INDIRECT RETAINERS IN REMOVABLE PARTIAL DENTURES
Download as PPTX, PDF12 likes5,748 views
The document presents an overview of indirect retainers in removable partial dentures, detailing their definition, function, and types. It explains how indirect retainers assist in stabilizing dentures against displacement by functioning through leverage on the opposite side of the fulcrum line. Additionally, it emphasizes the importance of proper design and placement of these retainers to ensure effectiveness and stability in dental prosthetics.
INDIRECT RETAINERS IN REMOVABLE PARTIAL DENTURES
- 1. INDIRECT RETAINERS IN REMOVABLE PARTIAL DENTURES BY:Dr.PrathameshFulsundar (MDS–Prostodontics)
- 2. Contents Introduction Definition of indirect retainer Function of indirect retainer Fulcrum lines Effect of rotational movement Factors determining effectiveness of indirect retainers Types of indirect retainer Conclusion References
- 4. A RPD derives support from two main sources periodontally sound natural teeth & residual alveolar processes and associated soft tissues. A RPD that is supported by healthy natural teeth possesses adequate stability and retention to resist functional displacement. However, a RPD that is not entirely bounded by natural teeth will move when a load is applied. INTRODUCTION
- 5. TYPES OF LEVER Mechanical Advantage= Effort Arm Resistance Arm
- 7. DEFINITION The component of a removable partial denture that assists the direct retainer in preventing displacement of the distal extension denture base by functioning through lever action on the opposite side of the fulcrum line when the denture base attempts to move away from the tissues in pure rotation around the fulcrum line. (GPT 9)
- 8. FUNCTIONS OF INDIRECT RETAINERS Reduces the antero-posterior twisting Helps in stabilization Acts as an auxiliary guiding plane. It splints the anterior tooth against lingual movement. May act as auxiliary rest to support major connector. It counteracts horizontal forces. It provides lateral stability. May provide first indication to reline an extension base. It acts as a third point for contacting the tooth structure to ensure accurate repositioning of the frame work on the tooth during rebasing and relining.
- 9. A fulcrum line is an imaginary line around which an RPD will tend to rotate. When an occlusal load is applied to a distal extension removable partial denture, the prosthesis rotates around a fulcrum line that passes through the most posterior rests one on each side of the dental arch Displacement of the prosthesis is limited by the hard and soft tissues of the residual ridge. FULCRUM LINE
- 10. Active tissues such as the tongue and buccinator muscle also may displace the denture base during speech, mastication, or swallowing. When a distal extension removable partial denture is subjected to such forces, the associated fulcrum line passes through the tips of the retentive clasps.
- 11. EFFECT OF ROTATIONAL MOVEMENT When the posterior portion of a Kennedy Class I or Class II removable partial denture is subjected to occlusally directed dislodging forces in the absence of properly designed indirect retention, two undesirable events occur: (1) The denture base moves away from the supporting tissues. (2) The anterior segment of the major connector impinges upon the underlying soft tissues.
- 12. Concept of indirect retention was originally advocated by Dr. W. E. Cummer as a means of resisting rotational displacement. When in positive contact with a rest seat, an indirect retainer contributes to the overall support and stability of the removable partial denture. For a long-span lingual bar, properly constructed indirect retainers can provide additional support and rigidity to the major connector.
- 13. FULCRUM LINES FOUND IN VARIOUS TYPES OF PARTIALLY EDENTULOUS ARCHES Class I arch The fulcrum line passes through the most posterior abutments, provided some rigid component of the framework is occlusal to the abutment’s heights of contour.
- 14. Class II arch The fulcrum line is diagonal, passing through the abutment on the distal extension side and the most posterior abutment on the opposite side.
- 15. In a Class III arch Indirect retention may not be needed as it is tooth supported. However in cases with non supporting posterior teeth, the adjacent edentulous area is considered to be the tissue- supported end, with a diagonal fulcrum line passing through the two principal abutments, as in a Class II arch.
- 16. Class IV arch The fulcrum line passes through two abutments adjacent to the single edentulous space.
