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Objective: To assess the effects of ceramic opacity and thickness on delivered radiant exposure and degree of conversion and microhardness of the light-cured resin cement.
Materials and Methods: IPS e-Max ceramic discs (Ivoclar Vivadent) were fabricated in 3 thicknesses (0.5, 1.0, and 1.5mm) and 4 opacities (HT, LT, MO, HO) (n=3/per group). Light-cured resin cement (Variolink Veneer Luting Cement - shade MVO, Ivoclar Vivadent) 50µm thick was cured through these ceramics disks using a quartz tungsten halogen curing light unit (Optilux 501, Kerr) with its radiant exposure measured by MARC from a fixed distance (1.5mm). Knoop microhardness was used to evaluate the bottom degree of cure and was correlated with the radiant exposure deliverd. Descriptive statistics were conducted. One- and two-way ANOVA with post-hoc Tukey's HSD test, Pearson correlation test, the simple linear regression analysis were used for the statistical analyses (alpha=0.05).
Results: Significant interaction was found between ceramic thickness and opacity on radiant exposure (p=0.0078). Subsequent analyses demonstrated that there was a significant simple effect for opacity and for thickness on radiant exposure under different conditions of thickness and opacity. A significant relationship was found between resin cement microhardness and radiant exposure (p=0.0001) below 4.5 J/cm2. Moreover, the Pearson correlation coefficient of 0.93 indicated a strong correlation between the two variables below 4.5 J/cm2 of radiant exposure delivered.
Conclusion: Ceramic opacity and thickness affect the polymerization of light-cured resin cements and need to be considered and compensated for when bonding indirect restorations. Based upon the findings of this preliminary study, the final study is ongoing.