Introduction of Removable Partial Denture - Design of Removable... · Introduction of Removable...

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Introduction of Removable Partial

Denture - Design and Retention

Introduction of Introduction of Removable Partial Removable Partial

Denture Denture -- Design and Design and RetentionRetention

By : Dr By : Dr ZaihanZaihan AriffinAriffinBDS(MalayaBDS(Malaya), ), GDCDentGDCDent (Adelaide),(Adelaide),Doctor of Clinical Dentistry (Adelaide),Doctor of Clinical Dentistry (Adelaide),FRACDS (Australia)FRACDS (Australia)

Type of dentureType of dentureFull dentureFull denturePartial denture Partial denture ––acrylic or Coacrylic or Co--crcrImmediate denture Immediate denture ––acrylic (commonly)acrylic (commonly)OverdentureOverdenture –– acrylic acrylic or Coor Co--crcrImplant supported Implant supported denturedentureSectional dentureSectional denture

Which Which endentulousendentulous areas should areas should restorerestore

Restore :Restore :Those Those endentulousendentulous areas which areas which patients wants to restore for patients wants to restore for aesthetics or functions.aesthetics or functions.Those areas which are needed to Those areas which are needed to restore or preserve restore or preserve occlusalocclusal integrityintegrity

Principles of designPrinciples of design

Existing dentureExisting dentureTissue preservationTissue preservationOcclusalOcclusal integrityintegrityOral hygiene and maintenanceOral hygiene and maintenanceResistance to various forcesResistance to various forces

Existing dentureExisting denture

Note details of Note details of exstingexsting denture, denture, What pt wantsWhat pt wantsAny modifications?Any modifications?Copy the nonCopy the non--traumatic elements of traumatic elements of previous dentureprevious denture

OcclusalOcclusal integrityintegrityAny tooth modification must leave the Any tooth modification must leave the occlusion at least as stable as it was.occlusion at least as stable as it was.When wearing either the upper or lower When wearing either the upper or lower denture, the patient must be provided denture, the patient must be provided with a stable occlusion with maximum with a stable occlusion with maximum possible natural tooth contacts in the possible natural tooth contacts in the intercuspalintercuspal positionpositionWhen wearing both denture, the patient When wearing both denture, the patient must have a stable occlusion with must have a stable occlusion with maximum natural tooth contactmaximum natural tooth contact

Oral hygiene and maintenanceOral hygiene and maintenance

Improvement and maintenance of Improvement and maintenance of OH is fundamental in all treatment.OH is fundamental in all treatment.recall and maintenancerecall and maintenanceSpecial lecture Special lecture ……

Tissue preservationTissue preservation

At least 1 mm clear of CEJ

Never finish any part of the denture on the gingivamargin

Keep denture compenents : ex – direct retainer to a minimum and simple but MUST apply the basic principle

Resistance to various forcesResistance to various forces

SupportSupportRetention : direct and indirect, guide Retention : direct and indirect, guide planeplaneConnectorConnectorStabilisationStabilisationBracing Bracing

Things to remember!Things to remember!

1. Saddles1. Saddles (yellow)(yellow)2. Support 2. Support (red)(red)3. Retention 3. Retention (green)(green)4. Bracing and reciprocation 4. Bracing and reciprocation (blue)(blue)5. Connector 5. Connector (black) (black) 6. Indirect retention.6. Indirect retention.

Support (rest)

Clasp -retention

bracing

Major connector

saddle

SupportSupportHOW: HOW: Mucosa and underlying Bone, Mucosa and underlying Bone, tooth or combinationtooth or combinationRests on Teeth: Rests on Teeth: occlusalocclusal; ; cingulumcingulum; ; incisalincisal; telescopic copings, precision ; telescopic copings, precision attachmentsattachmentsWHY: WHY: Increase Increase masticatorymasticatoryefficiencyefficiency

SupportSupport

OcclusalOcclusal rest : premolar and molarrest : premolar and molarCingulumCingulum rest : upper canine and rest : upper canine and incisorsincisorsInsicalInsical rest : lower canine and rest : lower canine and incisorsincisorsTissue coverage in case where Tissue coverage in case where endentulousendentulous require support from require support from mucosamucosa

