Fillers influence the viscosity and bond strength of experimental composites

Objectives: The aim of this study was to evaluate the effect of glass and silica fillercontent on push-out bond strength and film thickness of experimental composites cured with polywave and single-peak LEDs. Methods: Experimental composites containing BisGMA, BisEMA, UDMA and TEGDMA as organic matrix were manipulated, with the camphorquinone/amine system as the initiator. For the inorganic filler, four different composites were investigated: only Br-Al-Si glass fillers (C1), Br-Al-Si glass/SiO2 90:10 (C2), Br-Al-Si glass/SiO2 80:20 (C3) and Br-Al-Si glass/SiO2 70:30 (C4). The viscosity evaluation was done by film thickness of the non-polymerized experimental composites between glass plates (n=4). For the push-out bond strength, cavities were made on the buccal surface of bovine teeth (n=10). After that, teeth were restored with each one of the experimental composites (C1-C4) and photocured  by LEDs (Bluephase G2 – polywave or Radii-Cal – single-peak). The energy dose was standardized at 36 J. After 24 hours , specimens were tested using the Inston machine. Data were submitted to ANOVA and Tukey tests (α=0.05) . Results: the polywave and single-peak LEDs showed no difference for the bond strength values. However, C4 presented the higher bond strength values compared to C1 and C2. The composite C3 showed similar bond strength results compared to C4, C1 and C2 (p ≤ 0.001). The film thickness showed statistical differences in the decreasing way C4 > C3 > C2 > C1. Conclusions: The LED curing units did not influence the bond strength of the experimental composites. The higher the content of colloidal silica, higher the viscosity of the resin composite and push-out bond strength values.