Mouth Prep Rpd (Vikas)

7/27/2019 Mouth Prep Rpd (Vikas)

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DR VIKAS AGGARWAL


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INTRODUCTION

Fundamental to success of removable partial denture

Contributes to DeVans philosophy

"Mouth preparation" is a term intended to cover alltypes of changes effected in the teeth, foundationridges or oral structures which may be deemed

necessary to accomplish a better partial dentureresult. (Applegate 3rd ed)


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Classified as 1) pre prosthetic mouth preparation involves removal of

any hindrances to prosthetic treatment

2) prosthetic mouth preparation that involves mouthpreparation done to facilitate prosthetic treatment.

Pre prosthetic mouthpreparation1. Surgical preparation2. Conditioning of abused and

irritated tissues3. Periodontal preparation4. Treatment of muscular

symptoms5. Correction of occlusal plane6. Conservative/endodontic

preparation7. Correction of malalignment

Prosthetic mouth preparation1. Developing guiding planes2. Changing height of contour3. Modifying retentive undercut.4. Rest seat preparation


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Emergency procedure :

Relief of pain or infection :

As early in the treatment process as possible all teeththat are causing pain or discomfort because ofcaries ordefective restorations should be treated to eliminate the

possibility of an acute episode of pain occurring duringthe treatment procedure.

Asymptomatic teeth with advance carious lesion,

periodontal abscesses and other inflammatoryresponses should be treated in the same way.


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ORAL SURGICAL PREPARATION

Should be completed as early as possible.

Longer the interval between surgery & impressionprocedure, more complete the healing & more stable thedenture bearing area


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Extractions

Planned extractions should occurearly in the treatment but notbefore completion of a careful

and thorough evaluation of each

remaining tooth in the dentalarch.

Each tooth must be evaluated

concerning its strategicimportance and its potential

contribution to the success of theremovable partial denture.


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Residual roots should be

removed adjacent to

abutment teeth may

contribute to the progressionof periodontal pockets and

compromise the results from

subsequent periodontal

therapy.

Care of buccal and lingual

cortical plate should be taken

while extraction


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Impacted teeth

All impacted teeth

including those inedentulous areas andthose adjacent toabutment teeth, should be

considered for removal.

Asymptomatic impactedteeth in the elderly that are

covered with bone, withno evidence of apathological condition,should be left to preservethe arch morphology.


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Malposed teeth

The loss of individual teeth orgroups of teeth may lead toextrusion, drifting orcombinations of malpositioning

of the remaining teeth. In most instances the alveolar

bone supporting extruded teethwill be carried occlusally as theteeth continue to erupt.

In such situations individualtooth or groups of teeth and theirsupporting alveolar bone can besurgically repositioned iforthodontic treatment is not

possible


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Cysts and odontogenic tumors

Panoramic roentgenograms of the jaws arerecommended to survey for unsuspected pathologicalconditions.

When suspicious area appear an a survey film, aperiapical roentgenogram should be taken to confirm ordeny the presence of a lesion.

Diagnosis should be confirmed through appropriate

consultation and if necessary perform a biopsyof thearea.


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Exostosis and tori

The presence of abnormal bonyenlargements should not beallowed to compromise thedesign of the partial denture

The mucosa covering these

enlargements is thin and friable.Partial denture components inproximity to this type of tissuecan cause irritation and chroniculceration

Also, exostoses approximatinggingival margins maycomplicatethe maintenance of periodontalhealth and lead to the eventualloss of strategic abutment teeth


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Hyperplastic tissue

All these forms of excess tissue

should be removed to provide afirm base for the denture. Thisremoval will produce a morestable denture.

can be removed with any

preferred combination such asscalpel, curette, electrosurgery, orby laser

All such excised tissues should besent to oral pathologist for

microscopic study Fibrous tuberosities Soft flabby ridges Folds of redundant tissue in the vestibule

or floor of the mouth Palatal papillomatosis.