Tooth prep for Tooth prep for RPDsRPDs should be planned on should be planned on articulated study casts after they have been articulated study casts after they have been surveyed and a denture design producedsurveyed and a denture design producedShaping of enamel surfacesShaping of enamel surfaces is usually is usually undertaken with undertaken with rotary diamond instrumentsrotary diamond instrumentsof appropriate size and shapeof appropriate size and shapeRoughened enamel surface must always be Roughened enamel surface must always be smoothened and polishedsmoothened and polishedSubsequent application of a topical fluoride Subsequent application of a topical fluoride varnishvarnish-- to reduce the chance of carious to reduce the chance of carious attack of the modified enamel surfaces, attack of the modified enamel surfaces, should be carried out routinelyshould be carried out routinely

Rest seatsRest seats

Need to be prepared to:Need to be prepared to:Produce a Produce a favourablefavourabletooth surface for supporttooth surface for support

Prevent interference with Prevent interference with the occlusionthe occlusion

1 1 ––rest seat placed on an inclined rest seat placed on an inclined surface tend to surface tend to slide down toothslide down toothunder influence of under influence of occlusalocclusal loadload

2 2 ––provision of a rest seat result in provision of a rest seat result in vertical loading of tooth, vertical loading of tooth, >efficient >efficient supportsupport

1 1 ––occlusalocclusal rest placed at the arrowrest placed at the arrow2 2 ––create a create a premature contactpremature contact3 3 ––unless a rest seat was preparedunless a rest seat was prepared

Reduce the Reduce the prominence of a restprominence of a rest

1 1 ––rest placed on an unprepared rest placed on an unprepared tooth surface tend to tooth surface tend to collect food collect food particlesparticles

2 2 ––rest seat allow the rest to be rest seat allow the rest to be shaped so that it blends into the shaped so that it blends into the contour of toothcontour of tooth

Rest seats on post teethRest seats on post teethThe The designdesign of rest seats on of rest seats on post teethpost teeth1 1 ––occlusalocclusal viewview2 2 ––mesiodistalmesiodistal viewview3 3 ––proximal viewproximal viewRest seat of post teeth should normally be Rest seat of post teeth should normally be

saucersaucer--shapedshaped

Use of a boxUse of a box--shapes rest seat within a shapes rest seat within a cast restoration result in rest applying cast restoration result in rest applying damaging horizontal loads on the damaging horizontal loads on the abutment tooth (restricted to toothabutment tooth (restricted to tooth--supported dentures where the supported dentures where the perioperiohealth of the abutment teeth is good)health of the abutment teeth is good)

Rest should be Rest should be at least 0.8at least 0.8--1mm thick1mm thick for for adequate strength.adequate strength.

Pt asked to occlude on a strip of softened Pt asked to occlude on a strip of softened pink wax. The thickness of wax in the pink wax. The thickness of wax in the region of rest seat indicate sufficient region of rest seat indicate sufficient enamel has been removedenamel has been removed

Rests seats on anterior teethRests seats on anterior teeth

On On maxillary ant teethmaxillary ant teeth, , particularly particularly caninescanines, the , the cingulumcingulumis often well developed so that is often well developed so that modest prep to accentuate its modest prep to accentuate its form creates a rest seat w/o form creates a rest seat w/o penetration of enamelpenetration of enamel

A A cylindrical green stonecylindrical green stone with a with a rounded tiprounded tip should be used.should be used.

A spherical instrument tends to A spherical instrument tends to create unwanted undercuts. create unwanted undercuts.

Preparation for Preparation for mandibularmandibularanterior toothanterior tooth is shown from is shown from the:the:

1 1 ––labial viewpointlabial viewpoint2 2 ––lingual viewpointlingual viewpoint3 3 ––proximal viewpointproximal viewpoint

IncisalIncisal rest seatrest seat can be can be prepared using a prepared using a tapered tapered cylindrical diamondcylindrical diamond

