Hertzian cyclic fatigue properties of the glass-infiltrated alumina and spinel were evaluated using a WC sphere of radius of 3.18 mm in exact in vitro environment (artificial saliva) at contact loads from 200 N to 1000 N to investigate indentation damage and strength degradation. At 200 N, no strength degradation was observed up to 106 contact cycles. As the load increased from 200 N to 1000 N, the reduction in strength was found when the transition from ring to radial cracking occurred. The degree of strength degradation after critical cycling was more pronounced probably owing to the chemical reaction of the artificial saliva with the glass phase along the radial cracks introduced during the large numbers of contact cycles.