Correlative microscopy of enamel prism orientation.

Both mature and developing human enamel were studied by correlative light and electron microscopic techniques. Ordinary light microscopic observations of routinely prepared ground sections produced a totally inaccurate impression of enamel prism direction. In contrast, ground sections which were acid-etched and viewed with phase contrast optics, as well as thin (0.5 mum) sections, were in concert with further electron microscopic preparations. The appearance of longitudinally sectioned prisms as demonstrated on thick ground sections is often the result of structural interrelation between groups of obliquely sectioned prisms. The arrangement between enamel prism heads and tails is often such as to produce the light microscopic appearance of classical enamel cross striations. The production of such optical artifacts may be related to conflicting interpretations concerning enamel cross striations as well as light microscopic descriptions of the histopathology of enamel caries.