Statement of problem: Crown fit is a prerequisite for long-term clinical success; however, crown distortion may occur during porcelain firing. The dimensional stability of some high-palladium alloys at high temperatures has been questioned.
Purpose: The purpose of this study was to use a new method to measure the distortion of copings for metal-ceramic single units of selected high-palladium alloys with compositions representative of commercial alloys.
Material and methods: Four high-palladium alloys containing copper and 3 containing no copper were tested. A palladium-silver alloy was included for comparison, and a gold-palladium alloy served as the control. By using reference 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, and after 2 simulated dentin porcelain firings. The margin distortions for the various specimen groups representing combinations of alloys, stages, and measurement diameters were compared with the use of 1-way analysis of variance 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 alloys will not produce clinical problems. Several laboratory techniques are available to counteract the distortions.