Evaluation and Comparison of the Effects of Different Irradiation Patterns and New Suggested Light Exposure Pattern on Microhardness of Composite Resin

Statement of Problem: Overcoming the side effects of polymerization phenomenon has provoked many researches to find out the solution. Since a desirable polymerization of composite resin is effective in success rate of restorations with these materials, and as there is a direct relationship between light intensity and desirable polymerization or curing depth, therefore it is expected that a suitable exposure pattern to produce a desirable curing depth to could overcome the side effects of polymerization phenomenon. The aim of this study was to present a new light exposure pattern for composite curing and evaluation of its effect on microhardness and degree of polymerization of composite in respect to some other light exposure patterns. In an in vitro study, 4 groups of 5 brass cylinders were used and one bulky was filled with Tetric ®Ceram composite. Then samples in the first three groups were exposed 80 seconds to 3 types of Astralis 7® light exposed patterns, including: HIP (High Intensity Program), LOP (Low Intensity Program) and PUL (Pulse Program). The forth group was also exposed same time with SUP (Suggestive Progressive Polymerization) respectively. After sample preparation, they were analyzed with micro hardness tester in 6 different depths and dye penetration test was done for all samples and were evaluated by stereomicroscope. The data were analyzed statistically using One-way ANOVA and Duncan test through SPSS software. In absence of depth factor consideration, the mean micro hardness in all four groups of exposure patterns had no significant difference (p=0.362). The HIP, LOP, PUL, SUP light exposure patterns produced significantly different micro hardness in 0-5 mm depth significantly (p=0.001). In other words there was a significant difference in micro hardness in different depths in each testing group. In the same depths, there was no significant difference in composite microhardness between the 4 groups up to 4 mm depth, but at the depth of 5 mm in HIP group, micro hardness was significantly higher than the depth of 5 mm in the other group. The analyzes clarified that the suggestive light exposure pattern (sup) can control and guide the rate of polymerization along with having the same quality to the other light exposure patters in producing hardness up to the depth of 4 mm of composite restorations.