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Muscle attachments and frena

As a result of the loss of bone height,

muscle attachments may come near theresidual ridge crest.

The mylohyoid, buccinator, mentalis,and genioglossus muscles are thosemost likely to introduce problems ofthis nature.

mentalis and genioglossus musclesoccasionally produce bonyprotuberances at their attachments,which may also interfere withremovable partial denture design.

Repositioning of these supra-placedmuscles by ridge extension is necessaryin such condition to enhance comfortand function


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Bony spines and knife edge ridges

Sharp bony spicules should beremoved and knife-edge ridgesrounded to facilitate easydesigning of the partial

dentures. These procedures should be

carried out with minimal boneloss.


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POLYPS, PAPILLOMAS AND TRAUMATIC HEMANGIOMAS

All abnormal soft tissue lesions should be excised and

submitted for pathological examination New or additional stimulation to the area introduced by the

prosthesis may produce discomfort or even malignant changesin the tumor.

HYPERKERATOSIS, ERYTHROPLASIA AND ULCERATION

All abnormal, white, red or ulcerative lesions should beinvestigated regardless of their relationship to the proposed

denture base. A biopsy of areas larger than 5 mm should be completed, and if

the lesions are large (more than 2 cm in diameter), multiplebiopsies should be taken


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DENTOFACIAL DEFORMITY

Surgical correction of a jaw deformity can be made inhorizontal, sagittal or frontal planes.

Mandible and maxilla may be positioned anteriorly orposterior and their relationship to the facial planes may besurgically altered to achieve improved appearance.

Ridge Augmentation

Ridge augmentation can be carried out with either alloplasticmaterials like hydroxyapatite or with autogenous bone graftmaterials for proper bone support to the partial dentures


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OSSEOINTEGRATED DEVICES :

These devices offer a significant stabilizing effect ondental prosthesis through a rigid connection to living

bone. Inclusion of strategically placed implants can

significantly control prosthesis movement.


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TREATMENT OF ABUSED AND IRRITATED SOFT TISSUES

Many removable partial denturepatients will require someconditioning of supporting tissuesin edentulous areas before the

final impression phase of thetreatment.


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Symptoms:

Inflammation and irritation of the mucosa coveringthe denture bearing areas

Distortionof normal anatomic structures such as

incisive papillae, the rugae, the retromolar pads

Burningsensation in residual ridge areas

These conditions are usually associated with ill-fittingor poorly occluding RPD.


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A good HOME CARE PROGRAM.

Rinsing the mouth with a prescribed salinesolution

Massagingthe residual ridge areas, palatal rugae

and tongue with a soft tooth brush.

Removing the prosthesis at night and using aprescribed therapeutic multiple vitamin along withhigh protein, low carbohydrate diet.

Some inflammatory, oral conditions caused by illfitting dentures can be resolved by removing thedentures for an extended periods of time


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Use of tissue conditioning materials

The tissue conditioningmaterials are elastopolymersthat have massaging effect onirritated mucosa, and because

they are soft, occlusal forcesare probably more evenlydistributed.


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Maximum benefit from using tissue conditioning materialsmay be obtained by

Eliminating defective or interfering occlusal contacts of olddentures

Extending denture bases to proper form to enhance proper support,

retention and stability.

Relieving the tissue side of the dentures bases sufficiently (2 mm)to provide space for even thickness and distribution of conditioningmaterials.

Applying the material in amounts sufficient to providesupport and a cushioning effect

Following the manufacturer's directions


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The conditioning procedure should be repeated until the

supporting tissues display an undistorted and healthyappearance.

An improvement in irritated and distorted tissues is usually

noted within 3 or 4 changes of the conditioning material, but insome cases more changes are required.

The final impression procedure should be delayed until themucosa appears completely healthy.


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3) Periodontal preparation

The periodontal preparation ofthe mouth usually follows anyoral surgical procedure and is

performed simultaneously withtissue conditioning procedures.

