Comparative Evaluation of Fracture Resistance in Endodontically Treated Posterior Teeth Restored With Endocrowns Versus Conventional Post and Core Followed by a Full Crown: An In Vitro Study.

Introduction Endodontically treated posterior teeth are weakened by the loss of coronal structure and require durable restoration to prevent fracture. Conventional post-core-crown systems often involve additional dentin removal, which increases the risk of root fracture. Endocrowns may offer a conservative alternative that uses the pulp chamber for retention. This in vitro study aimed to compare the fracture resistance and failure modes of endodontically treated mandibular first molars restored with lithium disilicate endocrowns versus fiber post-core and lithium disilicate full crowns. Materials and methods Sixty extracted mandibular first molars were root canal treated, randomly divided into two groups (n = 30 each), and restored: Group 1 with computer-aided design and computer-aided manufacturing lithium disilicate endocrowns and Group 2 with fiber posts, composite cores, and lithium disilicate crowns. All specimens were cemented with dual-cure resin cement, stored in water for 24 hours, embedded in acrylic, and tested under compressive load (1 mm/min) using a universal testing machine. The fracture load (N) and failure mode (favorable versus unfavorable) were recorded. Data were analyzed using the Shapiro-Wilk test, independent samples t-test, and descriptive statistics (α = 0.05). Results The mean fracture resistance of teeth restored with lithium disilicate endocrowns was 1250.45 ± 152.30 N, whereas the post-core-crown group demonstrated a mean value of 1180.20 ± 178.60 N. Although the endocrown group exhibited slightly higher fracture resistance, the difference between the groups was not statistically significant (p = 0.106). Failure mode analysis revealed a marked difference in the pattern of fractures between the groups. Endocrowns showed a significantly higher proportion of favorable (restorable) failures, primarily involving debonding or fractures above the cemento-enamel junction. In contrast, the post-core-crown group exhibited a higher incidence of unfavorable (non-restorable) fractures, including vertical root fractures and post-related failures. Conclusions Within the limitations of this in vitro study, lithium disilicate endocrowns demonstrated fracture resistance comparable to conventional fiber post-core restorations followed by full crowns. Importantly, endocrowns were associated with a significantly higher proportion of favorable, restorable failure patterns, suggesting a biomechanical advantage. The absence of intraradicular post placement likely contributes to improved stress distribution and reduced risk of catastrophic root fractures. Clinically, these findings support the use of endocrowns as a conservative and reliable restorative option for endodontically treated posterior teeth with adequate coronal structure. Their use may enhance long-term prognosis while preserving tooth structure and simplifying the restorative procedure.