Introduction of Removable Partial Denture - Design and retention update no case.pdf

8/18/2019 Introduction of Removable Partial Denture - Design and retention update no case.pdf

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Introduction of

Removable Partial

Denture - Design andRetention

Introduction ofIntroduction of

Removable PartialRemovable Partial

DentureDenture -- Design andDesign andRetentionRetention

By : DrBy : Dr ZaihanZaihan AriffinAriffin

BDS(MalayaBDS(Malaya),), GDCDentGDCDent (Adelaide),(Adelaide),

Doctor of Clinical Dentistry (Adelaide),Doctor of Clinical Dentistry (Adelaide),

FRACDS (Australia)FRACDS (Australia)


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Type of dentureType of denture

Full dentureFull denture

Partial denturePartial denture ––acrylic or Coacrylic or Co--crcr

Immediate dentureImmediate denture ––

acrylic (commonly)acrylic (commonly) OverdentureOverdenture –– acrylicacrylic

or Coor Co--crcr

Implant supportedImplant supporteddenturedenture

Sectional dentureSectional denture


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WhichWhich endentulousendentulous areas shouldareas should

restorerestoreRestore :Restore :

ThoseThose endentulousendentulous areas whichareas whichpatients wants to restore forpatients wants to restore for

aesthetics or functions.aesthetics or functions. Those areas which are needed toThose areas which are needed to

restore or preserverestore or preserve occlusalocclusal integrityintegrity


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Principles of designPrinciples of design

Existing dentureExisting denture

Tissue preservationTissue preservation

OcclusalOcclusal integrityintegrity

Oral hygiene and maintenanceOral hygiene and maintenanceResistance to various forcesResistance to various forces


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Existing dentureExisting denture

Note details ofNote details of exstingexsting denture,denture,

What pt wantsWhat pt wants

Any modifications?Any modifications?

Copy the nonCopy the non--traumatic elements oftraumatic elements ofprevious dentureprevious denture


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OcclusalOcclusal integrityintegrity Any tooth modification must leave theAny 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 lowerWhen wearing either the upper or lowerdenture, the patient must be provideddenture, the patient must be provided

with a stable occlusion with maximumwith a stable occlusion with maximum

possible natural tooth contacts in thepossible natural tooth contacts in theintercuspalintercuspal positionposition

When wearing both denture, the patientWhen wearing both denture, the patientmust have a stable occlusion withmust have a stable occlusion with

maximum natural tooth contactmaximum natural tooth contact


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Oral hygiene and maintenanceOral hygiene and maintenance

Improvement and maintenance ofImprovement and maintenance of

OH is fundamental in all treatment.OH is fundamental in all treatment. recall and maintenancerecall and maintenance

Special lectureSpecial lecture ……


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Tissue preservationTissue preservation

At least 1mm clearof CEJ

Never finish any part of the denture on the gingivamargin

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


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Resistance to various forcesResistance to various forces

SupportSupport

Retention : direct and indirect, guideRetention : direct and indirect, guideplaneplane

ConnectorConnectorStabilisationStabilisation

BracingBracing


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Things to remember!Things to remember!

1. Saddles1. Saddles (yellow)(yellow)

2. Support2. Support (red)(red) 3. Retention3. Retention (green)(green)

4. Bracing and reciprocation4. Bracing and reciprocation (blue)(blue) 5. Connector5. Connector (black)(black)

6. Indirect retention.6. Indirect retention.


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Support (rest)

Clasp -

retention

bracing

Major connector

saddle


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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

attachmentsattachments

WHY:WHY: IncreaseIncrease masticatorymasticatory

efficiencyefficiency


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SupportSupport

OcclusalOcclusal rest : premolar and molarrest : premolar and molar

CingulumCingulum rest : upper canine andrest : upper canine andincisorsincisors

InsicalInsical rest : lower canine andrest : lower canine andincisorsincisors

Tissue coverage in case whereTissue coverage in case whereendentulousendentulous require support fromrequire support from

mucosamucosa


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Tooth prep forTooth prep for

