Path Of Withdrawal

Careful planning is required when selecting the path of withdrawal of tooth preparations for RPD retainers. Although conventional crowns generally have a path in the long axis of the tooth, RPD retainers may not. Surfaces where both guide planes and reciprocal planes are planned, as well as areas that require survey lines in the gingival third, typically need to be "overprepared" relative to the ideal conservative technique used on individual teeth. Because of the lingual inclination of mandibular molars, reducing them slightly more in the occlusal two thirds of the lingual axial surface is often necessary.

Selected Pressure Impression For Rpd

Fig. 21-18. A and B, A patient with extensively damaged teeth requiring a combination of fixed and removable prostheses. C and D, The teeth prepared for fixed retainers. E and F, Working casts. G and H, Fixed retainers at try-in. I, The impression for an RPD. J to L, Castings, framework, and the completed denture on altered master cast. The tissue surfaces have been modified with a wash impression. Continued

Fig. 21-18. A and B, A patient with extensively damaged teeth requiring a combination of fixed and removable prostheses. C and D, The teeth prepared for fixed retainers. E and F, Working casts. G and H, Fixed retainers at try-in. I, The impression for an RPD. J to L, Castings, framework, and the completed denture on altered master cast. The tissue surfaces have been modified with a wash impression. Continued

Similarly, the axial reduction of surfaces adjacent to an edentulous ridge often involves removal of additional tooth structure. Care must be taken that these modifications do not lessen the retention form excessively, because during denture removal the retainers are usually subjected to forces parallel to their path of withdrawal, and retention becomes even more important. Frequently the use of additional features (e.g., grooves, boxes, pinholes) is needed. It is certainly not mandatory that all retainers for an RPD have identical paths of withdrawal.

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