The periodontal procedures arenecessary to restore the mouth

to the state of health requiredfor definite treatment.


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OBJECTIVES OF PERIODONTAL THERAPY

Removal and control of all etiological factorscontributing to periodontal disease, along with a

reduction ofBLEEDING ON PROBING

. Elimination of or reduction in, pocket depths of all

periodontal pockets, with the establishment of healthygingival sulci.

Establishment of functional atraumatic occlusalrelationships and tooth stability

Development of a personal plaque control program anddefinitive maintenance schedule.


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Periodontal diagnosis and treatment planning

Diagnosis :

The diagnosis of periodontaldiseases is based on a systematicand carefully accomplishedexamination of the periodontium.

It is performed using direct vision,palpation, periodontal probe,mouth mirror, and other auxiliary

aids such as curved explorers,furcations probes, diagnostic castsand roentgenograms.


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Most important is careful exploration of the gingivalsulcus and recording the probing pocket depth.

The probe is inserted gently but firmly between thegingival margin and the tooth surface, and the depth ofgingival sulcus is determined circumferentially around

each tooth.

Acritical assessment of the sulcular health can be done byjudging the amount of bleeding on probing. This alongwith the pocket depth is an excellent indicator of healthand disease.


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Dental radiographs canbe used to supplement theclinical examination butshould not be used as asubstitute for it.

1. Type location and severity ofbone loss

2. Location, severity and distribution offurcation involvement.3. Alteration ofperiodontal ligament space.4. Alterations of the lamina dura5. Calcified deposits6. Location and conformity ofrestoration margins

7. Evaluation ofcrown and root morphologies.8. Root proximity9. Caries10. Evaluation of other associated anatomic structures, such as

mandibular canal or sinus proximity.


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Each tooth should be evaluated carefully for

mobility Normal mobility is in order of 0.05 to 0.10 mm.

Grade I mobility slightly more than normal.

Grade II moderately more than normal.

Grade III severe mobility with vertical

displacement.

Mobility is assessed with ends of two instruments.If fingers are used the movement of soft tissuemay mask accurate determination of mobility

Tooth mobility is usually caused by Inflammatory changes in the periodontal ligament Traumatic occlusion Loss of attachment Combination.

MOBILITY


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Treatment planning

Depending on the extent and severity of the periodontalchanges present, a variety of therapeutic procedures,ranging from simple to relatively complex, may beindicated.

Periodontal treatment planning can usually be divided intothree phases.

Disease control therapy phase-phase 1 Definitive periodontal surgery phase-phase 2

Maintenance phase- phase 3


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Initial disease control therapy (phase 1) :

a) Oral Hygiene Instruction : The most effective motivation techniques require a

good understanding by the patient of his/herperiodontal condition.

The patient should be instructed in the use ofdisclosing wafers, soft nylon toothbrush, andunwaxed dental floss

Without good oral hygiene ,any dental procedure,regardless of how well it is performed, is ultimatelydoomed to failure


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b) Scaling and root planning :

Without meticulous removal of calculus, plaque,and

toxic material in the cementum, other forms of

periodontal therapycannot be successful.

c) Elimination of local irritating factor otherthan calculus

Overhanging margins of amalgam & inlayrestoration.

Overhanging crown margins. Open contacts leading to food impactions.

Deep carious lesions should be eliminated beforethe start of definitive prosthetic treatment.


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d) ELIMINATION OF OCCLUSAL INTERFERENCES

Poor occlusal relationship may act as a factor thatcontributes to more rapid loss of periodontalattachment.

