Method: Notch disk specimens (5 mm diameter; 2 mm thickness) with a 90°angle V-notch (ø 45°) were prepared to determine the torque to fracture of the composites. The specimens were circle with a central V-shaped notch, which enables the stress concentration at the notch’s apex. Six composites were selected (EverX posterior-GC, Filtek Bulk Fill-3M Espe, Venus Bulk Fill-Heraeuz Kulzer, TetricEvo Ceram Bulk Fill-Ivoclar Vivadent, SDR-Dentsply and SupremeXTE-3M Espe). The specimens (n=10/group) were dry stored for one week at 37°C and then loaded in two-point Mode I tensile load until fracture. In the notched disc design the V notch resembled the fissure or the posterior tooth acting as a stress concentration site, whereas the roller fixed in the testing device acts as a stress concentrator resembling the antagonist. This in vitro test set-up enabled the assessment of two-point contact of the dental restoration under occlusion.
Result: One-way ANOVA followed by the Tukey post hoc (p=.05) revealed significant statistical difference between the groups (p<0.05). Torque to fracture (N/mm) was highest for the everX posterior (33.3±2.9) and lowest for the TetricEvo Ceram Bulk Fill (22.7±3.7). The fracture type analyze showed that everX posterior preserved the specimen’s integrity at the final fracture load, whereas the rest PFCs allowed the fracture of the specimens into two pieces at the final load.
Conclusion: This study showed that the short fibers in the resin composite provide increased resistance to tensile forces in two-point contact mode, when compared to conventional PFCs.