Evolution of Mechanisms of Enamel Formation and its Biological Significance.

本项目的目的是为了验证牙釉质和类牙釉质的形成机制，这是脊椎动物组织中矿化程度最高的。用显微放射照相和四环素标记比较研究了不同动物发育中的牙釉质和类牙釉质的递进矿化模式。通过计算机辅助图像处理对微射线图进行检测。牙釉质的形成过程分为基质形成阶段和成熟阶段。基质形成阶段是由分泌性成釉细胞形成的有机基质在奠定后立即轻微矿化，成熟阶段比前一阶段要长得多，基质矿化程度较重。在后期阶段，各层牙釉质的矿化梯度、完成时间和最终矿化程度不同。这些发现在从鱼类到哺乳动物的各种动物的牙齿细菌中都得到了一致的观察。结果表明，鱼类牙釉质是两栖动物、爬行动物和哺乳动物牙釉质的一种原始类型。对不同动物的牙釉质和类牙釉质进行显微放射学研究后，用电子探针测定了它们牙釉质和类牙釉质中微量元素的浓度和分布规律。根据类瓷体中氟化物的浓度可将鱼类分为两类，一类是类瓷体中氟化物含量高于约2.0%的鱼类，另一类是类瓷体中氟化物含量低于约0.2%的鱼类。类瓷体中氟化物浓度的差异似乎与鱼类的系统发育有关，而与环境水体中的氟化物浓度无关。在两栖动物、爬行动物和哺乳动物中，没有一种牙釉质像在第一组鱼类的类牙釉质中所观察到的那样含有如此高的氟化物。而在鱼类的类釉质和两栖动物的牙釉质中含量很低的氯离子浓度，在爬行动物的狭窄表面牙釉质和从食虫动物到有袋动物的哺乳动物的整个牙釉质中含量却急剧增加，并表现出非常奇特的分布模式。矿化釉质和牙釉质中氯离子的掺入程度与其形成机制的演化有关。铁的浓度也被认为与类珐琅质和珐琅质形成机制的演变有关。少

The purpose of present project was to verify the evolution of formation mechanisms of tooth enamel and enameloid, which are most highly mineralized in the tissues of vertebrate The project was consisted of following in vestigations.1).Progressive mineralization pattern of the developing enamel and enameloid of the various animals were investigated comparatively by means of microradiography and tetracycline labelling. The microradiograms were examined by the computer aided image processing.The process of enamel formation is composed of the matrix formation stage in which the organic matrix formed by the secretory ameloblasts is slightly mineralized immediately after it is laid down and the maturation stage which takes much longer period than the previous stage and in which the matrix is very heavily mineralized secondarily. During the latter stage, the gradient and the time of completion of mineralization and the final mineralization degree are different in the each layer of enamel and … More enameloid. These findings are consistently observed for tooth germs of various animals ranging from the fishes to the mammals. The results suggest that the enameloid of fish teeth is a primitive type of the enamel of amphibians, reptiles and mammals.2). The concentration and distribution pattern of the trace elements in the enamel and enameloid of the various animals were examined using the electron microprobe after the microradiographical investigation of their ground sections were made. The fishes may be divided into two groups in terms of fluoride concentration in the enameloid, the fishes whose enameloid contains fluoride higher than about 2.0% and those whose enameloid contains fluoride lower than about 0.2% Difference of fluoride concentration in the enameloid seems to be related to the phylogeny of fishes rather than to the fluoride concentration in the environmental water.In the animals of amphibians, reptiles and mammals examined, there is no enamel which contains so high fluoride as obsered in the enameloid of the first group of fishes. On the other hand, the chloride concentration which is very low in the enameloid of fishes and in the enamel of amphibians increase very highly in the narrow surface enamel of reptiles and in the entire enamel of the mammals ranging from insectivore to marsupials and shows very peculiar distribution pattern. It is considered that extent of chloride incorporation into the mineralizing enameloid and enamel is related to the evolution of their formation mechanisms. The iron concentration is considered to be also related to the evolution of formation mechanisms of enameloid and enamel. Less