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Indirect Retainer

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  • 1. 1 DEPARTMENT OF PROSTHODONTICS ROYAL DENTAL COLLEGE; CHALISSERY SEMINAR ON INDIRECT RETAINERS PREPARED BY SHABEEL .P.N ROLL NO;RDADBDS054
  • 2. 2 CONTENTS 1) DEFINITION 2) FUNCTIONS 3) MODE OF ACTION OF INDIRECT RETAINERS 4) FULCRUM LINES 5) PRINCIPLES OF INDIRECT RETENSION 6) FACTORS AFFECTING EFFECTIVENESS OF INDIRECT RETENTION 7) TYPES OF INDIRECT RETAINERS
  • 3. 3 INDIRECT RETAINRERS DEFINITION It is a part of a RPD which assists the direct retainers in preventing the displacement of distal extension denture bases by functioning through lever action on the opposite side of the fulcrum line (GPT) FUNCTIONS OF INDIRECT RETAINER 1) Primary function It shifts the fulcrum line away from the point of application of the force, there by counteracting the lifting force and stabilizing the denture 2) Auxiliary functions A) Reduces the antero-posterior twisting leverages on the principal abutments esp in the case of isolated tooth. B) Helps in stabilization C) Acts as an auxiliary guiding plane D) Splints the anterior tooth against lingual movement E) May act as auxiliary rest to support major connector esp in mandible F) May provide first indication to reline an extension base G) It counteracts horizontal forces by providing support and stability to the denture H) It provides lateral stability of PD by contacting axial tooth surface with rigid minor connector that is connecting indirect retainer I) It acts as a third point of contacting the tooth structure to ensure accurate repositioning of the frame work on the tooth during rebasing and relining
  • 4. 4 MODE OF ACTION OF INDIRECT RETAINERS Movement of distal extension denture base Towards the tissue away from the tissue Rest and rest seats Rotational movement about an axis Displacement of entire denture (occurs around an imaginary line passing through the teeth and component parts of the rpd, this imaginary axis is called fulcrum line) Other retentive components of rpd indirect retainers FULCRUM LINES An imaginary line around which a partial denture tend to rotate (GPT) A fulcrum line passes through terminal abutments Types a) retentive fulcrum line An imaginary line connecting retentive points of clasp arms, around which denture tend to rotate when subjected to forces such as the pull of sticky foods b) stabilizing fulcrum line an imaginary line connecting occlusal rests, around which denture tend to rotate when subjected to masticatory forces
  • 5. 5 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 edentulous space PRINCIPLE OF INDIRECT RETENTION It prevent displacement of denture base in two ways 1)resistance provided by rests ,extensions and rugae support 2) leverage advantage- a) Lifting forces will displace entire beam in absence of retainers b)with direct retainer ,at fulcrum ,lifting force will depress one end of the beam and elevate the other end c)with DR & IR forces will not lift the beam
  • 6. 6 PRINCIPLES FOR USING INDIRECT RETAINERS 1) more than one fulcrum line may present 2) IRs must be placed as far as possible from distal extension base ,for better leverage advantage 3) Most effective location for IRs is incisor region ,but due to their poor strength canines or premolars are used 4) Whenever possible two IRs ,closer to fulcrum line are taken to compensate for the compromise in distance FACTORS AFFECTING THE EFFECTIVENESS OF INDIRECT RETAINERS 1) Effectiveness of direct retainers In order to become IR effective proper functioning of DR should be present, I.e the retentive arms of the direct retainer must hold the principal occlusal rests properly 2) Distance from the fulcrum line a)Length of the distal extension base ; if it increases IR must placed far away from fulcrum line. b) Location of the fulcrum line; ideally IR should be located at a point perpendicular to the midpoint of the fulcrum line c) Distance from the fulcrum line; IR is placed as far as away from the fulcrum line 3) Rigidity of the connectors supporting the IR-It should be rigid
  • 7. 7 4) Effectiveness of the supporting tooth surface; IR should be placed on a definite rest seat .tooth inclines and weak teeth should not be used for support TYPES OF INDIRECT RETAINERS -AUXILIARY OCCLUSAL REST -CANINE EXTENSION FROM THE OCCLUSAL REST -CANINE REST -CONTINUOUS BAR RETAINERS AND LINGUO-PLATES -MODIFICATION AREAS -RUGAE SUPPORT -DIRECT INDIRECT RETENSION -INDIRECT RETENTION FROM MAJOR CONNECTORS -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 extension denture base -ideal location is central incisor, which is weak, therefore bilateral rests on first premolars are effective -rests on premolars do not interfere with tongue movements - in Kenneddy’s class1-bilateral rests on mesial fossa of first premolars -in Kenneddy’s class2 –mesial fossa of first premolar on opposite side -bilateral IR-An auxiliary rest for major connector -when distal abutment on modification side is poor(functional class1) 2) CANINE EXTENSION FROM THE OCCLUSAL REST -Consists of a finger extension from premolar rest to the lingual slope 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
  • 8. 8 3) CANINE REST(CINGULUM REST OR LINGUAL REST) -used when mesial marginal ridge of the 1st premolar is too close to the 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 should never be placed above the middle third of the teeth to avoid tooth movement(Kennedy class1 & 2) -as they rest on unprepared lingual surfaces they indirectly provide indirect retention 5) MODIFICATION AREAS -the occlusal rest on a secondary abutment in class ii modification 1 serve as an indirect retainer.
  • 9. 9 -if only one tooth is missing in the modification areas ,occlusal rest on this side should provide support for the unsupported major connector along with indirect retention 6) RUGAE SUPPORT -Rugae area is firm hence used for indirect retention esp for class I situations -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 to fulcrum line may act as indirect retainer 8) INDIRECT RETENTION FROM MAJOR CONNECTORS -in mandible retention from denture base itself help in indirect retention -in maxillary arch ,full palatal coverage is necessary for additional indirect retention esp when only anterior teeth are present -it is obtained from major connector’s resistance to distortion
  • 10. 10 9)INCISAL REST -On mandibular canines when mesial fossa of 1st premolar is close to fulcrum 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 11) DOUBLE LINGUAL BAR OR KENNEDY’S BAR -less effective -it rests on unprepared lingual surface, so indirect retention enhanced by terminal rests -it is extended far from fulcrum line
  • 11. 11 1)CLINICAL REMOVABLE PARTIAL PROSTHODONTICS- Stewart Rudd Kuebker- 2 nd EDITION 2)McCracken's REMOVABLE PARTIAL PROSTHODONTICS-Alan B.Carr, Glen P.McGivney ,David T.Brown-11 th EDITION. 3)THE GLOSSARY OF PROSTHODONTIC TERMS
  • 12. 12 4)TEXT BOOK OF PROSTHODONTICS- DR.DEEPAK NALLASWAMY