Prosthodonticsdd2011-2012 dr ghadeer

Complete Dentures

The shape and amount ofthe distobuccal extension of a complete mandibularedentulous impression is determined during border rnolding by the:

. Ramus of the mandible

. Position and action ofthe masseter muscle

. Lateral pterygoid muscle

. Tone ofthe buccinator muscle

. Size and location ofthe buccal frena

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When border molding a mandibular custom tray that will be used for a final dmture impression:. The distobuccal extension is determined by the position and action ofthe masseter muscle.. The distolingual extension is limited by the action ofthe superior constrictor muscle.. The buccal vestibule: proper extension into this area provides the best support for the mandibu-

lar denture. This area is refened to as the buccal shelf.. Lingual frenum: the proper borders must be established with movements ofthe tongue when bor-der molding. The genioglossus muscle influenc€s the lengdr ofthe flange during normal movements

of the tongue.. The mentalis muscle will elevate the mandibular ant€rior labial arer unless this border is estab-

lished by accurate border molding.. The retromol.r pad: marks the distal termination ofedentulous ddge. This structure needs to be cov-ered for support and retention.. The mylohyoid area: the flange in this ar€a must accommodate the movem€nt ofthe mylohyoidmuscle in swallowing.. The retromylohyoid area: this area is limited posteriorly by the action ofthe palatoglossus muscleand inferiorly by the lingual slip ofthe superior constrictor muscle.

Remember: The palatoglossus, superior pharlalgeal constrictor, mylohyoid, and genioglossus muscles

are influential in molding the lingual border ofthe mandibular impression for an edentulous patient.

Import.nt: The most important consideration in checking custom trays for accurate border molding is

stability and lack of displacement.

Note: The custom tray for a final mandibular or maxillary complete denture impression should have a

sprcer with stops to insule that th€ tray will be seated in proper relationship to the arch and that there

will be adequate room for the impression material. The space is created with wax covered by aluminum

foil over the master cast pdor to forming the tray.

The primary difference between border molding with a ZOE impression matcrial and border moldingwith modeling plastic is that the zoE impression material must be border molded during one inser-tion and within the setting time of the mate al

-as opposed to two insertions with modeling com-

oound.

. To increase the capacity of underlying struchrres to withstand the stress due to bitingforce and to improve appearance

. To provide balanced occlusion and to increase tongue space

. To increase the capacity of the underlying structures to withstand the stress due tobiting force and to increase the effectiveness ofthe seal

. To improve retention and to increase tongue space

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. I month and 3 months post extraction

. 4 months and 7 months post extraction

. 5 months and l0 months post extraction

. I year and 2 years post exhaction

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*** Key point -

undcrcxtcnsion ofthc pcriphcral bordcr ofa complctc mandibular dcntrrrc dccrcascs tissuc-bear-ing surfaccs, lhcrcby affccting dcnturc stability. Merked ridge resorption will occur ifa mandibular complctc dcn-turc base terminates short ofthc rctromolar pad-

Thc underlying basal bote (be eath lhe retromoldrpdd) is rcsistant lo rcsorption. Covemge ofthis arca will alsoprovide some bordcr seal- An overload ofthe mucosa will occur iflhc bascs covcring thc area are too smali in oul-

Remember: Mandibular denn[cs do not rely on suction from a pcriphcral scal for retention /ds do marillary den-|r,"es, but rather on dcnturc stabiljty in covcring as much basal bonc as possiblc $ithout i'rpinging on thc musclcattachmcnts. Thc active bord€rmolding perfonned bythc lips, chccks, and tonguc determines the peripheral areas

ofa mandibular arch, thus establishirg ma{imal basc bonc covcrage.

Limiting structurcs ofthc mrndibular dcnturc:. Mandibular lnterior labial area: thc action of the mentalis musclc and the mucolabial fold dctcrmincs thc cx-tcnsion ofthe denture flangc jn lhis arca.. Mandibular labial frenum: lhis band offib.ous conncctive tissue hclDs attach thc orbicularis oris musclc. Thcsizc ofthis s(ructurc limits thc cxtcnsion ofthc dcnturc bordcr. thc thickncss oflhc dcnturc basc, and aflects thcposition olthc mandibular tccth.. Buccal vestibule: is infiucnccd by the buccinator musclc which has musclc fibcrs that run in an obliquc dircc-tion and thcrcforc bave littlc displacing aclion- Propcr cxtcnsion into this arca provides the best support for thcmandibular dcnturc. Tlis arca is rcfcrred to as thc buccrl shelf.. :|Iasscter area: thc dcnturc is limited in a latcral dircction by lbc action ofthc massctcr musclc.. Retromolar padi marks thc distal termination ofcdcntulous ridgc. This structurc nccds to bc covcrcd fbr sup-pon and rctcntion. By doing lhis thc intcgrity ofbonc in lhis arca is maintaincd and allows for support.

' Lingurl frenum: thc proper bordcrs must bc cstablished with movemcnts ofthc longuc whcn bordcr molding.

Thc gcnioglossus musclc inlluenccs lhe length ofthc flangc during normal movcmcnts ofthe tongue.. Sublingual gland sreai maximum cxtcnsion dcsircd without ovcrcxtcnsion.

' \ll lohtoid area: thc flangc in this arca must accommodatc the movcmcnt ofthc mylohyoid musclc in swallow-ing. Retromllohloid area: this area is limitcd posteriorlyby thc action ofthc palatoglossus musclc and inferiorly byrhr lingual slip ofthc superior constrictor musclc. Ifthcsc musclcs arc impingcd upon, thc paticnt may dcvclop a

sora throat. Notei This is often ahc most diflicult are to manaqc.

Recontouring of the healing ridge progresses rapidly for four to six months and does

not become stable in fonn until l0 -12 months post extraction. Due to this, immediate

dentures become progressively more ill-fitting. They should be relined five months and

ten months after delivery in order to compensate for contour changes. Note: This is a gen-

eral timeline; each case needs to be evaluated monthly and, if necessary, relinesperformed.

A reline is indicated on any denture when the diagnostic information indicates that a re-

line rvill effectively solve the patient's chief complaint - when the denture base

adaptation is the major defect in the prosthesis. A reline is contraindicated when there is

excessive overclosure of the vertical dimension - a large decrease in vefticaldimension. In this case, new dentures are indicated at the proper vertical dimension.

Note: When a patient wears a complete maxillary denture against the six urandibular an-

terior teeth, it is very common to have to do a reline every so often due to the loss ofbone structure in the anterior maxillary arch

-evidenced by a flabby maxillary anterior

ridge.

. 3 hours aiier delivery

. 12 hours after delivery

. 24 hours afier delivery

. 48 hours after delivery

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. Gagging

. Cheek biting

. Reduced taste

. Speech aberrations

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This is done for the purpose of correcting undetected enors. Tissue trauna attributed todenture function manifests as h)?eremia, inflammation, ulceration, and pain.

The basic sequence ofthe clinical procedure for a 24 hour recall appointment is:

l. Remove the dentures from the mouth.2. Thoroughly examine the mouth.3. Ask the patient about the areas oftissue trauma which have been obseryed.4. Pemit the patient to describe additional complaints.

*** After collecting all ofthe diagnostic information, the dentist can determine the source

ofthe problem and the cure.

Remember: During the first few days following the insertion of complete dentures, the

patient should expect some difficulty in masticating most foods and excessive saliva -*hich is due to reflex parasympathetic stimulation ofthe salivnry glands. Over time this

u ill subside and become normal.

Important: Occlusal disharmony can be most accurately corrected on the articulatorafter patient remounting procedures.

Reduce the facial surfaces olmandibular molars to

create proper horizontal overlapPosterior teeth edge to edg€

Reline at corrected VDO, patient remount, fabricatenew denture

Inadequate vertical dimensionofocclusion

Biting comers of the mouth

\otesl. Lip biting may be due to reduced muscle tone and/or a large anterior hori-zontal overlap.2. Tongue biting may be caused by having posterior teeth too far lingually.

. Facial to the ridge

. Lingual to the ridge

. Exactly over the ridge

. lncisive foramen

. Palatal mucosa

. Hamular notch

. Posterior palatal seal

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A patient who wears a complete msxillary denture complains of a burningsensation in the palatal area of his/her mouth. This is Indicativ€ oftoo much

pressure bcing exerted by the denture on the:

Setting anterior teeth directly over the ridge usually causes poor esthetics of dentures.

Also, it is important to have accurate adaptation ofthe border seal and adequate bulk ofthe maxillary facial flange for good esthetics. Vertical dimension ofocclusion affects thelip support as well.

For most patients, the labial surface ofthe central incisor should be approximately 8 mmanterior to the center ofthe incisive papilla. The labioincisal onethird ofthe maxillarycentral incisors should support the lower lip when the teeth are in occlusion.

Important: The long ares of the maxillary central incisors should be perpendicular tothe occlusal plane; the long axes of the maxillary lateral incisors should have an asyrn-metric mesiodistal inclination.

Remember: Maxillary central incisors are the most important teeth when esthetics is

under consideration. Their placement controls the midline, speaking line, lip support andsrniling line composition. Note: Placement of maxillary anterior teeth in complete den-tures too far superiorly and anteriorly might result in difficulty in pronouncing "f'and "v"sounds.

Some ofthe common errors in the arrangement ofteeth include:. Setting mandibular anterior teeth too far forward to meet the maxillary teeth. Failure to make canines the tuming point ofthe arch. Setting the mandibular first premolars buccal to the canines. Establishing the occlusal plane by an arbiirary line on the face. Not rotating anterior teeth enough to give an adequately narrower effect

,,Note{,

1. A burning sensation in the mandibular anterior area is caused by pressure

on the mental foramen.2. A patient having trouble swallowing may have insufficient interocclusal

space -decreased

freeway space caused by excessive vertical dirrension oloc-clusion.3. The best dietary advice for an elderly denture patient is to eat foods rich inprotein and vitamins A, C, D, and B complex.

Important: Leaming to chew satisfactorily with new dentures requires at least 6-8 weeks.

This time is spent on establishing new memory patterns for both facial and masticatorymuscles.

Residual ridges can be ruined by the use of denture adhesives and home-reliners.Therefore. patients should be specifically warned about their uses. These agents can mod-

ifl the position ofthe denture on the ridge and result in change ofboth vertical and cen-

tric relations.

The tr€Ntment plan for a patient indicates thst both manilibular and maxi.llaryimmediate dentures are to be fabricated. The ideal wav to do this is:

. Fabricate the maxillary immediate denture first

. Fabricate the mandibular immediate denture first

. Fabricate the maxillary and mandibular imrnediate dentues at the same time

8Coplright O 201 I 201?, Denial Decls

The first step in the treatment of abuseat tissues

in a patient with existing dentures is to!

. Fabricate a new set ofdentures

. Reline the dentures

. Educate the patient

. Excise the abused tissues

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The main reason for this is to avoid setting the maxillary teeth to the likely malpositionsof the remaining mandibular teeth

Important: Ifthe master casts are altered in an immediate denture procedure (e.g., elim-ination ofgt"oss undercuts), it is advisable to construct a second denture base that is trans-parent (called a surgicol stent or template). This surgical stent is placed over the ridge after

the teeth are exhacted. Pressure points and undercuts are readily visible and surgical ridgeconection can be performed.

Remember: The duplication ofthe master cast used for the construction ofthe surgicaltemplate to be used at the time of immediate denture insertion is best rnade after waxelimination and after the cast is trimmed.

Note: A major advantage with immediate dentures is being able to duplicate theposition of the natural teeth.

Important: The patient should understand both the cause ofthe tissue deterioration and

the eventual outcome ifthe process is not arrested.

Treatment plan for tissue r€cov€ry from abused tissues:. Educat€ the patient. Remove the dentures: at least for 24 hours or until the tissues retum to normal size,

shape, color, consistency, and texture. Note: Ifthe constant wear ofunacceptable den-tures is the cause of the tissue abuse, the most efficient preliminary treatment is re-moval ofthe dentures. However, business and social commitments may not permitremoval for extended periods. In such patients, resilient tissue conditioning materi-als may be used to assist in the tissue recovery program.. Have the patient clean the dentures: with a sofi brush and no abrasive agents. Theyshould be instructed to soak the dentures for at least 30 minutes in a commerciallyavailable denture disinfectant solution.. Ifpatient has a Candida albicans infection (either generalized or angular cheilitis):should be treated by using nystatin oral rinses for generalized infection and nystatinh|ith tridmcinolone acetonide) cream for angular cheilitis.. Resilient tissue conditioning materials may be needed to assist in the tissue recov-ery program.

Other procedures recommended as aids in the treatment ofabused tissues include mas-

sage and warm saline rinses.

. The psychological comfort ofavoiding the loss ofall teeth

. The continuous functional feedback for the neuromuscular system from proprioceptorsin the periodontal membrane

. The preservation ofthe alveolar ridge

. The improved support and stability for the denture

. The increased retention ofthe denture

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. Linguoalveolar sounds or sibilants (such as s, z, sh, and ch)

. Fricatives or labiodental sounds (such as f, v, or ph)

. B, P, and M sounds

. Linguodental sounds (such as this, that, or those)

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The overdenture is a denture whose base is constructed to cover all ofthe existing resid-

ual ridge and selected roots. Retained roots help to prevent resorption of the alveolarridges. These roots also improve retention and afford the patient some proprioceptivesense of "natufalness" in function ofthe dentures.

It is not always necessary to cover a root beneath an overdenture, however, ifa root is

not covered, the exposed surfaces are highly susceptible to decay, The oral hygiene ofthe patient must be impeccable to prevent the decay ofthese roots.

Note: Retained roots are the most common findings when taking routine panoramicradiographs of patients who wear complete dentures (rol necessarily overdentures).

Important: The general rule for retained root tips with no radiolucency and the corti-cal margin ofbone intact is that they can remain in place; however, the patient shouldbe informed oftheir presence. They should be removed if the cortical plate is perforated

and/or the PDL or radiolucent area is getting larger

Speech sounds in the complet€ denture patlent:. Frictative or labiodental sounds (f, v, and ph): are formed between the maxillary inci-sors contacting the weVdry lip line of the mandibular lip. Note: These sounds help deter-

mine the position ofthe incisal edges ofthe maxillary anterior teeth.. Linguoalyeolar sounds or sibilants (s, z, sh, ch, and j): arc made with the tip of the

tongue and the most anterior part ofthe palate or lingual surface ofthe teeth. Note: These

sounds help determine the vertical length and overlap ofthe antedor teeth. Important: Awhistling sound with dentures is indicative ofhaving a posterior dental arch form that is too

narrow or high.. Linguodental sou nds (this, that, and those,),' the tip of the tongue should protrude slightlybetween the maxillary and mandibular anterior teeth. Note: These sounds help determine

the labiolingual position ofthe anterior teeth.. The b, p, and m solnds: are made by contact of the lips. Not€: Insuficient lip support

by the teeth or the labial flange can affect the production ofthese sounds.

Note: The two most probable causes of a patient complaining that whenever he/she tries to

make an "s" sound. it sounds like "th" are:. lncisor teeth are set too far palatally. Palate is made too thick

Important: To evaluate vertical dimension, have the patient pronounced the s sound; the in-terincisal sepantion should be I to 1.5 mm. This is known as the closest sp€aking space.

Remember:. Ifthe teeth are positioned too far lingually, the "t" will tend to sound like a "d." Ifthe teeth

are positioned too far labially, the "d" will sound more like a "t.". An increased occlusal vertical dimension can result in clicking ofteeth.

. The primrry role ofanterior leeth on a denture is:

. To incise food

. Occlusion

. Esthetics

. Stability of the denture

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. Fibrous tuberosities

. Too great a vertical dimension ofocclusion

. A lack ofposterior occlusion

. The maxillary denture teeth that were used are too short

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Spaces, lapping, rotation, and color changes can bejudiciously used to create a naturalappearance. Note: Proper lip support is provided by the facial surfaces of teeth and

sirnulated attached gingiva.

Setting the anterior teeth either too far lingually or facially to satisfy esthetic concems

should not be done. When selecting teeth, pre-extraction records are very valuable.

Maxillary and mandibular anterior teeth should not contact in centric relation.

The outline ofanterior teeth should harmonize with the form ofthe face:. Convex profile faces should have a similarly convex labial surface ofanterior teeth. Broader contact areas ofteeth look more natural on dentures as they seem more com-patible with advanced age

Whistling when a patient speaks with dentures (complete or partial wltich replaces the

incisors) may be caused by any ofthe following:. Vertical overlap is not enough. Horizontal overlap is too much. The area palatal to the incisors is improperly contoured (too high or too narroh,)

Note: In general, functional needs overshadow those ofesthetics when selecting pos-

terior teeth. Do not set mandibular molars over the ascending area ofthc mandiblebecause the occlusal forces in the area will dislodse the mandibular denture.

The patient's chiefcomplaint will be looseness ofthe maxillary denture. Thcy will also state thal they

can no longer see their upper teeth on the denture. These signs and symptoms are caused by a lack ofpostcrior occlusion.

Important: A patient wearing a maxillary complete denture and a mandibular bilateral distal-ex-

tension removable partial may show:. Decreased vertical dimension ofocclusion. A prognathic facial appearance

\ote: \\ftcn a complete maxillary dcnture opposes natural mandibular anterior tecth. the marillary tn-terior ridge often becomes very flabby.

Rememberi The best impression technique for an edentulous patient with loose, h)?erplastic tissue inrhe maxillary anterior region is to register the tissue in its passive position.

. 1. Denture support refe$ to rcsistance to vertical seating forces.

)-oter,. 2. Denture stability is necessary to resist dislodgement of a dcnture in the horizontal direc-tion.*' l. D"ntu." ."tertion is the ability ofthe denture to withstand dislodging forces exerted in the

venical plane. Surfaces of a denture that play a part jn retention:. Intimate contact ofthe denture base and its basal seat. Teeth: no occlusal prematurities to break rctention. D€sign of the labial, buccal, and lingual polished surfices: configuration harmoniouswith forces generated by thc tongue and musculature

4. Factors that influence denture sudace:. Adherion: saliva to denture and to tissues

-primary retentive force

. cohesion (the attraction ofmolecules lot each other) depends onr the area covc.cd and

the type of saliva /i.e. , thick, ropy -unfavorable;

thin, \,atery -

better retention). Atmosph€ric pressure: prcportionate to area covercd and depends on pe pheral seal. Mechanical: ridge size, shape, and inter-ridge distance

. Adequate coverage of tray borders with the material used for border molding

. Contours ofthe periphery similar to the final form of the denture

. Stability and lack ofdisplacement ofthe tray in the mouth

. Uniformly thick borders of the periphery

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. Residual ridges

. Palatal rugae

. Incisive papilla

. Maxillary tuberosity

. Buccal vestibule

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The ease and accuracy ofthe border molding depends upon:

l. An accurately fitting cuslom tray2. Control of bulk and temperature ofthe modeling compound3. A thoroughly dried tray

The custom tray fabricated on the preliminary cast is trimmed approximately 2 rnm short

of the mucosal reflection and frenae. This is done by first checking the borders in the

mouth and then trimmed down. This will allow a uniform thickness of 2 mm of model-

ing compound when borders are molded. Proper border molding results in contours re-

sembling the final form ofthe denture. However, the primary indicator ofthe accuracy

of border molding is the stability and lack ofdisplacement oftray in the mouth.

Border molding is completed in two stages. In the lirst stage the molding should ap-

proximate the borders but should be slightly overextended. Excess compound is trimmed

from inside and outside ofthe tray. The remaining modeling compound is then refined by

repeating the process. The final form ofthe border molding should represent an accurate

impression ofthe peripheral tissues. The modeling compound should have a smooth, al-

most polished appearance.

After border molding is cornpleted, some areas ofthe modeling compound should be re-lieved because the tissues are extremely displaceable and have probably been distorted

during the border molding process. These areas include around the maxillary labialfrenum and over the retromolar pad areas.

Remember: Modeling compound (plastic) has a relatively low thermal conductivity.

*** The primary support areas of the maxillary complete denture are thc residual ridges (the

ntatillan and palatine bones),

lmportant: In the mandibular arch, the primary support area is the buccal shelf because of itsbone structurc and its right anglc relationship to the occlusal plane. Proper extension into this area

is necessary- to more widely distribute the load ofmastication. The residual ridges iflarge and broad

can also be considered as lhe primary suppofl areas.

Limiting structures oflhe maxillary denture:

. ln the anterior region: the labial vestibule, which cxtcnds from the right buccal frenum to the

leil laterally, from the right and lcft buccal vestibules extending in the posterior aspect on each

side to the right and left hamular notches, respectively.. The posterior limit: extends to junctions of moveable and immovable tissue. This coincides'$'ith a line drawn through the hamular notches and approximately 2 mm posterior to the foveae

palatiJle (vibrating I ine).

Remember:. The secondary peripheral seal arca for a mandibular complete denture is thc anterior lin-gual border. Ifyou are labricating a mandibular complete denture for a patient with a knife-edge ridge,you need maximal extension of the denturc to help distribute the forces of occlusion over a

Iarger arca

Important: The most important factor for providing retention for complctc dentures is the pe-

ripheral seal.

\-

An overertended distobuccal corner of a mandibulrr denturewill push agrinst which muscle during function?

. Zygomaticus

. Orbicularis oris

. Temporalis

. Masseter

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After border molding the mandibuhr custom tray, it is importantto check for dislodgement in order to detect areas of:

. Underextension ofthe tray

. Overextension ofthe tray

. Thickness ofthe tray

. None ofthe above

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This is a very common area ofoverextension and should be checked very well when de-

livering the mandibular denture.

The buccinator muscle lies under the denture flange in this area but the fibers run an-

teroposterior in a horizontal plane and their action is weak; the anterior fibers of the

masseter muscl€ pass outside the buccinator at the distobuccal comer ofthe mandibulardenture and will push against the buccinator during function causing dislodgement.

Important: When the posterior maxillary buccal space is entirely filled with the den-

ture flange, the coronoid process may interfere with the denture upon opening of the

rrouth. This will cause dislodgement olthe maxillary denture.

L The superficial layer ofthe masseter muscle originates from the zygomaticprocess of the maxilla and inserts at the angle and lower lateral side of the

ramus of the mandible.2. The pterygomandibular raphe lies between the buccinator and superiorconstdctor muscles.

Check for dislodgement using the following techniques:. Pull gently upward on the patient's cheek. Pull the lower lip gently forward in a horizontal direction. Have the patient open widely. Have the patient move the tongue into the right and leit buccal vestibules. Have the patient protrude the tongue to touch the lower lip. Have the patient move the

tip ofthe tongue from one corner olthe mouth to the other

Dislodgement indicates overext€nsion and the border molding process should be refinedin the offending area. Common areas ofoverextension ofthe mandibular impression are

the labial and the truccal. This is suspected when the impression raises as the mouth is

opened.

The most critical area in the border-molding procedure for a maxillary denture is the

mucogingival fold above the maxillary tuberosity area. This area is extremely importantfor maximal retention. Other critical areas are the labial frena in the midline and the

frena in the bicuspid area. Overextension in these areas often leads to decreased reten-

tion and tissue irritation.

\ote: Pressure areas on the impression surface ofdentures is checked with PlP. Use dig-ital pressure only, one denture at a time. Special attention should be given to the hardpalate and the mylohyoid ridge areas.

. The inclination ofeach condyle

. Vertical dimension ofocclusion

. Centric relation

. Location ofthe hinge axis point

. Maintain the vertical dimension of occlusion

. Maintain bite registration

. Preserve the face-bow transfer

. All ofthe above

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A face-bow is a caliper-like device used to record the patient's maxilla / hinge axis rela-

tionship (opening and closing axis).It is also used to transfer this relationship to the ar-

ticulator during the mounting of the maxillary cast. Ifthe face-bow tratsfer procedure is

properly done, the arc ofclosure on the articulator should duplicate that exhibited by thepatient. This hinge-axis face-bow transfer enables alteration in vertical dirnension on

the articulator

Note: When altering vertical dimension (either through restorations or with dentures),

casts should be mounted on the hinge axis.

When the maxilla,4ringe axis relation is transfened to the fully adjustable articulator, itmay be necessary to obtain the precise tracing of the paths followed by the condyles. Apantograph is an instrument which carries out this task with the help of two face-bows.

One is attached to the maxilla and the other to the mandible using a clutch that attaches

the teeth in their resDeclive arches

When fabricating dentures, there are two methods used to preserve the face-bowtransfer:

l.Taking a plaster index ofthe occlusal surfaces of a maxillary denture before re-

moving the denture from the articulator and cast (see picture below).

2. Placing a piece of 10x wax on the occlusal surfaces of the mandibular teeth and

closing the articulator in centric relation. Chill the wa.x, drop the incisal guide pin totouch the incisal guide table (do not change).

Important: The plaster index method is the preferred method due to possible distortionofwax.

[tlaxillary Oenture

Plastor lndex Cast

. Faulty tooth position

. Excess vertical dimension ofocclusion

. Faulty palatal contours

. Faulty occlusion

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. The newness ofthe denture

. Defective tissue registration

. Premature occlusal contacts

. lncornplete polymerization of the denture base

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Spcech problcms due to faulty tooth position can be avoided by placing thc dcnturc tccth as close as possible to thcposition ofthc natural tccth. Note: Thc most cffcctivc timc to lcst for phonctics is at thc timc oflhc wax try-in oithct.ial dcrture frlrr rs l/s!d f thefourth appointmett). Faulty palatal contours can bc co.rcctcd by trial and crror Addwax to incrcasc contours and rcducc as nccdcd to improvc articulation ofsounds. Note: Paticnts who have becn eden-tulous for many years oficn havc more distorted spccch than thosc \r'ho havc bccn cdcntulous lbra shorllimc. This

is usually duc to a loss oftonus ofthc tonguc musculaturc.

At the first appointment after insertion ofcomplete dentures, the presence olgeneralized

soreness on the crest of the mandibular ridge is most likely due to improper occlusion(premature occlusdl contqcts). To identify these, the best method in the mouth is to use

disclosing wax that is slightly warmed. Insert the wax bilaterally and bave the patient

close into centric. The prematurities will show up as windows in the wax' Once centricis complete, be sure to check eccentric movements.

Important: Acrylic spicules, inaccurate denture bases and trapped food can all cause ul-cers as rvell. Ifan acrylic spicule is found, it should be reduced. Ifan inaccurate denture

base is suspected, it should be relined.

r - . - 1. After relining dentures, ifa patient constantly retums for adjustments due to

;:.iot{] sore spots on the ridge, check the occlusion. The relining procedure may have'@f changed the centric relation contacts.

2. Errors in occlusion may be checked most accurately by remounting the den-

tures on the articulator using remount casts and new interocclusal records.

Remember: Casts mounted with an interocclusal record are mounted more ac-

curately if the material used is selected according to the accuracy of the casts

bing articulated (casts produced with iteversihle hydocolloid are more accu-

rateb) mounted with wtu records, and casts obtained with elastomeric materi'sls are more accurately mounted with elsstomeric registration materials orzinc and eugenol paste).

maxillary ccntral incisors toirnpcde $e ail stream parsingb€tw€en ilE tonge aDd pal-ate. Crcat€ rugae ifnecs3sry

An sbcam passcs unimpcdcdor with inadequate impcdanccbclwcen lhe dorsal surface ofthc torgrc and lhc ani,crior pal-

The an strcam passing bctwccntle tongue and intc.iorpalalc iscxccssivcly impcdcd. usuallyby njgae or €xcessiv€ resin

Rcduco occlusal verlicaldimension u il prcmolarsno louer con&ct during

Reduce oc.iussl v€rlicaldineDsion unril premolasro longer contacl during

Maxillary & Mandibularircisots or p.emohrs conta.tduring sibilsnl /r s/,, z cr)

Eval a& Iip suppod andoverall apperance of anteriorte€rh as dley ar€ positioo€d.Reset to a more lingual posr-

tion as need.d- Incisal edge ofmaxillary incisors lhould con-racl thr wat/dfy junciion Justlingual to it during producrionolthe "F'& "V" sounds

Cliniciar obs€'ves that incisal€dg6 of naxillart incisorsco act lhe lower lip I mm ormoE labial to lhe wet/dry

of lower lip when "F '& "1f'lomds are nade

Maxillary teetl mal be sct loofar labially

. Frankfort's plane

. Camper's line

. Fox plane

. Horizontal condylar inclination

22Copright O 20l l-2012 - D€ntal D4ks

. Insufficient pressure on the flask during processing

. Insumcient material in the mold

. A rapid elevation in temperature to 212' F causing vaporization ofthe liquid

. insufficient time for processing

23Coplrighr O20ll-2012 - Dental D€cts

Occlusion rims are the resultant product after adding base plate wax to a record basein order to approximate the tooth position and arch form expected in the completed den-ture,

Occlusion rims are used to:. Determine and establish the vertical dimension ofocclusion. Make maxillo-mandibular jaw records. Establish and locate the future oosition ofthe artificial teeth

l. A good slarting point for determining the vertical length ofthe maxillary oc-clusion rim is a point approximately 2 mm below the upper lip when it is re-lared.2. When recording centric relation for a removable partial denture, the occlu-sion rirn should be attached to the completed partial denture framework in-stead ofa record base as used with a complete dentue.3. Ifat the tooth try-in appointment the teeth need to be adjusted to correct the

centric occlusion, the best way to do this is to take a new centric relation recordand remount.

Acrylic resin used for denture repairs should be under 20-30 psi air pressure while being

processed to help eliminate porosities. These porosities, ifpresent, will usually occur inthe thickest part ofthe denture. Self-cured resins are generally used for repairs instead

ofheat-cured resins because the risk of distorting the denture is less.

l. When there is a rapid elevation in temperature causing vaporization ofthe liq-uid, the vapor is then trapped as gas bubbles.2. Porosities will also occur if the packing and processing ofthe powder and

liquid resin is too pllstic (stringl or sandy/. This permits the liquid to vaporize

and, at the same time, does not allow sufficient pressure during closure of the

flask.

. Increased post-insertion care

. Increased post-insertion soreness

. Not being able to have an anterior tooth try-in to evaluate esthetics

. Greater complexity ofclinical procedures

. A higher cost oftreatment

21

Cop).righr O 201 l-2012 - Denlal Decks

. The face-bow is a caliper-like device used to record the patient's maxilla,/hinge axisrelationship (opening and closing axis)

. If the transfer is done properly, the arc of closure on the articulator should duplicatethat exhibited by the patient

. The face-bow transfer is a maxillo-mandibular record

. The face-bow transfer is used to transfer the maxilla/hingearticulator during the mounting ofthe maxillary cast

axls relationship to the

25Coplriglt C 201 l-2012 Dmtal Decks

Other drawbNcks of immediate dentures:.Increased post-ins€rtion care, including relining or remaking the denturcs. Contour changes occur inthe healing residual ridge for 8-12 months..Incrersed post-delivery soreness. The combination of post-extraction pain and denture related traumaoften produces greater discomfoit during the first few days following insertion.. Greater compl€xity ofclinical procedures. Forexample, bordermolding and final impressions are moredifficult when natural teeth remain.. Higher total cost of treatment Ther€ is an increased expense due to the need for relines and repeated equi-libration of the occlusion.