Where to place?Where to place?Where : the most desirable vertical support Where : the most desirable vertical support gainedgainedNext to the Next to the endentulousendentulous area for bounded basesarea for bounded basesAway from the Away from the endentulousendentulous area ; free end area ; free end saddlesaddleOther : by passing the weak abutment and place Other : by passing the weak abutment and place rest on next approximating toothrest on next approximating toothSpreading the load on two abutmentSpreading the load on two abutmentfor for cingulumcingulum rest : 2mm above the rest : 2mm above the gingivagingiva

marginmargin

ConnectorsConnectors

Major:Major: to join the Saddles Areas togetherto join the Saddles Areas togetherMandibularMandibular: Lingual bar, Lingual plate, : Lingual bar, Lingual plate, Sublingual bar, dental (Sublingual bar, dental (cingulumcingulum) bar, ) bar, labial barlabial barMaxilla: Full palatal coverage; Anterior Maxilla: Full palatal coverage; Anterior palatal bar, Midpalatal bar, Mid-- palatal Posterior palatal palatal Posterior palatal bar, Ring bar and horseshoe connector. bar, Ring bar and horseshoe connector. Minor:Minor: to join the rests, clasps and to join the rests, clasps and reciprocal elements to the major reciprocal elements to the major connector.connector.

ConnectorConnector

All major connector must be rigid.All major connector must be rigid.MandibularMandibular ::

lingual barlingual bar : more than 6mm above the : more than 6mm above the lingual lingual sulcussulcus and gingival margin.and gingival margin.

CingulumCingulum barbar ::i)i) insufficient room for lingual barinsufficient room for lingual barii)ii) The clinical crown are long enough for The clinical crown are long enough for

the bar to be adequately rigidthe bar to be adequately rigidiii)iii) There is good There is good mesiodistalmesiodistal contact contact

between the teethbetween the teeth

Lingual bar

Lingual plate :Lingual plate :If lingual bar and If lingual bar and cingulumcingulum bar are bar are contraindicatedcontraindicatedDo not use lingual plate behind Do not use lingual plate behind diastemadiastemaSublingual barSublingual barThere is insufficient room for There is insufficient room for lingulalingulabarbarPt have Pt have diastemadiastema

Lingual plate

Sublingual bar

Labial barLabial barTry to avoid this connector if Try to avoid this connector if possiblepossible-- difficult to place and difficult to place and uncomfortable to wearuncomfortable to wearUseful when the lower incisors are Useful when the lower incisors are markedly markedly retroclinedretroclined or where there or where there is is pronoucedpronouced torus torus mandibularismandibularis

ConnectorConnector

MaxillaMaxilla: Full palatal coverage; : Full palatal coverage; Anterior palatal bar, MidAnterior palatal bar, Mid-- palatal palatal Posterior palatal bar, Ring bar and Posterior palatal bar, Ring bar and horseshoe connectorhorseshoe connector

Palatal PlateThe basic functional requirement of a major connector is to link the various saddles and other RPD components.

A simple mid-palatal plate has been used. This is a very satisfactory connector for such situations as it:• Leaves all gingival margins uncovered.• Has a simple outline.• Is well tolerated as it does not encroach unduly on the highly innervated mucosa of the anterior palate.

horseshoe connectorhorseshoe connector

DIRECT RETENTIONDIRECT RETENTIONClasps: provide direct retention by Clasps: provide direct retention by engaging the undercut area on the engaging the undercut area on the tooth.tooth.Types: Types: GingivallyGingivally or or OcclusallyOcclusallyApproachingApproachingNames: Ring, Circumferential, INames: Ring, Circumferential, I--bar, bar, TT--bar, Lbar, L-- bar, Reverse.bar, Reverse.Should includes a rest, a clasp arm Should includes a rest, a clasp arm and a reciprocal arm.and a reciprocal arm.

Figure A Figure B

Retention will depend on:Retention will depend on:Dept of undercut : 0.25 mmDept of undercut : 0.25 mm-- cast cobalt cast cobalt

chrome;chrome;0.5 mm SS;0.5 mm SS;0.75 mm gold.0.75 mm gold.

Position of undercut: ex: high survey line Position of undercut: ex: high survey line ––gingivagingiva approaching claspapproaching claspAestethicsAestethicsPosition of the toothPosition of the toothOcclusionOcclusionShape of the Shape of the sulcussulcusPeriodontal healthPeriodontal healthNumber of clasp Number of clasp –– ex: bilateral gingival ex: bilateral gingival approaching clasp are preferredapproaching clasp are preferred

To be able to decide on the position To be able to decide on the position and type of retainer, the study and type of retainer, the study models need to be surveyed. models need to be surveyed.