Selective grinding procedure is generally applied at

this stage. Occlusion on natural teeth needs to be perfected only

to a point at which cuspal interference within thepatients functional range of contact is eliminated and

normal physiologic function can occur


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Guide to Occlusal Adjustment (Schuyler1935)

Accurately mounted diagnostic casts are extremely

helpful in determining static cusp to fossa contacts ofopposing teeth and as guide in the correction ofocclusion anomalies

1) A static coordinated occlusal contact of themaximum number of teeth when the mandible is incentric relation to the maxillae should be the firstobjective. The procedure is as follows:-

a) A prematurely contacting cusp should be reduced the cusp point is in premature contact in both centric

and eccentric relations.

If a cusp point is in premature contact in centric relation

only, the opposing sulcus should be deepened


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b) When anterior teeth are in premature contact incentric relations, or in both centric and eccentricrelations, corrections should be made by grinding theincisal edge of the lower teeth.

If only in eccentric relation grind lingual inclines ofmaxillary teeth


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2)evaluate opposing tooth contact or lack ofcontact in eccentric functional relations

First balancing side contacts are seen. Subluxation, pain, lack of normal functional movement of the joint, or

loss of alveolar support of the teeth involved may be evidence of excessivebalancing contacts.

care must be exercised to avoid the loss of a static supporting contact in

centric relation This static support in centric relation may exist between the lower buccal

cusp fitting into the central fossae of the upper tooth or between theupper lingual cusp fitting into the central fossae of the lower tooth ormay exist in both cases. Often only one of these cusps has this static

contact So contacting cusp must be left untouched to maintain this essential

support in the planned intercuspal position, and all corrective grindingto relieve premature contacts in eccentric positionswould be done on theopposing tooth inclines.


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3) To obtain maximum function and thedistribution of functional stress in eccentricpositions on the working side, necessary grindingmust be done on the lingual surfaces of the upperanterior teeth

Corrective grinding on the posterior teeth at this

time should always be done on the buccal cusp ofthe upper premolars and molars and on the lingualcusp of the lower premolars and molars


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4)Corrective grinding to relieve premature protrusivecontacts of one or more anterior teeth should beaccomplished by grinding the lingual surface of the

upper anterior teeth. elimination of premature protrusive contacts of

posterior teeth done on their non functional cusp

5) Any sharp edges left by grinding should be roundedoff


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SPLINTING

Some teeth loose their periodontal support rendering them

mobile To use these teeth as abutment additional support is

required

First the cause of mobility is to be eliminated

Teeth may be immobilized during periodontal treatment byAcid etching the teeth with composite resin,

Fiber reinforced resins

Cast removable splints

Intracoronal attachments


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Splinting can be achieved by a removable restorationor by fixed restoration which becomes a permanentsplint.

Splinting of weakened teeth in partially edentulousarch located in a position where the partial denturewill not require an unusual amount of support, isachieved by using fixed splinting,

this maintains the continuity of the arch, avoidsadditional modification spaces,

thus simplifying the construction and fitting of partialdentures and improving prognosis.

Fixed splinting must be accomplished with full orpartial coverage crowns soldered together; this givesadditional resistance to antero-posterior stresses.


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Definitive periodontal surgery

(phase 2)

Periodontal surgery

After initial therapy is completed, the patient isreevaluated for the surgical phase.

If oral hygiene is at an optimum level, yet pocketswith inflammation and osseous defects are still present,a variety of periodontal surgical techniques should beconsidered to improve periodontal health.


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Periodontal flaps :Periodontal f lap surgery

involves the elevation of eithermucosa alone or both the

mucosa and the periosteum.

Gingivectomysupra bony pockets of fibrotic tissue,

absence of deformities in theunderlying bony tissue & pocketdepth confined to attached gingiva


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Guided tissue regeneration :

Guided tissue regeneration(GTR) has been defined asthose procedures thatattempt regeneration of lostperiodontal structuresthrough differing tissueresponses..


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Periodontal plastic surgery :

Elimination of pockets that traverse the mucogingivaljunction.

Creation of an adequate zone of attached gingiva.

Correction of gingival recession by root coverage

techniques.