Advanlag€s of immediate dentures:. Continuously acceptable esthetics. Immediate dentures are esthetically advantageous in that the palientis never without either natural or artificial teeth.. Improved speech adrption. Immediate dentures rcquire only one period ofspeech adaptation, whereas

conventional denture trcatment requircs two; one afierthe teeth are extracted and anothcr after thc denturesare delivered.

' Protection of the extraction sites frcm trauma, Denhrres act as a typ€ ofbandage over the clot filled sock-ets.. Continuously acceptabl€ masticatory function. The patient retains some semblance ofchewing abilityduring the healing process.. Prevention oftongue enlirgement. When naiural teeth are lost and not replaced, the tongue tends to ex-pand into the available space.

To help the patient get through the fiIst day ofwearing immediate dentures, instruct him to do the following:. Do not remove the dentures . Retum in 24 hours. Eal soft foods

Recommended trvo-step schedule ottooth rcmoval;. First stepi extract all posterior teeth except a ma-rillary first prcmolar and its opposing tooth. This leavesa posrerior "stop" in order to maintain the vertical dimension ofocclusion.. Second step: after the posterior rcsidual ridges exiibit acc€ptable clinical healing, the second phase ofrreament, that ofdenture fabrication, can begin. The anterior teeth will be extracted at the time ofdcnnrrclnsertlon.

*** This is false; it is a record used to orient the maxillary cast to the hinge axis on thearticulator.

T = Tragus ofear OC = of the eyes

Several varieties of arbitrary face-t ows are available. All are based on an average lo-cation ofthe hinge axis and will yield an enor of2 mm or less in the majority ofpatients.Arbitrary rotational centers are generally located over measured points on the face or bysome type of earpiece. One average measurement (above picture) places the rotationalpoint 13 rnm anterior to the distal edge of the tragus of the ear' along a line from the

superior-inferior center ofthe tragus to the outer canthus of the eye. The condylar styli

of the face-bow are then placed directly over the dots.

J"",f {.

;"t

Outer canthus

. Is placed 3 mm posterior to the vibrating line

. Is not necessary when fabricating a complete denture on a patient with a flat palate

. Is not necessary ifa metal base is used

. Will vary in outline and depth according to the palatal form ofthe patient

26CopriShr C 201 I 'l0l: - Dental Decks

. Pterygomaxillary notch

. Vibrating line

. Hamular process

. Fovea palatinae

27CopFighr O 201l-2012 - D€nlal Deks

Posterior Palatal Seal

Ttre poslcrior line (A) indicatcs th cnd of thcdenture posteriorly across the palate. The anteriorlinc (B) marks thc location of the posterior palatal

scal that will b€ caRed intothe cast and transfcrcdas a bead onto the denture.

The dcnture cnds on thc cast at A. the bcad (B), locatcd 2

mm in front of the vibrating line, is extcndcd latcrallythrough thc ccntcr of thc hamular notchcs-

Bolh phoros m Fprcduced wnh pmission, fiom zdb GA,and BolenderCL.. Ptosthodontic Tredhent lot Edertulow Potients- Mosby,20,.J6.

The posterior palatal se|l is completed before the final arangement ofthe posterior teeth because this firalarrangement is a laboratory procedure and is done in the absence of the patient. The anterior lilre that indi_

cates the location ofthe poste or palatal sealis drawn on the cast in fiont ofthe line indicating the end ofthedenture. The width ofthe posteriorpalatal sealitselfis limited to a bead on the denture that is I to 1.5 mm highand 1.5 mm broad rt its base. A greater width creates an area oftissue placement that will have a tendency

ro push the denture downward gradually and to defeat the purpose ofthe posterior palatal seal ln other words,

rhe posterior palatal seal should not be made too wide.

A !'-sh|ped grcove I to 1.5 mm deep is carved into the cast at the location ofthe bead. A large, sharp scmper

is used to carve it, passing through the hrmuler notches and across the palate ofthe cast. The $oove will forma bead on the denture that prcvides the posterior palatal seal. The b€ad will be I to 1.5 mm high, 1.5 mmwide at its base, and sh|rp tt its apex. The depth ofthe grooves will be determined by the thickness ofthesoft tissue against which it is placed and will establish $e height of the bead.

Landmarks for Posterior Palatal Seal

. The posterior outline is formed by the "ah" line or vibrating line and passes

though the two pterygom xillary (hamrlay' notches and is close to the fovea palatini.. The anterior outline is formed by the "trlow" line and is located at the distal extentof the hard palate.

Note: Excessive depth ofthe posterior palatal seal will usually result in unseating ofthedenture.

Remember: The posterior palatal seal will vary in outline and depth according to thepalatal form of the patient.

Functions of the Posterior Palatal Seal:

. Completes the border seal ofthe maxillary denture

. Prevents impaction of food beneath the tissue surface of the denture

. Improves the physiologic retention of the denture

. Compensates for shrinkage of the denture resin during processing

. Deepening ofnasolabial groove

. Loss oflabiodental angle

. Retrognathic appeaxance

. Decrease in horizontal labial angle

. Narrowing of lips

. Increase in columella-philtral angle

2A

Cop}Tighr O 201 1,2012 - Dertal Decks

r ln rhc nnraaloin

. At the porcelain-metal interface

. In the metal

29Copyrighl O 20ll-2012, Dent.l Decks

It must bc emphasized that one or more of these items are also frcquently encountered in per-

sons with intact dentitions because the compromised facial support of the edentulous state is

not the cxclusive cause of thc morphological changes. Patient's weight loss, age, and hcavytooth attrition manifest orcfacial changes suggestive ofcompromised, or absent, dental support

for the overlying tissues.

Pre-extraction guides for selecting afiificial teeth from edentulous patients include:

. Photographs: provide general information about width and possibly outline fonn.

. Diagnostic casts: the form of the teeth can be very well judged from previous diagnostic

casts ofnatural teeth , if available (check with the patient's prerious dentist).. Intra-oral radiographs: the size and form can be d€termined but beware because radi-ogmphs can be distorted and usually are larger images ofthe tccth.. The teeth of close relatives: when no other means are available to get an idea about the

form, size and shade of teeth to be used for thc denture of an edentulous patient, records ofson's or daughter's teeth can give a clue. lt may also help in the arangement ofteeth as well. Extracted teeth: sometimes patients keep their cxtracted teeth, which could be an excellent

source and aid to delineatc the form ofthe teeth, thus helping in the selection process.

1. Degenerative joint disease is frequently scen in denture wearen but this may be

age related rather than the state ofthe dentition.2. The recording of centric relation is considered as an essential starting point inthe design ofthe artificial denture.

3. ln complete denture prosthodontics the position ofthe maximum planned in-tercuspation of teeth or centric occlusion, is established to coincide with the pa-

tient's centric relation.

One of the major reasons for the acceptance ofporcelain fused to metal restorations is

its greater strength and resistance to fracture. The combination of porcelain and metal,

fused together, is stronger than porcelain alone. Because true adhesion occurs, the bond

strength is such that failure or fracture will occur in the porcelain farther than at the

porcelain-metal interface.

Important points conceming the metal-ceramic crown:. The necessary thickness ofthe metal substructue is 0.5 mm. The minimal porcelain thickness is 1.0-1.5 mm. Based on the above points, the tooth reduction necessary for the metal-ceramtc crown

is approximately 1.5-2.0 mm. The labial shoulder width is ideally 1.5 mm.. The most frequent cause ofporosity in the porcelain is inadequate condensation ofthe porcelain. The effectiveness ofcondensing porcelain powder to reduce shrinkage is determined

by the shape and size ofthe particle

Rememb€r: Porcelain is much stronger under compressive forces than it is when sub-jected to tensile forces by the opposing teeth. Porcelain fracture in all-ceratnic restorations

can be avoided by keeping the angles ofthe pr€paration rounded.

. Porosity

. Thickness

. Surface area

. All of the above

30

CopFight C 201 l-2012 - Dental Decks

Which of the following are indications tbr lixed bridgework or importantconsiderations to think about when contemplating the fabrication of lixed

bridgework for a patient?

. A limited number ofedentulous areas which would not otherwise be more satisfactorily re-stored with a removable partial denture

. The need to prevent the over-eruption ofopposing teeth and the ddft of teeth neighboringthe edentulous space

. The presence of suitable abutment teeth -

favorable crowr/root ratio, adequate alveolarsupport, absence ofapical pathology, etc.

. Esthetics

. Patient motivation, including time availability

. Clinical and technical ability

. All ofthe above31

CopFiSh C 201 l,l0l2 - Dertal D€cks

Soldering is used in dentistry to connect bridgework and in fabricating orthodontic ap-pliances. Gold solders are generally used for fixed bridgework and silver solders for or-thodontic appliances. It is important that the solder melt at least 150oF below the fusiontemperatures ofthe metals or alloys being solders (for obvious reasons).

A good solderjoint between 2 castings requires clean surfaces and fr€e electrons pres-ent on the surfaces.

Commonly used dental solders include:

Note: The bonding ofthe solder is contingent upon wetting ofthejoined surfaces by thesolder, and not upon melting ofthe metal components.

Cleanliness is the most important prerequisite ofsoldering, since the soldering process

depends upon wetting ofthe surfaces to achieve bonding. Fluxing is the oxidative clean-ing ofthe area to be soldered. Fluxes are used to dissolve surface impurities and to pro-tect the surface from oxidation while heating. Note: Fluxing is also performed on moltenmetal alloys during the casting ofa crown or partial denture framework.

Contraindications for fi xed bridgework:. Poor oral hygiene. High caries rate. Multiple spaces in the arch or teeth likely to be lost in the near future. Space not detrimental to the maintenance of arch stability or dental health. Unacceptable occlusion. Bruxism

l. If the clinical and technical skills ofthe dentist do not match the demands\ote+ ofthe case, fixed bridgework should not be undertaken because a failed bridge

'.;** . is likely to be more detrimental to dental health than a failed removable partiald€nture.2.Unless specifrcally contraindicated, fixed restorations are always the treat-

ment of choice.3. Fixed bridgework can be used in conjunction with removable partials. Ex-ample: A patient with a couple ofmissing anterior teeth and no posterior teeth.

Treatment could be fixed bridgework in the anterior and a partial denture re-placing posterior teeth.

4. Although somewhat controversial, the literature recommends that you should

not splint natural teeth and implants in a fixed partial denture. Implantshave no periodontal ligament and so do not have the same capacity to ab-

sorb shocks as do natural teeth (they have dffirent mobilityb). When thisbridge is subject to occlusal loading, the difference has been shown to be

detrimental to the natural teeth as well as cause bone loss around the im-Dlants.

. Periodontal disease

. Recunent caries

. Vertical root fracture

. The need for an apicoectomy

32

Coplrigh O 201 l-2012 - Dental Decks

All of the following are indications for porcelain veneers EXCEPT one,Whieh one is the -EXCEPZOfr?

. Coverage of labial surface defects -hypoplasia

of the enamel

.Masking of discolored teeth -tetracycline

staining, discoloration following loss ofvitality

. The severe imbrication ofteeth

. Repair of structural damage -

fractured incisal edges

. Improvement of tooth contour *peg-shaped lateral incisors

. Reduction of spacing in cases when orthodontics would be inappropriate

Cop),right O 20ll-2012 - Dental Drcks

*** The main symptom will almost always be pain when biting. The radiograph usu-ally appears normal.

Advantages of using a post and core as opposed to a post crown when restoring en-

dodontically treated teeth:. The marginal adaption and fit ofthe restoration is independent on the fit ofthe post. The restoration can be replaced at some time in the future, ifnecessary without dis-turbing the post and core. Ifthe endodontically treated tooth is to serve as a bridge abutment, it is not neces-

sary to make the root canal preparation parallel with the line of draw ofother prepara-

tions - it can be treated as an independent abutment

The post and core, when used, is made separate from the final restoration. The crown isthen fabricated and cemented over the core just as a restoration would be placed over a

preparation done in tooth structure.

For teeth with little or no clinical crown that have roots with adequate length, bulk, and

straightness, a post and core can be utilized. For posterior teeth with less extensive de-

struction ofcoronal tooth structure, or for those possessing less favorable root conhgura-tions. a pin retained amalgam or composite core can be used.

*** Other contraindications to porcelain veneers include: traumatic occlusal contacts, un-

favorable morphology, insufficient tooth structure, and insumcient enamel.

Technique for Insertion of Porcelain Veneers

. The veneer should be tried in wet with either a drop of water or glycerine to check

for fit. A reliable estimate for the possible post-cementation appearance with try-inpastes can also be performed.. The veneer fit surface should be cleaned to rernove any saliva contamination or try-in composite. Ifthe fit surface has not previously been treated with silane and protected with light-cured unfilled resin, this should be done at this stage. The enamel surface should be cleaned with pumice and water. While protecting adjacent teeth with matrix strips, the enamel is acid-etched with di-luted hydrofluoric acid. Note: The etched surface is washed and dried and a layer ofunfilled bond resin is applied and thinned with oil-free air. An appropriate shade oflight-cured composite is applied to the fit surface ofthe ve-neer which is "puddled" into place on the tooth surface. Gross excess of composite should be removed and light-curing completed. Remaining excess composite is removed with finishing diamond burs, discs, strips,

etc., and the margins finely polished. The patient should be seen in approximately one week

. One

. Two

. Thiee

. Four

34Cop,.righl O2011,2012 - Denral Decks

. Maxillary premolar

. Mandibular premolar

. Mandibular molar

. Maxillary molar

35

Coplright @ 201 I -20 12 - Dental Deck

Important: One factor that limits th€ length ofthe pontic span is the abutm€nt teeth's ability to accept the ad-

ditional occlusal load while providing adequatc support to the cemented fixed partial denturc. Ant€'s law stales

that the root surface arca ofthe abutment tcelh supported by bone must equal or surpass the root surface area

ofthe teeth being replaced with pontics.

An edentulous spacc involving four adjacent te€th otherthan four incisors is usually best treated lvith a re-

movable partial denlure. [f more than one edentulous space exists in the same arch, even though each ofthcm could be individually rcstorcd with a bridge, it may be dcsirable to restore them with a removabie par-

tial denture. This is especially true ifthe spaccs arc bilateral and each one involves two or more missing teeth

Third molars can rarely be used as abutments, sinc€ they fiequently display incomplete eruption; shon, fused

roots; and a marked mesial inclination in the absence ofa second molar Note: Diverging multirooled, curv€d,

and broad labiolinglal roots are prefened over fused, single, conical, and round circumferential roots.

Remember:. Splinling adjacent abumlent teeth in a fixed bridge is primarily done to improve the distrit ution oftheocclusal load,. In order to maintain and protect the health ofthe gingival tissues and prcvent recession, lhe correct con-

tour of the cro$n's gingival one-third to one-fifth and interproximal areas are most impofiant in the final

restoratioD,.An anterior fixed bridge is contraindicated when there is considerable resorption ofthe r€sidual bridge.

A removable panial denrure would be indicated in this case.. Horizontal loads 1ol &,c"t on natural or abutmcnt teeth are most deslructive to the pcriodontium.. Abuimenls with hatfor l€ss ofbone support and loss ofattachment have a poor prognosis.. \\'hen replacing the maxillary or mandibular canine, the central and lateral should be splinled to prcvent

lateral drifting oflhe fixed bridge.. Aburment teeth must align to a common path of insertion (/o/ orvious reasons when lryng lo seat lhe

hrklge).. Short root-to-crown r^lio (less lhan./:21 with conical roots should be avoided as abutmenls.. \atural reeth exert more force than an RPD or complete denture when opposing a fixed bridge. Ideaff)--, rhe supportive surface area (peiodontium) of lhe abutment teeth should be equal to but notleis than !ha! ofthe teeth to be replaced

This design preserves the lingual surface and is indicated for restoring mandibular mo-lars with damaged buccal surfaces and intact lingual surfaces. It is also useful on teeth withsevere lingual inclinations where large quantities oftooth structure would be destroyed ifa full veneer crown were to be used.

The standard thre€-quarter crown is a partial veneer crown in which the buccal sur-face is left uncovered. It is the most commonly used form ofthe partial veneer crowns.

A patient with a high cari€s index, short clinical crowns, and minimal horizontal over-

lap would not be a candidate for partial veneer crowns. The restoration ofchoice wouldbe a full metal-ceramic crown,

Note: R€tention and resistance forms in full coverage preparations on short molai:s can

be enhanced by placing several vertical grooves or boxes.

According to the ADA classification for alloy systems usedfor metal-ceramic restorations. noble allovs:

. Have a noble metal content of 2 600lo

. Have a noble metal content of > 45%

. Have a noble metal content of > 25o%

. Have a noble metal content of ) [ 50%

36Copyright O 201l-2012 - Dental Decks

Periodontal health of the gingival tissues is a major concern when phnningany fixed prosthodontic treatment. For optimum periodontal health,

restoration linish lines should be:

. \\'ithin the sulcus at least 1.0 mm and away from the free gingival margin withoutencroaching on the biologic width

. Terminated at the free gingival margin

. Supragingival whenever possible (at least 0.5 mm from the free gingival ntargin) toallow for hygienic cleansing

. As far as possible subgingivally into the attachment apparatus

37Cop)righr O 20ll-2012 Dental Decks

ADA classification for alloy systcms uscd for metal-ccrumic rcstontions. High noble alloys (old tem was pre.ious netal)t > 60o/n noblc rr'ctal contcnt (gold > 40%). Nobfe alloys (o// ter"r, tr^r senripreciout metal): > 2570 noblc mclal contcnt ( o gold rcquircd). Base metaf affoys foll term was nonptecious metal): < 25y. notle fielzl conlent (tro god requile,l)

Remember: Noble alloys (gold, plaainuD\ and po adium) do not oxidize on casting. This featurc is important in amctal substmte so that oxidation althc metel-porcehin interface can be controlledby thc addition oftracc clcmcntsto thc metal (silicon, ituiiun, and iridiunl .

Desirable properties of alloys for metrl-cerrmic restorations:. High yield strength: minimizcs pcrmancnt dcformation und$ occlusal forcc and porcclain fracture duc to fmmc-work deformation. High modulus of elasti cilf (snfness)| minimizes flexure of long-span fixed bridgcs and porcelain fracturc ducto framcwork dcformation.. Casting Nccuncy: basc mctal alloys arc lcss accuratc lban gold. Biofogical compatibililf (for patient, dentist and lab technician): cat be a problcm with Nickcl and Bcrylliumin base mctal alloys (a/&/gler/. Corrosion resistanc€. The metal coeflicient ofthermrl expansion should bc highcr than thc porcciain to lcavc thc porcclain in com-prcsslon rn a stronSer statc

)letal based based on color or composition:. \'ello* gold: > 60% gold content.. $hite gold: > 50% gold content.. Lo\n (econom\,) gold (usualr te ow): < 600/0 gold (42yFs59/o). Higb prll.diurn whitc, mainly palladium, Gold (22,/, littlc coppcr or cobalt. Sifler-pa lladi u m: whi te, silvet (5 5a/F7 I %o) , palladium for nobi lity and control ling tamish (2J%- 27/o) , may orma) not contain a little gold or copper. Pelladium-silver: whitc, mainly palladium, silvcr up to 40%, -

Porcclain adhercs to mctal primarily by a chemical bond, A covalent bond is cstablished by sha;ng 02 with thc cl-cmcnts prcscnt in thc porcelain and the mctal alloy. These clemcnts includcsilicon dioxidc (SlO, in lheporcclain and

oxidizing clcmcnts such as indium, tin, and gallium in thc mctal alloy.

*** There is general agreement among dentists and researchers that optimum fixed pros-

thetic restorations will display supragingival finish lines.

Such positioning is quite often not possible because ofesthetic or caries considerations.

Subsequently. the margin must be placed subgingivally. Ifa margin needs to be placed sub-

gingivally, the major concem is not to extend the preparation into the attachment appa-

ratus. Ifthe margin does extend into the attachment apparatus, a constant gingival irritanthas been constructed and ultimatety the crown will fail. In this case, the tooth should

have had crown lengthening performed on it prior to final crown preparation.

Rememb€r: It is important to maintain the biological width (the combined width of the

connective tissue attachment and thejunctional epithelium, which averages approximately2 mm).

The most important criterion for a gingival margin on a crown preparation is that itsposition is easily discemible

-must be able to recognize it easily. Note: The most com-

mon complaint oflab technicians regarding a PFM prosthesis is improper margins in the

impression.

Rememb€r: The optimum margin for a casting is an acute edge with a nearby bulk ofmetal. This acute edge or angle can be easily bumished to improve its fit.

Note: A butt joint, as gpified by a shoulder, is the poorest type offinish line that can be

used with cast metal restorations.

When casting conventional gold rlloys, which typeof investment mat€rial is used?

. Silica-bonded investments

. Phosphate-bonded investments

. Gypsum-bonded investments

Coplriglit e 201I ?012 Denral Decks

. The metal and porcelain must have compatible melting temperatures as well as com-palible coe{ficient of thermal expansions

. The metal's melting temperature should be at least 300-500"F higher than the fusingtemperature of the porcelain

. The metal coping should preferably have sharp surfaces to prevent shrinkage of theporcelain

. In function, glazed porcelain on the occlusal surface removes 40 times as much oftheopposing tooth structure than gold

39

Coplright O 201 l-2012, Denral Decks

A dental inyestment is a refractory material that is used to surround the wax pattern during theprocedure of fabricating thc metallic p€rmanent restoration. It forms the mold into which thealloy is cast after the wax has been eliminated.

An investment material to be used for a casting mold should expand on setting and heating tocompensate for the shrinkage of molten metal as it solidifies. Metal casting alloys have diffcr-ent melting ranges

-only pure metals and alloys of eutectic composition have a melting point.

The melting range of gold casting alloys (aprox. 900'Q is lower than that of Co-Cr alloys(aprox. 1350'C), Therefore, investment materials used for gold casting alloys arc sometimesdifferent from those used for Co-Cr alloys. The investment material should be ofa suitable con-sistency for adaptation to the wax model and have a reasonable setting time. To withstand thetemperatures required for the casfing process there should be no distortion, no decomposition;thc investment should not fragment or disintegrate under the impact ofthe molten metal: the ma-terial should be porous to allow the escape ofair and gases and the investment should be easilyremoved from the casting after cooling.

Classification of Dental Investment Materials. GJ-psum-bonded investments: binder is gypsum (calcium sulfate hemihydrate). Used'when casting conyentional gold alloys containing 65yo to 75y. gold at temperahrres near

1.100'c.. Phosphate-bonded investments: binder is a metallic oxide and a phosphate. Two lypes :

Ti pe I is used when casting base metal alloys for rnetal-ceramic crowns and Type II is used

for removable partial denhrre frameworks. Are capable of withstanding high temperatures/abote 1,100"C).. Silica-bonded investments: binder is ethyl silicate. Not used much today.

The refractory material for thcse invcstments is either quartz or cristobalite. This material pro-lides the thermal expansion for the investment. Note: The expansion of the investment pro-vides a larger mold to compensate for the subsequent contraction ofthe alloy.

*** This is fals€; the metal coping must have all of its surfaces smooth and rounded to pre-vent porcelain shrinkage.

Note: The purpos€ ofthe metal coping is to ensure the fit ofthe crown and to maximize thestrength ofthe porcelain veneer.

Important points to remember conceming the metal coping or substructure ofa metal-ce-ramic ctown:

l. The metal must have proper thickness (0.5 mn) -

very important2. The outerjunction ofporcelain to metal should be at a right angle (to avoid burnishingoJ the metal and subsequent f-acture of the porcelain).3. All ofthe porcelain should be supported by metal.

When deliv€ry cast restorations, the following sequence should be used: (l) check the in-temal surface fit (2) adjust the proximal contacts and pontic-ridge relationship (3) check themaryinal integ ty (4 )check the stability (ifit is a bridge) (5) check the axial contours and lastbut not feast, (6) check the occlusion (centric qnd eccentrtic contacts).

Important: If your margins were all closed at the metal try-in appointment and when thecrown came back from the lab they are all open, check the contacts. They are probably toottght (over-bulked porcelain).

' ' . -. I . Porcelain that is baked onto a high-fusing gold alloy may exhibit a green discol-;'Note{ oration due most likely to contamination of the metal by copper traces.

W 2. The best measure ofthe potential clinical performance ofa casting alloy is itsADA c€rtification.

. Eniances resistarce form when buccal-tolingual forces are applied

. Serves as a positive stop when the casting is seated during cementation

. Relieves the functional cusp from additional stresses when the restoration is loaded inthe long axis ofthe tooth

. Provides space for restorative material of adequate thickness in an area of heavyocclusal contact

40Copynghr O 201 l':012 - Detual Deks

The preparation for a full veneer crown is begun with occlusal reduction. Thereshould be clearance on the functional cusps and rbout _

on the non-functional cusps.

. 0.5 mm; 1.0 mm

. L5 mm; 1.0 mm

.2.0 mm; 1.5 mm

. 2.5 mm; 2.0 mm

41

CoplriSht O 201 1,2012, Denial Decks

The functional cusp bevel is an area ofreduction over the functional cusps that allows for cxtmthickness ofmetal in this area ofhealy occlusal contact in centric occlusion as well as in lateralmovcments. The functional cusps are those that oppose thc ccntral fossae ofthe t€eth in the op-postte arch (buccal cusps on mandibular teeth, lingual cusps on ma-tilldry teetu.

Thc primary reason for choosing a r/4 crown over a full cast crown is tooth structure is spared.

Other advantages to the use of partial veneer restorations (three-quarter & seven-eighths

crowns).. A great deal ofthc margin is in an area accessible to the dentist for finishing and to the pa-

tient for cleaning.. Less ofthe restoration margin is in close proximity to the gingival crevice, thus lessening

the opportunities for periodontal irritation.. Can be more easily seated completely during cementation.. with at least part ofthe margin visible, complete seating ofa partial veneer crown is more

easily verificd by direct vision.. Ifit is evernecessary to conduct an electric pulp test on the tooth, a portion ofenamel is un-vcneered and accessible.

.. , 1. The path ofinsertion ofan anterior three-quarter cro*'n parallels the incisal l/2,\orec to 2/3 of the labial surface, not the long axis of the tooth. For a posterior three-,"-;* quarter crown it parallels the long axis ofthe tooth.

2. A pin modified three-quarter crown can preserve the facial surface and one prox-

imal surface. This is preferred in cases which require repairing of severe lingualabrasion on incisors and canines, avoiding other more destructive options like fullveneer metal-ceramic restorations.

Thjs reduction is done to eliminate undercuts and create space for suffcient metal to ensure adequate

strength ofthe crown.

Remember: In preparing a tooth for a metal-ceramic crown, it is necessary to create space for 0.5 mmofmetalpfus at lcast 1.0 mm ofporcelain lpreferably 1.5 mu) to cnsure adequate strength and optimum

esthetics of the ceramic material. Snpporling (fuhctiotlal) cusps require 2 mm of the reduction The

opposing walfs should convcrge no more than lO degtecs (6 degree tapet is reconmended). A chamfer

finish line /0.i l?r, and a1l maryins should be placed supragingivally when possible.

The same amount ofoverall tooth reduction is needed for a metal-ceramic crown as for an all-cerarniccro*n / L 5-2.0 nn). Howevet for all-cersmic restorations, the preparation needs to be well-rounded

\\ irh no shrrp angles to avoid porcelain liacture.

\ote: The most frequent causc of failure of a crown (reganlless ofa,hich ,*pe) is the lack of attention

ro rooth shape, position, and contacts. Important: For gingival health, the conect contour ofinterprox-imal gingival areas and the gingival third are most important.

Important: Gold is regarded as a more favorable material for the occlusal surface as its wear charac-

reristics are more in harmony with enamel; porcelain is considered to bc the cause ofaccelerated wear

of the opposing dentition. Gold would certainly be preferred for the restoration ofocclusal surfaces in

rhe presence ofa tooth-grinding h.bit.

.. l. Axial contours should correspond to the emergence prolile (usually flat or concave) of:{oteCl the tooth.

2. The buccolingual dimension of a cast restoration is usually determined by the occlusalja* morphology oflhe opposing tooth.

3. Occlusal point contacts between opposing teeth arc preferred to broad, flat occlusal con-

tacts to Dlevent weaf.4. Type I and II gold alloys are uscd for inlays.5. The most commonly used type ofgold for all-metal crowns and bridges is TyPe III.

Which ofthe following best describes 'rstrain hardening'tor 'rwork hardeningrt?

. Hardening (or deformation) ofa metal at room temperature

. Hwdening (or deformotion) of a metal at a very high temperature

. Softening a metal by controlled heating and cooling

. Softening a metal at room temperature

42Coplright O 20ll 2012 - Denral Decks

. A metal is elevated to a temperature above room temperature and held there for alength of time

. A metal is rapidly cooled frorn an elevated temperature to room temperature or below

. Softening a metal by controlled heating and cooling

. None ofthe above

43Coplrishr O 20ll'2012 - Dental Decks

In polycrystalline metal, dislocations (defects) tend to build up at the grain bound-aries. Also, the banier action to slip at the grain boundaries causes the "slip" to occuron other intersecting slip planes. Point defects increase and the entire grain mayeventually become distorted. Greater stress is required to produce further "slip" and

the metal becomes stronger and harder. The process is known as strain hardeningor work hardening. The latter term is derived from the fact that the process is a re-

sult ofcold work ( i.e., deformation at room temperature, in contrast to the effect ofworking at a higher temperature, such as in forging). The ultimate result ofstrainhardening, with further increase in cold work, is fracture.

The phenomenon ofcold work and strain hardening is familiar to everyone. For ex-

ample, one way to cut a wire is to bend it back and forth rapidly between the fingers.

When all the slip possible has occurred, the wire fractures.

Important: The surface hardness, strength, and proportional limit of the metal are

increased with strain hardening, whereas the ductility and resistance to corrosion are

decreased. However, the elastic modulus is not changed appreciably.

.. , l.Under a microscope, elongated grains in the microstructure of a wrought'rote*. wire indicate that the wire has been cold worked or strain hardened.

'*-i.". 2. A slip is a deformation process requiring the simultaneous displacement

ofan entire plane ofatom A, relative to the plane B, below it'

It is usually performed when a complete gold crown is cast and immediately quenched inu ater. This softens the alloy, making it more malleable for frnishing procedures.

Important: To achieve a softened condition for a Type III dental gold alloy, the casting

should be quenched in water immediately or within 30-40 seconds ofbeing made.

. l Hert treatment is the subjection of metals and alloys to controlled heating

}-oa3'. and cooling afier fabrication to relieve intemal stresses and improve their phys-

'.9." ical properties. Methods include annealing, quenching, and tempering.

