Bond Strength and Internal Adaptation of Experimental Bulkfill Composites

Objectives: The aim in this study was to evaluate the microtensile bond strength (μTBS) and internal adaptation (IA) of experimental bulkfill resin composites based on an elastomeric monomer.
Methods: Six bulkfill resin composites were made with ethoxylated bisphenol-A dimethacrylate (BisEMA), triethylene glycol dimethacrylate (TEGDMA) and different molar concentrations (2.3, 5.75 or 11.5 mol%) of urethane dimethacrylate (UDMA) or elastomeric monomer (Exothane 24). Barium boroaluminosilicate glass and colloidal silica were used as filler particles (77wt%). Tetric Evoceram Bulkfill™ (TEB) was used as control. Resin composites were inserted in bulk in Class I type cavities made in 70 human third molars and light-cured with 24 J/cm² (1,200mW/cm²/20s). Teeth (n=10) were sectioned after 24 h and the central slice of each tooth was used to calculate the imperfect margin percentage (%IM) in scanning electron microscopy (SEM). The other slices of each tooth were sectioned to obtain beams with a cross-sectional area of 1 mm² in order to evaluate the μTBS. The mode of failure was evaluated by SEM. Data was submitted to two-way ANOVA and Tukey’s test (α=0.05) and one-way ANOVA and Dunnet’s test (experimental to control group comparisons).
Results: Exothane-based composites showed higher μTBS (MPa) than UDMA-based composites. Experimental composites containing 2.3mol% of Exothane or UDMA presented higher μTBS and lower %IM. The %IM of the composites containing Exothane and UDMA were similar. Similar results were found between experimental composites and TEB, except for composites containing 5.75 or 11.5 mol% of UDMA that showed lower μTBS. Predominance of mixed failures was found for all composites.
Conclusions: It can be concluded that elastomeric monomer Exothane 24 improved μTBS of bulkfill composites in comparison to UDMA, but no significant improvements were found for experimental bulkfill composites in comparison to TEB.