Effect of Preheating on Micro-hardness of different Composite Resins

Abstract

The aim of this study was to assess the effect of preheating on the surface microhardness of different commercially available composite resins .Materials and Methods: Tubes of the composite resins were either kept at room temperature (24 ±1 0 C) or preheated for 40 min in a commercially preheating device to 40 0 C, 50 0 C and 60 0 C, respectively. From composite resin tubes, a total of 120 disk-shaped specimens (40 specimens of each composite resin, 10 disks from each temperature setting) were prepared by inserting uncured preheated composite resin into cylindrical nylon moulds (5 mm diameter × 2 mm height); before light polymerized for 40s with a lightemitting diode curing unit. The Vicker's microhardness number (VHN) of each specimen was measured. Two-way ANOVA and Tukey test were used to analyze the collected data at a significance level of 0.05. Results:In comparison to the room temperature, there was a significant increase in the mean VHNs of each composite resin by preheating to 40 0 C, 50 0 C and 60 0 C, respectively (p<0.05). For G-aenial posterior, Filtek Z350XT and Tetric-N-Ceram, at room temperature, the mean VHNs were 51± 4.3, 60.6± 3.7 and 76.6±1.4, respectively with significant difference between G-aenial posterior and Tetric-N-Ceram (p<0.05), while at 40 0 C, the mean VHNs were 65.7±2.5, 86.8±2.3 and 88.4±1.8, respectively with significant differences (p<0.05) between G-aenial posterior and the other two composites. At 50 0 C, the mean VHNs were 109.4±0.9, 104.4±3.4 and 114±0.71, respectively with no significant difference between composite resins. At 60 0 C, the mean VHNs were 122±3.2, 129±3.4 and 136±2, respectively with significant difference between G-aenial posterior and Tetric-N-Ceram (p<0.05). Conclusions:Preheating significantly increased the surface microhardness of all tested composite resins with the highest value observed for Tetric N-Ceram at 60 0 C preheating temperature.