A study of compressive strength between zirconia framework and veneering ceramic as a function of thermal expansion coefficient using Shell–Nielsen test method
Journal of Adhesion Science and Technology
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 bond strength between a zirconia framework and four veneering ceramic materials with varying coefficients of thermal expansions (CTE) using the Shell Nielsen bond strength test. Zirconia rods (N=40) (ICE Zirkon) (diameter: 4 mm, height: 20 mm) were milled in green state and sintered. After firing,
... d. After firing, the zirconia rods were air-abraded, ultrasonically and steam cleaned. They were randomly assigned to receive four veneering ceramic materials (n=10/group), namely a) Vita VM9 (VZ; 9-9.2x10 -6 K -1 ), b) Cerabien ZR (CZ; 9.1x10 -6 K -1 ), c) Matchmaker ZR (MM; 9.4x10 -6 K -1 ) and d) Ice Zirconia Ceramic (IZ; 9.6x10 -6 K -1 ). The veneering ceramics were then fired onto zirconia discs (height: 2 mm, thickness: 2 mm) circumferentially and were thermocycled for 6.000 times (5/55 0 C, dwell time: 30 s). Specimens were loaded from the top of the zirconia rods (crosshead speed: 0.5 mm/min) in a universal testing machine until debonding. Shell Nielsen bond strength values were calculated and expressed in MPa. The surfaces of the zirconia rods were evaluated under Scanning Electron Microscopy to determine the failure types. The data were then statistically analyzed using 1-way ANOVA and Tukey's tests (α=0.05). Weibull distribution values including the Weibull modulus (m), characteristic strength ( 0 ), and probability of failure at 5% ( 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 only significantly higher than that of IZ (P<0.05). The Weibull distribution presented the lowest shape value (m) for VZ (m=16.94) and the highest for MM (m=20.16). The specimens in all test groups demonstrated predominantly adhesive failure type between the framework and veneering ceramic followed by mixed failures. Veneering ceramics with a greater mismatch of CTE with the zirconia framework exhibited similar Shell Nielsen bond strength to those with fewer mismatches. Shell Nielsen bond strength test used in this study subjecting the zirconia framework-veneering ceramic assemblies to circumferential shear forces did not show the effect of CTE mismatch between the veneering ceramics accept those between CZ (9.1x10 -6 K -1 ) and IZ (9.6x10 -6 K -1 ).