Crystallographic structure of human tooth enamel by electron microscopy and x-ray diffraction: hexagonal or monoclinic?

Recently reports on the major stability of the monoclinic phase of hydroxyapatite compared with the hexagonal phase have established it as the most observable structure of hydroxyapatite in natural materials, such as hard tissues. In this work, the structural and crystallographic analysis of the inorganic component of sound human tooth enamel was done by transmission electron microscopy, electron diffraction and X-ray diffraction techniques. The results indicated that its unit cell is hexagonal not monoclinic.