REPAIR OF FIXED PROSTHESIS

REPAIR OF FIXED PROSTHESIS. DR. REWAA ABOU EL-HASSAN Lecturer of Fixed Prosthodontics Conservative Department.

Repair of fixed prosthesis. Seriousness of the problem 1. 2. 3. Leave it alone if not causing any serious harm Adjusting or repairing the fault Replace the crown or bridge.

Repairing the restoration inside the patient’s mouth to: Change the acrylic facing color. Restore chipped ceramic portion. Restore a perforation in the occlusal table either precious or non precious..

Repairing the restoration outside the patient’s mouth to: Correct over or undercontoured pontic . Correct overextended margin. Repair fractured solder joint. Repair perforated restoration with solder alloy..

Remaking the restoration: The need to change the bridge design . Losseness of the abutments . Fractured ceramic core . Cervical decay related to the crown margins ..

I. Biological Failure:. Occlusal Problems: Interfering centric or eccentric occlusal contact ,if detected early, the interferences can be eliminated by occlusal adjustments without permanent damage. In patients with bruxism night guards or occlusal splints may be given. Neuromuscular discomfort related to improper occlusion can be treated by selective reshaping of defective contacts to accommodate occlusal forces ..

II. Mechanical Failure:. 1. Loss of Retention: If the restoration dislodged from the prepared teeth without damage and no caries, it is possible to recement the prosthesis. Improper cementation procedures, such as contamination with moisture or increased cement space may be the problem. If the prosthesis reveals loss of adequate retention, teeth should be modified to improve the retention and resistance form. In case of grossly destructed teeth, core build up to support the retainer and a new prosthesis is fabricated ..

2. Connector Failure/ Solder Joint Failure: Join multiple unit bridges by solder joint in the middle of pontics before porcelain is added..

3. Occlusal Wear and Perforation: If perforation is detected early, a gold or amalgam restoration can be placed. Other materials – resin, composite and GIC. If metal surrounding perforation is extremely thin a new prosthesis should be fabricated. If occlusal surfaces are covered with porcelain, wear of ceramic is not a problem, instead the opposing natural teeth shows dramatic wear of enamel. This problem is exacerbated by heavy chewing forces..

The same occurs when porcelain opposes metallic restoration. So, in mouths in which occlusal wear is anticipated, it is better to place metal over occluding surfaces to minimize wear and maintain the integrity of natural teeth..

4-Porcelain Fracture: Porcelain fracture occur with both metal ceramic and all ceramic crown restoration. The majority of PFM fracture can be attributed to improper design characteristics of the metal framework or to problem related to occlusion. All ceramic restorations commonly fail because of deficiencies in tooth preparation or presence of heavy occlusal forces..

Fractured porcelain veneer: Usually it is related to faults in framework design, improper laboratory procedures, excessive occlusal function, or trauma. To save the patient additional discomfort, time and expense, an attempt to repair rather than a remake may be adjusted..

Methods of intraoral repair: 1. The bonding of the fractured part of porcelain with a composite resin to the remaining fractured porcelain restoration: If the fractured piece fits perfectly, this means the repair can be made by this way. HF gel was applied for 5 minutes, cleaned, and dried. The two prepared surfaces were luted with dual-cure composite resin.

2 . Direct intra-oral repair of the fractured restoration by composite resin: The porcelain surface adjacent to the fracture site is beveled with a coarse diamond bur, removal of surface glaze is Essential thus it create a poor bond The metal is prepared with deep retentive grooves and undercuts to provide mechanical retention for the composite resin to the metal surface . The porcelain surface is again treated with a silane bonding agent, which alters the porcelain surface so that chemical and physical bonding are possible..

Unfilled resin is applied both to the metal and porcelain surfaces and is cured. A composite resin metal opaquer is applied in a thin layer so that as little grey as possible can be seen from the underlying metal. Appropriate shade-filled resins are then contoured to restore the missing porcelain. The occlusion is adjusted to achieve contacts and eliminate occlusal interferences. The restoration is polished using routine methods..

Drawback is lack of longevity and discolouration . Retention of these materials is mainly due to mechanical interlocking so if used in areas of heavy occlusal forces repair often fails shortly after insertion. If fracture is due to heavy occlusal forces the contact should be avoided at the metal ceramic junction, and it should be at least 1.5mm away from the junction..

3. Indirect repair of the fractured restoration by an overcasting veneered with porcelain: Another approach is the placement of an indirectly-prepared overcasting veneered with porcelain. The procedure involves preparation of the fractured restoration with a diamond point to remove the remaining porcelain and develop resistance and retention form . Develop a box-type preparation 2 to 3 mm in deep with paralel vertical walls at the centre of the reduced occlusal surface. Provide a border of at least 1.5 mm of metal surrounding and the occlusal preparation to avoid distortion of the restoration during function. Make an impression of the preparation with an elastomeric impression material and articulate the die poured with a cast of the opposing dentition..

Invest and cast a 0.2 mm-to-0.3-mm-thick coping and apply the porcelain veneering. Glaze the porcelain veneer, polish the metal of the casting, and lute the restoration with the resin- based cement, using rubberdam isolations. The occlusal cavity preparation is critical for retaining the overcasting . The cavity preparation must have sufficient depth for adequate resistance and retention form. The desired form is more easily accomplished with endodontically -treated teeth or pontics without concerns for pulpal exposure.

4- The repair of the fractured restoration by indirect prepared porcelain veneer This more complex method has some risks during the repair preparation, such as metal perforation, distortion of the framework, weakening of the connections, and problems of overcontouring . This method has been best applied to fractured pontics In this method, make an elastomeric impression of the prepared area and then pour a refractory material into the impression to form a refractory die. Mark the outline of the fracture area with a pencil..

The ideal contour of the veneer repair restoration is fabricated on the die following the steps recommended for the porcelain system. The teeth and preparation are isolated with rubberdam ; the repaired porcelain is placed on the prepared surface of the fractured restoration. Both surfaces are etched with HF gel, rinsed, and dried. The two prepared surfaces are luted with dual-cure composite resin ..

Failure of solder joint 1- Remove the cemented prosthesis. 2- Clean both the abutment and the prosthesis from the adhesive cement. 3- The prothesis is replaced over the abutments and checked for proper seating. 4-A plaster impression is made with the prosthesis in place and the resoldering process is completed..

5-Marginal Deficiencies: A-Positive ledge (overhang):- It is an excess of crown material protruding beyond the margin of preparation. These are more common with porcelain than any other margins. Correct them without disturbing the restoration by grinding and polishing in situ..

B- Negative ledges:- This is a deficiency of crown material that leaves the margin of the preparation exposed but with no major gaps between the crown and the tooth. It is sometimes possible to adjust the tooth surface of the crown by pointed stone or bur..

C-Over extending margin Overextended margin of the restoration leads to gingival irritation, thus restoration should be removed, impression is made and a new cast is obtained, the restoration is adjusted in the new cast and recemented ..

Grinding and polishing in situ Porcelain margins: Heatless stone Diamond st point Followed by various composite finishing burs and discs Metal margins with positive ledges: Green stone. Tungsten carbide stones. Metal and linen strips.

III) Esthetic Failure:. Main reason reported by dental laboratories is poor colour match. The marginal fit or cervical form of a prosthesis can promote plaque accumulation, causing gingival inflammation, which produces an unnatural soft tissue colour or form that is esthetically unacceptable. Remake of the prosthesis is the only option..

Thank you.