Compatibility of machined Ce-TZP/Al2O3 nanocomposite and a veneering ceramic

Objectives Due to its high fracture toughness ceria-stabilized ZrO2/Al2O3 nanocomposite (Ce-TZP/A) could be superior to Y-TZP in clinical use. However, the compatibility to veneering ceramics is not yet investigated and therefore subject of this study. Methods Fracture strength and crazing resistance of veneered Ce-TZP/A frameworks (Nanozir, Matsushita Electric Works) were investigated in comparison to sintered and hipped Y-TZP (Hint-ELs). Frameworks were machined (HiCut, Hint-ELs), sintered where applicable (hiTherm, Hint-ELs), and veneered in a standardized procedure (Cerabien ZR, Noritake). Fracture strength of the crowns was assessed in a shear test (n = 10). Biaxial flexural strength of the core materials was measured according to ISO 6872 (n = 10). To assess the thermal compatibility between framework and veneer the coefficient of thermal expansion (CTE) of all materials was determined (n = 3) and a crazing test carried out (n = 12). Results Fracture strength was equal for crowns with Ce-TZP/A (866.6 ± 132.1 N) and sintered Y-TZP (904.5 ± 168.2 N), while crowns with hipped Y-TZP were significantly stronger (1380.6 ± 253.2 N) (Studentʹs t-test, p < 0.05). These values correlated with the biaxial flexural strength of the three core materials (Ce-TZP/A: 1238.0 ± 200.0 MPa, sintered Y-TZP: 1181.8 ± 232.5 MPa and hipped Y-TZP: 1521.8 ± 163.8 MPa). Failure of both hipped and sintered Y-TZP crowns occurred by chipping of the veneer or total fracture, while the Ce-TZP/A crowns predominantly failed by chipping of the veneer. In the crazing test both sintered and hipped Y-TZP performed slightly better than Ce-TZP/A. CTEʹs were as follows: Ce-TZP/A: 10.3 μm/m K, sintered Y-TZP: 10.7 μm/m K, hipped Y-TZP: 10.9 μm/m K, and Cerabien ZR: 9.9 μm/m K. Significance The CTE of the veneering ceramic has to be adjusted to Ce-TZP/A frameworks.