Objectives: The purpose of this study was to determine the relationship between the concentration of fluoride in drinking water and the prevalence of dental caries and fluorosis in seven Japanese communities with different concentrations of fluoride occurring naturally in the drinking water.
Methods: A total of 1,060 10- to 12-year-old lifetime residents were examined to determine the prevalence of dental caries and fluorosis in communities with trace amounts to 1.4 ppm fluoride in the drinking water in 1987. Systemic fluorides (drops or tablets) have never been available in Japan and the market share of fluoride-containing toothpaste was 12 percent at the time of the study.
Results: The prevalence of dental caries was inversely related and the prevalence of fluorosis was directly related to the concentration of fluoride in the drinking water. The mean DMFS in the communities with 0.8 to 1.4 ppm fluoride was 53.9 percent to 62.4 percent lower than that in communities with negligible amounts of fluoride. Multivariate analysis showed that water fluoride level was the strongest factor influencing DMFS scores. The prevalence of fluorosis ranged from 1.7 percent to 15.4 percent, and the increase in fluorosis with increasing fluoride exposure was limited entirely to the milder forms.
Conclusions: The findings of this study conducted in 1987 in Japan parallel those reported by Dean et al. in the early 1940s.