Correlation of ameloblast size with enamel prism Pattern: use of scanning electron microscope to make surface area measurements

Summary

The area of the secretory territories of ameloblasts was measured from scanning electron micrographs of the surface of the developing enamel of a variety of mammals selected to show the various prism Patterns described by Boyde (1964). Details are given of the precautions which were undertaken to ensure that comparable areas were examined and photographed at a standard magnification at normal incidence of the electron-probe to eliminate foreshortening. Area measurements were derived by weighing photographic paper cut out to contain only the images of complete depressions, which were then counted. The results are presented in the table as the average area (in μm²) covered by individual ameloblasts in a plane at a tangent to the overall surface of the developing enamel.

The smallest ameloblasts are associated with the development of longitudinal rows of Pattern 2 prisms or the modified Pattern 2 prisms found in rodent incisor inner-enamels, and the largest ameloblasts, covering 2 to 3 times the area of the former group, were found to be characteristic for Pattern 3 prism formation. The symmetrical, cylindrical Pattern 1 prisms are formed in relation to intermediate sized cells. No direct explanation of this surprising correlation is offered, but it is noted that these size differences help to explain differences in the degree of divergence of the crystallites within prism domains, which can now be understood to increase with increasing depression diameter through Patterns 2 to 1 to 3.