22: Repairs and Additions to Removable Partial Dentures

CHAPTER 22 Repairs and Additions to Removable Partial Dentures

Chapter Outline

Broken Clasp Arms
Fractured Occlusal Rests
Distortion or Breakage of Other Components—Major and Minor Connectors
Loss of a Tooth or Teeth Not Involved in Support or Retention of the Restoration
Loss of an Abutment Tooth Necessitating Its Replacement and Making a New Direct Retainer
Other Types of Repairs
Repair by Soldering

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:

1. Breakage may result from repeated flexure into and out of too severe an undercut. If the periodontal support is greater than the fatigue limit of the clasp arm, failure of the metal occurs first. Otherwise the abutment tooth is loosened and eventually is lost because of the persistent strain that is placed on it. Locating clasp arms only where an acceptable minimum of retention exists, as determined by an accurate survey of the master cast, can prevent this type of breakage.
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.
3. Breakage may occur because of careless handling by the patient. Any clasp arm will become distorted or will break if subjected to excessive abuse by the patient. The most common cause of failure of a cast clasp arm is distortion caused by accidental dropping of the removable partial denture. A broken retentive clasp arm, regardless of its type, may be replaced with a wrought-wire retentive arm embedded in a resin base (see Figure 22-1C and D) or attached to a metal base by electric soldering. Often this avoids the necessity of fabricating an entirely new clasp arm.
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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.

Fractured Occlusal Rests

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/>

Related posts:

  1. 19: Work Authorizations for Removable Partial Dentures
  2. 2: Considerations for Managing Partial Tooth Loss: Tooth Replacements From the Patient Perspective
  3. 21: Relining and Rebasing the Removable Partial Denture
  4. 9: Denture Base Considerations
  5. 11: Surveying
  6. Biomechanics of Removable Partial Dentures

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

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