Effects of deformation rate variation on biaxial flexural properties of dental resin composites

Objectives: This study aimed to determine the biaxial flexural strength (BFS) of resin composite materials at distinct deformation rates. Methods: Two micro-hybrid [Filtek (TM) Z100 (TM), Restorative (Z100), Filtek (TM) Z250 (Z250)] and two nano-filled Filtek (TM) Supreme XT Body (FSB), Filtek (TM) Supreme Translucent (FST)] composite resins were selected. Disc-shaped (12 x 1 mm) specimens were fabricated using nylon split moulds. Bar-shaped specimens (25 x 2 x 2 mm) were fabricated from each material to determine the flexural modulus. The specimens were tested for BFS and flexural modulus under dry and wet conditions after 1, 13, and 52 weeks. Results: The highest BFS was recorded for Z250 (162 +/- 19 MPa), followed by FST (154 +/- 16 MPa), Z100 (150 +/- 18 MPa), and FSB (136 +/- 18 MPa). The materials exhibited a clear trend of increase in BFS with deformation rate. Following immersion for 1 week, the BFS was 126 +/- 18 MPa. for ZI00, and 124 +/- 17 MPa. for Z250, which were higher than those of FSB (99 +/- 16 MPa) and FST (115 +/- 19 MPa) under comparable conditions. There was a remarkable reduction in the flexural moduli of the specimens immersed for 1 week compared to those of the dry specimens: Z100 (from 18.3 +/- 1.2 GPa for dry specimen to 15.7 +/- 0.8 GPa after immersion for 1 week), Z250 (from 16.7 +/- 0.8 GPa to 13.3 +/- 1.4 GPa), FSB (from 13.7 +/- 0.6 GPa to 11.0 +/- 2.1 GPa) and FST (from 12.7 +/- 2.3 GPa to 10.4 +/- 1.0 GPa). Conclusion: This study concludes that the BFS and flexural moduli of resin-based dental restoratives decline when they are immersed in an aqueous medium until saturation with water. However, after equilibrium is established, the immersion medium does not affect the restorative materials further. Variations in deformation rate did not have a significant effect on the BFS of resin-based dental restoratives.