CHAPTER 22 Repairs and Additions to Removable Partial Dentures
The need for repairing or adding to a removable partial denture will occasionally arise. However, the frequency of this occurrence should be held to a minimum by careful diagnosis, intelligent treatment planning, adequate mouth preparations, and the carrying out of an effective removable partial denture design with proper fabrication of all component parts. Any need for repairs or additions will then be the result of unforeseen complications that arise in abutment or other teeth in the arch, breakage or distortion of the denture through accident, or careless handling by the patient, rather than faulty design or fabrication.
It is important that the patient is instructed in proper placement and removal of the prosthesis so that undue strain is not placed on clasp arms, on other parts of the denture, or on contacted abutment teeth. The patient also should be advised that care must be given to the prosthesis when it is out of the mouth, and that any distortion may be irreparable. It should be made clear that there can be no guarantee against breakage or distortion from causes other than obvious structural defects.
Figure 22-1 Fractured direct retainer on canine abutment. The reason for breakage is likely the long-term repeated flexure from movement associated with this 8-year-old distal extension prosthesis. The denture must be evaluated for prospective serviceability if the retainer arm is repaired. Often, the patient will best be served by replacing the denture with a new restoration. A, The cast produced from an irreversible hydrocolloid pick-up impression. The height of contour is shown in pencil, with a red line illustrating to the laboratory the location of repair wire (18-gauge). B, Clasp adapted to the designated line on the canine and fitted into the resin trough distal to the canine and palatal to the first and second premolars. Note the curvature placed at the end of the wire to prevent movement within the polymerized resin. C, Finished and polished wire repair from the buccal. D, Palatal view.
Breakage of an occlusal rest almost always occurs where it crosses the marginal ridge. Improperly prepared occlusal rest seats are the usual cause of such weakness: an occlusal rest that crosses a marginal ridge that was not lowered sufficiently during mouth preparations may be made too thin or may be thinned by adjustment in the mouth to prevent occlusal interference. Failure of an occlusal rest rarely results from a structural defect in the/>