Fracture Resistance of Endodontically Treated Teeth Restored With Short Fiber Reinforced Composite and a Low Viscosity Bulk Fill Composite in Class II Mesial-Occlusal-Distal Access Cavities: An Ex-vivo Study

Background Teeth undergoing endodontic therapy are prone to structural weakening and increased risk of fractures. The absence of marginal ridges and pericervical dentin further compromises the fracture resistance. The choice of the post-endodontic coronal seal is crucial for the effectiveness of endodontic therapy. Aim and Objectives This study compared the fracture resistance and fracture modes of endodontically treated teeth (ETT) with mesial-occlusal-distal (MOD) cavities restored with two different posterior composite resins: e-glass fiber reinforced composite (FRC) (everX Posterior) and flowable bulk fill composite (SDR Flow+). Materials and Methods Sixty human maxillary first bicuspids were divided into four groups: Group PC- positive control (intact teeth), Group NC- negative control (unrestored endodontically treated teeth), Group EXP- samples restored with everX Posterior and nano-hybrid composite, and Group SDR- samples restored with SDR Flow+ and nano-hybrid composite. The NC, EXP, and Smart Dentin Replacement (SDR) samples underwent endodontic procedures and MOD cavity preparation. The samples from EXP and SDR groups were restored with composite resins as post-endodontic coronal seals. The fracture resistance was evaluated using a Universal Testing Machine (UTM), and fracture modes were examined under a dental operating microscope (DOM) at 6x magnification. Statistical tests were performed using One-way ANOVA and Tukeys' post hoc tests. Results The mean fracture resistance of the experimental groups was as follows: PC- 880.1 ± 209.3 N; NC- 238.1 ± 15.4 N; EXP- 766.1 ± 50.2 N; SDR- 540.8 ± 49.4 N. The highest fracture resistance values were observed in the PC group, whereas the NC group showed the least. The EXP group exhibited significantly higher fracture resistance than the SDR group. Adhesive failure was observed in most samples in the EXP group, whereas samples in the SDR group showed more cohesive failures. Favorable fractures were more prevalent in samples restored with EverX posterior. Conclusion The study findings suggest that everX Posterior can enhance the fracture resistance of structurally compromised ETT. Samples restored with everX Posterior showed a favorable mode of fracture, which can be restored. Applying FRCs can contribute to the longevity and success of endodontic treatment by reinforcing the weakened tooth structure and preventing fractures.