Shear Bond Strength of Porcelain to a Base-Metal Compared to Zirconia Core

STATEMENT OF PROBLEM: Recent clinical results for Zirconia all-ceramic restorations have revealed that the fracture rate 6-15% of the Zirconia framework is so low and the core of Zirconia has high stability. However, chipping-off fractures of porcelain are the most common reason for failures of Zirconia in the fixed partial dentures. OBJECTIVES: The purpose of this study was to compare the shear bond strength (SBS) of porcelain in the porcelain fused to metal and all-ceramic crowns with Zirconia core. MATERIALS AND METHODS: Two groups were selected: porcelain fused to metal (PFM) and porcelain fused to Zirconia (PFZ) (n = 30).In the PFM group, a wax model (10 × 10 × 10mm)was used to cast metal base (Ni_Cr alloy). In the PFZ group, an acrylic cubic model (10 × 10 × 10mm) was made as Zirconia model for scanning.15 cubic Zirconia samples were milled by CAD-CAM. The procedure of porcelain veneering was conducted by the conventional layering technique up to 2 mm thickness (2.5 × 2.5 × 2 mm). All specimens were stored in water for 48 hrs. Thermal cycling was conducted for 20000 cycles between 55°C and 5ºC alternatively for 30s.All samples were mounted in acrylic resin and the SBS test was performed, using a universal testing machine. The analysis of data was performed at a significance level of 0.05 using Kolmogorov-Smirnov and Mann-Whitney U-test. RESULTS: Mean of SBS in PFM and PFZ was 24.57 and 20.88, respectively. The results of Mann-Whitney test showed that there was no statistically significant difference between the two groups of porcelain fused to metal and Zirconia in item shear bond strength (p = 0.455). CONCLUSIONS: There was no significant difference between the two groups of PFM and PFZ in the item SBS.