Degree of Conversion and Microhardness of Resin Cements Beneath Glass-ceramic

Objectives: This study evaluated glass-ceramic shade, thickness and translucency effects on degree of conversion and microhardness of different resin cements photoactivated using halogen lamp or light emitting diode.
Methods: The factors thickness (2, 3, 4mm), shade (A2, A3, A3.5) and translucency (high-HT or low-LT) of a lithium disilicate glass-ceramic, light sources (HAL and LED) and four resin cements (dual-cured RelyX ARC and RelyX U200; light-cured RelyX Veneer and self-cured C&B cement) were studied. The degree of conversion (DC) by FT-Raman spectroscopy and Knoop microhardness (KHN) of resin cements (n=3) were measured without barrier or interposing ceramic specimens. Photoactivation was performed for 30 seconds (1350mW/cm² for LED Bluephase; 950mW/cm² for HAL Demetron). DC and KHN of dual-cured cements without photoactivation were compared to C&B cement (n=3). Data analysis (α=5%) were performed by ANOVA and Tuckey for DC; Kruskal-Wallis, Dunntest and Bonferroni correction for KHN.
Results: There was effect of ceramic shade, translucency and thickness on DC of RelyX ARC, U200 and Veneer (p<0.0017). Light source had no effect (p=0.9512) . Higher DC values were observed for self-cured and light-cured, followed by dual cements. Without photoactivation, dual cements showed the lowest DC. For KHN, there was no significance for shade (p=0.1717) and light source (p=0.1421), but there was effect of ceramic translucency and thickness, and type of resin cement (p=0.0001). KHN were higher for U200, followed by ARC, with lowest values for Veneer.
Conclusions: High translucency ceramics were associated with higher KHN of the underlying cement compared to low translucency ceramics. Degree of conversion was affected by ceramic shade, translucency and thickness. KHN was dependent of ceramic translucency, followed by thickness. Although HAL produced 30% less energy density, there was no difference between light sources concerning KHN or DC. Best DC and KHN were achieved with dual-cured cements photoactivated under 2 or 3mm-thick.