An epidemiological survey on the prevalence of dental fluorosis and measurement of fluoride concentration in drinking water has been performed in natural fluoride areas, in Kitatsugaru since 1974. The region of Kitatsugaru is located at 40°45', north latitude; the annual mean temperature is 9.6°C and annual mean maximum temperature is 14.1°C. Dental fluorosis is caused by excessive intake of fluorides during calcification of teeth. Therefore, the relationship between the occurrence of dental fluorosis and fluoride concentration in the drinking water, which the subjects had been drinking since birth, was evaluated. 248 elementary school children in 3 areas, from age 6 to 9, were examined. The severity of fluorosis was examined by an experienced examiner and recorded according to the WHO classification (1971).
Thirty-seven deep wells in natural fluoride areas of Kitatsugaru were divided into 7 groups, according to their fluoride concentrations (Mean±S. D.): Group I, 0.34±0.04 ppm; Group II, 0.64±0.13 ppm; Group III, 0.95±0.19 ppm; Group IV, 1.72±0.20 ppm; Group V, 2.50±0.52 ppm; Group VI, 1.01±0.95 ppm; and Group VII, 1.15±0.61 ppm. Coefficients of variation (C. V.) of fluoride concentration from Group I to V were stable within about 20%, but unstableness of C.V. was found in Group VI and VII.
The moderate [MO] and severe [S] types of dental fluorosis were not found in natural fluoride areas, in Kitatsugaru. A mild type [M] of dental fluorosis was first observed in Group III and increased from 4.6 to 25.0% to the maximum level of Group V, with the increasing fluoride concentration of the water. Community fluorosis indices of each fluoride concentration group were as follows: Group III, 0.33-negative zone; Groups IV and V, 0.86 and 0.88-higher than borderline zone, respectively; Group VI, 0.25-negative zone; and Group VII, 0.50-borderline zone.
The percentage of school children having nonfluoride enamel opacities was less than 5% in natural fluorides areas in Kitatsugaru. On the basis of the severity of dental fluorosis and CFI, the optimum fluoride concentration in drinking water in this area appears to be 0.9 ppm.
