ABSTRACT
These in vitro studies evaluated the marginal distortion of ceramo-metal restoration under the effect of marginal metal thickness and type of ceramo metal alloy. Two types of ceramo metal alloys; nickel chromium alloy [Wiron 77], and cobalt chromium alloy [Remanium CSE], and one type of dental porcelain [Ceramco II] were used in this study. A master model consisted of three stainless steal master dies fixed on a master base were fabricated. The dies were prepared with shoulder finish line with three different depths [0.5mm, 0.8mm and 1.0mm]. Thirty wax patterns were divided into three groups [10 each] according to finish line depth, and each group subdivided into two subgroup [5 each] according two type of alloy. Porcelain was built up and fired according to the manufacture's instructions. Marginal discrepancy between the cast and the die was measured under stereomicroscope with 16X magnification at four points following each firing stage of porcelain [degassing, opaque, body porcelain and glaze] firing cycle. The results revealed that, both types of alloys revealed no significant differences although the nickel chromium alloy had been shown lower marginal distortion than cobalt chromium alloy. Thinning of metal margin is preferred where there was no significant difference between different finish line depths tested. Porcelain firing had significant effect on marginal distortion, specially in degassing stage