percent to an average approaching 25 percent. In communities where the water has a low fluoride concentration (0.3 mg/liter or less), the prevalence has increased from less than 1 percent to slightly more than 10 percent. These findings reflect levels of fluoride ingestion by some children with developing teeth that are higher than heretofore.

Moreover, a recent national survey (Wagener et al., 1995) found that dietary fluoride supplements were used by 15 percent of children under 2 years of age, 16 percent by those 2 through 4 years of age, and 8 percent by those 5 to 17 years of age. In their study of infants born in Iowa City, a university community with a high socioeconomic status, Levy et al. (1995) reported that from 19 to 25 percent of infants between the ages of 6 weeks and 9 months were given fluoride supplements. Pendrys and Morse (1990) and Levy and Muchow (1992) are among those who have found that supplements are often prescribed at the wrong dosage and in areas where they are not recommended because the water is already fluoridated at recommended levels. Recommendations have been made to reduce fluoride intake from nondietary sources (NRC, 1993; USPHS, 1991; Workshop Reports, 1992).

Risk Characterization

Although the prevalence of enamel fluorosis in both fluoridated and nonfluoridated communities in the United States and Canada is substantially higher than it was when the original epidemiological studies were done some 60 years ago, the severity remains largely limited to the very mild and mild categories. As recorded in the original studies, the prevalence of cases classified as moderate or severe increases with the concentration of fluoride in the drinking water. These relationships are illustrated in Table 8-5, which summarizes data from several U.S. studies done in the 1980s (USPHS, 1991).

These data suggest that the UL (0.1 mg/kg/day) is exceeded by approximately 1 in 100 children in areas where the water fluoride concentration is 1.0 mg/liter or slightly higher. In the 1930s and 1940s, no moderate or severe cases of enamel fluorosis were recorded in these areas, and because fluoride intake from water and the diet appears not to have increased since that time, the additional intake by children at risk of enamel fluorosis almost certainly derives from the use of fluoride-containing dental products.

The virtual absence of evidence of skeletal changes consistent with a diagnosis of skeletal fluorosis indicates that the UL for older children and adults is not being exceeded in the United States or Canada.

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