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.