Photoactivation mode and irradiation distance influence on degree of conversion of a resin composite

Objective: To evaluate the degree of conversion of a resin composite varying irradiance × irradiation time and distance between light source and composite surface. Methods: For this analysis, Esthet-X (Caulk/Dentsply) A2 samples (cylindrical shaped, 5 mm diameter and2 mm height) were cured in accordance to the following protocols: 600 mW/cm2 for 40 s, 400 mW/cm2 for 60 s or 200 mW/cm2 for 20 s + 500 mW/cm2 for 40 s; distance light sourcecomposite of 0, 3 or 7 mm. There were nine experimental groups (n = 3). The degree of conversion was determined by FT-Raman spectrometer to provide the amount of remaining carbon double-bonds. Results were analyzed by three-way ANOVA and Tukey’s test. Results: The distance of the light source and the analyzed face were significant (p < 0.05). The degreeof conversion averages (in %) were 59.13 ± 2.32, 58.61 ± 3.08 and 56.85 ± 2.24 for 0, 3 and 7 mm distances; only 0 and 7 mm showed statistical differences. Radiated and nonradiated faces demonstrated degree of conversion averages (in %) of 59.01 ± 2.56 and 57.40 ±2.67, respectively. Conclusions: It was concluded, therefore, that continuous or two-stepped irradiations provide similar degrees of conversion in resin composite. Increasing the distanceof the light source there is a reduction of the degree of conversion. This is especially important in deep restorations.