In China, water fluoridation was begun in Guangdong province in Guangzhou in 1965 and in Dongguan in 1974, and was stopped in 1983 and 1986, respectively. There is at present no fluoridation being practiced in China. Both cities are located north of Hong Kong and belong to the subtropical zone (mean temperature=71.1°F). According to Minoguchi's formula, an optimal fluoride concentration is 0.6-0.7ppm. The fluoride concentration was unstable for the first 10 years, when annual fluoride concentrations ranged from 0.8ppm to 0.9ppm, higher than the optimal fluoride concentration. After that the concentration was about 0.7ppm. The fluoride concentration of drinking water in Guangzhou may have been sometimes higher than the optimal fluoride concentration. In December 1990, seven years after fluoridation was discontinued, a dental survey of schoolchildren aged 15 was made in Guangzhou, and also in Fushan (0.2ppm) as a control area. Two dentists examined dental caries and one dentist examined dental fluorosis with Dean's Index, and other enamel defects were also recorded. Subjects were 62 students in Guangzhou and 71 students in Fushan. The mean DMFT was 0.44 (SE=0.10) in Guangzhou and 2.20 (0.33) in Fushan. The percent difference was 80% (p<0.001). The prevalence rate of dental fluorosis was 21% in Guangzhou and 2.8% in Fushan and the CFI was 0.42 and 0.08, respectively. Many dark brown teeth, not caused by fluoride, were found. They may have been caused by tetracycline or exanthematous fevers. The present study proved that water fluoridation produced high caries-preventive effects and the favorable effects remained for seven years after discontinuation of water fluoridation without serious dental fluorosis in Guangzhou.
