the upper

surface of which must be entirely free of folds(Figure 28A).

2. Flame the tray gently to dry it and ensure thatthe compound will adhere to it. Place the compoundover the centre of the tray with the wrinkled surfacein contact with the metal (Figure 28B).

3. Mould the compound so that it is spreadoutwards to fill the tray and to develop a shallowgroove corresponding to the alveolar ridge crest.This is best done by holding the tray with theimpression material uppermost and the handlepointing away from you. The compound is nowmoulded by both thumbs, commencing in themidline and working round to the heels of the tray(Figure 28C).

4. Flame and temper in hot water as for themandibular impression (Figure 28D,E).

A

Record the impression1. Work from behind the patient.2. Rotate the loaded tray into the mouth.3. Instruct the patient to slightly close the mouth,

and lift the upper lip upwards and forwards. (If thefirst and second fingers of the left hand are hookedunder the upper lip at each side this retraction isvery easy.) (Figure 29).

4. Move the tray forward into its final position andraise it so that the anterior part of the alveolarprocess contracts the composition.

5. Seat the tray anteriorly, ensuring that a smallexcess of compound flows into the labial sulcus.

6. Raise the posterior part of the tray until thecompound contacts the tissue. Instruct the patientto breathe firmly through the nose. This not onlyoccupies the patient's mind but also helps to seal themouth from the nasopharynx and prevents back-ward flow of the impression material.

7. Apply an upward and backward force on thetray by placing the first finger of each hand on theunder-surface of the tray on each side.

8. Continue to apply force until the compoundflows to fill the vestibular area and also emergesfrom behind the posterior border of the tray (Figure30).

9. Keep the tray stationary whilst the compoundcools. (This may be accelerated by syringing withcold water.)

B

Figure 28A The softened composition has been moulded into a ball. B The ball of composition has been placed in theupper impression tray.

c

19

D

E

A

Figure 28 continued C The softenedcomposition has been adapted to the ridgeform. D The surface of the composition isfurther softened over a bunsen flame. ETempering the surface of the composition bydipping it in water at 60°C. This will preventinjury to the patient's oral mucosa.

Figure 29 Two stages of seating the anterior part of the loaded impression tray.

B

20 Clinical stage 2

I

ll~II1I

Figure 30 The tray is pushed into place posteriorly untilmaterial flows from behind the tray.

Remove the impression1. Instruct the patient to partially close the mouth.2. Raise the cheeks to break the air seal and push

downwards on the flange of the impression in thefirst molar region. It may be necessary to apply adownward and forward pull on the handle of thetray.

Check the impression (Figures 31, 32)

Necessary landmarks are:1. Alveolar ridge - to be completely recorded.2. Palate - to be covered as far as the vibrating

line (B), indicated by the presence of the foveaepalatae.

3. Extension of the hamular notch - to berecorded (A).

4. Extension to vestibular reflection - to becomplete.

5. Extension into whole of tuberosity sulcus - tobe complete.

6. Labial and buccal fraena - to be recorded (Cand D).

Common faults1. Incomplete impression of the palate due to

insufficient material or failure to seat impressioncompletely. This will also occur if the impressionmaterial is allowed to cool and has therefore lost itsproperty of flow.

2. Deficiency in tuberosity regions. Mouth opentoo wide when the tray was being seated, withobstruction of the tuberosity sulcus by the coronoidprocess of the mandible. Failure to adapt compoundin the tray before taking impressions (Figure 33).

Figure 31 Landmarks of the upper impression: A Hamularnotch; B Foveae palatinae; C Notch for buccal fraena; DNotch for labial fraenum.

Figure 32 Upper composition impression.

3. Deficiency in labial sulcus. Mouth open toowide when the tray was being seated. The lip wasnot lifted forward to allow the compound to flowinto the sulcus.

Alginate wash1. Remove excess composition which will have

flowed backward onto the soft palate (behind thevibrating line) and which may hang down into themouth obstructing the tongue.There may also be excessive composition in thebuccal and labial border regions; if so it should beremoved (Fig. 34).

Figure 33 The composition impression is deficient in thetuberosity sulci.

Figure 34 Trimming the upper composition impression.Note that the border has first been reduced vertically - thisshows clearly the varying thickness of the border which canthen be reduced until it is uniform.

2. Any deficiencies should be corrected by theaddition of low-fusing compound. Temper in hotwater and reinsert into the mouth.

3. Apply a thin alginate wash as for the lowerimpression (Fig. 35A). A slightly more fluid mix canbe used for the upper wash because of the greaterdistance it must flow from the palate to the border.Place a little material in the palate and in the sulcusopposite each maxillary tuberosity. Seat the tray (asas done with impression plaster in Figure 74, p. 39).

4. Remove the impression from the mouth andcheck, using the same criteria as applied to thecomposition impression (Figure 35B).

ReferencesJ. N. Anderson (1976) Applied Dental Materials, 5th

ed., Chap. 21. Oxford, BlackwellR. G. Craig (1976) Restorative Materials, 6th ed., Chap.

8. London, Kimpton.

References 21

A

B

Figure 35A A coating of alginate impression material hasbeen applied to the composition. B the alginate wash inthe composition impression.

Laboratory procedures 1

The preparation for the visit at which the secondaryimpressions will be made involves the constructionof casts from the primary impressions and theconstruction of special trays on these casts.

Constructing casts from the primaryimpressions

These instructions apply to constructing casts fromall alginate impressions. It is very important that thealginate impressions be cast as soon as possible afterthey have been made, otherwise distortion mayoccur.

1. Rinse the alginate impression under cold,running water until all traces of mucus have beenremoved. Shake the impression to remove anyexcess water. If necessary, blow this out with a nottoo fierce blast of compressed air.

2. Block out the tongue space of the lowerimpression with a ball of moist cloth or paper(Figure 36).

3. Mix pure hydrocal. Use 60 ml of water and 180g of powder (powder/water ratio of 3:1). Spatulatethis thoroughly for 1 minute. If desired, half thequantity of hydrocal can be replaced by plaster. Thismakes it easier to trim the cast but of course it willbe of inferior strength.

4. Vibrate this into the impression (Figure 37).Add the hydrocal in small quantities, vibrating itfrom one end of the impression around to the otherend. When the impression is just filled up withhydrocal put it aside. Pile the rest onto the castingtile and gently vibrate the impression on to this(Figure 38).

22

Figure 36 The tongue space of the lower impression hasbeen blocked out with a ball of moist cloth.

Figure 37 Hydrocal is being vibrated into the upperimpression.

Figure 38 The upper impression has been pushed gentlydown onto a small mound of hydrocal.

Figure 39 Making sure there is sufficient material behindthe posterior part of the lower impression.

Be careful with the lower impression, and see thatthere is adequate material behind the most posteriorpart of the impression (Figure 39).

5. Let this set for 1 hour covered with a dampcloth. The napkin with which you covered theimpression after making it can be used for thispurpose. Do not leave the impression on the cast formore than this time.

6. Immerse the cast impression in hot water for 5minutes. Do not use water too hot or the composi-tion will melt and adhere to the cast; 65°C should beadequate.

Remove the tray and composition together withthe alginate. Trim the cast, preserving the complete

Construction of special trays 23

Figure 40 Trimming the upper model.

sulcus reflection with a supporting land of at least 3mm width (Figure 40).

7. Allow the cast to dry.

Construction of special trays

These trays can be most suitably made from self-curing acrylic resin. They can be made by eitherlaying down a sheet of dough over the cast andadapting it with wet cotton-wool or the fingers, orby constructing a wax pattern of the finished tray onthe cast, investing, boiling out, and packing theresultant mould with self-curing resin.

However the trays are made, it is necessary to beaware that the primary impressions may haveproduced an excessive amount of tissue deforma-tion. A tray which is excessively extended will needconsiderable reduction at the chairside with conse-quent waste of time. Therefore the outline of theprepared tray should be marked on the cast.

There are several landmarks which facilitate thedetermination of this outline, but in other areas thisdecision is of necessity more arbitrary. This isparticularly true of the extension of the tray into thelabial and buccal sulcus. The aim is to produce a traywhich in the mouth has a periphery that lies justshort (say 1 mm) of the reflection of the mucosawhen the tissues are at rest. Such a position is notat all easy to decide on a cast, particularly in thepresence of a degree of tissue distortion. Thereforea point is chosen where the mucosa begins to turnoutward into the sulcus. This will be called the tissuereflection point (Figure 41).

24 Laboratory procedures 1

cv=vJ• •.....••... . .

A

B

Figure 41 Cross-section of A upper and B lower modelsshowing tissue flexion lines.

Determining the outline of the special trays onthe casts

The upper tray (Figure 42) Draw a line across thepalate passing 1 mm distal to the hamular notchesand 2 mm distal to the fovea palatini. If the foveaeare not evident draw the line straight across fromhamular notch to hamular notch. The aim is toproduce a tray which just covers the vibrating line.Continue the line into the tuberosity sulcus on eachside at the tissue reflection point, and continue itforward, avoiding the labial and buccal fraena.Within each fraenum is a fibrous strand and the trayshould not impinge upon it at all. The border of thetray should clear it by 1 mm.

The lower tray (Figure 43)1. Buccal sulcus: Draw a line across the back of

the retromolar pad at right-angles to the ridge.Draw a line 1 mm lateral to the external obliqueridge. Join the posterior end of this line to the lateralend of the first line with a line which runs at an angleof about 45°C to the alveolar ridge.

Now, starting at the anterior end of the externaloblique ridge, continue the line forward around thebuccal fraenum at the tissue reflection point. Repeatfor the other side.

2. Lingual sulcus: Prior to outlining the lingualperiphery it is necessary to provide a means wherebythe tray will be spaced over the mylohyoid muscleso that this may contract freely when making theimpression. This is accomplished by outlining thearea overlying that part of the muscle which lies

A

B

CFigure 42 The outline of the upper special tray. The foveapalatinae and hamular notches are marked.

Figure 43 The outline .of the lower special tray and waxrelief of the mylohyoid area.

directly beneath the mucosa. This lies below themylohyoid ridge but should not include the retromy-lohyoid fossa.

Draw a line along the mylohyoid ridge. This willjoin the sulcus reflection in the premolar region.From the posterior end of the mylohyoid ridge drawan oblique line forward and down to the sulcus in

/ front of the retromylohyoid fossa. The outline of thetriangular area overlying the muscle has now beendrawn, its lower border being the sulcus reflection.Cover this with a 2 mm layer of wax.

Draw the rest of the lingual border with a line atthe tissue reflection point. Posteriorly, this will passupward just behind the retromylohyoid fossa. Jointhis part of the lingual end of the line crossing theretromolar pad.

Constructing the trays- of self-curing acrylicresin

The upper tray1. Spaced tray (for use with impression plaster):

Carefully lay down a sheet of 0.9 mm casting waxover the outlined area of the cast (Figure 44), thusproviding a space between cast and impression tray.Prepare a sheet of self-curing acrylic resin dough(Figures 45,46). Adapt a sheet of self-curing acrylicresin 2 mm thick to cover the outlined area. Attacha stub handle of acrylic resin in the midline over theridge crest (Figure 47). Do not roll out the sheet toothin because the tray must be rigid. If the tray isflexible it will distort while the impression is beingmade.

2. Close fitting tray (for use with impressionpaste): Prior to making a close-fitting tray, block outany undercut areas and cost the cast with separatingmedium. Adapt a sheet of self-curing resin directlyto the cast and proceed as for the spaced tray.

Construction of special trays 25

Figure 44 In the preparation of a spaced special tray a sheetof modelling wax is adapted to the cast.

c-·-(

Figure 45 Equipment and materials for preparation ofacrylic dough.

The lower tray (Figure 48) The procedure is as fora close-fitting upper tray. If there should be a deepundercut in the retro-mylohyoid fossa do not leverthe tray off the cast but cut away the cast in the area.

Three stub handles should be placed over theridge crest; one in the midline and one in each firstmolar region. These should be approximately 1 cmhigh by 1 cm long by 4 mm wide. These handles willensure that the tray is kept in position by the tips ofthe index fingers without the fingers encroaching onthe border of the impression.

26

A B

Figure 46A The soft ball of dough is sandwiched between the brass plate former and a sheet of glass. Wet cellophanesheets are used as a separating medium. B The glass plate is pressed down until it contacts the former.

A

AFigure 48 The close-fitting lower tray.

B

c Figure 47 The spaced upper tray on the cast.

B

Clinical stage 2 (continued)

Secondary Impressions

ObjectiveTo obtain an impression from which a retentivedenture base can be constructed.

The denture base should satisfy the followingrequirements:

1. It must be extended until its~ lies ondisplaceable tissue where a seal can be developed.

2. The tissues adjacent to the border should be@efurmed!enough to achieve a seal but not so muchthat they tend to displace the denture or sufferinjury. Muscles related to the border must not beprevented from free activity.

3. It should have th closeSDPossible contact withthe surface of the mucous embrane lying beneathit.

4. Extensio to provide retention ensures themaximum coverage of the jaw, and this in turnensures that the minimum force per unit area istransmitted to the supporting tissues by the dentureduring function.

The extent to which these aims can be achieveddepends upon the properties of the materials inwhich the impression is taken and the nature of thetissues.

Instruments and materials (Figure 49)1. Handpiece and acrylic trimmer.2. Clean apron.3. Mirror and tweezers.4. Indelible pencil.5. Clean head-rest cover and paper towel for

bracket table.6. Patient's record card.

Mandibular impressions1. Acrylic resin close-fitting special tray.2. Low-fusing tracing compound (Kerr's green).3. Zinc-oxide-eugenol impression paste.4. Mixing pad.5. Spatula.6. Cold cream or petroleum jelly.

Maxillary impression1. Acrylic resin spaced special tray.2. Low-fusing tracing compound (Kerr's green).3. Plaster spatula.4. Small plaster mixing-bowl.5. 50 g of Calspar impression plaster and 32 ml of

water at 20°C, or 50 g of white superfine plaster and32 ml of AE8 solution.

Alternatively:1. Acrylic resin close-fitting special tray.2. Low-fusing tracing compound (Kerr's green).3. Zinc-oxide-eugenol impression paste.4. Mixing pad.5. Spatula.6. Cold cream or petroleum jelly.

Alternative materialsThe advent of vinyl-poly siloxane offers an alterna-tive material for upper and lower impressions. It isof suitable consistency and gives an excellent surfaceto the cast and dentures. Polyether materials arealso used. No substantial change of technique isneeded for these and so we have chosen to describethe use of more traditional materials.

27

//

28 Clinical stage 2 (continued)/

.•Figure 49 Instruments and materials for the secondary impressions.

Procedures

Before the patient's arrival1. Change the head-rest cover.2. Obtain new paper towel for the bracket table.3. Fill a clean tumbler with warm mouthwash.4. Fill a denture bowl with cold water.

On arrival of the patient1. Seat the patient and adjust the chair - the

patient should be erect with the head in line with thebody. The back-rest should be adjusted to supportthe spine.

2. Protect the patient's clothing with an apron.3. Height of chair. When taking the lower

impression the patient's lower jaw should be on alevel with the operator's shoulder. When taking theupper impression the patient's upper jaw should beon a level with the operator's elbow.

4. Position of operator. For the lower impress-ion the operator should be in front of the patientand on the right side. For the upper impression theoperator should be to the right and a little behindthe patient.

Mandibular impression

Check the trayCheck the tray for correct extension and adjust ifnecessary. Areas calling for special attention are:

1. Retromolar pad: The posterior border of thelower tray should extend onto the glandular part ofthe retromolar pad to ensure that a seal is obtained.This tissue is displaceable and lies beyond theanterior part of the pad which is dense, fibrous, andunyielding (Figures 50,51).

2. External oblique ridge: This comprises densecortical bone which will withstand loads transmittedby the base with minimal resorption. The trayshould therefore be extended to cover this area.

Figure 50 A longitudinal section of the retromolar pad. The soft-tissue specimenhas been removed from the underlying bone. Note the glandular mass (x3).

A

B

Figure 51A Marking the glandular part of the retromolarpad. B The special tray is extended onto the glandular partof the retromolar pad.

Although the buccinator muscle is attached to theexternal oblique ridge (and indeed in some casesmay be inserted into the lateral aspect of thealveolar ridge), its fibres run parallel with thedenture border and may be displaced to a degree(Figure 52).

3. Masseter temporalis region: Although we havejust indicated. that the buccinator muscle may bedisplaced, this is in sharp contrast to the treatmentwhich may be afforded to either the temporalismuscle (some fibres of which are attached to theposterior end of the external oblique ridge) or themasseter muscle (whose fibres pass lateral to theposterior part of the external oblique ridge to beinserted onto the lateral surface of the mandible).The fibres of these muscles run at right-angles to thedenture border and when contracted will press themucosa against the border. Since the teeth will bein occlusion when these muscles are contracting, thebase cannot be displaced and the mucosa may beinjured.

The part of the border which is affected by thesemuscles is that which lies between the retromolar

Secondary impressions 29

Figure 52 A transverse section of the mandible and relatedsoft tissues showing the mylohyoid muscle attachment, thebuccinator muscle attachment, and the tongue musculature(x3).

Figure 53 Checking the posterior position of the buccalborder and its relationship to the areas of influence of themasseter and temporalis muscles.

30 Clinical stage 2 (continued)

pad and the external oblique ridge. The tray shouldbe trimmed to run obliquely at an angle of about 45°to the alveolar ridge crest (Figure 53).

4.Mylohyoid muscle and retromylohyoid fossa:Insert the tray and ask the patient to swallow, lickhis lips, and thrust his tongue forcefully into thepalatal vault. Check that these movements do notcause the patient any discomfort or gross movementof the tray. If they do, this indicates overextensionof the tray or restriction of the activity of themylohyoid muscles (Figures 54-57). If overextended correct, by reducing the extension of thetray, using an acrylic trimmer and a handpiece(Figure 58A). If the mylohyoid muscle is obstructedreduce the inner aspect of the lingual flange of thetray without affecting its depth (Figure 58B).

The extension of the tray into the retromylohyoidfossa sometimes prevents the direct seating of thetray. In such a case the tray must be pushed a littlefurther posteriorly until the lingual extension can be

Figure 54 A diagram showing a cross-section of themandible, the mylohyoid muscle and the body of the hyoidbone at rest and during swallowing.

seated and then drawn forward to seat the rest ofthe tray.

5. The sublingual fold and papillae: Whcn thetongue moves there is a considerable range ofmovement of the floor of the mouth in the area oneach side of the midline. Indeed it is not oftenpossible for the denture border to remain in contactwith the tissues over the whole of the range of thismovement. If it is extended to contact the tissues attheir lowest position it will cause their excessivedeformation when the floor of the mouth rises. If itis only extended to contact the tissues at theirhighest position then contact (and retention) will belost when the floor of the mouth drops. Fortunately,the presence of the sublingual fold and papillae willin most cases alleviate this difficulty. If the base isextended until its border lies in contact with the foldand papillae when the mouth is open, and thetongue is in a slightly protruded position, then aborder seal will be maintained. The slightly protru-ded position of the tongue, with the tip just

"'yJnJ!ro1d YUKi.. MylchyQid MURCh-Cona_etP.d At Relit

Figure 55 A diagram showing the relationship of themylohyoid muscle to the lower border of the lingual flangeat rest and in swallowing.

Figure 56 A diagram showing the relationship of the retromolar pad tothe palpable portion of the mylohyoid muscle.


Figure 57 Drawing showing the relationship of the lower denture base to the main structures surrounding it.Note the post-mylohyoid extension of the base.

A B

Figure 58A Reducing the posterior border of the lingual flange. B Reducing the inner aspect of the lingual flange inthe mylohyoid region.

Temper and reseat the tray. Instruct the patient toswallow, and to open and close the mouth.]:l}.iSWIllensure that the retromyloh oid fossa is recorded.

emove the ray y a backward diSiJiacii18 move-ment and chill the compound. Remove any excesscompound (Figure 59).

2. ~ry the tray")~.. 3. Apply cold cream or petroleum jelly to the

Record the impression patient's lips and the operator's fingers. (This is to1. Apply low-fusing compound to the tissue . prevent the impression paste from adhering to the

surface of the distal part of the lingual flange. skin.)

overlying the incisal edges of the lower anteriorteeth, is the one adopted when the mouth is openfor the reception of food. It is therefore the tongueposition (and so the floor of the mouth level) atwhich retention is most necessary.


A BFigure 59A Applying low-fusing composition to theretromylohyoid fossa.

A

B The composition has recorded an impression of theretromylohoid fossa. Note that the matt surface of thecomposition shows that it has been in contact with thetissues.

Figure 60 Suitable quantities of impression paste have been dispensed. B The impression paste has been spatulated for 45seconds.

B

4. Mix zinc-oxide-eugenol impression paste. Spa-tulate together until a mix of even consistency andcolour is achieved (Figure 60).

5. Coat the tissue surface of the tray with an evenlayer of paste.

$6. Instruct the atient to rinse his mouth ~/Em e mucus).

7. Insert and seat the tray. Have the tongue raisedwhile you do this so that it is not trapped beneaththe lingual flange. Keep the lips and cheeks out ofthe way with the fingers so that no air-pockets aretrapped around the border. Hold the tray steady by

placing the first and second fingers of the right handon the posterior stub handles and the thumbbeneath the mandible (or the first fingers of bothhands on the handles and both thumbs below themandible) (Figure 61A-D).

8. After 30 seconds commence to develop theform of the borders by instructing the patient to:

a. Open the mouth widely./ b. ut t e tongue forwar (Figure 61 E). This wJ.!ldetermine the de t and form of the lingual sulcus.There has always been a problem in deciding whattongue manoeuvres the patient should perform. The

A

c

ideal manoeuvre would be to reproduce the rangeof tongue movement and associated muscular con-traction that accompany normal tongue activities.This is not, however, a practical possibility whilemaking an impression. It seems to us that the simplemanoeuvre of putting the tongue forward gives aposition of the floor of the mouth which is compati-ble with our aim of making a retentive base. It alsoensures that the mylohyoid muscle is contracted.Being a simple manoeuvre it allows the student toconcentrate on kee ing the tray firml in lace whilethe material sets. -


B

D

E

Figure 61A The coated tray is rotated as it is inserted intothe mouth. Care must be taken to see that the posteriorlingual flange is in place. B The anterior part of the tray isseated first. The lip is retracted so that this can be donewith accuracy and to avoid trapping air-bubbles. C Theposterior part of the tray is seated with pressure on theposterior stub handles. The lips and cheeks are held awayto aid vision and to avoid trapping air-bubbles. D The lipsand cheeks are retracted to check that the tray has beenproperly seated. E The tray is held firmly in place and thepatient is instructed to protrude the tongue.

9. Wait for a further 3 minutes for the paste toset. Keep the tongue in its protruded position.

Check the impression (Figure 62) Necessary land-marks are:

1. Retromolar pad - to be covered.2. Temporalis/masseter - not to be encroached

upon.3. External oblique ridges - to be covered.4. Labial and buccal sulcus reflection - to be

correctly displaced.


A

B

Figure 62 The completed lower impression.

Figure 63 The tray is trimmed where it shows through thepaste impression.

5. Retromylohyoid fossa - to be recorded.6. Mylohyoid muscle - recorded in contracted

form.7. Anterior lingual border - to be extended to the

region of the sublingual papillae.8. If the tray shows through the border of the

impression this indicates overextension. The trayshould be trimmed (Figure 63), the paste removed,

and the impression remade. After removing areas ofoverextension, be sure to smooth the border of thetray.

It is commonly supposed that when areas of thefitting surface of a tray show through the impressionmaterial the denture will bear heavily in this regionand cause irritation of the mucous membrane.However, this is not borne out by the only criticalanalysis reported.

Rodegerdts (1964), investigating 72 subjects,found that only 18 per cent of the tray exposuresresulted in irritation of the oral mucosa. In thecircumstances it is wise to ignore such areas and torelieve only those sites beneath the completeddenture where irritation of the mucosa occurs. (SeeClinical Stage 6, p. 111).

If the border of the impression is imperfectlyformed this may indicate underextension. If this isso, remove the impression paste and apply low-fusing compound to the border of the tray.However, deficiency in the lingual flange is muchmore likely to be due to faulty tongue positioning.

More about tongue position Figure 64 shows againthe tongue correctly protruded. The body of thetongue appears relaxed. This indicates that theprotrusion has been brought about by elevation ofthe floor of the mouth with contraction of themylohyoid muscle. In Figure 65 only the tip of thetongue has been protruded by contraction of theintrinsic muscle. This has left the posterior part ofthe dorsum of the tongue depressed. The results ofthis on the impression can be seen in Figures 66 A,66 Band 66 C. Note that there is no record of theposterior lingual sulcus or of the contracted mylo-hoid muscle. Indeed, material along the sharpirregular and incomplete posterior lingual borderhas flowed under the mylohyoid ridge. This borderwill cause trauma when the floor of the mouth iselevated in swallowing. This fault is most commonin lower impression making and is the usual causeof failure in lower denture extension. It is oftenmisinterpreted as over-extension but is of coursemal-extension. It emphasizes the absoloute import-ance of correct tongue position.

Maxillary impression (using plaster-of-Parisimpression material)

Tray in the special tray and check for correctextension)

1. Mark the vibrating line with an indelible penciland extend this line to run through the hamularnotches. Seat tray to line (Figure 67).

2. Lift up the lip and cheek until the sulcusreflection is visible and seat the tray. When the tray

Figure 64 The tongue has been correctly protruded. Notethat it appears relaxed.

Figure 65 Only the tip of the tongue has been protrudedby means of contraction of the intrinsic muscles. Theposterior part has not been elevated in this manoeuvre.

IS In position its border should be seen to lie justshort of the sulcus reflection (Figure 68).

3. In the tuberosity sulcus area it is difficult to seethe reflection of the mucosa. If there is doubt aboutthe extension then add a little low-fusing compoundto the border.

Correcting the tray1. If the tray is overextended reduce the periphery

by using an acrylic trimmer in the handpiece (Figure69).

2. If the periphery is underextended trace low-fusing compound to make good the deficiency. Astick of compound is softened in a flame and themolten material traced along the border of the tray(Figure 70A). The tray should now be immersed inhot water (60°C) to temper the compound and thetray is again tried in the mouth. By moving thecheeks and lips the compound can be moulded tothe correct position in the sulcus, and after this has


A

B

cFigure 66A, Band C. In these three illustrations the resultof incorrect protrusion of the tongue can be seen. There isno formed posterior lingual border and no sign ofcontraction of the mylohyoid muscle.

been done the tray should be removed andimmersed in cold water to chill the compound.

Note: If the compound has been in contact withthe tissue, its glazed surface becomes matt (Figure70B). If the surface is still glazed there is a need toadd more material.

36

A

B

Figure 67A The vibrating line has been marked on thepalate with an indelible pencil. B The posterior border ofthe upper tray has been trimmed to coincide with thevibrating line.

Figure 68 Checking the relationship of the border of theupper tray to the buccal sulcus reflection.

Figure 69 Reducing the flange of the tray where this isoverextended.

A

B

Figure 70A Applying low-fusing composition to the buccalflange in the tuberosity region. B The mouldedcomposition shows a matt surface which indicates that ithas been in contact with the tissues.

Mixing the plaster and loading the tray1. Place the measured quantity of water (32 ml)

in a shallow mixing-bowl. Slowly shake the mea-sured quantity of impression plaster (50 g) into thewater, ensuring an even distribution. This shouldtake 15 seconds. After pausing for a further 15seconds to allow the water to soak into the plaster,the mix should be vigorously spatulated with thebroad-bladed spatula until a uniform mix has beenobtained. Spatulation time is usually 30 seconds(Figure 71A-E).

A

c

E


A mechanical spatula tor may be used and this willgive a more consistent amount of mixing thanmanual spatulation. Twenty-five turns of the handleat the rate of two turns a second will give a creamymix and adequate working time (Figure 71F).

2. The tray should be loaded when the mix hasjust commenced to thicken to a creamy consistency.The quantity of impression material used should besufficient to fill the alveolar groove and to cover thepalatal vault with a thin layer (Figure 72). Afterloading the tray, the consistency of the plaster

B

D

F

Figure 71A 32 ml of water have been measured into the plaster bowl and its temperature is checked (21°C). B Commencingto add the known weight (50 g) of impression plaster to the water. C The impression plaster has been added in 15 seconds.D A further 15 seconds are allowed for the plaster to absorb the water. Spatulation can now begin. E Spatulation iscomplete in 30 seconds. F Using a mechanical plaster spatulator.


Figure 72 Enough plaster has been loaded in the tray tofill the alveolar groove and to produce a thin wash overthe palatal vault.

remaining in the bowl should be tested until it justfails to fall off the spatula when it is inverted.

Record the impression1. At this time plaster should be placed in the

patient's palate and in the buccal vestibule lateral tothe tuberosity (Figure 73). Load a narrow-bladedspatula with plaster and a~~nt to half-close.his ~~PQsifion:-(Tftnemouth is 0 en too far the Q!esence ofthe coronoidprocess of the rnandib e lateral to the ~rosity

Figure 73 A narrow-bladed spatula is used to place someplaster in the palate and tuberosity sulcus. Note that thecheek is retracted when this is done.

restricts the access to th~s). Place the plaster1nThesulcus On each side and in the palatal vault.

