IN-VITRO DEMINERALIZATION BY STRAINS OF ACTINOMYCES-VISCOSUS AND STREPTOCOCCUS-SOBRINUS OF SOUND AND DEMINERALIZED ROOT SURFACES

Root sections were inoculated with one of two strains of Actinomyces v iscosus or a strain of Streptococcus sobrinus and then incubated for 9 days in Trypticase soy broth (TSB) containing 0.25% glucose or TSB su pplemented with 0.25% sucrose (TSB + S). Lesion progression was measur ed from microradiographs. One section from each group was examined wit h a transmission electron microscope. Lesion progression was associate d with a fall in the pH of the medium. However, lesion progression was not correlated with the mean 48-hour pH of the medium. In both TSB an d TSB + S, lesion progression with A. viscosus was significantly great er than in the S. sobrinus group. However, the mean 48-hour pH value i n TSB + S was lower than that in the S. sobrinus group. Plaque formati on in TSB was, subjectively, least in the S. sobrinus group. Examinati on of transmission electron micrographs revealed bacteria penetrating the surfaces of the sections and extending into the lesion in the A. v iscosus groups but not in the S. sobrinus group. This in vitro bacteri al plaque model of root caries may be suitable for investigations of t he bacterial etiology of root-surface caries and the virulence factors associated with pathogenicity.