22: Repairs and Additions to Removable Partial Dentures

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.

Broken Clasp Arms

The following are several reasons for breakage of clasp arms:

2. Breakage may occur as a result of structural failure of the clasp arm itself. A cast clasp arm that is not properly formed or is subject to careless finishing and polishing eventually will break at its weakest point. This can be prevented by providing the appropriate taper to flexible retentive clasp arms and uniform bulk to all rigid nonretentive clasp arms. Wrought-wire clasp arms may eventually fail because of repeated flexure at the region where it exits from the resin base (Figure 22-1), or at a point at which a nick or constriction occurred as a result of careless use of contouring pliers. They also may break at the point of origin from the casting as a result of excessive manipulation during initial adaptation to the tooth or subsequent readaptation. Clasp breakage can best be prevented by cautioning the patient against removing the removable partial denture by sliding the clasp arm away from the tooth with the fingernails. A wrought-wire clasp arm can normally be adjusted several times over a period of years without failure. It is only when the number of adjustments is excessive that breakage is likely to occur. Wrought-wire clasp arms also may break at the point of origin because of recrystallization of the metal. This can be prevented by proper selection of wrought wire, avoidance of burnout temperatures exceeding 1300°F, and avoidance of excessive casting temperatures when a cast-to method is used. When wrought wire is attached to the framework by soldering, the soldering technique must avoid recrystallization of the wire. For this reason, it is best that soldering be done electrically to prevent the wrought wire from overheating. A low-fusing (1420°F to 1500°F), triple-thick, color-matching gold solder should be used rather than a solder that possesses a higher fusing temperature.

Jan 17, 2015 | Posted by in Prosthodontics | Comments Off on 22: Repairs and Additions to Removable Partial Dentures
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