RPDsRPDs

should be planned onshould be planned on

articulated study casts after they have beenarticulated study casts after they have been

surveyed and a denture design producedsurveyed and a denture design produced

Shaping of enamel surfacesShaping of enamel surfaces is usuallyis usually

undertaken withundertaken with rotary diamond instrumentsrotary diamond instruments

of appropriate size and shapeof appropriate size and shape

Roughened enamel surface must always beRoughened enamel surface must always be

smoothened and polishedsmoothened and polished

Subsequent application of a topical fluorideSubsequent application of a topical fluoride

varnishvarnish-- to reduce the chance of cariousto 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


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Rest seatsRest seats

Need to be prepared to:Need to be prepared to:

Produce aProduce a favourablefavourable

tooth surface for supporttooth surface for support

Prevent interference withPrevent interference with

the occlusionthe occlusion

11 ––rest seat placed on an inclinedrest seat placed on an inclined

surface tend tosurface tend to slide down toothslide down tooth

under influence ofunder influence of occlusalocclusal loadload

22 ––provision of a rest seat result inprovision of a rest seat result invertical loading of tooth,vertical loading of tooth, >efficient>efficient

supportsupport

11 ––occlusalocclusal rest placed at the arrowrest placed at the arrow

22 ––create acreate a premature contactpremature contact

33 ––unless a rest seat was preparedunless a rest seat was prepared


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Reduce theReduce the

prominence of a restprominence of a rest

11 ––rest placed on an unpreparedrest placed on an unpreparedtooth surface tend totooth surface tend to collect foodcollect food

particlesparticles

22 ––rest seat allow the rest to berest seat allow the rest to be

shaped so that it blends into theshaped so that it blends into the

contour of toothcontour of tooth


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Rest seats on post teethRest seats on post teeth

TheThe designdesign of rest seats onof rest seats on post teethpost teeth

11 ––occlusalocclusal viewview

22 ––mesiodistalmesiodistal viewview

33 ––proximal viewproximal view

Rest seat of post teeth should normally beRest seat of post teeth should normally be

saucersaucer--shapedshaped

Use of a boxUse of a box--shapes rest seat within ashapes rest seat within a

cast restoration result in rest applyingcast restoration result in rest applying

damaging horizontal loads on thedamaging horizontal loads on the

abutment tooth (restricted to toothabutment tooth (restricted to tooth--supported dentures where thesupported dentures where the perioperio

health of the abutment teeth is good)health of the abutment teeth is good)

Rest should beRest should be at least 0.8at least 0.8--1mm thick1mm thick forfor

adequate strength.adequate strength.

Pt asked to occlude on a strip of softenedPt asked to occlude on a strip of softened

pink wax. The thickness of wax in thepink wax. The thickness of wax in the

region of rest seat indicate sufficientregion of rest seat indicate sufficientenamel has been removedenamel has been removed


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Rests seats on anterior teethRests seats on anterior teeth

OnOn maxillary ant teethmaxillary ant teeth,,

particularlyparticularly caninescanines, the, the cingulumcingulum

is often well developed so thatis often well developed so that

modest prep to accentuate itsmodest prep to accentuate itsform creates a rest seat w/oform creates a rest seat w/o

penetration of enamelpenetration of enamel

AA cylindrical green stonecylindrical green stone with awith arounded tiprounded tip should be used.should be used.

A spherical instrument tends toA spherical instrument tends to

create unwanted undercuts.create unwanted undercuts.


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Preparation forPreparation for mandibularmandibular

anterior toothanterior tooth is shown fromis shown from

the:the:11 ––labial viewpointlabial viewpoint

22 ––lingual viewpointlingual viewpoint

33 ––proximal viewpointproximal viewpoint

IncisalIncisal rest seatrest seat can becan be

prepared using aprepared using a taperedtaperedcylindrical diamondcylindrical diamond


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Where to place?Where to place?