2. Annealing is controlled cooling of a material to increase ductility andstrength. The process involves first h eaing a mateial (usually glass or metal)

for a given time at a given temperature, followed by slow cooling.3. Fritting is a process ofmanufacturing low and medium fusing porcelains. Itinvolves raw constituents ofporcelain to be fused, quenched, and ground backto an extremely fine powder This "frit" can be added over by other metallicsubstances to produce color in porcelain.

. Dowel crowns to be cast in silver-palladium alloys

. Titanium crowns and copings

. The substrucfure for metal ceramlc crowns

. Type IV gold alloys

. None ofthe above

. All ofthe above

44

Cop)righr O 20ll-2012 - Dental Decks

. Be perpendicular to the incisal one-half of the labial surface rather than the long axisof the tooth

. Be parallel to the incisal one-halfto two-thirds ofthe labial sudace rather than the longaxis ofthe tooth

. Be parallel to the long axis ofthe tooth

. Be parallel to the cervical one-third ofthe labial surface rather than the long axis of thetooth

45Cop)'righr C 201 l'2012 - Dental D€cks

Dowel cores do not require as much expansion as do crowns. So even though they are

cast with Ag-Pd alloys (alloys that require a high temperature for expansion) , a gypsumbonded mold is used and heated to only 1200'F. Type I, II, and III Gold alloys can alsobe cast in g]?sum bonded investmen! material.

The substructures for metal ceramic crowns ard Type IV Gold requires heating above2100'F. These are invested in phosphate bonded material. Any alloy with a casting

temperature in excess of 2100'F (115f" C) shouldbe cast in an invesfinent with a binder

other than gypsum. High temperatures cause decomposition of calciurn sulfate in the

gypsum binder with the resultant release ofcontaminating sulfur into the mold.

Magnesium phosphcte reacts with primary ammonium phosphate to produce magne-sium ammonium phosphate which gives the investment its strength at room temperature.At higher temperatures, silicophosphates are formed which give the investment its great

strength.

The metal-ceramic alloys must have a high melting range so that the metal is solid wellabove the porcelain baking temperatures to minimize distortion (sag) ofthe casting dur-ing porcelain procedures. A high sag factor will lead to distortion of bridge spans whenthe porcelain is fired. Remember: When casting a cedain alloy, make sure you use a cru-cible that has not been used for other allovs.

*** Important: If the path of insertion is made parallel to the long axis ofthe tooth, the

labio-incisal comer will be sacrificed and an unnecessary display of gold will result.

Two factors that must be dealt with successfully to produce an anterior % crown with a min-imat display ofgold:

l. Path of insertion and groove placem€nt2. Placement and instrumentation of extensions

. Proximal extensions must be done with thin diamonds and hand instruments from a

lingual approach to minimize the display ofgold. They should be extended facially to acleansable area without destroying the facial contour ofthe tootlt.

Note: The anterior three-quarter crown is not used as fiequently today as it once was. Un-sightly and unnecessary displays of gold in poor examples of this restoration have made itless popular with the public and dentists alike. However, the standard three-quarter crownon a maxillary anterior tooth need not show large quantities ofgold ifprepared correctly.

. The length ofthe abutment teeth can be accurately gauged

. The true inclination ofthe abutment teeth will be evident

. The presence ofperiodontal pockets and the crown-to-root ratio of potential abutmentleeth

. Mesial,Distal drifting, rotation, and faciolingual displacement of potential abutmentteeth can be clearlv seen

46CopFight O 20ll 2012, DentalDecks

All of the following statements concerning pontics aretrae EXCEPT one. Which one is the EXCEPTIOM

. With regard to the ease of cleaning and good tissue health; proper pontic design ismore important than the choice of material used in fabricating the pontic

. The contour and nature ofthe pontic contact with the ridge is very important

. The area ofcontact between the pontic and the ridge should be small

. The portion ofthe pontic approximating the ridge should be as concave as possible

.The pontic should exert no pressure on the ridge (pdssive contact with no blanchingofthe tissue)

17

Cop)righr (, 201I -2012 - Dental Decks

*** Important: The presence ofperiodontal pockets and the crown-to-root ratio ofpotential abut-ment teeth cannot be determined by studying diagnostic casts. You need to do an exam and have

x-rays in order to obtain this information.

More information that can be obtained by studying the diagnostic casts:

. It allows an unobstructed view ofthe edentulous areas and an acaurate assessment ofthe span

length, as well as its occlusogingival dimension.. The curvature ofthe arch in the edentulous region can be determined, so that it will be pos-

sible to predict whether the pontic(s) will act as a lever arm on the abutment teeth.. A thorough evaluation ofwear facets, their number, size, and location is possible when they

are viewed on casts. Excessive wear on occluding surfaces ofteeth usually results from a dishar-

mony between centric occlusion and cenhic relation.

1. lrreversible hydrmolloid or alginate is the material ofchoice to produce diagnos-tic casts.

2. Tray adhesive should always be used to prevent distortion at the time ofremoval.3. The greater the bulk that the alginate has, the more favorable the surface area:vol-

ume ratio and the lower the susceptibility to water loss or gain and, thercfore, unwanted

dimensional change.4. The tlay should be removed 2 to 3 minutes after gelation.

5. The irnpression should be rinsed and disinfected with glutaraldehyde oriodophorbe-fore pouring.6. Pouring with ADA type IV or V stone is recommended.

7. Do not disturb poured impressions until they are set, the time varies between 30 and

60 minutes depending on which type ofstone is used.

*** This is false; the portion ofthe pontic approximating the ridge should be as conv€x as pos-

sible.

Pontic design and selection directly impact periodontal health. Pontics should contact kera-

tinized attached tissue and rest passively, free ofpressure, to prevent ulcerations and plaque

buildup. Pontic designs with concayities (such as the saddle-shaped pontic), are difiicult to

clean because oftbe depression on their inner surface is inaccessible to conventional methods

oforal hygiene. Egg- or bullet-shaped pontics are the easiest to clean because they are con-

vex in all aspects and contact the residual ridge at a single point.

Most important: Whatever pontic is used, it must be properly designed to prev€nt an un-

healthy response to the underlying ridge mucosa. The pontic must:

. Be nonporous, smooth, and have a polished surface

. Make passive pinpoint contact with the gingival tissue

. Not be concave in two directions

. Be readily cleanable by the patient

. Be narrow€r at the expense of the lingual aspect of the ridge

. Be on as straight a line as possible between the retainers to prevent any torquing ofre-tainers or abutnents.

Important: Excessive tissue contact has been cited as one ofthe major causes of failure offixed bridges.

Glazed porcelain, polished gold, unglazed porcelain, and polished acrylic are prefened inthat order for their acceptability to the soft tissue.

. J: I

.l:l

. 1:2

.l:l

a8Cop)nght @ 201 1,201 2 , D€ntal Decks

. Sodium pyroborate

. Alum

. BoraK

. Silica

49Coplright O 2011,2012, Dental Deck

This high a ratio is rarely achieved, however, and a ratio of 2:3 is a more realisticoptimum. A ratio of l:1 is the minimum ratio that is acceptable for a prospective abutment

under normal circumstances.

The crown-to-root ratio alone is not adequate criteria for evaluating a prospective abu!ment tooth. Root configuration is an important point in the assessment ofan abutment's

suitability from a periodontal standpoint. Roots that are broader labiolingually than they

are mesiodistally are preferable to roots which are round in cross section. Multi-rootedposterior teeth with widely separated roots will offer better periodontal support than

roots which converge, fuse, or generally present a conical conhguration. Single-rootedteeth with an irregular configuration or with some curvature in the apical third ofthe rootare preferable to the tooth which has a nearly perfect taper. Root surface area of the

prospective abutments should also be evaluated.

All ofthe following are factors in fixed bridgework design:. Root configuration. Crown-to-root ratio. Axial alignment of teeth. Length ofthe lever arm (span) Note: R€placing three teeth is maximum!l!

Remember: Parallelism ofabutment preparations is best determined by the long axis ofthe DreDarations.

Soldering flux dissolves surface oxides and allows the melted solder to wet and flow onto theadjoining allow surfaces. It is composed of sodium pyroborate (5 5%.), borax (35%.), and sil-rca ( 10%) .

In addition to the usual reducing and cleaning agents incorporated in a flur, a flux used forsoldering stainless steel or cobalFchromium alloys also contains a fluoride to dissolve thepassivating film supplied by the chromivm (chromium osidey'lz). The solder will not wet themetal $ hen such a film is present. Potassium fluoride is the most common agent.

Soldering is thejoining ofmetal components by a filler metal, or solder, which is fused to eachofthe pans beingjoined. To be biologically and mechanically acceptable, a solderjoint shouldbe circular in form and occupy the region ofthe contact area. The strength ofthe solderjointis increased by increasing the height ofit (as opposed to the wldlr. Not€: The recommendeddistance /i|ldrlr/ between the parts to be joined should be 0.25 mm.

Cleanliness is the prime prerequisite ofsoldering. Corrosion products, such as oxides and sul-tides that are present as a result ofthe casting process, interfere with bonding. Flux is placedon the surfaces to be soldered before they are heated. When it melts, the flux displaces gases

and removes conosion products by either combining with them or reducing them. The fluxin tum is displaced by the solder, which can now form an interface with and bond to the sur-face being soldered.

Note: Antiflux is a material used to outline the area to be soldered in order to restrict the flowof solder. The most common antiflux is a soft graphite pencil. Iron oxide (rouge) may alsobe used.

. The saddle-ridgeJap pontic

. The sanitary ftygienic) pontic

. The modified ridge-lap pontic

. An ovate pontic

. A conical pontic

50

Cop}tghr O 20ll-2012 - Denlal Deck

. The first statement is true; the second statement is false

. The first statement is false; the second statement is true

. Both statements are true

. Both stalements are false

5tCoplright O 20ll 2012, Dental Decks

The pontic is the suspended member ofa fixed bridge that replaces a missing tooth. Thistooth substitute must provide patient comfort, convenient contours for hygiene, and be

esthetic, if indicated.

Most Common Pontic Designs:. The sanitary @1,glenic) pontic design leaves a space between the pontic and the ridge.

Is most commonly used where esthetics are not important (nonqppearance zone, pos-terior mqndible). Convex in all areas.. The saddle-ridge-lap pontic design looks most like a tooth. Covers the ridge labi-olingually with a large concave contact. Impossible to clean, should not b€ used.. The modified ridgeJap pontic design uses a ridge lap for minimal ridge contact.

Gives the illusion ofbeing a tooth, but possesses all convex surfaces for ease ofclean-ing. This design is the one of choice for pontics in the appearance zone (where es-

thetics are important) for both maxillary and mandibular bridges.

Conical pontic: rounded (rop) and conical (bottom). Suited for molars without esthetic re-

quirements (in non-appearance zone).

Olat€ pontic: a sanitary substitute for saddle-ridge-lap design. Set in the concavity oftheridge hllicl is eilher ptesent or surgically made)that gives the appearance that it is grow-

ing from the tooth.

Remember: The faciolingual dimension ofthe occlusal portion ofpontics is determined

b1 the faciolingual position ofthe opposing centric holding contact areas

"t li.rcasins a cement's po$dcr,lo,liquid ratio decrcases thc solubility ofrhe ccmcnr.

Lutins agents /.prrdrrt:. Zinc phosphaae cement: onc ofthc oldesr and most widcly uscd ccmcnts, zinc phosphatc ccmcnt is thc stan-Jrd rlirinst $hich nc$ ccmcnts arc mcasulcd. Advantages: Iong rccord ofclinical acceprability, high compres-.:': strcngth. acccptably thin film thickncss. Disadvantages: low initial pH which may lcad to poslccmentation.:rr:trr rtr'. lack ofan abilily to bond chcmically to tooth structure and lack ofan anlicariogenic cflcct.lmportant:Z:n. phosfhatc ccmcnt is mixcd using thc "frozen slab" rcchniquc which grcarly cxtcnds thc working timc fb.t,J ' .ak h as 340'i;). Note: Tlc pH of ncwly mixcd zinc phospharc ccmcnt is |ndcf 2 ( tbo lalers ol vtnish m sl;.)ep!ieloraftlertoprotectthepulp)blJtnscslo5.9within24boursandisncarlyneutralat.l8hours.Thcfilmra:.kn.ss ofzinc pbosphatc is about 25 !rm-. Zinc pohcarbor]late cement: also known as zinc polyacrylarc ccmcnq was one of the first chemically adhe-site denial mate.ials. Thc adhcsivc bond is primarily to cnamcl although a wcakcrbond io dcntin aiso forms. This:. Ju. ro rhe faci that bonding appcars lo be the rcsult ofa chelation rcaction bcrwccn the carboxyl groups of rhc.J:x.nt and calcium in thc tooth structure; hencc, tlrc more highly mincmlizcd Ihc tooth structure, rhe sronger the:{nd.\drsntsges:kindlothepulp,chcmicallybondslotoorhstrxchrre.Disadvantagestshortworkingtimc,rc,;urrss scparalc tooth conditioning stcp prior to ccmcnlation. Note: il is more viscous whcn mixed and has a shorle.\rrking timc than docs zinc phosphate cement.

. Class ionomercement: Advantages: chemical bond ro cnamcl and dentin, anticariogenic cflcctlrcleases Iu,,rr,1r. cocllicicnt oftbcrmal cxpansion similar to that oftooth structurc, high comprcssivc strcngth, low solubil-:n Disadvantages: low initial pH which may lead to postccmentation scnsiriviry. scnsirivity ro both moisturc.onramination and dcsiccation. Notet Its mcchanical propcrties arc supcrior to zinc phosphatc and polycarboxy-

. Resin-modified glass ionomerluting agents; have propcnics similarto glass ionomcrccmcnts. but have higher5trenglh and lower solubility. Note: Thcy should not bc uscd wilh all-ccramic rcstorations dues to rcports ofcc-r3nlic fracturc, most likcly thc rcsult ofcxpansion from watc. absorprion.

. Resin luting agentsr arc unfillcd resins that bond to dentin, which is achicved with organophosphonatcs, /2-1,)-dro]reth\ I ttrcthacrylate IHEMAII, or 4-mcthacryloyloxycthyl trimellirarc anhydridc (4-Mf,TA). Advanrrges:hr!h comprcssivc strcnSth, low solubility. Disadvant.ges: irritating cfl'ects on thc pulp, high film thichcss p -?J1]r'l. Note: As a gcncml nrlc, rcsin cements are thc bcst choice for luting ccramic rcstorarions_

Important: Thc film thickncss at thc margins shouid be minimizcd to rcduce the solubility of the luting agenr.Tl.ough c|rcful tcchnique, a marginal adaptation below l0 pm can bc obrained consistcntly. Noter Factors that in,.r.asc the cement spacc for crowns include (l) thc usc ofdic spacers (2.)incrcased expansion ofthc investmcnt mold.

. Zinc phosphate

. Zinc polycarboxylate

. Glass ionomer

. Resin-modified glass ionomer

Coplrighr O 201 l-2012 - Dental Decks

. Shoulder

. Shoulder with a bevel

. Chamfer

. Bevel or feathered edge

Coplright O 201 I -20 12 - Ddtal Decks

Ide.lMaterial

ZincPoly-

crrboxylete

GlasrIotromer

Resin-modified

GlassIonomer

Resinlutingrgents

Film thickness(rn)

Low <25 <25 <25 >25 >25

Long 1.5-5 L75-2.5 2.3-5 2-4 3-10

Setting time(nt r)

Short 5-14 6-9 G9 2

Pulp irriration Low Modelate Low Hieh Iligh Hich

Solubility High High Low Iligh to veryhigh

Microleakage Very low High High to veryhigh

Low to very low lligh to veryhigh

Retenlion High Mod€rate Low to moder-ate

Moderate to high High Moderate

l. Cemenrs do not rdd to the retentive chamcteristics ofa crown. Ccmcnts act by increasing the fric-tional rcsistance between tooth and restoration. Thc ccmcnt prcvcnts two surfaccs from sliding. Al-though they do not prcvcnl onc surtacc from bcing liftcd from another2. A toolh should bc wiped dry before cementation ofa crown as opposcd to drying the tooth with al-

cohol and warm airto dccrease the possibility ofpulp damagc.

3. Always apply cement to both the rcstoration and tooth.4. One way to rcducc thc potential for post-cementation sensitivity with zinc phosphate and Slass-ionomcrccmcnts is to use a resin based descnsitizeron thc prcparcd tooth p.ior to luting.5. Cement film thickncss is dependent upon powder-to-liquid ratio, powdcrparticle sizc, and pressure

gencratcd dunng seating of the casting.

However, in practice this finishing line is difficult to read on both the impression and die and may lead

to inaccurate extension and also distortion ofthe wax pattem, and subsequent casting, as a result ofthethin wax. It also offcrs the least margid.l strength to the casting-

The chamfer prepamtion is the preferred linishing line for cast gold restorations. The resultant cast-

ing has sufficient marginal strength; at the same time it allows the slidingjoint at its periphery to mini-mize the gap between the tooth and preparation, thus rcducing the thickness of the cement. Awell-prepared chamfer margin combines the advantage of an easily definable margin, on both the im-pression and die, with minimal tooth prcparation.

The shoulder preparation is the finishing line of choice for porcelain jacket and tll-ceramic crownpreparations, The edge strength of porcelain is low; therefore, a butt joint is required. The shoulder

provides resistancc to occlusal forccs and minimizes stresses in the porcelain. The margin can be easily

read on both the impression and die. The main disadvantage is that any inaccuracies in the fit ofthecro$n Nill be reproduced at thc margin, resulting in an increased thickness ofcement.

Tle should€r with a bevel allows a sliding fit to occur at the margin and therefore may be used on thc

proximalbox ofinlays and the occlusal shoulder ofthe mandibular three-quarter crowns ltmayalsobeused for the labial margins ofmetal-ceramic crowns. Providing these margins are placedjust in the gin-

gival crevice, little display ofmetal will be noted.

Four Tlpes of High-Gold Alloys:

l. ADA t-ype I highest gotd content, 83o/o noble metals. Intended for small inlays. Easily bumished

due to high ductility.2. ADAtype II: $eatcrthan 78olo noble metals. Intended for larger inlays and onlays. Can also be bur-

nished.

3. ADA type UI: greater than 75o% noble mctals. Intended for onlays and crowns Capable ofbeingheaFtreated.4. ADA type Iv: greatcr than 7570 noble metals. Intended for bridges and removabJe partial dent-

ures Also capable ofbeing heat-treated. Hardest ofhigh-gold alloys.

. The diameter of the sprue pin should be equal to or greater than the thickest portionof the pattem

. The diameter of the sprue pin should be equal to or smaller thar the thickest portionofthe pattem

. The diameter of the sprue pin should be equal to or greater than the thinnest portionofthe pattem

. The diameter of the sprue pin should be equal to or smaller than the thinnest portionofthe pattem

54Cop'.righr O 2011-2012, Dental Decks

.Akey

. A keyway

. A kev and a keyrvay

Copltigh O 201 l'2012 - Dental Decks

The sprue is a small diameter (10-12 gauge) pin made ofwax or plastic.

A 10 gauge sprue pin can be used on most patterns, while the l2 gauge is used on smallpremolar pattems. The sprue should be attached to the wax pattem at its point ofgreatestbulk and at an angle (45) that will allow the incoming gold to flow freely to all portionsof the mold. Spruing at a thin area of the pattem can produce the same result as using asprue that is too small

-shrink back porosity. This is caused by turbulence in the flow

ofthe molten metal which in tum creates a shrinkage void, or suck-back porosity.

Note: Low investment permeability and insullicient wind-up of the casting machine

may also cause this shrink back porosity.

A nonrigid connector is a broken-stress mechanical union ofretainer and pontic, instead

ofthe usual rigid, solderjoint.

The most commonly used nonrigid design consists ofa T-shaped key that is attached to

the pontic and a dovetail keyway placed within the retainer. The path ofinsertion ofthekey into the keyway should be parallel to the pathway of the retainer not involved withthe keyway.

Its use is restricted to a short span bridge, replacing one tooth. It is indicated when re-

tainers cannot be prepar€d to draw together without excessive tooth reduction. Pros-

theses rvith nonrigid connectors should not be used ifprospective abutment teeth exhibitsignificant mobility.

Important: When abutment teeth are in normal alignment and have good bone support

tcanine and /irst molar.r), the connectors of choice are solder joints.

. 90 degree, 1.0 mm shoulder

. Bevel

. Chamfer

. 45 degree, .25 mm shoulder with a bevel

56

Copraight e 20ll-2012 - Dental Decks

. To remove hyperplastic gingival tissue where it has proliferated into preparations orover crown margins

. In place of gingival retraction cord where substantial attached gingiva is present

. Where attached gingival tissues are thin, or where an underlying dehiscence issuspected

. For crown-lengthening procedures prior to fabricating a provisional crown

57

CopFiglu O 201 I -2012 - Dental D€cks

Unlike thc metal-ceramic .estoration, which will accept any marginal design (a bevel, chamfer, orshoulder), marginal tooth prepamtion for the all-ceramic crown or porcelainjacket crown mustbe a shoulder foptrn ally 90 degrees and 1.0 mm).

There are indications and contraindications for all-ceramic crowns, and violating these will com-promise the success of a restoration. All-ceramic crowns generally are accepted to be superioresthetically, but their lack ofa metal substructure makes them inherently weak, As a result, they

are rarely indicated for use on posterior teeth, and are not indicated at all for anterior teeth in aClass III edge-to-edge relationship, where the occlusal forces can subject them to fracture. There

are few acceptable instances where all-ceramic crowns may fuuction as irxed partial denture abut-

ments, such as during the replacement ofanterior teeth when a favorable anterior guidance occlusal

scheme exists.

The main reason for the use of porcelain jacket crowns and all-ceramic crowns is superior es-

thetics. These tlpes of crowns have the capability to mimic the optical properties ofthe natural

tooth. However, the guidelines for usage, such as tooth preparation, are more critical and in gen-

eral more complicated than for the metal-ceramic restorations. ln general, it is advisable to use

these more esthetic crowns only in the anterior segment, where esthetics is the dominant factor.

Dilferent materials used in the fabrication ofa full crown require dilferent marginal designs:. All-ceramic or porcelain jacket crowns

-shoulder. \Ietal ceramic with porcelain extended to maryinal edge -shoulder. Vetal ceramic with metal collars shoulder with beYel or chamfer

. Full gold crown -

bevel (feather edge) or chamfer

*** This is a contradiction to electrosurgery -gingival

r€cession may be marked following the use ofthis p.ocedure.

Objectives of electrosurgery:. Coagulation. Hemostasis. Access to cavosurface margin.Reduction ofthe inner wall ofthe gingival sjulcts (removal ofa thin layer ofcrevicular gingiwl tis-

sue)

Electrosurgery, although considered by many to be a more radical means ofrefiaction ofgingival tis-

sues. is an acceptable method. It functions by passing small curents ofelectricity through the gingival

rissue, causing the cells to desiccate, or scorch. Electrosurgery usually results in sorne delayed healing

because ofthe lack of proper clot formation. It is very good at stopping hemorrhage. Note: Too low a

current in an electrosurgical electrode can be detected by tissue drag.

Important points about elechosurgery:. Use pfastic instruments (nirror explorer, erc) instead of metal to prevent buming and tissue de-

struction of the surface contacted.. Rapid, single, light strokes should be used with the electrode. 5 secotrd intervlls should be used when cutting. The electrode should not contact metallic restorations or tooth skucture (may cause ineversiblepulp damage).

Great care must be employed when performing electrosurgery as the potential exists forserious damage to the PDL and surrounding bone, resulting in loss ofattachment ofthe tooth.

Note: elechosurgery is not recommended for thin attached gingiva.

Important: Electrosurgery is contrai[dicated in patients using medical devices such as cardiac pace-

make$, a trancutaneous electrical nerve stimulation (TENS) :urit, or an insulin pump, and in patients

with delayed healing.

if you look at bfue color obiects (drupes, charts, wall-color or anyothet object arcund,) while selecting the shade, it will help to

accentuate tbe ability to discriminate yellow shrdes.

. The first statement is true; the second statement is false

. The first statement is false; the second statement is true

. Both statements are true

. Both statements are false

58

Coplright O 201 l-2012' Dntal Dech

. Equate

. Contract

. Expand

. None ofthe above

59

Cop)'right O 201 I 2012 - Denial Decks

Shade selection sequence:. Use the same shade guide as given by the manufacturer. Match the shade before you do any preparation ofthe tooth. Remove all distractions (e.g., Iipstick, dark glasses, heavy make-up, etc.). Quick rubber cup and paste prophylaxis can make shade selection more accurate. Position yourselfbetween the patient and the light source. When observing, do not gaze for greater than 5 seconds at a time. Prolonged gazing

decreases the ability to discriminate colors and shades. Proceed by process of elimination. Exclude first, shades which are too light or dark. Half-closed eyes can increase the sensitivity of retinal rods to better choose the

"value" ofthe color

Remember: "Blue" fatigue accenhrates "yellow" sensitivity. This means that ifyou lookat blue color objects (drapes, charts, wall-color or any other object around) while se-

lecting the shade, it will help to accentuate the ability to discriminate yellow shades.

Four mechanisms play a role in producing an expanded mold and thus compensating forthe solidification shrinkage ofthe alloy.

l. Setting expansion: results from normal crystal growth. In air, it is about 0.4% but itis partially restricted by the metal investment ring.

2. Hygroscopic €xpansion: employed to augment normal expansion by allowing the

investment to set in the presence of water. It is said that this water will replace the

water used by the hydration process and thus maintain the space between the growing

crystals. Allows continued expansion outward rather than restricting them. This

expansion ranges from 1.2%o to 2.2o/o.

3. Wax pattern expansion: the wax pattem is warmed while the investment is stillfluid. The heat may come from the chemical reaction of the investment itselfor the

s'ater bath in which the casting ring is immersed.

4. Thermal expansion: occurs when the investment is heated in the bum out oven. Italso serves to eliminate the wax pattem and to prevent the alloy from solidifing be-

fore it comoletelv fills the mold.

. Mesiobuccal margin is positioned slightly distal to the middle ofthe buccal surface

. Distobuccal margin is positioned slightly mesial to the middle ofthe buccal surface

. Mesiolingual margin is positioned slightly distal to the middle ofthe lingual surface

. Distolingual margin is positioned slightly mesial to the middle ofthe lingual surface

60Cop)right @ 201l-2012 - D€nbl Decks

. Predominantly glass

. Particle filled glass

. Polycrystalline

61

coplrishr @ 201 l-2012 - Dertal Decks

A partial crown is a cast restoration made entirely from metal and covers more than halfbut not all ofthe tooth's clinical crown. A partial crown is named according to the frac-tional amount ofthe clinical crown it covers. Examples are the half, three-quarters, foul-fifths, and seven-eighths crowns. In most instances, the facial surface ofthe tooth is notdisturbed for esthetic reasons.

The seven-eighths crown design is especially effective either as a single tooth or an abut-

ment restoration on maxillary molar teeth where both proximal surlaces are involved as

well as the distal buccal suface ofthe tooth. In many instances, the mesio-buccal cusps

of maxillary first and second molars can be preserved for esthetics and still provide ade-

quate extension to include extensive areas ofdestruction.

Seven-eighths crown:. It can be used on any posterior tooth.Esthetics is good since the veneered distobuccal cusp is obscured by the mesiobuccal

cusp. Distobuccal finish line is easy to access, which makes preparation easier to do. It also

makes cleaning ofthe margins easier for the patient. \4ore coverage than the standard 3/4 crown which improves its resistance. Especially useful when the distal surface has caries or decalcification. Serves as an excellent abutment for a bridse

Metal ccramic restorations have been available for more than three decades. This type ofrestora-tion has gained popularity from its predictable perlomance and reasonable esthetics. Despite its

success, the demand for improved esthetics and the concems regarding the biocompatibility ofthemetal has lead to the introduction ofall-ceramic restorations.

Two concepts help in simplifying the understanding of dental ceramics: First, ceramics fall into

three main composition categoriesl. Predominantly glass. Particle filled glass. Polycrystalline

Second, ce.amics can be considered as a composite material, in which the matrix is a glass that islightly or heavily filled with crystalline or glass particles.

Predominantly glass: have a high content ofglass making this type of dental ceramic highly es-

thetic. This type is the best ir mimicking the optical properties ofenamel and dentin. Optical ef-

fects are controlled by manufactures by adding small amount of liller paniclcs.

Particle-filled glass; filler particles are added to the glass matrix to improve the mechanical prop-

enics. Fillcrs can be crystalline particles ofhigh-melting glasses.

Polycrystalline: this type ofce.amic contains no glass. Atoms are packed into regular crystalline

arrangement making it toughcr and less susceptible to crack propagation. lt is important to under-

stand the lact that highly esthetic ceramics are predominately glass, and ceramics that exhibit high

strength are generally crystalline.

Note: It is important to understand the fact that highly esthetic ceramics are predominately glass,

and ceramics that exhibit high strength are generally crystalline.

. Nickel

. Cobalt

. Chromium

. Silver

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Cop).righl O 20ll-2012 - Dental Decks

CS tr'irrad Drtrs*lr,

AII of the following are resins used for fabricating provisionalrestorations .EXClgPl one. Which one is the EXCEPTIOM

. Polymethyl methacrylate

. Polyethyl methacrylate

. Pol)'vinyl methacrylate

. Polyacryl methacrylate

. Bis-acryl composite resin

. Msible light-cured (ltLC) urethane dimethacrylate

CoplriShr q 20ll'?012 Dfrtal Decls

*** Silver is a precious metal.

Metals are classified as noble elements based on their lack of chemical reactivity. Thenoble metals include gold, platinum, palladium, and other inert metals. Alloys with less

than 25olo noble elements are called base metals. Note: Silver is not considered noble;it is reactive and improves castability but can cause porcelain "greening."

Remember: Noble metals are precious, but not all precious metals re noble (i.e., sil-ver).

Base metal (nickel, chromium and cobalt) alloy advartages are principally found onlyin their strength and low density.

As compared to T)?e IV gold alloys, base metal alloys have:. A higher resistance to deflection in thin segments. A lower yield strength. A higher modulus ofelasticity. A lower specific gravity. A much higher melting temperature (230CF to 260CF)

Remember: The nickel in the composition ofbase metal alloys is responsible for ductil-iq of the alloy. It is also measured as a percentage of elongation and determines howmuch margins can be closed by bumishing. Chromium produces a passivating film forconosion resistance and cobalt increases the rigidity ofthe alloy.

Provisional restorations:

Requirements:. Provide pulpal protection. Positional stability. Occlusal function. Easily clcancd margins. Strength and retention. Esthetics

Resins for prorisional restorations:. polvmelhvl methacrylatc. Polvcthyl mclhacrylatc

' Pollinyl mcthacrylatc. Bis-acryl composite rcsin. \'isiblc lighccurcd /,/ZC) urethane dimethacrylatc

\l€thods of fabric.tion:. Prefabricated: Uscd for single tooth restoration (e.g., anatonic netal crown fon,$, deu celuloid shells andt.roth ol orcd polr@rbonate crovns).. Custom-made: uscd for single and multi -unit lixed b.idges-There are a variety of tcchniqucs for f'abricating thcmould used to form the outcr surface ofthc custom provisional rcstoraljon /i.e., take an inpression prior to prcpar-ing te€th fiIh algilnte. elastomenc i tpression material or use tle .liagnostic &st ond clear lhetmoplastic resinatrix [wcuunt fon'ing machineJ).The innc' s[rface will be providcd by the preparation.

