Evaluation of bond strength between zirconia milled ceramic material and veneered dental porcelain

This study aimed at examining the bond strength between zirconia and ceramic veneer, following the ISO 9693 guidelines. A total of fifty specimens of zirconia/ceramic-veneer system were produced using two commercial zirconias (VITA YZ-HT^White and Zolid HT+ White, referred to as Group A and Group B, respectively) and a ceramic-veneering material (Zirkonia 750). The microstructure (via x-ray diffraction analysis, XRD and Secondary Electron mode, SEM) and the mechanical properties (via 3-point bending tests) of the two groups were assessed. Then, experiments were conducted according to the ISO 9693 and conventional protocols applied for producing zirconia/ceramic-veneer restorations. Bond strength values, measured by 3-point bending tests, were 34.42 ± 7.60 MPa for Group A and 31.92 ± 6.95 MPa for Group B. SEM observations of the cohesively fractured surfaces (on the porcelain side) and the examination for normality using the Shapiro-Wilk test suggested the use of Weibull statistical analysis. Median strength (σ_50%) for Group A and Group B was 34.76 and 32.22 MPa, while the characteristic strength (σ_63.2%) was 35.78 and 33.14 MPa, respectively. The Weibull modulus disparity between groups (12.69 and 13.07) was not significant. Bond strength exceeded the ISO 9693 minimum of 20 MPa, suggesting satisfactory strength for clinical use.