Investigation On Nanoscratch Behaviour And Remineralization Repairment Of Human Tooth Enamel On Longitudinal Section

Since the excellent wear resistance of human teeth is closely related to its microstructure, it is of great importance to study the tribological properties of human molar. With a nanoscratch tester, the microtribological behavior of human tooth enamel was investigated by a spherical diamond tip. Before tests, the molars were longitudinally sectioned, well polished and etched in 0.001 M citric acid solution for 1 min. The experimental results confirmed that the scratching behavior of enamel was closely associated with its microstructure. Due to the "buffer" effect of the inter-rod enamel, the scratch-induced damage along the parallel direction to the enamel rod axis was weaker than that along the vertical direction especially under high loads. Under the same applied normal load, the scratch depth on the inter-rod enamel was much larger than that on the enamel rods, which was mainly resulted from the difference of structure between rod and inter-rod enamel. When the normal load increased from 0 to 0.5 mN during scratching, the size of enamel hydroxyapatite (HA) particles was found to gradually decrease from 70 nm to 20 nm, and the size would keep the same even though the normal load became larger. Since such behavior may be helpful to release the stress concentration and prevent the propagation of micro cracks in teeth during the masticating process, it can effectively improve the wear property of teeth and be considered as self-protection behavior of teeth. Finally, after the scratched sample was remineralized in the artificial saliva solution for 30 min, the size of HA particles inside the scratch was found to increase to about 80 nm. When the time of remineralization reached to 2 h, the diameter of the HA particles both inside and outside the scratch would reach to 200 nm and the scratching damage could be repaired to some extent. The results can not only help us understand the microtribological behavior of tooth enamel, but also provide useful suggestions on the development of dental restorative materials and biomimetic materials.