2. Ins the tray into the mouth and vibr te .slightl from Sl e use it.in place. Theront of the tray should be raised first, the upper lip

being held upward and forward with the first andsecond fingers of the left hand (Figure 74A,B). Inthis way it can be seen that the tray is correctlypositioned anteroposteriorly and laterally. Providedthe correct amount of material has been placed inthe tray, when the back of the tray is pushed firmlyup into place no great excess should flow down intothe patient's throat (Figure 74C). When the tray isseated it should be held in J2.!ace with the indexInger of the lef~~outh should be opened

wide. This brings the coronoid process forward. Ifthis is not done the forward movement of thecoronoid process may be obstructed by the buccalflange of the base. The cheeks and lips should berelaxed (not retracted) (Figure 74D).

3. Test the plaster remaining in the mixing-bowlto determine when it is set. When a portion of theplaster removed from the side of the bowl breakswith a snap the impression is ready for removal fromthe mouth.

Remove the impression from the mouth1. Instruct the atien to half-close his jaws

togeth'enmcnl1eilfift up the lip. This will assist theremoval of the impressl n y breaking the seal atthe border (Figure 75). Whilst the lips are nowparted, a sharp downward displacing force is appliedto the tray and this should dislodge .the impressionand allow its removal from the mouth.

".....If difficulty is encountered it may be useful tosquirt a little water around the periphey of theimpression, having first placed a saliva ejector in thefloor of the mouth.

2. Inspect the impression as soon as it has beenremoved from the mouth. Examine it for anydeficiencies and look in the mouth for fragmentswhich may remain there. The impression is mostlikely to break in the region of the tuberosities andlabial sulcus. These broken pieces should be care-fully removed with tweezers and placed in theappropriate position On the impression.

3. When you are satisfied that the impression iscomplete, and not before, the patient should beallowed to rinse his mouth.

4. Assemble the impression - allow the impress-ion and broken fragments to dry before attemptingto reassemble them. Clean the broken surfaces withcompressed air or a chip syringe. As each brokenfragment is seated on the impression it should besecured in place by dropping molten sticky wax ontothe outer surface of the impression (Figure. 76).

A

c


B

D

Figure 74A The lip is lifted up to facilitate accurate location of the anterior part of the tray. Good visibility is essentialin this procedure. B The anterior part of the tray is seated until plaster flows into the sulcus. C The back of the tray ispushed up until plaster flows from behind the posterior border. D The tray is supported while the material sets. Thepatient holds the mouth open and the lips and cheeks are relaxed.

Check the impression (Figure 75)Necessary landmarks are:

1. Labial and buccal vestibular reflection - thisshould be recorded with the correct* degree oftissue displacement. Particular attention should bepaid to the tuberosity region. The tray should notshow through the plaster nor should the border beexcessively thick. The plaster surface should besmooth and free of creases or defects.

2. Hamular notches - to be recorded.3. Palate up to vibrating line - to be recorded.

'The decision that the amount of displacement of thetissues lying in relationship to the border of the denturebase is 'correct' is an empirical decision. Assuming that theimpression material is always used at the same consistency,the amount of tissue displacement will vary from patientto patient and will depend on the displaceability of thetissues. An average dimension for the width of a well-formed border is 4 mm. If the border is considerablythinner or thicker than this, it is wise to look again at thenature of the tissues to estimate how displaceable they are.

Alternative maxillary impression(using zinc-oxide-eugenol impression paste)

Check tray1. See that the tray is extended until its border is

just short of the vestibular sulcus reflection, covers

Figure 75 Removing the impression. The lips are lifted tobreak the seal at the border.


A

B

C

Figure 76 Assembling a fractured plaster impression.

the hamular notches, and extends to the vibratingline.

2. If overextended, adjust. If underextended, addlow-fusing compound - be especially careful intuberosity sulcus.

Record the impression1. Mix zinc-oxide-eugenol impression paste as

described for mandibular impression - load the trayin a similar way.

A

B

Figure 77 The uppe,r pla~ter secondary impression. A Viewfrom above; B Oblique view.

2. Seat the tray as for maxillary plaster impression- anteriorly first and then posteriorly. Seat firmly.Have the patient open his mouth wide.

3. Allow the paste to set for 3 minutes andremove.

4. Check by the same criteria as were applied tothe plaster maxillary impression.

The location of the vibrating line and thedistribution of displaceable soft tissue in theregion of the vibrating lineOn p. 42 the subject of the addition of a post-damfor the upper denture base is discussed. Note that itis recommended that this should be added to thepermanent base in self-curing acrylic resin afterestablishing a posterior border seal in the mouth,with low-fusing compound.

If, however, it is decided to incorporate anarbitrary post-dam when constructing the acrylicbase plate, then it will be necessary at this stage todetermine the exact position of the vibrating line(which is the limit of posterior extension of the

Figure 78 Palpating the soft tissues of the palate in thevicinity of the vibrating line. A ball-ended instrument isbeing used for this.

upper base) and also to make a note of thedisplaceable soft-tissue distribution in the area.

1. Examine the tissues of the palate for theirdisplaceability. Where there is considerable displa-ceable tissue the distance between the front and theback of the post-dam area will be large, say 6-8 mm,and where little displacement occurs it will be small- 1 mm (Figure 78).

2. As a result of your examination, mark the frontand back of the post-dam area on the primary. Asthe separation between this and the posterior borderdepends upon the differing displaceability of thesubmucous layer, the area outlined will resemble abow in shape.

References 41

Figure 79 Outline of displaceable tissue area is marked onthe primary model.

The greatest dimension will normally be midwaybetween the vault of the palate and the alveolarprocess (Figure 79).

3. This information will be used in the proceduredescribed on p. 45, Figure 85A-F.

ReferencesC. R. Rodegerdts (1964) Relationship of pressure

spots in complete denture impressions with muco-sal irritations. J. Prosthet. Dent. 14, 1040-1050.


At this stage the permanent bases are made and waxocclusion rims are added to them in preparation forthe next clinical step of recording the jaw relation-ships.

Preparing the secondary casts

Having taken every care to develop the correctborder of the secondary impression, it is essentialthat this is reproduced in the completed denturebase. In order to do this the cast must reproduce thedepth and width of the sulcus. To achieve this andto avoid tiresome trimming of the set hydrocal, theimpressions should be 'boxed in' (Figure 80).

Apply a roll of beading wax to the outside of eachimpression 5 mm from the deepest part of the sulcusso that it extends laterally from the border of theimpression by 5 mm. For the lower impression thetongue space should be filled in by attaching anappropriately shaped sheet of wax to the beadingwax.

A sheet of boxing wax should now be wrappedaround the border of the beading and sealed to itwith a hot knife. In the case of the lower impressionthe box is formed so that it encloses the blocked-outtongue space (Figure 81). Apply separating mediumto the surface of the impression (Figure 82). Pourthe cast using pure hydrocal (Figure 83). Removethe boxing wax and separate the cast from theimpression (Figure 84).

Modifying the upper cast to provide anarbitrary post-dam

If it had been decided to provide an arbitrary post-dam in the upper cast by carving upon the cast then

42

reference is made to the primary impression castwhich has been previously marked (see p. 00). Thepositions of the vibrating line and the displaceablesoft-tissue distribution are traced onto the secondaryimpression cast.Then:

1. Cut into the cast to a depth of 1 mm along theposterior border of the dam. Divide the post-damarea with contour lines separated by 2 mm at thewidest point. In some cases there will be only 2 mmbetween the back and the front of the post-damarea, and in others there may be about 6 mm (Figure85A).

2. Shade the area between the posterior borderand its nearest contour line with a soft lead pencil(Figure 85B).

3. Now scrape this shaded area of the case in thefollowing way (Figure 85e). (The best knife to beused for this purpose is one with an angle of about50° between its back and its cutting edge. Adissecting scalpel is very suitable for this purpose.)With the front of the cast facing towards you, placethe tip of the knife on the line marking the back ofthe post-dam area. Now scrape the cast, producinga slight bevel sloping backwards.

When the pencilled area has been removed shadethe area between the next contour line and the backof the post-dam area and scrape this (Figure 85D).Continue shading and scraping the cast until the linemarking the front of the post-dam area is reached(Figure 85E).

As a result of the modifications which you willnow have made to the cast, a denture constructedupon it will displace the tissue at the back of thedenture-supporting area in a graduated manner andeffect an adequate seal.

The reason why the dam extends over an area isso that the tissues are gradually displaced frombefore backwards and because the seal is moreeffective over a wider area. Should the extension of

A

D

B

E

Acrylic baseplates 43

c

F

Figure 80A A line is drawn on the impression outlining the depth of sulcus to be reproduced in the cast. B The line onthe impression indicates the approximate posterior limit of the denture supporting tissues. The beading must not encroachupon this. C Adapting the beading wax. D, E The application of beading wax has been completed. F A sheet of boxingwax has been applied to the outer surface of the wax bedding.

Figure 81 The secondary lower impression has been boxed.

the denture base have to be shortened for anyreason, there is a chance that at least some of thedamming effect can be maintained.

Some people inscribe a line about 1 mm in depthalong the posterior border of the cast to act as apost-dam. It should extend through both hamularnotches and be 1.5 mm anterior to the posteriorborder of the base (Figure 85F).

Acrylic baseplatesThe baseplates which you are going to constructnext are the foundation of the complete dentures. It

Figure 82 Separating medium is applied to the plasterimpression.

is important that they fit the tissues underlying themaccurately and are correctly extended around theborder. If these conditions are to be fulfilled, caremust be taken to avoid distortion in the processingof the baseplates.

During the polymerization of acrylic resin thematerial shrinks. Also, if it is under stress when itpolymerizes, then strains are induced in the materialwhich are released when the baseplate is removedfrom the cast. Polymerization shrinkage is mini-mized by ensuring the correct monomer-polymerratio. The distortion arising from the shrinkage canbe reduced by the appropriate variation in the


A BFigure 83A In preparation for casting the impression is placed on the vibrator. B An adequate amountof hydrocal mix has been poured and vibrated into the boxed impression.

Figure 84 The completed upper secondary cast.

thickness on the baseplate. The induction of strainscan be reduced by care in processing.

The wax patterns

1. Upper baseplate: Lay one sheet of wax in thepalate extending to within 1 ern of th crest of the

ridge. Do not overheat the wax in the flame - itshould merely be softened. Fill up the border sulcuswith wax flush with the top of the land (Figure 86).Lay one sheet of wax over the whole of the model.The wax baseplate is thicker in the middle andaround the border (Figure 87). This thicknessdistribution increases the rigidity of the baseplateand decreases distortion.

The step in the palate and around the borderprovides a place for finishing the next layer of acrylicwhen the teeth are added.

2. Lower baseplate: Fill the labial, buccal, andlingual sulcus to the level of the land (Figure 88).Adapt one sheet of wax overall (Figure 89).

Investing

Invest the casts in the lower half of the flask,bringing the plaster flush with the land (Figure 90).Complete investment using hydrocal in the top halfof the flask. When the investment is set, separateand boil out the wax.

Separating media (Figure 91)

Although tin-foil has been largely superseded by thesubstitute sodium alginate, this is a matter ofexpediency. A layer of tin-foil is to be preferred forthe following reasons:

It is impermeable to water - the layer of watervapour between the acrylic and the plaster duringprocessing leads to a lack of a clear surface in theacrylic.

It allows complete polymerization of the surfaceof the acrylic - this may be inhibited by the sodiumalginate layer.

A

c

E

45

B

D

FFigure 8SA The post-dam area is divided with contour lines 2 mm apart. B Pencil shading of the next posteriorzone. C The model is scraped until the shading has been removed. D The zone between the second contourline and the posterior border is now shaded and then scraped. E The whole post-dam area has now beenshaded and then scraped. F A line post-dam has been inscribed on the model. Note that it is anterior to theposterior border of the base.

A BFigure 86A,B The sheet of wax has been adapted to the centre of the palate and the sulcus has been filled withwax flush to the land.


Figure 87 Cross-section of diagram showing distribution ofwax over upper cast.

Figure 88 The sulcus of the lower cast has been filled withwax.

Figure 89 The lower cast with a sheet of wax adapted.

A

B

Figure 90A The upper cast and wax baseplate invested. BThe lower cast and wax baseplate invested.

Very fine surface convolutions in the modelsurface which would otherwise lead to a roughenedtissue surface of the denture base are smoothed out.Some people believe that this roughness can causeinflammation of the mucosa.

Processing and finishingWhen the mould is cold, pack it with clear acrylicdough. Do not pack in a warm mould because thisso accelerates polymerization that complete closureof the flask becomes difficult.

In removing the casts from the base plates, sectionthe casts and remove in fragments. Do not try to liftthe not baseplate off the intact cast - you will distortor even fracture it if you do.

When trimming and polishing the baseplate donot remove any acrylic from the border. (Figure 92)

A

Constructing wax occlusion rim 47

B

Figure 91A A sheet of tin-foil has been adapted to cover the upper cast and will provide a separating medium. B Analternative separating medium is sodium alginate which is applied to the cast with a brush.

Figure 92 Trimming the fhash from the clear acrylicbaseplate.

Constructing the mounting casts

Wax out all undercuts on the fitting surface of eachbaseplate and pour mounting casts in plaster-of-Paris (Figure 93). Remove the acrylic bases fromthese mounting casts.

Constructing wax occlusion rims

1. Roughen the ridge area of the polished surfaceof the baseplates. Soften some ready prepared waxocclusion rim and adapt.

2. The anterior surface of the upper rim shouldbe about 8-10 mm anterior to the incisive papilla(Figure 94). The upper rim should stop short of themaxillary tuberosity on each side. The lower rimshould not be any higher than the middle of theretromolar pad.

A

B

Figure 93 A plaster-of-Paris mounting cast has beenconstructed for, A the upper and, B the lower acrylicbaseplates.


Figure 94 The relationship of the anterior surface of theocclusion rim to the centre of the incisal papilla.

Composition occlusion rims

A problem with wax occlusion rims is their tendencyto soften at mouth temperature. Composition occlu-sion rims provide an excellent alternative. However,although impression compound provides a rigidocclusion rim which does not readily distort, it is amaterial which is more difficult to trim than wax andany adjustments which may be necessary are timeconsuming. Modelling wax on the other hand isrelatively easy to trim. If obtainable it is wise to usea higher fusing wax which is more rigid at mouthtemperature, such as 'Beauty Wax'.

Clinical stage 3

Checking the permanent base

This is done as the first procedure of the visit duringwhich the jaw relationships are to be recorded.

Checking retention of the bases prior toestablishing jaw relationships

The unretentive baseIf the completed denture base is not retentive thismust be due to failure to properly develop the forcesof retention. This may be caused through:

1. Overextension - the tissues of the border havebeen displaced excessively and the tension in thesetissues causes displacement of the denture.

2. Underextension and/or lack of post-dam -elastic strain is not developed in the border tissues.

3. The unsatisfactory form and/or consistency ofthe tissues of the mouth.

4. Warpage of the base during processing.

Before going on to describe the methods ofdealing with the unretentive base, it will be neces-sary to discuss the method of ensuring a seal at theposterior border of the upper base where there is novestibular reflection.

Post-damThe retention of a complete upper denture is largelydependent upon the establishment of an effectiveseal against the ingress of air around its border. Inthe sulci the seal is developed by the. elasticdisplacement of the soft tissues by the rounded

border of the base but, of course, it must becontinued across the palate at the posterior border.The degree to which the soft tissues can be displacedin this situation depends upon the amount andconsistency of the submucous tissues. In some areasthe mucous membrane and periosteum are incontact, e.g. in the midline, whereas in others thereis an appreciable amount of glandular and fibroustissue which is interposed between them. There is afurther problem at the posterior border of thepalate. Because of the contraction that takes placewhen acrylic resin is heat cured the contact of thebase with the tissues of the palate in this area is oftendeficient.

The most effective means of establishing the sealat the posterior border of the denture base is bytracing low-fusing impression compound along theback of the palatal surface of a correctly extendeddenture (Figure 95), by flaming and tempering it inhot water, and then by seating the base with a firm,backward and upward force. It is an advantage ifthis is done with a transparent baseplate. By lookingthrough the clear palate of the denture one canensure that the added impression compound has notcaused the base to be lifted away from the under-lying tissues. The improvement in the retention ofthe base will at once be manifest.

On removing the denture base the compound willbe seen to have flowed over an area of the base andits thickness in different situations will be anindication of the displaceability of the soft tissues(Figure 96). Any excess will have been expressedfrom behind the denture base. If the low-fusingcompound is insufficiently softened it will flowinadequately and the base will not seat homeproperly. If it appears that compound is excessivelythick it should be reheated, tempered with hotwater, and firmly reseated in the mouth.

49

50 Clinical stage 3

A

B

Figure 95A Adding low-fusing impression compound along Bthe posterior border of the palatal surface of the upperdenture. B The completed addition of compound - notethe shiny surface.

As an alternative to developing the post-dam atthe chairside, it may be effected by modifying thecast in the laboratory prior to the completion of thedenture base. Although this introduces a degree ofempiricism into the construction of the denture, anacceptable result may be obtained (see LaboratoryProcedures 2, p. 42).

The overextended base

Instruments and materials (Figure 97)1. Jar of disclosing wax or paste.2. Stainless-steel spatula.3. Handpiece and acrylic trimmers.

Procedure Apply disclosing wax or paste to theborder of the base in the area thought to be

cFigure 96A The denture has been firmly seated until theexcess composition is extruded. B The denture removedfrom the mouth - note the composition now has a mattsurface. C The excess material has been trimmed from theposterior border.

Figure 97 Instruments and materials for correction of over-extended base.

Checking the permanent base 51

overextended (Figure 98A). Place the base in themouth and have the patient open the mouth wide.In the case of the lower base have the patientprotrude the tongue. On removing the denture basefrom the mouth, that portion of the border which isoverextended will show through the wax and can becarefully reduced with an acrylic trimmer in ahandpiece (Figure 98B-E).

Further applications of wax and insertion of thebases may be necessary, but as the border is reducedthe retention will be improved.

The underextended baseIt must be emphasized that the extensive addition toan existing base is an exacting and time consuming

A

D

B

C

Figure 98A A little disclosing wax applied over the area ofthe base where excessive tissue displacement is suspected.B retracting the corner of the mouth to avoid wiping thedisclosing wax from the denture base. C Displacement ofthe disclosing wax has revealed the area of excessivepressure. D Trimming that area of the base which wasshowing through the disclosing wax. E After the base has

E been burred the wax is no longer displaced.

52 Clinical stage 3

Figure 99 Instruments and materials for correcting theunder-extended base.

procedure. It is often attempted and equally oftenso badly done as to make matters worse.

Instruments and materials (Figure 99)1. Low-fusing impression compound (Kerr's

green).2. Hanau torch or pin-point frame.3. Bowl of hot water at 60°4. Bowl of cold water.5. Stanley knife.

Upper base Soften the compound in a gas flameand apply the molten material along the back of thepalatal surface of the upper base (see Figure 100).(This should not extend more than 5 mm seeforward from the posterior border.) Flame thesurface with the Hanau torch or pin-point flame.Temper in the hot water and seat the base in themouth with a firm upward and backward pressure.Leave in position for 2 minutes before removing andplunging into cold water. The compound will havecaused displacement of soft tissues and any excessmaterial will have flowed out behind the base.Backward extension of the denture may be achievedin this manner if necessary.

Dry the denture and now apply further moltencompound to the underextended portion of theborder of the base, about 2 em at a time, commenc-ing in the hamular notch and continuing forward oneach side until, if necessary, the entire periphery hasbeen encompassed. After the application of eachnew portion of compound, flame and temper in hotwater before reinserting in the mouth. When the lastportion of compound has been added the seal shouldbe completed and the optimum retention achieved(Figure 100).

Figure 100 Low-fusing compound has been added to theentire border of the upper base to effect a border seal,

Whilst the denture base is being seated with thesoft compound addition in place, the patient isinstructed to open the mouth wide. Care should betaken to ensure that the molten compound does notflow on the fitting surface of the dentures. If it doesit should be trimmed away with a Stanley knife.

Lower base In adapting the molten compound tothe border of the lower denture it is normally tracedalong the lingual border, commencing in the midlineand proceeding backwards. After the lingual borderhas been completed the material is adapted firstover the retromolar pad, and then forward along thebuccal and labial borders on each side until theymeet in the labial vestibule. The impression com-pound is replaced with self-curing acrylic resin at thenext laboratory stage.

Jaw relationships

At the outset we considered the essential role ofmuscle activity in the functions performed with thedentures. It is important that the finished denturesdo not impede such activities. In certain of theseroles, principally mastication and swallowing, theteeth are brought together, and the degree of jawseparation at which this occurs will determine oneof the conditions under which the muscles will beacting.

It is therefore of considerable importance in theconstruction of complete dentures to select a suit-able degree of jaw separation at which the teeth willbe in contact. The amount of such separationbetween the jaws of a patient with natural teeth is

determined by the positions to which the teeth haveerupted. The teeth will be brought together bycontraction of the elevator muscles and such asituation cannot be maintained for very long. Forthe most part the muscles are in a partially restingstate and the mandible is suspended in the restposition. This is a position of equilibrium in whichthere is balance between the elevator muscles andthe combined effect of the infra-mandibular musclesand gravity. It may be affected by muscle tone andbody posture.

When the mandible is in the rest position thenatural teeth are usually slightly separated (by anaverage of 2 mm in the premolar region). This spacebetween the opposing teeth is known as the 'freewayspace'.

The amount of separation between the jaws willalso decide the vertical dimension of the face and,since it is more convenient to make measurementson the face than in the mouth, two arbitrary pointsare selected which are conveniently located oneabove and one below the mouth (usually in themidline), and measurements are made betweenthem. The separation between these points whenthe teeth are together is known as the occlusalvertical dimension and that when the mandible is therest position is known as the rest vertical dimension(Figure 101).

Because the rest position is influenced by bodyposture and muscle tone, it is important whenmaking measurements to:

1. Ensure that the patient is holding his body andhead erect without any support from the chair, and

2. Ensure that the patient is relaxed.

Figure lOlA A diagram to illustrate the measurement ofthe rest vertical dimension with a Willis gauge. B Adiagram to show the measurement of the occlusal verticaldimension with a Willis gauge.

Jaw relationships S3

The occlusal vertical dimension will always besmaller than the rest vertical dimension and by anamount which is greater than the 'freeway space'(because the points on the face are farther from theopening axis).

When the natural teeth are lost, the means ofprecisely measuring the occlusal vertical dimensionhas gone. However, the measurement of the restvertical dimension can be determined, and thisprovides a link" whereby the occlusal verticaldimension can be deduced. The occlusal verticaldimension should be made less than the rest verticaldimension by 4 mm in the average complete denturepatient. This will ensure the presence of at least 2mm 'freeway space' in the premolar region: this isan absolute necessity if the patient is going to beable to wear the dentures with comfort.

Not only do the natural teeth influence thevertical separation, but by virtue of sensations fromthe periodontal membrane they also enable thepatient to develop a consistent closure with max-imum cuspal interdigitation (centric occlusion).Useful sensations also arise from associated mus-cles, joints, mucosa, and the tongue. When teeth arelost this means of precise location of the jaws isimpaired.

With the dentures it is important that the patientis able to bring the jaws into such a position that thetooth cusps on the dentures interdigitate. If they donot, movement of the dentures and trauma to theunderlying tissues will occur due to the effect of theopposing inclined planes making contact.

Nevertheless, it is a matter of clinical experiencethat the occlusal vertical dimension with the com-plete dentures must be less than the edentulous restvertical dimension if the patient is to be comfort-able. However, it is very important that the restvertical dimension is measured with only onedenture in the mouth. When both dentures (orocclusion rims) are in the mouth it is quite possiblethat the patient will adopt a posture with the teeth(or rims) apart (and therefore present a rest verticaldimension greater than the occlusal vertical dimen-sion) regardless of the occlusal vertical dimension.This invalidates the procedure of assessing theaccuracy of the occlusal vertical dimension byobserving the presence of a 'freeway space' betweenteeth (or rims).

"The link is very tenuous because the use of the edentulousrest position as a guide to the occlusal vertical dimensionis based on the assumption that the rest position of themandible when the natural teeth are present is the sameas that when the teeth have been removed. Recently it hasbeen realized that this is not the case and that the restposition often changes when the mandible becomesedentulous. For the most part (but not always) it is nearerto the maxilla - in other words, the rest vertical dimensioncommonly decreases after the loss of the natural teeth.

54 Clinical stage 3

It seems that the only position which the patientcan repeat consistently is the one with the condylesin their most retruded positions in the fossae. It iscertainly the only one which can be recordedconsistently. The lateral ligaments of the tempor-omandibular joint restrict the backward displace-ment of the condyle and it is necessary to applyconsiderable force to retrude the jaw beyond thispoint. When both the condyles are retruded in theglenoid fossae the mandible will also be located inthe lateral plane.

Having fixed the mandible in the horizontal planeand determined the vertical separation between thejaws, a three-dimensional relationship between themandible and maxilla has been established. This isknown as centric jaw relationship.

In order to record a relationship between thejaws, it is necessary to build occlusion rims on thebaseplates and to trim these to the necessary verticaldimension and to locate them in the appropriatehorizontal relationship.

Establishing jaw relationships withpermanent bases

Objectivesl. To accurately record centric jaw relationship.2. To take a facebow record to enable the

baseplate and occlusion rims to be positioned in thearticulator so that their relationship to the rotationalaxes of the articulator is the same as the relationshipthey will bear to the rotational axes of the mandiblewhen they are in the mouth.

Instruments and materials (Figure 102)

1. Occlusion rims on permanent bases.2. Denture fixative.3. Modelling wax.4. Wax knife5. Flat metal surface.6. Willis gauge or callipers.7. Eyebrow pencil.8. Bowl of cold water.9. Stanley knife.

10. Facebow.11. Clean apron.12. Clean head-rest cover and paper towel for

bracket table.13. Mouthwash.14. Patient's record card.

ProcedureInitially the permanent bases must be free fromdefects such as 'pimples' and checked to see thatthey are retentive. If they are not retentive then theymust be corrected before any further procedure iscarried out (see p. 00 et seq.).

Assess the lip supportStudy the patient in full face and profile. Whereinsufficient support has been given to the lip only asmall amount of the vermilion border will be seenand the nasolabial groove may be exaggerated

Figure 102 Instruments and materials for establishing the jaw relationships.

A

B

Figure I03A The upper lip is inadequately supported bythe occlusion rim. B The upper lip is distended by theocclusion rim.

(Figure 103). Excessive support produces deforma-tion of the overlying tissues and is easily recognized(Figure 103B)

Check the height and orientation of the occlusalplaneThese procedures of adjustment to the occlusalplane of the upper rim and its labial form are arenot strictly concerned with the registration of thejaw relation, but are a convenience so that at a laterstage the teeth may be set in approximately thecorrect position. The lower border of the maxillar~occlusion rim represents the level at which ths;.incisive edge of the upper central iiicisors will be set.This level decides How mucli ot the InCIsal edge willbe seen below the margin of the upper lip. Theamount varies with individuals and is less in patientswith a long lip (the teeth may not be seen) andgreater with those who have a short lip. The averageamount of tooth exposed is 1 mm (Figure 104).

Ad.i-llli.t the occlusion rim until it is the correctheight anteriorly and tri-rilit unu It IS arallel withfife i1aso-tIagalli~amper's line). From tIi"efrontit shoul~ear to be horizontal when the ~atientsm-wrth the head erect igure 105).

Establishing jaw relationships with permanent bases 55

A

B

Figure I04A A small amount of the upper occlusion rimshows below the lip of an elderly patient. B In a youngpatient a large amount of occlusion rim is shown.

Mark the centre line on the labial surface of theupper occlusion rim (see p. 82). This should corres-pond to the centre line of the whole face and is notnecessarily the centre of the lips, nose, or any otherindividual facial feature

Measure the rest vertical dimensionInsert only the upper base and occlusion rim. Thepatient should be asked to sit upright with his backunsupported by the chair. In this position, the

ran ort ane a la~ssing through the lowestpoint in the margin of the orbit and highest point inthe margin ofthe external auditQ.r~meatus should

e onzonta see Figure 105).The patient should now be asked to relax. It may

be helpful if at this stage the arm-rests are removedfrom the chair and the patient is asked to place hisfeet down on each side of the foot rest. A patient'sjaws return to the relaxed position immediately afterswallowing and after the pronunciation of certainspeech sounds. The following methods may be usedto assist the patient and they can all be used:

56 Clinical stage 3

VI. Instruct the patient to swallow and relax.~2. Instruct him to pronounce fern", 'em', 'em', and

/ relax.3. Instruct him to moisten his lips with the tip of

the tongue and relax,

A

B

Figure I05A Using an occlusal plane guide the upperocclusion rim has been made parallel to the naso-tragalline(Camper's line). Note that this plane makes an angle ofapproximately 8° with the Frankfort plane which is alsoshown. B Viewed from the front the occlusal plane shouldbe horizontal.

o

A

It is not practicable to measure the separationbetween the jaws intra-orally and therefore mea-surements must be made between fixed points onthe face and on the mandible. There are twomethods commonly employed. The first utilizes agauge which measures the separation between thelower border of the septum of the nose and thelower border of the chin, and the second involvesmarking points on the skin and measuring thedistance between them.

Method 1: The Willis gauge

1. In using the Willis gauge to measure jawseparation the handle is held so that the chin isfirmly wedged between the slide and the scale, andthe scale is extended until the right-angle at the topjust touches the underside of the nasal septum(Figure 106). The pressure exerted in seating thegauge will obviously affect the measurementrecorded, but in the hands of one operator multiplereadings should give the same value. The angulationof the gauge to the end of the nose and chin will alsoaffect the measurement and each individual shouldestablish a standard procedure for the gauge to beof any value. As supplied, the Willis gauge has acursor 40 mm in length which slides to contact thepatient's chin, as illustrated in Figure 107. Thelength of this arm may make it difficult to bring it

B

Figure l06A The use of the Willis gauge in measuring the vertical dimension. B The use of a dakometer for this purpose.

