The ultrastructure of the enamel organ related to enamel formation

Abstract

The ultrastructure of the cells of the enamel organ related to enamel formation was studied using the lower incisors of adult male rats. In the region of enamel deposition, stratum intermedium cells are stabilized by a system of intercellular bridges and intracellular fibrils. The mitochondria in these cells are positioned toward the extracellular channels through which any direct intercellular exchange between the capillaries and ameloblasts must occur. Tentatively, the mitochondrial arrangement is considered to be related to the movements of electrolytes and water across the capillary-ameloblast interval.In the region of transition, enamel deposition ceases and the ergastoplasm of the ameloblasts is removed, apparently by cytosegresomes, with an accompanying reduction in the height of the ameloblasts. Here, vesicles containing stippled material are infrequent compared to their occurrence in ameloblasts concerned with enamel deposition. Other vesicles, characteristically found in ameloblasts related to maturing enamel, f i s t appear in the transition region and seem to originate from the cell membrane abutting on the enamel.In the region of maturation, cytosomes are common in the Golgi region whereas vesicles and mitochondria predominate in the distal ends of the ameloblasts. The papillary cells contain an unusually large number of mitochondria, elaborate microvilli and vesicles, which suggests that these cells are extremely active, presumably in the movement of materials related to enamel maturation.The changes in structure of the papillary cells, which occur concomitantly with those of the ameloblasts during enamel formation, are indicative of interrelated functional changes and strongly support the concept of ameloblasts and papillary cells acting together as a functional unit.

Fine structure of the outer enamel epithelium in the cervical loop of the rat incisor.

“…However, no ultrastructural details of the outer enamel epithelium have yet been clarified. It was also shown by DECKER [3] that lipid granules are often seen within cells, while details of their distrubution in the CL have not been revealed. The author therefore studied these various points in detail using the growing end of the rat incisor, and observed, mainly by electron microscopy, the fine structure of the outer enamel epithelium in the CL during the process of tooth formation.…”

“…Previous electron microscopic studies have focused mainly on the morphological changes occurring in the process of inner enamel epithelial differentiation into secretory ameloblasts [3][4][5][6][7][8][9][10][11]. Only a few investigations have been made on the outer enamel epithelium using electron microscopy; PANNESE [12] [16] all briefly reported the fine structure of the outer enamel epithelium.…”

“…It was originally reported on the basis of light microscopic observations that the CL of the rat incisor was difficult to discriminate into the four cell layers, i.e., the inner enamel epithelium, the stellate reticulum, the stratum intermedium and the outer enamel epithelium [1]. Later, however, it was shown by WARSHAWSKY et al [2] that in the CL of the rat incisor, both the inner and outer enamel epithelia consisted of multilayers.Previous electron microscopic studies have focused mainly on the morphological changes occurring in the process of inner enamel epithelial differentiation into secretory ameloblasts [3][4][5][6][7][8][9][10][11]. Only a few investigations have been made on the outer enamel epithelium using electron microscopy; PANNESE [12] [16] all briefly reported the fine structure of the outer enamel epithelium.…”

A histochemical demonstration of calcium in the maturation stage enamel organ of rat incisors.

“…The development of extensive gap junctions between the adjacent papillary cells and between them and ameloblasts suggests their possible participation in calcium transport to the enamel as a functional unit with maturation ameloblasts (KALLENBACH, 1966;ELWOOD and BERNSTEIN, 1968;GARANT, 1972;SASAKI and HIGASHI, 1983;GARANT et al, 1984;SASAKI and GARANT, 1986).…”

“…The papillary cells have been implicated as playing a significant role in the regulation of minerals because of their cytological features typical of iontransporting cells (KALLENBACH, 1966;ELWOOD and BERNSTEIN, 1968;GARANT, 1972;SASAKI and HIGA -SHI, 1983;GARANT et al, 1984;SASAKI and GARANT, 1986). The weakness of GBHA reactions in the mitochondria of papillary cells, relative to those of adjacent ameloblasts, does not impair the value of such a speculation, but simply indicates possible differences in calcium-related biological features of mitochondria in both types of cells.…”