considers fluoride not to be an essential nutrient, yet, due to the beneficial effects of dietary fluoride on prevention of dental caries they have defined Water fluoridation is the controlled addition of fluoride to public water supplies to reduce tooth decay. Fluoridated water maintains fluoride levels effective for cavity prevention, achieved naturally or through supplementation. In the mouth, fluoride slows tooth enamel demineralization and enhances remineralization in early-stage cavities. Defluoridation is necessary when natural fluoride exceed Fluoride's adverse effects depend on total fluoride dosage from all sources. At the commonly recommended dosage, the only clear adverse effect is dental fluorosis, which can alter the appearance of children's teeth during tooth development; this is mostly mild and is unlikely to represent any real effect on aesthetic appearance or on public health. In April 2015, recommended fluoride levels in the United States were changed to 0.7 ppm from 0.7 to 1.2 ppm to reduce the risk of dental fluorosis. The 2015 Cochrane review estimated that for a fluoride level of 0.7 ppm the percentage of participants with fluorosis of aesthetic concern was approximately 12%. This increases to 40% when considering fluorosis of any level not of aesthetic concern. In the US mild or very mild dental fluorosis has been reported in 20% of the population, moderate fluorosis in 2% and severe fluorosis in less than 1%. The critical period of exposure is between ages one and four years, with the risk ending around age eight. Fluorosis can be prevented by monitoring all sources of fluoride, with fluoridated water directly or indirectly responsible for an estimated 40% of risk and other sources, notably toothpaste, responsible for the remaining 60%. Compared to water naturally fluoridated at 0.4 mg/L, fluoridation to 1 mg/L is estimated to cause additional fluorosis in one of every 6 people (95% CI 4–21 people), and to cause additional fluorosis of aes The WHO, FDI World Dental Federation, and the United States' Centers for Disease Control and Prevention endorse fluoridation as safe and effective at recommended levels. Critics question its risks, efficacy, and ethical implications. == Goal == 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. In 2011, the WHO reports that protection against dental caries begin at 0.5 mg/L and that most fluoridation standards target a range of 0.5–1.0 mg/L. The WHO itself does not give a target for fluoridation. The European Food Safety Authority's Panel on Dietetic Products, Nutrition and Allergies (NDA) considers fluoride not to be an essential nutrient, yet, due to the beneficial effects of dietary fluoride on prevention of dental caries they have defined an Adequate Intake (AI) value for it. The AI of fluoride from all sources (including non-dietary sources) is 0.05 mg/kg body weight per day for both children and adults, including pregnant and lactating women. In April 2015, recommended fluoride levels in the United States were changed to 0.7 ppm from 0.7 to 1.2 ppm to reduce the risk of dental fluorosis. The 2015 Cochrane review estimated that for a fluoride level of 0.7 ppm the percentage of participants with fluorosis of aesthetic concern was approximately 12%. This increases to 40% when considering fluorosis of any level not of aesthetic concern. In the US mild or very mild dental fluorosis has been reported in 20% of the population, moderate fluorosis in 2% and severe fluorosis in less than 1%. The critical period of exposure is between ages one and four years, with the risk ending around age eight. the decline in tooth decay was accompanied by increased fluorosis in both fluoridated and unfluoridated communities; accordingly, fluoride has been reduced in various ways worldwide in infant formulas, children's toothpaste, water, and fluoride-supplement schedules. === Safety === Fluoridation has little effect on risk of bone fracture (broken bones); it may result in slightly lower fracture risk than either excessively high levels of fluoridation or no fluoridation. There is no clear association between water fluoridation and cancer or deaths due to cancer, both for cancer in general and also specifically for bone cancer and osteosarcoma. The European Commission review states "No obvious advantage appears in favour of water fluoridation compared with topical prevention". Other fluoride therapies are also effective in preventing tooth decay; they include fluoride toothpaste, mouthwash, gel, and varnish, and fluoridation of salt and milk. Dental sealants are effective as well, with estimates of prevented cavities ranging from 33% to 86%, depending on age of sealant and type of study. Fluoride toothpaste is the most widely used and rigorously evaluated fluoride treatment. In the Republic of Ireland, fluoridation was legislated in 1960, and after a constitutional challenge the two major cities of Dublin and Cork began it in 1964; fluoridation became required for all sizeable public water systems and by 1996 reached 66% of the population. In other locations, fluoridation was used and then discontinued: in Kuopio, Finland, fluoridation was used for decades but was discontinued because the school dental service provided significant fluoride programs and the cavity risk It is not known how much is spent in industrial countries to treat dental fluorosis, which is mostly due to fluoride from swallowed toothpaste. Although a 1989 workshop on cost-effectiveness of cavity prevention concluded that water fluoridation is one of the few public health measures that save more money than they cost, little high-quality research has been done on the cost-effectiveness and solid data are scarce. Dental sealants are cost-effective only when applied to high-risk children and teeth. A 2002 U.S.