A

B

Figure 107 Using the Willis gauge to measure the restvertical dimension.

into contact with the chin when the soft tissues ofthe neck are bulky. The usefulness of this instru-ment can be considerably improved if the cursor isreduced to 20 mm in length.

2. Note the measurement on the gauge with themandible in the rest position (Figure 107).

Metho~

1. Place a mark on the point of the nose and onthe chin (Figure 108A). This should be done with agreasepaint or eyebrow pencil which can be easilyremoved, or small pieces of sticking plaster can bestuck to the skin to carry the markings.

2. When you are satisfied that the mandible is inthe r?sf position record the measurement betweenthe nose and the chin markers, This can be done~ with callipers or by placing a sheet ofcardboard against the nose and chin, and makingmarks on it (Figure 108B,C).


A

8

CFigure I08A Marks have been placed on the tip of the noseand on the chin. B With the patient's jaw in the restposition the distance between the marks is measured withdividers. C A sheet of cardboard is used to measure thedistance between the marks.

It is possible that an error may result from usingthis method if the lower marker, i.e. that on thechin, moves. This can easily happen if the patientattempts to occlude the rims when the occlusalvertical dimension is in excess of that of the restposition, because he will at the same time try tobring the lips together.

58 Clinical stage 3

/

Establish the occlusal vertical dimension)1. Insert the lower base and occlusion rim. Note

t'h'eocclusal vertical dimension using the same pointsof reference as were used to measure the restver'tical dimension. Reduce the lower occlusion nm _until the separation between these markers is thesame as that which existed in the rest position. Nowremove material from the lower rim until the"occlusal vertical dimension is 4 mm less than the rest.vertical dimension (Figure 109)

L.. CReek that both rims occlude evenly on closing.Particular attention should be paid to the relation-ship of the upper and lower baseplates in the regionof the tuberosities and retromolar pad areas (FigurellOA-E). On some occasions there is insufficient

A

c

E

Figure 109 The occlusal vertical dimension is measured ona Willis gauge.

B

D

FFigure BOA The rims do not contact posteriorly because of a premature contact between the acrylic bases. B Aninterocclusal wax record is made, and the occlusion rims removed from the mouth reveal the interference betweenthe opposing baseplates. C The soft part of the retromolar pad is marked. This is the limit of posterior extensionof the lower base. D This indication is transferred to the base. E Reducing the excessive thickness and extensionof the lower base plate. F The interference has been eliminated.

Figure 111 Reducing the height of the rim by 1 mm toaccommodate the wax wafer.

room to accommodate two thicknesses of baseplatein this region and if this is so the bases must bereduced to ensure freedom of jaw movement. Thisshould be done so as not to jeopardize retention.Remove a further 1 mm from the lower rim .toaccommodate a wax wafer (Figure 111).

//

Record the centric jaw relationshipvl. Cut notches in upper and lower occlusion rimsto locate the wax wafer. In the upper rim one singleV-shaped notch should be made in the occlusalSUrface in the premolar region of each side. In thelower rim two V-shaped notches should be placed inthe premolar region of each side. (This is necessaryso that it is easy to identify the upper and lowersurface of the wax wafer.) (Figure 112).J: Take a sheet of modelling wax and soften oneend by passing it over a bunsen flame until both

Figure 112 Cutting locating notches in the upper rim.

Establishing jaw relationships with permanent bases S9

A

c

:gureJ~ the softened end of a sheet ofbaseplate wax to produce a double thicknessvB/Thefolding is complete. Note that it is quite even in t~ickness.{;..Qlltting a strip of softened wax S mm wide. JYAdaptingthe strip of softened wax to the surface of the lowerocclusion rim.

60 Clinical stage 3

A BFigure 114A The occlusion rims are placed in the mouth. The lower rim is held firmly in place with the forefingersof both hands. B The patient closes in the most retruded position. The softened wax locates the relationship of theocclusal rims in this position.

sides of the wax are pink in colour and thereforethoroughly softened.

3. Fold one end of the wax over to form a doublethickness and cut a strip 5 mm wide from this. Adaptthis to the surface of the lower occlusion rim (Figure113).Jl. Reinsert the lower base into the mouth, place

the forefinger of each hand on the buccal flange tohold the base in place, and instruct the patient toclose together, ensuring that the mandible is in themost retruded position (Figure 114).

It is usually possible to feel the backward displace-ment of the mandible when it is in the most retrudedposition. Tell the patient to open the mouth.

Figure liS The completed registration. The lowerocclusion rim with the attached wax wafer shows the sharpindentation produced by the notches in the upper occlusionrim.

Remove the upper and lower rims together with thewax wafer, which should remain attached to thelower rim (Figure 115). Reinsert and check theretruded position at least twice. If there is any doubtas to the accuracy of this record discard and.repeat.

~ough we have described the use of wax forthe interocclusal record because it is the simplestmaterial to use, it has the potential disadvantage ofbeing too viscous. In such a circumstance the basesmay be displaced during the recording. The alterna-tive use of impression plaster or impression paste isoften advocated. Unfortunately, with these fluidmaterials which must set in the mouth it is difficultto be sure that the patient maintains the requisitejaw position during the procedure.

/Methods which may be used to assist the patientin closing to airetruded position

1. When the condyles are in the most retrudedposition in the fossae and the jaw muscles arerelaxed, the jaw can be moved in a simple hinge-likemanner - it will not move like this if there is anyprotrusion, which can only be produced by muscularcontraction. It follows that if this simple hinge-likeclosure is adopted the jaw must be in the mostretruded position. Instruct the patient to relax thejaw and to close together. --

~. Instruct the patient t allow and close/3. It ha~n suggested that the patient beinstructed to place the tip of the tongue against theposterior border of the upper base and h.Q!.lfiLh.erewhile closingthe jaws. In order to help the patientfOlocate this position, a knob of wax or compoundmay be placed at the posterior border in the midline.There may be a danger in using this method that,unseen by the operator, the tongue may moveforward and with it the jaw.

4. Gothic arch tracing.


A

B

When difficulty is experienced in accuratelyrecording centric jaw relation, resort may be madeto the Gothic arch tracing technique (Figure 116A-C).

Permanent acrylic baseplates are first mounted ina tentative centric relation on an articulator andthen the following procedure should be carried out:

A horizontal line is drawn along the outside of themandibular cast parallel to the flat bearing area ofthe molar and premolar teeth. A rim of modellingcompound is constructed on the lower acrylicbaseplate, the height approximating to the finalposition of the tips of the lower teeth. A stiff brassplate is inserted into the palate parallel to the linescribed on the lower surface of the outer cast andattached to the acrylic baseplate by means ofmodelling compound. A screw-jack centre bearingpoint is luted to the lower occlusion rim assembly asclosely as possible to the centre of the lower archand with the bearing point in contact with the

c

Figure 116A Upper baseplate carrying metal plate with alayer of blue wax in which the Gothic arch tracing has beenscribed. A thin sheet of perspex has been laid over thetracing with an orifice corresponding to the apex of thetracing. B The patient has retruded the mandible so thatthe stylus has dropped into the depression correspondingto the Gothic arch apex, and plaster has been injectedbetween the baseplates to seal them together. C Upper andlower casts have been mounted in the articulator with theaid of the Gothic arch registration.

opposing plate. Vertical adjustment of the bearingpoint may be achieved by means of the screw-jackwhich is secured by the locking nut.

Having checked the vertical dimension in themouth and ensured that there is no interferencebetween the baseplates in lateral excursion, thesurface of the brass plate is coated with a thin layerof blue inlay wax. With the assembly in position inthe mouth the patient is instructed to close the jawsuntil the bearing point exerts light pressure and thento move the mandible in turn to right and to left withan occasional protrusive movement. The resultingtracing is inspected and when a clearly defined apexis observed no further movements are required. Atthis point a thin perspex disc with a hole in thecentre is positioned so that the apex of the tracinglies below the centre of the hole and is attached tothe brass plate with sticky wax.

On return of the assembly to the mouth thepatient is instructed to manipulate his lower jaw

62 Clinical stage 3

until the centre bearing pin engages the small holein the disc and to hold the two baseplates togetherwith light pressure. Impression plaster is theninjected between the occlusion rim and the upperbase plate on either side using a syringe. When theplaster has set, the whole assembly may be removedas a single unit which is used to mount themandibular and maxillary casts in centric jaw rela-tion. /,Protrusive record

When a patient protrudes the lower jaw the con-dyles both move forward and downward, guided bythe form of the articular fossae. The downwardmovements of the condyles result in a similardownward movement of the lower molar region(Figure 117). The protrusive record measures theamount of the drop. With it the articulator isadjusted so that it will produce a similar amount ofdrop when a similar amount of protrusion is used.The teeth on the denture can then be arranged so

A B

Figure 117A The jaw is in the most retruded position, theocclusion rims meet evenly. B The jaw is protruded, thecondyle drops as it moves forwards on to the eminence,and the occlusion rims become separated posteriorly.

that contact between the posterior teeth is main-tained in protrusion (protrusive balance) (Figure118).

The amount that patients can protrude their jawsvaries. Some can move the jaw forward so far thatthe condyles may pass forward beneath the lowerextremity of the articular eminence (Figure 119),whereas others (e.g. Angle's Class III cases) havevirtually no protrusion.

The purpose of the protrusive record is to enablethe teeth to be positioned to give balanced occlusionwhen the patient incises or makes eccentric move-ments. The maximum amount of protrusion neces-sary is therefore the amount needed to bring theedges of the upper and lower incisor teeth together.An amount less than this makes it difficult to adjust

A

B

Figure 118A With the appropriate setting of the condylartrack angle on the articulator an equal amount ofseparation will be provided. B The teeth have beenarranged to provide contact posteriorly in this protrusiveposition.

Figure 119 With an excessive degree of protrusion thecondylar head has passed beyond the articular. This maydecrease the amount of condylar drop and therefore theamount of posterior separation of the rims.

the condylar tract angle of the articulator correctly,and an excessive degree of protrusion will oftenresult in the condylar track being set to an anglewhich is less than the inclination of the condylareminence. For this reason the ideal time to registerthe protrusive record is when the anterior teeth havebeen set up in the position which they will occupyon the finished dentures. The procedure is thereforedescribed on p. 89. However, since this involves anadditional clinical appointment, many operatorsattempt to register the protrusive record with theocclusion rims after establishing the centric jawrelationship. If the labial surfaces of the occlusionrims have been trimmed to provide the correctamount of lip support, the degree of protrusion usedin making the registration is the amount necessaryto bring the labial surface of the lower rim in linewith the labial surface of the upper.

The facebow record 63

Figure 121 The condylar track of the articulator has beenadjusted so that the rims sit evenly in the wax registration.

vi/. Use a strip of softened wax three layers thick.I YPlace this on the lower occlusion rim and havet'11epatient close his jaws together in a protruded ~position. (The patient is greatly hel~ed in this if he The facebow recordcan look In a mirror to see what he IS doing.) Thenremove the lower baseplate, chill the wax, reinsertin t~outh and check (Figure 120).~. Remove this record and keep it in cold wateruntil the baseplate and occlusion rims have beenmounted on the articulator with the centric relationrecord (Figure 121). See p. 91 for a description ofthe articular adjustment.

Procedure

Figure 120 The patient has closed on the wax wafer withthe lower jaw in a protruded position.

1. The facebow record will enable the baseplatesand occlusion rims to be positioned in the articulatorso that their relationship to the rotational axes ofthe articulator is the same as the relationship theywill bear to the rotational axes of the mandible whenthey are in the mouth. 1t will also relate the base-plates and occlusion rims to the horizontal plane ofthe articulator as they are related to the Frankfortplane (Figure 122A,B).

The rotational axes of the mandible which are ofconcern to us are:

a. The horizontal inter-condylar rotational axis(hinge axis)' which is the axis of a hinge-likeopening and closing movement.

b. The two vertical axes which pass through eachcondyle are the axes around which the mandiblerotates in a lateral movement.

2. An average position for the inter-condylar axisis determined on the face by marking that point

'Hinge-axis determination: The actual hinge-axis can bedetermined clinically by the use of a kinematic facebow.This is a device attached to the lower jaw or teeth with arod extending around onto the side of the face with its tiplying on the skin in the region of the condyle. The patientopens and closes the jaw in a hinge-like manner and theend of the rod is adjusted until its tip performs a purerotation only. The point on the skin opposite the tiptherefore lies on the hinge-axis. The two sides are usuallydone separately.

\

64 Clinical stage 3

A

B

Figure 122 The facebow in place on a skull and on thearticulator. A Viewed from the side; B Viewed from thefront.

which is 1 cm in front of the centre of the externalauditory meatus along a line from the tragi on (themost posterior point of the curve of the tragus) andthe outer canthus of the eye (Figure 123).

3. The condylar rods are adjusted so that themeasurement on each side is the same when theyare lightly contacting the skin overlying the markedpoints. The condylar rods are now locked in theposition and the facebow set aside.

4. The facebow fork (e.g. Dentatus, Hanau) isdesigned to be inserted into the labial surface of awax occlusion rim.

5. The prongs of the fork are heated in a bunsenflame and pushed into the labial face of the upperocclusion rim 3 mm above its lower border. Thehandle of the fork should be offset so that this willbe on the right of the patient when the rim has beenreinserted in the mouth (Figure 124A,B).

Figure 123 Locating the approximate position of theintercondylar rotational axis by reference to faciallandmarks.

A

B

Figure 124A Heating the prongs of the facebow fork. BEmbedding the fork in the lateral face of the upperocclusion rim.

Procedure

1. Place the upper occlusion rim together with theattached fork in position in the mouth. Thread thehandle of the fork through the sleeve of theappropriate universal joint on the facebow andadjust until the condylar rods are in the correctposition. Now tighten the locking nut. Note that thesleeve for the infra-orbital marker should be on thepatient's left and that for the facebow should be onthe patient's right. The telescope adjustment shouldbe screwed into place on the sleeve which accommo-dates the facebow fork.

In order to ensure that the facebow does not moveit is recommended that it be held in place with theforefingers of the operator's right hand. With his lefthand he holds the right condylar rod over therotational axis. An assistant positions the left condy-lar rod and tightens the locking nut (Figure 125A).

A

B

Figure 125A Locating the facebow and locking the forksinto position. Note that the hands of both operator andassistant are needed to perform this task with accuracy. BThe orbital pointer is next attached to the facebow. Notethat the end of the fork is held to avoid any danger ofinjury to the patient's eye.

Selection of teeth 65

2. Take the infra-orbital guide pin and threadthrough the other sleeve on the facebow andposition the pointer at the lower border of the orbit.Be careful of the patient's eye. Now lock in position(Figure 125B). It is important that when tighteningthe locking nut the lower part of the body of thelocking joint is gripped as shown in Figure 126,otherwise it may twist.

Figure 126 Tightening the locking nuts on the facebow.

With the older types of facebow fork it may benecessary to wrap softened wax around the fork andinsert it between the upper and lower occlusionrims. Instruct the patient to close firmly on the forkin order to hold it steady. Place the facebow inposition together with the infra-orbital marker aspreviously described.

Care should be taken to ensure that the facebowdoes not displace when the patient brings theocclusion rims together.

Selection of teeth

Objective

To choose artificial teeth whose form and colour willharmonize with the patient's features.

Instruments

1. Shade and mould guide.2. Willis gauge.

66 Clinical stage 3

Procedure

Choice of materialA decision must first be made as to whetherporcelain or acrylic teeth are to be used. Porcelainhas a hard glazed surface which is unaffected byabrasive food or cleansing agents and is not affectedby solvents. This ensures the continued efficiency ofmastication throughout the life of the denture.Acrylic teeth, on the other hand, may become worndown with consequent loss of vertical dimension.Because of their greater resilience, acrylic teeth aresaid to cushion the underlying supporting tissuesfrom the occlusal loads. However, since suchresilience is also exhibited by the resin of thedenture base, the effect of the teeth themselves isonly marginal. In any case, the resilience of acrylicresin is very small compared with that of theunderlying soft tissues and so the supposed effect isthereby worthy of consideration. Because acrylicteeth unite with the denture base resin by chemicalunion, they can be used in situations where there isinsufficient room to accommodate the diatoric holesand pins necessary to secure the mechanical anchor-age of the porcelain teeth.

The disadvantage of porcelain is that it is brittleand thus susceptible to fracture. It has a differentcoefficient of thermal expansion from the acrylicresin base material, and unless the dentures arecarefully processed crazing may appear round theteeth.

The combined use of porcelain teeth in onedenture occluding with acrylic teeth in the other hasbeen advocated by Myerson (1957). Provided theglaze on porcelain teeth is not removed, the wear ofthe opposing acrylic teeth will be less than wouldhave occurred if acrylic teeth had been used on bothdentures. Even if the occlusal surface of the acrylicteeth does become flattened by wear, the integrityof the occlusal surface of the porcelain teeth ensurescontinuing masticatory efficiency (Figure 127). Theuse of this combination is dependent upon teeth ofthe different materials being available in identicalmoulds.

Unfortunately, the present extensive use of acry-lic resin teeth' has chiefly been determined oneconomic grounds rather than on a consideration ofthe properties of the tooth materials and any clinicalindication.

Selection of mouldThe important thing is to choose a tooth of pleasingproportions. The length of the anterior teeth shouldpreferably be greater than their width. There is auseful correlation between the distance between thetips of the left and right canine teeth measured in astraight line and the width of the nose (Figure 128).

A

B

Figure 127A Sagittal view of complete upper and lowerdentures which have been worn for 6 years. Note thepattern of wear of the lower acrylic teeth which areopposed by porcelain uppers. B Occlusal view of samecase. Note the facets which have been generated by thepath of movement of the porcelain upper teeth.

This can be measured with a Willis gauge or anyother calliper (Figure 129). The extreme ranges ofnose widths are 28-45 mm, but, if three intercaninewidths are taken using values of 30, 35, and 40 mm,variations on each side of these measurements canbe produced by altering the arrangements of theteeth (by imbrication and spacing if necessary).Since the six anterior teeth are arranged on an arcand those on the mould guide are on the same plane,the measurement made on the guide should be 3-4mm greater than the value of the nose width, i.e.33,38, and 43 mm. The length of teeth used dependsupon having sufficient room to accommodate theselected mould in the space between the incisal edgeof the upper occlusion rim and the baseplate.

In many mould guides the teeth are arranged insquare, tapering, and ovoid forms following LeonWilliams's suggestion that there was a correlationbetween the shape of the upper central incisor teethand the shape of the face inverted. Another methodwhich has been used in selecting the shape of teethis to use the outline of the upper arch. Neither ofthese methods has any scientific basis, but the fact

1

B c D

Figure 128A Relationship between the intercanine distance and the nose width. B, C, D Three variations in nose width:30, 35, 40 mm wide respectively.

A B

Figure 129A The use of dividers tomeasure the nose width. B Thedividers have been opened by afurther 3 mm and this measurementis used to select upper anterior teethwith this intercanine distance.

67

68

-Wi • stz.. h•.

Figure 130 The four basic shapes of the face and the teeth shown contoured tocorrespond with them.

that they have been used for many years perhapslends strength to the view that shape is not all-important.

Lee (1962) has described a method of toothselection which may be easier to apply. He usesthree facial measurements and relates the propor-tions of the teeth to the proportions of the face(Figure 130). He compares the width of the front ofthe forehead and the width of the front of the faceat the level of the lips with the width of the faceacross the zygomata. The corresponding teethdimensions are gingival third, the incisal tip, and themaximum width.

Thus a patient whose facial dimensions are wideat the level of the forehead and lips will require atooth which is wide at the gingival third and incisaltip, and this would correspond to a square shape. Ifthe forehead and incisal tip dimensions were narrowby comparison with the interzygomatic width, anovoid type of tooth would be appropriate.

Selection of shadeThe colour of tooth substance is basically yellow.The addition of red to this basic colour makes itwarmer and the addition of blue makes it cooler.

References 69

With anyone colour, teeth can be produced withdarker or lighter shades. In order to produce alifelike appearance, teeth should be selected whichare warm and those with too much blue pigment(grey teeth) should be avoided. The colour ofnatural teeth is due to the underlying dentineshowing through a translucent enamel. As moresecondary dentine is laid down with advancing yearsthe shade darkens. This matter is also dealt with ingreater detail by Lee (1962).

ReferencesJ .H. Lee (1962) Dental Aesthetics, Chap IX, Wright,Bristol.R. L. Myerson (1957) J. Prosthet. Dent. 7, 625.


Adding the post-dam to the upperdenture base

If the post-dam has been added to the clear heat-cured base using tracing stick compound in themouth, the following procedure must be followed tomodify the base so that the post-dam is included:

1. Block out any undercut areas in the anteriorpart of the base with baseplate wax. Smear thewhole fairly lightly with Vaseline (Figure 131).

2. Mix hydrocal to a thick consistency and castinto the posterior part of the base, ensuring that allthe composition post-dam is included. When thehydrocal is set, separate the base from the cast(Figure 132).

3. Cut back the base until it is clear of the post-dam area and bevel the cut edge from the mucosalto the palatal side.

Figure 131 The anterior part of the base has been blockedout with wax prior to making the cast.

70

Figure 132 This shows the cast and the post-dam arearecorded in it.

4. Coat the cast with separating medium and allowto dry thoroughly. Replace the base on the cast andensure that it is fully seated; this is most important(Figure 133).

5. Mix some clear self-curing acrylic resin in asuitable pot. Add the powder carefully to the liquidwhile holding the pot on a vibrator. Stir gently andthen place the pot in a vacuum chamber. This willremove all air bubbles.

6. While the mix is still quite fluid add it to theuncovered area of the cast and the adjacent part ofthe base. The base must be held firmly in place onthe cast to preclude any possibility of liquid resinpenetrating beneath the base. At the same time noair should be trapped beneath the addition. Slowlybuild to full thickness as the material thickens(Figure 134).

Figure 133 The denture base has been cut back beyond thepost-dam area. Note that the base has been bevelledwidely to increase the area of contact of the old and newresin.

Figure 134 The self-cure resin is added to cover the post-dam area.

7. Allow the resin to set and do not attempt toremove the base from the cast until it is quite hard(Figure 135).

8. Trim and polish the addition.

At this stage the baseplates and rims are mountedin the adjustable articulator and then the teeth areset up in centric relation.

Selecting posterior teeth 71

Figure 135 The resin addition is set and after removal fromthe cast is trimmed and polished.

Mounting the baseplates and occlusionrims

Read the instruction manual that is provided withthe articulator. It contains much useful informationand explanation. Be sure that all the adjustingscrews are fully home and that the incisal pin is setat '0'.

First attach the upper mounting cast, seating inthe upper baseplate. The baseplates and occlusionrims are mounted on the articulator by attachingtheir mounting casts to the mounting rings withplaster, using the facebow as a support. Thefacebow is set symmetrically on the articular and theorbital pointer must touch the orbital plane guide -note that this guide and the condylar axis of thearticulator make up a horizontal plane (Figure 136).Mount the lower cast using the wax centric relationrecord to locate it to the upper rim. Note that thearticulator can be turned upside down to facilitatemounting the lower cast (Figure 137).

Trim the mounting neatly and wash all plaster offthe articulator. Never present a dirty articulator orrough untidy mounting - the work on it is usuallyslovenly.

Selecting posterior teeth

The cusps on natural teeth facilitate the shearing offibrous particles of food as the closing jaws obliquelyapproach the intercuspal position. The initial toothcontact is usually made on the ipsi-lateral ('work-ing') side and only when the chewing stroke iscompleted do the teeth on the contra-lateral ('non-working', 'balancing') side make contact. If such astate of affairs was allowed to occur when the teethwere set on a complete denture the initial unilateralcontact on the working side would cause the

72

A

Figure 136 The upper base is mounted on the articulator using the facebow record.

B

A

c

B

D

Figure 137A The lower base and mounting cast are located to the mounted upper base with the interocclusal record andattached with stieky wax. B The articulator is inverted to facilitate the attachments of the lower mounting cast to thearticulator. C Plaster is heaped on the lower mounting cast and the articulator framework closed until the pin is in contactwith the incisal table. D The completed mounting of the occlusion rims.

dentures to be displaced: we therefore arrange theteeth to provide occlusal balance. (described underLaboratory Procedures 4 on page 91).

In order to satisfy the requirements of balance,parts of the occlusal surfaces of the teeth mustparallel the path of mandibular movement and it isthe slope of the cusps which provide this parallelism.The shallower the slope of the cusp the more steeplymust the individual teeth be arranged to secure this.If no cusps project from the surface of the tooth (flator inverted cusped teeth) the curve of the occlusalsurface will need to be so steep that very few teethcan be fitted into the available intermaxillary space.From the foregoing it should be apparent that thepresence of cusps on posterior teeth and thesteepness of the cusp angle will have an importanteffect on the development of balance.

It has been suggested that the resolution ofmasticatory loads falling on the inclined planes,represented by the slopes of the cusps, will result inthe transmission of lateral forces to the denture basewhich will be damaging to the supporting tissues orcause displacement of the lower denture. This haslead to the development of the so-called 'invertedcusp' teeth and a variety of other 'non-anatomical'forms which are said to reduce the damaging lateralforces.

It is worth noting that this notion of cuspsproducing 'interference' to free movement is due toa misconception of cusp relations. In fact, properlyset posterior teeth are arranged so that the cuspsmove between each other not over each other (seeFigures 171A and 17B). This misunderstanding iswidespread and appears in much of the literatureand many text books. Tt has led to many torturedand fallacious methods of dealing with the occlu-sion, including the concepts of 'cuspless' teeth.

This fallacy is compounded by the notion of'lateral excursions'. Of course in normal functionpeople do not make 'excursions' but bring the teethtogether in the lateral position and then slide intothe intercuspal position - they make chewingincursions'. From this point of view, a sloping pathof contact cannot be obstructive.

We have just seen that to build a balancedarticulation without cusps on the posterior teethnecessitates very steep lateral and anteroposteriorbalancing curves. Tt is obvious that this will alsoproduce lateral stresses. What is more, the use ofnon-anatomical surfaces places limitations upon thesetting of the anterior teeth, discouraging the use ofany vertical overlap of the incisors and thus affectingthe cosmetic result. Because of the absence of theshearing action provided by the cusps, chewingefficiency is reduced and it has recently been shownthat the occlusal load is sustained for a longerperiod.

For the foregoing reasons we favour the use ofteeth with cusps, the angulation of which may be

Setting the teeth 73

selected according the path of mandibular move-ment which is determined by the slope of thecondylar and incisive angles.

Setting the teeth

You have now recorded the most retruded relation-ship of the mandible to the maxilla at the chosenocclusal vertical dimension. This relationship iscalled the centric jaw relationship because it is theone from which all other relationships are mea-sured. You will now replace the occlusion rims withartificial teeth.

You will arrange the teeth so that there ismaximum interdigitation of the cusps in the oppos-ing fossae; this arrangement is called centric occlu-sion. You will set up the teeth in centric occlusionwith the casts in centric relationship.

The following instructions relate to the setting upof teeth for a basic Angle's Class I relationship witha normal incisal relationship. This is dealt with ingreat detail in the books by Boucher (1970) and Lee(1962). On p. 92 we discuss the modifications totooth position and relationship which are necessaryin cases where there is a malrelationship of the jawsor abnormality of lip form or function.

The upper anterior teeth

Preliminary steps1. If you have trimmed the labial surface of the

upper occlusion rim to represent the requiredamount of upper lip support, then you can set theteeth directly into the wax surface. This, however,can prove to be difficult for the newcomer becauseafter some repeated attemps the necessary informa-tion is lost! It is therefore helpful to use a plasticocclusal template (Figure 138). This flat plate isplaced against the occlusal surface of the upper rimand supported on the lower mounting cast withplasticine. The labial contour is traced onto the platewith a pencil, the wax rim removed and the incisaledges of the teeth set against the traced line. Note,however, that contouring of the rim for labialsupport is most often faulty and a check must bemade of the relation of the central incisor edges tothe incisive papilla.

2. If the rims have been trimmed only to establishthe occlusal plane level and the occlusal verticaldimension, then, after recording the occlusal planelevel with dividers (Figures 139, 141), or setting upa plastic template as described above, the teeth areset using the incisive papilla as a guide (Figure 140).

The incisive papilla Tn the natural dentition thelabial surface of the upper central incisor is about 10- 12 mm anterior to the centre of the incisive papilla.


Figure 138 A plastic template has been supported on thelower base against the occlusal surface of the upper rim.

After extraction of the teeth and the subsequentbony remodelling there may be a slight upwards andforwards migration of the papilla, but even then thedenture incisors must be placed with the labialsurface at least 8 - 10 mm anterior to it. The incisivepapilla is one of the most useful biometric guides,on which more information is provided in a subse-quent chapter. Of course, the final definitive posi-tioning of the teeth can only be made at the trialdenture stage by moving the teeth in the wax andobserving them in the mouth.

Procedure1. Set up the central incisors with the long axes of

the labial surfaces vertical and their contact pointcoincident with the centre line of the face (Figure142).

A

B

c

Figure 139A An arbitrary point is marked on the frame ofthe plaster mount above the centre line. The dividers areopened to record the distance between this part of theocclusal surface of the upper rim. B, Posteriorly on eachside additional marks are made on the plaster mounting anequal distance above the occlusal surface of the tim. A linedrawn through these points will be parallel to the occlusalsurface. C The distance between the points of the dividersis permanently recorded on the side of the mounting cast.

