Ultrastructure of the human enamel organ. I. External enamel epithelium, stellate reticulum, and stratum intermedium.

The fine structure of external enamel epithelium, stellate reticulum and stratum intermedium in primary tooth germs (bell stage) from four human foetuses was investigated. Characteristically, the cells of the differentiated external enamel epithelium, stellate reticulum and stratum intermedium exhibit many free ribosomes, few rough endoplasmic reticulum cisterns, well-developed Golgi complexes, many coated and smooth vesicles, often in relation to the cell membranes, and many bundles of tonofilaments. The cells are connected by numerous desmosomes and gap junctions. A parallel differentiation of stratum intermedium - external enamel epithelium, and the ameloblast layer is demonstrated. The morphology of the cells of the three layers indicates that these have secretory, transport and supporting functions.