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Evaluation of the Proportion of Cariogenic Bacteria Associated with Dental Caries

Hiroya Gotouda, Noriko Shinozaki-Kuwahara, Chieko Taguchi, Michiharu Shimosaka, Mitsuhiro Ohta, Takanori Ito, Tomoko Kurita-Ochiai, Ikuo Nasu

Background: Public oral health surveys have shown that the prevalence of dental caries in adults is increasing worldwide, resulting in increased workload and costs of dental and other clinical oral health services.

Total streptococci are broadly grouped into mutans streptococci and three other species. They constitute a majority of bacteria found in the mouth. Of the total streptococci, the group of bacteria that primarily causes dental caries is mutans streptococci, which consists of seven species. Streptococcus mutans (S. mutans) is the mutans streptococcus most strongly associated with dental caries. To date, no simple assay (kit) has been developed for detecting S. mutans using plaque samples for caries risk assessment. This study aimed to evaluate the association between S. mutans and dental caries in adults based on the number and proportion of cariogenic bacteria in toothbrush plaque samples by culture methods to obtain basic data to develop clinical and chairside culture assay for caries risk assessment.

Materials and Methods: Plaque samples from 164 adult volunteers were obtained using sterile toothbrushes. The ratio of S. mutans to total streptococci (Sm/TS ratio) was determined by counting the number of colonies by culture methods. The extent of dental caries and the relative risk based on bacterial counts were assessed.

Results: The differences between Sm/TS ratios (%) in caries-free, medium-caries, and caries-active groups were statistically significant (p<0.001). The difference in the number of decayed, missing, and filled teeth (DMFT) in the four risk groups, each defined by Sm/TS ratio (%), was statistically significant (p<0.01). The risk associated with Sm/TS ratio was more significantly associated with the number of DMFT than with the number of S. mutans, and this parameter was useful in the selection of high-risk dental caries subjects.

Conclusions: The results of the present study suggested a significant association between the levels of S. mutans and dental caries using dental plaque samples in adults and indicate that quantification of Sm/TS ratio is effective for detecting subjects with the severity of dental caries. This approach has the potential for previous study of the development of simple culture assay for a risk assessment that may be incorporated into future clinical or epidemiological studies measures for the improvement of oral health wor ldwide.