A

Setting the teeth 75

B

Figure 140A This photograph of a model shows the relationship of the natural central incisors to the incisive papilla. B Acoronal section of the model.

Figure 141 Using the dividers to determine the position ofthe incisal edges of the central incisors.

Figure 142 The central incisors are set with their long axesof the labial surfaces vertical.

2. The lateral incisor is set with the long axis ofits labial surface inclined slightly distally and alsoslightly inward at the neck (Figure 143).

3. The canine is set with the long axis of its labialsurface vertical. Set in this way, the labial surfacehas a bulge at the neck which produces the effectthat the labial surface is inclined out towards theneck (Figure. 144).

The upper posterior teethDo not set the teeth too close together; leave a littlespace between each one of them (say 1 mm) (Figure145). If a template is used set the teeth so that allthe buccal cusps lie along the line which has beendrawn on the template (Figure 146A). If there is notemplate then the occlusal level of the posteriorteeth is determined by using dividers (Figure146B).Note that at this stage the teeth are set on a flatplane.

The lower anterior teeth

1. Set up the central incisors with incisal edgetouching the palatal surface of the upper incisor 2mm palatal to the incisal edge. The long axis of itslabial surface should be set vertically, but slightlyinward at the neck (Figure 147).

2. Set the lateral incisor so that its long axis isslightly inclined distally and in at the neck. Thisinclination should not be so pronounced as that ofthe upper lateral incisor (Figure 148).

3. Set the lower canine with its long axis verynearly vertical, with only a very slight distal inclina-tion (Figure 149).

76

Figure 143 using the dividers to determine the position ofthe incisal edge of the lateral incisor.

A

Figure 144 The six anterior teeth are set. Note the settingof the canines.

Figure 145 Posterior teeth set with a little space between them. A View from above; B View from the side.B

A

Figure 146A Posterior teeth set on template. B Posterior teeth set using dividers

B

A

77

B

Figure 147A A frontal view of the lower central incisor showing the long axis to be vertical. B A lateral view shows thelower central incisors to be set with a slightly labial inclination.

A

Figure 148A Frontal and, B, lateral views showing the setting of the lower lateral incisors.

B

A

Figure 149A Frontal and, B, labial views of the setting of the six lower anterior teeth.

B

78

A

c

8

D

Figure ISOA-E The lower posterior teeth are set one at atime in centric occlusion with the upper teeth.

Figure 151 Diagram to show buccal overjet (X) ofposterior teeth.

The lower posterior teeth1. Set these teeth in centric occlusion with the

upper posterior teeth.2. This will be facilitated by reducing the size of

the marginal ridges of the upper and lower posteriorteeth and also by the slight spacing of the upperteeth (Figure 150).

3. Be sure that you have allowed sufficient buccaloverjet (Figure 151).

4. Check that the long axes of the teeth are atright-angles to the occlusal plane.

References 79

References'Boucher's Prosthodontic Treatment for Edentulous

Patients. J. C. Hickey and G .A. Zarb, Sth edn, StLouis, Mosby.

J.H. Lee (1962) Denial Aesthetics, Chap. XXIII, Bristol,Wright

Clinical stage 4

The trial dentures

In the activities performed by the mouth, theteeth function within an environment of structuresmoved by muscles. On one side is the tongue andon the other side the lips and the cheeks. Thesestructures are intimately concerned with eating andwith speech. During mastication the tongue andcheeks keep the food on the occlusal surface of theteeth and the lips are sealed to keep it in the mouth.In speech the tongue, lips and teeth combine toproduce the various sounds.

When the patient has lost his natural teeth andhas been provided with dentures then the positionof the teeth on the dentures must be such that theactivities involving these muscles are not impaired.Neither should the muscular activities unseat thedentures.

If the teeth on the dentures are too linguallyplaced the movement of the tongue will be impededand will tend to displace the dentures in chewing.Also, food will tend to slide off the occlusal surfacesinto the cheek and the cheek will be unable to getit back. If the teeth are too labially or buccallyplaced the actions of the labial and buccal muscula-ture will tend to displace the denture, and thetongue will have difficulty in keeping food on theocclusal surfaces. There will also be a tendency forthe patient to bite his cheek. If the lower occlusaltable is too high the tongue and cheek will be unableto lift and hold the food on the occlusal surfaceswithout lifting the floor of the mouth so high as todisplace the dentures.

The teeth should be placed in such a position thatthe forces from the tongue are equalized by theforces from the lips and cheeks - they are then saidto be in the 'neutral zone'. The lower occlusal table

80

should be at such a height that the tongue can easilyplace the food upon it and also help hold the denturedown when the mouth is open wide and the lowerlip is tending to displace the denture posteriorly.

The muscular forces will have influenced thepositions into which the natural teeth erupted, andso the placing of the teeth in the neutral zone isaccomplished if they are placed in the approximatepositions of their natural predecessors. A guide tothis can be obtained by considering the pattern ofbone resorption when the teeth are lost.

In the upper jaw resorption occurs in the labialand buccal areas and so the residual ridge is to thepalatal side of the position occupied by the naturalteeth. Thus the artificial teeth should be placedlabially and buccally of the residual ridge if they areto be in the neutral zone.

In the lower jaw bone loss occurs on the labialside in the anterior region, equally on buccal andlingual sides in the premolar region, and lingually inthe molar region. Thus the residual ridge is morelingual in the anterior region, about the same in thepremolar region, and buccal in the posterior region.So the artificial teeth should be placed labially of theridge anteriorly, over the ridge in the premolarregion, and slightly lingually in the molar region - ifthe latter will give a lingual overhang, narrow teethshould be used. The natural teeth positions alsoinfluence the pattern of movements involved inspeech, and if they are radically altered speech mustbe affected (Figures 152,153).

When trying in the wax dentures initially theopportunity is taken to yet again check the jawrelationships. When you are satisfied that these arecorrect the position of the teeth can then be checkedand adjusted. When the wax dentures are satisfac-tory a protruded jaw relationship is recorded whichwill be used to adjust the condylar tracks of the

A B

Figure IS2A Diagram to show the relationship of theerupted natural posterior teeth to the tongue and cheeks.They are in the neutral zone. The shaded area shows theanticipated alveolar bone resorption. B Diagram to showthe relationship of the artificial teeth to the edentulousalveolar ridge when they have been positioned in theneutral zone.

Figure IS3A Diagram to show the relationship of theerupted natural anterior teeth to the tongue and cheeks.They are in the neutral zone. The shaded area shows theanticipated alveolar bone resorption. B Diagram to showthe relationship of the artificial anterior teeth to the tongueand lips. They are in the neutral zone. The shaded areashows the anticipated alveolar bone resorption.

The trial dentures 81

articulator. The articulator can be used to set up theteeth to balance eccentric occlusions.

Objective

To check that the arrangement of the teeth is suchthat speech and mastication will be restored and toensure that a pleasing appearance is obtained.

Instruments and materials (Figure 154)

1. Wax dentures.2. Articulator.3. Bowl of cold water.4. Bunsen burner.5. Wax knife.6. Sheet of modelling wax.7. Willis gauge.8. Indelible pencil.9. Patient's record card.

10. Mouthwash.11. Clean towel for bracket table (paper towel).12. Clean head-rest cover.

Procedure

Check the occlusal vertical dimension1. Measure the occlusal vertical dimension and

compare it with the resting vertical dimension.2. If an error exists this must be corrected.

However, if this should be only a small one, it canbe adjusted within the range of plus or minus 3 mmby raising or lowering the articulator pin andrearticulating the teeth to the correct verticaldimension. After this procedure, the dentures mustbe tried in again to check that no error has arisen inthe anteroposterior relation. An error will haveoccurred if the jaws do not open in a true hinge-likemanner or if the facebow record was inaccurate. Itis necessary that the geometry of the path of closureof the dentures on the articulator should be the sameas the geometry of the path of closure of thedentures in the mouth. The facebow is the calliperused to ensure that the geometrical relation of thedentures and the axes of rotation of the articulatorare the same as the geometrical relation of thedentures and the corresponding axes of rotation ofthe jaws.

3. If the error is greater than 3 mm it is necessaryto take a fresh recording and to remount the castson the articulator. This is done in the following way:

Having determined the amount by which theocclusal vertical dimension should be increased ordecreased, the teeth should be removed from the

82 Clinical stage 4

Figure 154 Instruments and materials for the try-in of the denture.

lower denture. The upper denture and lower base-plate are reseated on the models on the articulator.The pin may now be adjusted to the requireddimension and a wax occlusion rim constructed onthe lower base to this height. If the wax denture andlower occlusion rim are now returned to the mouththey should meet fairly evenly at the correct occlusalvertical dimension. Flow a little soft wax onto thesurface of the occlusion rim. A new centric jawrelation may be established which will enable thelower model to be rearticulated in its correctposition with the articulator returned to zero.

Check the anteroposterior jaw relationshipCheck that the teeth have been correctly set up onthe articulator in centric occlusion (maximum cuspalinterdigitation). If, when the denture is inserted inthe mouth, the opposing cusps fail to interdigitate,this will indicate that the previous centric jawrelation record was incorrect. In such a circumstancea new centric jaw relationship record will have to berecorded.

It is important that the same procedure should beadopted here as that already described for recordtaking. This will ensure that the patient closes incentric jaw relation. Repeated checks should bemade to ensure accuracy.

Care needs to be taken where there has beengross resorption of the alveolar bone, as the lowerbase may then be easily displaced on the mucousmembrane. This results in an apparent error wherenone may exist.

Assuming that the vertical dimension is correct,the wax upper and lower dentures should bereturned to the articulator, and the lower posteriorteeth removed and replaced by a wax occlusion rim.

The upper denture should now be returned to themouth, a little soft wax applied to the surface of thelower rims, and a new centric jaw relation estab-lished.

Care should be taken to ensure that when thepatient closes together none of the artificial teethremaining on the baseplate come into contact withthe wax upper denture. If this does occur theoffending teeth should be removed and the centricjaw relation recorded again.

Check the appearance (see Lee, 1962)With the upper and lower wax dentures 10

position:

I. Check the lip form to ensure that the upper andlower anterior teeth are in their correct positions.

2. Check the centre line (Figure 155).3. Check the orientation of the occlusal plane to

ensure that it is not running down on either side andthat the posterior teeth are arranged parallel to thenaso-auricular line (Figure 156).

4. Check that the shade and mould of teeth aresatisfactory.

5. Check the arrangement of the teeth to ensurethat they give a pleasing appearance.

Figure 155 The centre line between the central incisors lieson the centre of the face.

A

B

Figure 156A Using Fox's plane to check the orientation ofthe occlusal plane. From the front it should be horizontalwhen the head is erect. B Using Fox's plane, the occlusalplane should be parallel to the naso-auricular line.


6. When you are satisfied with the appearance andarrangement of the teeth the patient should be givena mirror and invited to comment on the appearanceof the dentures.

7. From time to time patients ask for teeth whichare too small or too white, and it is necessary toexplain to them that the natural teeth are basicallyyellow in colour and darken with age, and that onlythe deciduous dentition appears white.

Tooth positionsThe relationship of the teeth of the lower dentureto those of the upper will be decided by theunderlying relation of the jaws. * This means that ifthe lower jaw recedes behind the upper jaw (ClassII relation) the lower anterior teeth will be someway behind the upper teeth. If the jaws lie directlybeneath each other (Class I) then the lower anteriorteeth will bear a normal relation to the upper. If thelower jaw projects beyond the upper (Class III), thelower anterior teeth will be set anteriorly to thenormal position (Figure 157).

Within this framework the position of the teethwill be adjusted to be compatible with the muscularactivities of lips, cheeks, and the tongue. Theessential point is that the tongue must be givensufficient room but that the teeth must not encroachupon the cheeks or distort the lips.

For each segment of the arches the followingcriteria should be used:

1. The upper anterior teeth should provide suit-able lip support, as has already been discussed.

2. The upper posterior teeth will be positioned togive occlusion with the lower posterior teeth provid-ing adequate buccal overjet.

3. The lower teeth must be placed in the neutralzone. The lower posterior teeth must be positionedso that when the tongue is at rest it lies comfortablyagainst them and yet they do not encroach upon thecheek - it may be necessary to use narrow teeth orto grind the lingual cusps. The teeth should notoverhang the tongue. Given these positions theupper posterior teeth are adjusted to establishcentric occlusion (Figure 158).

To decide if these criteria have been met, havethe patient rest and partially open the mouth andobserve the relationships of the teeth to cheeks, lips,and tongue (Figure 159).

It is appropriate here to consider the setting of theposterior teeth called 'cross-bite'. In this the lowerteeth are set with the lingual cusps occluding in theupper central fossae. This is done when the lower

*For prosthetic purposes we use Angle's classification todesignate the basic jaw relationship.

84 Clinical stage 4

A B

o o

Jc

Figure 157A A Skeletal I Relation. The'angle SNA is 80° and the angle SNB is 78°. These are the average values foundwhere the dental bases are normally related to each other and to the cranial base. B A Type of Skeletal 2 Relationship.In this case the angle SNA is 80° and the angle SNB is 73°. There is a mandibular retrusion with a maxilla normally relatedto the cranial base. C A Type of Skeletal 3 Relationship. The angle SNA is 80° and the angle SNB is 83°. There is amandibular protrusion in this case with a maxilla normally related to the cranial base. (Reproduced from 'A Manual ofPractical Orthodontics', 3rd ed., edited by W. 1. Tully and A. C. Campbell, by kind permission of John Wright & Sons,1970.)

Figure 158 A view of the coronal plane to show therelationship of the posterior teeth to the tongue and cheekswhen set in the neutral zone.

ridge is much wider than the upper (as may occur ina class III base relation) and where normal settingwould resuht in the lower teeth encroaching on thetongue. However, the setting of the 'cross-bite is tobe deprecated because it produces a very disturbedand inadequate occlusion and precludes the properdevelopment of the lateral occlusion. It is muchpreferable to provide additional room for the tongueby reducing the width of the teeth from the lingualby grinding.

4. The lower anterior teeth should be positionedto provide adequate support for the lip. The lower

A

BFigure 159A With the patient's mouth slightly open therelationship of the teeth to the tongue and cheeks can beseen. B The lower occlusal plane is placed so that themaximum convexity of the resting tongue is slightly aboveit.


lip should rest against the incisal one-third of thelabial surface. The tip of the tongue at rest shouldbe comfortably behind the lingual surfaces (Figure160).

The height of the lower anterior teeth willdetermine the amount of vertical overlap - thehorizontal overlap will be largely decided by thebasic jaw relation.

In an Angle's Class II jaw relation it will benecessary to decide if the anterior teeth are to be setwith a large horizontal overlap (as in the naturaldentition with Angle's Class II, division 1 malocclu-sion) or with a small horizontal overlap (as in anAngle's Class II, division 2 malocclusion) (Figure161,162). The decision as to which will be appropri-ate must be made by reference to the soft-tissueform. This may not be easy and is greatly facilitated

Figure 160 A view of the sagittal plane showing therelationship of the lower incisors to the tongue and lipswhen set in the neutral zone.

A B

C

Figure 161A, B Photographs of patient with a Class II, division 1 malocclusion. CModels of Class II, division 1 malocclusion in permanent dentition. Good arches.

86 Clinical stage 4

A

B

CFigure 162A, B Photographs of patient with a Class II,division 2 malocclusion. C Model of a typical Class II,division 2 malocclusion.

by reference to photographs of the patient beforethe natural teeth were lost or other pre-extractionrecords. Immediate dentures which reproduced thepatient's natural teeth are of particular value.

In order to obtain a pleasing appearance the lowerteeth should show slightly above the lower lip withthe mouth opened.

Check that there is an adequate canine overjetwhich will ensure a free lateral excursion.

As long ago as 1933, Fish advocated shaping thepolished surfaces of the dentures so that the forcesproduced by the activity of the lips, cheeks andtongue would seat the dentures. If the bases havebeen correctly extended and the teeth correctlypositioned in the neutral zone, favourable contourswill inevitably result.

SpeechThe production of speech sounds involves a largenumber of organs:

1. The lungs.2. The larynx.3. The tongue, together with the roof and walls of

the oral cavity and the lips and teeth.

If the teeth are placed in incorrect positionsdefects in speech sounds may arise.

Difficulties with speech are uncommon if theprevious criteria of tooth position have been follo-wed and the teeth placed, as far as can be determi-ned, where the natural predecessors were.

Those with which we are concerned are thelabiodental sounds, i.e. 'f", 't', 'd', 'th', and 'sh',(Figure 163). The difficulty in pronouncing 'f' and'v' sounds arises through the upper anterior teethbeing placed too far back or the incisor tips beingplaced too low. Difficulties in pronouncing's'sounds very often occur due to an excessive overjetand this can usually be corrected by either bringingthe upper anterior teeth back or the lower anteriorteeth forwards, or by a combination of both thesetwo manoeuvres.

In order to detect whether or not the patient isable to enunciate all speech sounds clearly, -it isnecessary to engage him in conversation and tolisten for any abnormal sounds.

Determination of the arch formA common fault in the design of complete denturesis for the upper posterior teeth to be set 'over theridge', and this usually results in cramping of thetongue space as the lower posterior teeth are alsoset too lingually in order to achieve satisfactoryocclusion.

It is a fundamental principle of complete dentureconstruction that the teeth should be placed in

A

E

B

F

c

G


D

H

Figure '163 Sounds requiring the use of the tongue, teeth, palate, and lips. Note the two's' sounds; the 'high s' is madewith the tip of the tongue against the upper teeth and the 'low s' with the tip of the tongue against the lower anterior teeth.

POSItIOnS that could have been occupied by thenatural teeth and so it is valuable to have a conceptof the pattern of bone remodelling which occursfollowing their loss. This will enable us to place theteeth correctly in relation to the residual ridge.

In the anterior region bone loss is predominantlylabial, and so the residual ridge lies to the lingualand the teeth must be placed labially (Figure 164).This applies both in the upper and lower jaws.

In the upper premolar and molar region the boneloss is buccal and so the teeth must be placedbuccally (Figures 168B and I68C).

In the lower second premolar region the bone islost equally on both sides and the teeth can beplaced over the residual ridge (Figure 165).

In the lower molar region the bone loss is fromthe lingual and so the ridge is more buccal and theteeth should have a more lingual placement (Figure166). Incidentally, the differential bone loss in the

Figure 164 Following loss of the incisor teeth the boneresorption will be of the labial aspect of the ridge in bothmaxilla and mandible. The natural teeth are well to thelabial of the residual ridge.

88 Clinical stage 4

Figure 165 In the premolar region the natural maxillaryteeth are to the buccal of the residual ridge. In themandible the natural teeth are over the residual ridge.

Figure 166 In the molar region the maxillary teeth liebuccal to the residual ridge. In the mandible resorption isfrom the lingual side and therefore the natural teeth arelingual to the ridge.

upper and lower molar regions explains why thelower edentulous ridge appears wider in the mandi-ble than in the maxilla.

Watt, Durren, and Adenubi (1967) studied thepattern of bone resorption in 100 subjects over a2'l2-year period and observed that a landmark couldbe identified on the edentulous maxillary cast whichrepresented the remnant of the palatal gingivalmargin. Their biometric guides indicate the distanceat which the buccal and labial surfaces of the teethshould be placed in relation to this landmark andprovide a valuable guide both to the design of themaxillary occlusion rim and to the dimensions of thecompleted denture. Tn adopting this method it isimportant to ensure that the maxillary impressionhas fully developed the breadth of the vestibularsulcus and that this has been reproduced in the

denture border; thus the buccal contour of thecompleted denture will resemble that of the dentatemaxilla.

Tn an Angle's Class I case the arch form in thelower jaw will be determined by occluding the teethwith the biometric arrangement of the upper teeth.When patients exhibit an Angles's Class IT or TIlrelationship it is not always easy to determine thecorrect tooth position in the absence of definitivedata. Primarily it is a matter of being aware of thebasic base relation and of the variations in toothposition and arrangement that might accompany thisas has been previously discussed (see p. 113 andFigures 161 and 162).

Denture space impressionsAnother technique that has been advocated is thatin which an attenpt is made to record an impress ofthe 'denture space' (Figure l67A-D).

With the trial upper base in position the lowerdenture base has a rim of a suitable plastic materialadapted to the surface and the patient is asked toread aloud a selected passage of prose containing allthe representative speech sounds. The muscle activi-ties involved in speaking will mould the surfaces ofthe plastic rim into the form of denture which willbe compatible with the requirements, not only ofspeech, but also of mastication. It should bestressed, however, that forced swallowing of solid orliquid food occurs with the teeth together, forminga rigid chamber in which the tongue can generatevery large forces associated with the act of degluti-tion. Swallowing should not, therefore, be includedas one of the procedures to be used in the denturespace impression technique.

It is important that the material used to record theimpression of the denture space remains mouldablefor a sufficient period and flows readily under themuscle forces generated. Whereas silicone putty andmodified tissue conditioners have been used for thispurpose, the material which is preferred is a siloxanegel (di-methyl-siloxane).

This is easily adapted to form an occlusion rim onthe acrylic base and after the first reading can beexamined and adpated if necessary to place the baseand adapted rim onto the lower cast and then tobrush the surface with impression plaster until thegel is completely enveloped in plaster. When theplaster has set the gel may be removed and replacedby molten wax to produce a pattern of the denturespace, or the plaster matrix may be sectioned andused as a guide to the setting of the lower teeth.

The use of the denture space impression techni-que may revealed patterns considerably at variancewith the morphology of the previous dentures, It isclaimed that this method may help in resolvingdifficulties which in many instances have plaguedthe patient for many years.

A

c

Protrusive record (see p. 62)

When the patient protrudes the lower jaw thecondyles move forward and down onto the articulareminence. This drop in the condyles results in asimilar drop of the lower molar teeth. The protru-sive record measures the amount of this drop. Withit the articulator is adjusted so that a similar amountof drop will occur when a similar amount ofprotrusion is used. Then the teeth on the denturescan be moved until contact between the teeth ismaintained in this protrusion - this is protrusivebalance.

Having determined the amount of horizontaloverlap of the anterior teeth, the necessary degree


B

D

Figure 167A Siloxane gel adapted by speechexercise to define the denture space. B Denture spaceimpression invested with impression plater. C Havingremoved the gel and exposed the resulting void, moltenwax is being poured into the denture space. D Resultingwax occlusion rim resulting, which conforms to the denturespace.

of protrusion to give an edge-to-edge relationshiphas also been decided. It is at this degree ofprotrusion that the record should be taken - thisensures that balance is provided at this relationship.

Procedure1. Insert the upper denture.2. Place two rolls of softened wax about 6 mm in

diameter and 25 mm long, one on each side on thelower posterior teeth. Insert the lower denture andhold it in place while the patient, looking in amirror, protrudes the lower jaw and brings theanterior teeth edge-to-edge with the midlines coinci-dent (Figure 168).

3. Remove the dentures and chill the wax records.

90 Clinical stage 4

A BFigure 168A Softened wax rolls have been placed on lower posterior teeth. B The patient looks in a mirrorand brings the anterior teeth edge-to-edge with centre lines coincident.

References

E. W. Fish (1933) Principles of Full Denture Prosthetics.London, Staples.

J. H. Lee (1962) Dental Aesthetics, Chap. XXVII. Bristol,Wright.

D. M. Watt, C. M. Durren and L. O. Adenubi (1967)Biometric guides to the design of complete maxillarydentures. Dental Magazine and Oral Topics 84, 109.


At this stage the protrusive record is used to set thecondylar track angles and then the occlusion isadjusted to provide balance in eccentric positions.Following this the wax surfaces are contoured, thedentures are invested in a flask, and the wax isremoved and replaced by acrylic resin.

Setting the condylar track angles

The chilled wax protrusive record is placed on thelower occlusal surface with the dentures in place onthe Dentatus articulator. The condylar track anglesare now adjusted until the upper teeth sit evenly inthe upper surface of the wax protrusive record. Thisis done by releasing the locking screws and rotatingthe track forwards or backwards. This has the effectof rocking the upper teeth in the record. The mostfully seated position is selected. The condylar tracksare locked in this position. (Figure 169).

Figure 169 Condylar track of articulator adjusted untilteeth sit evenly in the protrusive wax record.

Developing the lateral and protrusiveocclusions

If, when the dentures are moved out of centricocclusion into lateral or protrusive occlusion, thereis contact both on the working side and on the non-working (balancing) side, then this occlusion is saidto be balanced. In a protrusive occlusion, theanterior teeth are edge-to-edge (a working occlu-sion), and balancing contacts will be sought betweenthe posterior, or at least the molar teeth. In a lateralocclusion, the teeth on the working side will be inbuccal cusp to buccal cusp interdigitated contact,and on the non-working side contact will be betweenthe lower buccal and upper palatal cusps of theposterior teeth (Figures 170, 171).

Occlusion at the working siteThere is little to be said about the occlusion of theincisor teeth in protrusion, other than that it is no

Figure 170 A balanced protrusive occlusion. Anterior teethare edge-to-edge and there are posterior contacts.

91


A

B

Figure I7IA The working side of a balanced lateralocclusion. B The balancing side of a balanced lateralocclusion.

disadvantage to have a well-defined occlusion pro-duced by a little judicious grinding of the labialaspect of the lower incisal edges and the palatalaspect of the upper incisal edges.

The occlusion of the posterior teeth in a lateralposition (presuming there to be a normal degree ofoverjet) should be such that the buccal and lingualcusps of the upper and lower teeth interdigitate.This intercuspation should be even and accuratebecause it is the initial occlusion of the teeth and ithas a stabilizing effect on the natural teeth and ondentures at the time of initial contact. Inclined planeor premature contacts will produce possibly undesir-able horizontal forces on the natural teeth andinstability of dentures.

Balanced protrusive occlusionsProtrusive balance is generally absent in modernman's dentition, being incompatible with the degreeof overbite and overjet present. In a Class I incisorrelationship an incisal angle of 60° is representative,rising to 70° or more in a Class II, division 2

relationship. Only in Class II, division 1, wherethere is a large overjet, does the angle descend to35-40° (Figure 172).

It follows that where naturalistic anterior tootharrangements are used in dentures protrusivebalance will be difficult to obtain. To providebalancing contacts between the molar teeth whenthere is an edge-to-edge incisal contact with anincisal angle of 20-50° or more (and it is seldom less)requires either a steeply angled occlusal plane or anexaggerated compensating curve, both of which areunsightly and tend to instability, or cusps of animpracticable height, which are difficult to obtainand to handle (Figure 173).

A solution to this problem is the reduction of theincisal angle by reduction of the overbite. Unlessthis is accompanied by reduction of the overjet,accomplished by labial or lingual movement of theanterior teeth into often unsatisfactory positions, anincomplete overbite (anterior open bite) results

A

B

Figure I72A A Class II, division 2 incisor relationship. BA Class II, division I incisor relationship. (Figures 174,175,~76, 181, 182, 183reproduced from R. I. Nairn (1973)'Lateral and protrusive occlusion', Journal of Dentistry, I,181-182, by kind permission of the Editor.)

~B

A

Figure 173 Occlusal contact in protrusion can bemaintained by (A) tilting the occlusal plane, (B) curvingthe occlusal plane, or (C) introducing a number of smallinclined planes (cusps).

Figure 174 Dentures constructed with an incompleteanterior overbite.

(Figure 174). Even in the natural dentition this isregarded as undesirable, being either the result orthe cause of (depending on one's point of view)functional disturbance. In dentures it may also beunsightly, either because of a visible gap or because

Developing the lateral and protrusive occlusions 93

the lower anterior teeth are too short or set too low.Acceptable tooth length will then be achieved onlywith an increased occlusal vertical dimension, whichis nearly always undesirable.

Protrusive balance should not be purchased at theexpense of having unstable tooth positions, dis-turbed function, or unsatisfactory appearance. Onlywhere the anterior teeth can be satisfactorily setwith an incisal angle of 20° or less can protrusivebalance be obtained with possible advantage.

Balance in protrusion (when practicable)1. Commence to provide a balancing contact

between Z j 7 with a protrusive relationship7T7

such that the incisor teeth arc edge to edge.2. Fix the articulator in this protrusive relation-

ship with the condylar stop extension (Figure175). Then tilt the mesial side of zJ2 downslightly and the distal side of 717 up slightlyuntil a contact is made (Figure 176 A,B). Thenreturn to the retruded relationship and adjust theteeth until they make a centric occlusal contact.

3. Slightly drop and similarly tilt ill (Figure6T6

176C) until contact is made, and return and checkthe centric occlusion. Because the gap whichappears between the posterior teeth in oc-clusion becomes less as we proceed forward, theamount of adjustment needed is less. Verysmall adjustment of 5 15 and 4 14 will be

515 414needed. The finished occlusal surface will be ashallow curve, the lowest point of which is themesial cusp of the first molar tooth (Figure 1760).

Figure 175 The condylar stop extension in use to secureprotrusive relationship.


A B

C DFigure 176A In the protrusive relationship there are no posterior contacts. Br~have been tilted to provide a posterior

contact. C l.!.2-havc now also been tilted to provide contact. D All the posterior teeth have now been adjusted to obtain116

contact in protrusion.

Note that 717 have not been raised from their7T7

positions on the occlusal plane. This maintains therelationship to the tongue level determined at thelast clinical stage.

Balanced lateral occlusionsThe provision of balancing contacts in a lateralocclusion does not present such difficulties becausecorrectly set teeth provide very little overbite in thelateral direction. Even though the incisor overbitemay be considerable, it can be much reduced at thecanines, and, as has already been mentioned, theposterior teeth have little effective overbite. There-fore the compensation needed on the balancing sideis principally for condylar drop and is easilyobtained by the height of the lower buccal and upperlingual cusps, with perhaps a slight degree of lateraltilt.