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Recall maintenance (phase 3)

This includes not onlyreinforcement of plaquecontrol measures but also

thorough debridement ofsupragingival andsubgingival calculus andplaque on all root surfaces


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4) TREATMENT OF MUSCULAR SYMPTOMS

Prior to adjustment of the occlusion of the teeth themuscular symptoms should be analyzed.

Therefore the first objective of the operator is to eliminatethis muscle spasm.

acrylic overlay splint with a flat occlusal surface which willeliminate premature tooth contacts causing deviation of themandible leading to spasm.

Adjunct therapies like short-wave therapy, infra-redradiation, and light massage are designed to increase the

volume of the blood flowing through the muscles andthereby removing the offending metabolites.

The use of muscle relaxant drugs like Diazepam 5-10 mgB.D is effective in relaxing the symptoms


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5) CORRECTION OF OCCLUSAL PLANE

The average plane established bythe incisal and occlusal surfaces ofthe teethit is not a plane, butrepresents the planar mean of the

curvature of these surfaces (gpt8th )

The occlusal plane in most partiallyedentulous mouths will be uneven


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Teeth that have been unopposed for a long time tend toovererupt, e.g. the maxillary molars if unopposed willmigrate downwards carrying the maxillary tuberosity withthem creating a problem to reestablish the occlusal plane


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The occlusal plane can be corrected by

Reducing the height of overerupted teeth.

The clinical crown lengthening to restorethe correct occlusal plane, such as whenteeth fail to erupt fully because ofinterferences from other teeth or lack ofstimulation.

TREATMENT:

Orthodontic treatment

Enameloplasty

The placement of cast onlays or crowns.

Extraction

surgery


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Orthodontic treatment


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Enameloplasty:

Enameloplasty is used to describe the removal of a portion of

the enamel surface of a tooth to accomplish specific purposes.

For the correction of the occlusal plane, the enameloplastyconsists ofreducing cusp height in order to level or harmonizethe curve of the occlusal plane .

Reduction is done with tapered diamond cylinder or stones inhigh speed hand piece. The cut enamel surface is smoothened

with carborundum containing rubber wheels and fluoride gels.


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Onlay

Conservative method

The occlusal surface of a tooth to be covered by an onlayrest should be free of pits and fissures or should be made soby eliminating the defects with small burs or stones.

The use of chrome- cobalt can cause extreme wear ofnatural teeth. Tooth colored resin may be processed overthe metal, however this will wear rapidly.

One of the simplest methods -the use of cast gold onlays,which an either lengthen or shorten the crown height of atooth.


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Crowns:

When the crown height of the tooth must be changed toharmonize the occlusal plane.

the facial, lingual, or proximal surfaces must be alteredto produce a more desirable height of contour, a guidingplane, or a retentive undercut.

Before the tooth is prepared to receive the crown,

mounted diagnostic casts should be measured to ascertainhow much crown reduction is necessary to correct theocclusal plane.


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Endodontics with Crown or Coping


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Endodontics with Crown or Coping

If strategically positioned teeth in the dental arch are

retained, the prognosis of the partial denture is improvedmarkedly.

These teeth include mandibular second or third molars thatmay be used to serve as posterior abutment so as the prosthesis

may be all tooth supported.Other are those in the center of a long anterior edentulousspan either mandibular or maxillary.


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If the overeruption has been so gross as to obliterate theremaining interarch space, the crown of the tooth canbe removed at the gingival crest and a copingconstructed.

The tooth will serve as a vertical stop, preventingexcessive vertical or horizontal movement of theprosthesis.


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Extraction

Eg. If orthodontic treatment cannot beaccomplished to realign severely malposedmolars or premolars, extraction must beconsidered.

When teeth interfere with theplacement of the major connector and noother solution (such as crowning thetooth) feasible, extraction must be

planned.


