Effect of Material, Cement and Design Type on Retention and Failure of Endocrowns: An In vitro Comparative Study

Background: Endocrowns offer a conservative treatment option for endodontically treated teeth, but optimal material and cement selection remains unclear. Objective: To evaluate and compare the retention and failure modes of endocrowns fabricated from metal, porcelain-fused-to-metal (PFM), and zirconia, when luted with glass ionomer cement (GIC) and resin-modified glass ionomer cement (RMGIC). Materials and Methods: Fifty-four extracted human mandibular molars were prepared with standardized endocrown cavities extending 1 mm, 2 mm, and 3 mm above the cementoenamel junction. Endocrowns were fabricated using Co-Cr metal, PFM, and Y-TZP zirconia via CAD/CAM technology. Specimens were randomly divided into six groups ( n = 9 each) and luted using GIC (Fuji IX) and RMGIC (Shofu Hy-Bond Resiglass). Retention testing was performed using a UTM at 5 mm/min crosshead speed. Failure modes were analyzed and categorized as adhesive, cohesive, or mixed. Statistical analyses included one-way ANOVA, Tukey post-hoc test, and Chi-square test (α =0.05). Results: Zirconia endocrowns demonstrated significantly higher retention values (272.3 ± 145.2N at 3 mm depth) compared to PFM (199.2 ± 51.4N) and metal (177.7 ± 16.2N) when luted with RMGIC ( P < 0.05). RMGIC significantly improved retention compared to GIC across all material groups ( P < 0.05). Preparation depth positively correlated with retention in all groups. Adhesive failures predominated with GIC (70–75%), while RMGIC showed more mixed (30–35%) and cohesive failures (25–45%). Conclusion: Zirconia-RMGIC combinations provide superior retention but exhibit more catastrophic failure modes. Metal endocrowns demonstrate favorable, reparable failure patterns and represent a cost-effective alternative. Clinical protocols should emphasize adequate preparation height (≥2 mm) and material-specific cement selection.