Provisional restorations can be classified by the t€chnique olfabrication used:. Direct technique: is done on the actual prepared leeth in the mouth. Disadvantagcs includc: potcntial tissuctrarma, poor marginal fit, and prolonged chairside time..Indirecttechnique: is done on the cast outside thepatient's mouth. Advantages include: no tissuc fauma, good

marginal fit, and minimum chairsidc timc.. Combination techniqte (inrlirect-direct): advzntages include: reduced tissue trauma, rcasonablc marginal fit,and reduced chairside timc.

Note: Thc provisional rcstoration is cemcntcd in with Temp Bond.

. Type I

. Type II

. Type III

. Type IV

54

Copyn8hr O 20ll-2012 - Denkl Decks

In mixing dental stone, why should the powderbe sprinkled onto the water in ths bowl?

. The addition ofpowder prevents the mix fiom becoming exothermic

. This is not recommended; the water should be added to the powder

. This process results in better powder mixing and reduced chance for air bubbles

. The powder is added to the water to avoid using more than one bowl

Cop)riglr @ 2011-2012 - Dental Decks

Type I Gypsum: 'lmprcssion Plastca'

. Comprcssion strcnglh: 580 psi

. Pcrccntagc ofcxpansion: 0.15%

. Uscsi not uscd much tod^y li.e., solderillg it leres)

llTe lf Gyps[rn: "Modeling Plastca'. Comprcssion strength: 1300 psi

' Pcrccntagc of cxpansion: 0.307;. Uses: orthodontics diagnostic casts

Type lll Gypsum: "Dcntal Stone"

. Compression strcngihr 3000 psi

. Pcrccntagc ofcxpansion: 0.20%

. Uscs: diagnostic casts, opposing arch casts, and removable prosthodontics

. Also called: "Ycllow Stone", or "Microslonc"

Ttpe IY Glpsum: Dic stonc. Low Expans;on". Conprcssion srcngth: 5000 psi. Pcrccntagc ofexpansioni 0.10%. Lscs: dics for crown, bridg€, and implants. {1so callcd: Dcnsitc or lmprovcd Dcntal Stonc"

Ttpe \. Gtprum: Dic Slonc, Hjgh Expansion"

. f..mpressron strcngth; 7000 psi

. P.rc.nlagc ofexpansion: 0.10%

. LiJs: di.s for crown and bridgc

. \1io callcd: "DieKccn"

Dental gypsum products are made up of hemihydrate particles whose size' shape, and

porosity differ for each material. These gypsum-based powders require differentamounts ofwater for mixing because the different particle shapes produce different pack-

ing efficiencies that affect the amount ofexcess water required for making a suitable mix-ture.

llixing:. lVater/powder ratio: the water/powder ratio is an important factor in detenniningphysical properties. When a high proportion ofwater is used, the powder particles are

farther apart. This results in less expansion with a retarded setting time and a weaker

product. Dental plasters generally require about twice as much water compared to

stones. Plaster has a higher setting expansion thar does stone.. \\'ater temperature: generally, the cold€r the water, the longer the setting time. Spatulation: rapid spatulation for a time equal to normal hand mixing for 1 minute

accelerates setting time and produces greatest strength. Do not spatulate to the point

$ here the mixture starts to harden. This will produce a cast that is much weaker.. Accelerators and retarders (modifiers):

- Retarder: borax. sodium citrate- Accelerators: gypsum, potassium sulfate, NaCl 28%

Remember: The setting expansion ofany gypsum product is a function ofcalcium sul-

fate dihydrate cystal growth. Some is the result of thermal expansion.

. Beta-hemihy&ate and dental stone has gamma-hemihydrate

. Alpha-hemihydrate and dental stone has beta-hemihydrate

. Gamma-hemihydrate and dental stone has beta-hemihydrate

. Beta-hemihydrate and dental stone has alpha-hemihydrate

66Cop"iSh O20ll-2012 - Dental Decks

Dental plaster rnd stone lre vibrated after mlxlng to:

. Minimize distortion

. Reduce setting time

. Eliminate air bubbles

. Increase the setting time

67Cop)'righr O 20ll'2012, Dertal Decks

The principal constituent of the dental plasters and stones is the calcium sulfatehemihydrate. Depending upon the method of calcination, different forms of thehemihydrate can be obtained

-either alpha or beta hemihy&ate. The beta-hemihydrate

is more popularly known as plaster ofParis, and these crystals are characterized by theirsponginess and irregular shape in contrast to the alpha-hemihydrate f.r/one) crystals!which are more dense and have a prismatic shape. When the alpha-hemihydrate is mixedwith water, the pro dtrct obtained (dental stone or die stone) is much stronger and harderthan that resulting from beta-hemihydrate (plaster). The chiefreason for this differenceis that the afpha-hemihydrate powder (stone) reqrires much less gauging water when itis mixed than does the beta-hemihydrate. The beta-hemihydr^te Q)lqster) requires morewater to float its powder particles so that they can be stirred, because the crystals are

more irregular in shape and are porous in character.

Note: All glpsum products that are reacted with water form calcium sulfate dihydrateas a reaction Droduct.

Using a vibrator when pouring models helps to eliminate ar bubbles (trapped air).Thisproduces a more accurate, usable model. Another way ofpreventing entrapment ofair isto place the proper amount of water in the mixing bowl first and then sift the modelplaster or stone into the bowl. When mixing dental plaster or stone, any ofthe following$,ill cause the gypsum product to set faster

-incr€ased spatulation, a lower water-pow-

der ratio, and using a mixture of water and ground-up set g'?sum particles to mix withthe plaster or stone.

Once the impression is poured, it should be allowed to harden for 45 minutes to I hour(or until cool to the touch) before removing the cast from the impression.

Casts can be disinfected by immersion in a l:10 dilution of sodium hypochlorite for 30

minutes or with iodophor spray.

If nodules of stone appear in the occlusal pits ofa stone cast, it is most likely due to the

entrapment ofair during the insertion and seating ofthe tray.

lrJote: All types of gypsum products are weaker in tensile strength than compressive

strength.

. Heating g)?sum in an open vessel at 150'C -160'C

. Heating gypsum under steam pressure in an autoclave at 120'C -150.C

. By boiling gypsum in a 30olo aqueous solution ofcalcium chloride and magnesiumchloride

68

Copr.right C 201 l-?012 - Dental Decks

. Shorten the gelation time

. Make the mix unusable

. Lengthen the gelation time

. Not affect the gelation time

69Cop)'right O 201l-2012 - Dental Decks

' Dr. Lozier r€quested that you mix alginat€ and take an imprcssion,Whil€ measuring the water, you got involved in a conversation withyour patient and did not notice how cold it was. This oversight will:

liotel

*** This process produces particles that are porous and inegularly shaped. Note: It isthe weak€st gypsum product.

Heating gypsum under steam pressure in an autoclave at 120'C - 150'C produces dentalstone. This process produces particles that are uniformly shaped and less porous.

Boiling glpsum in a 30o% aqueous solution olcalcium chloride and magnesium chlorideproduces high strength (improved) die stone. This process produces the least porousand strongest particles.

All gypsum products come ftom the mineral gypsum, which is the dihydrate form ofcalcium sulfate. During heating, (the manulircturing process), water is lost and g)?sumis converted to the hemihydrate form of calcium sulfate (p owder). When water is added

to the powder, a chemical reaction takes place and the hemihydrate is converted back tothe dihydrate form of calcium sulfate.

l. When mixing gypsum products always sprinkle the powder into the water.

This results in better powder mixing and reduces the chance for air bubbles.

2.When gypsum products are mixed with water, heat is given ofl This is calledan exothermic reaction.3. Exposure ofa stone cast to tap water should be minimized because erodingofthe cast will result.

***The best method to control the gelation time ofalginate impression materials is to alter the tem-

pemture ofthe water used in thc mix. The higher the tempemture, the shorter lhe gelation timc,the lower the temperature, the longer the gelation time. The mix is usable regardless ofwater tem-

penture as long as there is adequate ['orking tim€.

Changing thc water/powder ratio and the mixing time will alter the gelation time, but thesc mcth-

ods also impair ce ain properties ofthe matcrial. Too little ortoo nuch waterwill weaken the gel.

Undermixing may prcvent the chemical action from occurring evenly; overmixing Inay break up

the gcl.

Calcium sulfate (/re reactol in alginate), is not so soluble in watcr that is entircly consumed be-

fore gelation is con'lpleted. Therefore, the set mass becomes an entanglcment of calcium alginate

fibrils around residual sodium alginate sol, filler and water. The residual sodium alginate has thc

nasty habit ofreadily giving up water /.t),reresis) or gaining water (imbibitiotl). For accurate results,

thc cast should be poured imrnediately.

. L When taking an alginate impression fo. a partial denture, it is best to apply somc al-

\ores ginate directly on the teeth to eliminate bubbles and saliva from the rest seat prcparations.

2.lnaccuracies in imprcssions can be caused by fracture ofthe fibrils during gelation.' .3. Tray adhesivc should ahvays be used to prcvent distortion at the time ofremoval.

4. The greater the bulk lhat the alginatc has, the more favorable the surface area:vol-

ume ratio and the lower the susceptibility to water loss or gain and, therefore, unwanted

dimensional change.

5. The tray sltould be removed 2 to 3 minutes after Selation.6. The impression should be rinscd and disinfected with glutaraldehyde or iodophorbefbre pounng.7. Pouring with ADA type lV or V stone is recommended.

. Irreversible hydrocolloids

. Polysulfides

. Polyethers

. Condensation silicones

. Polysulfides

. Condensation silicones

. Polyvinyl siloxanes

. Polyethers

70

Copyright O 201 1 ,201? - Dertal D€cks

71

Coplright O 20ll-2012 - Denial Deckr

Polyether materials are dimensionally unstable in the presence of moisture. These materials are the mostrigid frt,r?s, and most dillicult to remove fiom the mouth. Note: Whcn removing the impression, break the

seal and rock slightly to prevent tearing.

Composition of polyether impression materials:. Base: amiDe teminated polyether polymer. Cross-linking agent: an alkyl-aromatic sulfonate. Catalysrs: glycol-based plasticizers. Filler: colloidal silica

*** Polyeth€$ are two-component materials. The base includes apolyether, silica filler and a plasticizer Theaccelerator contains a crossJinking agent. When mixed, a nrbber is formed by a cationic polymerizationprocess. Cationic polymerization is very similar to addition polymerization, except that instead ofa free rad-

ical, a cation fporirlyc ior, is the reactive molecule. \o reaction by-product is produced. Polyethers have ex-

cellent dimensional stability. They ar€ also t.uly hydrophilic, resulting in superior wettability.

Important regarding polyeth€r impr€ssion materials:. \\'arer, saliva, and blood affect polyether matenal. Added moistur€ will increase the impression's marginal discrepancy

These materials record surlace detail well and have excellent elastic propenies but a low tear strength. They

arc less expensive ihan polyvinyl siloxanes fdddition silicones) ard polyethers.

Composition of condensation silicones:. Base: poly dimethyl siloxane. Cross-linking agent: alkyl ortho silicate or organo hydrogen siloxane. Catalyst: organo tin compott ds (e.g., titl octoate). Fillers: silica or calcium carbonate

\\'hv poor dimensional strbitity? The principal reaction, which takes place during setting ofthis material, is

a condensation reaction and hence called condensation silicone. It occurs by elimin tior (evaporation) ofeth) l or methyl alcohol. This is also responsiblc for shrinkage ofthe material and resultant poor dimcnsionalitabilit\'.

l. Reaclion is sensitive to heat and moisture f'eill reduce working snd setting times).

2. Do not mix initially by haod (allergic rcaction to catalyst may occur).

Take care not tobreak teeth whenseparating casls

. Excellentdimedsiolalstability whell dry

. Short settirg tirne

. Dimensionally stable ifmore lhan one cas! is poured

. Slable ev€n ifpoured 24hours after taking impres-aion

. Automix available

. Set material very stiff

. Difficult to removefrom mouth

. Tears easily

. Limited shelflife

. May adhere to teeth

. Demonstmtes imbibi-tions

. Unpleasant taste

. Short working time

. Most impr€ssion6

Wait 20 to 30minutes beforepouring lbr sbessrelaxauon to occur

Plea-sant to useShon s€tting time

. Hydtophobic

. Poor wettingr Low stability. Limited sbelflife. Tray requires special

adbesive. The material is more

flexible, so there ismore chance ofdistor-tion during removal

. Dimensionally unstable

. Sets quickly

. Excellent detailed reproduction

. Sets hard

. No shrinkage even ifstore for many days

72

CopFighr @ 20: l'2012 - D€ntal Decks

'\The popularity of agar impression m

^teriz.l Oevercible hyfuocalloid)

is timited by the: )

. Difficulty in pouring the impressron

. Poor reproduction ofdetail

. Need for special equipment

. High cost

73

Cop).riglft C2011,2012 - Dmtal D€cks

*** This is fals€; ZOE impression paste is dimensionally stable

ZOE impression materials were once very popular. Today, however, ZOE materials have been

replaced by newer materials, such as polywinyl siloxanes, condensation silicones and poly-ethers.

Components of ZOE impression paste:. Calcium chloride (CaCI): ftncttons as an accelerator ofthe setting time. Oil ofcloves: contains 70-850/o eugenol. It is sometimes used in preference toeugenol because it reduces the buming sensation in the soft tissues ofthe mouth.. Mineral or {ixed v€getable oil: plasticizer, aids in masking the action of eugenol as an

irritant. Resinous balsam: often used to increase flow and improve mixing properties. Rosin: facilitates the speed of the reaction which results in a smoother, more homoge-

nous mixThe setting reaction that occurs is a typical acid-base reaction to form a chelate. This reaction

can take place either in solution or at the surface of the zinc oxide particles. The chelate is

thought to form as an amorphous gel that tends to crystallize, imparting increased strength tothe set mass.

. --.... 1. The dimensional stability ofa zinc oxide-eugenol impressionis most likely tobe

..'Note{,; affected by failure to use a custom-made impression tray.' ',i*tl: 2 . The setting time of a zinc oxide-eugenol impression paste may be acc€l€rated by

adding a drop ofwater to the mix.3. The setting time of a zinc oxide-eugenol impression paste may be r€tard€d byadding inert oils (olive or mineral oils) during mixing.4. Ifthe paste is too thin or lacks body before it sets, a filler----such as a wax or an

inen powder (lanolin, kaolin, etc.) may be added to one or both of the originalpastes

The use of agar impression material does require special equipment. The rcproduction is excellent, and the im-

pression is easy to pour compared to elastome c imprcssion mat€rial.

Reversible hydocoltoid is an impression material that changes its physical state ftom a sol to a gel and then

back to a sol.

Composition of reversible hydrocolloids:. 85% water. l2'.I5r/. agar (agar is an organic substance deri|ed from seaweed)*** Traces ofbomx fbr rtrerglr), potassium snlfate (improves gvsum r&r/dce/ and sodium tetrabomte

Conditioning bath for reversible hydrocolloid:. Three compartments:

. The first bath is for liquefying the semisolid material. A specialwater bath called a "hydro-colloid conditioner" at212"F (100'C) liq\refies the material. After Iiquerying, the preset thermo-

stat cools the tempcrature to 150oF /65.5"C/ automatically.. The second bath becomes a storage bath that cools the matedal, readying it for the impression.

At this temperature, the tubes are waiting for use.. A third bath is kept at 110" F (43.3'C) for tempering the material aller it has been placed in the

trav

. Zinc oxide

. Calcium sulfate

. Potassium titanium fluoride

. Diatomaceous earth fsilrca)

. Potassium alginate

. Tri-sodium phosphate

. lt will be grainy

. It will tear easily

. There will be irregularly shaped voids

. It will be distorted

Coplright O 201 I -20 l2 - Denral Decks

75

Coplrighr O 2011,2012 - D€ntal Decls

Alginate materials (incversible h,vdt'ocolloid) are the most widely used impression ma-

terials. They are termed irreversible impression materials because they will not reverseto a sol once they react and become a gel. Indications: diagnostic casts, not suitable forfinal impressions. Examplcs: Ieltrate (Dentsply / Caulk), COE Alginare (GC Americal

. 50% (fillcr)

. 20nh (dissolres in u,alet ./brming the sol)

. 16o/a (reactot)

. 7rA lpla.ttici:er)

. 60A (inpror,es gJpsum sutJace)

. |V. (tetarder)

. DiatomaceousfsrTical

. Potassium alginate

. Calcium sulfate

. Zinc oxide

. Potassium fluoride

. Sodium phosphate

. Unstablc ---) immediate pour, single cast

. Tears casily

. Poor accuracy and surfacc detail

. High permanent defbrmation

. Low cost

. Straight forward technique

. Rapid set

Problem Cause

Grainy material r Improper mixing. Prolonged mixing. Undue gelation. Water/powder ratio too low

Tearing . Inadequate bulk. Moisturecontaminationr Premature remoratfrom mouth. Prolonged mixing

Inegularly shaped voids o Moisture or debris on tissue

Rough or chalky stone . Inadcquate cleaning of impresston. Exccss water left in impression. Premature removal of cast. Leaving cast in impression too long. lmproper man ipulation ofstonc

Distortion . Imprcssion not poured immediate ly. Movcment oftray during gelationo Premature removal lrom moult. Improper removal from mouth. Tray held in mouth too long fort with certain brantls)

. Polyether

. Polysulfide

. Reversible hydrocolloid

. Vinyl polysiloxane

76

Coplrighr O 201l-2012 - Dental Decks

. Polyether

. Polysulfide

. Hydrocolloids (reversible and irreversible)

. Polyvinyl siloxane

77copyright o 201 l -20 l2 - Denral Deck

Polyvinyl sifoxanes (addition silicohes.) are the most widely used and are the most accurate of the

elastic impression materials. They have less polymerization shrinkage, low distortion, fast recovery from

deformation and a moderately high tear strenglh. Most ofthe pol;vinyl siloxanes can be pourcd up toone week after impression making and are stable in most sterilizing solutions. Important; Tle sulfurin latcx glovcs and in ferric and aluminum sulfate retraction solution will retard the setting ofadditionsilicone materials. Also, addition silicones are temperature sensitive

-increases in temperature will

shorten the working and sefting times.

Composition of polyvinyl siloxanes /addition si[icones):. Base: silicone polymer. Catalyst: chloroplatinic acid. Filler: colloidal silica. Scavengers: platinum or palladium /acr as scavengers for the hydrogen gas releosed)

1. The addition reaction that occurs with pol''vinyl siloxanes is terminated with a vinyl group

\otes, and crosslinked with hydride groups activated by a platinum salt catalyst No reaction by-: products are developed, but hydrogen gas release may occur ifa reaction betwem moisture

and rcsidual hydrides ofthe base polymer occurs. The result is a cast with small voids iftheimpression is poured too soon after removal from the mouth.2- Stiffness ofthc matcrial makes removal ofthe trav difficult.

Delay pouring ofsome materials toallow thc release

ofhydrcgen gas

. Dimensional stabilig

. Pleasant to use

. Short setting time

. Automix available

. Hydrophobic

. Poorwetting

. Some materials releasehydrogen gas

. Hydrcphilic formula-tions imbibe moisture

- lowest to highest. alginate, agar, polysulfide, condensation silicone, poly'vinyl siloxanes,

polyether

- best to worst. polyvinyl siloxanes, polyether, polysulfide, condensation silicone,

hydrocolloids

- best to worst. hydrocolloids, polyether, hydrophilic pollnr'inyl siloxanes, polysulfi de,

hydrophobic pol)'vinyl siloxanes, condensation silicone

- best to worst. hydrocolloids, hydrophilic polyvinyl siloxanes, polyether, polysulfide,

hydrophobic pol)'vinyl siloxanes, condensation silicone

- most to least. polyether, polyvinyl siloxanes, condensation silicone, polysulfide,

hydrocolloids

- greatest to least. polysulfide, polyvinyl siloxanes, polyether, condensation silicone ,

hydrocolloids

. Polyether

. Polysulfide

. Reversible hydocolloid

. Pol)'vinyl siloxane

. Polyethers

. Polysulfides

. Silicones

. Irreversible hydrocolloids

7aCop)righr O 201l-2012 - Dental Dek

79

Coplright C 201l-2012 - Denial Decks

ReversibleHydrocolloid

IrreversibleIlydrocolloid Polysulfide

Conderrsador!Silicor.

PollainylSiloxane Polyether

Boil, temper,slore

Pourder, urater 2 pastes 2 pastes orpaste/liquid

2 pastes 2 pastes

E se of use Techniquesensitive

Good Fair Fair Excellent Good

PstientReactlon

Thermalshock

Pleasantcleln

Unpleasant,slarns

PIeasant,clea1r

Pleasant Unpleasantcleat

Erse ofRemoval

Very easy Very easy Easy Moderate Mod€rateto difficult

Difficult

WorkingTime (min")

7 -15 2.5 3 2.5

SettirgTime (min.)

5 8- l2 6-E 3-7 4.5

Stability I hour100% RH

Immediatepollr

I hour lmmediatepour

I week Pouredr/ithin a few

hours

Weftebility& Castlbility

Excellent Excellerlt Fair Fair Fair togood

Good

Cost Low Very low Low Moderate High tovery high

Very high

\ote: Reversible and irreversible hydrocolloids have the advantage of wetting oral surfaces

\\ ell. but they have very limited dimensional stability because they include as much as 85%

$ater in their composition.

Irreversible hydrocolloids (alginate) is most accurate when at least 3 mm ofspace exists

befween the impression tray and the tissue. The other impression t)?es are most accurate

when a small but definite space exists between the impression tray and the tissue.

Remember: The setting time ofalginate is controlled by the amount of sodium phosphate

that is present. Sodium phosphate serves a retard€r in this reaction, which means itslows down the process. As long as sodium phosphate is present, it will react with solu-

ble calcium ions. Once all the sodium phosphate has reacted, then the sodium alginate re-

acts with the remainins calcium ions and calcium alginate is formed.

EN;"po;-l + Ec,sql- Ia",Go;l + l3-N"-sql

F""r-t."d + lZaso;l -sg l?;"r*;;l * lN;q I1. Fast removal ofimpression from the mouth increases both the compresstve

and tear strength of the impression.

2. All impressions must be rinsed and disinfected prior to pouring or sending

to the laboratory. Soak or spray for a minimum of 10 minutes. Important:Always follow the manufacturer's recommendation for the specific product!! !

Iot€n''

,\Today wae a very busy day for Ashley, the dental hygienist in our olllce. Ashley

took alginate impressions on her lirst patient in the morning, who needed anightguard. Since she was so busy, Ashley left the alginate impressions in thelab most ofths morning. Ashley decided to place the impressions in a bowl

of water so that they would not dry up before she had a cbance to pourthem up in dental stone. Which ofthe following was the result ofAshl€y

. Ieaving these inpressions immersed in water for a few hours?

. Gelation

. Hysteresis

. Syneresis

. Imbibition

80Copright C 201 l-2012 - Dental Decks

If your patient indicrtes r tendency to gag while taking elginNte impressions,afl of the following man€uvers can h elp EXCEPT one.

Which one is the EXCCPZOIW

. Lessening the time to take an impresslon

. Using cold water to mix the alginate

. Having the patient breathe through his / her nose

. Seating the patient in an upright position

. Seating the posterior portion ofthe tray first

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Cop)right O 201 l-2012 - Dental Decks

Imbibition occurs when the impression absorbs water, which expands the dimensions ofthe impression. When this occurs, the impression is no longer accurate. Shrinkage willoccur in alginate impressions, even when they are placed under 100% relative humidity.The shrinkage and exudation of water is called syneresis.

Since shrinkage is undesirable (causes distortion ofimpressions), alginate impressions

should not be left either inwater (v,ill expard) or exposed to air 6vill shink). They should

be poured in.rmediately after they are taken to ensure accuracy. When immediatepouring is not possible, they may be stored briefly in a rnoist paper towel.

Important: While taking an impression with alginate, it is advisable that the tray be

placed in the mouth after all critical areas are wiped with alginate. Critical areas are

buccal to the maxillary tuberosities and retromylohyoid space. Rest seats and guide planes

should be covered with alginate as well as any other soft tissue undercuts.

1. Gefation is the term given to the setting process (c/rrrglng afrom sol to a gel)Iotes of hydrocolloid material.

2. Hysteresis refers to a material's characteristic ofhaving a melting tempera-

ture different from its gelling temperature.

Cold water will make the alginate take longer to set.

Mixing the alginate material rapidly will cause setting to occur more rapidly.

Decreasing the water to powder ratio will cause alginate to set up more rapidly (affects

consistenc.,^ of the mit -mix

is much thicker v'hen less v'ater is used).

Note: The mandibular alginate impression is taken first since gagging is more likely to

occur when taking the ma"xillary impression. For the maxillary impression, the posterior

portion of the tray is seated first, then the anterior portion. This helps to prevent the

alginate material from being squeezed out of the tray, back torvard the patient's throat

hrhich may cause gagging).

Alrvays remove alginate impressions in one quick movement, with a snap. This helps to

decrease permanent deformation.

l. The setting reaction of alginate is a "double decomposition" reaction be-

.\-ores tween potassiurn alginate and calcium sulfate. Also remember that casts must

. , - -,,,. be poued within 24 hours and the impression must be kept damp.

2. Both under and over-mixing can reduce the strength ofthe impression-

3. Do not over-seat the tray - 0.25 inch (minimum) of alginate should remain

over all critical strucl]tj'es (especially occlusal surfaces).

Elastomers are rubbery polym€rs that are capable of elastic deformation fromundercut arcas to produce a complete impression for dentate situations.

fmpression materials must hrve some strength, but generallytheir design is focused more on accuracy, dimensional stability,

and flexibility (rr tear rcsistance),

. The first statement is true; the second statement is false

. The first statement is false; the second statement is true

. Both statements are true

. Both statements are false

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Copyrighr O 201 1,201 2 - Dental Decks

Custom trays arc an important part of rubber baseimpression tschniques, since elastomers are:

. More accurate in uniform, thin layers 0.5 to 1.0 mm thick

. More accurate in uniform, thin layers 1.0 to 1.5 mm thick

. More accurate in uniform, thin layers 2.0 to 4.0 mm thick

. \{ore accurate in uniform, thin layers 5.0 to 6.0 mm thick

83

Copltighr O 20ll-2012 - Dental Decl6

The simplest method ofclassifoing impression materials is by key properties: rigid' water-bas€d, and elas-tomeric. Of the rigid rlpes, impression plaster was the first material us€d for both edentulous and denolousimprcssions, it is no longer used for impressions. Impression compound is used for single tooth impressions

where there are no undercuts. zinc oxid€ eugenol (ZOE) is used for edentulous impressions.

Water-brsed systems include alginate fil,"e1,ersible lrydrocolloid) and ag^r-^g r (reversible hydrocolloid).Both types ofmat€rials are inherently unstable because wat€r is 85oZ ofthe composition. They are v€ry eas-

ily distort€d during syn eresis (loss of$'ater to lhe air or surrounding envirokmenl) or ifibibition (ahsorption

ofwaterfron the air).

Elastom€rs are rubbery polymers that are capable ofclastic deformation fiom undcrcut areas to produce a

complet€ impression for dentate situations. There are four major types (pollsullide, condensation silicone,

pol),ethe\ and pol\'ri nll si loxane).

Characteristics of elastomeric impression malerials:. Bas€: packaged as a paste in a tube, as a cartridge, or as putty in ajar. Catalyst: also kno$.n as lhe acceleratot is packaged as a paste in a tube, as a cartridge, or as a liquid .

Forms of elastomeric imprcssion materials:. Light-bodi€d: also referred to as syringe q!e, or wash O?e. This material is used because ofits abilityto flow in and about the details ofthe prepared tooth.Aspecial slringe, or extnrder, is used to place the light-bodied material on and immediately around the preparcd tecth.. Regular and heavy-bodied: often referred to as tray-typc matcrials, they are much thicker As the names

imply, they are used to fill the tray. Their stiffness helps to force the light-bodied material into close con-tact 1\ ith rhe prepared teeth and surrounding tissues to ensure a more accurate impression ofthc details ofa prepamdon.

Curing stages of elastomeric impression materials:. Initial set the first stage results in stiffening ofthe paste without the appeannce of€lastic prcperties. The

marerial may be manipulatcd only during this first stage.. Final set: the second stage begins with the appearance ofelasticity and proceeds through a gradual change

.o a solid rubberlike mass. The matedal must be in place in the mouth before the elastic properties ofihellnal set begin to develop.. Final cur€i the last stase occu$ from I to 24 hours.

With all elastomers, a custom tray should be fabricated with a plastic material. This tray

should be rigid, have occlusal stops to avoid permanent distortion during polyrrerizationand be coated with an adhesive. With hydrocolloid impre ssiors (ctlginate),a greater bulkof material produces greater accuracy, however, the thickness of rubberlike materials

should not only be less, but should be evenly distributed. lmportant: Let adhesive that

is applied to the tray dry completely. If it is wet, impression material may pull away.

Custom trays are recommended for the following reasons:

. They require less impression materials

. They facilitate uniform concentration ofthe impression materials

. Stock trays usually are short in the llange area

. with stock trays, the uneven bulk of the impression material is conducive to distor-

The accuracy and reliability of an elastic impression is controlled by the tray in which

it is taken. The best tray is one that is custom-made for each patient. In most cases, it isbest to take a complete arch impression, which will provide maximum reliability.

tion

. Poured immediately

. Poured within 15 minutes

. Poured within 30 minutes

. Poured within t hour

84CoplriSh O 201 1,2012 - Dmtal Decks

- The powdel used in mixing acrylic resin is referred to ar the:

. Dimer

.Initiator

. Polymer

. Monomer

85Coptrighr O 20ll-2012, D€nral Decks

Polysulfides have good flow properties and high nexibility and tear str€ngth. These materials show the

strongest resislance to tearing, but as a result, impressions can distort when removed from areas where deep

undercuts are prcsent. They have a long working time and a relatively long polymerization time, which may

add to patient discomfort. Their rcsistance to deformation is low. Generally, the use ofthis material demands

the construction ofa specialllray (custom tray) in order to control polymerization shrinkage by thc use ofa uni-form thickness ofimpression mat€rial. Note: The polymerization ofpolysulfides is exothermic and is acccl-

erated by an increase in the temperature or humidity.