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Surgery

Maxillary segmental osteotomy is done to superiorlyrepositioning posterior segments of maxilla. This is one of themost effective methods of regaining interarch space lost dueto downward migration of the teeth and tuberosity


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6) CONSERVATIVE/ENDODONTIC PREPARATION

Fillings:When fillings are required in abutment or otherteeth, only gold or amalgam are suitable materials tocome into contact with partial dentures as thesematerials have the necessary strengths to form a

foundation for occlusal rests Onlays: The occlusal surfaces of worn teeth can be

restored by onlays.

Endodontic with crown/coping:a grossly carious

tooth which can serve as strategic abutment tooth mustbe restored with endodontic therapy followed bycementation crown which will allow such tooth/teeth toserve as normal abutments.


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7) CORRECTION OF MALALIGNMENT

Teeth that are malposed, facially or lingually are moredifficult to correct There are definite, limitation to therepositioning of these malposed teeth.

Orthodontic correction of these malposed teeth is thefirst line of treatment. Enameloplasty and crowns arealso treatment choices. Surgical intervention isplanned only if all other measures fail to repositionthese malposed teeth


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II) Prosthetic Mouth Preparation

It is done to modify the existing structures to furtherenhance the placement of prosthesis.

It mainly involves reshaping of teeth

The steps involved are:

1. Developing guiding planes

2. Changing height of contour

3. Modifying retentive undercut4. Abutment preparation using cast crowns

5. Rest seat preparation


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Guiding Planes

Guiding planes are those surfaces on the teeth,parallel relationship to each other, so that they may serve todetermine positively the direction of appliance movement

(Applegate 1954)

GPT-8 defines them as two or more vertically parallelsurfaces of abutment teeth, so orientated as to direct the

path of placement of removable partial dentures.

Functions of guiding planes


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Functions of guiding planes

1. To provide single path of placement andremoval

2. To ensure planned and intended action of

the retentive and bracing components ofthe partial denture

3. To eliminate detrimental strain to theabutment teeth while placing andremoving the prosthesis

4. To eliminate gross food traps between theabutment teeth and the denture base


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Guiding planes on abutment teeth

adjacent to tooth supported segments:

A cylindrical diamond point isgenerally the instrument to make the

preparation. A gentle, light sweepingstroke from the buccal line angle tothe lingual line angle should be used


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The flat surface created shouldideally be 2 to 4mm in occluso-gingival height

The reduction must not be a

straight slice across the toothsurface; rather it should followthe curvature of the surface sothat nearly uniform amounts of

enamel are removed


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Guiding planes on abutment teeth adjacent todistal extension edentulous spaces

The tooth preparation on the proximal surface of abutmentteeth adjacent to distal extension edentulous spaces isaccomplished in the same manner with a cylindricaldiamond stone held parallel to the path of insertion.

The principal difference between this guiding plane and theplanes on teeth bordering a tooth-supported segment is thatthe occlusogingival height of the plane is reduced to 1.5 to2mm.

Thus provides graterfreedom to movementhence less torqueingforces


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Guiding planes on lingual surfaces of abutment

teeth

Mandibular posterior teeth are usually inclined lingually with aresultant high lingual survey line. Minor recontouring can frequentlyimprove the position of the survey line to allow placement of thereciprocal clasp arm in its proper position

To provide maximum resistance to lateral stresses.

The occlusogingival height of the preparation is 2 to 4 mm. Theplane ideally should be located in the middle third of the clinicalcrown of the tooth.

Guiding planes on anterior abutment


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Guiding planes on anterior abutmentteeth :

Guiding planes on anterior teeth adjacent to edentulousspaces provide

the parallelism needed to ensure stabilization,

minimize wedging action between the teeth,

decrease undesirable space between the denture and theabutment tooth,

increase retention through frictional resistance.


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When prepare parallel guiding surfaceson anterior abutment

Stay on the lingual half to optimize esthetics

Enameloplasty to modify retentive undercuts


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Enameloplasty to modify retentive undercuts

If abutment tooth has lessthan a sufficient retentiveundercut.

