Anisotropic fatigue behavior of human enamel characterized by multi-cycling nanoindentation

Single- and multi-cycling nanoindentations were performed on occlusal surface and axial section of human enamel rod using Berkovich indenter. Deviation of load–depth curve under multi-cycle from single-cycle could indicate the anisotropic fatigue damage during repeated indentations. On occlusal surface, fatigue damage is ascribed to the partial interface debonding between crystals and protein and incomplete refolding of domain bonds of protein molecules. While on the axial section, additional damages, i.e., fracture of crystals and debonding at the end of crystals are supposed to be dominant.