INDIRECT RETAINERS.ppt
- 1. INDIRECT RETAINERS DR HARSHA R MDS Dept Of Prosthodontics Navodaya Dental College
- 2. A removable partial denture design derives support from two main sources. Periodontally sound teeth Through properly constructed Rest contacting well prepared Rest seat. In edentulous region, Residual ridge and associated Soft tissue with a well adapted denture base Disparity provided by two presents distinct challenges in RPD design
- 3. DEFINITIONS Indirect retainer : the component of a partial removable dental prosthesis that assists the direct retainer(s) 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 moves away from the tissues in pure rotation around the fulcrum line. (GPT-9)
- 4. Indirect retention: The effect achieved by one or more indirect retainers of a partial removable denture prosthesis that reduces the tendency for a denture base to move in an occlusal direction or rotate about the fulcrum line. (GPT-9)
- 5. Fulcrum line 1.A theoretical line passing through the point around which a lever functions and at right angles to its path of movement . 2: An imaginary line, connecting occlusal rests, around which a partial removable dental prosthesis tends to rotate under masticatory forces. The determinants for the fulcrum line are usually the cross arch occlusal rests located adjacent to the tissue borne components. (GPT-9)
- 6. ROTATION is that movement of an appliance which may occur in a vertical direction while its occlusal rests remain in abutment contact. DISPLACEMENT is that movement of an appliance when the primary occlusal rests also lose tooth contact.
- 7. PRINCIPLE OF INDIRECT RETAINER
- 8. THE NEED FOR INDIRECT RETENTION Not all removable appliances are in need of indirect retention. IN CLASS III, SHORT SPAN CLASS IV occlusal rest - prevent movement toward basal structures direct retainer – prevent to a limited degree, movement away from the supporting structures no rotation can take place.
- 9. In Kennedy class I, II and long span class IV
- 10. PRE-REQUISITES FOR INDIRECT RETAINER periodontally sound teeth. They should contact as many teeth as possible to reduce the possibility of moving teeth by the application of excessive force. Extension of the denture base on mucosa is effective provided the mucosa is firm. They can only function in conjunction with direct retainer (clasps). Indirect retainer by itself does not provide retention. Indirect retainers are best made of cast alloy, so that they fit teeth accurately and appear as unobtrusive as possible.
- 11. FULCRUM LINES AND INDIRECT RETENTION The term “fulcrum line” was used by Prothero to designate an imaginary line extending through the occlusal rest areas of the principal abutments (those supplying the major retention).
- 12. For these definitions to be valid, the principal abutment teeth must have rests on them. This is not always true, since some partial dentures do not have a rest on the principal abutment tooth but on the next tooth in the arch.
- 14. INDIRECT RETENTION a second fulcrum line is produced
- 15. When a second fulcrum line is produced by indirect retention , the prosthesis rotates about the primary fulcrum line if the denture base is forced tissue ward, and about the secondary fulcrum line if the denture base is lifted off the tissue . PF SF
- 16. LOCATION OF INDIRECT RETAINER IDEAL POSITION longest right angle projection from the fulcrum line ending in a definite seat on a suitable tooth. An indirect retainer can be effective only if it is placed some considerable distance anterior to the direct retainers.
- 20. INDIRECT RETENTION WITH MESIAL AND DISTAL RESTS. A mesial rest, in conjunction with retention located distally on an abutment tooth, reduces the need for indirect retention as compared with a distal rest associated with retention that is located mesially on an abutment tooth. Force E tends to move the removable partial denture away from the tissue by rotating it around the mesial rest. As this rotation occurs, the retentive clasp arc engages the retentive area thus resisting movement.
- 21. Figure illustrates a distal rest with retention supplied by a retentive arm located on the mesiobuccal surface of the tooth. Force E tends to move the removable partial denture away from the tissue by rotating it around the distal rest (A). As this rotation occurs, the retentive clasp arm is disengaged from the retentive area and offers no resistance to movement.
- 22. FACTORS INFLUENCING THE EFFECTIVENESS OF INDIRECT RETENTION Distance from the fulcrum line
- 23. The objective is to increase the distance between the direct and indirect retention as much as feasible.
- 24. DIFFERENT FORMS OF INDIRECT RETAINERS Indirect retainer can be divided on the basis of their position in mouth. A further division occurs on the basis of tissue on which retainer rests. In the upper jaw either it can be teeth or the tissue where as in the lower jaw only teeth can be used for this purpose.
- 25. Position Tissue on which retainer rests Type of indirect retainer 1. Anterior Tooth Anteriorly placed occlusal arm or incisal rest. Continous clasp and its modification. Palate Palatal arm. Anterior palatal bar. 2. Posterior Tooth Posteriorly placed occlusal rest. Palate Posterior palatal bar or extension of palatal plate.