This will determine:This will determine:the path of insertion the path of insertion the position of undercut on tooththe position of undercut on tooththe depth of undercut on the tooththe depth of undercut on the tooththe presence of any boney the presence of any boney undercut on ridge.undercut on ridge.

ClaspsThe flexibility of a clasp is dependant on its design.• SectionA round section clasp will flex equally in all directions, whereas a half round clasp will flex more readily in the horizontal than in the vertical plane.• LengthThe longer the clasp arm the more flexible it is. Thus an occlusally approaching clasp on a molar tooth will be more flexible than one on a premolar.

• ThicknessThickness has a profound effect on flexibility. Thick clasp, less flexible.• Curvature• Alloy

Retention will depend on:Retention will depend on:

Dept of undercut : 0.25 mmDept of undercut : 0.25 mm-- cast cobalt cast cobalt chrome: 0.5 mm Ss chrome: 0.5 mm Ss 0.75 mm 0.75 mm –– gold.gold.

Position of undercut: ex: high survey line Position of undercut: ex: high survey line ––gingivagingiva approaching claspapproaching claspPosition of the toothPosition of the toothOcclusionOcclusionShape of the Shape of the sulcussulcusPeriodontal healthPeriodontal healthMaterial of denture baseMaterial of denture base

The position of the undercutA high survey line poses particular difficulties on a premolar tooth, it may be possible to position a flexible gingivally approaching clasp higherup the crown

The survey lines on the molar and premolar teeth-there is a larger undercut on that part of the tooth which is furthest away from the edentulous area.

Typical designs of retentive clasp are the occlusallyapproaching clasp on the molar and the gingivally approaching ‘I’ bar on the premolar tooth.

ClaspsTwo categories: 1) the occlusally approaching clasp on UL7 (27) and the2) gingivally approaching ‘I’ bar clasp on UL3Common variations in the design of clasps that may be selected primarily according tothe distribution of tooth undercuts include:1- the ring clasp (which is occlusally approaching).2 -the ‘L’- or ‘T’-shaped gingivally approaching clasp.3- I-bar (next slide)

Figure AFigure B

Comparison of occlusally and gingivallyapproaching clasps

Fig. A — RetentionOnly the terminal third of an occlusally-approaching clasp (stippled section) should cross the survey line and enter the undercut area.

Fig. B — RetentionA gingivally approaching clasp contacts the tooth surface only at its tip.The remainder of the clasp arm is free of contact with the mucosa of the sulcus and the gingival margin.The length of the gingivally approaching clasp arm can therefore be increased to give greater flexibility which can be a positive advantage when it is necessary to clasp a premolar tooth or a tooth whose periodontal attachment has been reduced by periodontal disease.

Comparison of gingival approaching clap and Comparison of gingival approaching clap and occlusalocclusal approaching claspapproaching clasp

Occlusalapproaching

Gingival approaching

More rigid(can also act as reciprocal arms – no undercut site)

Less rigid

Less aesthetic + can interfere with the occlusion

More aesthetic

+ plaque accumulation and caries

+ root caries and irritation to soft tissue

Retention will depend on:Retention will depend on:

Dept of undercut : 0.25 mmDept of undercut : 0.25 mm-- cast cobalt cast cobalt chrome: chrome: 0.5 mm0.5 mm-- ––SS SS 0.75 mm gold.0.75 mm gold.

Position of undercut: ex: high survey line Position of undercut: ex: high survey line –– gingivagingiva approaching claspapproaching claspPosition of the toothPosition of the toothOcclusionOcclusionShape of the Shape of the sulcussulcusPeriodontal healthPeriodontal healthMaterial of denture baseMaterial of denture base

The health of the periodontal ligament

Which type clasp Which type clasp would you used?would you used?

Shape of the sulcus.

The shape of the sulcus must be checked carefully.to ensure that there are no anatomical obstacles. Ex: the prominent frenal attachment would be traumatised by agingivally approaching clasp of correct proportions and position.

If there is no reasonable alternative to this clasp, - can considered surgical excision of the frenal attachment.

Indirect retention :Indirect retention :

Indirect retainer derived by placing components so as to Indirect retainer derived by placing components so as to resist resist ‘‘rotational or rotational or ‘‘tippingtipping’’ forces of the denture around the forces of the denture around the retainers ex: by position of clasps and rest and type of the retainers ex: by position of clasps and rest and type of the connector.connector.

