Influence of the coefficient of thermal expansion mismatch on the bond strength of bi-layered all ceramic system

Abstract

Statement of problem: In all-ceramic restorations, high occurrence of veneer chip-off has been reported in clinical studies. CTE mismatch is one of the factors that may increase the residual stress in the interface and affect the veneer-core bond strength. Purpose: The purpose of this study was to evaluate the effect of CTE mismatch on the bond strength of 5 veneering ceramics. Material and methods: 50 rectangular zirconia plates (Zenotec ZR ) were divided equally and veneered with 5 different veneering ceramics (Zenoflex, Cercon ceram kiss, Vintage ZR 1, Vintage ZR 2, and Vintage ZR 3). The bond strength test was performed according to ISO 10477 and the shear force was subjected by using universal testing machine. Fracture surfaces were examined under macroscope and SEM to determine the fracture mode. The collected data were analyzed with a 1- way ANOVA and Tukey HSD test (α=.05). Results: The mean shear bond strength in MPa (± SD) were 27.61 (± 5.56) for Zenoflex, 26.44 (± 5.5) for Cercon ceram kiss, 30.96 (± 7.82) for Vintage ZR 1, 37.64 (± 10.44) for Vintage ZR 2, and 31.32 (± 5.6) for Vintage ZR 3. Vintage ZR 2 had significantly higher mean bond strength than Zenoflex and Cercon ceram kiss. All groups exhibited either combined or cohesive fracture modes. Conclusion: CTE mismatch in the range of 0.5 -1.5 ppm/°C does not have a major effect on the bond strength between the veneering ceramic and zirconia substrate. Key words: Shear bond strength, CTE mismatch, Fracture mode, veneering ceramics.