Effect of Ceramic Thickness and Dentine on Color of CAD-CAM

Objective: Appearance of CAD-CAM restoration could be optimized by controlling ceramic thickness and background color.  This study evaluated the effect of ceramic thickness and dentine backing on optical parameters of CAD-CAM ceramic restoration.

Methods: Ceramic discs (Ø  8 mm) of 0.7, 1.0, 1.3, 1.6, 1.8, and 2.0 mm thickness were prepared from Empress CAD blocks shade A1, A2, A3, and A3.5 (15 discs / group).  Dentine discs (Ø 8 mm and 2 mm thickness) in light yellowish-brown (DLyb) and dark yellowish-brown (DDyb) shades were prepared from human extracted maxillary central incisors. The CIE color parameters of ceramic with dentine backing were measured upon white background using spectrophotometer (ColorQuest-XE) with D65 illuminant and 10 degree observer.  The L*, a*, b*, DE* and K/S values were statistically analyzed using ANOVA, Tamhane multiple comparison and regression analysis.

Results: Ceramic color was significantly altered due to ceramic thickness, dentine background and their interactions (P < 0.05).  Increasing ceramic thickness resulted in significant increasing   DE* and K/S values.  Combination of dentine to ceramic demonstrated significantly higher DE* and K/S values, but significantly lower   L* values.  High correlation (R²) between ceramic thickness and L*, DE* and K/S (shown in table), but low correlation with a* and b* were revealed.

Ceramic / Dentine	L*	DE*	K/S
A1 / DLyb	0.9600	0.9527	0.9706
A2 / DLyb	0.9623	0.9556	0.9777
A3 / DLyb	0.9512	0.9648	0.9783
A3.5 / DLyb	0.9500	0.9401	0.9679
A1 / DDyb	0.9823	0.9595	0.9465
A2 / DDyb	0.9694	0.9513	0.9655
A3 / DDyb	0.9650	0.9634	0.9737
A3.5 / DDyb	0.9648	0.9661	0.9756

Conclusion: Color of ceramic was influenced by ceramic thickness and dentine background.  Thicker ceramic combined with darker dentine backing resulted in increasing DE* and K/S, but decreasing L* values.  These values were highly correlation with ceramic thickness which were benefit for color prediction.