Fracture resistance of endodontically treated premolars restored with bulk‑fill composite resins: The effect of fiber reinforcement

Background: Coronal restoration of endodontically treated teeth (ETT) with mesio‑occluso‑distal (MOD) cavities is of a great importance in long‑term success of the treatment. This study evaluated the effect of fiber reinforcement on the fracture resistance (FR) of ETT restored with flowable or paste bulk (PB)‑fill composite resin compared to conventional composite (CC) resin. Materials and Methods: In this in vitro experimental study, eighty maxillary premolars were divided into eight groups (n = 10). The first group was left intact (G1) and the other groups received MOD cavities along with endodontic treatment. G2: Remained unrestored while the other experimental groups were restored with three types of composite resin with or without fiber insertion. G3: CC resin, G4: PB fill, G5: Flowable bulk fill (FB). G6: Fiber + CC, G7: Fiber + PB, and G8: Fiber + FB. FR was tested at crosshead speed of 1 mm/min and recorded in Newton. Data were analyzed using one‑way analysis of variance and Tukey’s tests at significance level of P 0.05. Results: G1 and G2 revealed the highest and the lowest FR, respectively. The mean FR of the testing groups in Newton was as follows: G1 = 1204.8 A, G2 = 352.1 C, G3 = 579.6 BD, G4 = 596.7 BD, G5 = 624.9 BDE, G6 = 858.3 E, G7 = 529.6 CB, and G8 = 802.5DE. Different uppercase letters indicate the significant difference between the groups. Conclusion: The effect of fiber insertion on FR depended on the type of composite resin; the highest reinforcing effect was obtained in the CC resin + fiber, followed by bulk‑fill flowable + fiber, and flowable bulk (FB)‑fill composite resin. The strength of the former was significantly higher than the conventional and PB fill with and without fiber.