AN INVESTIGATION OF NEW METAL FRAMEWORK DESIGN FOR METAL-CERAMIC RESTORATIONS

Statement of problem. Metal ceramic restorations have been implicated in the discoloration of associated gingival tissues. Attempts to remed y this by altering the design of the metal frameworks for such restora tions may lead to unacceptable decreases in fracture resistance. Purpo se. This study evaluated a new metal framework design for metal-cerami c restorations. Material and methods. Twenty artificial crowns were fa bricated with various degrees of facial metal reduction; 0, 1, 2, and 3 mm. The study was conducted in two parts. The first part evaluated c hanges in light transmission into adjacent root tissue. A light box wa s fabricated so sample crowns could be illuminated on a mounted natura l tooth. The root of the tooth remained outside the light box, and the light transmitted through the crowns into root tissue was measured wi th a light meter. The second part of the study evaluated changes in fr acture strength. The sample crowns were subjected to a vertical load u ntil fracture with use of an Instron machine at a crosshead speed of 1 mm per minute. The load at fracture was recorded. Results. Results in dicated a statistically significant increase in light transmission wit h 1 mm framework reduction or greater, and fracture strengths did not decrease with up to 1 mm of framework reduction. A 1 mm facial axial r eduction of the metal framework map be indicated for anterior metal-ce ramic restorations.