Decreasing caries prevalence in Japanese preschool children is accompanied with a reduction in mutans streptococci infection

Objective: To evaluate the association between decreasing caries prevalence in Japanese preschool children and mutans streptococci (MS) infection. Methods: The prevalence of caries and salivary MS was examined in 1- to 3-year-old preschool children in 1995 (n = 135) and 2000 (n = 118). Results: The caries prevalence for 3-year-old subjects significantly declined from 65.1% to 37.5% (p < 0.01), reflecting the data seen in Japanese national oral health surveys in 1993 and 1999. Salivary MS detection for 3-year-old subjects significantly declined from 68.3% to 37.5% (p < 0.05). On the other hand, the decrease in the prevalence of caries and salivary MS was not significant in 1- and 2-year-olds. The correlation between caries experience (dft) and the salivary MS score for 3-year-old subjects with low caries prevalence in the later examination (r_s = 0.479, p < 0.001) was comparable with that in 1995 (r_s = 0.462, p = 0.001). Conclusions: The recent decrease in decay in Japan is accompanied with a reduction in MS infection in the deciduous dentition. MS levels are closely related to caries prevalence in preschool children regardless of the extent of caries.