The Effect of Preparation Design on the Marginal Integrity of Monolithic Zirconia Crown

Marginal adaptation of full ceramic zirconia restorations are one of the important factors in their long-term success and one of the factors affecting marginal adaptation and their strength is the finish line design.This study was conducted to compare the effect of finishline design on the adaptation of monolithic zirconia crowns.

In this in-vitro study, 3 standard PEEK dies with 7 mm height and 5 mm diameter (in cervical) with convergence angle of 10°  in the walls was prepared by Ceramill motion 2 (Amann Girrbach, Austria) in three groups with chamfer,sloped shoulder and shoulder design. After pouring the molds made from PEEK dies with epoxy resin,30 dies(10 samples per group) were made.The construction of zirconia crowns (zolid preshades,Amann Girrbach, Austria) was performed using the Ceramill map extraoral scanner (Amann Girrbach, Austria) and the CAD / CAM method Ceramill motion 2 (Amann Girrbach, Austria). After cementing the crowns with Panavia F2,they were cut in the Buccolingual direction and the gap was measured at 7 points by the SEM (TESCAN S8000, China) at 500x magnification. In this study, one-way Anova statistical methods were used to show the effect of preparation design on marginal matching and Tukey HSD test to compare groups with each other.

Marginal gap values of the samples evaluated by the mean of AMO and MO,for Chamfer, Sloped shoulder and shoulder groups were (60.37±11.78/57.29±12.63),(73.37±14.79/68.08±14.21) and (95.42±9.60/92.59±10.83) microns and the internal gap values measured by Axial and Occlussal averages were (49.60 ± 10.37/120.37 ± 33.61),(46±9.37/124.41±32.10) and (69.43±9.73/163.49±27.79) microns respectively. There was a significant difference between Chamfer and sloped shoulder groups with shoulder group (P <0.05) but there was no significant difference between Chamfer and sloped shoulder group (P> 0.05).

From the results,it may be concluded that chamfer and sloped shoulder showed better marginal adaptation than that of shoulder,although the chamfer group had the better adaptation among all groups.