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 remedy this by altering the design of the metal frameworks for such restorations may lead to unacceptable decreases in fracture resistance. Purpose. This study evaluated a new metal framework design for metal-ceramic restorations. Material and methods. Twenty artificial crowns were fabricated with various degrees of facial metal reduction; 0, 1, 2, and 3 mm. The study was conducted in two parts. The first part evaluated changes in light transmission into adjacent root tissue. A light box was fabricated so sample crowns could be illuminated on a mounted natural tooth. The root of the tooth remained outside the light box, and the light transmitted through the crowns into root tissue was measured with a light meter. The second part of the study evaluated changes in fracture strength. The sample crowns were subjected to a vertical load until fracture with use of an Instron machine at a crosshead speed of 1 mm per minute. The load at fracture was recorded. Results. Results indicated a statistically significant increase in light transmission with 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 reduction of the metal framework may be indicated for anterior metal-ceramic restorations. (J Prosthet Dent 1997;78:295-301.).