High resolution electron microscopic observation of hydroxyapatite in tooth crystals.

Structure images taken with a high resolution electron microscope with a resolution of 0.18 nm revealed that the atomic arrangement in tooth-enamel hydroxyapatite (HA) corresponds with the calculated image using crystallographic data from mineral HA (Ca10(PO4)6(OH)2). Direct information on the two types of Ca and the OH- groups in the HA crystals was obtained from the observed image through [001] projection. The established correspondence between the observed image contrast and the arrangements of the columnar Ca, the screw-axis Ca, and the OH- groups suggests that HREM observations are useful to identify defects in HA crystals.