The goal of water fluoridation is to prevent tooth decay by adjusting the concentration of fluoride in public water supplies. Tooth decay (dental caries) is one of the most prevalent chronic diseases worldwide. Although it is rarely life-threatening, tooth decay can cause pain and impair eating, speaking, facial appearance, and acceptance into society, and it greatly affects the quality of life of children, particularly those of low socioeconomic status.
In most industrialized countries, tooth decay affects 60–90% of schoolchildren and the vast majority of adults; although the problem appears to be less in Africa's developing countries, it is expected to increase in several countries there because of changing diet and inadequate fluoride exposure. In the U.S., minorities and the poor both have higher rates of decayed and missing teeth, and their children have less dental care. Once a cavity occurs, the tooth's fate is that of repeated restorations, with estimates for the median life of an amalgam tooth filling ranging from 9 to 14 years. Oral disease is the fourth most expensive disease to treat. The motivation for fluoridation of salt or water is similar to that of iodized salt for the prevention of mental retardation and goiter.
Tooth decay declined substantially in prevalence and severity when Hong Kong children consumed less fluoride, indicative of a world-wide scientific trend revealing, with fluoride, less is best; none is better.
In 1988, Hong Kong reduced water fluoride levels from 0.7 parts per million (ppm) to 0.5 ppm. By 1995, 31% fewer 11-year-olds had cavities with a 42% reduction in average cavity rates, according to the Hong Kong Public Health Bulletin. Similar reductions occurred in 1978 when Hong Kong's fluoridation rates were first cut from 1 ppm to 0.7 ppm.
Hong Kong's dental health is superior to the United States, even though U.S. children consume 1 ppm fluoridated water and brush with 1,000 ppm fluoridated toothpaste. And Hong Kong children use lower concentrated (500 ppm) fluoridated toothpaste.
In British Columbia, Canada, "the prevalence of caries decreased over time in the fluoridation-ended community while remaining unchanged in the fluoridated community," reported in Community Dentistry and Oral Epidemiology.
In South Australia, dental examinations of 4800 ten- to fifteen-year-olds' permanent teeth reveal unexpected results - similar cavity rates whether they drink fluoridated water or not.