Thermal cycling distortion of metal ceramics: Part I--Metal collar width

The complex three-dimensional geometry of conventional full crown restorations severely complicates the study of thermal cycling distortion in metal ceramic castings. A simplified experimental geometry was developed to (1) maximize the measuring sensitivity, (2) eliminate the casting variables, (3) allow the direct measurement of casting distortion, and (4) evaluate the thermal cycling distortion of a wide range of metal collar widths. It was found that all of the one-walled castings distorted during the initial thermal cycling (oxidation) of the alloy. There was no significant distortion associated with porcelain application or glazing. The castings with an 0.8 mm metal collar had significantly less distortion than those with 0.1 and 0.4 mm collars at 2 of the 10 sites measured (inferior or facial margins).