Abstract:
This study evaluated the final optical quality of lithium disilicate glass-ceramic veneers on a darkened substrate, using or not an opaque composite resin as an intermediate layer. Four experimental groups (n=4) were determined according to the thickness of the ceramic discs - 0.5 mm, 0.8 mm, 0.9 mm and 1.2 mm (shade A1 LT) in order to mask the darkened substrate (shade C4, composite resin). In the groups with thicknesses 0.5 mm and 0.9 mm, an opaque resin (OP) in the thickness of 0.3 mm was used as an intermediate between the ceramic and the substrate. In the control group, A1 HT ceramics were used on A1 resin composite substrate. All specimens were cemented with translucent resin cement. After cementation, the CIE L* a* b* color parameters were analyzed using the Easy Shade (Vita) spectrophotometer. The results were submitted to analysis of variance (ANOVA) and Tukey's test (α=0,05). The higher ceramic thicknesses (0.9 and 1.2 mm) and the group with OP + 0.5 mm ceramic were more efficient in masking the darkened resin composite substrate, since they presented values of luminosity statistically similar to the control group (p>0.05). The use of an intermediate opaque resin contributed to increase the values of a * in relation to the control group (p <0.05), which may mean brown hue masking.
The use of OP resin between the substrate and the ceramic showed efficiency in masking the darkened substrate and also in reducing the need for dental removal since the thickness of 0.5 mm of ceramic was sufficient to reach values of L* similar to control.
