Methods: Seventy-five disc specimens from five light-activated restorative materials (n=15) of 14 mm diameter ( ± 0.1) and 2 mm thickness ( ± 0.1) were prepared in a poly tetra fluoroethyelene (PTFE) mold. Materials evaluated were: A) Tetric Ceram (Ivoclar–Vivadent), fine particle hybrid composite; B) Heliomolar (Ivoclar–Vivadent) microfilled composite; C) SpectrumTPH (Dentsply), sub-micron hybrid composite; D) Ideal Macoo (Ideal Macoo, Iran), hybrid composite, and E) Vitremer (3M ESPE), resin-modified glass ionomer restorative/core build up. Specimens were irradiated with two applications of overlapping exposures for a total of 120 s and then were stored in distilled water at 37° C for 48 hrs. Biaxial flexural strength (BFS) test was done by piston–on–three–ball method according to ASTM F 394 – 78 standard. Data were analysed by one–way ANOVA and post–hoc paired Tukey test.
Results: The mean BFS values for each material tested were; A) 44.17 ± 15.08; B) 33.72 ± 9.30; C) 51.91 ± 14.05; D) 20.04 ± 5.68, and E) 4.6 ± 2.04 (MPa ± SD). The mean BFS values for Groups E and D were significantly lower than that of other groups (P<0.001). Group C showed significantly higher BFS value than that of groups B, D, and E (P<0.001) but not significantly different from Group A (P>0.05). However no statistically significant difference was found between the BFS for groups A and B (P>0.05).
Conclusions: The biaxial flexural strength of microfilled resin composite (Heliomolar) was comparable with that of fine-particle hybrid composite (Tetric Ceram). Resin-modified glass ionomer restorative/core build up material (Vitremer) showed the lowest biaxial flexural strength compared with the resin–based composite materials evaluated.