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DEPARTMENT OFPROSTHODONTICS ROYAL DENTAL COLLEGE;

CHALISSERY

SEMINAR ON

INDIRECT RETAINERS

PREPARED BY SHABEEL .P.N

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ROLLNO;RDADBDS054

CONTENTS

1) DEFINITION

2) FUNCTIONS

3) MODE OF ACTION OF INDIRECT RETAINERS

4) FULCRUM LINES

5) PRINCIPLES OF INDIRECT RETENSION

6) FACTORS AFFECTING EFFECTIVENESS OFINDIRECT RETENTION

7) TYPES OF INDIRECT RETAINERS

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INDIRECT RETAINRERS

DEFINITIONIt is a part of a RPD which assists the direct retainers in preventing thedisplacement of distal extension denture bases by functioningthrough lever action on the opposite side of the fulcrum line (GPT)

FUNCTIONS OF INDIRECT RETAINER1) Primary function

It shifts the fulcrum line away from the point of application of theforce, there by counteracting the lifting force and stabilizing thedenture

2) Auxiliary functionsA) Reduces the antero-posterior twisting leverages on the principal

abutments esp in the case of isolated tooth.B) Helps in stabilizationC) Acts as an auxiliary guiding planeD) Splints the anterior tooth against lingual movementE) May act as auxiliary rest to support major connector esp in

mandibleF) May provide first indication to reline an extension baseG) It counteracts horizontal forces by providing support and stability to

the denture

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H) It provides lateral stability of PD by contacting axial tooth surfacewith rigid minor connector that is connecting indirect retainer

I) It acts as a third point of contacting the tooth structure to ensureaccurate repositioning of the frame work on the tooth duringrebasing and relining

MODE OF ACTION OF INDIRECT RETAINERS

Movement of distal extension denture base

Towards the tissue away from thetissue

Rest and rest seats

Rotational movement about an axis Displacement of entire denture(occurs around an imaginary line passing through the teeth andcomponent parts of the rpd, this imaginary

axis is called fulcrum line) Otherretentive components of rpd

indirect retainers

FULCRUM LINESAn imaginary line around which a partial denture tend to rotate (GPT)A fulcrum line passes through terminal abutments

Types

a) retentive fulcrum line

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An imaginary line connecting retentive points of clasp arms,around which denture tend to rotate when subjected to forcessuch as the pull of sticky foods

b) stabilizing fulcrum linean imaginary line connecting occlusal rests, around whichdenture tend to rotate when subjected to masticatory forces

Location of fulcrum lines for different classes of RPDs

1)Class1-passes through most posterior abutments

2) Class2-passes diagonally through most posterior teeth on one side

and abutment on distal extention side

3) Class3-passes through two principal abutments

4)Class4-passes through two abutments adjacent to the edentulousspace

PRINCIPLE OF INDIRECT RETENTION

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It prevent displacement of denture base in two ways1)resistance provided by rests ,extensions and rugae support2) leverage advantage-

a) Lifting forces will displace entire beam in absence of retainers

b)with direct retainer ,at fulcrum ,lifting force willdepress one end of the beam and elevate the other end

c)with DR & IR forces will not lift the beam

PRINCIPLES FOR USING INDIRECT RETAINERS

1) more than one fulcrum line may present2) IRs must be placed as far as possible from distal extension

base ,for better leverage advantage3) Most effective location for IRs is incisor region ,but due to their

poor strength canines or premolars are used4) Whenever possible two IRs ,closer to fulcrum line are taken to

compensate for the compromise in distance

FACTORS AFFECTING THE EFFECTIVENESS OFINDIRECT RETAINERS

1) Effectiveness of direct retainersIn order to become IR effective proper functioning of DR should

be present, I.e the retentive arms of the direct retainer must holdthe principal occlusal rests properly2) Distance from the fulcrum line

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a)Length of the distal extension base ; if it increases IR mustplaced far away from fulcrum line.

