Light-curing Duration of Photopolymerizable Bulk-fill Composite for Luting Endocrowns

Objectives: The purpose of this study is to evaluate the necessary minimal duration of light-curing to reach a sufficient polymerization of a novel photopolymerizable resin-based bulk-fill composite used to lute endocrowns.
Methods: Ten samples of a photopolymerizable resin-based bulk-fill composite (Filtek One Bulk Fill, 3M ESPE) were placed between two matrix strips and two glass slides and submitted to light curing by a high power LED LCU for 20 s as the positive control group. Five more groups (n=10) were then light-cured from three sites (labial, palatal and occlusal) through a 9.5 mm thick resin-based composite (RBC) CAD/CAM indirect restoration (Lava Ultimate A2 LT, 3M ESPE), for different durations: 90 s per site, 40 s per site, 30 s per site, 20 s per site and 10 s per site. Vickers microhardness (VMH) measurements were made 200 microns and 500 microns under the surface of the luting composite and test/control ratios were calculated. Ratios of 0.80 were considered as an adequate level of curing.
Results: Analysis of the means showed that 30x3 s is the shortest curing duration that presents a test/control ratio above 0.8 for both 200 and 500 microns depths (0.822 and 0.819 respectively). Quintile regressions showed that the required light-curing duration to reach a test/control ratio of 0.8 at a confidence level of 95% is 38 s and 36 s for 200 and 500 microns respectively. The values showed no significant differences in microhardness at 200 and 500 microns except for the light-curing duration of 10 s.
Conclusions: Within the limitations of this study, the results showed that 40 s per site light-curing of photopolymerizable resin-based bulk-fill composite under an endocrown restoration can be considered sufficient to reach 80% VMH of the control group. This study also showed no statistically significant differences between VMH at 200 and 500 microns under the surface except for 10 s.