Phylogenetic Study on Mineralization during Tooth Development. I.Initial Mineralization in Teeth of Elasmobranchs.

用电子显微镜和酶组织化学方法研究了牙本质发生过程中的矿化过程。在釉质基质形成阶段，大量直径20-30 nm、受单位膜限制的细小管状小泡占据基质。管状小泡常延续到成牙本质细胞部分，提示管状小泡来源于成牙本质细胞。细小的釉质晶体最初出现在管状小泡上，晶体周围有一层单位膜。因此，假设初始晶体是在管状小泡中形成的，成牙本质细胞参与了初始矿化。在釉质矿化阶段，许多釉质定义的晶体散布在釉质层中。在弹性肌牙釉质中未发现此类晶体沿胶原纤维堆积。在牙釉质成熟期，即牙本质矿化开始的阶段，在前牙本质中发现了许多基质小泡，通常含有细小的晶体。基质小泡可能参与了矿化，至少在部分牙本质中是如此。此外，柱状内牙上皮(IDE)细胞具有发达的丝氨酸，胞浆内有大量线粒体、小泡、空泡和电子致密小体。远端附近可见大量圆形或细长的小泡。碱性磷酸酶和钙镁依赖的腺苷三磷酸酶活性定位于IDE细胞的细胞膜。部分标本的外牙上皮(ODE)细胞胞浆内可见酸性磷酸酶活性。推测在牙釉质矿化和成熟期，IDE和ODE细胞在牙釉质中的有机基质的去除和钙向牙釉质的转运中起重要作用。

Mineralization during odontogenesis in elasmobranchs was investigated using electron microscopy and enzyme histochemistry.Abundant fine tubular vesicles, 20-30nm in diameter and limited by a unit membrane, occupy the matrix at the stage of enameloid matrix formation. The tubular vesicles often continue into the parts of odontoblasts, suggesting that the tubular vesicles are derived from odontoblasts. Fine enameloid crystals initially appear at the tubular vesicles and a unit membrane surrounds the crystals. Hence, it is assumed that the initial crystals are formed in the tubular vesicles and odontoblasts are deeply involved in the initial mineralization.At the stage of enameloid mineralization, many mell-defined crystals are scattered through the enameloid layr. No accumulation of such crystals along the collagen fibrils is found in elasmobranch enameloid. At the stage of enameloid maturation, at which mineralization in dentine begins, many matrix vesicles, which often contained slender crystals, are found in the predentine. The matrix vesicles are probably involved in the mineralization at least in the part of dentine. Otherwise, columnar inner dental epithelial (IDE) cells exhibit well-developed sER,many mitochondria, vesicles, vacuoles and electron-dense bodies in the cytoplasm. Large numbers of round or elongated vesicles are found near the distal end. Alkarine phosphatase and calcium-magnesium dependent adenosin triphosphatase activities are localized at the cell membrane of the IDE cells. Acid phosphatase activity is observed in the cytoplasm of the outer dental epithelial (ODE) cells in some specimens. It is postulated that the IDE and ODE cells play an important role in the removal of the organic matrix from the enameloid and in the calcium transport to the enameloid at the stages of enameloid mineralization and maturation.