<P> Existing evidence suggests that water fluoridation reduces tooth decay . Consistent evidence also suggests that it causes dental fluorosis, most of which is mild and not usually of aesthetic concern . No clear evidence of other adverse effects exists, though almost all research thereof has been of poor quality . </P> <P> Reviews have shown that water fluoridation reduces cavities in children . A conclusion for the efficacy in adults is less clear with some reviews finding benefit and others not . Studies in the U.S. in the 1950s and 1960s showed that water fluoridation reduced childhood cavities by fifty to sixty percent, while studies in 1989 and 1990 showed lower reductions (40% and 18% respectively), likely due to increasing use of fluoride from other sources, notably toothpaste, and also the' halo effect' of food and drink that is made in fluoridated areas and consumed in unfluoridated ones . </P> <P> A 2000 UK systematic review (York) found that water fluoridation was associated with a decreased proportion of children with cavities of 15% and with a decrease in decayed, missing, and filled primary teeth (average decreases was 2.25 teeth). The review found that the evidence was of moderate quality: few studies attempted to reduce observer bias, control for confounding factors, report variance measures, or use appropriate analysis . Although no major differences between natural and artificial fluoridation were apparent, the evidence was inadequate for a conclusion about any differences . A 2007 Australian systematic review used the same inclusion criteria as York's, plus one additional study . This did not affect the York conclusions . A 2011 European Commission systematic review based its efficacy on York's review conclusion . A 2015 Cochrane systematic review estimated a reduction in cavities when water fluoridation was used by children who had no access to other sources of fluoride to be 35% in baby teeth and 26% in permanent teeth . The evidence was of poor quality . </P> <P> Fluoride may also prevent cavities in adults of all ages . A 2007 meta - analysis by CDC researchers found that water fluoridation prevented an estimated 27% of cavities in adults, about the same fraction as prevented by exposure to any delivery method of fluoride (29% average). A 2011 European Commission review found that the benefits of water fluoridation for adult in terms of reductions in decay are limited . A 2015 Cochrane review found no conclusive research regarding the effectiveness of water fluoridation in adults . A 2016 review found variable quality evidence that, overall, stopping of community water fluoridation programs was typically followed by an increase in cavities . </P>

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