Objective To investigate the cyclic fatigue modes of Vita markⅡ machinable ceramics under Hertzian′s contact. Methods Hertzian′s contact technique（WC spheres r=3.18 mm）was used to investigate the cyclic fatigue of Vita markⅡmachinable ceramic. All specimens were fatigued by cyclic loading in moist environment, furthermore, surviving strength was examined by three point test and morphology damage observation. Results In homogeneous Vita mark Ⅱ machinable ceramics, two fatigue damage modes existed after cyclic loading with spheres under moist environment, including conventional tensile-driven cone cracking（brittle mode） and shear-driven microdamage accumulation（quasi-plastic mode）. The latter generated radial cracks and deeply penetrating secondary cone crack. Initial strength degradation were caused by the cone cracks, subsequent and much more deleterious loss was caused by radial cracks. Conclusion Cyclic fatigue modes of Vita mark Ⅱ machinable ceramics includes brittle and quasi-plastic mode.