Where : the most desirable vertical supportWhere : the most desirable vertical supportgainedgained

Next to theNext to the endentulousendentulous area for bounded basesarea for bounded bases Away from theAway from the endentulousendentulous area ; free endarea ; free end

saddlesaddle

Other : by passing the weak abutment and placeOther : by passing the weak abutment and placerest on next approximating toothrest on next approximating tooth

Spreading the load on two abutmentSpreading the load on two abutment

forfor cingulumcingulum rest : 2mm above therest : 2mm above the gingivagingivamarginmargin


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ConnectorsConnectors

Major:Major: to join the Saddles Areas togetherto join the Saddles Areas together MandibularMandibular: Lingual bar, Lingual plate,: Lingual bar, Lingual plate,

Sublingual bar, dental (Sublingual bar, dental (cingulumcingulum) bar,) bar,

labial barlabial bar Maxilla: Full palatal coverage; AnteriorMaxilla: Full palatal coverage; Anterior

palatal bar, Midpalatal bar, Mid-- palatal Posterior palatalpalatal Posterior palatal

bar, Ring bar and horseshoe connector.bar, Ring bar and horseshoe connector.

Minor:Minor: to join the rests, clasps andto join the rests, clasps and

reciprocal elements to the majorreciprocal elements to the majorconnector.connector.

C tC t


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Connector Connector

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 thelinguallingual sulcussulcus and gingival margin.and gingival margin.

CingulumCingulum barbar ::i)i) insufficient room for lingual barinsufficient room for lingual bar

ii)ii) The clinical crown are long enough forThe clinical crown are long enough for

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

between the teethbetween the teeth


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L i n g u a l b a r

>6 mm


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Lingual plate :Lingual plate :

If lingual bar andIf lingual bar and cingulumcingulum bar arebar arecontraindicatedcontraindicated

Do not use lingual plate behindDo not use lingual plate behinddiastemadiastema

Sublingual barSublingual bar

There is insufficient room forThere is insufficient room for lingulalingulabarbar

Pt havePt have

diastemadiastema


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L i n g u a l p l a t e


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Su b l i n g u a l b a r


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Labial barLabial bar

Try to avoid this connector ifTry to avoid this connector ifpossiblepossible-- difficult to place anddifficult to place and

uncomfortable to wearuncomfortable to wear

Useful when the lower incisors areUseful when the lower incisors are

markedlymarkedly retroclinedretroclined or where thereor where there

isis pronoucedpronouced torustorus mandibularismandibularis


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Connector Connector

MaxillaMaxilla: Full palatal coverage;: Full palatal coverage;

Anterior palatal bar, MidAnterior palatal bar, Mid-- palatalpalatalPosterior palatal bar, Ring bar andPosterior palatal bar, Ring bar and

horseshoe connectorhorseshoe connector


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Pa l a t a l P l a t e

The basic functional requirement of amajor connector is to link the varioussaddles and other RPD components.


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A simple mid-palatal plate has been used. This is a verysatisfactory 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 thehighly innervated mucosa of the anterior palate.


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horseshoe connectorhorseshoe connector


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DIRECT RETENTIONDIRECT RETENTION

Clasps: provide direct retention byClasps: provide direct retention by

engaging the undercut area on theengaging the undercut area on thetooth.tooth.

Types:Types: GingivallyGingivally oror OcclusallyOcclusallyApproachingApproaching

Names: Ring, Circumferential, INames: Ring, Circumferential, I--bar,bar,

TT--bar, Lbar, L-- bar, Reverse.bar, Reverse.Should includes a rest, a clasp armShould includes a rest, a clasp arm

and a reciprocal arm.and a reciprocal arm.


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Figure A Figure B


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Retention will depend on:Retention will depend on:

Dept of undercut : 0.25 mmDept of undercut : 0.25 mm-- cast cobaltcast cobaltchrome;chrome;0.5 mm SS;0.5 mm SS;

0.75 mm gold.0.75 mm gold. Position of undercut: ex: high survey linePosition of undercut: ex: high survey line ––

gingivagingiva approaching claspapproaching clasp

AestethicsAestethics

Position of the toothPosition of the tooth

OcclusionOcclusion

Shape of theShape of the

sulcussulcus

Periodontal healthPeriodontal health

Number of claspNumber of clasp –– ex: bilateral gingivalex: bilateral gingivalapproaching clasp are preferredapproaching clasp are preferred


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To be able to decide on the positionTo be able to decide on the positionand type of retainer, the studyand type of retainer, the study

models need to be surveyed.models need to be surveyed.This will determine:This will determine:

the path of insertionthe path of insertion the position of undercut on tooththe position of undercut on tooth

the depth of undercut on the tooththe depth of undercut on the tooth the presence of any boneythe presence of any boney

undercut on ridge.undercut on ridge.


