Fluoridation

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Water fluoridation is the controlled addition of fluoride to a public water supply in order to reduce tooth decay.[1] Its use in the U.S. began in the 1940s, following studies of children in a region where water is naturally fluoridated. Too much fluoridation causes dental fluorosis, which mottles or stains teeth, but U.S. researchers discovered that moderate fluoridation prevents cavities, and it is now used for about two-thirds of the U.S. population on public water systems[2] and for about 5.7% of people worldwide.[3] Although there is no clear evidence of adverse effects other than fluorosis, most of which is mild and not of aesthetic concern,[4][5] water fluoridation has been contentious for ethical, safety, and efficacy reasons,[3] and opposition to water fluoridation exists despite its support by public health organizations.[6]

Contents

[edit] Motivation

Water fluoridation's goal is to prevent tooth decay (dental caries), one of the most prevalent chronic diseases worldwide, and one which greatly affects the quality of life of children, particularly those of low socioeconomic status. Fluoride toothpaste, dental sealants, and other techniques are also effective in preventing tooth decay;[7] water fluoridation, when it is culturally acceptable and techically feasible, has substantial advantages over toothpaste, especially for subgroups at high risk.[8]

[edit] Implementation

Fluoride monitor (at left) in a community water tower pumphouse, Minnesota, 1987.

Fluoridation is normally accomplished by adding one of three compounds to drinking water:

  • Hydrofluosilicic acid (H2SiF6; also known as hexafluorosilicic, hexafluosilicic, silicofluoric, or fluosilicic acid), is an inexpensive watery byproduct of phosphate fertilizer manufacture.[9]
  • Sodium silicofluoride (Na2SiF6) is a powder that is easier to ship than hydrofluosilicic acid.[9]
  • Sodium fluoride (NaF), the first compound used, is the reference standard.[9] It is more expensive, but is easily handled and is used by smaller utility companies.[10]

These compounds were chosen for their solubility, safety, availability, and low cost.[9] The estimated cost of fluoridation in the U.S., in 1999 dollars, is $0.72 per person per year (range: $0.17–$7.62); larger water systems have lower per capita cost, and the cost is also affected by the number of fluoride injection points in the water system, the type of feeder and monitoring equipment, the fluoride chemical and its transportation and storage, and water plant personnel expertise.[1] A 1992 census found that, for U.S. public water supply systems reporting the type of compound used, 63% of the population received water fluoridated with hydrofluosilicic acid, 28% with sodium silicofluoride, and 9% with sodium fluoride.[11]

Defluoridation is needed when the naturally occuring fluoride level exceeds recommended limits. It can be accomplished by percolating water through granular beds of activated alumina, bone meal, bone char, or tricalcium phosphate; by coagulation with alum; or by precipitation with lime.[12]

In the U.S. the optimal level of fluoridation ranges from 0.7 to 1.2 mg/L (milligrams per liter, equivalent to parts per million), depending on the average maximum daily air temperature; the optimal level is lower in warmer climates, where people drink more water, and is higher in cooler climates.[13] In Australia optimal levels range from 0.6 to 1.1 mg/L.[5] Some water is naturally fluoridated at optimal levels, and requires neither fluoridation nor defluoridation.[12]

In the U.S., the use of bottled and filtered water grew dramatically in the late 1990s and early 2000s. U.S. regulations for bottled water do not require disclosing fluoride content, so the effect of always drinking it is not known. Pitcher or faucet-mounted filters do not alter fluoride; the more-expensive reverse osmosis filters remove 65%–95% of fluoride, and distillation filters remove all fluoride. About two-thirds of low-income parents never give unfiltered tap water to their children: one-third always give bottled water, and one-third use filters, most of which preserve fluoride. Minority children have higher rates of untreated cavities, and poor children have less dental care, especially dental sealants.[14]

[edit] Mechanism

Water fluoridation operates by creating low levels (about 0.04 mg/L) of fluoride in saliva and plaque fluid. This in turn reduces the rate of tooth enamel demineralization, and increases the rate of remineralization of the early stages of cavities.[15] Fluoride is the only agent that has a strong effect on cavities; technically, it does not prevent cavities but rather controls the rate at which they develop.[16]

[edit] Evidence basis

Existing evidence strongly suggests that water fluoridation prevents tooth decay. There is also consistent evidence that it causes fluorosis, most of which is mild and not considered to be of aesthetic concern.[5] The best available evidence shows no association with other adverse effects. However, the quality of the research on fluoridation has been generally low.[4]

