In order to search out the mechanisms of dental caries occurrence and its progress in the enamel, the author observed, by way of the electron microscopic observation, the deeper layer of normal enamel, the artificially decalcified enamel layer, enamel layer under the carious lesion, the carious enamel layer, and the rough surface carious enamel, in which pigmentation was readily observable.
As material, caries presenting 18 teeth with small cavities were selected. Teeth were extracted from young patients because of other diseases. The teeth were sufficiently fixed-by 10percent neutral formalin after extraction.
Cleaving core of the teeth, the cleaved surfaces of carious enamel were obtained from their fragments. Then filmy replicas were taken from the desired areas of the caries cones
successively from the surface layer to the deep layer. On the other hand, the rest of the teeth were ground by means of Whet-stones.
The obtained results were as follows:
1. The enamel rods, rodsheaths, and intei´fod substance underwent decalcification simultaneously.
2. The initial decalcification was most prominent in the enamel rods, less in interrod substance, and the feast in the rod sheaths.
3. As the caries progressed, hydroxy apatite lost crystaline shape and their layout and distribution became more irregular. Ultimately, their boundaries grew more indistinct and were gradually destroyed.
4. In the carious process, the boundaries of enamel rods became gradually obscure.
5. In the carious process, rod sheaths resisted the caries longer than enamel rods or interrod substance.
6. It seems to be devoid of bacterial invasion in a zone of incomplete demineralization.
7. In the advanced carious process, the inorganic components were chemically dissolved, so that what remains was organic in the rod sheaths.
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