The effect of ceramic thickness and number of firings on the color of ceramic systems: An in vitro study Bulent Uludag, DDS, PhD, a Aslihan Usumez, DDS, PhD, b Volkan Sahin, DDS, PhD, c Kursat Eser, DDS, PhD, d and Ertugrul Ercoban, DDS, PhD e Faculty of Dentistry, Ankara University, Ankara, Turkey; Faculty of Dentistry, Selcuk University, Konya, Turkey; Gulhane Military Medical Academy, Dental Unit, Ankara, Turkey Statement of problem. Although all-ceramic restorations are widely used, there is a lack of information on how color is affected by fabrication procedures. Color matching problems may be encountered in a definitive restoration despite careful shade selection. Purpose. The aim of this study was to evaluate the effect of dentin ceramic thickness and repeated firings on the color of glass-infiltrated aluminum-oxide (In-Ceram) and leucite-reinforced (IPS Empress) all-ceramic systems using a colorimeter. Material and methods. Twenty-one disc-shaped specimens, 10 mm in diameter with a 0.6-mm core thick- ness and 0.5-, 1-, or 1.5-mm dentin ceramic thickness, were made from each of 2 ceramic systems (n=7) . Repeated firings were performed for each group, and the color differences were compared with the color after the initial firing. Color differences among ceramic specimens were measured using a colorimeter (XL-20 Color- imeter), and data were expressed in Commission Internationale d’Eclairage (CIE) LAB system coordinates. Repeated-measures analysis of variance was used to analyze the data (number of firings, ceramic brand, and ceramic thickness) for significant differences. The Tukey honestly significant difference test and paired 2-tailed tests were used to perform multiple comparisons (a=.05). Results. The L*a*b* values of ceramic systems were affected by the number of firings (3, 5, or 7) (P,.01) and ceramic brand (In-ceram or IPS Empress) (P,.01). L* and a* values were affected by ceramic thickness (0.5, 1, or 1.5 mm) (P,.01); however, b* value was not affected by ceramic thickness (P=.075). Significant interactions were present in L*, a*, b* values between number of firings and ceramic brand (P,.01), and between ceramic brand and ceramic thickness (P,.05). Significant interactions were present between number of firings and ceramic thickness (P,.01) in L* and b* values but not in the a* value (P=.379). Conclusion. The analysis revealed that there were substantial changes in L*a*b* color data as the number of firings increased, which resulted in perceptual color changes in L*a*b* color parameters. (J Prosthet Dent 2007;97:25-31.) CLINICAL IMPLICATIONS The results of this in vitro study suggest that dentin ceramic thickness and repeated firings of the all-ceramic materials tested are important factors for the color of definitive restorations and should be considered during shade selection and fabrication. Color matching between ceramic restorations and natural teeth has been a major challenge in dentistry. 1 A dentist is commonly satisfied with the selection of a shade; however, the completed restoration frequently does not match the shade guide, as the esthetic appear- ance of many ceramics is affected by translucency. 2 Clinically, it is important that ceramic restorations re- produce the translucency and color of the natural teeth. 3 There are many components affecting the match, such as translucency, opalescence, fluorescence, surface texture, and shape. 3 Many ceramic systems have layered veneer porcelains for esthetics because the relatively opaque core materials contribute to the overall color of the res- toration. 4 Controlling the ultimate translucency of the core and veneer system is important for achieving the de- sired esthetic result. Translucency is the relative amount of light transmission or diffuse reflectance from a substrate sur- face through a turbid medium. 5 Ceramic translucency can be affected by many factors, including thickness, 6,7 micro- structure, 8 and the number of firing cycles. 9 Dentin constitutes the bulk of a tooth and is largely responsible for its color. 1 The color in a natural tooth a Professor, Department of Prosthodontics, Faculty of Dentistry, Ankara University. b Associate Professor, Department of Prosthodontics, Faculty of Den- tistry, Selcuk University. c Research Fellow, Department of Prosthodontics, Faculty of Den- tistry, Ankara University. d Associate Professor, Department of Prosthodontics, Gulhane Military Medical Academy, Dental Unit. e Private practice, Ankara, Turkey. JANUARY 2007 THE JOURNAL OF PROSTHETIC DENTISTRY 25