Composition of polysulfide impression material:. Base: mercaplan firnctional polysulfide. Cross-linking agent /dccelerator): stJlfur andlor lead peroxide. Plasticizer: dibutyl phthalate. Catalyst: lead dioxide, copper hydroxides, zinc percxide or organic hydroperoxide. Fille(to add strength): titanium dioxide or zinc sulfate. Retardei oleic or steric acidNotes: (l) Tle lead dioxide is responsible for the broum color and difficulty in cleaning clothes that come

in contact with this impression mat€rial(2) On polymerization water is releas€d as a b)?roduct causingdi_mensional contmction. The cast must be poured within I hour fdt rre lalest, some literature sals 45 min'

Components of Acrylic Resins:.Powder: Pofymethyl meth,,cryl^te (PMMA) polymer, benzoyl peroxide initiator, and pigments.. Liquid: Pure methyl methg,cryl^te (MMA) monome., hydroquinone inhibitor, crosslinking agents, and

ch€mical activator fdi methrl-ploluidine). Not€: This activator is only present in self_cured resins to bringabout polymerization.

Remember: mechanical properti€s of resins are influenced by the following:. Molecufar weight of the polymer (the grealer the molecularweigllt, the betler the pollmerization and the

harder the resin). Degree of cross-linking (need difunctional monomers which contain tu)o areas for reaction) is direcllyproportional to lhe degree ofpol)rnerization. A polymer with a greatcr molecular weighl is formed if more

crosslinking occurs.. Tle composition ofthe mororner ( prepares lhe polymer)

: '. - - .. . 1. Acrylic resins will expand when immersed in water and become distorted when dried out

:NoteJ;2.shrinkageofanacrylicr€sinoccu$but€xcessiveshrinkagemayoccuriftoomuchmonomer, i tliqurll is added to the polymer lpov'derJ. The volumetric monomer-to-polymer ratio is l:3...&1 3. The polynrerization reaction of methyl methacrylate is €xothermic

-gives out heat

4. Inhibitors are added to the monomen to aid in preventing polymerization during storage.

5. Cross-linking contributes greatly to the strength ofthe polymer6. H€al-cured materials: heat is used as an accelemtor to decompose benzoyl peroxide frre ,rit alol) into fre€ radicals, These fiee radicals initiate the polymerization ofMMA into PMMA Th€pol]'rnerization process continues as new PMMA is formed as a matrix around residual PMMApowder particles.

7. Self-cured (auto-cured, cold cureA materials: a chemical activator such as dimethyl-p_tofuidine flvri., is a lertiory amine) is ?dded to the monomer fMM,'r' This chemical activator

causes decomposilion of the b€nzoyl peroxide (lhe initiator) into free mdicals. These f.ee radi_

cals initiate the polymerization ofMMA and PMMA. Tle polymerization process continues the

same as in heat-curing materials.8- The pofymerization range is the temperaturc mnge, approximately 60"C (l1f F) to 77"C

f17rP-F), at which the major part ofpollmerization occurs in a heat-cured resin.

9.The heat-cured resins have less residual monomer and a higher molecular weight than the self-cured resins; therefore, they are stronger. They also have superior color stability.

Z\An edentulous patient has slight undercuts on both tuberosities and also on the

faclal ofthe &nterior maxilla. To construct a satisfactory maxillary complete

* denture, you should reduce which ofthe following? ,

. All undercuts

. The anterior undercut only

. Both tuberosity undercuts

. None ofthem

86

CoplYigh O 201 1,201: - Denlal Decks

. Upper (mandibular.fossa - articular disc) compartment

. Lover (condyle - anicular disc)

. Both the upper and lower compartments

a7

CoplriShr O 201l-2012, Derral Decks

Undercut tuberosities will interfere with the seating ofthe denture.

Explanation of answer: Maxillary anterior undercuts are very cornmon and present nospecial problems unless accompanied by large bilateral posterior undercuts. Even this sit-uation can usually be managed by reducing the inner surlace ofthe denture lateral to thetuberosities.

The maxillary sinus appears to enlarge throughout life if it is not restricted by naturalteeth or dentures. As the sinus enlarges, the tuberosity moves downward. Ifthere is no con-tact with the retromolar pad at the vertical dimension ofocclusion, the tuberosity must bereduced.

If a fow tuberosity is not removed before constructing new dentures (C/C), an acciden-tally underextended mandibular denture will probably be made and limited space to po-

sition posterior teeth will occur.

A submucosal vestibuloplasty is usually performed on the maxillary arch to improvethe available denture base area. This procedure is favored because no raw tissuesurface remains to granulate and re-epithelialize.

The temporomandibularjoints are considered to be the most complex joints in the humanbody because they must provide for rotational movements, sliding movements (trqnskr-to\) motion) and an infrnite range ofcombined movements and functions, unlike any otherjoint in the body.

When the mouth opens, two distinct motions occur at thejoint. The first motion is rota-tion around a horizontal axis through the condylar heads. The second motion is transla-tion. The condyle and meniscus move together anteriorly beneath the articular eminence.

ln the lower (condyle - articular disc) compartment, only a hinge-type or rotary mo-tion can occur. This rotational or terminal hinge-axis opening oflhe mandible is possi-ble only when the mandible is retruded in centric relation with a conscious effort by thepatient or by the dentist's control. Note: A pure hinging movement is possible only in theterminal hinge position.

ln the upper (mandibular./bssa - articulqr disc) compa'rtment, only sliding movementsor translatory motion can occur. When the lateral pterygoid muscles contract simulta-neously, the discs and condyles slide forward down over the articular eminence (prctru-sion), or can move backwards together (retrusion) during opening and closing of themouth, respectively.

Remember: The TMJ is a ginglymoarthrodial joint fn eaning that it glides and rotates),permitting both hinge-like rotation and sliding (gliding) movements. Ginglymus meansrotation, and arthrodial means freely movable.

. Arcon articulator

. Nonarcon articulator

. Epinephrine

. .Llurn (aluminum potassium sufatu)

. Zinc chloride

. Any ofthe above

88Copyrighr O 20ll-2012 - Denral Decks

89Copright @ 20ll-2012 - Denhl Decks

Thc capability of the articulator to closcly simulatc the movcments ofthc mandiblc is dcpcndcnt upon thc ajustabil-

ity ofthc articulator elemcnts.

f,lements of an articular;. Horizontal axis of rot|tion: variability ofthc position ofthc horizontal a\is ofrotation in rclationship to thc max-

illary dental cast. Condylar incliration/fossa components: variability ofthc anglc ofthc cmincntia, dircctionaL guidance of thc

supcrior, postcrior. and medial walls ofthc fossa, and ability to simulatc lalcrotmsive 'novemcnt. Inter Condyl|r distance: adjustability ofthe distancc bctwccn ihc vcrlical axcs ofrotation

. Bennett , ngle/Bennett movement:adjustability ofthc anglc and capability ofsimulating sidcshift movcmcnt

. Incisal guidance: adjustability and ability lo simulatc the aoterior guidancc ofthc natural dcntilion

Types ofArticulators:. Cl^ss | sinple hi ge).-The movcmcnt ofthese articulators is limitcd to inaccuratc hinge opcning and closing

arcs about a fixcd axis. The maximum intercuspation position is the only position that can be reproduced. Casts

are arbitrarily mounted without use ofa facebow. Cl^ss ll (rlrbitrary nllrc -Plane line): Evolvcd from the Class I articulator dcsign, thesc aniculators arc capa-

ble oflatcral movement. Some are capablc ofvariablc location oflhc horizontal a{is ofrotalion //, et, arc li.tl si:e

and capable o.f acceptitg a facebo\,), but a1l of this tlpe have fixed, arbitrary condylar inclination scllirrgs. verti-

cal axcs ofrotation settings, and Bcnnctt Anglc. No adjustment ofthcsc posterior elcmcnts is availablc. Some

havc a provision for incisal guidance.. Cl^.s lll (Seni-adiusta6le): These a(iculators can simulate lateral, protrusivc a d llcnnett movcnents to vary-

ing degrces. By utilizing a facebow and intraoral maxillo-mandibular records, thesc articulators can bc pro-

grammed to sinrulate thc curvi linear anatomical movcmcnts. Thcrc are cssentialiy two designs ofscmi-adjustablcarticulators. Onc which has thc guidance ofcondylar movcmcnt in thc maxillary menbcr and the centers ofaxialroration in thc mandibular member This dcsign is termed arlon articulators. Thc ton-arcon arliculator dcsign has

rhcsc elements reversed -lhcuppcrand

lower members arc rigidly attachcd. Theocclusal planc is relatively fixed

lo rhc occlusal planc of the nrandibular casl. Note: Arcon arc more accurate fbr fabricating fixed rcstorations,

Nhile nonarcon providc casicr control in sctting tceth for complet€ 8nd partial dentures.

'Cl^ssly (filh adjustarle/: This class ofarticulatom accepls registration ofall anatomic dctcrminant ofocclusal

morphology, and mosrcloscly simulates the movement dircctcd by thcsc controls. Thc postcrior clcmcnts ofthcsc

controls are dircclcd and adjusted by an cxtm-oral tcchnjque called a p.ntogr{phic rcgistration. This class tvillaccept a "hinge axis. kinemstic transfer bow. The incisal guidancc cl]n closely simulatc thc paths ofthe natu-

ral dcntirion. This class is fully utilizcd in cxtcDsivc rcstorative procedures, as rvcll as adjunct to diagnostic dctcr_

minations of lcmporomardibular joint dysfunction f?iMJr.

Epinephrine causes local vasoconstriction, which in nrm results in transitory gingival shrinkage Epincphrine

impregnat€d cord has been shown to produce minimal physiologic changes uhen placed in an intact gingival

sulcus. Howeve( there is evidence ofincreased heart rate and elevated blood pressure when the cord is applied

ro the severely lacerated gingival sulcus. For those patients with medical conditions such as certain tlpes ofcardiovascular disease or hyperthy'roidism, or a kno\r'n hyPersensitivity to epinephrine, a cord impregnatcd

with alum should be substituted.

Note: Zinc chforide is caustic and causes delay€d healiDg lcdute.t ,?ecrosis ofthe sulcular ePitheliu and the

adjacenl lq:er ofconnecliv? lissre). Therefore, it should not be used in impregnatcd cord-

Tissue retraciion is necessrry to:. Control bleeding. Refiact the gingival tissues slightly away from the margins. Allow imDression material to flow into the sulcus. Expose all gingival margins

Modes to achieve tissue displacement wh€n taking impressions:

. Mechanical modes- Cords: which stretch the circumferential periodontal fibers. They can be rwisled, braided, or knitted

These cords can be impregnaled with chemicals such as aluminum, iron salts or epinephrine which

cause transient ischemia and shrinkage ofthe gingival tissue, and absorb seepage ofgingival fluid They

are supplied in different diametcrs.

. Surgical modes:

- El€ctrosurgery: when cord will not produced the desired gingival displacement, this method can be

used.

Fluid control when taking impressions:. M€chanical means: saliva ejectors, cotton rolls, cotton sponges. Medications: anticholinergic drugs such as atropine. dicyclomine, glycopyrrolate, and methantheline act

as anti-siafogogues f/educe salivary secrctiont. Notei Anticholinergic drugs should not be given to pa-

iients with narrow-angl€ glaucoma. They should be used wilh caution in patients with heart disease.

. Hamulus

. Hamular notch

. Maxillary tuberosity

. Fovea palatini

90

CopFShr O 20ll-2012 - Dental Deck

. 2olo ofthe population

. 20% ofthe population

. 50olo ofthe population

.75% of the population

91

Coplriglrt O 201 I -20 l2 , Dental Dects

*** It is a thin, curved process that serves as the superior attachment of the pterygo-mandibular raphe. This raphe is a tendon between the buccinator and superiorconstrictor rnuscles.

The hamular notch is a thin cleft between the maxillary tuberosity and the hamulus. The

vibrating line is an imaginary line drawn across the palate that marks the begiming of mo-tion in the soft palate when an individual says "ah". It extends from one hamular notch to

the other. At the midline, it usually passes about 2 mm in front ofthe fovea palatinae.

Remember: The distal end ofthe maxillary denture must cover the tuberosities and ex-tend into the hamular notches. Overextension at the hamular notches will not be tolerated

because of pressure on the pterygoid hamulus and interferences with the pterygo-mandibular raphe. When the mouth is opened wide, the pterygomandibular raphe is pulled

forward. Ifthe denture extends too fff into the hamular notch. the mucous membrane cov-ering the raphe will be traumatized.

The fovea palatinae are indentations near the midline ofthe palate formed by a coales-

cence of several mucous gland ducts. They are always in soft tissue, which makes theman ideal guide for the location ofthe posterior border ofthe denture.

Palatal tori are bony enlargements located at the midline ofthe hard palate. They occurin approximately 20% ofthe population and are more prevalent in women than men. Theyusually reach maximum size in the third or fouth decade. Because the torus is usually cov-ered by thinner and less resilient mucosa than the residual ridge, it may act as a fulcrumand cause rocking ofthe ma"rillary denture.

Because the soft tissues over the torus are generally thin and have a poor blood supply,

post-operative healing is slow. It is best to cover the opemted site with a surgical stent linedwith a sedative dressing. Ifa patient is having all oftheir maxillary teeth out at one time,it is best to also remove the tod at the same time.

Note: Palatal tori are usually not removed for denture fabrication whereas mandibulartori are usually removed prior to denture fabrication. The following conditions warrart re-

moval ofpalatal tori, ifit: (1) impinges on the soft palate (2) is so large that it fills the vault

and prevents the formation ofan adequate dentue base (3) is undercut (4) extends so farposteriorly interfering with the posterior palatal seal (5) is psychologically disturbing to

the patient (cancetphobia) .

. It will make the patient feel better

. It will make the face-bow lransfer easier to perform

. To provide a firm, stable base for the denture

. The final impression material will flow better

92

Coplright O 20ll-2012 - Dental Dech

When inflannatory papillary hyperplasia is seen on the palate of a patientwearing a maxillary complete denture, the condidon fu most

likely going to be associated with:

. A vitamin B deficiency

. A sudden increase in body weight

. A hypersensitivity ofthe patient to the acrylic denture base

. Ill-fitting dentures and a poor state oforal hygiene

93

Coplaight O 201 I 2012 - Dental Decks

Treatment may include:. Tissue rest. Soft reline ofexisting dentures. Change in denture habrts (not wearing them 24 hours a dav). Surgical removal oftissue (y'ti.rsaes changes are extensive)

Note: Mandibular tori, sharp pron.rinent mylohyoid ridges, and epulis fissuratum shouldalso be evaluated for surgical removal trefore the iabrication ofnew dentures is begun.

Curent concepts of impression making for complete dentures recommend using atechnique that:

. Affords placement and control ofthe impression material in recording border tissues(bonler molding). Results in minimal displacement oftissues under the dentLre (registers the tissue inIts passive position). [s dependent on the oral conditions present.

\ote: The best impression technique for a patient with loose hyperplastic tissue is to reg-

ister the tissue in its passive position. There must be intimate contact of the

impression material with the tissue.

The hyperplasia is produced in respons€ to ifiitation from movement ofthe denture and from accumu-

lating food debris. The masses prescnt as painless,Iirm, pink, or red nodular pmliferations ofthl] mu-

cosa. Candida albicans may contribute to the inflammation.

Conditions that compromise the optimal function ofcomplete dentures:

. Frenectomy; common for labial, less for buccal, rare for lingual. Surgery is usually Z-plasfy whichmust include fibrous attachment to bone.. H;-permobile ridge: ifinflamed. trcat with a tissue conditioner. Lascr suryery may bc needcd. Epulis Iissuratum: a hyperplastic tissue reaction caused by an ill-fitting or overextended flange in

a denture.. Fibrous maxillary tuberosity: common occurrence when largc maxillary tuberosities contact

mandibular retromolar pads.. Combination syndrome: refers to $hat is believed to be a specific pattem ofbone resorption in the

anterior ponion ofan edenfulous maxilla, caused by wearing a complete denture opposing natural an-

terior teeth.. Papillarl' h!perplasia: found in the palatal vault. Caused by local irritation, poor-fitting denture,

poor oral hygiene, and leaving the denture dentures in all day and night. Candidiasis is the primarycause.. Paget's disease of bone: a denture or RPD in a patient with this disorder may have to be remade

periodically due to bone expansion

, 1. Alveoloplasty is the improvement ofthe alveolar bone by surgical reshaping or rcmoval.

Noled,2.Palataltorishouldberemovedonlyif(l)itissolargcthatitfillsthevaultandprcvents,...., :. the formation of an adcquf,te denture base when it is undercut, (2) it interferes with the place-r&a;-

ment ofthe posterior palaral seal, or (3) ifthe patient is canccr phobic.

3. Vestibuloplasty: this tcchnique increases the relative height ofthe alveolar process by api.

cally repositioning the alveolar mucosa and the buccinator mentalis, and mylohyoid mus-

cles as they insert into the mandible.4. Augmentation: (l) Bone gmfts l'rources include anleior iliac crest ofthe hip or the rib)(2) Hy&oxyapatite (3) Freeze-dried bone

. Agrng

. Alcoholism

. Vitamin A or Vitamin B deficiency

. The use ofdrugs to manage chronic diseases

. Diabetes

94Coplright C 201 l-2012 - Dental Decks

. Vemrcous lulgaris

. Inflammatory papillary hyperplasia

. Stomatitis nicotina

. Epulis fissuratum

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Xerostomia is a possible side effect associated with more than 400 drugs including anti-hlpertensives, antidepressants, antihistamines, bronchodilators, anticholinergics, andsedatives. Mouthwashes, alcohol, tobacco, and caffeine may alter salivary flow or cause

dryness ofthe oral mucosa.

Even though xerostomia is not a disease, it can be a symptom ofcertain diseases. It can

cause health problems by affecting nutrition as well as psychological health. It can con-tribute to and increase the chances ofhaving tooth decay and mouth infections.

Temporary relief may be found from several sources:. Saliva substitutes. Sugarless hard candies. Glycerine-based cough drops and lemon flavored glycerine mouthwash. Medications may be added, changed, or dosages altered to provide increased salivary

florv

Remember saliva has several important functions:. \vashes away food debris and plaque from the teeth to help prevent decay. Limits the growth ofbacteria that cause tooth decay and other mouth infections. Bathes the teeth and supplies minerals that allow remineralization ofearly cavities. Lubricates foods so they may be swallowed more easily. Provides enzymes that aid in digestion. Helps us enjoy foods by aiding in the "tasting" process. \'loistens the skin inside the mouth to make chewing and speaking easier

The cleft-like lesions ofepulis fissuratum result primarily from overextension ofden-ture flanges. The overextension may result from long-term neglect or settling subsequentto residual ridge resorption. Trar.rmatic occlusion of natural teeth opposing an artificialdenture may also cause this condition.

Denture stomatitis is a localized or generalized chronic inflammation of the denturebearing mucosa. Clinically, there is redness and a buming sensation. There may be ormav not be discomfort. Trauma and secondary fungal infection appear to be the mostlikeh causes of denture stomatitis.

The treatment generally consists of:1. Improved oral hygiene2. Tissue rest

-1. Antifungal therapy (ny*atin)-+. Resilient tissue conditioners5. New. well-fittins dentures

. Addison's disease

. Paget's disease

. Hashimoto's disease

. Multiple sclerosis

96Coplrighr O 20ll-2012 - Dental Deck

. Delayed healing

. Rapidly progressing periodontal disease with marked alveolar bone loss

. Mucosal bleeding

. Increased calculus formation

. A predilection for periapical abscesses

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, Not"* l

Paget's disease (also called osteitis deformans) ofthebone is a chronic bone disorder inwhich bones becorne enlarged and deformed. The exact cause is not known. It ischaracterized by excessive breakdown of bone tissue, followed by abnormal boneformation. The new bone is shucturally enlarged, but weakened with healy calcifications.

Important: Involvement of the skull may enlarge head size and cause hearing loss andblindness if the cranial nerves are damaged by the bone growth.

Dental Considerations -relieving

the tissue surface of the dentures and relining withresilient materials can extend the life of the dentures. However, remaking the dentures

freouentlv is unavoidable.

1. Children who wear dentures and patient's with acromegaly who wear den-tures also often need to have their dentures relined or remade to allow for bonegrowth.2. Diseases ofbone growth or expansion are much rarer than those ofboneloss.

3. Osteoporosis is the most common change associated with systemic disease.

This condition is a generalized defect in which the quantity and quality ofbonein the skeleton is reduced.

Diabetes is a disease that can affect the whole body - your eyes, nerves, kidneys, heart,

and other important systems in the body. It can also affect your mouth. People with dia-betes face a higher than normal risk of oral health problems. The link between diabetes

and the development of oral health problems is high blood sugar If the blood sugar is

poorly controlled, it is more likely that oral health problems will arise. This is because un-

controlled diabetes impairs white blood cells, which are the body's main defense against

bacterial infections that can occur in the mouth.

Just as studies have shown that controlling blood sugar levels lowers the risk of majororgan complications of diabetes - such as eye, heart, and nerve damage - so too can

good diabetes control protect against the development oforal health problems.

Even controlled diabetics present problems for the prosthodontist. The oral mucosa is

prone to the development of sore spots which heal poorly and often become secondarilyinfected.

Principles to keep in mind when constructing dentur€s for patients with any debilitatingdrsease:

. Maximum extension

. Narrow occlusal table

. Non-pressure impression technique

. Do not use porcelain teeth

. Establish a good occlusion

. Reinforce oral hygiene

. Place on 6-month recall (sooner ifnecessary to reinfor ce oral hygiene)

. Masseter muscles

. Medial pterygoid muscles

. Lateral pterygoid muscles

. Temporalis muscles

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Assume that a patient wearing complete dentures for a number ofyears isgiven an oral exarnination and it is determined that the verticat dimension

ofocclusion has been decreased. This would cause:

. An increased vertical dimension that leaves the teeth in a clenched. closed relation innormal positions

. An occluding vertical dimension that results in an excessive interocclusal distancewhen the mandible is in the rest position

. An insufficient amount of interarch distance because ofhearry, bony ridges

. An inability to open the mandible because of temporomandibular joint pathosis

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Muscles acting on the TMJ:. Opening (depress): lateral pterygoid, digastric (anterior belly) and the omohyoidmuscles.. Closing (elevate): masseter, medial pterygoid, and the temporalis (anterior fibers)muscles.. Protrude: laterals pterygoid muscles acting together. Retract: posterior fibers ofthe temporalis muscle. Lateral displacem€nt: lateral pterygoid muscles acting individually.

Important:. The lateral pterygoid muscles are mostly responsible for positioning and translatingthe condyles.. Ifthe mandible fractures, upward displacem€nt ofthe fractured segment would be

caused by the closing muscles (masseter medial pterygoid, a d temporqlis).

Interocclusal distance: also called "freeway space" is the vertical distance or space between the incisaland occlusal surfaces ofthe maxillary and mandibular teeth with the mandible in the physiological rest

position. The average interocclusal distalce is about 3 mm. Too much interocclusal distance may re-

sult in muscuiar imbalance.

vertical dimension of occlusion is the vertical length ofthc face as measured between two arbitrarilyselected points, one above and one below the mouth, when the teeth or any substitute ma1e'rial (occlu-

Jiorl ,'rrril are in contact in centric relation. Excessive vertical dimension may result in trauma to thcunderlling supporting tissues (in a derlrtre patient) and strrir'jng ofthe closing muscles as well as

ad\erseft affecting the interocclusal distance (decreasedfreewal, space).

\ertical dimension of rest is the vertical length of the face as measured between two arbitrarily se-

lecred points. one above and one below the mouth, when the mandible is in the rest position; in thephlsiologicalJy healthy individual, there will always be a vertical space between the teeth (freewal' space)

\hen the mandible is in the rest position. This position is important in complete dentute fabrication be-

cause it p.ovides a guide to the vertical dimension ofthe occlusion.

l. Vertical Dimension ofOcclusion + Interccclusal Distance = VerticalDimellsion ofRest.Notesi 2. Thc vcrtical dimension ofrest is always greater than the vertical dimcnsion ofocclusion.

l. A protrusive record registe$ the anterior-inferior condyle path at one particular point** in rhe translatory movement ofthe condyles. Some clinicians use this q?e ofrecord to de-

temine the amount of space between maxillary and mandibular teeth or occlusal rims in order

to maintain balanced occlusion throughout the mandibular functional range of movement$'hen aniculating teeth.

4. Thc space that opens between the posteriorteeth during anterior movemcnt ofthe mandible

is called Christensen's PheDomenon. This posterior separation is increased if the incisalguidance is increased. Tte amount of posterior separation is affccted by both the incisalguidance and the horizontal condylar guidance. The separation is increased as both IG and

HCG increase -the

effect ofIC is greater anteriorly and the effect ofHCG is greater pos-

teriorly.

The anteroposteri or curvrtarc (in the median pltne) ^nd

themediolat€rrl curv^tare (in thefrontal plane) in the

^lignmentof the occluding surfaces and incisal edges of artificial teetithat are uscd to develop balanced occlusion is called:

. Curve of Spee

. Compensating Curve

. Curve of Wilson

. Curve of Pleasure

. Tooth-to-tooth relation

. Occlusal relation

. Bone-to-bone relation

. Balanced relation

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The lorm ofthe compensating curve is entirely under the control ofthe dentist, For ex-ample, ifduring a try-in evaluation, a dentist notes that a protrusive excursion movementresults in the separation of posterior teeth, the problem can be corrected by simply in-creasing the compensating curve. The value of the compensating curve is that it allowsthe dentist to alter the effective cusp angulation without changing the form of the manu-factued denture teeth. The function ofthis curve is to help provide a balanced occlusion.Not€: As the condylar inclination increases, the compensating curve must increase tokeep a balanced occlusion. A prominent compensating curve is required when there is asteep condylar path associated wilh a low degree of incisal guidance.

Orientation of the occlusal plane: The occlusal plane is an imaginary surface which isrelated anatomically to the cranium and which theoretically touches the incisal edges ofthe incisors and the tips ofthe occluding surfaces of the posterior teeth. lt is not a plane

in the true sense ofthe word, but represents the mean curvature ofthe surface. The ante-rior point of the occlusal plane is determined by the position of the anterior teeth. Theposterior determinants are anatomical lanalmarks

-two-thirds the height of the retro-

molar pads. Therefore, it is debatable as to the extent ofcontrol the dentist may exercise

over the orientation ofthe occlusal plane.

Cusp inclination is the angle made by the slopes ofa cusp with a perpendicular line bi-sectin-q the cusp, measured mesiodistally or buccolingually. This is under control of thedentist (choosittg j0" degree teeth or cuspless teeth, etc.).

Remember: Anterior guidance in complete denture occlusion should be avoided toDrevent dislodsement ofthe denture bases.

Centric refation (CR) (also called the retrudecl contact position) is considered a t€rminalhinge position and is defined as "the maxillomandibular relation in which the condyles ar-ticulate with the thinnest avascular portion oftheir respective discs with the complex in theanterior-superior position against the shapes ofthe anicular eminences". This position is in-dependent of tooth contact. This position is clinically discemable when the mandible is di-rected superiorly and anteriorly. It is restdcted to a purely rotary moyement about thetrans\ierse horizontal axis. Important: This is a relationship of the bones of the upper andloserjarvs without tooth contact.lmportant points about centric relation:

. The mandible cannot be forced into centric relation fiom the rest Dosition because the Da-tient s reflex neuromuscular defense would resist the applied force. The mandible should be relaxed and gently guided into centric relarion. In fixed and removable prosthodontics, centric relation should be established prior to de-si_uning the frameworks. \\'hen a centric relation record is taken in the natual dentition, imprints ofthe teeth shouldbe confined to cusp tips and the registration material should not be perfomted

Important point: The current concept about centric relation: it occurs when the condyles arein their most superoanterior position, resting on the posterior slopes of the articular emi-nences rvith the discs properly interposed.

Whl do we n€ed to know this? This position is considered to be an optimum relative posi-tion between all ofthe anatomic components. And more importantly, it is a repeatable refer-ence position to mount the casts on the articulator.

Helpful hint: Having the patient swallow, tuming the tongue upward towards the palate, re-laxrng the jaw muscles, or protruding and retruding the mandible can be effective ways tohelp in recording centric relation.

Which of the following stNtements concerning selective grinding incomplete d€nture fabrication for centric relation is not true?

. Primary centric holding cusps are the maxillary lingual cusps

. Secondary centric holding cusps are the mandibular buccal cusps

. Selective grinding of the imer inclines of secondary holding cusps can be done ifthere is a working side interference

. Grind only the cusp tips of the upper buccal and the lower lingual (8. U.Z.Z.) cusps ifthey are premature in centric, lateral or protrusive movements

102CopriShr O 201l'2012 - Dental Decks

Brlancing side fn on-working side) interferenc€sgenerally occur on th€ inner aspects ofthe:

. Facial cusps ofmandibular molars

. Facial cusps of ma"rillary premolars

. Lingual cusps ofmandibular molars

. Facial cusps of maxillary molars

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Selective grinding in centric r€lation:. Ideally selective grinding should result in harmonious cusp-fossa contacts olall upper andlower fossa (and maryinal ridges of bicttspi"ds). Do not grind the upper lingual or lowerbuccal cusps. A forward slide from centric can be corrected by grinding the mesial inclinesof maxillary teeth and distal inclines ofmandibular teeth. Primary centdc holding cusps are the maxillary lingual cusps. Never grind these cusps.See note below.. Secondary c€ntric holding cusps are the mandibular buccal cusps. Grind these cuspsonly ifthere is a balancing side interference. Only grind cusp tips ifthey are premature in centric, lateral, and protrusrve movements.

Check before grinding.

Selective grinding in working-side relation: The rule ofselective grinding for interferences

in $orking -side movements is the &lgqlEIJ:LL!. luccal cusp inner inclines ofupper teeth. lingual cusp inner inclines oflower teeth

Selective grinding in balancing side relation:. Grind the inner inclines ofthe mandibular buccal cusps. \ever gind the maxillary lingual cusps (primary centric holding cusps)

\ote: For the National Board Exam questions, you can reduce the maxillary lingual cuspifit is high in centric as w€ll as oth€r occlusal positions

-in reality, you should not.

Working side interferences generally occur on the inn€r aspects ofthe lingual cusps ofmaxillary molars.

Protrusive interferences generally occur between the distal inclines of the facial cusps

of maxillary posterior teeth and mesiat inclines ofthe facial cusps ofmandibular poste-

rior teeth. The proximity ofthe teeth to the muscles and the oblique vector ofthe forces

make contacts between opposing posterior teeth during protrusion potentially destructive.

The purpose of making a record ofprotrusive relation is to register the condylar pathand to adjust the condylar guides ofthe articulator so that they are equivalent to the condy-

lar paths of the patient.

-{ centric interference (fot'wqrd slide) can be corrected by grinding the mesial inclinesof maxillarv teeth and distal inclines ofmandibular teeth.

qDn(wwR\C] IJ V

wk

I

. On the maxillary mesial inclines and mandibular distal inclines

. On the maxillary mesial inclines and mandibular mesial inclines

. On the maxillary distal inclines and mandibular mesial inclines

. On the maxillary distal inclines and mandibular distal inclines

104Coptrighr O 201 1,2012 - Dental Decks

Which of the following best describes Camper'sline (plane)?

