The fine structure of initial mineralisation during tooth development in the gummy shark, Mustelus manazo, Elasmobranchia.

In the enameloid matrix a large number of tubular vesicles appeared around the odontoblast processes at the stage of enameloid matrix formation. The tubular vesicles were limited by unit membrane and the membrane often seemed to connect with that of the odontoblast processes. The tubular vesicles probably originated from the odontoblasts. Electron-dense granules were observed in the tubular vesicles before the appearance of crystals and then, in the stage of mineralisation, initial enameloid crystals appeared in each tubular vesicle. Parts of the odontoblast process surrounded small aggregations of tubular vesicles in the unmineralised dentine matrix. There were many multivesicular bodies and lysosomes in the odontoblasts forming the dentine. The odontoblasts probably absorb and break down the tubular vesicles after the beginning of dentinogenesis. Only in the predentine, during the enameloid maturation stage, did a few matrix vesicles appear, but no crystals were found in them. Hence, the initial mineralisation in tooth germs of the shark can be said to be different from that in teleosts.