Methods: Forty non-carious human premolars and molars were prepared in a standardized manner for full-cast crown restorations. Crowns were made from a noble alloy using a standardized technique. The specimens were randomly divided into four groups of cementing agents and cemented according to the manufacturers' instructions: 1) Rely X Unicem with pretreatment (self-adhesive resin cement); 2) Rely X Unicem without pretreatment; 3) Panavia F2.0 resin cement, and 4) Fuji Plus hybrid ionomer cement. The specimens were stored in distilled water at 37°C for two weeks and then subjected to thermocycling. They were then placed in a silver nitrate solution and vertically cut in mesiodistal direction. Subsequently, the objects were evaluated for microleakage and marginal gap using a stereomicroscope. Data were analyzed using a non-parametric Kruskal-Wallis test at a P<0.05 level of significance. Results: The Rely X Unicem (with or without pretreatment) showed significantly the smallest degree of microleakage and marginal gap at both tooth-cement and cement-crown interfaces (P<0.01). The mean microleakage value for Fuji Plus hybrid ionomer cement was significantly higher at the cement-crown interface than all other cementing agents tested (P<0.05). No statistically significant difference in the marginal gap values was found between cementing agents tested (P>0.05).
Conclusions: The Rely X Unicem self-adhesive resin cement either with or without pretreatment provided a much better sealing ability for the noble alloy full-cast crowns.