Balance in a lateral occlusion1. Fix the articulator in one lateral occlusion by

unscrewing one condylar stop extension. The

amount of excursion should be such that the buccalcusps of the working side (the side of no condylartranslation) arc brought edge-to-edge (Figure 177A). Check to sec that these buccal cusps arcinterdigitating and if not make adjustments untilthey are (Figure 177 B) Some slight grinding of thecusp inclines may be necessary - preferably of theupper buccal cusps because these are not used incentric occlusion. Return and check the centricocclusion. Note that in the lateral position the incisalpin of the articulator may be slightly raised from thetable because as the buccal cusps come into theedge-to-edge position there is a slight degree ofseparation due to the cusp inclines. Do not try toeliminate this because to do so will involve excessivegrinding of the buccal cusps. Repeat the procedurefor the opposite lateral occlusion.

2. Now note that the teeth on the balancingside (the balancing side side of condylar trans-lation) are separated because of the condylar dropwhich has occurred (Figure 178 A). This separ-ation is eliminated by tilting the palatal

side of ili down and the buccal side of 7T7up until contact is made. Note that this is betweenthe upper palatal cusp and the lower buccal cusp,

A

Developing the lateral and protrusive occlusions 95

Figure 177A In a lateral excursion to the left there is inadequate interdigition of the buccal cusps of this workingside. B The working side buccal cusp interdigitation is now correct.

B

A

Figure 178A In a lateral excursion to the left there is no balancing contact. B The teeth have been moved to providebalancing contacts.

B

which would be distal to it in centric occlusion(Figure 178 B). Return to centric occlusion andadjust if necessary. Repeat the procedure for thefirst molars and both premolars, noting that separa-tion is less as you progress forward.

Repeat for the opposite side.

The desirability of balancing contacts

Having considered the extent to which balancingcontacts can or cannot be readily obtained it remainsto examine their desirability.

First, it seems reasonable to contend that abalanced eccentric occlusion providing contactbetween the anterior and posterior teeth in protru-sion, and on both the working and the balancingsides in a lateral position, is the least importantfactor in denture construction.

Why is it that 'enter bolus exit balance' is only ahalf truth? Certainly an arrangement of balance onan articulator incorporates incisal or working sidecontacts, and when these are separated, e.g. by foodbetween the teeth, so are the balancing contacts, butby a distance which is smaller than that in theunbalanced condition. If a denture should displace,it will not displace so much and might be more easilyreplaced. It seems desirable to produce as close anapproach to balance as can be achieved withoutproducing other disadvantages.

In the reconstruction of the natural dentition it isdifficult to see any good reason for producingbalancing contacts, and their pursuit introduces thepossibility of an inadvertent premature balancingcontact being formed. A premature balancing con-tact should never be produced; it is reasonable tosuppose this to be a most crippling occlusal defectin either the natural or artificial dentition. It is


A BFigure 179 A premature balancing contact in a lateral occlusion. A Balancing side-contact. B Working side-nocontact.

A

B

Figure 180 A posterior premature contact in centricocclusion (A) can be compensated by adoption of aprotrusive occlusion with condylar displacement (B).

unlikely to occur in protrusion, but can be all tooreadily produced in a lateral position (Figure 179).

Consider first a premature occlusal contact occur-ring when the madibular condyles are in a retrudedposition in the fossae, e.g. a posterior prematurecontact in centric jaw relationship. Slight protrusionof one or both condyles produces some condylardrop and clears the premature contact. The man-oeuvre into 'a bite of accommodation' may not bevery satisfactory but it is possible (Figure 180).

Secondly, a premature contact occurring when thecondyle (or condyles) is already in a protrusiveposition, e.g. a premature balancing contact, cannotbe cleared by further condylar protrusion andcondylar retrusion may make the matter worse(Figure 181). It is perhaps wise to ensure that the

Figure 181 In the presence of a premature balancingcontact the moving condyle is already displaced.

balancing side contact is a near miss to allow forpossible mucosal (or periodontal) displacement onthe working side under load (see Figure 178).

The advantage in the use of an adjustable articula-tor lies not so much in the provision of balance butin the avoidance of premature balance. It is indis-pensable to the establishment of a proper workingocclusion and unobstructed articulation.

Occlusal grindingSee Laboratory Procedures 5 (p. 107) for notes onocclusal adjustment by grinding.

Contouring and finishing the waxsurfaces

The shaping of the wax surface falls into two parts.The first is concerned with the general form. If theteeth have been correctly positioned the contour ofthe wax work should resemble that of the alveolarprocess supporting the natural teeth. The idea ofshaping the buccal contour of the upper and lowerdenture to produce a concavity, which was prop-ounded by Fish, is based upon a misconception ofthe action of the perioral musculature. The buccina-tor muscle forms a curtain which, on the workingside, prevents the food which is being eaten fromfalling into the buccal vestibule. The maximumcontraction occurs early during the closing part ofthe masticatory cycle. It is only effective if the cheekteeth are correctly positioned. If a large buccalconcavity is built into the dentures it means that theteeth must be lingually displaced, and, as the muscleis incapable of functioning without adequate sup-port, patients will complain of food falling into thecheek, from which position it is difficult to recover.Even though very narrow teeth may be used, it isdifficult to avoid some degree of tongue cramping.

The upper anterior teeth will follow the contourof the occlusion rim so as to produce a pleasingcosmetic result. Although a satisfactory appearanceis equally dependent upon the support given by acorrectly placed lower tooth, there has been somehesitancy on the part of prosthetists to align thelower teeth with .any degree of proclination on theground that lip pressure would cause instability.Experience with the use of lower denture spaceimpressions has shown that in certain casts it is onlywith appropriate proclination of the lower anteriorteeth that proper stability of the lower denture canbe secured. This is because if the teeth are incor-rectly placed the tongue is incapable of functioningwithout causing the denture to be displaced.

Contouring and finishing the wax surfaces 97

The buccal flanges, from the premolars back,should face downward and outward for the upper,and upward and outward for the lower. The lowerlingual flange should face upward and inward. Thesecontours will occur in most cases if the bases areproperly extended and the teeth are in the correctposition (Figure 182).

The upper labial flange is shaped so that togetherwith the teeth it provides a pleasing form for the lip.This will have been determined during the trialinsertion. The lower labial flange is similarly con-cerned with the form of the lower lip. The necks ofthe incisor teeth should be placed slightly linguallyto form a shallow V-shaped groove between thelabial surface of the tooth and the labial surface ofthe base (Figure 183).

The second part is the appearance of the labialsurfaces and this is concerned with the particularcontouring of the surfaces to reproduce the appear-ance of natural gingivae (Figure 184).

Detailed instructions for producing these will notbe given here, but there are certain points whichneed emphasis.

Root prominences, gingival margins, and papil-lae Remove the dentures and the mounting ringfrom the articulator.

It is important that there should be sufficient waxpresent to allow adequate carving and that the waxshould be solid and not laminated. To achieve this,remove most of the wax from around the teeth andthe labial aspect of the base, and add more wax inthe molten state, slowly building up a mass wellthickened around the necks of the teeth and fillingthe interdental space below the contact point.

Buccal and labial surfaces: Start at the secondmolar. Carve around the neck of each tooth with anAsh NO.5 or Le Cron carver. This carving shouldbe carried out with a knife at an angle of 45° to the

B cFigure IS2A Favourable contours resulting from narrow teeth on a well-extended base. The resultant of the forces istowards the supporting tissues. B Unfavourable contour resulting from normal sized tooth on an under-extended base and,C from too wide a tooth lingually placed on correctly extended base.


cFigure 183A Favourable contour of incisor region resulting from correct positioning and inclination of tooth on base. BThe teeth have been placed too far labially. C The teeth have been placed too far lingually. ~

A

B

Figure 184 Healthy natural gingivae.

vertical and should expose the crowns down to theirjunction with the ridge lap.

Again, starting at the first premolar, scrape awaywax from the buccal and labial surfaces to produceshallow grooves in the inter-radicular spaces. Thesegrooves should not extend to the gingival margins,which should be slightly raised in the interdentalspace to form a papilla.

Lingual and palatal surfaces: The border thicknesshaving already been determined in the constructing

the baseplates, the shaping of the lingual and palatalsurfaces should be directed forwards, producing theappropriately concave surfaces which provide formaximum space for the tongue. The cervical mar-gins should be trimmed in the same way as for theouter surface but no contouring should be attemp-ted. The introduction of inter-radicular grooves andthe grooving of the gingival crevice merely causeirritation to the tongue and sometimes cause defec-tive speech.

Stippling: Good carving of the wax producescontouring which simulates natural gumwork, pro-duces the right amount of light scatter, and, if thecolour of the denture base is satisfactory, producesa very pleasing result.

As an alternative or an adjunct to gingivalcontouring some people stipple the wax and thisproduces a finished dentures whose surface showsan 'orange-peel' effect. This may be produced bytapping the surface of the wax with the bristles of atoothbrush after first warming the surface to softenthe wax, or by running over the surface of the waxwith a small burnishing bur rotating in a handpiece(Figure 185). A disadvantage of stippling is that itproduces a denture which is more liable to contami-nation by calculus deposits. If it is done it should beconfined to the area of the denture which can beseen when the patients grins broadly, i.e.4321 11234

Processing dentures

You have now set up all the teeth and havecontoured and finished the wax surfaces. This waxis now to be replaced by acrylic resin which will jointhe teeth to the baseplate. You will, in doing this,reprocess the clear acrylic baseplate. With thisprocedure there is the possibility of increasing thedistortion of the base in the second processing cycle.

A

Processing dentures 99

8

Figure 185A Stippling is produced with the bristles of a toothbrush. 8 The completed stippling. Note that this hasbeen incorrectly extended to include that part of the denture which represents non-stippled mucosa.

Because of this, particular care must be taken toensure that the processing is carried out at lowtemperature (72 °C for 9 hours) to keep distortionto a minimum. The development of colour-stableself-polymerizing resins may help to solve thisproblem. If used the technique is identical, exceptthat no heat is needed during the period of polymer-ization.

1. Cast pure hydrocal into the baseplates and besure to enclose the border. Do not attempt toremove the baseplates from the casts as these willprovide them with firm support. Taper the sides ofthese casts (Figure 186).

Figure 186 Hydrocal has been cast into the bases and thesides tapered.

2. Invest the dentures on the casts in the shallowhalf of the flask. Give the dentures a posterior tiltso that there is no possibility that the anterior aspectof the denture will present an undercut area - sucha situation can interfere with the separation of thetwo halves of the flask (Figure 187).

A posterior tilt to the lower denture will alsoprotect the posterior ends of the lower base fromdamage.

Figure 187 The waxed-up dentures on their casts have beeninvested in the lower half of the flasks. Note that they havebeen tilted to avoid an anterior undercut.

3. Invest the upper half with 50:50 hydrocal andplaster. Pure plaster is too soft for this purposebecause the teeth must be strongly supported - thevery large pressures built up in packing acrylic resindough may very well push the teeth into a plasterinvestment. It is even better to complete investmentin two stages. A mix of 50:50 hydrocal and plasteris carried up to the level of the occlusal surfaces ofthe teeth. When this is set, pure hydrocal is used tocover the occlusal surfaces and complete invest-ment. When the investing stone has set (at least 1hour), the flask is heated to soften the wax so thatthe two halves can be separated.

4. Do not overheat the flask in softening the wax- the wax should not liquefy as it may run under thebaseplate and you will not be able to get it out. Donot pour boiling water on the invested baseplate asit will warp. Remove any remaining trace of waxfrom the baseplate with a solvent and detergent.

5. Allow the flasked moulds to stand overnightbefore packing. This will allow the plaster andhydrocal to reach its full strength. It will also ensurethat the mould is quite cold.


A

B

Figure ISSA The processed dentures have been removedfrom the flasks totally embedded in the investing plaster.B The first section of the investing plaster has beenremoved from the lower denture.

Apply two coats of separating medium to theplaster surfaces, letting each dry. Do not getseparator on the acrylic base or on the exposednecks of the teeth.

6. Now pack the mould with pink acrylic resin.Keep the vessels containing the prepared mixture ofmonomer and polymer cool (in a refrigerator forpreference), to prolong the doughing period for aslong as possible. During the doughing period do notunnecessarily remove the lid from the mixing vesselor handle the material. Evaporation of monomerand contamination from the hands can lead touneven doughing and unsightly streaking in thematerial. Do not pack before the full doughing stagehas been reached. These measures ensure themaximum solution of the polymer particles by

A

B

Figure IS9A The processed dentures still on the hydrocalcasts and completely divested of plaster. B The denturescompletely divested.

monomer, and give a dough which will flow readilyand can be packed with minimum pressure.

7. In deflasking be sure that the whole of thecontent of the flask is removed in one piece (Figure188) Do not strike the flask with a metal hammer.Remove the investing stone piecemeal from andaround the denture. Do not prise the denture out atany time - if you do so you will either break or warpit (Figure 189).

8. In trimming and polishing remember not totouch the border of the baseplate.

9. Replace the dentures on the mounting castsand check that the centric occlusal contact has notbeen deranged during processing. If an error isfound, correct by grinding.

Clinical stage 5

Inserting the completed dentures 4. To advise them on the limitations to beexpected of artificial dentures.

Objectives1. To check the retention and the accuracy of the

jaw relations of the completed dentures, and toadjust where necessary.

2. To instruct the patients in the correct use oftheir dentures.

3. To advise the patients on the proper care oftheir dentures and of the denture-supporting tissues.

Instruments and materials (Fig. 190)

1. Completed dentures.2. Bowl of cold water.3. Burs and stones.4. Laboratory handpiece.5. Willis gauge.6. Articulating paper.

Figure 190 Instruments and materials for insertion of complete dentures

101

102 Clinical stage 5

7. Modelling wax.8. Mouthwash.9. Clean towel for bracket table (paper towel).

10. Clean head-rest cover.11. Patient's record card.

Procedure

Inspect the dentures1. Fitting surfaces: Ensure that there are no

projecting nodules of acrylic or sharp edges whichmay injure the mucous membrane.

Ensure that all traces of plaster-of-Paris or otherforeign materials have been removed from thefitting surfaces.

2. Denture border: Ensure that there arc no sharpor angular margins.

3. Polished surfaces: Examine the polished surfa-ces of the dentures to ensure that they have beenadequately finished and that there is no plastercontained in the gingival crevices.

Test for retention of dentures1. Seat the upper denture with a firm upward and

backward pressure.2. Allow the tissues of the lips and cheeks to settle

around the dentures.3. Grip the buccal surfaces of the upper denture

between the thumb and forefinger in the premolar

A

region. Apply a firm downward force and assessresistance to it.

4. Reseat the denture if necessary. Place theforefinger of the right hand on the palate behind theupper incisor teeth and apply a forward leveragedesigned to displace the posterior border of thedenture. Assess the resistance to this force (Figure191A).

5. Test the retention of the lower denture,applying an upward force, bearing in mind that theextent to which retention can be developed in thelower denture is commonly less than that of anupper (Fig. 192B). If the retention is poor then thebase must be corrected (see p. 49 et seq.).

Check the centric jaw relationshipCheck the centric jaw relationship by following theprocedures already detailed under record taking.Have the patient close in centric jaw relationshipand note the manner in which the opposing teethocclude.

Irrespective of whether an error has been notedor not it is always necessary to take a check record.This is because displacement of the supportingtissues and movement of the base may prevent anerror from being seen. For this reason it is also notpossible to detect the errors by the use of articulat-ing paper in the mouth.

If correcting an error in centric relation by takinga check record is to be a valid procedure, it isnecessary to reposition the upper denture on thearticulator in the same relationship to the articulator

B

Figure 191A Testing the retention of the upper denture by attempting to break the posterior palatal seal with' leverage inthe anterior region. B testing the retention of the lower denture by applying an upward and backward force with a probeinserted between the lower incisors. The tongue should be at rest behind the lower incisor teeth. If the tongue is retractedthe anterior lingual seal wil be broken.

axis as it bears to the intercondylar axis when it isin the mouth. If the models have been retained onthe articulator this record will have been preserved;if not, a facebow record is necessary to position theupper denture.

Check record materials

The method to be described here uses wax as theinterocclusal material for the check record. Theadvantages of wax are that it is easy to manipulateand when the teeth close into it the record isimmediately fixed. However, it is a viscous materialand the possibility exists of displacement of thedentures due to load transmission to the supportingtissues. This can be avoided by care to use only asmall amount and to ensure that it is evenly andthroughly soften.

Many people prefer to use a fluid material suchas zinc-oxide-Eugenol paste or impression plaster.

c

Inserting the completed dentures 103

This will avoid the possibility of base displacement.However, it is essential that the jaw is maintainedin the most retruded position with the teeth justapart while the material sets. This is not always easyto achieve.

Taking the check record1. Thoroughly soften one end of a sheet of

modelling wax in the bunsen flame. Do not allowthe wax to melt. Fold this end over to form a strip4 mm wide. This will be a double thickness. It maybe desirable to fold this over once more to providea triple thickness. See Figure 113 (p. 00).

2. This is then divided into two, one half beingplaced on the molar and premolar regions of thelower denture on each side (Figure 192A).

3. With the upper denture in position the lowerdenture is returned to the mouth and the patient isinstructed to gently close in the retruded position

B

Figure 192A The strips of softened wax have been placed over the lower malar teeth. B The patient closesinto the wax with the jaw in the most retruded position. Closure must cease just short of the occlusal contact.C The completed interocclusal record in position on the lower denture. D The upper denture has been locatedin the wax record.


but not to penetrate the wax (Figure 192B). If theteeth are allowed to make contact the bases may bedisplaced or the jaws guided into an eccentricposition.

4. The use of two wax wafers makes it easier toassess the degree of jaw separation by observing therelationship of the anterior teeth.

5. The lower denture together with the wax recordshould now be removed from the mouth andimmersed in cold water (Figure 192C,D).

6. After cooling the wax record the dentureshould be reinserted in the mouth and the jawrelationship checked.

7. When a satisfactory record has been obtainedthis should be used to reposition the lower denturebase on the articulator to facilitate evaluation of theerror and its correction (see Laboratory Procedures5, p. 000).

8. After the occlusion has been adjusted thedentures are reinserted.

Instructions to patients regarding theuse of the dentures

1. Stress the limitations of artificial dentures, thatis that the maximum occlusal load which may bedeveloped with complete upper and lower denturesis one-tenth of that possible with a full naturaldentition.

2. Point out that in the early stages it is wise forpatients to limit themselves to items which requirelittle mastication. They should cut up their food intosmall pieces and should not favour one side inchewing.

3. Point out that dentures are constructed to fitexisting ridges and that some resorption will con-tinue to occur. This may be small, but the denturesmust be regularly checked and will have to bereplaced in time if damage to the oral tissues is tobe avoided and if they are to provide maximumcomfort.

Advice to patients on proper care ofdentures

1. Point out that food debris and calculus canadhere to the dentures and advise patients concern-ing the cleaning of their dentures.

2. They should not use a hard brush or anyabrasive substance as acrylic resin is very easilyscratched. They should not use household abrasivecleansing powder which may be damaging to thematerials of the denture base.

3. If the dentures are cleaned regularly after eachmeal with a soft brush and soap, most food debriswill be removed.

4. Patients should be warned to clean theirdentures over a bowl of cold water so that shouldthe denture slip from the hands it will have its fall

broken by the water, thus avoiding fracture. Theyshould also be warned not to grip the dentures inthe palm of the hand whilst brushing them as this isa common cause of breakage, particularly of thelower denture.

5. If deposits of calculus form on the denture is isnecessary to use a cleansing agent which willdissolve this material.

6. Advise the patient against wearing dentures atnight. During the first few days following theinsertion of the dentures it may assist the patient inadapting himself to them if they are worn at night,but after this initial period such a course should bediscouraged. It is an unnatural state for the mucuousmembrane to be covered. The continued pressure ofthe dentures may interfere with the normal capillarycirculation and micro-organisms can be harbouredbeneath the dentures which cause injury to theunderlying tissues.

When the dentures are not worn they should bestored in water in order to avoid dimension changescaused by loss of absorbed water.

Denture cleansersFood debris, bacteria, and calculus will all con-taminate dentures and it is important that they areregularly cleaned. Apart from the unsightly appear-ance of dirty dentures, such contamination may beresponsible for infecting the tissues of the mouthand the alimentary and upper respiratory tracts.Soiling of dentures occurs in three phases:

1. Mucin and food debris accumulates upon thesurface. This deposit offers little resistance to thesimplest cleaning process and may be removed bylight brushing with soap.

2. Mucilaginous surface contaminants appear togain attachment to the denture base material toform a plaque and this acts as a matrix for thedeposition of stains derived from the breakdown offood substances and from tobacco smoke. They mayalso be invaded by calcium salts released from thesaliva.

3. When calcification has progressed until theorganic matrix has become completely petrified, thethird phase, that of tartar formation, has beenreached. This only occurs on those surfaces of thedenture adjacent to the openings of the salivaryducts.

It is when dentures have been affected by stain ortartar deposits that resort to chemical or physicalmethods of cleaning with proprietary cleansers ismost necessary. Many of these are manufacturedand a selection is shown in Figure 193.

Denture cleansers are either chemical or abrasivein their mode of action. The chemical cleansers maybe defined as:

Denture cleansers 105

A

B

Figure 193A A selection of immersion denture cleansers. B A selection ofbrush-on denture cleansers.

1. Alkaline hypochlorites.2. Alkaline peroxides.3. Dilute acids.

The hypochlorites are used because of their abilityto dissolve the organic matrix upon which the tartarforms. As these materials cause metal componentsof dentures to corrode they were for some timediscredited, but the addition of anti-corrosive subst-ances, such as sodium hexametaphosphate, com-monly used as a water softener, and an excess ofalkalinity have overcome this disadvantage. Thistype of cleanser is unsuitable in powder form and sois sold as a liquid, and therefore does not lend itselfto convenient packaging.

The second group is comprised of a powder ortablet which when dissolved in water becomes analkaline solution of hydrogen peroxide. These pro-ducts usually include an oxygen liberating agentsuch as sodium perborate or percarbonate and analkaline detergent such as tri-sodium phosphate.The liberation of bubbles of oxygen from thesesolutions exerts a mechanical cleansing effect onlightly held contaminants. When used regularly,from the time a new denture is supplied, theseproducts effectively remove mucin and lightly heldfood debris. These products can cause little or noharm to denture base material and are effective inthe majority of cases.

The acid cleansers are mostly 5 per cent solutions


of hydrochloric acid; phosphoric acid is also usedeither alone in a concentration of about 15 per cent,or to supplement the action of the hydrochloric acidcleanser. The efficacy of these cleansers is prop-ortional to the degree of dissociation of the acid.Since they attack the inorganic phosphate of thecalculus deposit, these deal very effectively withobstinate stains which resist the action of theperoxide type of cleanser. These products are meantto be applied to the denture with a brush or spongeand the period of exposure of the denture to theaction of the cleanser is short. Because of the high

Table I. Proprietary denture cleansers available in theUnited Kingdom.

AlkalinePeroxides

Immersion Cleaners

Acids

Brush-on Cleansers

Abrasives

ClensadentDentroEucryl

(Smokers)LibroxMilton

DenturePowder

OxydentSanidenSteradent

PowderSteradent

Tablets

Hypochloriles

DenturalHousehold

cleanserscontaininghypochlorites

BrobatParazone

DenclenDenisolDentifoamDentilineDentyr

BleachO-De·Dent

DentifreshDentu

CremeEucryl

DenturePowder

KolynosPowder

LustreDent

OraliteSoap

acidity of these products, they may be harmful toclothing. A further limitation of this type of productis that it should not be used on dentures whichcontain metallic elements, i.e. the majority ofpartial dentures, since the acid will attack the basemetal elements, causing weakening of these compo-nents.

Twenty of the proprietary cleansers available inthe United Kingdom are listed in Table 1, accordingto the nature of the principal active ingredient. Mostof the acid cleansers are supplied as solutions andare applied either with a special applicator or witha sponge or brush. Two of them are formulateddifferently. One is in the form of a paste similar toa dentifrice and the other is a liquid slurry.

The best medium for cleaning dentures is onewhich is effective, safe and causes no damage to thedenture materials. Whereas it may be possible forsome patients to keep their new dentures clean bybrushing them with soap and water after every meal,most resort to toothpaste or proprietary denturecleansers. Daily overnight immersion of dentures inan alkaline peroxide solution provides a safe and.effective means of cleaning of dentures.

Since brushing is carried out for only 1 or 2minutes on each occasion the abrasive cleansersprovide an alternative to immersion cleaning forthose patients who have only one set of dentures andwho are unwilling to leave them out at night. Theseproducts cause damage to acrylic resin and thus onlythose showing the minimum of abrasiveness shouldbe used.

Brushing with soap and water has been shown tobe ineffective in removing stains and tartar.


After a check centric jaw relationship record hasbeen taken, the lower denture must be remountedin the articulator, and adjustment of the centric andeccentric occlusions made.

Remounting

The upper mounting model will not need to beremounted unless it is felt that there was some errorin the previous facebow record. The lower mountingmodel is removed from the attached ring which iscleaned of plaster.

The upper and lower dentures are seated in thecheck record and joined together with sticky wax(Figure 194A). The upper denture is seated on theupper mounting model on the articulator and thelower mounting model is seated in the lowerdenture. It is often convenient to turn the articulatorupside down before adding the plaster which willreattach the lower model to the articulator. (Figure194B,C).

Reforming centric. lateral, andprotrusive occlusions

it is very important to realize that occlusal adjust-ment by grinding is applicable only to small errors.Any attempt to correct for large errors (that is tomake large changes in the occlusal form) willinevitably result in the destruction of the occlusal

surfaces. Large errors can only be dealt with byremoval and replacement of the teeth.

1. Reforming centric occlusion (maximumintercuspation}There are, in general, two types of jaw relation errorwhich call for reforming centric occlusion. In thefirst, while the cusp-fossae relationship of theopposing occlusal surfaces are not misaligned, theocclusal surfaces meet prematurely at one point(usually in the last molar region on one side) and noother teeth meet. In the second, while the occlusalsurfaces meet, the cusp-fossae relationships of theopposing occlusal surfaces are disturbed (usually thelower teeth are posteriorly related to their oppo-nents). Of course the error present is often acombination of both types (Figures 195, 196).

The rules for grinding in this circumstance are:

I. If there is no misalignment of the cusp-fossaerelationships of the opposing teeth, then the oppos-ing fossae should be deepened until there is evencontact everywhere.

2. If there is misalignment of the cusp-fossaerelationships, then this must be corrected first bygrinding of the mesial and distal slopes of the cuspsof the opposing teeth until cusp-fossae alignment isre-established. For example, if a little is groundfrom the mesial slope of the cusp, it moves that cuspdistally without shortening it appreciably (Figure197A-D). Then the opposing fossae can be deep-ened until there is even contact.

The re-alignment of cusp-fossae relationships isoften best done by eye - articulating paper is seldoma help until the error is too small to be easily seen.Cusp-fossae contacts and fossa deepening is carriedout with the aid of thin articulating paper.

107


A

B

cFigure 194A The dentures seated in the interocclusalrecord are sealed together with sticky wax. B The upperdenture is seated on its mounting block, and plaster isplaced on the lower mounting block and the lowerarticulator ring. C The articular is inserted while the freshplaster sets.

Figure 195 Here the centric relation error is such that theinitial occlusal contact occurs posteriorly on the right sideonly.

Figure 196 This shows a centric relation error in which thejaw relation record has been made in an anterior position.With the posterior shift of the mandible into the moreretruded position, there is no intercuspation at the initialcontact.

2. Reforming the protrusive occlusionThis is seldom required other than to ensure thatthere is a good contact between the incisor teeth andthat there is a smooth path of movement from theprotrusive occlusion back to centric occlusion. Thepalatal sides of the upper incisor edges and the labialaspect of the lower incisal edges are ground (Figure198). In the rare event of a premature contact beingpresent at the balancing site posteriorly, it is usuallypossible to apply the BULL rule, i.e. grind theBuccal Upper or Lingual Lower cusps. Although itwill be necessary to shorten these cusps, it must bedone by grinding their slopes so that a cusp form isretained.

A

B

c

Figure 197A The cusp has been moved without excessiveloss of height or form by grinding of the shaded area. BMovement of the upper cusp mesially and the lower cuspdistally has re-established the cusp-fossa relationship. CThe cusp has been shortened with loss of occlusal form bygrinding of the shaded area. D The embrasure has beendeepened without loss of form.

Reforming centric, lateral, and protrusive occlusions 109

Figure 198 The incisal edges have been ground to providea good contact by reduction of the palatal side of the upperincisal edge and the labial aspect of the lower incisal edge.

3. Reforming the lateral occlusions

a. The working side Here again it is essential thatthe proper alignment of the opposing cusps is re-established and, in this case, until the cusps andtheir opposing embrasures are aligned. If necessarythe cusp slopes of both upper and lower teeth mustbe adjusted as for the analogous stage of centricocclusal adjustment. After alignment is achieved,then the BULL rule is followed to produce evencontact (Figure 199).

b. The balancing side The cusps in contact here arethe upper palatal and lower buccal (Figure 200).More exactly, the lower buccal cusp has moved upthe disto-palatal incline of the upper palatal cuspmesial to it, and it is this incline which must bereduced if a premature balancing contact is present.As has been pointed out previously, in the sectionon setting teeth (Laboratory Procedures 4, p. 95),premature balancing contacts of this sort must beavoided.

