OBJECTIVETo study dynamic relation between periodontal pathogens and cariogenic bacteria under analogous oral environment.

METHODSEight periodontopathic and cariogenic bacteria of Porphyromonas gingivalis (Pg), Actinobacillus actinomycetemcomitans (Aa), Fusobacterium nucleatum (Fn), Provotella intermedium (Pi), Streptococcus mutans (Sm), Streptococcus sanguis (Ss), Actinomyces viscosus (Av) and Lactobacillus acidophilus (La) were used. These eight strains were cultured in modified chemostat under analogous oral environment which contained 600 ml modified BM medium supplemented with 2.5 g/L porcine gastric mucin, respectively. After 1, 24, 48 and 96 h, optical sectioning of plaque biofilms on removable and replaceable hydroxyapatite disks was analyzed by the combination of live bacterial Gram fluorescence staining and confocal laser scanning microscopy. Biofilm thickness and reconstruction of the three-dimensional architecture of plaque biofilms were made.

RESULTSBiofilm thickness increased significantly with time (P < 0.001). Biofilms of Aa were thinner than those of Ss and eight-specie biofilms were thicker than those formed by Ss and Aa per time point. Three-dimensional images showed periodontal pathogens mainly occurred in cariogenic bacterial complex or on the biofilm surface.

CONCLUSIONSGram-positive cariogenic species initially predominated in artificial plaque, followed by the increasing proportions of Gram-negative periodontal pathogens. The relation between microecological balance among bacteria and diseases is worthy of further studies.