The Effect of Irradiation Time and Distance on the Microhardness of Three Commercial Nanohybrid Resin-Based Composites

The properties of resin-based composites as polymeric materials are related to the quality of polymerization. Microhardness measurement is an indirect method to predict this quality. Irradiation time and distance as factors related to light-curing process play important roles in this issue. The purpose of this study was to evaluate the effect of irradiation time and distance on the microhardness values of three different commercial nanohybrid resin-based composites. A total of 180 disk-shaped specimens (60 specimens for each commercial resin-based composite) from three nanohybrid resin-based composites [Grandio (Voco), Simile (Pentron) and Tetric N- Ceram (Ivoclar Vivadent)] in A2 shade were prepared. The specimens were randomly subdivided in 6 subgroups (3 subgroups for evaluating irradiation time: 10 s, 20 s and 40 s, 3 subgroups for irradiation distance: 0 mm, 3 mm and 9 mm) which 10 specimens from each commercial resin-base composite were used for each subgroup. Vickers microhardness test was performed for the top and bottom surfaces of each sample using a microhardness tester under a 200 gr load and a dwell time of 15 s. Three random indentations were taken for each surface and a mean value was calculated. Data were analyzed by two and three way ANOVA and Tukey’s post-hoc test at the 95% significance level. The microhardness distances showed statistically significant differences between the groups on both top and bottom surfaces values for different irradiation times and distances (p value ≤ 0.001).The only exception was Simile group which there was no significant difference for microhardness values between 0 and 3 mm distances. Grandio showed the highest microhardness values among others. Increasing the irradiation time and decreasing the irradiation distance caused to increase the microhardness values. Also, the microhardness of the resin-based composites was affected by the chemical structure of the material.