4. Providing a smooth articulationSmooth the paths of movement from the eccentricpositions back to centric - use the articulator onlywith such a movement. Use articulating paper todetect points of uneven contact along the paths. Onthe working side look particularly at the palatalslopes of the upper buccal cusps (along which thelower buccal cusps move). On the balancing non-working side look at the buccal surfaces of thepalatal upper cusps (along which lower buccal cuspsmove). Do not grind any cusp tips at this stage.


Figure 199 In a right lateral occlusion there is even contactand intercuspation on the right (working) side.

Figure 200 On the left (non-working) side the lower buccalcusps are in contact with the next anterior upper palatalcusp.

Check also the smoothness of movement from theprotrusive position of edge-to-edge incisive contactback into centric occlusion. The paths to examineare those on the palatal surfaces of the upperincisors.

At the end of this stage the movements of theteeth over each other from the eccentric to thecentric occlusion should be quite smooth and even.

5. The rationale of the rules of grinding

These are readily understood if it is appreciatedthat:

a. In centric occlusion the lower buccal cusps andthe upper palatal cusps meet opposing fossae andthis contact supports the occlusal vertical dimension.Shortening of these cusps could affect this support.

b. On the working side of a lateral occlusion, theupper buccal cusps interdigitate with the lower

buccal cusps and the upper palatal cusps interdigi-tate with the lower lingual cusps.

c. On the balancing side of a lateral occlusion, thelower buccal cusps contact the upper palatal cusps(See 3b, above).

d. In protrusion, the working contact is betweenthe incisal edges of the upper and lower anteriorteeth and the posterior contact (if present at all) willvary, depending upon the angle the arch form makeswith the direction of protrusive movment, the lowerbuccal cusps being in contact with upper buccalcusps or anterior fossae.

6. The order of prioritiesIt is helpful to keep to certain priorities in theseprocedures. The cusps have a priority of immunityfrom grinding.

Priority 0: The lower lingual cusps - used only ina working occlusion and not very important for that.Can be ground at any time or removed altogether ifnecessary.

Priority 1: The upper buccal cusps - used only ina working occlusion; should be reshaped to ensurea good interdigitation with the lower buccal cusps.

Priority 2: The upper palatal cusps - used inworking occlusion, where they can be ground(unimportant aspect of this occlusion); in centricocclusion (a secondary function), where they can beground; and in the balancing occlusion where theyshould be ground to avoid any premature contacts.

Priority 3: The lower buccal cusps - these are ofprime importance in most occlusions and shouldonly be reshaped to correct the centric occlusion.The upper buccal cusps should be fitted to them inthe working occlusion and the upper palatal cuspsfitted to them in the balancing occlusion.

There are general priorities as well which can besummed up:

Of first importance is centric occlusion, whichshould be free of uneven contacts, and of secondimportance is a working occlusion of the buccalcusps, which should have precise, even interdigita-tion. Equally, there must be a smooth path ofmovement on the working side back into centricocclusion with freedom also from any interferingcontacts on the balancing side.

If balancing contacts are missing, the situationshould be accepted unless they can be established byvery minor adjustment to the working occlusion.

The working side occlusion between the lingualcusps and palatal cusps is of low importance, as isthe centric contact between palatal cusps and thelower fossae.

Clinical stage 6

Adjustment of dentures

After the patient has worn his dentures for a shortperiod, preferably no longer than 48 hours, heshould be asked to return to the surgery. You willthen ascertain whether his dentures are causing himany discomfort and will examine the mouth for anysigns of injury. At this time such injury is usuallyindicated by an area of redness. Only if the injurywere particularly severe would any ulceration bepresent. This demonstrable trauma to the tissueswill be due either to excessive displacement of thetissues (as may occur at the border where the baseis over-extended) or to severe pressure on thesupporting mucous membrane lying beneath thebase. The latter may be due either to irregularitiesin the fitting surface of the denture or on thealveolar bone, or it may be due to displacement ofthe denture base under the influence of inclinedplane effects produced by occlusal disharmony.Occlusal error must always be suspected before anyother cause is considered.

If it is decided that the injury is due to excessivedisplacement of the tissues then localization of theoffending portion of the base is essential. For thispurpose disclosing wax is the material of choice. Itis easy to destroy the close contact and border sealof the base by indiscriminate grinding.

Use of disclosing wax and pressure relief creamOn the borderWhen it is necessary to identify areas of the dentureborder where soft tissues are being excessivelydisplaced by the denture or where movement of thefraenal strands under the influence of the orofacialmuscles is being impeded, disclosing wax is the mostsuitable material. The following procedure shouldbe followed (Figure 201):

1. Look in the mouth and seen the approximatelocation of the sore area.

2. Apply a little of the wax over the appropriatearea of the denture border. Dip this in some warmwater.

3. Seat the denture carefully home in the mouthtaking care to avoid wiping off the wax. Leave fora minute and then have the patient perform functio-nal movements of the orofacial tissues.

4. Remove dentures and trim away a little of thebase which shows through the wax.

5. Repeat this procedure until the base does notshow through.

On the fitting surface

After any occlusal imperfections have been cor-rected by means of the check record procedure,pressure relief paste is used to identify areas ofexcessive tissue displacement of the denture-bearingtissues at the initial insertion stage (Figure 202A-D).This may arise because the impression material usedfor denture construction does not differentiatebetween the differing degrees of displacement in thedenture-supporting mucosa. It will, for example,indicate whether the imcompressible tissue in themidline of the palate is being required to bear tooheavy a load, necessitating relief.

The paste is painted thinly over the whole fittingsurface of the denture with the brush marks runningin the same direction. Each denture is then placedin position on the supporting tissue and firmpressure is exerted on the occlusal surfaces of theteeth. The fitting surface is then inspected. Wherethe pattern of the brush marks in the indicator pasteis disturbed is an indication of the site requiringadjustment. The acrylic in this area is carefullytrimmed and a further application of the paste ismade and the dentures are returned to the mouth

111


A B

Figure 20lA Disclosing wax being applied to the border ofthe lingual flange. B Note that no displacement of the waxhas occurred peripherally. The dispacement of the waxreveals an area of localized pressure. C The base has been

C reduced, and no longer shows through the wax.

for testing. This procedure is continued until nofurther sites of excess pressure are revealed.

When a patient complains of soreness beneath thedenture base after it has been worn for some timethere is likely to be inflammation and swelling of theinjured tissue. It is unwise to excessively relieve thedenture over these swollen areas because once thetrauma has been reduced the swelling will subsideand too much base reduction will leave an area ofpoor contact.

Subsequent visits

The patient should be recalled for subsequent visitsat no more than weekly intervals until there is nofurther discomfort from the dentures. If the patienthas persistent difficulty then a careful reappraisal ofthe dentures must be made.

It is important to be aware that persistentlocalized soreness beneath the base over the alveo-lar ridge is most often due to an error in the centric

jaw relationship. There may be a premature occlusalcontact or there may be a lack of cuspal interdigita-tion when the patient brings the dentures together.Either of these situations will produce movement ofthe dentures when the teeth come together and thismovement will be under occlusal load. It willtherefore be very likely to produce soreness.

If the patient should complain of persistentgeneralized soreness over the lower ridge which isnot readily localized and is accompanied by atiredness in the musculature and a desire to removethe dentures when they have been worn for a fewhours, then it is almost certain that the occlusalvertical dimension of the dentures is too great andit must be carefully assessed yet again.

If there is an error in the centric relation or in theocclusal vertical dimension, this can only be cor-rected by taking a centric relation check record (anda facebow record if the previously mounted eastshave not been retained). The denture must then bemounted on an articulator, and the occlusionadjusted by selective grinding or by removal of theteeth, whieh are then reset and processed.

A

c

Adjustment of dentures 113

B

D

Figure 202A Complete upper denture prior to the application of pressure relief cream. B A thin layer of cream is beingpainted over the tilting surface of the denture base. C Sites of excess pressure have been revealed by displacement of thecream. D These areas are being carefully relieved.

Part IIAssociated topics

Diagnosis • Prognosis • Rebasing • Copying • Relief. Resilientlinings. Implants. Preprosthetic surgery. Cross infection. Overdentures• Tissue conditioners

Additional topicsThese following sections provide some information about a number of additional topics which arise from theconsideration of the principles and techniques of complete denture construction.

The coverage is by no means meant to be comprehensive but to give a summary outline covering the mostimportant principles of the topics. It is hoped that they will give the reader some understanding which hecan use as a basis for further study.

115

Diagnosis

Patients who are dissatisfied with their dentures willfor the most part complain that the dentures areloose, or hurt, or that they are unhappy with theirappearance. Sometimes they will have difficultywith speech.

Now that you are familiar with the principlesunderlying the construction of efficient dentures youshould be able to listen carefully to the patient'scomplaint, and deduce what faults could account forthe difficulty. There is great value in coming to aprovisional conclusion, from the history, about thecause of the problem, before examining thedentures and the patient's mouth.

It may well be that on examination you will finda number of faults in the dentures and yet only onemay be at the root of the problem and be, for thispatient, of paramount importance. This can bediscovered only by listening carefully to what thepatient says. You will then know which factors willneed particular attention during the construction ofnew dentures.

It is useful to summarize the general categories ofpatients' complaints.

The loose denture

If a denture moves about in use it may be due to anunretentive base or to instability.

The upper denture which falls down when thepatient opens his mouth is almost certainly unreten-tive - the base may be underextended with lack ofa border seal, or overextended, causing too muchtissue displacement or interfering with the movingcoronoid process of the mandible. The lowerdenture which rises up when the mouth is opened isalso most probably unretentive for similar reasons.

If, however, the dentures stay in place when themouth is opened but displace during chewing orspeech, then it is more probably the case that theyare being unstabilized. Such unstabilizing forces willarise from:

I. Incorrect centric jaw relationships with apremature occlusal contact, particularly between thelast molar teeth.

2. Incorrect tooth positions with excessive unba-lanced forces from the tongue, lips, or cheeks. Teeththat are too lingually placed may cramp the tongue,or if the lower occlusal table is too high the tonguecannot get above it when the mouth is open or whenfood is being manipulated.

3. Interfering occlusal contacts in lateral excur-sions. A particularly serious example of this canoccur where there are natural lower anterior teethand a complete upper denture.

It must be remembered that the less the possibilityof developing a retentive base (as will occur whenthe border tissues are poorly displaceable) thegreater will be the need to eliminate possibleunstabilizing forces. If the bases are very retentiveindeed then unstabilizing forces may well not besufficient to overcome the retention and displace thedenture.

Conversely, in the absence of an alveolar ridgewhere the potential of stability is low, it is importantthat the retentive forces be maximally developed.

The denture which causes pain

If the denture base is overextended and causing painit is very obvious, with redness and ulceration of thetissues at the border - if this is not to be seen thenthe pain is not due to overextension.

\17

118 Diagnosis

If the soreness is over the alveolar ridge and isdue to a sharp bony lump, thcn it is equally obvious,the lump being palpable, tcndcr , red, and probablyulcerated.

If the cause is not perfectly obvious then the painis most probably due to faulty jaw relationships. Ifthere is a generalized soreness of the lower ridgewhich comes on after the dentures have been wornfor a short while and becomes worse until it iseventually intolerable and the lower denture mustbe taken out, then almost certainly the occlusalvertical dimension is too great. Sometimes thiscondition produces a burning sensation in the palateand tiredness in the jaw muscles and the floor of themouth.

If the pain is not generalized but arises from a

succession of sore spots over the ridges, then anerror in centric jaw relationship must be suspected.The movement under occlusal load that arises fromuneven occlusal contacts will soon cause discomfort.

Faulty jaw relationships are the commonest causeof persistent discomfort under complete dentures.Rare causes of pain arc rare" and call for considera-tion only when the bases and jaw relationships havebeen found correct and eliminated as a cause.

It should be borne in mind that patients differ inthe discomfort they experience from the samestimulus - this does not mean that the complaint iswithout foundation, but it does mean that quitesmall errors will have to be guarded against in theconstruction of the new dentures.

*This is not a tautology but an important observation tobe constantly borne in mind. For example, patients with ared palate or a tender lower ridge arc often said to besuffering from 'acrylic allergy". This allergy is so rare as tobe non-existent but excessive occlusal vertical dimensionsor oral candidiasis are comparatively common.

Factors influencing the prognosis of completedenture treatment

The success of complete dentures depends uponhow expertly the foregoing procedures have beenaccomplished, but there are a number of factorswhich render successful treatment more difficult.

The personality of the patient

The level of intelligence of patients obviously variesa great deal. Some understand instructions andexplanations which are given them and co-operatewell with the dentist. Others are unable to respondin the same sort of way and this clearly increases thedifficulty of constructing satisfactory dentures.

The personality of an individual affects the easewith which he may be treated. This is too complexa subject to allow for a detailed description in thisbook. However, experience of treating large num-bers of patients results in an improved knowledge ofhuman nature and an ability to recognize thepotentially difficult personality.

A further difficulty arises if one is unable tocommunicate with the patient satisfactorily. Thismay be due to his low intelligence but can also arisethrough the patient's deafness or inability to under-Mand the language.

The elderly patient

A lot has been written about the prosthetic treat-ment of the elderly and it is sometimes implied thatthis treatment should be in some way different fromthat provided for other people. So it must be saidthat, unless the elderly person is severly handicap-ped by senility or dementia, the treatment can andshould be the same as for younger people. Theprinciples of good denture construction are asimportant, if not more so, in this group as for othersand no compromise, or alternative technique, isrequired.

It should be remembered too that the success ofdenture provision is much more sensitive to tissueage than to chronological age and in this contextthere are many young people of 80 years and manyelderly people of 50 years. Reeognition of this factoris of great importance in prognosis.

Structural variations which affect the success ofprosthetic treatment

I. Gross resorption oJ alveolar bone This results ina reduction in the resistance offered to the antero-posterior and lateral movements of the denture(Figure 203). It also reduces the area of jaw whichcan provide effective support for the denture. In anextreme case the dental nerve may come to lie insuch a position that the denture may exert pressureupon it.

2. Sharp bony prominences These, be they causedthrough irregular resorption or the accentuation of

Figure 203 Photographs of lower jaw showing grossresorption of alveolar bone.

119

120 Factors influencing the prognoisis of complete denture treatment

Figure 204 Photograph of a sharp and prominentmylohyoid ridge on the left side of the mandible.

Figure 205 A bulbous undercut maxillary tuberosity.

normal structures such as the mylohyoid ridge(Figure 204), cause pain due to the covering mucousmembrane being nipped between the sharp boneand the hard denture base. Any attempt to extenda complete upper denture into a tuberosity undercutalso causes pain, or prevents the proper extensionof the denture base into the sulcus. Unless theseunfavourable forms are modified by surgery, suc-cessful treatment is jeopardized (Figure 205).

3. Abnormalities in the development of the palateIn addition to cleft palates, which obviously presentvery special problems, other anomalies in thedevelopment of the palate occur which add to thcdifficulties of providing a satisfactory completeupper denture. In cases of torus palatinus the twopalatal processes unite in the midline with theheaping up of bone into the oral cavity in the formof bilateral ridges. These are sometimes undercutand are always covered by a very thin layer of

A

B

Figure 206A A bi-lobed torus palatinus. B A non-lobulartorus palatinus.

Figure 207 Palate showing a midline fissure.

Factors influencing the prognosis of complete denture treatment 121

A

B

Figure 208 Patients with, A Angle's Class II jawrelationship and, B Angle's Class III jaw relationship.

mucoperiosteum (Figure 206). If these are coveredby a denture base they must be relieved to preventthe denture flexing over the torus. The bulk ofdenture material results in a marked restriction ofspace for the' tongue.

Sometimes the union of the two palatal processesleaves a deep fissure in the midline (Fig. 207), andit is difficult to establish a seal between the palatalmucosa and the denture.

Figure 209 A flabby ridge in the anterior maxillary area isbeing displaced with the handle of an instrument.

A

B

Figure 210A Deep notching of the labial flange of thecomplete upper denture to accommodate a high labialfraenum. B Removal of the denture reveals how high thisfraenal attachment is. To avoid the denture beingdisplaced by the movements of the fraenum, the flangewould need to be notched even more deeply and this wouldpredispose to midline fracture.

4. Disparity in arch form and size between thejaws When opposing jaws are of widely differentsizes there is some difficulty in positioning the teethon the dentures in such a manner that they occludenormally and at the same time are in positionscompatible with fulfilling the other requisites ofcomplete dentures. Cases of maxillary and mandibu-lar prognathism (Angle's Classes II and III) presentthis type of problem (Figure 208).

122 Factors influencing the prognoisis of complete denture treatment

5. Flabby ridge When a complete upper denturehas been worn for some time opposed only by loweranterior natural teeth, it is common to find thealveolar bone replaced by fibrous tissue, thusproducing a 'flabby ridge' (Figure 209). This abs-ence of support for the front part of the upperdenture presents special problems. In order torecord an impression of this area without displacingthe flabby tissue special impression techniques arerequired.

6. Variation in supporting mucous membrane Thenature of the soft tissue overlying the alveolar andpalatal bone and forming the lining of the mouthvaries with age and health of the individual. Healthyyoung adults have a thick epithelial layer and anunderlying connective tissue layer rich in glandularand adipose tissue. In old age there is a gradualatrophy of the soft tissue and this is also seen indebilitating disase and those suffering from malnut-rition. In addition there is a gradual deterioration inthe elastic quality of the fibrous tissue stroma. Thesechanges make it more difficult to develop the borderseal necessary for complete denture retention andthe atrophic type of mucosa is readily traumatized.

7. High fraenal attachments Crossing the vestibularsulcus from cheek and lips to alveolar bone are anumber of fibrous strands enclosed in an epithelialcovering. These move under the influence of thefacial muscles. When fraena are attached near to thealveolar crest it is very difficult to maintain a borderseal and movements of the cheeks and the lips tendto cause displacement of the denture (Figure 210).

8. Muscular dystrophies There are a number ofneuromuscular disorders which adversely affect theprognosis of complete dentures. The hypertonicityof muscle found in spastic paralysis, the flacciditywhich occurs in poliomyelitis and facial paralysis,and the weakness occurring in myasthenia gravisand disseminated sclerosis add to the difficulty ofdeveloping a border seal and result in diminishedmuscular control of the dentures. Patients withParkinson's disease suffer in a similar way and theuncontrollable tremor is sometimes responsible forthe dentures being shaken out of the mouth.Dyskinesia as a side effcct of psychotropic drugadministration is a recent and possibly growingproblem.

9. Denture-related stomatitis Inflammation of thedenture-supporting mucosa may occur in response

to mechanical trauma, infection and as a result ofchemical irritation. This is usually referred to as'denture-induced stomatitis'. The incidence of thiscondition seems to vary between 21 per cent, foundamong denture wearers in the United States Army,and as high as 40 per cent found in Denmark, asreported by Budtz-Jergensen. It occurs at least twiceas often in women as in men. The isolation ofcandida from mouths exhibiting oral stomatitis hasfocused workers' attention on this organism as theprimary cause of denture-induced stomatitis.

It should be pointed out, however, that thisorganism is a normal commensal of the mouth andonly becomes involved in tissue pathology when itis in its hyphal form. For this to happen denotessome deviation from the normal state of health.

The factors which may predispose to a candidalinfection in a prosthetic patient are:

1. Poor oral hygiene.2. Trauma.3. Anaemia.4. Diabetes.5. Malnutrition and malabsorption.6. Menopause.7. Reduced salivary flow due to senile atrophy

of the glands.8. Reduced salivary flow due to irradiation.9. Oral antibiotic therapy.

10. Steroid therapy.11. Malignant disease.12. Treatment with immunosuppressive drugs.

It has been shown that in many cases recovery iseffected by merely correcting occlusal errors andrelining the dentures to eliminate trauma. The useof antifungal drugs such as nystatin and amphoter-icin B usually results in the tissues returning tonormal in 14 days. It should be borne in mind,however, that the organisms are also infecting thedenture base itself, and therefore there is noadvantage in eliminating the fungus from the mouthif an infected denture is to be replaced. The dentureshould, therefore, be immersed overnight in a 1 percent solution of sodium hypochlorite. Indeed,denture stcrilization and clcansing alone will oftenproduce a remission of the clinical signs.

Recurrence of denture stomatitis is common if thepredisposing cause has not been dealt with.

Persistence of candidiasis after the elimination oftrauma and infection should indicate the need for athorough medical examination.

Rebasing complete dentures

The useful life of complete dentures depends largelyupon the rate at which the underlying alveolar boneresorbs. This change in the contour of the denturesupport is insidious and patients only become awareof the changes which have taken place when thedentures become really loose.

When a patient presents complaining of thisdeterioration in the fit of their dentures, examina-tion of the dentures and of the mouth may alsoreveal;

a) a loss of the occlusal face height.b) a failure of the teeth to occlude evenly when

the mandible closes in centric relation.

If it is not intended to replace the dentures at thisstage, and provided they are otherwise in goodcondition, it may be decided to reline or rebase theexisting prostheses. It must be emphasized that thisprocedure must be reserved for dentures whose soledefect is a lack of retention. In cases where there isa history of pain or looseness due to instability thenrebasing will almost always do more harm thangood.

It should be remembered that lack of retention ina denture does not necessarily mean that theadaptation of the fitting surface is poor. It may bean indication of underextension of the base with aninadequate border seal. These criteria should, ofcourse, be assessed before relining or rebasing arecontemplated.

ReliningThis is the readaptation of the tissue surface of thedenture by the addition of a layer of new basematerial. Its use should be confined to improvingthe fit of local areas of the denture base following

the limited resorption which takes place after thefitting of an immediate denture or to correct forimperfections in the adaptation of dentures whichare otherwise satisfactory. The addition of resin tothe fitting surface of the upper and lower denturesmay improve the fit but also incorporates a distinctrisk that the occlusal vertical dimension will beincreased and that the anteroposterior tooth rela-tionship will be changed as well. As an additionallayer of denture base material has been added it alsoincreases the bulk of the denture, and thus in thecase of the upper denture the thickness of thepalate.

Rebasing

This is different from relining in that after newimpressions have been made in the existing denturesthe whole of the denture base is replaced. It is NOTthe addition of another layer of acrylic to the fittingsurface.

Clinical procedure of rebasingThis procedure describes rebasing of both upper andlower dentures. It is, of course, the same if only onedenture is being rebased.

Having checked the occlusion of the dentures andsatisfied oneself that there are no gross imperfec-tions, the undersurface of the dentures are trimmedto eliminate any undercuts and to provide sufficientroom for the wash impression material (Figure 211).The border should be reduced by 1 mm andadditional spacing should be provided over themylohyoid muscle. Each denture is in turn loadedwith impression paste and firmly seated in themouth (Figure 212). The technique used is precisely

123

124 Rebasing complete dentures

Figure 211 Undercuts are removed from the fitting surface.

Figure 212 An adequate, but not too thick, layer ofimpression paste is applied to the fitting surface.

that of taking secondary impressions and is descri-bed on pages 27-41. An excessive thickness ofmaterial in the palate must be avoided so that theupper occlusal plane will not be changed more thanmay be necessary (Figure 213.)

An interocclusal check record and a face bowrecord are then taken (Figure 214). When theimpressions are made there is no way of ensuringthat the dentures have not moved in relation to theunderlying bone, thus disturbing the jaw relations.It is a not uncommon practice to have both denturesin the mouth while making the impressions and havethe patient bring the teeth together in occlusion.This is very likely to make matters worse becausethe mandible will not be in the retruded positionwhile the impression material is setting. This diffi-culty is overcome by making a check record. Byusing a face bow record, suitable adjustments can bemade on the articulator (see page 000).

Of course, the thickness of the impression mate-rial and the interocclusal check record produces anincrease in the occlusal vertical dimension. Theamount of this increase must be determined by

Figure 213 The minimum thickness of paste after theimpression is unlikely to be less than 1 mm.

Figure 214 An interocclusal record has been made. It canbe seen that a disturbance of the occlusal relation hasoccurred - the upper denture has moved slightly forward.

Figure 215 After mounting the wax record has beenremoved and the occlusal error is apparent.

assessment of the rest vertical dimension and anadjustment must be made during the laboratorystage if it is excessive.

Laboratory procedures for rebasing

Casts arc poured into the impressions made in thedentures and the face bow and jaw relation records

A

B

cFigure 216 A Most of the base acrylic has been removed.B The upper teeth have now been correctly replaced inintercuspation.C Shows that there is a space between the upper dentureand the cast to allow movement for occlusual replacement.

Rebasing complete dentures 125

Figure 217 The upper denture is waxed to the cast.

are used to mount them in the articulator. When thisis being done the incisal pin must be raised enoughabove '0' to compensate for the increase in theocclusal vertical dimension due to the thickness ofthe impression materials and the check record(Figure 215).

The upper denture is removed from its cast and,except for the resin uniting the teeth together, therest is ground away. The remaining tooth supportingsection is then reseated with the teeth in occlusionwith those of the lower denture to which they aresecurely attached using sticky wax. The incisal pinis adjusted until it again is set at '0' (Figure 216).

Softened wax is then placed over the ridge of theupper cast and the lower arm of the articulator israised until the incisal pin makes contact with theincisal guidance table. Once the wax has hardenedthe occlusal surfaces of the teeth may be separatedand the upper denture may be waxed up in thenormal manner (Figure 217). The process is nowreversed whilst the lower denture is remodelled in asimilar manner. At this point both dentures may bef1asked, packed and processed.

A warning

Unless meticulously carried out, rebasing denturesis a hazardous procedure. Again and again patientsare seen wearing and complaining of discomfortwith, dentures that have been rebased, or worserelined, often more than once. Invariably thevertical dimension of occlusion has been increasedand a centric jaw relation error introduced.

Denture copying

When a patient is wearing dentures which wereprovided as immediate replacements for his originalteeth it is clearly desirable that when they need tobe replaced the new dentures reproduce the posi-tioning of the teeth and the contouring of thedenture as accurately as possible. In the absence ofimmediate replacements, when a patient has suc-cessfully worn dentures for many years, and thesedentures in every way fulfil the principles of dentureconstruction, it may be advantageous to incorporatetheir good features in the new dentures. Denturecopying is one way of doing this. Of course, if thedentures can be rebased , then this is preferable.Copying can also be for the patient who hasexcellent dentures and requires a spare set.

The procedure to be described enables you tomake new dentures which preserve the tooth posi-tions and form of the polished surface of the olddentures whilst improving the fit and base exten-sion. It achieves this result with the minimum ofclinical and laboratory time.

The procedure described under Clinical Stage Ion p. 5 et seq should be followed and once you havesatisfied yourself that the mouth is in a suitablecondition to receive dentures the following proce-dure should be followed.

If the denture border is underextended in anyarea this deficiency can be remedied by the additionof low fusing impression compound to the dentureborder. It is unlikely that the denture will beoverextended, but if this should be the case or iffraena have not been adequately provided for,adjustments to the denture border should be carriedout.

Laboratory procedureSmall pieces of sticky wax 0.5-1 cm in length areattached to the tuberosity region of the upper

126

denture and to the retromolar pad area of the lowerto form sprues which are attached to stiff wire rodsabout 12 cm long which are warmed and attachedacross the top of the two sprues as shown in Figure218.

The dentures are suspended in tapered duplicat-ing flasks (Figure 219). The depth of the flask shouldbe such that the denture does not touch the side orthe bottom of the flask. The flasks containing thesprued dentures are then placed into a cooling tankaround which cold water can be circulated. Liquidagar duplicating fluid is poured into the flasks at atemperature of 50°C, taking care that it does notdisplace the denture against the side of the flask.Duplicating material is added until it covers thedenture and reaches the top of the wax sprues(Figure 220).

When both flasks have been filled in this way coldwater is circulated through the tank to accelerate thegelation of the agar. After about 20-30 minutes theagar gel will have set and, following removal fromthe cooling bath, the flasks may be inverted and theagar gel displaced. Using a sharp narrow-bladedknife the agar is sectioned lengthwise so that thedenture can be removed from the mould (Figure221A,B).

At this stage the sprues can be removed, and afterthe denture has been cleaned it may be returned tothe patient. The halves of the agar mould are thenreassembled in the flask and a thin slurry of coldcure acrylic resin is poured down one of the sprueholes until excess appears at the other (Figure 222).

Whilst the acrylic is being poured into the mouldthe flask may be gently vibrated anr,rotated toensure the release of any air which may be incorpo-rated in the mould. When the excess of acrylic flowsout of the second sprue hole the mould has beenfilled, and when both flasks have been loaded withacrylic they are placed in a pressure vessel which is

Figure 218 Wax sprues have been attached to the heels ofupper and lower dentures and joined to the steel rod bywhich they will be suspended in the duplicating flask.

Figure 219 The sprued dentures are suspended in thespecially prepared flasks.

sealed and the pressure is raised to 207 kPa (30 lblsq. in). Polymerization of the acrylic resin will thentake place at room temperature in 30 minutes. Afterthis time the air pressure is released and thepolymerized replicas of the patient's dentures maybe removed from the mould and the sprues cut off(Figure 223).

Laboratory procedure 127

Figure 220 The flasks have been imersed in a coolingchamber and molten agar is being poured around thesuspended dentures.

A

B

Figure 221A The agar has set, the flasks have been invertedand the gel has been removed. This is being carefullysectioned with a sharp knife. B This shows separation ofthe two halves of the agar mould and removal of thecomplete upper denture.

128 Denture copying

Figure 222 The mould has been reassembled in the flask and a fluid slurry ofself-curing acrylic resin is being poured down one sprue hole. This continuesuntil an exeess flows out of the other. Whcn both moulds have been filled thetwo flasks will be inserted into the pressure vessel in which polymerization takesplace at room temperature over a period of 10 minutes at a pressure of 207 kPa.

