Influence of Curing-Light Tip Design on Microhardness of Bulk-Fill Composites

Objectives: This study evaluated the effect of curing-light tip design (regular or homogenizing) on microhardness of two bulk-fill composites.
Methods: The influence of two types of curing-light tip designs (Regular tip, RT, 680 mW total output and Homogenizer tip, HT, 592 mW total output) of Bluephase Style (9.3 mm optical diameter at tip) (Ivoclar Vivadent) was tested using two bulk-fill composites: SonicFill (SOF, Kerr Corp.) and Tetric EvoCeram Bulk Fill (TEC, Ivoclar Vivadent). Composite disks (4-mm thick,10-mm diameter) were prepared using silicone molds and were light-activated for 10s through a 0.5-mm thick glass slide. Knoop microhardness (KHN) was measured at the top and bottom surfaces of each composite specimen. Curing-light tips were positioned in the same position, in order to measure the microhardness in three sets of measurements that corresponded to location of the three LED chips: two blue (456nm) and one violet (409nm) on the composite surface. Microhardness data for each composite were analyzed by three-way ANOVA and Student’s test (α = 0.05).
Results: Use of the HT increased microhardness of SOF only at the position of violet LED chip at bottom surface, and for TEC at the top for all LED chip locations. Microhardness was significantly higher at top than that at the bottom for both composites. Locations on the composite surface at which the violet LED chip irradiated the surface demonstrated significantly lower microhardness than those areas irradiated by blue LED chips, regardless the type of tip.
Conclusions: The type of the tip can affect composite surface microhardness, especially for SOF at the top. Microhardness at the bottom surface decreased, compared to the top. Non-homogeneity of light irradiation influenced the microhardness at the top and bottom surfaces.