Evaluation of curing light distance on resin composite microhardness and polymerization

This study evaluated the influence of the curing tip distance on cure depth of a resin composite by measuring Vickers microhardness and determining the degree of conversion by using FT-Raman spectroscopy. The light curing units used were halogen (500mW/cm2) and LED (900mW/cm2) at a conventional intensity and an Argon laser at 250mW. The exposure time was 40 seconds for the halogen light, 20 seconds for the LED and 20 and 30 seconds for the Argon laser. The curing tip distances of 0, 3, 6 and 9 mm were used and controlled via the use of metal rings. The composite was placed in a black matrix in one increment at a thickness of 1 mm to 4 mm. The values of microhardness and the degree of conversion were analyzed separately by ANOVA (Analysis of Variance) and Tukey test, with a significance level set at 5%. Correlations were analyzed using the Pearson test. The results obtained conclude that greater tip distances produced a decrease in microhardness and degree of conversion values, while increasing the resin thickness decreased the microhardness and degree of conversion values. A higher correlation between microhardness and the degree of conversion was shown. This study suggests that the current light curing units promote a similar degree of conversion and microhardness, provided that the resin is not thicker than 1 mm and the light source is at a maximum distance of 3 mm from the resin surface.