In the absence of the specialized equipmentrequired to follow the above procedure a plasticpudding basin may be substituted for the metal flaskand a liquid mix of alginate may taken the place ofthe agar (Figure 224A-D). In this case, approxi-mately twice the normal water-powder ratio is usedin preparing the slurry of alginate which needs to bevibrated into position around the suspendeddentures. Setting of the alginate, of course, occursquite quickly and it is likely that there will be someentrapment of air in the mould so that the resultantdenture replica may have a number of acrylic blebson the surface, which will need to be removed.

Figure 223 The completely polymerized replicas of thepatient's dentures have now been removed from the flask.After the sprues have been cut off, these duplicates will beavailable as special trays and occlusion rims for therecording of impressions and jaw relationships.

Clinical procedureThe completed upper and lower replica dentureswill now be used in the clinical stage for recordingimpressions and jaw relations. This procedure isvery similar to that used in rebasing.

First, any undercuts on the fitting surface of thedentures must be removed. The upper replica isthen tried in the mouth and checked for the positionof the teeth in relation to the lip line. It might be

Clinical procedure 129

A

c D

Figure 224A-D Showing a simple technique using readily available materials which will enable the practioneror his nurse to construct an acrylic replica. In this case a liquid slurry of alginate is used in place of the agar.This is likely to be rather more porous and the resulting replicas may suffer by having a number of blebs ofacrylic distorting the denture outline.

possible to make small changes to the position of theanterior teeth by the addition of composition or waxstops to the fitting surface. However, this will alterthe relation of the border to the sulcus reflection andmay make for difficulties with the reline impression.

If stops are added it should be in the tuberosityand incisive papilla regions. Then the dentures areremoved from the mouth and the wax or composi-tion are chilled preparatory to the use of thedentures for recording a reline impression.

Zinc-oxide-Eugenol is the material used for thispurpose, and when the upper denture replica has beencarefully loaded with the paste it is conveyed to themouth and seated in position. The clinical methodthen followed is that described on pages 34-40.

When the upper impression has been completedthe lower replica is used to record the lowerimpression following the method set out on pages28-34.When the lower impression has been satisfactorilycompleted it will be necessary to make a jaw relationrecord. A little plaster or softened wax is applied tothe occlusal surface of the relined lower denture,and with the upper denture in place, the patient isrequired to close lightly in centric relation.However, care must be taken to ensure that theteeth do not make contact through the plaster orwax.

It is most necessary at this stage that the occlusalvertical dimension is assessed (see page 55 et seq).

130 Denture copying

Figure 225 After removal of any undercuts from the fitting surface of the replicadenture, an impression of the upper jaw is taken in zinc-oxide-eugenol impressionpaste. A facebow registration is taken to enable the maxillary cast to be mounted inthe articulator in the correct relationship.

Figure 226 The zinc-oxide-eugenol impression which has been taken in the duplicatelower denture is shown mounted in the articulator using a pre-contact plaster centricrelationship record.

Figure 227 The relined upper replica denture has beenremoved and the upper teeth have been set to occlude withthe lower replica. This will then be removed and replacedby a baseplate on which the lower teeth will be set toocclude with the upper. After a trial insertion of thewaxed-up dentures, these will be processed in the normalway.

A

Clinical procedure 131

Figure 228A The completed dentures are shown remounted on the articulator with a plaster check record. B Followingremoval of the check record and closing of the articulator arm, the nature of the occlusal error is revealed. Adjustmentof the occlusion is made on the articulator in the manner described in Laboratory Procedures 5.

If it is too large, another record must be made. Iftoo small then a decision must be made if a furtherrecord will deal with the problem or if recourse willhave to be made to adjustment on the articulator byraising the incisal pin.

When the 'pre-contact centric relationship record'has been completed this should be set aside and withthe relined upper denture in position a facebowregistration made to ensure that the cast of themaxillary jaw can be correctly mounted on thearticulator in relation to the hinge axis (Figure 225).

Hydrocal is cast into the two impression surfacesand the resulting casts are mounted in the articulatorusing the facebow record and the precontact centricrelationship record (Figure 226).

When this has been completed the interocclusalrecord can be removed, and the decision madeabout the occlusal vertical dimension at which the

new dentures are to be constructed. As the castshave been mounted with the facebow this adjust-ment may be made by raising or lowering the pin onthe articulator.

At this stage one or other of the lined replicadentures are removed from the cast and a temporarybaseplate laid down on the model with the otherreplica still in place. The teeth may be set up oneby one to occlude with the opposing denture usingthe existing replica as a guide to tooth positioning(Figure 227). After one has been set up in this waythe other relined replica is removed from the castand a similar procedure carried out until all the teethhave been set up on the temporary bases and waxedup for trial insertion. The procedure for try-in, finishand check record (Figure 228A,B) are as in thestandard procedures.

Relief areas

The bone which ultimately provides the support forcomplete denture is covered by varying amounts ofsoft tissue. In certain areas, such as in the midlineof the palate and over bony prominences such asmandibular tori, the mucous membrane lining themouth is united to the periosteum to form a virtuallyunyielding mucoperiosteum. In other parts there isa definite submucous layer which may containvarying quantities of fibrous tissue, fat, and mucousglands, all of which contribute to the displaceabilityof this tissue.

If the secondary impression is taken in animpression material which has a low viscosity, littleor no displacement of the soft tissues overlying thealveolar ridges and palate will occur. Such animpression is often called 'mucostatic'. A rigiddenture base constructed on a cast obtained fromsuch an impression will transfer the masticatory loadto the virtually unyielding areas of the jaws and ifsuch areas are centrally placed rocking of thedentures about this fulcrum may occur. The degreeof movement which takes place will depend uponthe amount and distribution of the displaceabletissues.

In an attempt to prevent this movement reliefareas are sometimes incorporated in the denturebase. The extent of the area to be relieved and thedepth of the relief area are determined by examina-tion of the tissues. This is carried out with anexploring finger or a blunt instrument. When theareas of unyielding tissue have been outlined on thesurface of the cast, tin-foil of an appropriatethickness is burnished over this area and fixed inposition with oxyphosphate cement. The thickestfoil used is gauge 7 (0.508 mm thickness), whichwould be used in cases exhibiting the greatestvariation in the displaceability of the denture-supporting tissue. The thinnest foil used is gauge 1

132

(0.152 mm thickness). When a base is processed onsuch a modified cast there will be a recess on thefitting surface of the completed denture correspond-ing to the outline of the relief. The sharp edges ofthis recess should be bevelled, otherwise they mayact as stimuli to epithelial proliferation.

It should be borne in mind that the contractionwhich takes place during the polymerization ofacrylic resin frequently results in the base of acomplete upper denture being out of contact withthe palate in the midline, thus obviating the neces-sary for midline relief.

The presence of a relief area can also lead to theupper denture base being thinner in the midline andthis in turn increases the likelihood of midlinefracture. On the whole, such relief areas should beavoided.

When impressions with viscous impression mate-rials are taken, such as impression compound ormaterials of intermediate viscosity (e.g zinc-oxide-Eugenol paste), displacement of the supportingtissue may occur thus obviating the need for relief.Such impressions are referred to as 'mucocom-pressive' .

Relief of the superficial mental nerveWith extensive resorption of the mandibular alveo-lar bone the mental foramen, through which themental nerve emerges to supply the mucosa of thecheek and lip, lies immediately beneath the muco-periosteum which supports the denture. When thisoccurs the nerve will be contused by pressure fromthe denture each time the teeth are brought intoocclusion and the patient will suffer pain. Pressureon a nerve trunk will cause interference with nervefunction and so the symptom of tingling in the lipwill be present on the same side. Should this occur

the solution is to ensure that there is sufficient spacebeneath the denture for the nerve to pass withoutbeing traumatized.

To achieve this end the position of the foramenand the course of the nerve should be located bypalpation and this should be marked on the surfacewith an indelible pencil. The dye will then betransferred to the surface of the imression and thento the stone cast. By covering this area of the castwith a layer of No 7 tin-foil (0.5 mm) which iscemented to the underlying stone the processedacrylic denture will be relieved from the superficialnerve, which thereby passes in a tunnel free frominjury.

Sometimes when patients complain of persistentpain beneath a lower denture there is a temptationon the part of the dentist to resort to th~ use of aresilient lining material. (see relevant section of thetext).

If a nerve lies just beneath the surface of thedenture-bearing tissues, the resilience which allowsfor the wider distribution of occlusal loads alsopermits the downward displacement of the denturebase and hence contusion of the nerve. If thetolerance of the denture supporting tissues is so lowthat the use of a resilient lining is thought to benecessary, the thickness of the relief for the mentalnerve should be doubled.

Relief areas 133

Relief over incisive papilla.

Normally the fibrous tissue of the papilla affordssufficient protection to the emergin~ anterior pa~a-tine nerve but with extensive resorption of the labIalsurface of the premaxillary bone the papilla comesto occupy a position either on the ridge crest or evenfurther forward. At the same time there is often athinning of both the epithelial surface and of theunderlying fibrous tissue and when this has occurredpalpation of the papilla will elicit a painful respo~se.Under these circumstances it is prudent to relievethe surface of the denture by laying a sheet of No.7 foil on the stone cast over the outline of the papillaso that the finished denture will not apply pressureover this site.

The routine relief of the tissues in the mid-line ofthe palate on the grounds that the denture will bearheavily on this area is based upon a false conception.In most cases the shape of the palate is such thatwhen the small amount of contraction associatedwith the polymerization of acrylic resin occu~s thiswill cause the base to be least closely adapted In themid-line. In the event of pressure being localizedover a small area of the denture-supporting tissuesthis is best localized and adjusted using pressurerelief cream as described on page 111.

Resilient linings

Manufacturing companies have developed resilientmaterials with which dentures may be lined with aview to increasing the comfort with which they maybe worn. It should be borne in mind, however, thatthese materials are no panacea for resolvingpatients' problems and have a very limited role inprosthetic treatment.

The principal shortcomings of the use of resilientlinings may be summarized as follows:

i) May mask errors of jaw relations.ii) In the bulk which is needed they may weaken

the denture to the extent of potentiating fracture. Ifused in thinner section they are ineffective.

iii) Difficult to keep clean. The plaque which soreadily gains attachment to the surface becomes thenidus for the deposition of calculus and may becomecontaminated by pathogens.

iv) It is difficult to adjust the fitting surface of thedenture, should easing become necessary.

v) Bonding of the lining material to the denturebase resin is difficult.

vi) Do not afford any protection to the dehiscentmental nerve.

vii) Those relying on the presence of a plasticizerfor their resiliency will gradually harden as thisconstituent leaches out of the resin.

To be effective the resilient layer must be ofsufficient bulk and a thickness of 1.5-2 mm isnecessary. This means that it cannot be employed inthe upper denture, the total thickness of whichshould not exceed this range.

These materials fall into two categories, plasti-cized acrylics and siloxane polymers. Whereas theplasticized resins form a chemical bond with themethyl methacrylate which is superior to that of thesilicones, and are easier to keep clean the initial

134

resilience is gradually reduced as the plasticizerleaches out and their use can be only temporary.

The siloxane polymers have a low glass-transitiontemperature and hence remain soft in the mouth. Itis necessary to use an adhesive to attach them to thebase material and this bond may sometimes fail.They readily support the growth of fungal hyphaeand bleach very readily or undergo seriousdeterioration if cleaned with hypochlorite cleansers.

However, because of their continuing resiliencythe silicone materials tend to find greatest favourand Molloplast 'B' is the one which seems toperform most satisfactorily

Indications for use

These materials must not be used unless there is apersistent history of pain under the denture whichhas resisted all other prosthetic attention. It is notat all uncommon for soft linings to be put indentures when these are at fault, particularly withan increased occlusal vertical dimension or a grosserror in centric jaw relation. There are very fewpatients indeed, given soft linings, who cannot bemade perfectly comfortable with correctly madeconventional dentures.

Where the mucosa is friable and tender to thetouch, benefit might be possible but it is wise to seeif a temporary soft lining material gives relief. If not,then a permanent resilient lining is unlikely to be ofuse.

Of course, it must be appreciated that if it is theintention to protect the mucosa from pressure on theunderlying bone then the soft material should bebetween the mucosa and the bone, not between thedenture and the mucosa. This really calls intoquestion the whole rationale of their use and leads

to the speculation that their rarely successful appli-cation has a strong psychogenic content.

TechniquesIf a resilient lining is to be used then severaltechniques for their incorporation in the denture canbe used. Two are briefly described.

1. This method is appropriate where an existingdenture is to have a resilient lining added. However,particular care must be taken to ensure that there isa well extended lower base, a correct occlusalvertical dimension and an accurate centric relation.

If the base has undercuts they are removed and athin wash of zinc-oxide-Eugenol paste is used tomake a reline impression. It must be rememberedthat if the jaw relations are disturbed here they willbe almost impossible to correct with the soft liningin place.

A cast is made to the relined base and the denturemounted in an articulator against an occlusal key. Itis then removed from the cast and because of thelack of undercuts, and the presence of the layer ofpaste, the cast should not suffer damage. A suffi-cient amount of the denture base is then groundaway to leave room for the required thickness ofresilient lining. The denture is placed back on thearticulator in the occlusal key and waxed to the cast.

Resilient linings 135

It is then flasked as if it were a wax trial denture.The flask is separated, the wax boiled out, andbonding material is painted on the acrylic surface.The resilient material is then packed, the flaskreassembled, and polymerization allowed to occurin accordance with the manufacturer's instructions.After deflasking any flash can be cut off and thedenture polished.

2. This method is to be preferred when a newdenture incorporating a resilient lining is to bemade.

The denture is constructed using a temporary coldcure acrylic baseplate of thickness commensuratewith the amount of soft lining to be used. It iscompleted to the wax trial denture stage. This isthen flasked in the usual way, the wax boiled out butthe baseplate left in place in the lower half. Theacrylic dough is then packed in the upper flask halfwith several layers of separating film between theflask halves. These are left in place during proces-sing. After processing the flask is separated, thebaseplate removed (if necessary by heating it), theprocessed acrylic surface ground as needed, thebonding material applied and the resilient materialpacked into the space left in the lower half. Theflask is reassembled and polymerization allowed tooccur.

Implants

The possibility of transmitting the chewing forcesdirectly to the bone and enhancing the stability ofthe denture by anchoring it to the bone has been theaim of clinicians for many years. One of the causesof failure was the absence of biocompatibilitybetween the bone and the metals used to constructthe implant.

In the 1950s advances in materials science resultedin the development of inert alloys and this gave freshimpetus to innovative practitioners to develop newtechniques. Over the last 30 years we have evaluateda number of methods but these have all provedunsatisfactory because the body has attempted toexfoliate the implant. During the last 10 years,however, techniques have been developed in whichbone has bonded with the implanted metal and rigidattachment of the denture to this integrated stucturehas been obtained. The advent of the ankylosedtitanium implant means that we have for the firsttime a potentially successful means of providing anartificial replacement for a tooth root.

The reasons for this success are clearly enoughdue to the material and the technique of placement- asepsis, avoidance of trauma and a very tightprimary fit. The pioneering work of Branemark 1.2

with dental implants was directed towards theprovision of upper or lower anterior fixed bridge-work with five or six fixtures and one-piece super-structure from premolar to premolar. In this way theimplant system is used as an alternative to completedentures. In this system the implants, which are ofa screw pattern, are placed in the bone and themucoperiosteum closed over them. After a comple-tely unloaded healing period of about 6 months thehead of the implant is locally exposed through themucosa and the transmucosal abutment placedwhich will carry the superstructure. The greatsuccess of this method can be ascribed to themetallurgical purity and preparation of the implant,

136

its careful engineering design, the meticulous prepa-ration of the implant site, in which all cutting is doneat slow speeds (less than 1500 rpm is recommendedin this technique) with copious saline cooling, toavoid any bone cell damage, instrumentation whichensures metallic compatibility and a precision fitwith absolute primary stability (no discerniblemovement at all is permitted).

The costs of this method, because of the dedicatedinstrumentation, the number of implants required,and the subsequent bridgework, are high and thisnecessarily limits its application in the generalcommunity. Its widespread use in its country oforigin, Sweden, is due to substantial support fromthe state and industry.

There are now a great many competing systemsusing the same or different materials, although thefundamental principles of placement remainunchanged.

From the removable prosthetic point of viewthere has been a recent trend towards the use of theimplants as overdenture abutments. The manifestsuccess of the judicious retention of tooth roots andthe provision of overdentures leads us to expect thatthe placement of artificial tooth roots will be equallyadvantageous. This is indeed the case and thisapplication is widespread and growing.

Examples of this use are four fixtures united by abar with clip attachments inside the completedenture or two isolated fixtures in the canine or firstpremolar regions, replacing those tooth roots asoverdenture abutments (Figure 229). This trend isan attempt to lower costs and to widen the scope ofintegrated implant use to a greater number ofpeople and to use them to stabilize completedentures rather than provide a substitute.

Another development is the one-stage transmuco-sal implanr':", which suggests that the preliminarystage of burial is not essential and has greatly

A

B

Figure 229 Two isolated Strauman 'Bonefit' implants withmale 'Dalbo-Rotax' attachments.B The female parts of the attachments can be seen in thefitting surface of the complete lower denture.

simplified the procedure. Simple instrumentationand lower cost of the implants makes their provisionapplicable to a much wider field of patients.

Implants are being used to replace single missingteeth anteriorly or posteriorly, to allow the place-ment of a crown where otherwise a bridge might beneeded, with extensive preparation of sound abut-ments, or the provision of a bridge instead of a freeend saddle partial denture. Provided that it isremembered that the precise surgical location andangulation of implants is not as easy as it seems, andthat there is a prerequisite for an ample amount ofsuitable bone to put them in, this use is well worthdevelopment.

Indications in the edentulous patient.

Our particular concern here is the use of implantsto help edentulous patients with a denture wearingproblem. This is quite distinct from their elective usefor patients who just do not like the idea of wearingdentures and have the wealth to afford a substitute.

Implants 137

Usually these are lower denture difficulties, butproblems of upper denture retention can occasio-nally be very severe. The patient should have acomplaint of looseness or pain which has notresponded to careful denture construction, i.e. thebases are properly extended and retentive, the jawrelations are correct, and the teeth have beenproperly positioned on the denture.

Persistent looseness in a patient where there hasbeen considerable bone loss will be the commonestsituation, although occasionally a patient with wellformed ridges has this problem. Unfortunately,where the bone loss has been very great, and theimplant is most dearly needed, there may beinsufficient bone for its placement.

Very rarely, a patient has an intractably looseupper denture or cannot tolerate an upper dentureat all. These are both circumstances in whichimplants might be considered and where the mecha-nical retention provided by attachments might beneeded.

Denture provisionAfter the successful placement of the implants theprosthetic method adopted to utilize them willdepend upon the dentist's objectives, and there aremany very complete descriptions available in theliterature.

However, any dentures or fixed appliances mustfollow the strictest standards of accomplishment,with very particular reference to accurate jawrelations and refinement of the occlusion. Thepatient must be convinced of the absolute necessityfor the maintenance of a high level of oral anddenture cleanliness. Traumatic loading or inflamma-tory processes are very likely to prejudice thechances of long term success.

It is now generally agreed that success of theimplants after 5 years will be judged by continuedimmobility (no detectable movement) and no morethan 2 mm of crestal bone loss seen radiographicallyadjacent to the implant. Of course the success of thetreatment will also depend on the patient's substan-tial and sustained improvement in denture comfort.

This comparatively new technique, used properly,offers us a powerful tool in our endeavours to helpdenture wearers. Unfortunately, it could be open toabuse and in such a circumstance the patient couldfinish up in a worse condition. It will be a disasterif the use of implants is thought to be a substitutefor careful prosthetic care.

References1. Branemark PI et al. (1977) Osseointegrated implants

in the treatment of the edentulous jaw. Experience from

138 Implants

a IO-year period. Scandinavian Journal of Plastic andReconstructive Surgery 11: supp!. 16

2. Adell R et al. (198 I) A IS-year study of osseoi ntegratedimplants in the treatment of the edentulous jaw.International Journal of Oral Surgery 10: 387-416.

3. Sutter F, Schroeder A (1988) The new concept of ITIhollow-cylinder and hollow-screw implants: Part I.

Engineering and design. International Journal of Oraland Maxillofacial Implants 3: 161-172.

4. Buser DA et al. (1988) The new concept of IT! hollow-cylinder and hollow-screw implants: Part 2. Clinicalaspects, indications, and early clinical results. Internatio-nal Journal of Oral and Maxillofacial Implants 3: 173-181.

Preprosthetic surgery

Introduction

Pre prosthetic surgery which does not arise from,and which is not directed to the attainment of, clearand specific principles of denture construction isunlikely to be of benefit to the patient. Preprostheticsurgery not followed by denture construction whichtakes advantage of the surgical procedures becomesa wasted effort.

And yet properly directed pre prosthetic surgery isof inestimable value as an aid to successful completedenture construction and occasionally for partialdentures. These small, conservative, atraumaticprocedures offer great prosthetic gains. Carried outcarefully, with proper respect for the soft tissues,they subject the patient to minimal discomfort. Theytake very little time to do and they heal rapidly.

ClassificationThey can be classified according to the prostheticprinciple they support and can be divided into threegroups.

A. those related to the development of a retentivedenture base.

B. Those related to the provision of a stabledenture base.

C. Those which will allow the establishment of acorrect occlusal vertical dimension

Unless they are clearly understood in relation tothe prosthetic principles, they cannot be appropri-ately employed or their benefits properly utilized.

A. Surgery related to the development of aretentive dentureMost pre prosthetic surgical procedures of value aredirected towards enabling the construction of a

retentive denture base, and it is hardly possible tounderstand them let alone carry them out, withoutsome knowledge of the principles of denture reten-tion. Retention of a denture base is obtained byutilizing the physical forces of retention, and theseare developed by extending the base until its borderlies on displaceable tissue, establishing exactly theamount of tissue displacement to provide a seal andensuring that the base has close contact with theunderlying tissues.

Let us consider the surgical procedures related toeach of these principles.

Base extension Base extension requires the remo-val of any obstructing undercuts on the sides of theridges. The lateral bony enlargment of the maxillarytuberosity (the inheritance of neglect to reduce thelast molar socket on extraction) is a prime andcommon example. This bony undercut must becompletely reduced. It must be remembered thatnot only will it prevent extension but it may alsointerfere with the forward movement of the coro-noid process. This is why suggestions that only oneside need be reduced are so often at fault. Theinevitable consequence of not removing the under-cut, and either leaving the extension short orrelieving the base, is to provide only a partiallyretentive base.

Following the removal of the six or more anteriorteeth for the fitting of an immediate denture theanterior labial ridge may prevent labial flangeextension because of an undercut or because a labialflange placed over it will distort the lip. Reductionhere by alveolotomy allows denture base extensionand the potential for retention. The lack of a labialflange (the 'gum fit') ensures a lack of retention.Incidentally, a missing labial flange, or one cleft in

139

140 Preprosthetic surgery

the midline to accomodate a labial frenum, predis-poses to midline fracture of the denture base.

Undercuts can sometimes be packed out sub-periosteally, but only with autogenous material.Attempts with foreign bodies are hardly moresuccessful than their use in ridge augmentation.

Border seal Border seal requires that the bordertissues are soft, displaceable and elastic. This is afeature of the normal mucosa and submucosa of thesulcus reflection. It is not a feature of frena (fibrousbands which do not contain muscle fibres), scartissue or graft tissue. Pre prosthetic procedureswhich leave scar tissue in the region of the borderare contraindicated.

Frenectomy is a valuable procedure if carefullyand simply done and accompanied by an anchorsuture at the sulcus reflection (Figure 230). Theupper labial frenum is most commonly reduced, butsometimes the buccal frena or the lingual frenummust be treated.

The prominent genial tubercle, or ossified geniog-lossus insertion, interferes with the anterior lingualseal. Its reduction must, however, be undertakenwith particular care because of possible connectionswith the spaces of the neck beneath the floor of themouth (Figure 231).

Denture-inducedhyperplasi£llyingat the border is bestreduced after a period of healing in order to reducethe amount of residual scar tissue.Close contact Close contact requires a smoothridge without sharp bony lumps because easing thedenture over these means loss of close contact.Other than random adventitious lumps and spicules,the aftermath of careless exodontia, or the some-times very sharp mentalis tubercle, the prominentand sharp mylohyoid ridge is a common example.

This should be smoothed and reduced only. It isquite unnecessary to cut away the muscle or resect

Figure 230 Labial frenectomy. An anchor suture is placedat the level of the sulcus reflection. This maintains sulcusdepth after healing.

Figure 231 The bony genial tubercle is exposed through asagittal incision. The attached genioglossus muscle iscarefully pushed off and the bony protuberence removed.

Figure 232 The sharp and prominent myohyoid ridge isreduced and smoothed with a bur.

the ridge with a chisel. No sulcus deepening elementis needed or advantageous or really ever obtained.Done conservatively, the procedure takes but a fewminutes and results in a minimum of postoperativepain swelling or haematoma (Figure 232). Takenadvantage of with full base extension into the wholeof the lingual sulcus and the retromylohyoid area, itis usually evident how little need there was for ridgeimprovement or reconstruction.

The so called 'Knife edged ridge', with a bead ofdisplaceable soft tissue running along its upper edgeis resistant to satisfactory surgical removal. There isa danger of attaching the floor of the mouth to thecheek in a movable sheet.

B. Procedures related to the provision of astable base.Stability means lack of those movements (mostlyhorizontal) which are produced by forces arising

from the musculature surrounding the dentures -the muscles of mastication acting through theocclusal surfaces, the muscles of lips and cheeks andtongue acting on the polished surfaces of thedentures.

The contours of the underlying bone and thenature of the covering soft tissues will decide thepotential resistance to horizontal forces. The ridgecovered with firm mucosa is patently going to offerbetter lateral resistance than the ridge covered withflabby soft tissue.

Impression techniques aimed at producing selec-tive and predictable tissue displacement, or nodisplacement, are of very speculative value. What-ever the result, under some conditions the base mustmove. It is preferable to remove the masses ofdisplaceable tissue. This may leave very little ridgeat all, but very little ridge is better than a flabby softtissue denture foundation (Figure 233).

The amount of improvement in ridge height thatcan be achieved by surgery in the face of gross boneloss is very limited and often unsatisfactory, butsome improvement is sometimes obtainable in theupper anterior region with alveoloplasty, particu-larly when combined with the removal of flabbytissue. Very rarely, skin grafts might help a little inthis area.

C. Surgery to assist the establishment of acorrect occlusal vertical dimension.A most common fault in the construction ofdentures is the establishment of too great an occlusal

A

Introduction 141

vertical dimension. There are many reasons why thisis so and one of them is is due a physical difficultywherein the maxillary tuberosity is enlarged verti-cally. The genesis of this usually fibrous mass isobscure, but when it is present it prevents us fromextending the bases fully over the tuberosity and theretromolar pad (for retention) and establishing anocclusal vertical dimension suitably less than the restvertical dimension. In such a case there is noalternative to reducing the tuberosity vertically.Unfortunately, there are rare occasions where thereis generally too much alveolus to allow a correct jawrelationship and then more extensive surgery isneeded.

ConclusionWell founded simple preprosthetic surgery offersadvantages far beyond the time and effort expendedon it.

However, there are patients who, because of ageor infirmity, cannot have such procedures done andit is then that the prosthetist must be able to seewhat compromises will be forced upon him and whatthe consequences will be. If he understands clearlythe reasons for, and the advantages of, preprostheticsurgery he will be able more accurately to foreseethe difficulties that will arise when it cannot bedone.

B

Figure 233A A flabby anterior ridge. B The flabby tissue has been removed and the sulcus depth increased a little withan alveoloplasty.

Cross infection

Prosthetic treatment of patients suspected ofsuffering from infection with infective hepatitisor with Human Immunodeficiency Virus

In order to reduce the risks to health care personnelfrom exposure to the viruses associated with infec-tive hepatitis and acquired immune deficiency syn-drome a strict regime should be followed. AlthoughHTL V III is not as easily transmissible as isHepatitis B and is readily inactivated by heat anddisinfectants, it is prudent to take measures alongsimilar lines to those taken for that condition. Bothof these viruses can be transmitted by blood andsaliva. It is important that all instruments are eitherdisposable or sterilizable. Protective clothing,including gowns and gloves, must be worn by thosedental personnel directly involved in dental proce-dures and, in view of the aerosols containing bloodand saliva that may be generated by low and highspeed dental drills and irrigation/air syringes, thewearing of protective eyewear and masks is essen-tial.

Disposable equipment and materials should beused whenever possible. All instruments that are notdisposable should be sterilizable, preferably byautoclaving. Those which cannot should be decon-taminated in 2% glutaraldehyde for 1 hour, afterwhich this solution is discarded. The equipmentshould then be physically cleaned in detergent andwarm water to remove any organic matter, rinsedand then left in 2% glutaraldehyde for 3 hours.

A special problem arises with regard to themaking of impressions of the mouth to avoidinfecting laboratory staff who are called upon tohandle these impressions. Disposable trays shouldbe used and silicone elastomers are used for both

142

complete and partial denture impression. This isbecause glutaraldehyde, which is the recommendedsterilizing agent will react with other materials,producing distortion of the surface.

After removal from the mouth the impression isexamined and either discarded in the contaminatedwaste container or it should be immersed in a 2%glutaraldehyde solution in a sealable container for 1hour. It should then be placed in a fresh 2%glutaraldehyde solution for at least 2 hours (orovernight if convenient). The impression is thenwashed with tap water and packed in a polythenecontainer and sent to the laboratory where it maybe handled without any further precautions.

