Hardening Of Light-polymerized Resin Cements Through Lithium Disilicate Glass-ceramic Veneers

Objectives: The aim of this study was to evaluate the effect of ceramic veneer type and thickness on light attenuation and on microhardness of light-polymerized resin cements.

Methods: Three types of ceramic blocks were used (IPS E.max CAD, Ivoclar-Vivadent; Celtra-Duo, Dentsply; VITABLOCS Esthetic-Line, Vident). Shades A2 & B1 were selected. Specimens measuring 0.5, 1.0 and 1.5 mm were cut from these blocks. Two light-polymerizations units were used (Deep-cure 3M/ESPE; Blue-phase Ivoclar-Vivadent). Light irradiance through the specimens was measured with MARC-Patient Simulator (Blue light Analytics). Two resin cements were polymerized through the specimens (Rely-X Veneer-3M/ESPE; Variolink-Esthetic-Ivoclar-Vivadent) using two-time intervals (10 & 20 sec). Micro-hardness of cements specimens was measured using microhardness tester with Knoop indenter. Data were statistically-analyzed using one-way and factorial ANOVA.
Results: Ceramic type and thickness had statistically-significant effects on light attenuation (p<.05). Specifically, IPS e.max CAD had significantly-lower light attenuation at 0.5mm compared to the other 2 ceramics. However, at 1.0 and 1.5mm, Celtra-Duo had significantly-higher light attenuation compared to the other ceramics.
Mean microardness of Rely-X Veneer cement was significantly higher than that of Variolink Esthetic cement. Deep-cure resulted in higher mean microhardness values compared to Blue-phase at 0.5 and 1.0mm specimen thickness, but not at 1.5mm. Moreover, a direct correlation was found between polymerization time and mean microhardness for both resin cements.
Conclusions: Increased veneer thickness negatively affected light irradiance in a significant manner. Light attenuation resulted in a significant decrease in mean surface microhardness for the two resin cements. Increasing light polymerization time increased mean microhardness values for both cements.