Human carious dentin was examined through the electron microscope by means. of the replica method. Some significant images in carious dentin have been reported and illustrated with representative electron micrographs. The findings have been compared with those of previous publications and discussed concerning their relations.

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The determination of arsenic which migrated into the dental hard tissues was carried out by means of neutron activation analysis. As a results, it was established that the arsenic concentration is greater in the arsenic-devitalized human tooth than in non-devitalized tooth (cf. Table 1). It also became known that the arsenic which migrates into the dental hard tissues remains in that locality extending for a fairly long period of time, though it gradually decreases in amount.
The amount of arsenic thus retained in the tooth for 18 years after arsenic pulpdevitalization is found to be 3.14μg (2.36μg/g of dental tissues).

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In the early stage of cemental caries, surface and subsurface areas of carious cementum became markedly poor in mineral components. Even in inner areas of carious cementum, the gradual decrease of minerals is evidently recognized with carious defects of various forms and sizes. This is apparently due to remarkable carious demineralization that took place first in the beginning of cemental caries. Following this step, carious destruction seems to appear in organic substance of cementum which has been exposed through carious demineralization out of embedding in cemental minerals. Consequently, cross-striations characteristic of collagen fibrils in the matrix of cementum are usually shown in the weakened or lost state as a result of carious devastation, and numerous carious defects can be seen in carious cementum in different forms and sizes as clear indications of carious destruction of inorganic and organic components in cementum. Repetition of the above carious process goes on making increase carious defects in size.
Microbial parasitism is found concentrated mostly on the surface areas, being sometimes sparsely found in subsurface portions of carious cementum. In the inner areas of carious cementum, there exist no microbes at all.

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