The casts poured into these impressions shouldnot leave the laboratory. Care should taken indesigning special trays to avoid the necessity forchairside adjustment, but when this is necessary anyfragments trimmed from the denture base must fallinto the sack for contaminated waste. The workingimpressions are treated in exactly the same manneras the primary impressions.

Occlusion rims on acrylic bases and trial denturesare sterilized in the same manner as the impressions.Wax trimmed from the occlusion rims must bedisposed of as contaminated waste. Face-bow reg-istrations should not be made and shade and mouldguides should not be placed in the patient's mouth.

Remounting of the case on the articulator tocorrect errors of occlusion cannot be undertaken forthese patients. Any adjustments to the denturesmust be made in the protected surgery with frag-ments falling into the infected waste receiver. If it isnecessary to polish the denture after these adjust-ments the same sterilizing procedure will need to befollowed.

Overdentures

The retention of some roots of teeth in an otherwiseedentulous jaw in order to assist with the stability ofcomplete dentures is now a well recognized practice.These roots have a coronal portion which has beenreduced and shaped in such a way that a completedenture will cover them completely, and thisdenture is then called an overdenture. The functionof the retained and prepared roots is to providestability to the denture by assisting the ridge formto resist movement in the horizontal plane. It issometimes advocated that they should also be usedto assist retention by the addition to the root ofretaining attachments. This, however, adds consid-erably to the complexity and expense of the proce-dure.

Partial dentures or overdenturesWhen there are a few remaining natural teeth thedecision has to be made whether overdentures orpartial dentures are to be constructed. If there arevery few teeth, then the retention of a partialdenture is often difficult, particularly if these teethdo not have a good retentive form.

Of particular concern is the case where there aresix remaining lower anterior teeth occluding againsta complete upper denture. It is well known that thisis a hazardous situation.

The construction of a retentive and stable partiallower denture is difficult and the consequence of thedenture not being worn is destruction of the upperanterior ridge. The retention of the lower canineteeth with the extraction of the incisors and theprovision of an overdenture may be preferable tothe extraction of all the teeth.

One of the advantages of overdentures is that ifone of the roots should fail and have to be extracted,then of course the consequences are not severe. No

real reconstruction of the denture is needed, thehole in the undersurface merely having to be filledup. This is in contradistinction to partial denturesmade with a few remaining teeth, where the loss ofa tooth calls for a great deal of reconstruction of thedenture. It should be remembered here, too, thatwhere a soft-tissue-borne partial denture is madearound a few remaining teeth, there can be greatproblems with the opposing occlusion.1f this is acomplete denture very destructive effects are possi-ble. The provision of an overdenture allows for aneven and untraumatic occlusion to be provided.

IndicationsThere is no doubt that overdentures do have veryconsiderably improved stability compared withunsupported dentures. Because of this it might wellbe said that the indications for overdentures are'whenever possible'.

There are contraindications to the retention ofroots as overdenture abutments. There may be lackof room for the subsequent denture because of theheight of the bone around the roots, or theangulation of the teeth may be such that there arelabial or buccal undercuts which will prevent theproper insertion of the complete overdenture. If thedenture base is cut away a large part of theadvantage of the retention of the roots is lost.

The question arises as to the suitability of retainedroots to become overdenture abutments. Teethwhich have suffered some bone loss due to theperiodontal disease may still be suitable if at leasttwo thirds of the root is still properly supported inthe bone. It should be remembered that thereduction of the crown in overdenture root prepara-tion improves the crown root ratio and any leverageeffects on the root.

143

144 Overdentures

Overdentures are most usually used and probablymost frequently indicated in the lower jaw becauseof the lower resistance of this jaw to destabilizingforces with complete dentures. Overdentures aresometimes used in the upper jaw, but generallyspeaking it is unusual to find an upper jaw wherethere has been a great deal of resorption and stillsome suitable retained teeth.

Root preparationEndodontics: Generally speaking, it is necessary todevitalize the teeth before their preparation and thispresupposes that good endodontics can be carriedout. Unless this is the case, there is the prospect ofthe loss of the teeth due to apical infection orinflammation. To a certain extent this limits thechoice of abutment teeth to those in which success-ful endodontics can most satisfactorily be carriedout. In this sense canine teeth are ideal, having along root with a good crown/root ratio and acomparatively straight and simple canal form.Coronal form: Once the tooth has been root-filled,the crown can be reduced, and it is probably mostsatisfactory that this should be aimed at the produc-tion of a dome-shaped abutment sufficiently high toprovide good lateral resistance to movement but notso high as to cause complexity in the dentureconstruction by reduction of denture space.

It IS possible, of course, for the root preparationto be made flush with the gingiva and for the rootcanal to be prepared for the reception of a post andcoping made of gold (Figure 234). However, experi-ence over the years has shown that this is probablyunnecessary and if the tooth surface is prepared anda small amalgam placed in the coronal part of theroot canal then the prognosis is quite good (Figure235). It is often advantageous for the surface of theexposed dentine to be treated with fluoride paste.The patient must be instructed in the necessity forrigorous cleaning of the root surface and the internalsurface of the denture overlying it.

Attempts may be made to utilize teeth as overde-nture abutments by the preparation and reductionof the crown without devitalization of the tooth andwith the provision of a gold coping. However, thisprocedure leaves a very large abutment which caninterfere with the proper placement of the denture,or sometimes even protrude through the basematerial of the denture.

Denture retentionIn the matter of the retention of overdentures, it hasalready been stated that attachments might be used,but these are by no means necessary and, it mighteven be said, not even desirable, it being muchbetter to utilize the tooth roots to stabilize the

A

B

Figure 234 A Two overdenture abutments fitted with goldcopings.B Matching gold female components fitted inside thedenture.

denture and to gain retention by the proper exten-sion of the base and the development of a borderseal.

Denture supportThe support of overdentures is a matter of import-ance, because as can well be imagined, it would beundesirable if the denture loads fell wholly on thesurface of the overdenture and not on the mucosa.This could produce stresses in the denture andperhaps unwelcome loads on the root. It is thereforeprudent to ensure that when the overdenture isunder load that the pressures are equally disposedupon the mucosa and the root surface.

ConclusionOverdentures do not in any way reduce the need forgood denture bases, properly extended, with the

A

c

maximum support and retention. Overdenture tech-niques are not a substitute for good prosthetictechnique. Overdentures can be very beneficial andshould always be considered as an alternative

Overdentures 145

B

Figure 235 A The desirable form for overdentureabutments in dentine with copings. Shown here on amodel.B Similar preparations in the mouth. The ideal formcannot always be realized.C A cast showing the position of the abutments withrespect to the ridge.

treatment when the patient has lost a large numberof teeth and a decision has to be made whetherpartial dentures or complete dentures should beprovided.

Tissue conditioners

When a patient has worn an ill fitting denture forsome time the soft supporting tissues becomedeformed. They may also be swollen and inflamed.The denture will be loose and uncomfortable andthe patient may suffer pain during function.

Before new impressions are made it is importantthat the tissues recover their health and untraurna-tized form. Otherwise, the new dentures maypropagate the previous tissue conditions. This tissuerecovery is best achieved by leaving the dentures outand the patient should be so advised. However, thismay be very inconvenient and so materials havebeen devised which can be placed in the denturesand will, it is suggested, aid tissue recovery whilethey are being worn.

These materials are called 'tissue conditioners'.They provide a viscoelastic medium which flowsunder steady load but is highly elastic and resilientunder sudden loads. They consist of a powder whichis an acrylic polymer or co-polymer, e.g. poly (ethylmethacrylate) and a liquid which is a mixture of anester, e.g. butyl-phthalyl-butyl-glycolate, or di-n-butyl phthalate plus benzyl silicate together withethyl alcohol. The ester behaves like a plasticizerand the alcohol is a penetrant, which speeds up theprocess of forming a gel. The liquid contains nomethacrylate monomer, hence these materials donot cure in the conventional sense and there is norisk of residual monomer contaminating the oralmucosa. The plasticizer and alcohol are leached outby the oral fluids (generally within a week or two)and the conditioner hardens.

If the material is used in the presence of inflam-mation, it should be changed every 2-3 days, sincethe tissue changes shape as the inflammationresolves. If the material is used for a temporarylining, its life varies from 1 to 3 months and isdetermined by leaching of the alcohol, and to the

146

lesser extent of the ester, from the material, causinggradual hardening and dislocation. The greater lossat the surface tends to cause roughness; also the useof alkaline perborate denture cleansers is detrimen-tal. They should be cleaned with soap and water.

Wright (1984) found the clinical success rate of85% for the soft lining did not correlate with eitherthe appearance or condition of the material. Fre-quently the material had hardened in use but thepatient seemed unaware of it.

This brings into question the 'tissue conditioning'effect and raises the suggestion that their beneficialeffects are due to the provision of a better fittingdenture which no longer traumatizes the tissues.Indeed they are excellent temporary relining mate-rials and should be thought of and used as such.

They can be used to help a patient who is waitingfor new dentures to be made, post-surgically wherethere has been a change of ridge form, and in manyother applications. They are undoubtedly a mostvaluable addition to our armamentarium.

They should NOT be used as 'functional' impress-ion materials. They are most unsuitable for thispurpose. Because of their gel-like qualities theborder tissue displacement is usually incomplete andirregular and after they have been worn for a while,although they provide increased comfort, they willnot have the close adaptation required of animpression. A denture rebased on such a reline willbe poorly fitting from the start and is highly likelyto incorporate occlusal error.

ReferenceWright PS (1984) The success and failure of denture soft

lining materials in clinical use. J. Dent. 12: 319-327

Further Reading

This manual was designed to provide the studentwith a grounding of the principles to be appliedduring the clinical and laboratory stages of completedenture construction. To enable him to furtherenlarge his knowledge the following list of text-books and papers has been compiled.

General text-booksBasker R.M., Davenport J.e. and Tomlin H.R.

(1983) Prosthetic treatment of the endentulouspatient, London, MacMillan

Beresin V.E. and Schiesser F.J. (1978) The neutralzone in complete and partial dentures, 2nd Edn.St Louis, e.V. Mosby

Fish E.W. (1933) Principles of Full Denture Prosthe-tics, London, Staples

Hickey J.e. and Zarb G.A. (1980) Boucher'sProsthodontic treatment for edentulous patients,8th Edn. London, Mosby

Lee J.H. (1962) Dental Aesthetics, Chap. XXVII,Bristol, Wright

Morrow R.M. (1978) Handbook of ImmediateOverdentures, St Louis, e.V. Mosby

Sharry J.J. (1974) Complete Denture Prosthodon-tics, New York, McGraw-Hill

Watt D.M. and MacGregor A.R. (1976) Designingcomplete dentures, Philadelphia, W.B. Saunders

ImpressionsBohannan H.M. (1954) A critical analysis of the

mucostatic principle. J. Prosthet. Dent. 4(2),232-241

Buckley G.A. (1955) Diagnostic factors in thechoice of impression materials and methods. 1.Prosthet. Dent. 5(2), 149-161

Hardy I.R. and Kapur K.K. (1958) Posterior borderseal - its rationale and importance. J. Prosthet.Dent. 8(3), 386-397

Rodegerdts e.R. (1964) The relationship of press-ure spots in complete denture impressions withmucosal irritations. 1. Prosthet. Dent. 14, 1040-1049

Anatomy and base extension retentionBrill N., Tryde G., and Schubeler S. (1959) The role

of exteroceptors in denture retention. 1. Prosthet.Dent. 9(5), 761-768

Craig R.G., Berry G.C. and Peyton F.A. (1960)Physical factors related to denture retention. J.Prosthet. Dent. 10(3), 459-467

Lye T.L. (1975) The significance of the foveapalatini in complete denture prosthodontics. 1.Prosthet. Dent. 33, 504-510

Further reading 147

Preiskel H. W. (1968) The posterior extension ofcomplete lower dentures. J. Prosthet. Dent. 19,452-459

OverdenturesMiller P.A. (1958) Complete dentures supported by

natural teeth. J. Prosthet. Dent. 8(6), 924-928

Jaw relationshipsAtwood D.A. (1956) A cephalometric study of the

clinical rest position of the mandible. J. Prosthet.Dent. 6(4), 504-509

Atwood D.A. (1957) A cephalometric study ofclinical rest position of the mandible. Pt II. 1.Prosthet. Dent. 7(4),544-552

Bolender e.L. (1956) The significance of verticaldimension in prosthetic dentistry. J. Prosthet.Dent. 6(2), 177-182

Boos R.H. (1940) Intermaxillary relation estab-lished by biting power. J. Amer. Dent. Assoc. 27,1192

Boos R.H. (1956) Physiological denture technique.J. Prosthet. Dent. 6(6),726-740

Brill N. (1957) Reflexes, registrations and prosthetictherapy. J. Prosthet. Dent. 7(3), 341-360

Christiansen R.L. (1959) Rationale of the face-bowin maxillary cast mounting. J. Prosthet. Dent.9(3), 388-398

Cohen S. (1957) A cephalometric study of the restposition in edentulous persons: influence of varia-tion in head position. 1. Prosthet. Dent. 7(4),467-472

Coulouriotes A. (1955) Free-way space. J. Prosthet.Dent. 5(2), 194-]99

Hickey r.c., Williams B.H. and Woelfel J.B. (1961)Stability of mandibular rest position. J. Prosthet.Dent. 11(3), 566-572

Kapur K.K. and Yurkstas A.A. (]957) An evalua-tion of centric relation records obtained byvarious techniques. J. Prosthet. Dent. 7(6), 770-786

Nairn R.T. and Cutress T.W. (1967) Changes inmandibular position following removal of theremaining teeth and insertion of immediate com-plete dentures. British Dental Journal, 122, 303-306

Nairn R.T. (1974) Maxillomandibular relations andaspects of occlusion. 1. Prosthet. Dent. 31, 36]-368

Shanahan T.E.J. (]956) Physiologic vertical dimen-sion and centric relation. J. Prosthet. Dent. 6(6),74]-747

Shpuntoff H. and Shpuntoff W. (1956) A study ofphysiological rest position and centric position byelectromyograhy. J. Prosthetic. Dent. 6(5), 621-628

148 Further reading

Tallgren A. (1957) Changes in adult face height d~eto aging, wear, and loss of teeth and prosthetictreatment. Acta. Odont. Scand. 15 (Supp. 24), 1-122

Timmer (1969) A reproducible method for deter-mining the vertical dimension of occlusion. J.Prosthet. Dent. 22, 621-630

Walker R.C. (1962) A comparison of jaw relationrecording methods. 1. Prosthet. Dent. 12(4), 685-694

AppearanceFrush J.P and Fisher R.D. (1956) How dentogenic

restorations interpret the sex factor. J. Prosthet.Dent. 6(2),160-172

Frush J.P and Fisher R.d (1956) How dentogenicsinterprets the personality factor. J. Prosthet.Dent. 6(4),441-449

Frush J.P and Fisher R.D. )1957) The age factor indentogenics. J. Prosthet. Dent. 7(1), 5-13

Tooth selectionHeath M.R. (1970) A study of the morphology of

the denture space. Dent. Pract. Dent. Rec. 125,109

Neill D.J., Kydd W.L., Nairn R.I. and Wilson J.(1989) Functional loading of the dentition duringmastication. J. Prosthet. Dent. 62, 218-228

Sosin M.B. (1961) Re-evaluation of posterior toothform for complete dentures. J. Prosthet. Dent.11(1), 55-61

Watt D.M. (1978) Tooth positions on completedentures. J. Dent. 6, 147

Weinberg L.A. (1958) Tooth position in relation tothe denture base foundation. J. Prosthet. Dent.8(3), 398-405

Woelfel J.R., Hickey J.C. and Allisin M.L. (1962)Effect of posterior tooth form on jaw and denturemovement. 1. Prosthet. Dent. 12(5), 922-939

Woelfel J.B., Winter C.M. and Ishigari T. (1976)Five-year cephalometric study of mandibularridge resorption with different posterior occlusalforms. Pt I Denture construction and initialcomparison. J. Prosthet. Dent. 36, 602-623

Tissue damageLytle R.B. (1957) The management of abused oral

tissues in complete denture construction. J. Pros-thet. Dent. 7(1), 27-42

Lytle R.B. (1959) Complete denture constructionbased on a study of the deformation of theunderlying soft tissues. J. Prosthet. Dent. 9(4),539-558

Osseo-integrated implantsAdell R. et al. (1981) 15-year study of osseointe-

grated implants in the treatment of the edentulousjaw. Int. J. of Oral Surg. 10, 387-416

Branemark P.L. et al (1977) Osseointegratedimplants in the treatment of the edentulous jaw.Experience from a lO-year period. Scand. J. ofPlastic and Reconstructive Surg. 11 suppl. 16

Buser D.A. et al. (1988) The new concept of ITIhollow-cylinder and hollow-screw implants; Pt IIClinical aspects, indications and early clinicalresults. Int. J. of Oral and Maxillofacial Implants.3,173-181

Sutter F. & Schrorder A. (1988) The new conceptof ITThollow cylinder and hollow screw implants.Pt.I Engineering and design. Int. 1. of Oral andMaxillofacial Implants. 3, 161-172

Dental materialsWright P.S. (1984) The success and failure of

denture soft lining materials in clinical use. 1.Dent. 12, 319-327

DiagnosisBolender C.L., Swoope C.C & Smith D.E. (1969)

The Cornell Medical Index as a prognostic aid forcomplete denture patients. J. Prosthet. Dent. 22,20-29

Douglas W.H., Wilson H.J. and Bates J.F. (1965)Pressures involved in taking impressions. Dent.Practit. 15, 284

Faigenblum M.J. (1968) Retching, its causes andmanagement in prosthetic practice. British DentalJournal. 125, 485

Landa J.S. (1959) Trouble shooting in completedenture prosthesis. Pt I. Oral mucosa and borderextension. J. Prosthet. Dent. 9(6), 978-987

Landa J.S. (1960) Trouble shooting in completedenture prosthesis Pt II. Lesions of the oralmucosa and their correction. J. Prosthet. Dent.10(1), 42-46

Lawson W.A. (1978) Current concepts and practicein complete dentures. Impression: principles andpractice. J. Dent. 6, 43

Nairn R.I. and Brunello D.L. (1971) The relation-ship between denture complaints and levels ofneuroticism. Dent. Practit. 121, 156

Schole M.L. (1959) Management of the ageingpatient. J. Prosthet. Dent. 9(4), 578-583

Index

Acid cleansers, 105-106Acrylic resin

allergy to, 118baseplates, 43-48, 132, 133denture copies, 126-128dentures, 98-100resilient linings, 134teeth, 66trays, 23, 25

Adjustment of dentures, 111-112Agar duplicating gel, 126Alginate impression materials, 16

in denture copying, 128in primary impressions, 7, 16-18,

20-21Alkaline peroxide cleansers, 105-106Alveolar bone resorption, 119, 123,

132Alveolar ridge

'flabby ridge', 121and primary impressions, 18, 20and secondary impressions, 29, 30soreness over, 112, 118and tray construction, 24

Alveoloplasty, 141Alveolotomy, 139Arch

formdetermination of, 86-88disparity in, 120

width, measurement of, 8-9Articulator, Dentatus, 71, 81-82, 89,

91,96, 107

Base, denture, 6, 27checking of, 49-52, 54construction of, 43-48mounting of, 71replacement of, 123-125reprocessing of, 98-100

Bone resorption, 3, 80, 82, 87-88,104, 119

implants and, 137rebasing and, 123-125relief areas and, 132-133relining and, 123, 125

Border seal, 6, 27, 122surgery and, 140see a/so Post-dam

Boxing wax, 42Buccal fraena, 15,20,24, 140Buccal overjet, 79, 83, 86Buccal sulcus

and baseplate construction, 44and secondary impressions, 34-35and tray construction, 23, 24

Buccinator muscle, 29, 97

Callipers, 8-9Candidiasis, oral, 118, 122Canines

distance between, 66in lateral occlusion, 94setting of, 75, 86

Care of dentures, 104-106see a/so Cleaning

Castsinfection and, 142mounting, 47, 71from primary impressions, 22-23from secondary impressions, 42

Centric jaw relationship, 54, 59-62,73

checking of, 102-104errors in, 112, 117, 118, 123, 125

Centric occlusion, 53, 73, 79, 82, 83,91,100

adjustment of, 107, 110Check record, 102-104, 107, 111, 112

in rebasing, 124Classification of jaw relationships, 83

Cleaning of dentures, 104-106, 122,134, 137, 144, 146

Cleft palate, 119Close-fitting trays, 25Colour of teeth, 69, 82, 83, 142Communication with the patient, 119Complaints, patients', 5, 117-118Condyle(s), 54, 60, 62

track angles, 91Contouring, 97-98Copying dentures, 126-131Coronoid process, 38, 117, 139Cross-bite, 83-84Cuspal interdigitation, 53, 73, 91, 92

errors in, 112

Denture space impression technique,88

Diagnosis, 5,117-118Disclosing wax, IIIEndodontics, 144External oblique ridge, 15,24,28-29,

33

Facebow record, 54, 63-65, 81, 103,107, 112

in copying, 131infection and, 142in rebasing, 124

Fovae palatinae, 20, 24Fraena

high attachments, 122in primary impressions, 15,20surgery of, 140and tray construction, 24

Frankfort plane, 55'Freeway space', 53Fungal infection, 118, 122, 134

Genial tubercle, 140Gingival margins, 97-98

149

150 Index

Glenoid fossa(e), 54, 60Gothic arch tracing, 61-62Grinding, 107-110, 112

Hamular notch(es)in primary impressions, 9, 20in secondary impressions, 34, 39, 40and tray construction, 24

Hepatitis virus, 142Hinge axis, 63Human Immunodeficiency Virus

(HIV),142Hydrocal, 22-23, 42, 44, 70, 99Hydrocolloids, irreversible see

Alginate impression materialsHypochlorite cleansers, 105-106, 122

TIl-fitting dentures see Instability;Looseness

Implants, 136-137Impression(s)

in copying, 129cross infection during, 142of denture space, 88displacement of tissues during, 6,

23, 28-30, 39with 'flabby ridge', 121instruments for, 7, 27materials for, 6, 7, 11-12, 27, 32,

37-38mucocompressive, 132mucostatic, 132primary, 6, 7-21in rebasing, 123-124for resilient linings, 135secondary, 6, 27-41, 132

Incisive papilla, 47, 73-74relief of, 133

Incisorsin lateral occlusion, 94in protrusion, 91-92, 93, 108setting of, 74-75, 86

Inflammation, 112,122,137,144,146Instability

forces of, 117implants and, 136-137overdentures and, 143-145rebasing and, 123surgery and, 140-141see also Looseness

Intrinsic muscle, 34Investment, 44, 99

Jaw relationships, 52-53, 73, 83errors in, 118, 120record of, 53-65

checking of, 80, 81-82, 83, 102-104

copying and, 129see also individual relationships

'Knife-edged ridge', 140

Labial frenum, 15,20,24, 140

Labial sulcusand baseplate construction, 44and primary impressions, 16, 18,20and secondary impressions, 34, 38and tray construction, 23

'Lateral excursions', 73Lateral occlusion, 91, 94-95, 96

adjustment of, 109, 110Lingual frenum, 15, 140Lingual sulcus

and baseplate construction, 44and primary impressions, 15and secondary impressions, 33, 34and tray construction, 24-25

Lip support, 54-55, 73, 83, 84-85Looseness of dentures, 117

tissue trauma from,S, 34, 53, 111-112,146

see also InstabilityLower jaw

baseplate for, 44correction of, 51, 52

bone resorption at, 80, 82, 87-88looseness of dentures for, 117measurement of, 9overdentures for, 144primary impressions of, 8, 9,10-11,

12-18casts from, 22, 23trays from, 24-25

secondary impressions of, 27, 28-34

casts from, 42setting of teeth for, 75, 79, 80, 83-

86, 87-88Low-fusing compound

and base extension, 52and post-dam, 49in primary impressions, 16, 21in secondary impressions, 31, 34,

35,40

Mandible see Lower jawMasseter muscle, 29-30, 33Maxilla see Upper jawMeasurement see RecordingMental nerve, 119, 132-133, 134Mentalis tubercle, 140Mounting casts, 47, 71Muscles, oral

restriction of, 6, 27, 52, 80, 111see also individual muscles

Muscular dystrophies, 122Mylohyoid muscle

and primary impressions, 15, 16,17,18

and secondary impressions, 30, 33,34

and tray construction, 24-25Mylohyoid ridge, 119, 140

Neutral zone, 80, 83, 86Nose width, intercanine distance and,

66

Occlusal balance, 73, 91-96Occlusal vertical dimension, 53, 73,

93, 110errors in, 112, 118rebasing and, 124, 125record of, 58-59

checking of, 81-82copying and, 129, 131

relining and, 123, 125surgery and, 141

Occlusion, lateral, 91,92-94,95-96adjustment of, 109, 110

Occlusion, protrusive, 91, 92-94, 95-96

adjustment of, 108, 110Occlusion rims, 47-48

infection and, 142measurements using, 53-65mounting of, 71

Overbite, 92-93, 94Overdentures, 143-145Overextended base, correction of,

50-51,126Overjet, 79, 83, 86

Pain see SorenessPalate

abnormalities of, 119-120displaceability of, 41, 111in primary impressions, 20relief of, 132, 133in secondary impressions, 38, 39and tray construction, 24

Palatine nerve, 133Parkinson's disease, 122Partial dentures, 143Paste, impression, 25, 32, 39-40, 129,

132Personality of the patient, 119Plaque, 104-106, 134Plaster of Paris

casts, 22, 47impressions, 25, 37-38investment, 44, 99

Porcelain teeth, 66Position of patient (and operator)

for impression-taking, 7-8, 28for jaw measurements, 53, 55-56

Post-dam, 40-41, 42-43, 49-50, 70-71

Post-mylohyoid fossa, 15,25,30,31,34

Pre-contact centric relationshiprecord, 131

Premature balancing contacts, 95-96Premaxillary bone resorption, 133Pressure relief cream, 111-112, 133Prognathism, 120Prognosis,S, 119-122Protrusive occlusion, 91, 92-94, 95-

96adjustment of, 108, 110

Protrusive record, 62-63, 80-81, 89Psychotropic drugs, 122

Rebasing dentures, 123-125Recording

of arch width, 8-9of jaw relationships, 53-65see also Check record; Facebow

recordRelief areas, 132-133Relining dentures, 123, 125Resilient linings, 133, 134-135Rest vertical dimension, 53, 55-57,

124Retention, 6, 27,117

of base, 49-52, 54of completed dentures, 102lack of see Instabilityof overdentures, 144surgery and, 139-140

Retromolar pad(s)and occlusion rim, 47and primary impressions, 9, 15and secondary impressions, 28, 33and tray construction, 24, 25

Retromylohyoid fossa, 15,25,30,31,34

Root preparation: for overdentures,144

Seating see Position of patientSeparating media, 44, 46Shade see Colour of teethShape of teeth, 66, 69, 82, 142Siloxane gel

for denture space impressions, 88for resilient linings, 134

Skin grafts, 141Sodium alginate separating medium,

44,46Soreness, 6,117-118

rebasing and, 123relief and, 132-133resilient linings and, 134see also under Tissue(s)

Spaced trays, 25Speech, 86, 88, 98, 117Sterilization of dentures, 122Stippling, 98Stomatitis, denture-related, 5, 122Sublingual fold and papillae, 30-31,

34Sulcus

and baseplate construction, 44and primary impressions, 7, 15, 16,

18,20and secondary impressions, 33, 34-

35, 38, 40and tray construction, 23-25

Surgery, preprosthetic, 139-141Swelling, 112, 146

Tartar, 104-106Teeth

colour of, 69, 82, 83, 142porcelain, 66selection of, 65-69, 71, 73setting of, 73-79, 80

checking of, 82-86copying and, 131errors of, 117

Temporalis muscle, 29-30, 33Temporomandibular joint, 54Tin-foil

and relief, 132, 133as separating medium, 44, 46

Tissue(s), oraldisplacement of, 40-41

excessive, ill-fitting dentures and,5,34,53,111-112,146

impression-taking and, 6, 23, 28-30,39

post-dam and, 40-41,42-43,49infection of, 104irritation of, tray exposure and, 34relief over, 132-133variation in, 121-122

Index 151

Tissue conditioners, 5, 88, 146Tissue reflection points, 23-25Tongue, 80, 83, 84, 86, 97, 98, 117

in secondary impression-taking,30-31,33,34

Torus palatinus, 119-120Trays, special

checking of, 28-30, 34-35construction of, 23-25infection and, 142

Trial dentures, 80-90Tuberosity sulcus, 20, 24, 35, 38, 40

Ulceration, 111, 117Undercuts, surgical removal of, 139-

140Underextended base, correction of,

51-52, 126Upper jaw

baseplate for, 44bone resorption at, 80, 87-88looseness of dentures for, 117measurement of, 9overdentures for, 144primary impressions of, 8, 9,10,11,

18-21trays from, 24, 25

secondary impressions of, 27, 28,34-41

setting of teeth for, 73-75, 80, 83,86,87,88

Vibrating line, 24, 34, 40location of, 40-41

Viral infection, 142

Willis gauge, 56-57, 66

Zinc-oxide-Eugenol impressionpaste, 25, 32, 39-40, 129, 132


Complete Denture Prosthetics

Documents

external oblique

external oblique

occlusal vertical

gothic arch

british dental

rest vertical

full denture

mr john lee