[Cellular changes at the level of the outer enamel epithelium during vascularization of the enamel organ in the rat].

In the albinos rat, at day 20 in utero, the outer epithelial layer of the first molar is depressed by numerous capillaries. The mesenchymal cells of the follicle present cytoplasmic extensions which are in close relationship with the basement lamina of the external epithelial layer with fibrillar material adherent to the basement lamina. The endothelial cells of the capillaries also present cytoplasmic extensions in contact with the basement lamina. At day 21 in utero, the capillaries penetrate deeply into the stellate reticulum. The fact that the epithelium which surrounds the capillaries is separated from the latter by a basement membrane indicates that the vascular penetration induces a very deep invagination of the epithelium and the basement membrane. This vascular penetration could play a role in the transport of precursors towards the secretory ameloblasts. The mesenchymal and endothelial tissues of the capillaries could have an inductive role on the external epithelial layer through the basement membrane, leading to a disorganization of the enamel organ.