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INDIRECT RETAINERS

INDIRECT RETAINERS . Dr. Waseem Bahjat Mushtaha Specialized in prosthodontics. Definition: Indirect retainer:

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INDIRECT RETAINERS

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  1. INDIRECT RETAINERS Dr. Waseem Bahjat MushtahaSpecialized in prosthodontics

  2. Definition: Indirect retainer: It is a component of a tooth mucosa borne RPD, which is placed on the opposite side of the fulcrum line assisting the direct retainer in preventing displacement of an extension base through mechanical leverage. Fulcrum line: An imaginary line between the two occlusal rests on the terminal abutment about which the denture rotates when the base moves away from the residual ridge

  3. Principle of indirect retention: -In the case of a distal extension base rotational movement around the fulcrum line, either towards the tissue or away from the ridge, may occur as forces are applied. -The vertical component of rotating motion towards the ridge can be controlled by stable denture base support. -Sticky foods. muscle action and gravity in maxillary dentures may exert a pull and tend to lift the denture base away from the ridge. This vertical component of force occurs in the direction away from the ridge is counteracted by the indirect retainers

  4. Factor influencing the effectiveness of indirect retainers: 1-The effectiveness of direct retainer: The direct retainer should hold the main rests in their seats. If total displacement of the rest occurs, there would be no rotation about the fulcrum, and no indirect retention. 2-Distance from the fulcrum line: As the distance between the indirect retainer and the fulcrum line increase the indirect retention increase. 3-Rigidity of the connectors: All the connectors must be rigid for the indirect retainer to function properly. 4-Support for the indirect retainer: Tooth inclines. should never be used to support indirect retainer. It must be placed in a definite rest seat on which slippage or tooth movement cannot occur.

  5. Forms of indirect retainers: 1-Auxiliarv occlusal rest: The most commonly used indirect retainer is an auxiliary occlusal rest placed far away from the extension base as much as possible. For class I arch, bilateral rests on the mesial marginal ridge of the first premolars are used . For class II arch. The indirect retainer is placed on the marginal ridge of the first premolar on the opposite side of the distal extension base . For long class IV, indirect retainers are placed posterior to the fulcrum line on molars as much posterior as possible.

  6. 2-Canine extension from occlusal rest: A finger extension from, a premolar rest placed on prepared lingual slope of adjacent canine serves as indirect retainer . This method is used when a first premolar must serve as a primary abutment. 3-Canine rest: Cingulum or incisal rests on canine are used as indirect retainer when the mesial marginal ridge of the first premolar is too close to the fulcrum line. This indirect retainer is more effective if the minor connector is placed in the embrasure anterior to the canine.

  7. 4- Cingulum bars (continuous bars) and lingual plates: The indirect retainers in case of cingulum bars and lingual plates are actually the terminal rests in the form of auxiliary occlusal rests or canine rests. 5-Modification areas: In class n modification (1) RPD, the fulcrum line extends between the abutment adjacent to the distal extension base and the most distal abutment on the tooth-supported side. The rest on the anterior abutment on the tooth supported side acts as indirect retainer in addition to its supporting function. 6- Rugae support: The rugae area is firm and well situated to provide indirect retention for the distal extension base . However, the tissue support is less effective than posterior tooth support and rugae cover is undesirable if it can be avoided.

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