Bacterial colonization of mineralized and completely demineralized dentine in situ.

The changing environment in a developing root lesion may result in a succession of the microbial flora in the dentine. As demineralization proceeds, the collagenous matrix is exposed, which could be conducive to the growth of specific microorganisms. In this study both sound and completely demineralized dentine were placed together in the partial prothesis of 8 individuals to test whether the type of substrate influenced the composition of the bacterial flora. After 6 weeks the degradation of the collagenous matrix, the demineralization of the dentine and the microbial composition were assessed. The collagen loss varied between 0 and 69 wt%. Mineral loss from the originally sound dentine specimens ranged from virtually none to complete demineralization. Percentages of total streptococci, mutans streptococci, Actinomyces and lactobacilli isolated from both dentinal substrates did not differ significantly. The percentage of lactobacilli in the dentine specimens was positively correlated to the lesion depth. The percentage of Actinomyces species was significantly higher in both the dentine specimens that had been demineralized in vitro and those that were found to be completely demineralized in situ compared to the partially demineralized dentine specimens. In vitro, no collagenolytic activity of the predominant flora isolated from both dentinal substrates could be shown.