b) Location of the fulcrum line; ideally IR should be located at apoint perpendicular to the midpoint of the fulcrum line

c) Distance from the fulcrum line; IR is placed as far as away fromthe fulcrum line3) Rigidity of the connectors supporting the IR-It should berigid4) Effectiveness of the supporting tooth surface; IR should be

placed on a definite rest seat .tooth inclines and weak teeth shouldnot be used for support

TYPES OF INDIRECT RETAINERS -AUXILIARY OCCLUSALREST

-CANINE EXTENSION FROMTHE OCCLUSAL REST

-CANINE REST-CONTINUOUS BAR

RETAINERS AND LINGUO-PLATES-MODIFICATION AREAS-RUGAE SUPPORT-DIRECT INDIRECT

RETENSION-INDIRECT RETENTION

FROM MAJOR CONNECTORS

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-INCISAL REST-EMBRASSURE HOOK -DOUBLE LINGUAL BAR OR

KENNEDY’S BAR

1) AUXILIARY OCCLUSAL REST-Most frequently used

-located on the occlusal surface far away from distal extensiondenture base-ideal location is central incisor, which is weak, therefore bilateralrests on first premolars are effective-rests on premolars do not interfere with tongue movements- in Kenneddy’s class1-bilateral rests on mesial fossa of firstpremolars

-in Kenneddy’s class2 –mesial fossa of first premolar on oppositeside

-bilateral IR-An auxiliary rest for majorconnector

-when distal abutment on modificationside is poor(functional class1)

2) CANINE EXTENSION FROM THE OCCLUSAL REST

-Consists of a finger extension from premolar rest to the lingualslope of adjacent canine

-applied when first premolar is the primary abutment-should always used with terminal rests to prevent tipping leverage

as in single cingulum canine rest

3) CANINE REST(CINGULUM REST OR LINGUAL REST)

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-used when mesial marginal ridge of the 1st premolar is too close tothe fulcrum line-when the teeth is lapped to render the fulcrum line is inaccessible-the rest can be more effective by placing the minor connector more

anterior to canine

4) CONTINUOUS BAR RETAINERS AND LINGUO-PLATES

-Terminal rests are actual IRs-a continuous bar retainer or superior border of the linguo-plate shouldnever be placed above the middle third of the teeth to avoid toothmovement(Kennedy class1 & 2)-as they rest on unprepared lingual surfaces they indirectly provideindirect retention

5) MODIFICATION AREAS

-the occlusal rest on a secondary abutment in class ii modification 1serve as an indirect retainer.

-if only one tooth is missing in the modification areas ,occlusal rest onthis side should provide support for the unsupported major connector

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along with indirect retention

6) RUGAE SUPPORT

-Rugae area is firm hence used for indirect retention esp for class Isituations-it can be used in case of ‘ u ‘shaped designs-less effective than a tooth supported IR

7) DIRECT INDIRECT RETENSION

Reciprocal arm of a direct retainer located anterior tofulcrum line may act as indirect retainer

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8) INDIRECT RETENTION FROM MAJOR CONNECTORS

-in mandible retention from denture base itself help in indirectretention-in maxillary arch ,full palatal coverage is necessary for additionalindirect retention esp when only anterior teeth are present-it is obtained from major connector’s resistance to distortion

9)INCISAL REST

-On mandibular canines when mesial fossa of 1st premolar is close tofulcrum line-produces tipping force

10) EMBRASSURE HOOK

-less desirable, which engages anterior inter proximal areas-used when less positive seat to stabilize the indirect retainer-unaesthetic due to metallic display

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11) DOUBLE LINGUAL BAR OR KENNEDY’S BAR

-less effective-it rests on unprepared lingual surface, so indirect retention enhancedby terminal rests-it is extended far from fulcrum line

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1)CLINICAL REMOVABLE PARTIALPROSTHODONTICS- StewartRudd Kuebker- 2nd EDITION

2)McCracken's REMOVABLE

PARTIAL PROSTHODONTICS-Alan B.Carr, GlenP.McGivney ,David T.Brown-11th

EDITION.

3)THE GLOSSARY OF

PROSTHODONTIC TERMS

4)TEXT BOOK OFPROSTHODONTICS-DR.DEEPAK NALLASWAMY

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