Evaluation of high-temperature distortion of high-palladium metal-ceramic crowns

Statement of problem. Crown fit is a prerequisite for long-term clinical su ccess; however, crown distortion may occur during porcelain firing. The dim ensional stability of some high-palladium alloys at high temperatures has b een questioned. Purpose. The purpose of this study was to use a new method to measure the d istortion of copings for metal-ceramic single units of selected high-pallad ium alloys with compositions representative of commercial alloys. Material and methods. Four high-palladium alloys containing copper and 3 co ntaining no copper were tested. A palladium-silver alloy was included for c omparison, and a gold-palladium alloy served as the control. By using refer ence points scribed on the margin, the mesiodistal and buccolingual margin diameters of identical copings were measured with a traveling microscope at 4 stages: as-cast, oxidized, after 2 simulated opaque porcelain firings, a nd after 2 simulated dentin porcelain firings. The margin distortions for t he various specimen groups representing combinations of alloys, stages, and measurement diameters were compared with the use of 1-way analysis of vari ance and a multiple range test. Results. Most of the high-palladium alloys had high-temperature distortions that were not significantly different from those of the control alloy. The distortions occurred principally during the oxidation cycle. The effect of mesiodistal groove reinforcement on preventing distortion was not the same for all alloys. Conclusion. The results suggest that small observed distortions of these al loys will not produce clinical problems. Several laboratory techniques are available to counteract the distortions.