[edit] Effectiveness

Water fluoridation is the most effective and socially equitable way to achieve wide exposure to fluoride's cavity-prevention effects,[5] and has contributed to dental health worldwide of children and adults.[1] A 2000 systematic review found that fluoridation was associated with a decreased proportion of children with cavities (the median of mean decreases was 14.6%, the range −5% to 64%), and with a decrease in decayed, missing, and filled primary teeth (the median of mean decreases was 2.25 teeth, the range 0.5 to 4.4 teeth). The review found that the evidence was of moderate quality: many studies did not attempt to reduce observer bias, control for confounding factors, or use appropriate analysis.[4] Fluoridation also prevents cavities in adults of all ages;[17] a 2007 meta-analysis found that fluoridation prevented an estimated 27% of cavities in adults (range 19%–34%).[18]

The decline in tooth decay in the U.S. since water fluoridation began in the 1950s has been attributed largely to the fluoridation,[13] and has been listed as one of the ten great public health achievements of the 20th century in the U.S.[19] Initial studies showed that water fluoridation led to reductions of 50%–60% in childhood cavities; more recent estimates are lower (18%–40%), likely due to increasing use of fluoride from other sources, notably toothpaste.[1] The introduction of fluoride toothpaste in the early 1970s has been the main reason for the decline in tooth decay since then in industrialized countries.[15]

In Europe, most countries have experienced substantial declines in cavities without the use of water fluoridation, indicating that water fluoridation may be unnecessary in industrialized countries.[15] For example, in Finland and Germany, tooth decay rates remained stable or continued to decline after water fluoridation stopped. Fluoridation may be more justified in the U.S. because unlike most European countries, the U.S. does not have school-based dental care, many children do not attend a dentist regularly, and for many U.S. children water fluoridation is the prime source of exposure to fluoride.[20]

Although a 1989 workshop on cost effectiveness of caries prevention concluded that water fluoridation is one of the few public health measures that saves more money than it costs, little high-quality research has been done on the cost-effectiveness and solid data are scarce.[1][13]

[edit] Safety

At the commonly recommended dosage, the only clear adverse effect is dental fluorosis, most of which is mild and not considered to be of aesthetic concern. Compared to unfluoridated water, fluoridation to 1 mg/L is estimated to cause fluorosis in one of every 6 people, and to cause fluorosis of aesthetic concern in one of every 22 people.[4] 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.[5] There is no clear association between fluoridation and cancer, deaths due to cancer, bone cancer, or osteosarcoma.[5]

In rare cases improper implementation of water fluoridation can result in overfluoridation, resulting in fluoride poisoning. For example, in Hooper Bay, Alaska in 1992, a combination of equipment and human errors resulted in one of the two village wells being overfluoridated, causing one death and an estimated 295 nonfatal cases of fluoride intoxication.[21]

Adverse effects that lack sufficient evidence to reach a scientific conclusion[5] include:

  • Like other common water additives such as chlorine, hydrofluosilicic acid and sodium silicofluoride decrease pH, and cause a small increase of corrosivity; this can easily be resolved by adjusting the pH upward.[22]
  • Some reports have linked hydrofluosilicic acid and sodium silicofluoride to increased human lead uptake;[23] these have been criticized as providing no credible evidence.[22]
  • Arsenic and lead may be present in fluoride compounds added to water, but there is no credible evidence that this is of concern: concentrations are below measurement limits.[22]

The effect of water fluoridation on the environment has been investigated, and no adverse effects have been established. Issues studied have included fluoride concentrations in groundwater and downstream rivers; lawns, gardens, and plants; consumption of plants grown in fluoridated water; air emissions; and equipment noise.[22]

[edit] Politics

Main article: Water fluoridation opposition

Almost all major health and dental organizations support water fluoridation, or have found no association between fluoridation and adverse effects.[6][24] These organizations include the World Health Organization,[25] the Centers for Disease Control and Prevention,[1] the U.S. Surgeon General,[26] and the American Dental Association.[27]

