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.