Indirect retainerIndirect retainer ::

The component of a removable partial denture The component of a removable partial denture that assist the direct retainer(s) in preventing that assist the direct retainer(s) in preventing displacement of the distal extension base by displacement of the distal extension base by functioning through lever action on the opposite functioning through lever action on the opposite side of the fulcrum line when the denture base side of the fulcrum line when the denture base moves away from the tissues in pure rotation moves away from the tissues in pure rotation around the fulcrum line around the fulcrum line

(Academy of (Academy of ProsthodonticsProsthodontics, 1999)., 1999).

Particularly important with freeParticularly important with free--end saddles and end saddles and large anterior saddles. large anterior saddles.

F = Fulcrum F = Fulcrum ——indirect retainer, a indirect retainer, a component which component which obtains support.obtains support.R = Resistance R = Resistance ——retention retention generated by the generated by the clasp.clasp.E = Effort E = Effort ——displacing force, displacing force, egega bolus of sticky a bolus of sticky food.food.

E-Effort

Resistance and Fulcrum

Ex: by placing a rest on the premolar tooth, this rest (indirect retainer) becomes the fulcrum of movement of the saddle in an occlusaldirection causing the clasp to move up the tooth, engage the undercut and thus resist the tendency for the denture to pivot.

It can thus be seen that to obtain indirect retention It can thus be seen that to obtain indirect retention the clasp normally be placed between the saddle and the clasp normally be placed between the saddle and the indirect retainerthe indirect retainer

Examples of RPD designs which include indirect Examples of RPD designs which include indirect retentionretentionKennedy I: Kennedy I: Indirect retention in this design is provided Indirect retention in this design is provided by by incisalincisal rests on LR3 (43) and LL3 (33).rests on LR3 (43) and LL3 (33).

The RPI systemThe RPI system

The RPI system is a combination of The RPI system is a combination of 1)occlusal rest 1)occlusal rest -- (R) placed (R) placed mesiallymesially..2)distal guide plate 2)distal guide plate -- (P) (enhanced (P) (enhanced retention and ought to reduces rotations retention and ought to reduces rotations movements)movements)3) 3) gingivallygingivally approaching I bar clasp (I)approaching I bar clasp (I)--principal direct retainer.principal direct retainer.

= used primarily with = used primarily with mandibularmandibular distal distal extension saddles (free end saddle).extension saddles (free end saddle).

RPIRPI

The RPI system is designed to allow vertical rotation of a distal extension saddle into the denture-bearing mucosa under occlusal loading without damaging the supporting structures of the abutment tooth.

As the saddle is pressed into the denture-bearing mucosa, the denture rotates about a point close to the mesial rest.

Both the distal guide plate and the I bar move in the directions indicated and disengage (acts as the recriprocalarm) from the tooth surface. Potentially harmful torque is thus avoided.

RPIRPI

Reciprocals: Reciprocals: a part of the denture a part of the denture that resists the action of a clasp on a that resists the action of a clasp on a tooth as the denture is inserted or tooth as the denture is inserted or removed from the mouth.removed from the mouth.

Bracing (cont)Bracing (cont)

The lateral forces in particular are capable of inflicting considerabledamage on the periodontal tissues and alveolar bone in theedentulous areas.

Bracing on teeth may be achieved by means of rigid portions of clasp arms(1) or plates (2). Bracing on the ridges and in the palate is obtainedby means of major connectors and flanges (3).

Prepare metal framePrepare metal frame

Study models with denture Study models with denture designs, master cast.designs, master cast.

Process and finish denturesProcess and finish denturesSetting the teeth and waxing

ReferencesReferences::British Dental Journal 2000 (RPD).British Dental Journal 2000 (RPD).Oxford handbook of clinical dentistry, Oxford handbook of clinical dentistry, 19991999Clinical Dentistry 2002, Clinical Dentistry 2002, IvorIvor G. G. ChestnuttChestnutt and John Gibson.and John Gibson.Removal Partial Removal Partial ProsthodonticsProsthodontics, Dr , Dr Sybille K Sybille K LechnerLechner and Prof AR and Prof AR MacGregorMacGregor, 1994., 1994.

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