Influence of the direct composite restauration on the fracture strength and failure modes of endodontically treated premolars restored with posts

Aim: The long-term success of endodontically treated teeth requires maintaining structural integrity, functionality, and aesthetics. The combined use of endodontic fiber posts with resin-based micro- and nano-composites seems to be an intriguing solution for the reinforcement of the damaged tooth structures. This in vitro study aimed to evaluate the mechanical behavior and fracture patterns of premolars restored with different combinations of endodontic fiber posts and composite resins, subjected to thermomechanical aging and masticatory force simulation. Methods: Fifty extracted maxillary premolars were divided into five groups, including a control group of healthy teeth and four experimental groups with two types of fiber posts (hollow and compact) and two composite resins with different elasticity (traditional and bulk-fill). After cyclic fatigue testing, fracture strength and failure modes were analyzed using statistical methods. Results: The control group exhibited significantly higher fracture resistance (1909±177) than the experimental groups, with no significant differences among experimental groups (p. value >0.05). However, teeth restored with bulk-fill composites demonstrated slightly higher fracture resistance and a higher percentage of favorable fractures than other samples. The combination of bulk-fill composite and hollow fiber posts was associated with more favorable fracture outcomes (n=8 favorable fractures). Conclusion: These findings suggest that bulk-fill composites, due to ease of use and favorable fracture behavior, may be a viable restorative option. Further studies with larger sample sizes are needed to confirm these results.