Human tooth is mainly composed of outer enamel and inner dentine.Enamel is the hardest tissue in body,and possesses excellent wearresistance.Compared with enamel,dentine,the inner layer of tooth crown,contains more organic substances and is widely considered to be elastic and soft.The effect of dentinelayer on the mechanical properties of human tooth was investigated using a microhardness tester and a laser confocal scanning microscope(LCSM).Results show that the existence of dentinelayer has no obvious influence on the surface microhardness of enamel.But the surface fracture toughness of enamel is reduced once the dentine layer is removed,and the reduction of fracture toughness becomes obvious with the increase of normal load.Obviously,the mechanical properties of human tooth are closely associated with its unique microstructure.Although the hardness of dentine is much lower than that of enamel,the existence of dentine layer could effectively prevent tooth surface from brittle damage.