SUMMARY
This study evaluated the microleakage in zirconia crowns cemented with bioactive vs resin cements at two margin locations: cementum/dentin deep margin and composite-elevated margins. Standardized mesial box cavities were prepared in 30 molar teeth, with proximal cavosurface margins placed 1 mm below the cemento-enamel junction (CEJ) and restored with resin composite. The teeth were prepared for zirconia crowns, with mesial margins on the composite and distal margins on tooth structure 1 mm below the CEJ. Following digitization and zirconia crown fabrication, the specimens were randomly allocated into five groups based on the type of cement used: one multistep adhesive resin, one self-adhesive resin, one bioactive hybrid ionic resin, and two bioceramic cements. Microleakage was evaluated by measuring the percentage of dye penetration depth at the interfaces, with data analyzed using two-way ANOVA. The results revealed a significant interaction between cement type and margin location, with elevated margins exhibiting less leakage than deep ones across all cement types (p≤0.001). However, the effect of margin location on microleakage varied depending on the cement type, with variations in microleakage scores at each margin location ranging from statistically nonsignificant (p>0.05) to statistically significant (p≤0.05). Adhesive resin and hybrid bioactive cements significantly outperformed others in reducing microleakage at both margin interfaces.