Microhardness of different thicknesses of resin composite polymerized by conventional photocuring at different...

This in vitro study sought to evaluate the influence of photocuring modes and polymerization time on the microhardness of a hybrid composite resin. Sixty composite resin specimens were prepared at random and divided into 12 experimental groups (n=5), consisting of four curing tip distances (2.0 mm, 4.0 mm, 6.0 mm, and 8.0 mm) and three sample thicknesses (0.5 mm, 1.0 mm, and 2.0 mm). All samples were polymerized with a continuous output at 550 mW/cm2. After 24 hours, Knoop microhardness measurements were obtained on top and bottom surfaces of the sample, with a load of 25 g for 10 seconds. Five indentations were made on each surface of each sample. Subdivided parcels ANOVA test and Tukey test were performed (p = 0.05). There were no statistical differences among the experimental groups for the top surface. On the bottom surface, 0.5 mm and 1.0 mm sample thicknesses showed significantly higher hardness means for all photocuring tip distances when compared with the 2.0 mm sample thickness. In terms of the photocuring tip distance, the 2.0 mm and 4.0 mm distances showed significantly higher hardness means for all sample thicknesses when compared with the 8.0 mm distance. For all experimental conditions, the top surface showed higher hardness than the bottom surface. It was concluded that the resin composite increments should be decreased to improve the polymerization of the resin composite bottom surface in deep cavities.