. It is a line (plane) which is determined by the occlusal surfaces of the teeth

. It is a line (plane) which extends from the outer canthus of the eye to the superiorborder ofthe tragus ofthe ear

. It is the hne (plane) running from the inferior border of the ala of the nose to thesuperior border ofthe tragus of the ear

. None ofthe above

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Anteriorly the facial surface of the lower incisors will contact the guiding inclines /lz-gual) of the tpper incisors and canrnes.

Protrusive movement is accomplished when the mandible is moved straight forwarduntil the maxillary and mandibular incisors contact edge.to-edge. This movement is bi-laterally symmetrical in that both sides ofthe mandible move in the same direction.

In any restorative case involving all teeth in the mouth, the protrusive condylar path

inclination will have its primary influence on the same inclines (distal ofmaxillary andmesial ofmandibular).

The pathway followed by the anterior teeth during protrusion may not be smooth orstraight because ofcontact between the anterior teeth and sometimes the posterior teeth.

The mandibular movements include movements:. Approximately 9 - l0 mm anteriorly (protrusive movement). Approximately 50 - 60 mm inferiorly (opening). Approximately l0 mm laterally. Approximately I mm posteriorly (retrusive movement)

Signilicance of the Camper's line: the plane of orientation for complete denture con-

struction is established in the anteroposterior direction with the rnaxillary occlusal wax rimparallel to Campers line, which is an imaginary line traced from the ala ofthe nose to the

tragus of the ear, and with the interpupitlary line in the transverse plane, which is an

imaginary line drawn between the eye pupils.

l{ote: The posterior determinants ofocclusion (two-thirds the height ofthe retromolarpa&./ have the greatest effect on the setting ofthe mandibular second molars.

Rememb€r: The Frankfort horizontal plane extends from the outer canthus ofthe eye

to the tragus ofthe ear. It is commonly used in orthodontics for cephalometric analysis.

In the intercuspal position, the mesiolinguat cusp ofa permanentmaxillary lirst molar occludes where?

. Central fossa ofthe mandibular first molar

. Central fossa ofthe mandibular second molar

. The interproximal marginal ridge areas between mandibular first and second molars

. The interproximal marginal ridge areas between mandibular second and third molars

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. The lingual groove ofthe mandibular first molar

. The mesiobuccal groove ofthe mandibular first molar

. The buccal groove ofthe mandibular second molar

. The distobuccal groove ofthe mandibular first molar

. The space between the mesiobuccal and distobuccal cusps of the mandibular firstmolar

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Examples:

l The mesiolingual cusp of the mandibular first molar opposes the lingualembrasure between the maxillary first molar and second premolar2. The mesiolingual cusp of the mandibular second molar opposes the lingualembrasure between the maxillary second molar and first rnolar

\ote: The distolingual cusp of the mandibular first molar fits into fopposes) thelingual groove ofthe maxillary first molar.

Remember: The lingual cusp ofpermanent mandibular first premolars does not occlude* ith anlthing.

Important: During mandibular movements (working, non-working, e/c.) the outer as-pects of the lingual cusps of the mandibular molars will not contact their maxillary an-usonists. All other areas of buccal and lingual cusps may contact during mandibularmo\ ements (this is assuming that all occlusal reletionships are normal).

\ote: In unilateral balanced occlusion, contact between mandibular buccal cusps andmaxillary buccal cusps, along with simultaneous contact between mandibular lingualcusps and maxillary cusps will most likely occur in laterotrusive movements.

. Premolars

. First molars

. Incisors

. Canines

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. The central fossae ofmandibular posterior teeth

. The lingual inclines of facial cusps ofmandibular posterior teeth

. The lingual inclines of lingual cusps ofmandibular posterior teeth

. The facial inclines oflingual cusps ofmandibular posterior teeth

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This is called canine or cuspid protected occlusion. It is an occlusal relationship in which thevertical overlap ofthe maxillary and mandibular canines produces a disclusion (separation)of all ofthe posterior t€eth when the mandible moves to either side. All other teeth, once theymove from centric relation, do not contact. If there is contact of other teeth. it is termed a"working side" or "non-working side" interference depending on which side the mandiblemoves towards. Note: When placing a crown on a maxillary canine, if you change a canineprotected occlusion to group function you increase the pot€ntial for a "non-working side" in-terference.

Group function (sonetimes called unilqteral balanced occlusiotr) is an occlusal relationshipin which all posterior teeth on a side contact evenly as the jaw is moved toward that sideIrlorkitrg side). All teeth on the non-working side are free of any contact. The group func-tion ofthe teeth on the working side distributes the occlusal load. The absence ofcontact on

tbe non-working side prevents those teeth from being subjected to the destructive, obliquelydirected forces found in non-working interferences. lt also saves the centric holding cusps,

i.e.. the mandibular buccal cusps and the maxillary cusps, from excessive wear. The obviousadlantage is the maintenance of the occlusion.

l. Some relationships are not conducive to cuspid protected occlusion such as Class

-\otes II or end-to-end relationships.

^:. _. 2. Some relationships are not am€nable to group function such as Class II, deep

venical overlap.3. Regardless ofwhat lateral concept is used. no non-working side contacts ar€ a

must because; (l) They are damaging (2) They are difficult to control due tomandibular flexure and (3) They deliver more force to the teeth than other contacts..1. Horizontal forces on teeth are the most destructive to the periodontium.

Remember:

Centric Occlusion Working side Balancing side

\otes on contacts in balancing occlusion (posterior teeth):. Ideal Class I: cusp-fossa contact in centric occlusion. Lateral excursion:

. \\rorking side: contact ofopposing cusps

. Balancing side (z on-vtorking): contact of maxillary lingtal atsps (lingual inclines)and mandibular facial cusps (lingual inclines)

. The facial embrasure between their class counterpart and the tooth mesial to it

. The facial embrasure between their class counterpart and the tooth distal to it

. The opposing central fossae

. The opposing mesial marginal ridge

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I Io tha ioturcusprl posltlon, the distobuccal cusp of o permanentmandibular second molar occludes wbere?

. The interproximal marginal ridge area between the maxillary second bicuspid and firstmolar

. Central fossa of the rnaxillary first molar

. Cenfal fossa ofthe maxillary second molar

. The interproximal marginal ridge area between the maxillary first molar and secondrnolar

't'fiCoplright O 201l-20t2 - Denral Dects

*** See picture below

Examples:

1. The facial cusp tip of a maxillary first premolar opposes the facial embrasurebetween the mandibular first and second premolars (see note below).2. The facial cusp tip of a maxillary second premolar opposes the facial embrasurebetween the mandibular second oremolar and mandibular first molar.

\ote: During lateral excursive movements, the facial cusp ridge of the maxillary firstpremolar on the working side opposes the distal cusp ridge ofthe first premolar and the

mesial cusp ridge of the second premolar.

. Backward and upward direction

. Downward and forward direction

112Coplright O 201 I -20 l2 ' Dental Decl!

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.Pr

.E

.T

. RCP

.ICP

Important:. A protrusive movement requires the condyles to move downward and forwarddirection.. In lat€ral movements, the working condyle moves down, forward, and laterally.. In lateral movements, the non-working condyle moves down, forward, and medi-ally.

Remember: In complete dentures, the path ofthe condyle during free mandibular move-ments is governed primarily by the shape of the fossa and meniscus (articular disc) as

well as the muscular influence.

The inclination of th€ condylar path during protrusive movement can vary from steep

to shallow in different patients. It forms an average angle of about 3ff with the horizon-tal reference plane. Ifthe protrusive inclination is steep, the cusp height may be obviouslylonger. Similarly, if the inclination is shallow, the cusp will be shorter. This factor is themost important aspect of condylar guidance that affects the selection of posterior teethwith appropriate cusp height.

Anterior guidance (vertical and horizontal overlap of anterior teeth) also affects thesurface morphology ofposterior teeth. The greater the overlap, the longer the cusp height.Important: Anterior guidance must be preserved, especially when restorative proce-dures change the surfaces of aaterior or posterior teeth that guide the mandible in excur-sive (lateral, protrusiv€) movements.

ICP : Intercuspal position (1P) or centric occlusion (CO)

RCP = retruded contact position or centric relation (CR)

PR = Maximum protrusion

E = Edge+o-edge position ofincisors

PR-T = the anterior border movement of the mandible

RCP-R = the rotational movement of the condyles retuming to centri c relation (tetmi'nal hinge ais opening)

R-T = the translational moyement ofthe mandible retuming to where the condyles are

in centric relation

Tog€ther these line segments (RCP-R and R-T) make up the posterior border move-ments of the mandible.

. Intercuspal position f1P)

. Retruded contact position (RCP)

. Protruded contact position (PCPI

. Centric relation fCR)

. Maximum

. Not present

. Premature

. qli ohr

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1t5Coptright O 201l-2012, Dental Decks

*** IP is also called centric occlusion.

Remember: When the teeth are in centric occlusion, the position of the mandible inrelation to the maxilla is determined by the intercuspation ofthe teeth.

Empty mouth swallowing occurs frequently throughout the day and is an impofiantfunction that rids the mouth ofsaliva and helps to moisten the oral structures. The hourlyrate of non-masticatory swallowing is apparently related to the amount olsalivary flowand, in most instances, may be an involuntary reflex activity.

, ., . , l. The masseter muscles contract and the tip ofthe tongue touches the roofof.r Note*: the mouth during normal swallowing.

\&|| 2. Tooth contacts are of longer duration in swallowing than in chewing, butthere is wide variation in frequency and duration from one person to another.

This position results when the mandible and all of its supporting muscles (eight muscleso-/'ntastication plus the supra - and inf'ahyoids) are intheir restingpostve (there is a rel-atie nruscular equilibrium). The term used to describe this absence ofcontact is "free_rr a'r' space" or "interocclusal distance". It usually averages between 2_6 mm. Thisposition is a 'rmuscle-guidedfi position. It is the beginning and end point of mostmandibular movements-

The retruded contact position (also called centric relation) is a "ligament-guided"position. It is the closing end point ofthe retruded border movement (the terminal hingenlol en1enu.

The intercuspal position (a/so called centric occlusion) is a "tooth-guided,' position.\\-hen the teeth are in centric occlusion, the position of the mandible in relation to thema')rilla is determined by the intercuspation ofthe teeth.

The protruded contact position is s),rnnetrical, and the underside of the meniscus /ar_ticular disc) moves distally relative to the superior surface of the mandibular condvle.The condyle moves forward and canies the disc with it.

record should haye what important characteristic?

. Offer a maximum resistance to the patient's jaw closure and have high flow atmixing

. Offer a marimum resistance to the patient's jaw closure and have low flow at mixing

. Offer a minimum resistance to the patient's jaw closure and have low flow at mixing

. Offer a minimum resistance to the patient'sjaw closure and have high flow at mixing

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Which of the following materials rvailable for recording centric relationwhen frbricating a remov|ble partial denture is the least satisfsctory?

. Modeling plastic

. Wax

. Quick-setting impression plaster

. Metallic oxide bite registration paste

. Silicone impression materials

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In recent years, polyvinyl siloxane (addition silicones) impression materials have domi-nated the IOR (interocclusal record) market. These materials have very low flow whenmixed and become rigid after setting.

In the past, an interocclusal record was made by placing the IOR material into the mouthand closing the patient's jaws into the material at the desired relationship. Although thisconcept is acceptable

-and may produce a relatively accurate IOR

-the act of closing

into any material, regardless of its lack of viscosity, often causes a deviation of themandible away from the desired contact position.

A more desired method ofobtaining an accurate interocclusal record is as follows:. Close jaws into centric occlusion (zost interdigitated position). With teeth occluded tightly, inject the addition-reaction silicone material in betweenthe marillary and mandibular teeth. Inject material only into areas where teeth havebeen prepared and not around the entire arch.. Advise patient to place tongue forward, short ofgoing between teeth, thereby makinga matrix for the lingual aspect ofsilicone. Let silicone set for about two minutes. Remove IOR and him with a sharp knife. Mount casts with IOR material present only in areas of tooth preparations

Materials used to record jaw relationships have varied widely over the years An ideal

recording medium would be characterized as easy to handle, uniformly soft while the

record is being made, rapid setting, and totally rigid but not brittle when set. Rapid set-

ting plastet zinc oxide and eugenol pastes, and modeling plastic all approach the ideal.

Avoid soft waxes as a recording material. They never become rigid and are likely to be

distorted during the cast mounting procedure.

If sufficient natural posterior occlusion exists, the mandibular cast may be mounted incentric occlusion using a zinc oxide-eugenol reinforced wax bite. In the case ofthe dis-tal extension partial denture' base plates and occlusion rims should be placed on theframework ard the patient closed into softened recording wax or zinc oxide-eugenol

pxste (preferred). Whether this record will be in centric occlusion or centric relation willdepend upon the individual case and is dictated by the presence or absence of any natu-

ral posterior occlusion in the patient.

A retiable method is to use a record ofall remaining occluding surfaces in a wax waferwith the mandible in the terminal hinge position ard the teeth just out ofocclusion.

Primary requirements for making a centric relation record when fabricating a removable

dentue:. To record the correct horizontal relation ofthe mandible to the maxilla. To stabilize the lower record base with equalized vertical pressure. To retain the record in an undistorted condition until the casts have been accurately

mounted on the articulator or until a previous record can be verified

. Non-supporting and working

. Supporting and balancing

. Supporting and working

. Non-supporting and balancing

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Copyrighl @ 201 t -2012 - Denral Decks

. Horizontal overlap

. Vertical overlap

. Horizontal and vertical overlap

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Coplrishr O 2011,2012 - Dental Decks

Five Common Characteristics of Supporting Cusps

l. They contact the opposing tooth in the intercuspal position.2. They support the vertical dimension ofthe face.

3. They are nearer the faciolingual center ofthe tooth than the non-supporting cusps.

4. Their outer incline has a potential for contact.5. They have broader, more rounded cusp ridges than non-supponing cusps.

Remember: The supporting cusps are the maxillary lingual and the mandibular buc-cal. These cusps do grinding work because they occlude in a fossa or marginal ridge and

are also called working cusps. They are sometimes called centric cusps because theyhold the occlusion in a middle position (centric position).

The non-supporting cusps are the maxillary buccal and the mandibular lingual. These

cusps do not occlude or fit into fossa or marginal ridge areas and are called balancing ornon-c€ntric cusps. These cusps allow the dentition to move apart, out ofocclusion. They

allow teeth to "unlock" and move back and forth and side to side. These cusps have

sharper cusp ridges that serve to shear food as they pass close to the supporting cusp

ridges during chewing strokes

Supporting Cusps

WNon-supporting Cusps

Non-supporting Cusps

WSupporting Cusps

MaxillaryRight

First Molar

MandibularRight

First Molar

Anlerior guidance (sometimes called anterior coupllng) is a tightly overlapping rela-

tionship ofthe opposing maxillary and mandibular incisors and canines, which produces

disclusion of the posterior teeth when the mandible protrudes and moves to either side.

-{nterior teeth have a mechanical advantage over posterior teeth, due to the fact that they

are fanher away from the fulcrum (condyles), giving them better leverage to offset the

closing musculature. This apparent is apparent when one tries to occlude maximally withanterior teeth as opposed to occluding maximally in the molar region. The further away

lrom the site of muscle action, the less force is exerted.

Important point ofall this: ifanterior guidance can be accomplished, the least amount

of tbrce u'ill be placed on the teeth during muscular contraction.

Incisal guidance is a measure of the amount of movement and the angle at which the

lo* er incisors and mandible must move from the overlapping position of centric occlu-

sion to an edge-to-edge relationship with the maxillary incisors.

It is the second end-controlling factor in articulator movement. It is, to some degree, under

the control ofthe dentist. Influencing factors include: l) esthetics, 2) phonetics, 3) ridge

relations, 4) arch space, and 5) inter-ridge space. Esthetics and phonetics are the primary

factors limiting the dentists control of incisal guidance. The incisal guidance on the ar-

ticulator is the mechanical equivalent ofhorizontal and verlical overlap.

Note: The right and left condylar mechanisms are the other end-controlling factors in ar-ticulator movement.

. Optimum occlusion requires minimum adaptation by the patient

. Bilateral balanced occlusion dictates that a minimum number of teeth should contactduring mandibular excursive movements

.Unilateral balanced occlusion or "group function" calls for all teeth on the working sideto be in contact during a lateral excursron

. Mutually protected occlusion, also called "canine guided" or "organic" occlusion is theone in which anterior teeth protect posterior teeth in all mandibular excursions

. Mutually protected occlusion is the most widely accepted anangement ofocclusion

120Coplrighr g 2011,2012 DentalDecks

. The amount of vertical overlap of the anterior teeth

. The contou ofthe articular eminence

. The height ofthe pulp hom ofthat particular tooth

. The amount and direction oflateral shift in the working side condyle

. The position ofthe tooth in the arch

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Coptrighr O 201 1,201 2 , D€ntal Decks

Important: In bilateral balanced occlusion the maximum number ofteeth should con-

tact during mandibular excursions. This concept ofocclusal arrangement, though ideal, is

very difficult to achieve.

The determinants of occlusion include the right and left TMJ, the occlusal surfaces ofthe teeth and the neuromuscular system. The concepts of occlusal arrangement aim toplace the artificial teeth in harmony with the TMJ and the neuromuscular system. If this

is done properly, it will result in minimum stress on the teeth and only a minimum effortwill need to be expended by the neuromuscular system when performing mandibular

movements.

There are four features ofthe human dentition which directly affect the health ofthe PDL

and its hard tissue anchorage in terms ofresisting occlusal force:

l Ant€rior teeth have slight or no contact in the intercuspal positton.2, The occlusal table is less than sixty percent ofthe overall faciolingual width ofthetooth.3. The occlusal table of the tooth is generally at right angles to the long axis of the

tooth.,1. Crowns of mandibular molars are inclined about l5-20 degrees toward the lingual.

The four theoretical determinants needed for restoring a complete and functional oc-clusal surface ofa tooth are:

1. The amount ofvertical overlap ofthe anterior teeth

2. The contour of the articular eminence3. The amount and direction of lateral shift in the working side condyle4. The position of the tooth in the arch

However, the jaw relationship most frequently used in the actual design of restorations

is the acquired centric occlusion.

Note: The anterior determinant of occlusion is the horizontal and vertical overlap

relationshio of anterior teeth.

. The maximum distribution ofocclusal stresses in centric relation

. The forces of occlusion should be bome as much as possible by the long axis of theteeth

. When there is point-to-surface contact of flat cusps, it should be changed to asurface-to-surface contact

. Once centric occlusion is established. never take the teeth out ofcentric occlusion

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. The distobuccal groove ofthe mandibular first molar

. The buccal groove ofthe mandibular second molar

. The mesiobuccal groove ofthe mandibular second molar

. The developmental groove between the distobuccal and the distal cusps of themandibular first molar

123Cop).right O 20ll-2012 ' Dertal Decks

*** This is false; when there is surface-to-surface contact of flat cusps, it should be

changed to a point-to-surface contact.

The basic principles for occlusal adjustment include:. Maximum distribution olocclusal stresses in centric relation.. Forces ofocclusion should be bome as much as possible by the long axis ofthe teeth

(Picture A).. When there is surface-to-surface contact of flat cusps, it should be changed to a

point-to-surface cofiact (Pictut? B).. Once centric occlusion is established, never take teeth out of centdc occlusion

,w'-wSurface-to-surlace point-to-suface

Important:. The mesiobuccal cusp ofthe maxillary ftrst molar opposes the mesiobuccal groove

ofthe mandibular first molar. This relationship is a key factor in the definition of Class

I occlusion.. The distobuccal cusp ofthe maxillary first molar opposes the distobuccal groov€ ofthe mandibular first molar. Note: This distobuccal groove also serves as an escapeway

fol the )IL cusp ofthe maxillary first molar during non-rvorking excursive movements.. The oblique ridge ofthe maxillary first molar opposes the developmental groovebe-t\\'een the distobuccal and distal cusps ofthe mandibular first molar

Remember: The maxillary buccal (facial) and the mandibular lingual cusps are guid-ing cusps. The inner occlusal inclines leading to these cusps are called guiding inclinesbecause in contact movements they guide the supporting cusps away from the midline.Thus. there are the bucco-occlusal inclines (lingual inclines oJ the buccal ctrsps) of themaxillary posterior teeth and the linguo-occlusal inclines (huccal inclines of the lingttolc u.rp.s) ofthe mandibular posterior teeth.

. Non-working side condyle only

. Working side condyle only

. Both the non-working and working side condyles

. Neither ofthe condyles

. Maxillary lingual cusps

. Maxillary buccal cusps

. Mandibular lingual cusps

. Mandibular buccal cusps

124Coplrigh e 201 I 2012, Denral Decls

125

Coplrigh O 201l-201? ' Dental Dec16

When posterior teeth are in a normal ideal relationship, which of thefollowing cusps are consider€d to be guiding cusps?

In a lateral movement, the non-working side condyle moves downward, forward, andmedially. The working side condyle moves laterally. Since the mandible is a solid bone,the amount that the non-working condyle moves medially determines how far the work-ing side condyle moves laterally. The Bennett movement is sometimes called the lateralshift of the mandible or immediate side shift.

Important: This movement influences the lingual concavity of the maxillary anteriorteeth and directional placement of the ridges and grooves on the mandibular posteriorteeth as well as the mesiodistal position ofthe cusps of posterior teeth. Note: The Ben-nett angle is the angle formed by the sagittal plane and the path of the non-workingcondyle during lateral movement ofthe mandible, as viewed in the horizontal plane.

Right Mandibular MovementOn the right side (worhng side), the condyle moves from C (centric) to right working/I//. This movement is the Bennett movement.

These cusps are also called balancing, non-supporting, non-centric or shearing cusps.

These cusps do not occlude or fit into fossae or marginal ridge areas on the opposite arch

They allow the dentition to move apart, out ofocclusion. They allow the teeth to'.lln-lock" and move back and forth and side to side.

Supporting cusps are the maxillary lingual cusps and the mandibular buccal cusps. These

cusps are also called working, stamp or centric cusps. Centric stops are areas ofcon-tact that a supporting cusp makes with opposing teeth. For example, the mesial lingualcusp ofthe maxillary frst molar (a supporting cusp) makes contact with the central fossa

lcentric stop) of the mandibular first molar.

Supporting cusps contac! the opposing teeth in their corresponding faciolingual center

on a marginal ridge or a fossa. Non-supporting cusps overlap the opposing tooth with-out contacting the tooth.

\ote: In posterior cross-bite situations, the supporting and guiding cusps are opposite.

The maxillary buccal and the mandibular lingual would be supporting and the maxillarylingual and the mandibular buccal would be guiding.

of Prmthodontic Terms't defines balanced occlusion rs:

. An occlusion of the teeth which presents a harmonious relation of the occludingsurfaces in centric only within the functional range

. An occlusion of the teeth which presents a harmonious relation of the occludingsurfaces in eccentric positions only within the functional range

. An occlusion of the teeth which presents a harmonious relation of the occludingsurfaces in centric and eccentric positions within the functional range

126Coplright C 20ll-2012 - Dental Decks

. After a fixed bridge or a partial denture is delivered to a patient

. Before constructing a fixed bridge or a partial denture for a patient

. After a fixed bridge but before a partial denture is delivered to a patient

. After a partial denture but before a fixed bridge is delivered to a patient

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Cop"ighr @ 201| '2012 - Dental Decks

Five significant factors that govem the establishment ofbalanced articulation are:

. Inclination ofthe condylar guidance: totally diatated by the patient

.Inclination ofthe incisal guidance: horizontal and vertical overlap

. Inclination ofthe occlusal plane: plane oforientation

. Convexities ofthe compensating curve

. Angle and height ofthc cusps

Some ofthese,ifnot all, are

contolled bythe dentist.

tron.

Recommended occlusion for complete dentures: Recommended practice is to develop maxi-mum intercuspation of complete dentures to coincide with CR at an acceptable OVD. Failure toachieve that can lead to intolerance, usually because of instability of the dentures or because ofpain ofthe alveolar mucosa as a result ofuneven load disftibution and high stress concentralions.It is also recommended that a balanced occlusion is provided in order to help give occlusal stability.Note: Balanced occlusion requires that the maxillary lingual cusps of the posterior teeth on the

non-working side contact the lingual incline of facial cusps ofmandibular posterior teeth in con-junction with balanced contact ofteeth in the working side.

Balanced centric occlusion in partial dentures is necessary for the stability ofthe appliance. De-

sign ofthe framework and the relationship ofthe teeth to the ridges also influences the stability ofthe partial. Bilateral ecceltric balance is not an objective in partial denture construction unless

the partial prosthesis is opposed by a complete dentur€. The vertical relation for RPD'S is usuallydetermined by the remaining natural teeth (unlike complete dentures).

- , I . Eccentric occlusion is defined as protrusive and right and left lateral contacts of the

fiotei. inclined planes of the teeth when the jaw is not moving.

=;jji 2. Articulation can be defined as the relationship ofteeth during movements into and

awav from eccentric Dosition while the teeth are in contact.

*** This is done to prevent duplicating the deflective occlusal contacts in the final restora-

Note: One cornmon case in which it would be pr€ferable for selectiv€ grinding to be

completed after the fixed bridge or partial dentue is in place is when a fixed or remov-

able partial denture is to be constructed for a space over which the opposing tooth has ex-

truded slightly. The bridge or partial is frequently constructed to the ideal plane ofocclusion and the opposing tooth is adjusted after insertion.

The most common complaint after cementation of a fixed bridge is sensitivity to hot /cold and is an indication ofa deflective occlusal contact. The teeth involved may also be

sensitive to touch and this may be noticed by the patient while brushing. In these cases,

an immediate correction ofthe occlusion must be made.

The purpose of selective grinding is to remove all interferences without destroyingcusp height. With such an objective in mind, whenever interferences exist in centric butnot in lateral excursions, the fossa or marginal ridge opposing lhe premature cusp is deep-

ened. It is important that whenever a prematurity is found, the occlusion be checked in allcentric positions before any adjustment is performed. Ifcusps are found to interfere withone another in excursions, then only the non-holding cusps should be ground to prevent

a decrease in vertical dimension.

Important: Ifyou plan on changing a patient's vertical dimension through crowns,it is critical to mount a patient's casts on the true hinge axis (use a Jbce bow).

. Recurrent decay

. A periodontal problem

. Occlusal trauma

. An open margin

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Coplright O 20ll-2012 - Dental D€cks

. A pontic should b€ in contact in centric occlusion

. A pontic may or may not be in contact in working-side movements

. A pontic should be in contact in non-working side movements

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Coplright O 201 I -20 l2 - Dental Deck

If centric relation occlusion is high, patients will complain of cold sensitivity and painupon biting down hard. All patients should have an appointment specifically to check theocclusion on all crowns and bridges. Excursive movements should also be evaluated.Many times patients will complain of pain on chewing soft foods, which indicates im-proper balancing or working contacts. The occlusion ofgold restorations is best checkedwith silver plastic shim stock.

Important: Initial sensitivity can be caused by acid irritation accentuated by dehydrateddentin from prolonged drying ofthe tooth before cementation or incorrect liquid / pow-der ratio ofthe cement.

Radiographic signs ofocclusal trauma include hypercementosis, root resorption, alter-ation ofthe lamina dura, and alteration of the periodontal space.

Note: If a marginal ridge is left higher than an adjacent marginal ridge, an interferencein retrusive movement may occur.

*** This is false; a pontic should not be in contact in non-working movements.

Remember: The success or failure of a bridge depends mostly on the design of thepontic. The design is dictated by function, esthetics, ease of cleaning, patient comfort,and the maintenance by the patient ofhealthy tissue on the edentulous ridge.

Proper d€sign is more important to cleanability and acceptable tissue well-being than isthe choice of materials (porcelain, gold, etc.).

Note: Multiple adjacent pontics on an anterior fixed bridge have reduced facial embra-

sures to enhance esthetics.

. Is totally controlled by the dentist

. Is totally dictated by the patient

. Is padially dictated by the patient but can be adjusted by the dentist ifnecessary

. Can be adjusted by the laboratory technician

r30Coprighr O 201 l-2012 - Denlal Decks

. A loss of interocclusal distance when the mandible is in the rest positton (decreased

free*^ay space)

. An excessive interocclusal distance when the mandible is in lhe restoosrtron ftncreased

freeway space)

. Neither ofthe above, vertical dimension ofocclusion does not affect interocclusal dis-tance

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Condylar guidance is the mechanical device on an articulator which is intended to pro-duce similar guidances in articulator movement that are produced by the paths of thecondyles in mandibular movements.

It is important to realize that condylar guidance is a factor which is totally dictated bythe patient. It cannot be varied or "adjusted" by the dentist. The inclination of condylarguidance depends on: 1) the shape and size ofthe bony contour ofthe TMJ (fossae anddisc),2)the action ofthe muscles attached to the mandible, 3) the limiting effects oftheligaments, and 4) the method used for registration.

Rememb€r:. The incline or angulation ofthe condylar element on the articulator is anatomicallyrelated to the slope of the condylar articular eminences (condylar inclination).. When adjusting the condylar guidance for protrusive relationship, the incisal guidepin on the articular should be raised out of contact with the incisal guide table. Theprotrusive record is probably the least reproducible maxillomandibular record.

Note: When restoring the entire mouth with crowns, the protrusive condylar pathinclination influences the mesial inclines ofthe mandibular cusps and the distal inclinesof the marillarv cusos.

A classic example of a decreased vertical dimension: People with no teeth or people who have womdentures fora long time present with the lower portion ofthe face scrunched up or do not show their lips

anymore (poor facial proftle).

Solution: Make new dentues and increase the vertical dimension ofocclusion. By doing this, you willdecrease the int€rocclusal distance and decrease freeway space.

Some effects ofexcessive vertical dimension ofocclusion:. Exccssive display ofmandibular teeth. Comf'laint of faligue oImuscles ofmasticalion. Clicking ofpostcrior teeth when speaking. Strained appearance ofthe lips. Patient not able to wear dentures. Discomfofi. Excessive trauma to the supporting tissues. Gagging

Some effects of insulficient vertical dimension of occlusion:. Aging appearance ofthe lower third ofthe face due to thin lips, wrinkles, chin too near the nose,

overlapping comers of the mouth. Diminished occlusal force. Angular cheilitis

Conect vertical dimension ofocciusion is evaluated using the foJlowing methods

l- Overall appearance offacial support.2. Visual obser.r'ation ofspace between the occlusal fims at rest.

3. Measurements between dots on the face f)rrich were placed for thri rearor?./, when the jaws are at

rest and when the occlusal rims are in colltact.4. Observations when the "s" sound is enunciated accurately and repeatedly. This ensures adequate

speaking space between the occlusal rims/occlusal plane.

