Mechanical properties of human dental enamel on the nanometre scale

Atomic force microscopy (AFM) combined with a nano-indentation technique wa s used to reveal the structure and to perform site-specific mechanical test ing of the enamel of third molars. Nano-indentations (size < 500 nan) were made in the cusp area to measure the mechanical properties of single enamel rods at different orientations. The influence of etching on the physical p roperties was studied and etching conditions that did not significantly alt er the plastic-elastic response of enamel were defined. Elasticity and hard ness were found to be a function of the microstructural texture. Mean Young 's moduli of 87.5 (<plus/minus>2.2) and 72.7(+/-4.5) GPa and mean hardness of 3.9 +/- 0.3 and 3.3 +/- 0.3 GPa were measured in directions parallel and perpendicular to the enamel rods, respectively. Analysis of variance showe d that the differences were significant. The observed anisotropy of enamel is related to the alignment of fibre-like apatite crystals and the composit e nature of enamel rods. Mechanical properties were also studied at differe nt locations on single enamel rods. Compared to those in the head area of t he rods, Young's moduli and hardness were lower in the tail area and in the inter-rod enamel, which can be attributed to changes in crystal orientatio n and the higher content of soft organic tissue in these areas. (C) 2001 El sevier Science Ltd. All rights reserved.