Henry Trendley Dean, a U.S. Public Health Service public-health dentist, collaborated with McKay in identifying “mottled enamel” or fluorosis as being associated with fluoride in the drinking water. Dean also discovered that there was an association between caries in children, mottled enamel and fluoride levels in the drinking water. He advocated that 1 ppm of fluoride be tested for its effects on caries.