Evolution of Mechanisms of Enamel Formation and its Biological Significance.

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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