Curing dental composites : effect of light curing devices and duration on mechanical properties, curing depth, and temperature rise

Abstract

Purposes: To evaluate the following: 1 - Effect of different light curing units and curing durations on the level of cure of different composite resins at different depths. 2 - Effect of different light curing units and curing durations on the depth of cure of different composite resins. 3 - Effect of different light curing units and curing durations on the flexural strength and modulus of different composite resins. 4 - Effect of different light curing units and curing durations on the temperature change upon polymerizing Bulk Fill composites. Methods: Six composites were used in this study; Surefil SDR flow, Tetric EvoCeram Bulk Fill, Venus Bulk Fill, Filtek Bulk Fill, Tetric EvoCeram, Filtek Supreme Ultra, and three light curing units were used; LED Bluephase 16i (High & Soft-Start) mode, LED Fusion Light, and QTH Astralis 10. Specimens were fabricated as cylinders. After curing for (10, 20, 40, 60) seconds, the level of cure was assessed through Vickers microhardness testing. Depth of cure lSO 4049 specimens were fabricated as cylinders. After curing for (10, 2O, 40, 60) seconds, uncured resin was scrapped away using a plastic spatula and length of the remaining material was measured using a digital caliper. Flexural strength and modulus specimens were formed into bars by curing them for (10, 20, 40, 60) seconds and tested under the universal testing machine lnstron. To assess the temperature rise, specimens were fabricated in Teflon cylindrical molds after securing three thermocouples through each mold at (2, 4, 6) mm depth. Thermocouples were attached to a data logger that was attached to a computer. Composites were polymerized in the molds for 60 seconds. Temperature increase data was collected using “lab view”software. Results: An increase in microhardness, depth of cure, flexural strength and modulus with the increase in the curing duration (p value [less than] 0.05). Also, upon comparing temperature rise of the composites when light cured for 1O seconds to 5 (p value [less than] 0.05). Upon comparing all light curing units together for the rise of temperature for each composite tested (p value [greater than] 0.05). Conclusions: - Bulk Fill composites tested fulfilled a percent of cure of 80% or above, when light cured for 20 seconds or longer. This agreed upon percent of cure was not met among the conventional composites. - The depth of cure increased significantly with the increase in the light curing duration upon polymerizing the composites with all the light curing units tested. - Light curing the Bulk Fill composites with 10 or20 seconds of light curing duration achieved depth of cure results that were higher than the conventional composites among all the different light curing units tested. - The flexural strength and modulus increased significantly with the increase in the light curing durations of the composite tested. - The deeper the depth levels the lower the temperature change when light curing Bulk Fill composites. - The temperature change with 10 seconds of light curing duration was significantly higher than 5 seconds through out (2, 4, 6) mm depth levels.