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Abstract
This study investigated the adhesion between zirconia framework and four veneering ceramic (VC) materials with varying coefficients of thermal expansions (CTE). Zirconia rods (N = 40) (ICE Zirkon) (diameter: 4 mm, height: 20 mm) were milled and sintered. After firing, the zirconia rods were air-abraded and cleaned. They were randomly assigned to receive four VCs (n = 10/group), namely (a) Vita VM9 (VZ; 9–9.2 × 10−6 K−1), (b) Cerabien ZR (CZ; 9.1 × 10−6 K−1), (c) Matchmaker ZR (MM; 9.4 × 10−6 K−1), and (d) Ice Zirconia Ceramic (IZ; 9.6 × 10−6 K−1). The VCs were then fired onto zirconia rods (height: 2 mm, thickness: 2 mm) circumferentially and were thermocycled for 6000 times (5/55 °C, dwell time: 30 s). Specimens were loaded from the top of the zirconia rods (0.5 mm/min) in a universal testing machine until debonding. Shell–Nielsen bond strength values were calculated (MPa). Failure types were evaluated under SEM. The data were statistically analyzed (one-way ANOVA, Tukey’s; α = 0.05). Weibull distribution values including the Weibull modulus (m) (0.05) was calculated. The highest mean bond strength (MPa) was obtained for CZ (42.08 ± 4.08), followed by VZ (41.77 ± 4.92), MM (40.7 ± 3.64), and IZ (40.05 ± 5.78). While mean bond strength for VZ, MM, and IZ were not significantly different (p > 0.05), CZ was significantly higher than that of IZ (p < 0.05). The lowest shape value was for VZ (m = 16.94) and the highest for MM (m = 20.16). Mainly, adhesive failures followed by mixed failures were observed. VCs with a greater mismatch of CTE with the zirconia framework exhibited similar Shell–Nielsen bond strength to those with fewer mismatches. CTE mismatch did not affect the results of CZ (9.1 × 10−6 K−1) and IZ (9.6 × 10−6 K−1).