Photoactivation of Bulk Fill Composite Restorations in Human Molars

Objectives: To characterize four light curing units (LCUs) and evaluate the effect of their characteristics and different curing times on the polymerization of four bulk fill resin-based composites (RBCs).
Methods: Tip diameter, radiant power, irradiance, emission spectrum and light beam profile of four LCUs – Bluephase 20i; Celalux 3; Elipar DeepCure-S; Valo Grand were characterized. A mold with a MOD preparation was made using human molar tooth and filled with two RBCs – Filtek Bulk Fill Posterior Restorative and Tetric EvoCeram Bulk Fill. These RBCs were photoactivated for 10 and 20 seconds, with the LCUs positioned at the center of the mold. Knoop microhardness of the transverse surface was measured after 24 h. Twenty indents were made at the center, mesial and distal regions of the specimen, at every 0.5 mm (8 at each side; 4 at the center). Hardness maps were made using the mean hardness values (N=5 specimens). Two-way ANOVA and Tukey post-hoc tests were applied (α:0.05). The light that reached the bottom of the specimen with the tip of the LCUs in different positions was also assessed.
Results: There were significant differences between the hardness measured at the center and at the sides (mesial and distal) of the specimens, independently of LCU or RBC (p<0.05). LCUs with wider tips resulted in higher hardness at the sides of the specimen (p<0.05). Increased exposure times resulted in higher hardness results. Very little light reached the bottom of proximal boxes, even with the use of LCUs with wider tips.
Conclusions: These four LCUs displayed different characteristics that in turn influenced the polymerization of bulk fill RBCs. LCUs with wider tips and longer exposure times are preferable for the photoactivation of large restorations made with bulk fill RBCs. However, more than one light exposure may be necessary at two or more locations.