Do repeated firings affect the color properties of porcelain-fused-metal restorations that are fabricated differently?

Abstract

Repeated firings can affect the quality of the porcelain color. The purpose of this study is to evaluate the effect of repeated firings on the color changes of porcelain-fused-metal restorations that are manufactured using different methods. A total of 60 cylindrical shaped cobalt-chromium alloys (O=10 mm and h=1.5 mm) were fabricated using casting (C), milling (M), direct metal laser sintering with and without annealing (EL+, EL-), and selective laser melting with and without annealing (CL+, CL-). The samples were veneered with A2 (as indicated by the Vita Shade Guide) dentin porcelain of 2 mm thickness. Then the samples subjected to the repeated firings (2nd, 4th, 6th, 8th, and 10th), and the color of each sample was recorded using a spectrophotometer. The CIEDE2000 (E-00) formula was used to calculate color differences of the samples on repeated firings. Repeated measures analysis of variance (ANOVA) and post-hoc Tukey's test were utilized to analyze the results (a=05). The L*, a*, and b* values of porcelain-fused-metal specimens were significantly affected by the number of firings (P<0.001) and fabrication techniques (P<0.001). The E-00 values for C, M, CL-, and EL- groups after 10th firing were above 0.8 unit, which indicates that visually perceivable color differences are clinically acceptable. On the other hand, the E-00 values for CL+ and EL+ groups were above the PT value after 8th repeated firings. The color properties of porcelain-fused-metal restorations were affected by the fabrication techniques and the number of firings.