Effect of occlusal-convergence and resin cement on retention of cubic-zirconia based crowns

Purpose. The purpose of this study was to evaluate the retention of cubic zirconia crowns with two occlusal convergence preparations and cementation with two resin cements.
Materials and methods. 28 dies were divided according to the convergence angles into two main groups. Group (1): 20° (n=14) Group (2): 12° (n=14) Each group was subdivided according to resin cement used into two subgroups. Subgroup A: RelyX Unicem (3M/ESPE, USA) (n=7) Subgroup B: Panavia v5 with clearfil primer plus (Kurary, Japan) (n=7) Two stainless steel master dies were prepared by a milling machine to simulate all ceramic full coverage crown preparation of a maxillary premolar. Each Steel die was machined with height 5.5 mm and two planes occlusal reduction with palatal cusp bevel. The external diameter of the cylinder was 7.5 mm. one die was prepared with 12˚ and the other with 20˚ occlusal convergence angle. Impressions of the main master dies were taken and poured using a non-shrink epoxy resin material. The crowns were cemented. Instron universal testing machine was used to test the retention. The cemented crowns were pulled off along the path of insertion with a crosshead speed of 0.5 mm/minute. The forces required for dislodgment of the crowns were recorded in N. Data were statistically analyzed using one-way ANOVA and many comparisons were made using .Tukey’s test at pResults. Retention of the zirconia crowns was significantly affected by the occlusal convergence and by the type of resin cement. Self-etching resin cement showed a higher significant result in comparison to self-adhesive. Retention values with occlusal convergence 12° was highly significant with both cements
Conclusions. The Retention of cubic zirconia ceramics varied significantly depending on the type of resin cement and degree of occlusal convergence of the preparation.