For the procedure to besuccessful, the buccal andlingual surfaces should benearly vertical.

If surface to receive undercutis sloped, indentation has tobe excessively deep.

If opposing surface is sloped,the reciprocal clasp arm

cannot prevent retentive clasptip from dislodging. A round end tapered diamond

held parallel to gingivalmargin is used to create agentle depression


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The retentive undercut must be createdin the form of a gentle depression, not apit or hole

Retentive undercut should be in theform of a gentle depression. Createslight concavity (0.010 inch deep, 4mmMD, 2mm OG), parallel to gingivalmargin


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Enameloplasty to change height of


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p y g g

contour

height of contour -a line encircling a

tooth and designating its greatestcircumference at a selected axialposition determined by a dentalsurveyor gpt 8th

The height of contour is changedmost frequently to provide better

positions for clasp arms Ideally the retentive clasp arm should

be located no higher than the junctionof the gingival and the middle thirds.

This position not only enhances the

esthetic quality of the clasp, but alsoplaces clasp nearer the tooths centreof rotation

The height of contour is best loweredby using tapered diamond stones.

.


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Abutment preparation using Inlays Onlays and Crowns

If the remaining teeth do not possess usable naturalcontours and enamel surfaces cannot be corrected toproduce them, cast restorations must be planned.

Guiding planes, height of contour and retentive undercuts

can be placed in the wax patterns for the cast restorations. Also many abutment teeth will require restorations for

more routine reasons such as caries, endodontic therapyetc.

Sh i th W P tt


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Shaping the Wax Pattern

The die of the tooth preparation in the cast of theremainder arch is analyzed on the surveyor.

Once correct tilt is established substitute analyzingrod with wax knife and carve guiding plane by

shaving the wax. Pattern must be carved to place height of contour

at the junction of gingival and middle third for

retentive clasp. Refining can be done in cast restoration.


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Occlusal rest seat preparation


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Rest -rigid extension of a partial removable dentalprosthesis that contacts the occlusal surface of a tooth orrestoration, the occlusal surface of which may have beenprepared to receive it

Rest seat-the prepared recess in a tooth or restorationcreated to receive the occlusal, incisal, cingulum, orlingual rest


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Transmit the forces apically Act as a vertical stop

Maintain the retentive clasp inits proper position


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Function as an indirect retainer in a distal extensionpartial denture.

Designed between spaced teeth to reestablish

continuity of arch and prevent further drifting ortipping of tooth

It is used as onlay on abutment tooth to establish amore acceptable occlusal plane and to prevent

extrusion of tooth

Conventional rest preparations in posterior


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teeth

Form

Triangular in outlinewith base at marginal ridge and apexpointing towards the centre of the tooth.

Apex of the triangle should be rounded as should allexternal margins of preparation

Should follow outline of mesial or distal fossa.


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Extension

1/3rd to 1/2 of mesiodistaldiameter.

1/2 of the distance

between buccal andlingual cusp tips.


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Floor

Inclined towards the center.

Spoon shaped.

Enclosed angle with the proximalsurface less than 90


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An occlusal rest must be at least 1 mm thick at its thinnestpoint ifchrome alloyis used for the framework or 1.5 mm ifgold is to be used


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Preparation


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Preparation

Create an outline using small diamond bur

The island of enamel within the outline can then beremoved with the same bur.

Deepest portion of the rest seat is towards the center ofthe tooth.

Verify preparation by red beading wax.

Polishing of preparation is done using carborundum

impregnated rubber point in low speed hand piece


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Occlusal rest seat preparations in new castrestorations :

Occlusal rest seats in cast restorations should always be

placed in thewax patterns. The preparation for the rest seat must be carved in the wax

after the establishment of guiding planes.

O l l t t ti i i ti t


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Occlusal rest seat preparation in existing castrestorations

If the existing restorations display marginal integrity andocclusal harmony, an attempt should be made to contourthem to satisfy the requirements of the proposedprosthesis.

