EPIDEMIOLOGICAL STUDIES IN THE DISTRICT WHERE MUNICIPAL WATER SUPPLY HAD BEEN ACCIDENTALLY FLUORIDATED FOR NINE YEARS

Abstract

A survey of prevalence of dental caries and mottled enamel was made on 1, 200 school children (6-12 years of age) at Kasaoka city of Okayama prefecture in western Japan, where the municipal water supply had been accidentally fluoridated at 1.2-1.3 ppm or more for nine years.Results were summarized as follows:1. At the period of survey, the fluoride concentration of the municipal water supply ranged from 0.9 to 1.3 ppm in tap water of several spots In the city; however, it would have ranged from 1.4 to 1.8 or more during the earlier period of the water supply operation, because there were four water source wells which started respectively to operate at different dates.2. The domestic well water in this district contained also an average of 0.52 (±0.44) ppm of fluoride.3. The percent of persons with one or more DMF teeth was significantly lower than that of the non-fluoridated group (inhibitory rate: 40%), while the percent of persons with mottled enamel was in average 40% in this group (however, moderate or severe grade cases were only 8.5%).4. There were no significant difference in the dental caries prevalence between the municipal water group and the domestic water group, while the mottled enamel prevalence was distinctly higher in the former.5. Several numbers of moderate grade cases of mottled enamel were found even in groups taking fluoride lower than 1.0 ppm and also there were several cases in taking as low as 0.5 ppm.6. There is likely a correlation between the fluoride concentration of drinking water and urine in the range from 0.5 to 3.2 ppm in water.