Stereo electron microscopy of enamel crystallites.

Stereo microscopy was used to examine enamel crystallites in routine thin sections of rat and Chinese hamster incisors. Freeze-fracture replicas were also made of rat incisor enamel. These studies revealed that enamel crystallites are thin, flat, twisting ribbons of unmeasurable length and uniform width. Images previously interpreted as hexagonal crystallites are due to perspective distortion caused by oblique views along cut segments of these flattened ribbons exaggerated by curling, which occurs at the cut crystallite ends. Images of central crystallite dissolution, resulting from beam sublimation, are due to oblique views of hole-pitted crystallite surfaces. Finally, it was concluded that previous measurements made from two-dimensional images of crystallites in electron micrographs are not reliable.