Fine structure of the epithelial dental organ in the frog during early odontogenesis.

Abstract

AbstractA total of 227 tooth germs in different developmental stages were dissected from the maxillae of 58 leopard frogs (Rana pipiens). Five fixatives and three buffers were used and optimum preservation of the odontogenic epithelium was observed in specimens fixed in cold 4% glutaraldehyde at pH 7.3 for three hours followed by 1% osmium tetroxide for one hour. The inner dental epithelium showed mitotic figures limited to the initial stage of odontogenesis. The cells contained numerous free ribosomes, tonofilaments, few mitochondria and sporadic cisternae of endoplasmic reticulum. Their distal portions were drawn into processes studded with numerous hemidesmosomes. At a later stage of development yet prior to amelogenesis, these processes disappeared. The preameloblasts followed two pathways of histodifferentiation depending on their location. Ventrolabially the columnar cells exhibited progressive differentiation in contrast to the cuboidal cells on the ventrolingual surfaces of the cusps.The external dental epithelial cells were flattened, closely packed and connected by numerous desmosomes. Their cytoplasm contained mainly mitochondria and tonofilaments, as well as few Golgi vesicles. With the beginning of amelogenesis large intercellular spaces and lysosomal‐like bodies were frequently observed and the Golgi complex is more prominent.We concluded that at early odontogenesis the epithelio‐mesodermal interaction in the frog's dental organ is similar to that of mammalian species but the frog's internal epithelium shows a different pattern of histodifferentiation.