Background: The most important change in the mechanical properties of endodontically-treated teeth is the reduction of fracture strength. The aim of the present study was to compare the fracture strength of teeth restored with bulk-fill composite, flowable bulk-fill composite and conventional composite resin in the presence or absence of fiber.
Materials and Methods: In this laboratory study, 120 intact maxillary first premolar teeth were selected and placed in eight groups. The groups were designed with three types of composites (conventional, bulk-fill, flowable bulk-fill) with and without fiber and two negative control groups and positive, Mesio-occlusal-distal (MOD) cavity was prepared in all groups. After the endodontics, the composite of the same group was used in each group to restore the teeth by incremental method. All restorations were polished, mounted and tested by Universal testing machine.
Results: The fracture strength in the fiber-reinforced bulk-fill composite group was significantly higher than the fiber-free group. The teeth restored with fiber-free composites had lower fracture strength. The fracture strength was the same in the samples treated with conventional and bulk-fill composite resins, and it was significantly lower in the samples treated with flowable bulk-fill composite than those treated with conventional and bulk-fill composites. There was a significant difference in fracture strength of fiber-reinforced composites.
Conclusion: Tooth restoration reduces fracture strength. Fiber addition has no significant effect on increasing the fracture strength of composites.