Influence of deep marginal elevation on the marginal adaptation and fracture resistance of zirconia endocrowns constructed on endodontically treated premolar teeth: in vitro study.

Introduction: One of the most conservative approaches to restoring teeth that have undergone endodontic treatment is the use of endocrowns. This study evaluated the marginal adaptation and fracture resistance of endodontically treated premolars restored with endocrowns fabricated from translucent multi-layered zirconia ceramic following deep marginal elevation.

Methods: Eighteen freshly extracted intact human maxillary premolars were endodontically treated, and standard endocrown preparations were performed. Specimens were divided into two groups (n = 9 each) based on the location of the proximal margin. Group I: Butt-joint endocrown design with a cavity 2 mm in width and 1 mm above the cemento-enamel junction (CEJ) prepared at the middle of the mesial surface (without deep marginal elevation). Group II: Butt-joint endocrown design with a cavity 2 mm in width and 2 mm below the CEJ prepared at the middle of the mesial surface. Deep marginal elevation (DME) was performed using composite resin. All endocrowns were fabricated from translucent multi-layered zirconia ceramic. Endocrowns were luted using dual-cure adhesive cement. Thermocycling was performed after incubating the samples in distilled water at 37°C for 24 h. Marginal adaptation was examined using a stereomicroscope (× 40) at three specific locations along the mesial border. Fracture resistance was assessed using a universal testing machine.

Results: No statistically significant difference was detected in marginal adaptation or fracture resistance between the two groups (p = 0.121 and 0.589, respectively). Catastrophic failure (fracture below the CEJ) was more frequently observed in both groups.

Conclusion: DME has no significant effect on either marginal adaptation or fracture resistance of premolars restored with multi-layered translucent zirconia endocrowns. DME slightly improved the failure mode.