Layered color of all-ceramic core and veneer ceramics

Statement of problem Color of an all-ceramic restoration is the result of interaction between core and veneer ceramics. However, the influence on color of the different types of all-ceramic core and veneer combinations at clinically relevant thicknesses is not well understood. Purpose The purpose of this study was to measure the layered color of all-ceramic core and veneer combinations with the thickness of the core set as the clinically minimum thickness to mask the background, and the thickness of the veneer set as the remaining available thickness within a clinically allowable thickness. Material and methods The A2-corresponding shade of 7 all-ceramic core materials, and 1 sintering ceramic and 1 alloy core as references, were prepared in clinically minimum thicknesses (0.4 to 0.8 mm) to mask the background (n=7). The A2 and A3 corresponding shades of each recommended veneer ceramic were used to fabricate specimens that were 1.5 mm thick. The color of the core, veneer, and layered specimens was measured with a reflection spectrophotometer. Two-way ANOVA with the independent variables of the types of core and veneer ceramics on the layered color was used to analyze the data (α=.05). The influence of the color coordinates in the core and veneering ceramics on the layered color was analyzed with multiple regression analysis. Results CIE L*, a*, b*, and C*ab values of A2- or A3-veneer layered specimens were influenced significantly by the combination of core and veneer ceramics (P<.001). The CIE L* values of layered specimens were primarily influenced by the CIE L* values of the core ceramic (P<.001). The other 3 parameters were primarily influenced by each corresponding parameter of veneer ceramic, based on multiple regression analyses (P<.001). Conclusion The layered color of all-ceramic core and veneer ceramics in the clinically allowable thickness was different even when the same shade, keyed to a VITA guide, of core and veneer ceramics were layered. The color difference between each pair of A2- or A3-veneered specimens by the combination of core and veneer ceramics ranged from 1.4 to 5.6 ΔE*ab units