Microhardness of a Resin Cement Polymerized by Light-Emitting Diode and Halogen Lights through Ceramic

Purpose: This study evaluated the curing efficiency of light-emitting diode (LED) and halogen quartz tungsten halogens (QTH)] lights through ceramic by determining the surface microhardness of a highly filled resin cement.
Materials and Methods: Resin cement specimens (Variolink Ultra; with and without catalyst) (5-mm diameter, 1-mm thick) were condensed in a Teflon mold. They were irradiated through a ceramic disc (IPS Empress 2, diameter 5 mm, thickness 2 mm) by high-power light-curing units as follows: (1) QTH for 40 seconds (continuous), (2) LED for 20 seconds, and (3) LED for 40 seconds (5-second ramp mode). The specimens in control groups were cured under a Mylar strip. Vickers microhardness was measured on the top and bottom surfaces by a microhardness tester. Data were analyzed using analysis of variance (ANOVA) and a post hoc Bonferroni test at a significance level of p < 0.05.
Results: The mean microhardness values of the top and bottom surfaces for the dual-cured cement polymerized beneath the ceramic by QTH or LED (40 seconds) were significantly higher than that of light-cured cement ( p < 0.05). The top and bottom surface microhardness of dual-cured cement polymerized beneath the ceramic did not show a statistically significant difference between the LED and QTH for 40 seconds ( p > 0.05).
Conclusions: The efficiency of high-power LED light in polymerization of the resin cement used in this study was comparable to the high-power QTH light only with a longer exposure time. A reduced curing time of 20 seconds with high-power LED light for photopolymerizing the dual-cured resin cement under ceramic restorations with a minimum 2-mm thickness is not recommended.