The effect of repeated firings on the color of feldspathic ceramics

The aim of this study was to determine the extent to which repeated firings would change the color of feldspathic ceramics. Specimens were fabricated from five commercially available feldspathic ceramics using a circular stainless steel matrix 11 mm in diameter and 1.0 mm thick (n = 10, shade = A3). Repeated firings were performed and color analysis was completed with a colorimeter using the CIELA B color coordinates. Two-way ANOVA was used to analyze the data, followed by Tukey's post-hoc test (a = 0.05). Three factors were used as determinants: a, a measure of the chroma along the red-green axis; b, a measure of the chroma along the yellow-blue axis; and L, a measure of the lightness-darkness of the specimen on a scale from 0 (black) to 100 (white). The results indicated that a and b values increased and L values decreased after repeated firings, resulting in reddish, yellowish, and darker specimens, respectively (P = 0.001). As the number of firings increased, significant color alterations occurred in the color parameters of the specimens. These alterations resulted in color changes (delta E) that could be considered unacceptable in clinical practice.