Fracture Resistance and Failure Patterns of Endodontically Treated Maxillary Incisors Restored Using Different Coronal Strategies After Thermomechanical Aging: An In Vitro Study

Objectives To investigate the influence of different coronal restorative strategies on the fracture resistance and failure patterns of endodontically treated maxillary incisors following thermomechanical aging. Materials and Methods Seventy extracted human maxillary central incisors were randomly assigned according to the coronal restorative approaches (n = 14): intact teeth (control), direct composite restoration, composite restoration with metal–ceramic crown, fiber post with composite core, fiber post with composite core and metal–ceramic crown. Standardized endodontic procedures, followed by restorative protocols, were applied. The samples underwent 6000 thermal cycles between 5°C and 55°C and were embedded in acrylic resin with a simulated periodontal ligament. Static load-to-failure testing was performed using a universal testing machine by applying a compressive load at 135° to the long axis of each specimen at a crosshead speed of 1 mm/min. Maximum fracture load was recorded in newtons (N), and fracture modes were categorized as favorable or unfavorable based on their relation to the cementoenamel junction. Statistical analysis was performed using one-way analysis of variance with Bonferroni post hoc comparisons following confirmation of normality and homogeneity of variances (α = 0.05). Results The control group exhibited significantly greater fracture resistance than all restored groups (p < 0.001). No statistically significant differences in maximum fracture load were detected among the different restorative strategies (p > 0.05). Post-retained restorations demonstrated a higher incidence of unfavorable root fractures compared with non–post-retained restorations. Conclusions Within the limitations of this in vitro study, incorporation of a fiber post did not enhance fracture resistance after thermomechanical aging and was associated with a greater likelihood of non-restorable failure. Clinical Relevance Conservative restorative approaches that prioritize preservation of coronal dentin may improve the reparability of failure in endodontically treated maxillary incisors.