Examination of the histological and bacteriological features of the interface between bacterial deposits and root dentin using a device that included exposed root dentin reproduced pulpal pressure in vitro.

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We evaluated structural change of the dentin and alteration of the localization and carbohydrate metabolism of bacteria in dental plaque and into dentinal tubules on the root dentin specimens in vitro and in situ, that we could observe with the progress in the time. In vitro experiments demonstrated that pH of the medium used for mixed culture with Streptococcus mutans and Lactobacillus casei was lower than it of the independent culture on a device which reproduced pulpal pressure by supplying the saline pressurized through dentinal tubules exposed in the pulpal side of root dentin specimens.On microscope analysis, the numbers of bacterially infected dentinal tubules in specimens used for the mixed culture was significantly more abounding than it of the independent culture. By periodate-thiocarbohydrazide-silver proteinate-physical development (PTSP) staining method, which could detect the intracellular polysaccharide in bacterial cells, it was clarified that much intracellular polysaccharide exists in most bacteria within which exist in microcolonies of plaque layer nearest the dentin surface and in which invaded into dentinal-tubules.On the other hand, in a root-dentin specimen, compulsorily exposed the surface and to the oral environment for only two months, the penetration of the bacteria into the dentinal tubules was visible, while in a twelve-month root-surface specimens in situ, some microcavities coalesced an indicated more wide-ranging cavities, but subsequent destruction of the dentin was not observed. The existence of mantle dentine was indicated as the factor by which brought about the difference of these results. It became clear to dynamically change in the time-dependent destruction of the dentin, which progresses on localization and abundance ratio of PTSP-positive-bacteria by means of image processing technology by the computer.