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Histological examinations of erupted teeth and tooth germs in juvenile and adult dog salmon, Oncorhynchus keta, were carried out by light microscopy, scanning and transmission electron microscopy. As results of these observations, it was found that 1) cap enameloid may only be present in the teeth of juveniles and 2) the inner dental epithelial cells (i. d. e. cells) had great influence on the absorption of the majority of the cap enameloid matrix containing collagen fibers rather than on the formation of tooth matrix.In the teeth of juveniles, the tips of teeth were recognized as hypermineralized and collagen free portions by light microscopic, microradiographic, scanning and transmission electron microscopic observations. In the teeth of adults, however, no such features were seen in the tips of teeth. It seems that cap enameloid is absent in adult teeth.In the stage of matrix formation, the features of the inner dental epithelial cells (i. d. e. cells) indicated that the cells had begun their secretory activity. However, the morphological features of i. d. e. cells indicated that activity of the cells in matrix formation was at a low level and that a great quantity of epithelial secretions widely spread out in the tooth matrix was not obtained except around the basal lamina.On the contrary, active absorptive function at the distal margin of i. d. e. cells is expected and it is considered that absorption of organic substances from the cap enameloid area by i. d. e. cells had already begun in the late stage of matrix formation. Therefore, in the case of juvenile dog salmon, it is assumed that the i. d. e. cells play little part in the formation of tooth matrix and that the majority of the tooth matrix originates from the odontoblasts.In the stage of maturation, the taller and clear i. d. e. cells possessing a remarkable ruffled border at the distal margin were found in the portion surrounding the cap enameloid. It is assumed that such cells absorb the organic matrix containing collagen fibers from the cap enameloid area and make it a hypermineralized area. On the contrary, though the i. d. e. cells corresponding to collar enameloid became taller at this stage, the remarkable ruffled border was not found in these cells. The outermost layer of the collar enameloid area, about 0.5μm in thickness, became more electron-dense and the crystals, which appeared to be arranged perpendicular to the tooth surface, were gathered densely. Considerable difference in the formation mechanism may be present between cap and collar enameloid.

Histological examinations of tooth germs in juvenile dog salmon (chum salmon), Oncorhynchus keta, were carried out by transmission electron micoscopy in order to observe fine structures of initial calcification sites in dental matrix and to determine the relationship between electron-dense fibrous substances and matrix vesicles reported by Igarashi (1983). A number of matrix vesicles round or oval in shape and 300-700 A in diameter appeared in the apical dental matrix around the odontoblasts during the stage of matrix formation and about half of them contained more electron-dense crystal-like structures. On the other hand, matrix vesicles relatively decreased in number, but electron-dense fibrous substances consisting of flocculent substances and fine granular substances became well-developed and longer and increased in number in the apical dental matrix distant from the odontoblasts. These fibrous substances also contained more electrondense crystal-like structures. The stereophotographs showed that the fibrous substances exhibited filmy structures in three dimensions and continued to more electron-dense crystal-like structures. Moreover, the electron-dense fine granular substances would seem to attach to these filmy structures in parts. It seems that these filmy structures are the initial form of crystal. A number of matrix vesicles existed near the fibrous substances and some came into contact with the fibrous substances. A state indicative of the unit membrane of these matrix vesicles having broken and part of the contents disappeared was often obtained. It seems that these fibrous substances appeared later than matrix vesicles because of the observation in the early stage of matrix formation. These observations lead us to the conclusion that the fibrous substances derived from the contents of matrix vesicles. Fibrous substances indicated a positive reaction with ruthenium red staining. No fibrous substances appeared in the basal dental matrix during the stage of matrix formation in the basal portion in spite of the appearance of a number of matrix vesicles and small aggregates of crystal-like structures. It seems that this difference is closely concerned with the fact that the apical dental matrix is the initial portion to begin the calcification of tooth.

In this paper, the eleven molars of four Asiatic elephants (Elephas maximus LINNE) in two zoos are described. They were found in the straw where the elephants slept, except one premolar, artificially removed just before shedding.Compared with the molars in function, the shed molars exihibit the following: smaller number of lamellae, shorter crown length, lower crown height by abrasion, resorbed roots, smooth mesial wearing surface with shallow dentin inlets and indistinct enamel foldings and broad distal facette. Root resorption is more evident in the mesial portion than in the distal; the buccal and lingual third parts are more resorbed than the intermediate third portion, on the buccal side in the upper molar and on the lingual side in the lower molar, than the opposite sides in basal aspect.It is shown in specimens no. 6 and 7 that the crown height decreased by 14-15mm through abrasion during three years (P1. I, 1-4). It was noted that the distal lamellae, (specimen no.11) were shed three months earlier than the mesial ones (specimen no.10, P1. I, 5-7)