Centric occlusion (CO) is ^2

. "Muscle-guided" position

. "Ligament-guided" position

. "Tooth-guided" position

132Coptright O 20ll-2012 Denial Decks

. A prerequisite for the use of this technique for the restoration of a single tooth is thepresence ofa Class III occlusion

. This technique allows the cuspal movements of the dentition to be recorded in waxintra-orally and transferred to the articulator in the form ofa static plaster cast

. This static plaster cast is also called the ftnctional index

. By registering the pathways of the opposing tooth sudaces during mandibularmovements, the technique allows a laboratory technician to provide a restoration withan occlusal surface less likely to incorporate occlusal interferences

t33Coplri8ht Ci 2011,2012 - DentalDecks

Three Basic Jaw Positions

1) Centric occlusion {'CO) or the intercuspal /C) position is the relationship between maxillary andmandibular occlusal surfaces that provides the maximum contact and or intercuspation independentofcondylar position. It is a "tooth-guided" position.2) Centric rel.tion fCR) (also called the retruded contact position) 1s the most unstrained, retrudedanatomic and functional position ofthe heads ofthe condyles ofthe mandible in the mandibular fgle-noid) fossae ofthe temporomandibular joints. This is a relationship of the bones ofthe upper andlowerjaws without tooth contact. The presence or absence ofteeth, or the type ofocclusion or mal-occlusion, are not factors. It is a "ligament-guided" position. Note: The mandible cannot be forcedinto cent c relation from the rest position because the patient's reflex neuromuscular defcnse wouldresist the applied force. The mandible should be relaxed and gently guided into cenhic relation.3) The rest position of the mandible or the postural position is determined mostly by the muscu-lature, The usual reflex cited as the basis for the postural position of the mandible is the tonic stretchreflex ofthc mandibular levators fi.€., the myotatic rellex).lt is a "muscle guided" position.

-.. -. L In most people (90o/o), CR and CO do not coincide.

No&j.,'2.AccurateCRinterocclusalrecordsrequiremanipulationofthemandiblebythedentist.,, .-,.--,'11 3. The most common mate als used for interocclusal records are wax f,4/rwax) and fast-e'

setting elastomeric materials such as polyvinyl siloxane and polyether.3. Woelfel leaf gauge method of recording CR: a thin flexible wafer is customized. Usedwith its leafgauge it helps to guide the mandible superiorly and posteriorly and to maintainthe desired rninimum vertical opening. The recording material ofchoice is polyether, next is

zinc oxide-eugenol paste.

4.. Casts mounted with an interocclusal record are mounted more accurately ifthe materialused is selected according to the accuracy ofthe casts bing afiiculated, (casts produced withirreversible hydocolloid are more acctrately mounted with vaa records, and casls obtainedvith elastomeric materials are more accurateb mounted v,ith elaslomeric registration ma-

terials or zinc and eugenol paste).

*** This is false; a prerequisite for the use ofthis technique for the restoration ofa sin-gle tooth is the presence ofan optimal occlusion.

A major difficulty for any dental laboratory technician is to determine the cuspal move-ments ofthe dentition using hand-held casts or casts mounted on a simple hinge articula-tor. The functionally generated pathway technique allows these movements to be recordedin wax intra-orally and transferred to the articulator in the form ofa static plaster cast (the

functional index).

The involved tooth should be immobile and the recording material (low-fusing hi-Ji wax)

retained on the prepared tooth, not moving separately, during the generation ofthe FGP

wax record. The involved tooth should have unprepared teeth anterior and posterior to itto act as refer€nce surlaces for checking the complete seating ofthe functional core ofthe$,orking cast. There should be no occlusal interferences pre-operatively and the op-

posing surfaces should be properly restored.

I . The functional index becomes a static registration of all the movements ofthe opposing cusps.

2. The important consideration in generating this functional pathway is that allmotion ofthe mandible must be directed from an eccentric to a centric posi-tion, never the reverse.

3. Full case articulation is more universally applicable in obtaining occlusal

relationships for the fabrication ofa wax pattem.

,, Notedt

Wi

(A) A decreased vertical dimension of occlusion refersdi stance (i n cr e a s e d fre ew ay s p a c e)

(B) A decreased vertical dirnension of occlusion refers

to excessive

to the loss of

interocclusal

interocclusaldistance in the rest position

(C) Al excessive vertical dimension frequently results in cheek biting(D) An excessive vertical dimension is the usual cause ofclicking ofteeth(E) Phonetics helps in verifying the vertical dimension ofocclusion(F) Esthetics helps in verifying the vertical dimension ofocclusion

. (A), (C), and (E) are true

. (B), (D), ard (F) are fue

. (A), (C), (E) and (F) are true

. (B), (C), (E) and (F) are true

. (A), (D), (E) and (F) are true

. All of the above statements are true

13r|

Copyrighr O 2011"2012 - Denral Decks

One disadvantage ofd€ntal porcelaln restorations ls:

. Poor esthetics

. Expansion

. Brittleness

. Radioactivity

'| 35

Copyrigh O 201 I ,2012 - Dental Decks

The following must be considered while verifying the vertical dimensions of theocclusion:

. Pre-extraction records

. The amount ofinterocclusal distance (freeway space) to which the patient was previ-ously accustomed to. Esthetics

-facial harmony should be noted along with facial expresston

. Phonetics -speech

sounds. Length ofthe lip in relation to the teeth. The condition and amount of shrinlage ofthe ridges

The compressive strength ofceramic bodies is greater than either their tensile or their shear strength The

tensile strength is low because ofthe unavoidable surface defects. The shear strength is low because ofthe lack ofductility or ability to shear, caused by the complex stluctule ofthe glass ceramic materials.

The shear and tensile strengths of the fired porcelain are so low that the slightest imperfection in the

preparation ofthe cavity in the tooth may cause thejacket crown to ilactue in service.

Remember;. Tle tooth preparation reduction for the mettl-ceramic restorations (1.5-2.0 nn) must provide

space for the metal f0. 5 ht ) and porcel^in (1 .0- 1.5 nm). The metal substructure provides support and increases the strength ofthe porcelain. All intemal line angles where porcelain is veneered should be rounded to prevent shess concen-

tration. The metal-porcelain junction should be at a right atrgle to avoid porcelain fracture. Occlusal contacts must be at least 1.5 mm away from porcelain/metal junctton. The coefficient ofthermal expansion ofthe porcelain must be slightly lower thafl that ofthe metal

to place the porcelain in slight compression when cooled. Porcelain is stronger under compressive forces than it is in tensile forces. Metal oxide formation is necessary for the metal-cemmic bond

1. Many porcelains rust at a temperature over 2000pF.

,. *-o6g] 2. The glaze firing is the last firing and it produces a smooth, translucent surface.

e_ _ i 3. Denlal porcelain has good biocompatibility. but is very brinle.ry 4. All-porcelain crowns are superior to ceramo-metal crowns in esthetics oriy (as compared

wilh stre gth, hanlness and toughness).

5. In a ceramo-metal unit, the porcelain surfacc should be under slight compressive stress(it should not be under tensile or shear stress).

6. The core material in an all ceramic crown is usually a high strength sintered ceramic.7. Porcelain substrate alloys, when comparcd to faditional alloys, melt at a higher tem-perature.

. Interposition ofan intermediate metal layer

. Mixing of oxidized metal layem with porcelain oxides

. Wetting ofthe porcelain onto the metal surface

. Mixing of the metal atoms with the porcelain structure

136

Coplrighr O 20ll-2012 'Denial Decks

. Hue

. Chroma

. Value

.Intensity

137

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Porcelain attaches to metal substrates by mechanical and chemical bonding. Roughness from sand-blasting the cast metal restoration allows porcelain to mechanicaliy bond to metal. The mixing ofoxi-dized metal layers with porc€lain oxides allows the porcelain to chemically bond to metal. Note: Tleelements Sn,In, Fe, and Cr all conhibute to metal oridation for chemical bonding to porcelain. Im-portant: (l) Fe is key in PFM bonding to gold b.sed alloys (2) Cr is key in PFM bonding to gold-sub-stitute alloys.

Three layers of porcelain. The opaque porcelain must mask the dark oxide color as well as provide the porcelain-metal bond. The body porcelain makes up the bulk ofthe restolation, providing most ofthe color or shade. The incisal porcelain is a translucent layer ofporcelain in the incisal or cuspal portion ofthe tooth

The opaque is applied lirst to mask the metal and to give the restoration its basic shade. Body porce-lain is then added overthe opaque. Incisal porcelain is added to the incisalone{hird to give translucency.The restoration is bufked out (overcontoured) to compensate for the 20yo shrinkage, which occurs dur-ing firing.

Opaque porcelain showing through on the facial surface ofa metal-cemmic crown may be caused bythe following:

. Inadequate tooth reduction -

fault ofthe dentist. The metal is too rhick fault ofthe lab. The opaque porcelain is too thick

-fault of the lab

. Inadeouate thickness ofthe bodv Dorcelain -fault

ofthe lab

L All ofthe following can lead to "pop-off' ofporcelain from PFM crowns:. Contamination of the porcelain-to-metal interface. Thick layers ofsurface conditioners on the metal. Under-firing ofthe opaque layer

2. Surface mic.o-cracks in porcelain are caused by cooling stresses related to thc poor thcr-mal conductivjty of porcelain.3.Built-in strcsscs in the Dorcelain contributcs most to PFM failure.

Thre€ standard descriptions of color:

l. Chroma: is the saoration or sffength ofa color fdegree ofsaluration ofthe lue)2. y^hte (or brightness): is the relative amount oflightness or darkness in a color3. Hue: refels to color tone (e.g., rerl, hlue, vellov, etc.) and is synonymous with the term coLor.

- 1. Value is the single most important factor in shade selection.

l.lntensit\ is included rn the term value.'toY I fh. hu".hould be <elected first \rhen picking a shade.

-1-a- 4. The Vitepan r'r 3D-Master shade guide ft'?/e nt, Brea, CA) is ananged in five lightness levels

and a level for bieached teeth. Each lightness level has sufTicient variations in chroma and hue to

cover the natural tooth color space.

Characterization is the ar! ofreproducing natural dcfects. This can be particularly successful in making a

cro\\ n btend \\'ith the adjacent natural teeth. T}e addition ofyellow stain increases the chroma ofa basically yellow shade. Addition oforange has the

same effect on a crowl as ayellow-red hue. Too high a chroma is impossible to decrease in hue or increase

tn |aluc.. The only two modifications that usually are done to hue are: pink-purple will move yellow toward yql-

lo\l'red. whereas yellow will decrease the red content ofa yellow-red shade. Note: This is because a natu-

ral tooth always lies in the yellow-red to yellow rangc.. Adding a aomplimentary color can reduc€ value. Violel is used on ycllow restorations, which has the

added effect of mimicking translucency.. Stains are metallic oxides that fuse to the porcelain during a predetermined firing cycle. Staining a porcelain restoration will reduce the value fas t1,i11 ll sing 4 complementarv color). It lsalmost impossible to increasc the value

\ote: In esthetics, the value ofa denture tooth depends upon the relative whiteness orblackness of its color

The surface characteristics ofporcclain can affect the perceived form ofthe final restomtion in the follow-ing ways:

. A smooth surface will give the impression ofa larger size

. Changes in contour can be used to alter the apparent long axis inclination of a tooth

. Fluorescence

. Metamerism

. Opaqueness

. Opalescence

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Cop),righr O 201 I -20 l2 - Dental D€cks

. Obtained by heating the previously fired body very slowly for 60 minutes at its fusingtemperature

. Nonporous, resists abrasion, possesses esthetic ability and is well tolerated by thegingiva

. Not as durable (in its surface characteristics) as an over-glazed porcelain

. All of the above

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This property is important in matching the shade of a metal-ceramic crown to a natualtooth. Thus, ifpossible, color matching should be done under two or more different lightsources, one of which should be sunlight. Note: Staining ofthe porcelain will increasemetamenc responses,

Fluorescence is the optical property by which a material (for example, teeth) reflects r0.l-

traviolet radiation. The energy that the tooth absorbs is converted into light with longerwavelengths, in which the tooth actually becomes a light source. Human teeth fluorescemainly blue-white furcs (400450 nm range). Fhtorescence makes a definite contribu-tion to the brightness and vital appearance ofnatural teeth.

Opalesence is the light effect of a translucent material (incisal edge of some teeth) ap-pearing blue in reflected light and red-orarge in transmitted light.

Note: The production of color sensation with a pigment is a physically different phe-

nomenon from that oblained by optical reflection, refraction and dispersion. The color ofa pigment is determined by selective absorption and selective radiation (scattering).

Remember: The light source affects the perception of color, because the light sourcemust contain the wavelensth ofthe color to be matched in order to see that color.

At least three stages are generally recognized in the firing of dental porcelain: 1) lowbisque firing 2) medium bisque firing and 3) high bisque firing. The temperature at whicheach occurs depends upon the type ofporcelain used.

A natural glaze occurs when the porcelain restoration itselfis glazed by a separate firing(this process is referred to as "the glaze firing'). Ifthe body, previously fired as a highbisque, is heated rapidly (10- I 5 ninutes) to its fusion temperature and maintained at that

temperature for approximately 5 minutes before it is cooled, the glass grains flow over the

surlace to form a vitreous layer, which is called a glaze. Note: This type ofglaze is much

more permanent than the overglazes.

Overglazes (or applied glazes) are ceramic powders that may be added to a porcelain

restoration after it has been fired. A transpa:ent, glossy layer forms over the surface of the

porcelain restoration at a maturing temperature lower than that ofthe body porcelain. The

result is a glossy or semiglossy surface that is non-porous. Erosion of this overglazemay occur in the mouth and this leaves a rough and sometimes porous surface.

Note: Glazed porcelain (either type) is the least irritating to the gingival tissues com-pared with polished cast gold, polished direct filling gold and polished acrylic resin.

. Denture teeth

. All ceramic crowns

. Metal-ceramic crowns

. All ofthe above

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Cop"ighr O 201 l'2012' D€ntal Deks

prior to adding porcelrin is called:

. Quenching

. Pickling

. Degassing

. Investing

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coptright @ 20ll-2012 - Denbl Decks

The difference beween low- medium- and high-fusing porcelains is the firing temperature used to fuse

the glass. Today's low-fusing porcelain was developed to be less abrasive to opposing dentition by in-

corporating finer leucite crystals in lower concentrations.

Classifi cation based or\ fusion (vitrif ic a t io n ) temperature:

. High-fusing: 1288 to 137l"C (2350 to 2500"F): wed for denture teeth

. Medium fusing: 1093 to 1260'C (2000 to 2300"F): $ed fot all-ceramic and porcelain Jacket crowns

. Low fusing: 8'71to 1066"C (1600 lo /950'F): uesd for metal-ceramic crowns

Remember:I. The compressive strength (350-550 MPa) of a porcelain testoration is greater than its tensile(20-60 MPa) or shear strengths, which is typical ofa brittle solid.2. Aluminous porcelain uses alumina instead ofquartz as a strengthener. This type ofporcelain is

considerably stronger than conventional porcelains.3- Dental porcelain restorations are brittle and are not capable ofmuch plastic deformation.

Ceramic Properties:L Physical Properties:

. Inrermediate density (1.0-3.8 gns/cc)

. High melting point (: reJi'actory,t

. Low coefficient ofthermal expansion (l-l5 ppmfC)

2- Chemical Properties:. Low chemical reactivity. Low absorption and solubility

J. \Iechanical Properties;. High modulus ofelasticity. Much stronger in compression than tension (approximately 10X). Biftle (\o'|, plostic deformation (<0.1%o);low fracture toughness

-+. BiologicalProperties:. Relatively inert

It is necessary for all gold-porcelain systems. Degassing ofthe metal at too low a tempera-

ture will effect the formation of the oxide layer, which is important in bonding ofthe porce-

lain. The number ofbubbles formed at the interface decreases as the time and temperature ofdegassing are increased.

After degassing the casting is ready for porcelain addition. The metal liamework must not b€

contaminated by handling prjor to porcelain addition. Ifit is, the bond ofthe opaque will be

veakened.

Causes of porcelain fracture at porcelain-m€tal interface:. Poor metal fiamework design: main cause offracture. Fusing the opaque coat ofporcelain at too low a temperature or for too short a time. Degassing ofthe metal at too low a t€mp€ratur€, which effects the formation oftheoxide layer. thus decreasing the bond. Contamination of metal prior to opaque application

\ote: Both the metal (alloy) and ceramic (porcelain) must have coefficients of thermal ex-pansion that are clos ely malched (alloy is usually slightl, harder) ifundesirable tensile stresses

at the interface are tobe avoided (racnre of the porcelain). Alloys should have a high pro-portional limit, and particularly, a high modulus of elasticity. Alloys with a high modr.rlus

\\'ill reduce shess on the porcelain.

Pickling is the process ofremoving surface oxides from a casting prior to polishing. The cast-

ing is placed in an acidic solution which reduces the surface oxides. To prevent injury safety

goggles should always be wom when pickling.

. The first statement is true; the second statement is false

. The first statement is false; the second statement is true

. Both statements are true

. Both statements are false

142Coplrighr O 201 l-2012 - Denrnl Decks

. Sintering ofa ceramic:

. Involves heating the raw materials above the melting point

. Results in an increase in porosity

. Decreases its mechanical strength

. Increases its density

143CoptlighrO 20lt 2012, Denral Decks

Classilicstion according to method of frbrication:. Powder condensation:This is considcrcd thc tmditional way for f'abrication ofan all-ccramic rcstoration. Thistcchniquc involvcs applying moist porcelain using a spccial brush, thcn compacting the porcelain by rcmoving thccxccss moisturc- Thc porcclain is (hcn fircd undcr vacuum allowing fu(hcr compaction. Ccramics fabricatcd bythis technique havc a great amount oftranslucency and are highiy csthciic, and arc uscd maidly as vcnccrirg ]ay-crs. Notei Powder condcnsation utilizcs fcldspathic porcclain.

Feldspathic porcelain: Potassium and sodium fcldspars arc naturally occurring clcmcnts composed mainly ofpotash(K20) and sod^ (Na 20) , thcy also contain alumina (Al2O) and soda (Na2O) . Leucitc and a glass phasc arc fonncdwhcn potassium feldsparis fircd to high tcmpcraturcs. Thisglass phase softens during firing allowing coalescencc ofthc porcclain powdcr particlcs. This proccss is callcd liquid phasc sintcring. This proccss occurs at a relativcly hightemperaturc allowing thc formation ofa dense solid. Sincc lcucitc has a largc cocfl'icient ofthermal cxpansior, it is

added to somc glasscs to control thcir thcrmal expansion. Feldspathic porcclain is composed mainly ofoxidc com-poncnfs including:

. SiO2 62-62 "'t

%)

'Al2O/ll-16fl!/o). Na2O (5-7 wt %). Li"O and B2O as additivcs

Since the porosity ofa ceramic is highly correlated with ils mechanical properties, reducing thc number ofdcfbcts ina ccramic is a common way ofincrcasing its sfcngth, Thc most common way oflowcring a ccmmic's porosity is sin-iering. During sjntcring a ceramic material isheated in a fumace or ovcn likc dcvice;where it is crposcd 10 high lem-pcratu.cs. Thcse tcmpcratures depend on the material,butyou should know that they\yill alwaysbe below thc mcltingpoint of$e ceramic. During thc sintcring proccss thc porcs in thc ccramic will closc up thcrcby reducing the num-ber oidelccts. Sintered all-cerNmic mat€rials include: alumina based ceramic, leucitc-rcintbrccd feldspathic porcc-

lain, magncsia-bascd corc porcelain, heat-pressed all-cemmic matcrial and lcucite-based Iithium disilicate basc.

. Slip Casting: This techniquc involves forming a mold ofthc desired framework gcomctry and pouringa slip inlorhe formcd mold. Gypsum is usually utilized to form thc mold due to its ability ofcxtracting somc ofthe watcrfrom ihe slip. Thc slip thc bccomcs compactcd against thc mold forminga fiamcwork. Thc frameq,ork is thcn re-molcd from the mold by partial sintcring. Thc rcsulting ccramic is vcry wcak and porous and must be infiltcred$ith glass or fully sinlcrcd bcforc application ofthcvcnccring porcclain. Matcrials processed by this tcchniquc tcndro halc tcwcr defects from proccssing, and cxhibit highcr toughncss lhan thc convcntional fcldspathic porcclain.Thc usc of this tcchnique in dcntistry has been limited to one ofthrce products. This limitation might bc duc thccomplicatcd stcps, which makcs achicving an accuratc fit diflicult. Slip cast all-ceramic materials include: alu-mina brscd. sDincl zirconia-based. and machined all-ceramic material.

Firing porcelain causes the powders to become "sintered." Sintering changes the porce-

lain from a powder to a solid. The powder is not melted, so the general shape is main-tained. Sintering porcelain is the same process that is used to fire clay pots, china, and

ceramic tiles. Reducing the porosity of the resulting product is very important. The less

porous (more dense) the product is, the greater the strength of the final product will be.

After sintering, the final shape ofthe restoration is refined by grinding.

l. When porcelain is fired too many tirnes, it may devitrify. This appears as a

"milky state" and makes glazing very difficult.2. Aluminum oxide is added to low-fusing dental porcelains (during its man-

tufacture) in order to increase its resistance to "slumping down" during firing.3. Glass, which is a prevalent phase in dental porcelain is arnorphous and frag-ile.4. The strength ofa ceramic decreases with flaw size.

5. Ceramic restorations are severely damaged by acidulated fluoride.6. All-ceramic restorations are more prone to fracture ifthe preparation line an-

gles are not rounded.7. Machine grinding of ceramics induces surface cracks.

;Xot"J;:. .':.

. A tooth-bome removable partial denture

. A bilateral distal extension removable partial denture

. A unilateral distal extension removable partial denture

. None ofthe above

144Cop}Tighl O 20ll-2012 - Denral Decls

The mrjor connecter fu:

. The connecting tang between the denture and other units ofthe prosthesis

. The part of the denture base which extends from the necks of the teeth to the borderof the denture

. The unit of a partial denture that connects the parts of the prosthesis located on oneside ofthe arch with those on the opposite side

. None of the above

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Cop).righr O 20ll-2012, Dental Decks

,: iiote3'rl. ::;:i:::,.:l

A distaf extension removable partial dentve (either bilateral or unilateral) receives itssuppoft ftom the residual ridge, tissue-bearing areas, selected abutment teeth and the fi-brous connective tissues overlying the alveolar process.

The most important factor in detemining the success of distal extension removable par-tial dentures (bilateral and unilalera, is proper coverage over the residual ridge. Cov-erage of the free-end should extend over the retromolar pad to create stability of the

RPD and to minimize the torquing forces on the abutment teeth.

1. The first step in relining a distal extension removable partial denture is tov€rify the fit ofthe framework. Important: This is done first even if you are

also relining a marillary complete denture which is opposing this distal exten-sion.2. When relining a distal extension panial denture, apply finger pressure to therests and indirect retainer.3. Ifthe indirect retainers are not seated as the extension bases are depressed. thebases need relining.

Important: Ifa patient complains ofsensitivity to percussion on an abutment tooth of adistal extension partial denture, the most likely cause is the occlusion on this abutment.

Deflective occlusal contacts can also cause a feelins of "looseness" to the denture.

The major connector must be rigid so that stresses applied to any one portion ofthe den-

ture may be effectively distributed over the entire supporting area. lt connects other com-ponents ofthe prosthesis and provides cross-arch stabilization.

They should be designed and located with the following guidelines:

. They should be free of movable tissues

. Relief should be provided

. They should not impinge on gingival tissues

. Bony and soft tissue prominences should be avoided during placement and removal

Note: A minor connector is the connecting link (or tang)between the major connector

or base ofthe partial dentue and other units ofthe prosthesis, such as clasps, indirect re-tainers and occlusal rests.

. Lingual plate

. Lingual baro Labial bar

. Palatal plate

. Single palatal strap

. Anterior-posteriorpalatalstraps

. Single palatal bar

. Horseshoe design

. Anterior-posterior palatal bars

. 2-4 mm wide

. 6-8 mrn wide

. 8-10 mm wide

. At least 12 mm wide

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CoplriSh O 201 l-2012 - Dental Decl!

. 3 mm ofvertical height between the gingival margin and the floor ofthe mouth

. 5 mm ofvertical height between the gingival margin and the floor ofthe mouth

. 7 mm ofvertical height between the gingival margin and the floor of the mouth

.9 mm ofvertical height between the gingival margin and the floor ofthe mouth

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Copyrighr o 201 t,2012 - Dentat Decks

Structurally, this combination of major connectors exhibits many ofthe same disadvan-tages as the single palatal bar To be sufficiently rigid and to provide the needed supportand stability, these comectors could be too bulky and could intefere with tongue func-tron.

Pllrt l plrt€: is a thin, broad conueclor ihat is indicated when all posterior te€th are missing bilat-eratly. when used the portion contactiDg the teeth rnust have positive lupport hom adequate restsea6.Slngle prlstaf strrp: is indicated in tooah-bot[ e &PDs (Keknedy Class 1,4, s'ith bilat€ral, shortspan edentulous areas,Anterlor-posterior p.lrtd strapsi structumlly, this is a rigid palatal major connector; it lnay be

used in almost any maxillary partial denture design.Sirgle palrtal brr: are obj€ctiomble because they lack rigidity. Their use is limited to tooth-bomerestorations for bilateml short spar edenlulous areas. The wide, thirr bar 6tdp) is more riSid withless bulk compared 10 a narow bar.Hors€shoe designi is the le.st rigid maxillary connertor; should only be l]sed when a large,

inopemble palalal torus pr€venls the use ofo$er desigts.Ant€rior-posterlor pslatal baft: to b€ sufficieDtly rigid to pfovide required suppon and stability,these majoi connector must be excessively bulky, which ofien irterteles with the tonglle.

Remember: The major and minor connectors must be rigid in order for the functionalstresses that are applied to the partial dentures to be distributed evenly throughout the

mouth

Linguoplrte: used when the depth ofthe lingual vestibule is less than 7 mm; when lingual toriare present and when al1 posteiior teeth are to be replaced bilaterally. Contraindication is

severe anterior crowding.Lingual bar: requires a minimum of 7 Inm of vertical heiglt between the gingival margin and

the floor of the mouth. Lingual bars should be placed so that the upper border is a minimum of3 mm below the gingival margins 8nd at least 4 mm is required for ihe vertical height ofthelingual bar; simplest and most commonly used major cormector.

Labial bar: is .sr€ly indicared. It can be used satisfactorily when large mandibular tod inter-

fere with conventionat lingual bar placement or when lower teeth are severely lingually tippedand placement ofthe lingual ba! is aot possible.

\ote: Lingually inclined mandibular premolars interfere most frequently with major

mandibular connectors.

. Resistance to tamish

. Low material cost

. Low densiry (weight)

. High flexibility

. High modulus of elasticity (stffiess)

ta8CoplriSht O2011,2012 - Dental Decks

. Looking at the x-rays

. Talking to the patient

. Surveying the cast

. The initial try-in of the metal framework

't4t'

Cop)'right O 201 I -2012 - Dental Drck

A high yi€ld strength and low modulus ofelasticity produce higher flexibility' The gold al-loys are approximat€ly twice as {lexible as the chromium-cobalt alloys, which is a distinctadvantage in the optimum location or retentive elements ofthe framework in many instances.

Note: The std?ess ofthe chromium-cobalt alloys can be overcome by including wrought-wire retentive €l€ments in the framework.

The popularity of chrcmium-cobalt alloys for fabrication ofcast frameworks for removablepartial dentures has been attributed to their low density (weight), hrgh modulus ofelasticity(stffiess),low material cost and resistance to tamish. Note: Chromium-cobalt alloys are more

rigid in comparison to gold or palladium alloys.

Composition of chromium alloys for partial dentures:. Chromium: ensures that the alloy will resist tamish a\d corrosion (due to formationof a complex chromium oxide Jilm). Cobalt: contributes strength, rigidness and hardness. Nickel: increases ductility. Minor constituents: carbon has a pronounced effect on the strength, hardness and duc-

tility. Tin, indium and other readily oxidized minor components ofthe alloy firnction to im-prove bonding.

Remember: The form ofchrome-cobalt alloy connectors is flat, broad and reinforced along

the borders by the bead on the tissue surface. The process ofbeading not only helps maintain

tissue contact, but also provides additional strer,gth (for maxillary major connectors).

Possible causes of fracture of chromium-cobalt partials include cold-working (which re'duces the percentage of elongation that causes a decrease in hardness), shrinkage porosity

Ithese alloys shrink approximately 2.3o.4 and the result is porosi4,), low percent €longation/is directl!- related to greater brittleness) and excessive carbon in the alloy (wrlrlch rcucts with

the other constituents to form carbides).

Surveying is generally perfomed at right-angles to the occlusal plane in the first instance, as this is the

likely path ofdisplacement. Sun'eying will identiry three principal factors: (1) The pfesence ofunder-

cuts (2) The contour ofthe undercuts rclativc to the gingival margin and (3) The depth ofthe undercuts

Extracoronal retainers are the most common type ofdirect retainer that is used for removable par-

tial dentures. They arc called clasps. The purpose ofthe clasp is fetain the RPD by means ofthe abut-

ments. To prevent horizontal movement of the clasp, this should encircle the tooth more than 180

degrees or one-halfthe circumference ofthe tooth. Their ability to provide retention is based on the re-

sistance of metal to defotmation. Note: Retentive clasps should beoome active only when dislodging

forces are applied to thcm. There are two basic categories ofextracoronal retainers: suprabulge and in-fr.bulge retainers.

Requirements ofa properly designed clasp:l. Support - against vertical forces

2. Bracing - against horizontal forces3. Retention - resist forccs in a occlusal direction4. Encirclement - of more than halfit's circumference5. Rcciprocity - equal and opposite forces by clasp arms

6- Passivity - at rest when seated

Intracoronal retainers (precisio attuchmettlt are the other tlpe ofdirect retainer that is somctimesused for removable partial dentures. These are attachments which are built into the contour of a crown

/c.rs,ingl to produce mechanical and frictional retention. By eliminating the need for a visible retentive

clasp, these retainers give optimtl esthetics. They provide vertical support through the rest seat located

more favorably in relation to the horizontal axis ofthe abutment teeth.

lmportanti Intracoronal retaineas are not used when a partial denture depends upon an edenfulous area

for support /distdl eiter.slorl. These retainers may provide a rigid con[ection between the denture and

the abrltment (line for looth-bone pdrlials). However, in distal extensions, functional motion must bepermitted without torquing the abutment teeth.

. Below the height ofcontour

. Above the height ofcontour

. Above the 0.08" undercut

. Above the occlusal surface of most molars

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Copyrighr O2011,2012 - Dental Decks

. More efticient retention

. Less distortion ofcoronal contours

. Less tooth contact

. Cleaner

. Less bothersorne to vestibular tissues

. Less prone to caries

. Esthetically superior in most cases

. Greater adjustability 151

Coplright O 201 I -20 12 - Denral Decks

Clasps that originate from above the survey line, usually liom an occlusal rest, and angle downward across

the cfinical cro\rn until the tip is located in a prescribed amount ofundercut are suprabulge ret^iners (clasps).

