Method: Fifty human superior premolars were divided into 5 groups (n = 10), prepared as follows: Sound teeth used in G1 as control; in the other experimental groups (G2, G3, G4 and G5), MOD cavities were prepared, extending toward the palatal cups and root canal treatments were performed. Groups were restored varying the restorative technique: G2 – only with composite resin (CR), G3– fiber post + CR, G4- polyethylene fiber (Ribbond) + CR and G5- Fiber post + Ribbond + CR. The teeth were thermocycled 1000 times between 5°C and 55°C. After 24 h, the specimens were loaded in a universal testing machine until fracture (N) and failure mode was checked. One-way ANOVA and Tukey-Krammer tests were used for the statistical analysis (α = 0.05).
Result: Fracture strength of control (G1- 0.41 ± 0.11) was not significantly different (P >0.05) from Ribbond + CR (G4- 0.30 ± 0.08) and Fiber post + Ribbond + CR (G5- 0.38 ± 0.11). Specimens restored only with CR (G2- 0.18 ± 0.05) and fiber post + CR (G3- 0.26 ± 0.09) were statistically similar (P >0.05) between themselves, but both had mean values different from control (P <0.05). Longitudinal and oblique crown fractures were found in all groups.
Conclusion: Ribbond-fiber reinforced resin restorations increased the fracture resistance of premolars with extensive cavities when compared to conventional direct restorative techniques.