Effect of three veneering techniques on fracture resistance and marginal adaptation of zirconia-based crowns

The aim of this study was to evaluate the fracture resistance (FR) of zirconia-based crowns veneered with different methods and to assess marginal gap before and after veneering.

Thirty zirconia copings fabricated by Computer Aided Design/Computer Aided Manufacturing (CAD/CAM) were divided into three groups. In the porcelain layering (PL) group, the copings were manually veneered with VM9 feldspathic porcelain. In the indirect composite (IC) group, the Gradia indirect composite was veneered on zirconia copings, and for the CAD-on (CO) group, the CAD/CAM-fabricated Vita Mark II veneer was cemented onto the copings. For each sample, the marginal gap values at four points (buccal, lingual, mesial and distal) were measured using stereomicroscope and computer software (Motic Images plus 2.0 ML) before and after veneering process. All crowns were cemented on their dies with resin cement and then were loaded by a universal testing machine for failure. Data were analyzed using one-way ANOVA and post-hoc Tukey tests at significant level of 0.05.

Mean FR was statistically higher in PL group (3005 N) than IC (2026 N) and CO (1605 N) groups (P=0.000). Before and after veneering, mean marginal gap was 43.42μm and 48.47μm for PL group, 44.69μm and 51.06μm for IC group as well as 53.03μm and 56.08μm for CO group, respectively. Marginal gap had no significant difference in study groups before and after veneering (P=0.56 and 0.18, respectively). The lowest change in marginal gap was observed in CO group.

The PL technique might increase the failure resistance of Zirconia-based crowns compared to IC and CO techniques. The marginal gap rate following veneering in all three techniques was within acceptable clinical limits.