A study of compressive strength between zirconia framework and veneering ceramic as a function of thermal expansion coefficient using Shell–Nielsen test method

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).