Comparison of the Microhardness of Two Resin Cements (light cured and dual cured) Following Light-Activation through Porcelain Block Using Two Photo-Curing Units with Two Curing Times

Incomplete polymerization of resin cement leads to a decrease in its physical properties increases its water sorption, solubility and pulpal irritation. Measurement of surface hardness is one of the methods for assessment the degree of polymerization. The aim in this study was to evaluate the effect of two photo-curing units with two curing times on the microhardness of two resin cements. In this labrotory study total numbers of 80 porcelain disks were made. After etching with HF (hydrofluoric acid) and using silane and bonding agent, samples were divided randomly into 8 groups (n=10). Dual-cured and light-cured cements were used in groups 1-4 and 5-8, respectively. In prepared samples from each type of cement, 20 samples were irradiated using QTH (Quartz Tungsten Halogen), (10 samples were cured for 30 seconds; groups 1 and 5 and 10 samples were cured for 60 seconds; groups 2 and 6). The remaining 20 samples were cured using LED (light-emitting diode) in the same manner (groups 3 and 7) and (groups 4 and 8), respectively. Microhardness of the cements was measured. In order to compare the microhardness in study groups, three-factor ANOVA was used. There were statistically significant differences in microhardness mean values depending on the time, the type of cement and the curing unit (P<0.0005). Microhardness of the cements increased with an increase in curing time with two light-curing units. The use of LED resulted in an increased microhardness in two cements. Regardless of the time and the type of the light-curing unit, microhardness of the dual-cured cement was higher than that of the light-cured cement.