Spectrophotometric Analysis of the Influence of Metal Alloy Choice, Opaque Thickness, and Repeated Firing on the Shade of Metal Ceramic Restorations.

Abstract

To determine the effect of type of base metal alloy, opaque thickness, and repeated firing on color of metal ceramic restorations. Four nickel chromium and four cobalt chromium were selected with one noble alloy as a control. Ten discs (16 mm 0.5 mm) were prepared for each group. Color of specimens were measured using a spectrophotometer and were calculated using CIEDE2000 formula (ΔL', ΔC', ΔH', ΔE') between experimental groups and control at six stages of porcelain constructions: opaque 0.1 and 0.3 mm, dentine, enamel, glaze, and three times repeated firing. Shade A3 was used. One-way analysis of variance and Bonferroni multiple test were performed (α = 0.05). Alloy type and stage showed statistical significance on total color and color parameter differences from the control and there was significant interaction between them (p < .05). Nidour alloy was the closest to control. Increase in ΔC' and a decrease in ΔH' and in a* and b* was the commonest in comparison with the control. However, ΔE' was below acceptability threshold for all alloys at all stages. Despite the statistical significance, base metal alloys performed as good as noble metal control. Neither opaque thickness, nor repeated firing affected color variations from the control group. There was no obvious trend in the behavior of metal alloys at all stages. However, increase in chroma and a decrease in hue, with green blue shift, was the most common. Records of the effects of eight commonly used base metal alloys on the color of final shade of the metal-ceramic restorations, at various stages of ceramic buildup, have considerable value. (J Esthet Restor Dent 28:S56-S67, 2016).