- 26. OCCLUSAL REST The most commonly used indirect retainer is an auxillary occlusal rest located on the occlusal surface. In the mandibular class 1 arch the location is on the mesial marginal ridge of the first premolar on each side of the arch.
- 27. The ideal position of the indirect retainer is perpendicular to the fulcrum line that is mostly vicinity of the central incisors, which are too weak and have lingual surfaces that are too perpendicular to support a rest.
- 28. The bilateral rest on the first premolar are quite effective even though they are located closer to the axis of rotation Rest on the premolar is not only effective without jeopardizing the weaker single rooted tooth but also interference with the tongue is far less. The minor connector can be placed in the embrasure between the canine and premolar rather than anterior to the canine.
- 29. Indirect retainer for class 2 partial dentures is placed on the marginal ridge of the premolar on the opposite side of the arch from the distal extension base. Bilateral rest are seldom indicated except when an auxillary occlusal rest is needed to support the major connector or when the prognosis of the distal abutment is poor and provision is being considered for later conversion to class1 partial dentures.
- 30. CANINE EXTENSIONS FROM OCCLUSAL RESTS A finger extension from the premolar rest is placed on the prepared lingual slopes of the adjacent canine. Such an extension is used to increase the indirect retention by increasing the distance of resisting elements from the fulcrum line
- 31. CANINE RESTS INDICATION When the mesial marginal ridge of the first premolar is too close to the fulcrum line.When the teeth are overlapped, that fulcrum line is not accessible the adjacent canine may be used. Such a rest may be made effective by placing minor connector in the embrasure anterior to the canine either curving back on to the prepared lingual rest seat or extending to the mesio incisal rest.
- 32. INCISOR REST The root form, root length, inclination of the tooth and the ratio of the length of the clinical crown to the alveolar support must be considered in determing the site and form of rest placed on incisor. Incisal rests are placed at the incisal angles of the anterior teeth. It is placed generally in enamel
- 33. CINGULUM BARS (CONTINUOUS CLASP AND LINGUOPLATE) The first continuous clasp was made by Dr. J. Wright Beach of Buffalo and was used to stabilize a lingual bar. It acted in the capacity of an indirect retainer. Dr. Beach called his appliance the “wrought continuous interdental support.
- 36. MODIFICATION AREAS The occlusal rest on the secondary abutment in class 2 partial dentures may serve as indirect retainer. This depends on distance of the secondary abutment from the fulcrum line. The anterior abutment on the tooth-supported side is a secondary abutment securing to support and retain one end of the tooth supported segment as well as adding horizontal stabilization to the denture
- 38. RUGAE SUPPORT Some clinicians consider the coverage of rugae area of the maxillary arch as a means of indirect retention because the rugae area is firm and usually well situated to provide indirect retention for class1 situation
- 39. AUXILLARY FUNCTIONS OF INDIRECT RETAINER It reduces antero-posterior tilting leverages on the particular abutment. This is particularly important when an isolated tooth is being used as an abutment ‘a situation that should be avoided whenever possible. The proximal contact with the adjacent tooth prevents such tilting of the abutment as the base lifts away from the tissues.
- 40. AUXILLARY FUNCTIONS OF INDIRECT RETAINER Contact of its minor connector with axial surfaces aid in stabilization against horizontal movement of the denture. Such tooth surfaces when made parallel to the path of placement may also act as auxillary guiding planes. Indirect retainer act as vertical stops for the anterior portion of the denture, thus preventing food from forcing the major connector onto the underlying soft tissues.
- 41. AUXILLARY FUNCTIONS OF INDIRECT RETAINER Anterior teeth supporting indirect retainer are stabilized against lingual movement. It may act as auxillary rest to support a portion of major connector. Example; a lingual bar may be supported against settling into the tissues by the indirect retainer acting as an auxillary rest.
- 42. AUXILLARY FUNCTIONS OF INDIRECT RETAINER Prevents settling of the major connector - in the absence of the indirect retainer there is upward movement of the distal extension base which is accompanied by the downward movement of the major connector causing impingement of the soft tissues. By preventing the downward movement of the partial denture, the indirect retainer force the direct retainer to activate when movement away from the basal seat is attempted by extension bases.
- 43. AUXILLARY FUNCTIONS OF INDIRECT RETAINER It may provide the first visual indication for need to reline the partial denture. Deficiencies in the basal seat support are manifested by the dislodgement of the indirect retainer from their prepared rest seat. It helps to stabilize the major connector against the vertical and lateral forces and decrease the stresses on the principal abutment teeth by transmitting forces to other teeth in the arch.