Color change during the surface preparation stages of metal ceramic alloys

Statement of problem: Even though metal ceramic restorations (MCRs) are widely used by clinicians, the influence of the metal on the color of overlaying porcelain is unknown.

Purpose: The purpose of this study was to analyze the color alterations of different types of metal ceramic alloys during several stages of metal surface preparation and to determine the effect of those changes on the resulting color of opaque porcelain (OP).

Material and methods: Seven different types of alloys (3 base metal, 3 noble, and 1 high noble) were used to prepare disk-shaped specimens (1 mm × 10 mm, n=3), followed by OP application (0.1 mm). L*a*b* values of specimens were recorded after different stages of metal surface preparation (ingot, after casting, after oxidation, and after the OP application) in addition to the shade tab of OP B1 (target shade). L*a*b* values of alloys were measured from the ingot structure to the OP application stage and statistically analyzed (Repeated measures ANOVA, and Bonferroni corrected paired t test, α=.05). L*a*b* values of OP applied groups and the OP shade tab (target shade) were analyzed (1-way ANOVA with Dunnett's multiple comparison test, α=.05). The color differences of the target shade both before and after OP application were calculated and statistically analyzed (1-way ANOVA, Ryan-Einot-Gabriel-Welsch Multiple Range Test, α=.05).

Results: The L* values of all alloys changed significantly after each stage except for 2 alloys (V-Deltaloy SF (N-VDSF)) and (Gnathos Plus (HN-GP)) after casting and airborne-particle abrasion (P<.05). The a* value of all alloys increased after casting. Changes in the a* coordinate were significant except for one of the base metal alloys (P<.05). The a* coordinate changes of alloys showed variation in direction after oxidation and OP application (P<.05). The b* coordinate changes of alloys showed variation in direction after each stage (P<.05). The L*a*b* values of some OP applied alloys were significantly different from that of the OP shade tab (P<.05). Color difference values (ΔE (OP applied alloy-target shade)) of 2 OP-applied alloys (Cerapall 2 (N-CP2) and Ceradelta (N-CD)) were significantly different (P<.05) and higher than the other OP-applied alloys.

Conclusions: The achromatic color behavior of different alloys was all in the same direction at all metal surface preparation stages. The chromatic behavior of the different alloys was primarily towards the same direction after casting and airborne-particle abrasion, whereas it varied after oxidation and OP application. The color difference of OP for all alloys, regardless of their type, was not visually perceivable when compared to the target shade (ΔE<2.6).