Temperature Increase with Two Different Light-Curing Units

The photo-activation process produces a temperature increase due to an exothermic reaction process and to the light energy absorbed. Objectives: The purpose of this study was to investigate the temperature changes during the photo-activation with two light-curing units with different irradiation times. Methods: One halogen (Optilight 501, Demetron), and one second generation LED (LEC, MM Optics) LCUs with 500 mW/cm2 during 10, 20, 30, 40, 50, and 60 s were used in this study. The composite resin used was a microhybrid FiltekTM Z-250 (3M/ESPE) at color A2. The samples were made in a metallic mold (2 mm in thickness, 4 mm in diameter) and previously light-cured during 40 s. A thermocouple (Model 120-202 EAJ, Fenwal Electronic, Milford, MA, USA) was introduced in the composite resin to measure the temperature increase (TI) during the light-curing process. The TI (°C) was calculated and the results were submitted to ANOVA and Tukey's test (p<0.05). Results: The highest temperature increase was recorded with a Curing Light 2500 halogen LCU (from 9.5 ± 0.15 to 31.0°C ± 0.76 after 10 to 60 s of irradiation times), while the lowest temperature increase was recorded for the LCU based on second generation blue LED (from 6.3 ± 0.46 to 22.°C ± 0.47 after 10 to 60 s of irradiation times. A significantly lower temperature increase occurred through illumination with LED when compared to the halogen LCU. Conclusion: There was a quantifiable amount of heat generated during the visible light curing of a composite resin, mainly to the halogen LCU. The amount of heat generated was influenced by the characteristics of the light-curing units used and the irradiation times.