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C l a s p s The flexibility of a clasp is dependant on its design. • Se c t i o n

A round section clasp will flex equally in all directions,

whereas a half round clasp will flex more readily in thehorizontal than in the vertical plane. • Length

The longer the clasp arm the more flexible it is. Thusan 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


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R t ti ill d d


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Dept of undercut : 0.25 mmDept of undercut : 0.25 mm-- cast cobaltcast cobaltchrome: 0.5 mm Sschrome: 0.5 mm Ss

0.75 mm0.75 mm –– gold.gold. Position of undercut: ex: high survey linePosition of undercut: ex: high survey line ––

gingivagingiva approaching claspapproaching clasp

Position of the toothPosition of the tooth

OcclusionOcclusion

Shape of theShape of the sulcussulcus Periodontal healthPeriodontal health

Material of denture baseMaterial of denture base


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The position of the undercut

A high survey line poses particular difficulties on a premolar tooth,

it may be possible to position a flexible gingivally approaching clasp higher up the crown


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The survey lines on the molar and premolar teeth-

there is a larger undercut on that part of the tooth which isfurthest away from the edentulous area.

Typical designs of retentive clasp are the occlusally

approaching clasp on the molar and the gingivally approaching

‘I’ bar on the premolar tooth.


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ClaspsTwo categories:

1) the occlusally approaching clasp on UL7 (27) and the

2) gingivally approaching ‘I’ bar clasp on UL3Common variations in the design of clasps that may be selected primarily according to

the 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)

M D


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Figure AFigure B

Comparison of occlusally and gingivally


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Comparison of occlusally and gingivallyapproaching clasps

Fig. A — Retention Only the terminal third of an occlusally-approaching clasp

(stippled section) should cross the survey line and enter theundercut area.

Fig. B — Retention A 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 canbe a positive advantage when it is necessary to clasp a

premolar tooth or a tooth whose periodontal attachmenthas been reduced by periodontal disease.

Comparison of gingival approaching clap andComparison of gingival approaching clap and


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p g g pp g pp g g pp g p

occlusalocclusal approaching claspapproaching clasp

Occlusal

approaching

Gingival

approaching

More rigid

(can also act as

reciprocal arms – no

undercut site)

Less rigid

Less aesthetic + caninterfere with the

occlusion

More aesthetic

+ plaque accumulation

and caries

+ root caries and

irritation to soft tissue



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Dept of undercut : 0.25 mmDept of undercut : 0.25 mm-- cast cobaltcast cobaltchrome:chrome:

0.5 mm0.5 mm-- ––SSSS0.75 mm gold.0.75 mm gold.

Position of undercut: ex: high survey linePosition of undercut: ex: high survey line

–– gingivagingiva approaching claspapproaching clasp Position of the toothPosition of the tooth

OcclusionOcclusion

Shape of theShape of the sulcussulcus Periodontal healthPeriodontal health

Material of denture baseMaterial of denture base


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Th e h e a l t h o f t h e

p e r i o d o n t a l

l i g a m e n t

Which type claspWhich type clasp

would you used?would you used?


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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 a

gingivally approaching clasp of correct proportions and position.

If there is no reasonable alternative to this clasp,

- can considered surgical excision of the frenal attachment.



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Indirect retention :Indirect retention :

Indirect retainer derived by placing components so as toIndirect retainer derived by placing components so as to

resistresist ‘‘rotational orrotational or ‘‘tippingtipping’’ forces of the denture around theforces of the denture around the

retainers ex: by position of clasps and rest and type of theretainers ex: by position of clasps and rest and type of theconnector.connector.


