Correlation between Caries Prevalence and Mutans Streptococci by Real-time PCR

Objectives: The purpose of this study is to compare the presence of mutans streptococci with the prevalence of dental caries in Japanese pre-school children by real-time PCR. Methods: Dental plaque samples from upper primary central incisors of 106 pre-school children from three-years-old to six-years and two-months-old (mean; four-years and six-months-old) were analyzed and the children's dt scores were also recorded. DNA was extracted with InstaGene (BioRad). Real-time PCR was performed with LightCycler (Rosche Diagnostics) with primers for Streptococcus mutans (Sm F5 and Sm R4) or for total bacteria (prbac). A 415 or 300 bp fragment amplyfied and detected by agarose gel electrophoresis was confirmed, respectively. The amounts of chromosomal DNA of S. mutans and total bacteria were calculated using S. mutans ATCC 25175 as a standard. The ratios of S. mutans to total bacteria were calculated. Mann-Whitney test was used for statistical evaluations. A p value of less than 0.05 was regarded as statistically significant. Results: The ratios of S. mutans to total bacteria with and without dental decay in the primary central incisors were 0.034 ± 0.092 and 0.0034 ± 0.011 (mean ± SD), respectively (p<0.01). The dt scores of the children positive for S. mutans were statistically higher than those negative. Conclusions: These results indicate that the children showing a higher ratio of mutnas streptococci to total bacterial count have a higher caries risk factor.