8: Indirect Retainers

CHAPTER 8 Indirect Retainers

Role of Indirect Retainers in Control of Prosthesis Movement

As was described in Chapter 4, partial denture movement can exist in three planes. Tooth-supported partial dentures effectively use teeth to control movement away from the tissues. Tooth-tissue–supported partial dentures do not have this capability because one end of the prosthesis is free to move away from the tissue. This may occur because of the effects of gravity in the maxillary arch or adhesive foods in either arch. Attention to the details of design and location of partial denture component parts in control of functional movement is the strategy used in partial denture design.

When the distal extension denture base is dislodged from its basal seat, it tends to rotate around the fulcrum lines. Theoretically, this movement away from the tissues can be resisted by activation of the direct retainer, the stabilizing components of the clasp assembly, and the rigid components of the partial denture framework, which are located on definite rests on the opposite side of the fulcrum line away from the distal extension base. These components are referred to as indirect retainers (Figures 8-1 and 8-2). Indirect retainer components should be placed as far as possible from the distal extension base, which provides the best leverage advantage against dislodgment (Figure 8-3).

For the sake of clarity in discussion of the location and functions of indirect retainers, fulcrum lines should be considered the axis about which the denture will rotate when the bases move away from the residual ridge.

An indirect retainer consists of one or more rests and the supporting minor connectors (Figures 8-4 and 8-5). The proximal plates, adjacent to the edentulous areas, also provide indirect retention. Although it is customary to identify the entire assembly as the indirect retainer, it should be remembered that the rest is actually the indirect retainer united to the major connector by a minor connector. This is noted to avoid interpretation of any contact with tooth inclines as part of the indirect retainer. An indirect retainer should be placed as far from the distal extension base as possible in a prepared rest seat on a tooth capable of supporting its function.

Although the most effective location of an indirect retainer is commonly in the vicinity of an incisor tooth, that tooth may not be strong enough to support an indirect retainer and may have steep inclines that cannot be fav/>

Jan 17, 2015 | Posted by in Prosthodontics | Comments Off on 8: Indirect Retainers
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