Comparison of the effects of microfilled and hybrid composite resin restorations on the fracture resistance of extensively weakened teeth

Composite resins can play an important role in dentin support and enamel strength via bonding to tooth structure. The purpose of this study was to compare the effects of hybrid and microfilled composite restorations on the fracture resistance of extensively weakened teeth. In this case control study 40 intact maxillary premolars were mounted in transparent acrylic resin blocks. The samples were divided into 4 groups (n=10 each). Group PC comprised of intact teeth, without preparation and restoration. In other three groups MOD preparations with constant depths and converged walls toward occlusal surfaces were prepared. Group NC composed of teeth with preparations but without any restoration. Group HR included prepared and restored teeth using a hybrid composite and Group MR contained prepared and restored samples with a microfilled composite. Samples were thermocycled (500 cycles in 5-55° C), then were placed under compressive loads in a universal testing machine, and the curves were drawn with a software called Test Xpert. Mean fracture resistance in HR, MR, PC, and NC groups were 48.1010, 59.1773, 83.1420, and 21.9220, respectively. There was a statistically significant difference among the groups(P<0.05). The increasing effect of microfilled group on the fracture resistance of restored teeth is significantly more than that of hybrid group.