The evaluation of digital color model for layered CAD/CAM crowns

Objectives: The objective of this study was to test the effectiveness of newly developed digital color model for layered CAD/CAM crowns. The hypothesis was that it is possible to achieve more than one color of layered porcelain restoration solely by variation in porcelain thickness. Methods: Two zirconia copings (BioZyram®) shaded according to a new recipe (L*=70.2, a*=9, b*= 35) were veneered with 2 colorgroups: A and B (n=20) of translucent porcelain, developed by CYRTINA®. The porcelain was applied on copings, sintered and milled to a standardized anterior crown shape (CYRTINA®, Oratio B.V., Zwaag NL). The veneer thicknesses of 0.3, 0.5, 0.7 and 0.9 mm (n=5) were combined with different copings thicknesses for total vestibular thickness of 1.5 mm. The CIEL*a*b* coordinates of 40 specimens were obtained with spectrophotometer (MHT SpectroShade). The L*a*b values corresponding to Vita A1, A3, B1 and B3 were considered target colors (TC) and tested layered specimens were color matching specimens (CM). Repeated measures ANOVA was used to analyze the influence of ceramic thickness and independent T-tests were used to establish the correlation between TC and CM. The dE<2.6 was considered a visually perceptible color-match. Results: The L*, a* and b* values of the layered crowns were exponentially affected by the veneer thicknessess independent of ceramic color (p<.01). The color match (dE<2.6) with A3 (TC) could be achieved by veneer (shade A) in thickness of 0.5 mm and color match with A1 (TC) could be achieved by veneer (shade A) in thickness of 0.9 mm. The correlation between CM and TC converged. This implies that more than one TC could be achieved from CM specimens by manipulating thickness of porcelain. Conclusions: The spectrophotometric analysis revealed that it was possible to achieve more than one color match by manipulating only porcelain thickness.