The effect of curing lights and modes on dentin bond strength of bulk-fill composites applied in different thickness

Abstract

To investigate shear bond strength (SBS) to dentin of a conventional and three bulk-fill composites applied in different increment thickness and cured by mono- and multi-wave LED LCUs. Two hundred and fifty-two extracted sound human molars were prepared for SBS test. The teeth were divided into four groups according to the resin composites used. Conventional composite: Tetric N-Ceram (control); high-viscosity bulk-fills: Tetric N-Ceram Bulk Fill, X-tra Fil, and SonicFill. Each group was subdivided (n = 7) according to increment thickness (2, 4, and 6 mm) and cured by standard mode of a mono-wave LED or two different modes (standard and xtra power) of a multi-wave LED. The failure mode was stereomicroscopically determined at 40x magnification. Data were analyzed using Three-way ANOVA and further comparisons were assessed by Bonferroni's multiple comparison test. There were no significant differences within X-tra fil and Tetric N-Ceram Bulk Fill groups for any of the variables (p > 0.05). A significant decrease in SBS values with increase of layer thickness was observed for SonicFill and control groups. Also, curing mode had a significant effect on both composites at 6 mm thickness and standard mode of multi-wave LED caused the highest SBS value (p < 0.05). Adhesive failure was the most common fracture pattern especially at 6 mm thickness applications. Based on the results of this study, the bulk-fill composites can be safely applied in one-step with 4 mm increments, although the examined composites performed better at 2 mm thickness. The performance of the composites at 6 mm increment may show differences related to the curing lights and modes.