High-Resolution Electron Microscopy Study of Enamel Crystal Growth in Human Foetus

Abstract

The mineral component of human dental enamel is formed by nonstoichiometric carbonated hydroxyapatite crystals. The presence of relatively large amounts of impurities in mature enamel crystals as well as their external shape are related to their growing mechanism. Enamel crystal growth was investigated previously directly with low resolution electron microscopy or by comparison with synthetic apatite crystal growth. The growing process of enamel crystals is still unknown and the aim of this study was to investigate foetal enamel growth during secretory stage by high resolution transmission electron microscopy.Developing enamel from 5 month-old human foetuses was fixed for 3 hours in a 2% glutaraldehyde and 2% paraformaldehyde solution in 0.1 M sodium cacodylate buffer. After 2 hour postfixation in 1% OsO4 in the same buffer and embedding in Epon, non decalcified ultrathin sections were obtained with a Sorvall-Porter MT-2C microtome equipped with a diamond knife and floated on demineralized water saturated against hydroxyapatite (200mg/l). The sections were observed in a Philips EM 430 transmission electron microscope operating at 300 kV equipped with a double tilt specimen holder. This microscope possessed a Sherzer resolution of 0.19 nm and the absence of drift and astigmatism was checked for each micrograph by an optical diffraction.