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 (G(1)) and the other groups received MOD cavities along with endodontic treatment. G(2): Remained unrestored while the other experimental groups were restored with three types of composite resin with or without fiber insertion. G(3): CC resin, G(4): PB fill, G(5): Flowable bulk fill (FB). G(6): Fiber + CC, G(7): Fiber + PB, and G(8): 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: G(1) and G2 revealed the highest and the lowest FR, respectively. The mean FR of the testing groups in Newton was as follows: G(1) = 1204.8 (A), G(2) = 352.1 (C), G(3) = 579.6 (BD), G(4) = 596.7 (BD), G(5) = 624.9 (BDE), G(6) = 858.3 (E), G(7) = 529.6 (CB), and G(8) = 802.5(DE). 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.