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Differentiation of the Enamel Organ
During the early stage of tooth formation, the enamel organ consists of the outer enamel epithelium (OEE), the cells of the stellate reticulum (SR), the stratum intermedium (SI), and the inner enamel epithelium (IEE) (see Fig 1-6). The cells of the outer enamel epithelium are generally cuboidal. They attach by hemidesmosomes to a basal lamina separating them from the adjacent dental sac, a connective tissue of ectomesenchymal origin. Cytoplasmic organelles in the OEE include a moderate number of mitochondria, a small number of cisterns of rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum, and a poorly developed Golgi complex. The presence of coated vesicles in the peripheral cytoplasm and along the plasma membrane facing the basal lamina suggests that the OEE is involved in specific endocytosis of extracelluar substances.
Soon after the onset of enamel formation, the OEE becomes convoluted by indentations of highly vascularized connective tissue. This structural change becomes pronounced during enamel maturation, when the OEE, the SR, and the SI form the papillary layer to increase the surface area between the enamel organ and the adjacent blood supply. This change is pronounced in the continuously developing incisor of the rat, the most thoroughly investigated model of tooth development.
The cells of the