Optical Properties of CAD-CAM Ceramic as a Function of Thickness

Objective: CAD-CAM ceramic restorations offer superior translusency to be used where esthetics are paramount. The esthetic success of ceramic restorations depends on good color determination of ceramic restorative material, cement, and dentine which directly relate to their optical properties. This study determines the effect of CAD-CAM ceramic thickness on their optical parameters.

Methods: Four hundred and twenty ceramic discs (10 mm in diameter) at different thickness of 0.7, 1.0, 1.3, 1.6, 1.8, 2.0 and 15.0 mm  were prepared from Empress CAD^Ò ceramic blocks shade A1, A2, A3, and A3.5 (15 discs for each group).   The ceramic discs were polished with 1mm diamond abrasive in Ecomet^Ò3.   The color parameters of specimen were determined in the CIE color system using a spectrophotometer (ColorQuest^ÒXE) with D65 illuminant and 10 degree observer.  The L*, a*, b*, DE, C*, H*, and K/S parameters were evaluated and statistically analyzed using ANOVA and Tukey multiple comparison test.  

Results: Changing in ceramic thickness resulted in alteration of color parameters (P ≤ 0.05) in each shade.  As the ceramic thickness increased, significant increasing in DE and K/S but significant reduction in L* values were demonstrated (P ≤ 0.05).  Regression analysis was performed to calculate the strength of correlation coefficients (R²) between ceramic thickness and each color parameter for each shade as shown in the table.  High correlation coefficient demonstrated with L*, DE *, and K/S values.

Shade	L*	a*	b*	DE	C*	H*	K/S
A1	0.962	0.073	0.513	0.960	0.505	0.398	0.960
A2	0.971	0.426	0.077	0.967	0.084	0.228	0.961
A3	0.960	0.816	0.523	0.949	0.053	0.839	0.963
A3.5	0.972	0.849	0.091	0.963	0.095	0.848	0.970

Conclusion: The optical parameter values of the CAD-CAM ceramic restorative material were affected by thickness. There were highly correlation between the thickness of ceramic and the L*, DE *, and K/S values which will be benefit for color prediction of restoration.