Loading rate effect on nanohardness of human enamel

In the present work, nanoindentation technique has been utilised to study the physics of deformation at the scale of micro/nano-structure of tooth enamel which is basically the hardest natural biomaterial in the human body comprising of a hybrid combination of hydroxypatite ceramic nano-crystal and organic-protein matrix. We have observed about 8 % increase in the nanohardness of human enamel with the increase in loading rate from ~1 × 103 μN s−1 to 3 × 105 μN s−1. The results have been explained in terms of the maximum shear stress generated underneath the nanoindenter.