Changes in Dental Fluorosis Following an Adjustment to the Fluoride Concentration of Hong Kong's Water Supplies

In June, 1978, the fluoride concentration in Hong Kong water supplies was reduced from 1.0 to 0.7 mg/ L. The objectives of this study were (1) to determine whether, as a result of this minor adjustment, a consequent reduction in the prevalence and severity of dental fluorosis came about, and (2) to determine whether dental fluorosis develops during enamel secretion and primary mineralization or during the maturation stage of enamel development. Dental fluorosis was assessed by Dean's community fluorosis index (CFI) on upper central incisors in 2382 children aged from 7 (exposed to 0.7 mg/L only) to 13 years. The children were selected from four districts served with drinking water by four different water treatment stations. Differences in the distributions of dental fluorosis scores across ages were significant in all districts. The susceptibility to fluoride was assessed statistically through a series of analyses whereby the fluoride concentration in the drinking water (both coincident with enamel secretion and periods of enamel maturation) was correlated with CFI. It was concluded (1) that CFI values were reduced following a minor adjustment to the fluoride concentration in drinking water, (2) that dental fluorosis develops during the maturation stage of enamel development, (3) that the development of dental fluorosis may occur over a period of 16 to 24 months, commencing from 12 to 32 months following enamel secretion, and (4) that Dean's index is a suitable instrument for monitoring the effects on dental fluorosis of minor adjustments to the fluoride concentration in drinking water.