Role of coefficient of thermal expansion on bond strength of ceramic veneered yttrium-stabilized zirconia

Background: Incompatible coefficient of thermal expansion (CTE) is supposed to be a reason for chipping of ceramic veneered zirconia.This study evaluates the effect of veneering ceramic at varied CTE on bond strength to zirconia.Material and Methods: Zirconia disks (Z, Ø 10 mm, 1.0 mm thickness) were prepared from Y-TZP (Cercon ® ) and sintered at 1350°C for 6 hours.All zirconia disks were veneered with ceramics ((Ø 7.0 mm, 1.5 mm thickness) with varied CTE including VITADur ® alpha (VDα), VITAVM ® 7 (VM7), VITAVM ® 9 (VM9), Cercon ® ceramkiss (CCK), IPSe.max ® ceram (IeC), and IPS dSIGN ® (IdS) (n=15).The specimens were thermo-cycled (5-55 °C, 500 cycles) prior to determine the shear bond strength on a universal testing machine.The veneering ceramic and zirconia rods (Ø 4 mm, 30 mm length) were prepared for CTE evaluation.ANOVA and Tukey's multiple comparisons were used to determine the statistically significant difference (α=0.05).Weibull analysis was applied for survival probability, Weibull modulus (m), and characteristics strength (σ o ) of the shear bond.The interfaces were microscopically examined.The phase transformation of zirconia was determined using X ray diffraction.Results: The mean±sd (MPa), m, and σ o of bond strength were 20.45±2.32,9.25, 19.47±4.53,4.66, and 20.31 for Z-VM7, 21.05±3.96,5.61, and 21.88 for Z-IeC, 25.85±2.74,9.93, and 27.15 for Z-VM9, 25.82±4.39,6.27, and 27.06 for Z-CCK, and 2.96±0.73,4.11, and 3.28 for Z-IdS.The CTE (×10 -6 /°C) were 10. 80, 7.83, 7.87, 9.86, 9.93, 10.03, and 12.95 for Z, VDα, VM7, IeC, VM9, CCK, and IdS.The bond strength was significantly affected by the CTE difference (p<0.05).The t→m phase transformation related with the CTE difference.Conclusions: The CTE's differences induced stress that affected the bond strength.CTE's compatibility of veneering ceramic to zirconia is crucial for enhancing the bond strength.The CTE difference approximately 0.77-0.87×10-6 /°C was recommended.