Factors Influencing the Final Color of Lithium-disilicate Restorations

The aim of the study was to evaluate the effect of different substrate colors, cement colors and thicknesses, different thicknesses and translucency levels of core ceramics, and different thicknesses of veneering ceramics on the final color of a model representing lithium-disilicate restorations.

Method:

A total of 55 cylindrical specimen of Natural Die (11 x 5 mm) (n = 11/5 colors) in ND1, ND3, ND5, ND7 and ND9; 120 disc specimen of IPS e.max Press in 4 thicknesses (0.5, 0.7, 1.0, 1.2 mm) and 3 translucency levels (HT, LT, MO) (n =10/group); and 30 IPS e.max Ceram in 3 thicknesses (0.3, 0.5, 0.8 mm) (n =10/group) were prepared. One ND disc of each color served as a control, while on the other 10 a layer of Variolink II resin cement was applied in 5 colors (transparent, white, white opaque, yellow and brown) and 2 thicknesses (80 or 150 μm). Core discs with and without veneering ceramics were overlapped with the background discs to measure L*a*b* values spectrophotometrically. Color differences ΔE* were calculated and data was statistically analyzed by means of ANOVA (STATISTICA 10.0). 

Result:

A significant influence of substrate color, thickness and translucency level of LiS₂ceramics, color and thickness of cement, and the thickness of veneering ceramics (p < 0,001 respectively) on the color parameters was found. Although the color and thickness of the cement had a statistically significant effect, only the white opaque cement caused clinically significant color shifts. Veneering ceramics had a statistically significant impact on the color parameters of the model which simulated an all-ceramic restoration, whereby, besides increasing lightness, a decrease of the clinical impact of underlying colors (substrate and cement) was noticed. 

Conclusion:

For optimum color-matching results the thickness of the restoration, substrate, and conditionally luting agent color need to be taken into account.