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Evaluation of Dental Caries and Concomitant Infection Based on the Ratio of Cariogenic Bacteria using Plaque Samples in Adults

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

Background: The aim of this study was to evaluate the association between dental caries and concomitant infections of Streptococcus mutans (S. mutans) and Streptococcus sobrinus (S. sobrinus) according to the ratio of cariogenic bacteria in plaque samples from adults to obtain basic data to develop clinical and chairside culture assay (kits) for assessment of dental caries risk.

Methods and Materials: Plaque samples from 192 adult volunteers (age range, 20-28 years) were obtained using sterile toothbrushes. Caries history and the number of decayed, missing, and filled (DMF) teeth were determined. Subjects were divided into high- and low-risk groups according to the ratio of S. mutans to total streptococci (Sm/TS ratio) and the number of S. mutans.

Results: The numbers of S. mutans and S. sobrinus and the Sm/TS ratio were significantly greater in the cariesactive (CA) group than in the caries-free (CF) group. The number of bacteria and the Sm/TS ratio for the high-risk S. mutans plus detectable S. sobrinus subgroup was significantly greater in the CA group than in the CF group. High levels of S. mutans and S. sobrinus were significantly associated with dental caries. A significantly high caries risk was found between DMF teeth and the Sm/TS ratio for S. mutans when S. sobrinus was detected.

Conclusions: The number of dental caries was greater in adults with plaque samples concomitantly infected with high levels of S. mutans and S. sobrinus than in those with a single infection. These findings indicate the usefulness of analysis of cariogenic dental bacteria to detect adult populations with the severity of dental caries according to the Sm/TS ratio using dental plaque samples.