It is usually not too difficult to prepare acceptable guidingplanes in existing restorations.

Patients must be always be thoroughly informed of thepossibility of need to replace existing restorations before

mouth preparation.

If an existing crown, onlay, or inlay is penetratedduring the rest seat preparation, the restoration mustbe replaced.


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Occlusal rest seat preparation an amalgamrestorations :

An occlusal rest preparation in a multi surface amalgamrestoration is less desirable than that in either soundenamel or a gold restoration.Amalgam alloy tends to flow

when placed under constant pressure.


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Rest Seat Preparation

for Embrasure Clasp:

Preparation extends over the occlusal embrasure of two approximatingposterior teeth, from the mesial fossa of one tooth to the distal fossa ofother.

Insufficient tooth removal will generallylead to occlusal interferencesbetween the clasp and the opposing cusps.

Relieving the metal to gain occlusal freedom ultimately lead tobreakage of the clasp during function.

A h i


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As the preparationpasses over the buccal

and lingual embrasures,It should beapproximately 1.5 to 2mm wide and 1 to 1.5

mm deep.

The inclines of thepreparation must be

rounded after thepreparation is complete


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Rest seat preparation on anterior teeth

Lingual, or cingulum, rests on canine and incisorteeth An occlusal rest on a molar or a premolar is

preferred over a lingual or an incisal rest on anteriorteeth to provide support for a partial denture.

Forces are better directed along the long axis of theabutment tooth by an occlusal rest than by a lingualor incisal rest.

A canine is preferred over an incisor for support of a

denture. When a canine is not present, multiple rests onincisor teeth are needed in place of a single rest on asingle incisor tooth.

A lingual rest is preferred to an incisal rest.

Li l S i I l


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Lingual Rest Seat preparation In Enamel

A lingual rest seat may be prepared in the enamelsurface of an anterior tooth

if the tooth is sound

the patient practices good oral hygiene

the caries index is low.

The cingulum should also be prominent to present agradual slope to the lingual surface rather than a steep

vertical slope. This is the principal reason whymandibular canines are poor candidates for a lingualrest

Outline Form -


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Half moon shaped formingsmooth curve from one

marginal ridge to other. Should cross the centre of

tooth incisally to cingulum.

The rest seat itself is V

shaped. The labial incline of lingual

surface makes one wall.

Other wall starts of cingulum

and inclines labio-gingivallytowards the centre of tooth.

The deepest point of the restseat will be over the cingulum.


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Lingual rest seat preparation in cast restorations

If a cast restoration is to be placed on the abutment tooth,the rest seat should be carved in the wax pattern and notcut in the cast restoration.

When the rest seat in the wax pattern is carved, a definiterest preparation can be developed that will direct the forcesof occlusion through the long axis of the abutment tooth.


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Incisal rest seat preparation :

Incisal rest seats should be used only on enamel surfaces.

Although incisal rests are the least desirable rests for anteriorteeth, they may be used successfully on select patients if theabutment tooth is sound.

On incisor teeth an incisal rest is usually used as a last resort to

stabilize the removable prosthesis.

The incisal rest seat preparation is begun with a f lame-shapedd d b h h d h d


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diamond bur in a high-speed handpiece

The first cut is made vertically1.5 to 2 mm deep in the form of a slice

or notch and approximately2 to 3 mm inside the proximal angle ofthe tooth.

After all sharp angles and points have been reduced by the flame-shaped diamond point, the preparation is polished with

carborundum-containing wheels.

The incisal restwill restore the lost contour of the incisal edge.Although some metal will show, the display can be kept to a

minimum without jeopardizing the effectiveness


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CONCLUSION The preparation of mouth is fundamental to a

successful removal partial denture. The primeobjective of all the mouth preparation procedures is to

return the mouth to optimum health and to eliminateany condition that compromises the success of thepartial denture.


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Thank you

Mouth Prep Rpd (Vikas)

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