Examples of suprabulge ret.iners:. Circumlerentirl clasp: is composed ofa buccaland lingual arm originating from a common body. Usu-ally one arm is retentivc while thc other functions in bmcing. This clasp is used to engagc underculs locaicdon the side /merrdl-disr.r// ofthe tooth opposit€ to the site ofthe rest.. Ring clasp: encircles nearly all ofa tooth in order to €ngage an undercut located on the same side of the

tooth as the rcst. It should not be us€d where the caries rate is high orwhere esthetic considerations are dom-inant.. Embrasure clasp: is used when no edenlulous space exists at the clasp assemblysite.. Reverse-action clasp or hairpinchsp: may be used to engage an undercut located on the same side ofthe abutment as the r€st. It may be used on any posterior tooth, but it covers a lot oftooth surface and maybe esthetically objectionable.. Extended ,rm clasp: is a circumferential clasp which extends to neighboring teeth in order to provid€increased splinting and to engage a more favombly located undercut.. Halfand halfclasp: consists ofone circumf€rential clasp emanating liom the rest area and another armfrom the minor connector on the opposite side.

The current concept ofbar clasp design is the R.P.I. system:. Nlesial rest - point ofrotation which exerts a mesial force on the tooth. P.orimal plate - supeior edge at bottom ofguide plane to disengage during loading. Slightly lingual for

. I Bar - 2.5 mm liom gingival margin, crosses at right angles in a .01" undercut at the greatest M-D promi-nence to permit it to disengage during function

Adrantages of the R.P,I.:l. Proximal plate and I bar move away from the tooth during function to reduce torque.2. \Iesial minor connector and proximal plate provide reciprocation and eliminate need for a lingual arm.

-i. I bar more esthetic.,1. \linimal contact alters contour less, advantageous on caries p.one individual.5.. Mesial rest eliminates Class I lever.

*** This is false; infrabulge retainers are more bothersome to vestibular tissues.

Other disadvantages of infrabulge retainers:. Too flexible for effective bracing. Can be esthetically objectionable in patients with a high lip line. Where there are not enough guideplanes to positively establish the path of insertion,opposing cross-arch u.ndercuts can be used. In these cases, the effectiveness ofinfrab-ulge clasps are diminished because the unseating motion (without guideplanes) is ro-tary vertical and horizontal.

Infrabulge retainers are clasps that originate from below the survey line. They are metalprojections emanating from the denture base struts in the framework. They course tluoughthe denture base and project parallel to the mean plane ofthe gingiva until they make a

gentle right angle tum. Then they cross the gingiva and come to rest upon the abutmenttooth in a specified undercut area.

Infrabulge retainers must not be placed into tissue undercuts, nor should they contact theabutment at any place except at the specified undercut.

The bar clasp arm has been classified by the shape of the retentive terminal. These in-clude the T, modified I I, or Y. These bar clasp arms and circumferential clasp arms (a

suprabulge retainet), both provide retention by the resistance of metal to deformation,rather than frictional resistance created bv the contact ofthe clasD arm to the tooth.

The one located the closest to the clasp tips which is located furthest from theedentulous area

The one located the furthest from the clasp tips which is located nearest to theedenfulous area

The one located the furthest from the clasp tips which is located furthest from theedentulous area

152Copltish O 201l-2012 - Dental D€cts

r

IWhich of the folowing Kennedy classes of removlble partial

dentnres are not tooth-borne?

. Class I

. Class II

. Class III

. Class IV

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Coplriehr O 201 l-2012 - Dertal Decks

Explanation ofansw€r: As unseating occurs in the edentulous segments, a line throughthe rests located furthest from the retentive clasp tips acts as the fulcrum in a Class III leversystem. Moving the fulcrum line still further from the clasp tips improves the mechani-

cal advantages ofthe lever arm system. By maintaining this position, the most distantrests augment the retentive action ofthe clasp and indirectly contribute to retention. Thus,the term indirect retainers Dertains to rests. which ausment mechadcal ret€ntion.

As the denhrre base moves upward, the most anterior rcst (lrhich is the indirectretainer) rcsists downward movement and this increases the effectiveness of the directretainer.

teeth for support.

Kennedy classifications are based on the most posterior edentulous area to be restored. AlthoughClass Ilt and IV partial dentures are supported entirely by the abutment teeth, Class I and ll partial

dentures are supported also by the residual ridge, the subjacent tissues and the fibrous connective

tissue overlying the alveolar process.

Applegates rules governing the application ofthe Kennedy classification system:. Rule l: the classification should follow, not precede extractions.. Rule 2; ifa 3rd molar is missing and not to be replaced, it's not considered in the classifica-hon-. Rule 3: if a 3rd molar is present and not to be used as an abutment, it's not considered in the

classification.. Rule 4: if a 2nd rnolar is missing and not to be replaced, it's not considered in the classifica-

tron.. Rule 5: the most posterior area always determines the classification.. Rule 6: edentulous areas other then those determining the classification are referred to as rnod-

ifications and are designated by their numbers.. Rule 7: the extent ofthe modification is not considered, only the number ofadditional eden-

tulous areas.. Rule 8: there are no modification areas in Kennedy Class IV arches.

Note: The alveolar ridge resorption under the distal extension partial denture is ofparticular con-

cem and can be reduced by maximizing the coverage ofthese supporting areas.

Very Important! Likewise, the periodontal damagc to abutment teeth is avoided with firm tissue

support -maintaining

a stable base-tissue relationship.

Rememb€r: Rests should be placed on abutment teeth next to the edentulous areas for maximum

support when designing a tooth-bome partial. These rests limit movement ofthe denture in a gin-

eival direction.

Tooth-borne removable partial dentures fclass 1/1and Class IV) depend entirely on abutment

. Kennedy Class I

. Kennedy Class II

. Kennedy Class III

. Kennedy Class IV

The followlng partially edentulous rrch would be classilied as:

'i:-_(-- \

-_:- I -- s<

1gCoplaight O 201l-2012, Denral Decks

. A conventional six - unit fixed bridge

. No treatment

. A removable partial denture

. A Maryland bridge

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Coplaight O 20ll-2012 - Dertal D€cks

What is the recommended treatuent for a patient who has losther four maxillary incisors some time ago and has suflered

excessive ridge resorption?

\

Kennedy Class IBilateral distal extension

Kennedy Class IIUnilateral distal extension

Kennedy Class IVAnterior extensions

crossing the midline

Any other additional edentulous area is referred to as modification (except in Class IV)e.g.. If Kennedy Class I (bilateral clistol extension) above, also has another edentulousarea anteriorly, then it would be referred to as Class I modification I.

Remember: Craddock classification is based upon the denture type.. T.'-'pe I: Mucosa bome. Type II: Tooth-bome. Type III: Mucosa and tooth-bome

*** Ifexcessive ridge resorption has occurred after tooth loss in the anterior region, the

pontics required to replace these teeth may be quite unesthetic. A removable partial den-

ture rvith its tissue colored acrylic base can provide this esthetic consideration.

Other situations in which a removable partial denture is specifically intended rather

than a fixed bridge:

. Distal extension: obviously, ifseveral teeth must be replaced and no posterior abut-

ment is present, then a removable partial denture must be used (other option would be

irplarls). It is possible, howevel to cantilever one tooth in a fixed bridge if at least two\.ery sound teeth exist anterior to the space.

. Long span edentulous area: sufftcient abutment teeth are not present to support the

occlusal forces, which would be placed on the fixed bridge.

. Periodontally involved abutment teeth: the bracing and cross-arch stabilization ofa removable partial denture in this case makes it the ideal treatment.

. Following recent extractions: a temporary removable padial denture may be pro-

vided until tissues have had time to heal properly and fixed bridgework can be done.

. Economics: may force the use ofa partial denture as an interim solution to a prob-

lem that must evcntually be solved with fixed prosthodontics.

. When the lingual frenum is high or the space available for the lingual bar is limited

.In Class I situations in which the residual ridges have undergone excessive vertical re-sorption

. For stabilizing periodontically weakened teeth

. Severe anterior crowding

. When the futue replacement of one or more incisor teeth will be facilitated by the ad-dition ofretention loops to an existing linguoplate

'| 56

Copltigh C 201 l-2012 - Dertal Decks

. More than 25%o, allowing the clasp to bend without microstructure changes that couldcompromise its physical properties

. More than 6%, allowing the clasp to bend without microstructure changes that couldcompromise its physical properties

. Less than 6%, allowing the clasp to bend without microstructure changes that couldcompromise its physical properties

. Less than 250lo, allowing the clasp to bend without microstructure changes that couldcompromise its physical properties

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*** This is a contraindication to the use oflinguoplate

The linguoplate is a lingual bar that has been extended upward to cover the cingula and in-terproximal spaces between mandibular anterior teeth. It should be thin and follow the con-tours ofthe teeth and embrasures. The upper border should be located at the middle thAd ofthe lingual surface ofthe teeth and extend upward to cover interproximal spaces to the con-

tact Doint.

Mandibular linguoplate Mandibular lingual bar

Mandibular labial bar

A lirought wire clasp is fabricated by d&wing the metal from which it is made into a wire.

The success ofwrought wire clasps depends on their physical properties and the changes that

ma-,- occu during fabrication. Laboratory ptocedures can compromise desiable physical prop-

enies due to improper heating and cooling. Manufacturer directions should be followed foreach panicular alloy. It is important that a wrought wire clasp have an €longation percentag€

ofmore than 670, allowing the clasp to bend without microstructure changes that could com-promise its physical properties. Tapering a wrought wire clasp to 0.8 mm at the tip before con-

rouring allows for more uniform stress distribution throughotlt the clasp, making it more

sen iceable and efficient. Remember: The most important mechanical property involvedwhen a clasp is adjusted is elongation.

Desig:ning a chrom€ cobalt clasp to engage less undercut is the most reliable way to de-

crease its retentiveness; switching to a gold clasp while maintaining the same amount ofun-dercut will have a similar result. Gold clasps offer half the retention ofchrome cobalt clasps

$hile engaging identical undercuts. Because the grain size ofchrome cobalt is large by com-parison, it possesses a lower proportional limit; as a result, the risk offracture increases as its

bulk decreases. Since cobalt work hardens more rapidly than gold, bending chrome cobalt

clasps is associated with an increased likelihood of fiacture.

Note: A cast m€tal is any metal that is m€lted and cast into a mold (e.g., an inlay, crown orc/nspl. When the casting is cold-worked in some manner to provide the required article or ap-

pliance (e.g.,lrire), it is calted a wrought metal in contrast to a cast metal. As stated above,

many mechanical properties ofthe wrought structure are sup€rior to those ofthe cast struc-

i)re (e.g., tensile strength, hardness and strength). Tttis means that a wrought structue hav-

ing a smaller cross-section than a cast stmctue may be used as a retainer arm (retentive) to

Derform the same function.

. It is a rest seat

. It is located as far anterior as possible

. The function is to prevent vertical dislodgement ofthe distal extension base ofa remov-able partial denture

. It is usually an MO rest seat on a first molar

Coplright () 201 1,2012 - Denral Decks

The strength, hardness, and tensile strength of wrought wire is approxlmatelyi

. 50lo greater than the cast alloy from which it was fabricated

. 25olo greater than the cast alloy from which it was fabricated

. 50% less than the casl alloy from which it was fabricated

. 7570 greater than the cast alloy from which it was fabricated

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***This is false; it is usually found on a canine or premolar.

Indirect r€tention is the component ofan RPD that assists the direct retainers (clasps)

in preventing displacement of a distal extension base by functioning through lever ac-

tion on the opposite sid€ of the fulcrum line when the denture base rotates away fromthe tissues around the fulcrum line.

It is an anti-rotational devic€ fabricated by a rest/connector combination and placed as

far forward from the embrasure clasp as possible. It counteracts the upward rotation oftheedentulous base. This also serves as a 3'd reference for seating ofthe framework and mak-ing altered cast impressions. Note: The indirect retainer may be omitted in some designs

- tooth-bome partial dentures.

Indirect retainers also serve another related function. In their absence, upward dis-lodgement ofdistal expansion bases would be accompanied by downward motion oftheanterior part of the major connectot By preventing such downward movement, the in-direct retainer protects the soft tissues from impingement by the major connector.

Remember:. An indirect retainer should be placed as far from the distal extension base as pos-

sible in a prepared rest seat on a tooth capable of supporting its function. The term indirect retainer pertains to rests, which augment mechanical retention

Wrought wire clasps:. Have a gr€ater flexibility and adjustability than the cast clasps. Are tougher than cast clasps

Har,e a greater tensile strength than cast clasps and therefore can be used in smaller

diameters to provide greater flexibility without fatigue and ultimate fracture

Important: Having been formed by being drawn into a wire, the wrought-wire clasp has

toughness and ductility exceeding that of a cast clasp arm. The clinical effect of this is

that there is an increased capacity for deformation ofthe wrought-wire without breaking.

Horvever, the yield strength ofboth gold and chromium-cobalt alloy wrought wires can

be drastically reduced simply by subjecting the wire to too much heat. lfthe heat is high

enough. the fibrous microstructure of the wrought wire disappears and is replaced by a

grain or crystalline microstructure. This process is known as recrystallization or gain

gro$th and is a most undesirable occurrence in wrought-wire retainer arms.

\ote: The terminal end ofthe retentive arm is optimally placed in the middle ofthe gin-

gival third ofthe clinical crown. However, it is acceptable to place it at thejunction ofthegingival and middle one-third ofthe clinical crown. When the partial is completely seated,

the retentive arm should be passive and applying no pressure on the teeth.

. Rigid plating

. Minor connectors

. Guide planes extended around the vertical line of abutments

. Achieving balanced occlusion

. Contact ar€as ofproximal teeth

. Reciprocal clasp arms

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Coplri8h O 201l-2012 - Deotal Decks

. Maxillary lateral incisors

. Maxillary canines

. Mandibular lateral incisors

. Mandibular canines

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Coplriehr @ 201 l'2012 - Dental Decks

Reciprocation as applied to partial dentures refers to the function of the lingual clasp arm(which is the reciprocal clasp arm or stabilizing clasp orm) to counteract forces exerted bythe buccal clasp arm (which is the retentive clasp arm).

Reciprocation is the means by which one part ofthe fiamework opposes the action of the re-tainer in function. Reciprocation may be achieved by opposing flexible retainers with guideplanes, minor connectors, rigid clasp arms or plating. lf true reciprocation is to occur, the re-

ciprocating element must be placed opposite the direct retainer and must contact the abutment

as the retentive tip passes over the height ofthe contour ofthe tooth,

Remember: Th€ curr€nt conc€pt of bar clasp design is the R.P,I. system:. Mesial rest - point olrotation which exerts a mesial force on the tooth. Proximal plate - superior edge at bottom of guide plane to disengage during loading.Slightly lingual for reciprocation. I Bar - 2.5 mm from gingival margin, crosses at right angles in a.01" undercut at thegreatest M-D prominence to permit it to disengage during function

Important: The term guiding plane is defined as two or more parallel, vertical surfaces ofabutment teeth, so shaped to direct a prothesis during placement and removal. The functionsofguiding plane surfaces are as follows:

. To provide for one path ofplacement and removal ofthe denture

. To ensure the intended actions ofreciprocal, stabilizing, a nd retentive components

. To eliminate gross food haps between abutment teeth and components ofthe dentue

As a rule, proximal guiding plane surfaces should be about two thirds as $ide as the distance

benveen the tips ofadjacent buccal and lingual cusps or about one third ofthe buccal lin-gual width of the tooth and should extend vertically about two thirds of the length of theenamel crown portion ofthe tooth from the marginal ridge cervically. Note: Proximal plates

are metal plates that contact the proximal surface or guide plan€ ofan abuhrent tooth.

*** These teeth have a gradual lingual incline and a prominent cingulum. In some in-stances, cingulum rests may be placed on mfiillary central incisors. The lingual slope ofthe mandibular canine is usually too steep for an adequate cingulum rest to be placed inthe enamel.

The cingulum rest is a veftical stop on an anterior tooth whose lingual anatomy lends irselfto ready preparation for a positive seat.

. Inverted V or U shape

. Mesiodistal length = 2.5 to 3 mm

. Labiolingual width : 2.0 mm

. incisoapical depth = 1.5 nm*** Not all teeth have sufiicient cingulum contour to receive a seat (i.e., mandibularcentral snd lateral incisors).

The incisal rest is employed when other preferred support is not available. The high place-

ment ofthis style ofrest may be esthetically objectionable. The distal incisal rest is usu-

ally less esthetically visible than the mesial incisal rest. Never place an incisal rest so deep

that it interferes with the proximal contact.

. Rounded notch at an incisal anele

. Width = 2.5 rnm

. Depth = 1.5 mm

Note: Two advantages of a cingulum rest over an incisal rest are: l) It is more esthetic;

2) The resulting stress relayed to the abutment has a less torquing influence.

Important: The prirnary purpose of the rest (any type -+ occlusal, cingulum or incisal)is to provide vertical support for the removable partial denture.

. Occlusal third

. Middle third

. Gingival third

162Cop}1ighl O 20ll-2012 Denial Decks

Which of the following is delined as "The qurlity of a restoration tow|lrc|l ol r|lc lurrowr[g rs ocrxrcu ru '' rI|c qu![ty ot a rcslorauofl tobe lirm, steady constant and not subject to change of position

when forces are applied?"

. Retention

. Stability

. Adhesion

. Reciprocation

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Retentive components should be located as close as possible to th€ tooth's horizontal axis ofrotation. It is easier to overstress the tooth support by clasping it near the occlusal surface.The distal extension moves up and down during function, indicating that a clasp design in thegingival third ofthe tooth that disengages the undercut during function would be less stress-

ful to the periodontal support ofthe tooth.

The clasp assembly consists ofa retentive clasp arm and a reciprocal or stabilizing clasparm, plus any minor connectors and r€sts fiom which they originate or with which they are

associated.

The functions ofthe r€ciprocal clasp arm of a removable partial denture include reciproca-tion, stabilization and auxiliary indirect reterfii.on (bracing). Points to remember concerningreciprocal clasp arms:

. ln positioning cast clasps on abutment teeth, the horizontal undercut is considered a sig-nificant measurement and height of contour is considered a controlling factor in clasp po-sittLoning. (Reciprocal clasp should contacl tooth on or qbove contour). See note below.. In general, you should not use retentive areas on the buccal and lingual ofthe same tooth.Reciprocal bracing on the lingual and retenlive portion of the clasp on the buccal is

more desirable.. As with all clasps, they should be designed to permit insertion and removal without ap-

plying excessive force.

. _ l. Altering the natural tooth form to allow effective clasping may involve produc-

Noredi ing guiding planes or changing the location of th€ h€ight of contour. Facial and,*-- proximal contours of premolars and molars most often need to be altered. Crown

fabrication may be necessary to provide the appropriate contour.2. Guiding planes serve to ensure predictable clasp retention. Failure ofpartials due

to poor clasp design can be avoided by altering tooth contours.

In dentures, stability is the relationship of the denture base to bone that resists dis-lodgement of the denture in a horizontal direction. In removable partial dentures sta-

bilit_v is best insured by incorporating a harmonious occlusion.

Retention is that quality in a restoration, which resists the force ofgravity, sticky foods

and tbrces associated with mandibular movement. Note: For RPD's the distal parts of the

rerenti\ e clasps produce the aclive retention.

Reciprocation is the means by which one part ofa restoration is made to counter the ef-fects created by another part. Note: For RPD's true reciprocation can only be achieved ifthe reciprocating element touches the tooth before the retentive clasp

For panial dentures, support is given by occlusal rests and the edentulous ridge areas. Thisdesign characteristic (support) is most important to oral health. Other design character-

istics of a partial denture include:

. Retention: by clasps placed in undercut areas of abutment teeth

. Bracing: or horizontal force transmission through placement of rigid portions ofclasps or other parts ofthe partial denture in non-undercut areas of abutment teeth. Guidance: during insertion and removal obtained by contact of rigid parts of the

framework with areas on axial tooth surfaces parallel to the path of insertion

. Labial notch and labial flange

. Buccal notch and buccal flange

. Posterior border

. Distobuccal flange

. The functional load technique

. The altered cast technique

. The residual ridge technique

. The total occlusal load technique

1UCoplrighr O 201l-2012 - Denral Decks

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Cop]rishr O 201 l-:012 - Dental Decks

Free end saddles are liable to be displaced under occlusal pressure(onteru-posterior rocking around the abutment tooth,lehich acb as a pivol).This is as r result ofthe displaceability ofthe mucosa. \trhich technique is

employed to try and prevent this by taking an lmpression ofthemucosa under controlled pressure?

. f otedr'

Excessive thickness of this area can lead to this problem. As the buccal frenum movesposteriorly during smrling (or otherfacial expressions) it encroaches on the denture bor-der that is too thick and the denture becomes loosened.

You can test the borders for overextension by slowly seating the denture. Ifyou observepremature contact with frenae or vestibular tissues as the denture conlinues toward its

final position, then the border is probably overextended. Adapt a thin roll ofdisclosing waxto the denture border Seat the denture and instruct the patient to exeft vigorous muscle

function. In about one minute, the wax will soften and be displaced by muscular actionacross the overextended denture border

l. The complaint that the denture becomes loose when the mouth is wide opened

as in yawning, could be due to the distobuccal flange ofthe denture being toothick. This may interfere with the movement ofthe coronoid process.

2. Ifpatient complains ofsore gums and aching muscles at the bottom ofthe face

after wearing dentures for several hours, opposing teeth ofthe denture have in-sufficient space. Reduce the vertical dirnension of the occlusion.3. Tingling or a numbing sensation at the comer ofthe mouth or in the lower lipafter a few days of denture wearing is caused by excessive pressure from th€lower truccal flange in the region of the mental foramen.

Impression materials cannot record anatomic form ofthe teeth and physiologic form ofthe soft tis-

sue in a functional relationship all at the same time. To achieve these objectivcs, the altered casttechnique can be used. This technique is a secondary irnpression system which utilizes the metal

frame\\'ork to hold customized impr€ssion trays for the edentulous area. The advantage of the al-

tercd cast procedure is that an accurate relationship between the denture base and the metal frame-

$ork is established prior to tooth arrangement which should result in less occlusal adjustment at th€

time of insertion. The objectives ofthe altered cast technique are to obtain thc maximum possible

support from the distal extension base ofthe RPD and to accurately relate the soft tissue sur-

face ofthe denture basc to the metal ftamework

Distal extension removable partial dentures fRPDb/ derive their support from the abutment teeth

and the mucosal tissues overlaying the residual alveolar process. There are di{Iering philosophies

in the scientific literature regarding how much support should be provided by the abutment teeth and

how much support should bc provided by the soft tissues. Howevet th€re is consensus that: (1) oc-clusal stress should be shared by both in such a manner that neith€r the abuhnent teeth nor the resid-

ual ridge is abused; (2) accurate fit ofthe denture base is an important factor in minimizing stress

on the abutment teeth; (3) stability ofthe prosthesis is the most important requirement fbr prop€r

function and patient comfort.

Important points to remember conceming removablc paiial dentures:. In order to determine whether the alveolar bone is capable ofwithstanding occlusal forces ofa rcmovable partial denturc, an x-ray should b€ taken ofthe abutment teeth and the bone lovel sur-

rounding these teeth should be evaluated.. Periodontal health of the abutment teeth and maintaining th€ health ofthe supporting tissues

is best achieved by maintaining tissue support (preserving denture bone support) ofthe eden-

tulous areas.. The total occlusal load applied to an RPD is influenced by the occlusal surface area, occlusal

efliciency and the number ofexisting teeth.

. The periodontal ligament ofthe abuftnent teeth

. The alveolar suppod ofthe abutment teeth

. The residual ridge

. All ofthe above

't66

Coprright O 2011,2012 - Dental Decls

. They provide retention without an unsightly display of metal

. They are easy to repair

. The functional load is dispersed down the long axis ofthe abutments by virtue ofthelow central loading at the base ofthe attachments

. The restorations permit the patient access to all areas of the tissues when the dentureis not in place

. If both sides of the dental arch have this t)?e of restoration and are joined by a rigidmajor connector, excellent bilateral stabilization is provided to the abutments

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Cop),righr O 201l-2012 - Dental Decks

When these devices are incorporated next to a free-end distal extension RPD, the thrustof the functional stress is directed onto the residual ridge, Only minimal transfer offunctional stress to the abutment teeth occurs. Since vertical and horizontal forces are

concentrated on the residual ridge, increased ridge resorption frequently occurs. Relin-ing ofthe free-end saddle area must be done when needed to prevent excessive ridge re-sorptlon.

Types of Stressbreakers:

1. Have a flexible connection between the direct retainer and the denture base:

. Simplest form ofstress reliefis the wrought-wire retentive clasp

. Split bar major connectors; example is the Ticonium "Hidden-Lock" design

2. Have a movable joint between the direct retainer and the denture base:

. The "DE" hinge

. The Dalbo attachment

. The Crismani attachment

. The ASC-52 attachment

\ote: When a stressbreaker is placed on the distal surface of a pontic, occlusal forces$ ill tend to unseat the key from the key.

*** This is false; precision attachment restorations are difficult to repair.

A precision attachment (intracoronal direct retainer) is preconstructed with male and

fernafe portions (both constructed ofa metql) that f\t together in a precise fashion with lit-tle tolerance. It may be rigid in function or it may incotporate a movable stress control unitto reduce the torque on the abutment.

Disadvantages of precision attachments:. They must n€ver be used in a distal extension removable partial denture withoutusing a stressbreaker the primary indication for precision attachments is when teeth

are present on both ends ofthe edentulous area. Full cast crowns must be prepared for all abutments. They cannot be used on short clinical crowns. They cannot be used when the pulp is large (requires extensive tooth reduction). Both clinical and laboratory procedures require special skill. They are difficult to repair. The metal parts wear and lose retention. The cost is much greater

A semiprecision attachment is cast into the crown and the RPD. The female portion is

normally made ofpreformed plastic that is positioned into the wax form and then cast. The

male portion is cast with the RPD framework. The female and male parts fit together withmuch more tolerance than in the precision attachment, resulting in less retention.

When surveying casts, the clinician/technician must perform an important stepin order to correclly record the path of insertion, the position ofthe

survey line and the location of undercut and noD undercut Nreas.tttL:^L ^f.L^ a^tl^-..:-- :- -^--:,J^--rWhich of the following is considered to be that step?

. The recontouring ofproximal walls ofabutments parallel to the path ofinsertion

. The use of indelible lead marker

. Placing tripod marks on the cast to record the orientation of the cast to the surveyor

. Fixing the casts with screws on the surveying table

. All of the above steps are equally imponant

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Which primary design-quality ofthe occlusal rest wouldcategorize it as a gpositive" rest?

. Allow no tilting ofthe appliance

. Prevent the movement ofthe appliance

. Transmit stress down the long axis olthe tooth

. Form acute angles with the minor connectors that connect them to the major connectors

. Have a thickness of 1.5 mm

. All of the above

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Cop)rightO 20ll-2012 - Dental Decks

The tripod marks (which are three spots placed at three different locations around abut-ment teethfrom a single point ofview) ensure reproducible orientation ofthe cast to the

surveyor.

The dental surveyor (picture on left) is an instrument used to

determine the relative parallelism oforal anatomy. Note: Areas

used for support cannot be determined by surveying.

When surveying casts, the corect procedure is to lirst adjust

the tilt to permit the establishment ofguiding planes. The ante-

rior edentulous space will frequently dictate the angulation se-

lected. Normally, some recontouring ofthe proximal walls ofabutments is necessary to improve guideplane alignment.These alterations are accomplished by disking the proximalsurface parallel to the path of insertion.

Tilting of the cast during surveying changes the:

. Path of insertion

. Position ofthe survey line

. Location ofthe undercut and non-undercut areas ofeach tooth

The prirnary purpose ofthe rest is to provide vedical support for the RPD.

Note: Occlusal rests are prepared primarily to resist the vertical forces of occlusion. Indoing so the rest also does the following:

. It maintains established occlusal relationships by preventing settling ofthe denture

. Prevents impingement of soft tissues

. Directs and distributes occlusal loads (through the long at, to abutment teeth

Forrn of the occlusal rest and rest seats:

l. The outline form should be a "rounded" triangular shape with the apex toward the

center of the occlusal surface.2. It should be as long as it is wide and the base ofthe triangular shape should be at least

2.5mm for both molars and premolars.

3. The marginal ridge ofthe abutment tooth at the site ofthe rest seat must be loweredto permit a sufiicient bulk of metal for strength and rigidity. This means that a reduc-

tion of the marginal ridge of about l.5mm is usually necessary.

4. The floor ofthe occlusal rest should be apical to the marginal ridge and be concave

or spoon shaped (no sharp edges or line-angles in the prep).5. The angle formed by the occlusal rest ald the vertical minor connector from whichit originates should be less than 90o.

Rememb€r: The rest must be rounded (spoon shaped) to permit functional movement.

. The useful posterior tooth space

. The lip line ofthe patient

. The age ofthe patient

. The characteristics ofthe denture-supporting tissues

. The face-bow tralsfer

170Cop)'right C 201l-2012 - Dental Decks

. 20 - gauge

. 19 - gauge

. l8 - gauge

. 16 - gauge

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Coplright c) 201 1,2012 - Denial tlecks

Factors which are relevant to the selection of posterior teeth for a removable partialdenture:

. Occlusogingival length: the most important factor in determination ofposterior toothlength is the available interarch space.. Mesiodistal width: the total mesiodistal space available for the posterior teeth is de-termined by measuring from the distal of the lower canine to the point where themandibular residual ridge begins to slope upward.. Buccolingual width: the buccolingual width is narrowed in r€lation to the missingnatural tooth. It is thought that reducing the area of the occlusal table decreasesstressed transferred to the denture support area during food bolus penetration. Addi-tionally, reducing the buccolingual width increases tongue space.. Shade: the shade for posterior teeth is usually selected to harmonize with that oftheanteriors.. Occlusal surface form: at this time, it appears that no superior tooth form or arrange-ment is identified. It is therefore logical to use the l€ast complicated approach that ful-fills the needs ofthe patient.. \Iaterial: plastic bonds well to the acrylic resin and therelore plastic teeth are re-tained bener than oorcelain leeth

*** 20 - gauge or finer, as < 7 mm, is a short arm clasp and shorter length clasps musthar.e a finer gauge of wire for optimum flexibility.

The flexibility ofa retentive clasp arm depends on:. Length of the clasp: the flexibility of a clasp varies directly with the cube of itslengrh. Thus, increased length results in a marked increase in flexibility. Thickness of the clasp: as a clasp becomes thicker; its flexibility is reduced by a

cube ratio. Width of the clasp: as the width of a clasp increases; its flexibility decreases by a

ratio of l: I. Cross-sectional form: a rourd form is equally flexible in all directions. In contrast,a half-round form flexes readily only when the stress is applied perpendicular to theflat surface. Taper of the clasp: a uniform taper permits increasing flexibility toward the tip ofthe clasp. Clasp material: different metals flex more than others. Remember: Wrought wireretentive arms have increased flexibility