High-resolution electron microscope study of human enamel crystallites: Size, shape, and growth

Abstract

For the first time, high-resolution transmission electron microscopy (TEM) has made it possible to perform crystallite measurements in human enamel through counting of lattice planes, from the first stages of development to posteruptive maturation. The slope of the curve relating width to thickness is a logarithmic function. During the course of a first stage process under the influence of the ameloblasts, the crystals grow rapidly in width, slowly in thickness. At the end of this first stage process, they have reached their final average width. Thereafter a very slow process occurs during which the crystals grow only in thickness up to their mature dimension. During the first stage of enamel development, about 1240 crystallites per square micrometer could be measured. Only 558 crystallites per square micrometer could be measured in mature enamel, indicating a decrease of 55% attributable partly to fusions observed in high-resolution TEM. The morphology of mature enamel crystallites can roughly be described as flattened hexagonal prisms. Average values are 263 ± 21.9 A in thickness and 683 ± 134 A in width, the average width to thickness ratio being 2.59 ± 0.40. The existence of an organic “sheath” enclosing crystallites is discussed.