Observations on the structural features and characteristics of biological apatite crystals. 1. Observation on the shape and arrangement of the cross sectioned enamel crystals.

In a series of studies to investigate the structural features of biological crystals, using transmission electron microscope, the observations have been made on the shape and arrangement of the cross-sectioned crystal obtained from cross sections through the body of adult human enamel rod, in the surface layer, and in the middle and deep layers. The shapes of the cross sectioned crystals in the surface layer of the enamel are generally different from those in the middle and deep layers. In the surface layer of the enamel, the cross sectioned crystals show a considerable variation in shape and size, and have an irregular shape. The crystals are densely packed. Each crystal is adjacent to the neighboring one, and usually, the arrangement of crystals have an appearance rather like a "stone wall". In contrast, the cross sectioned enamel crystals in the middle and deep layer, are somewhat small than those in the surface layer, and have greater gaps between the crystals. In the middle and deep layers of the enamel, it is rare for the shapes of the crystals to be irregular, therefore, they retain their original shape, most of which are long and hexagonal.