- 17. FACTORS DETERMINING EFFECTIVENESS OF INDIRECT RETAINERS 1. The principal occlusal rests on the primary abutment teeth must be reasonably held in their seats by the retentive arms of the direct retainers. 2. The following three areas must be considered: Length of the distal extension base Location of the fulcrum line Distance from the fulcrum line
- 18. 3. The connectors supporting the indirect retainer must be rigid. 4. Effectiveness of the supporting tooth surface The indirect retainer must be placed on a definite rest seat on which slippage or tooth movement will not occur. The Tooth inclines and weak teeth should never be used to support indirect retainers.
- 19. TYPES OF INDIRECT RETAINERS 1. Auxiliary Occlusal Rest 2. Canine Extension From The Occlusal Rest 3. Canine Rest 4. Continuous Bar Retainers And Linguo-plates 5. Modification Areas 6. Rugae Support 7. Direct Indirect Retension 8. Indirect Retention From Major Connector 9. Incisal Rest 10. Embrassure Hook 11. Double Lingual Bar Or Kennedy’s Bar
- 20. 1- AUXILIARY OCCLUSAL REST -Most frequently used. -Located on the occlusal surface far away from distal extension denture base. -It is placed perpendicular to the midpoint of the fulcrum line. -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.
- 21. PREPARATION OF OCCLUSAL REST Rounded triangle Base at the marginal ridge and apex at the centre of the tooth One-half the intercuspal distance and one-third/one- half the mesiodistal width Base must be less than 900 to long axis of tooth. Depth 0.5 at the thinnest portion and 1.5mm at the marginal ridge.
- 22. 2- CANINE EXTENSION FROM THE OCCLUSAL REST -Consists of a finger extension from premolar rest to the lingual slope of adjacent canine. -Used when first premolar is the primary abutment. -This design avoids the tipping action produced in a single cingulam canine rest.
- 23. 3-CANINE REST(CINGULUM REST or LINGUAL REST) •Canine rest is used when mesial marginal ridge of the 1st premolar is too close to the fulcrum line. •Lingual rest is prepared mostly on maxillary canines •Rest seat are V shape & half moon shape.
- 24. 4-CONTINUOUS BAR RETAINERS & LINGUO- PLATES As they rest on unprepared lingual surfaces they aid the terminal rests by providing indirect retention. They also help to splint weaker anterior teeth. 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).
- 25. 5- MODIFICATION AREAS The occlusal rest on a secondary abutment in class 2 modification 1 serve as an indirect retainer. 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.
- 26. 6- RUGAE SUPPORT Rugae area is firm hence used for indirect retention espcially for class I situations. Used for indirect retention for palatal horseshoe major connector. Less effective than a tooth supported indirect retainer.
- 27. 7- DIRECT INDIRECT RETENSION Reciprocal arm of a direct retainer located anterior to fulcrum line may act as indirect retainer.
- 28. 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. It is obtained from major connector’s resistance to distortion.
- 29. 9- INCISAL REST On mandibular canines when mesial fossa of 1st premolar is close to fulcrum line.
- 30. 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.
- 31. 11- DOUBLE LINGUAL BAR OR KENNEDY’S BAR Less effective. It rests on unprepared lingual surface, thus enhancing the indirect retention at terminal rests. It is extended far from fulcrum line.
- 32. CONCLUSION Proper designing the connector for the partial edentulous space is necessary to perform function. It is important for clinician to understand the possible movements in response to function and help control these movements.
- 33. REFERENCES Clinical removable partial prosthodontics- stewart rudd kuebker- 2nd EDITION Mccracken's Removable Partial Prosthodontics-alan B.Carr, glen P.Mcgivney ,david T.Brown-11th Edition. Ernest L.Miller and Joseph E.Grasso,Removable Partial Prosthodontics, ed 2. 1979,Williams and Willkins. A.A.Grant and W.Johnson,Removable denture Prosthodontics, ed 2.1992,Churchill livingstone Inc. William E. Avant.Indirect retention In partial denture Design.J Prosthet Dent.16:1103-1110 The glossary of prosthodontic terms
- 34. Thank you