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Indirect retainerIndirect retainer ::

The component of a removable partial dentureThe component of a removable partial denturethat assist the direct retainer(s) in preventingthat assist the direct retainer(s) in preventing

displacement of the distal extension base bydisplacement of the distal extension base byfunctioning through lever action on the oppositefunctioning through lever action on the oppositeside of the fulcrum line when the denture baseside of the fulcrum line when the denture basemoves away from the tissues in pure rotationmoves away from the tissues in pure rotation

around the fulcrum linearound the fulcrum line(Academy of(Academy of ProsthodonticsProsthodontics, 1999)., 1999).

Particularly important with freeParticularly important with free

--end saddles andend saddles and

large anterior saddles.large anterior saddles.


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F = FulcrumF = Fulcrum ——indirect retainer, aindirect retainer, a

component whichcomponent whichobtains support.obtains support.

R = ResistanceR = Resistance ——

retentionretentiongenerated by thegenerated by theclasp.clasp.

E = EffortE = Effort ——displacing force,displacing force, egega bolus of stickya bolus of stickyfood.food.

E-Effort

ResistanceandFulcrum


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Ex:

by placing a rest on the

premolar tooth, this rest(indirect retainer) becomesthe fulcrum of movementof the saddle in an occlusal

direction causing the claspto move up the tooth,engage the undercut andthus resist the tendency

for the denture to pivot.


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It can thus be seen that to obtain indirect retentionIt can thus be seen that to obtain indirect retention

the clasp normally be placed between the saddle andthe clasp normally be placed between the saddle andthe indirect retainer the indirect retainer


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Examples of RPD designs which include indirectExamples of RPD designs which include indirect

retentionretention

Kennedy I:Kennedy I: Indirect retention in this design is providedIndirect retention in this design is providedbyby incisalincisal rests on LR3 (43) and LL3 (33).rests on LR3 (43) and LL3 (33).

The RPI systemThe RPI system


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The RPI systemThe RPI system

The RPI system is a combination ofThe RPI system is a combination of

1)occlusal rest1)occlusal rest -- (R) placed(R) placed mesiallymesially..

2)distal guide plate2)distal guide plate -- (P) (enhanced(P) (enhanced

retention and ought to reduces rotationsretention 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 distaldistalextension saddles (free end saddle).extension saddles (free end saddle).


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RPIRPI


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RPIRPI

The RPI system is designed to allow vertical

rotation of a distal extension saddle into thedenture-bearing mucosa under occlusal loadingwithout damaging the supporting structures of

the abutment tooth.


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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 thedirections indicated and disengage (acts as the recriprocalarm) from the tooth surface. Potentially harmful torque isthus avoided.

RPIRPI


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X

Y

Z



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gg






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Reciprocals:Reciprocals: a part of the denturea part of the denture

that resists the action of a clasp on athat resists the action of a clasp on atooth as the denture is inserted ortooth as the denture is inserted or

removed from the mouth.removed from the mouth.

Bracing (cont)Bracing (cont)


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g ( )g ( )

The lateral forces in particular arecapable of inflicting considerable

damage on the periodontal tissuesand 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 theridges and in the palate is obtainedby means of major connectors and

flanges (3).

Prepare metal framePrepare metal frame


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Study models with dentureStudy models with denture

designs, master cast.designs, master cast.

A B C

D

E


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Process and finish denturesProcess and f inish denturesSetting the teeth and waxing


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ReferencesReferences::

British Dental Journal 2000 (RPD).British Dental Journal 2000 (RPD).Oxford handbook of clinical dentistry,Oxford handbook of clinical dentistry,

19991999

Clinical Dentistry 2002,Clinical Dentistry 2002, IvorIvor G.G.ChestnuttChestnutt and John Gibson.and John Gibson.

Removal PartialRemoval Partial ProsthodonticsProsthodontics, Dr, DrSybille KSybille K LechnerLechner and Prof ARand Prof ARMacGregorMacGregor, 1994., 1994.

Introduction of Removable Partial Denture - Design and retention update no case.pdf

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