Despite support by public health organizations and authorities, efforts to introduce water fluoridation meet considerable opposition whenever it is proposed.[6] Controversies include disputes over fluoridation's benefits and the strength of the evidence basis for these benefits, the difficulty of identifying harms, legal issues over whether water fluoridation is a medicine, and the ethics of mass intervention.[3] Opposition campaigns involve newspaper articles, talk radio, and public forums. Media reporters are often poorly equipped to explain the scientific issues, and are motivated to present controversy regardless of the underlying scientific merits. Internet websites, which are increasingly used by the public for health information, contain a wide range of material about fluoridation ranging from factual to fraudulent, with a disproportionate percentage opposed to fluoridation. Conspiracy theories involving fluoridation are common, and include claims that fluoridation is part of a Communist or New World Order plot to take over the world, that it was pioneered by a German chemical company to make people submissive to those in power, that it is backed by the sugar or aluminum or phosphate industries, or that it is a smokescreen to cover failure to provide dental care to the poor.[6] Specific antifluoridation arguments change to match the spirit of the time.[28]

[edit] Use around the world

U.S. residents served with community water fluoridation, 1992 and 2006. The percentages are the proportions of the resident population served by public water supplies who are receiving fluoridated water.[29]
Main article: Fluoridation by country

About 5.7% of people worldwide drink fluoridated water;[3] this includes 61.5% of the U.S. population.[30] 12 million people in Western Europe have fluoridated water, mainly in the United Kingdom, Spain, and Ireland. France, Germany, and some other European countries use fluoridated salt instead; the Netherlands, Sweden, and a few other European countries rely on fluoride supplements and other measures.[31] The justification for water fluoridation is analogous to the use of iodized salt for the prevention of goiters. China, Japan, the Philippines, and India do not fluoridate water.[32]

Australia, Brazil, Chile, Colombia, Canada, Hong Kong Special Administrative Region of China, Israel, Malaysia, and New Zealand have introduced water fluoridation to varying degrees. Germany, Finland, Japan, the Netherlands, Sweden, and Switzerland have discontinued water fluoridation schemes for reasons which are not systematically available.[3]

[edit] Alternative methods

Water fluoridation is one of several methods of fluoride therapy; others include fluoridation of salt, milk, and toothpaste.[33]

The effectiveness of salt fluoridation is about the same as water fluoridation, if most salt for human consumption is fluoridated. Fluoridated salt reaches the consumer in salt at home, in meals at school and at large kitchens, and in bread. For example, Jamaica has just one salt producer, but a complex public water supply; it fluoridated all salt starting in 1987, resulting in a notable decline in the prevalence of cavities. Universal salt fluoridation is also practiced in Columbia, Jamaica, and the Canton of Vaud in Switzerland; in France and Germany fluoridated salt is widely used in households but unfluoridated salt is also available. Concentrations of fluoride in salt range from 90 mg/kg to 350 mg/kg, with studies suggesting an optimal concentration of around 250 mg/kg.[33]

Milk fluoridation is being practiced by the Borrow Foundation in some parts of Bulgaria, Chile, Peru, Russia, Thailand and the United Kingdom. For example, milk-powder fluoridation is used in Chilean rural areas where water fluoridation is not technically feasible.[34] These programs are aimed at children, and have neither targeted nor been evaluated for adults.[33] A 2005 systematic review found insufficient evidence to support the practice, but also concluded that studies suggest that fluoridated milk benefits schoolchildren, especially their permanent teeth.[35]

[edit] History

1909 photograph by Frederick McKay of G.V. Black (left) and Isaac Burton and F.Y. Wilson, studying the Colorado Brown Stain.[36]
Main article: History of water fluoridation

The history of water fluoridation can be divided into three periods. The first (c. 1901–33) was research into the cause of a form of mottled tooth enamel called the Colorado Brown Stain, which later became known as fluorosis. The second (c. 1933–45) focused on the relationship between fluoride concentrations, fluorosis, and tooth decay. The third period, from 1945 on, focused on adding fluoride to community water supplies.[2]

The foundation of water fluoridation in the U.S. was the research of the dentist Frederick McKay. McKay spent thirty years investigating the cause of what was then known as the Colorado Brown Stain, which produced mottled but also cavity-free teeth; with the help of G.V. Black and other researchers, he established that the cause was fluoride.[37]

In the 1930s and early 1940s, H. Trendley Dean and colleagues at the U.S. National Institutes of Health published several epidemiological studies suggesting that a fluoride concentration of about 1 mg/L was associated with substantially fewer cavities in temperate climates, and that it increased fluorosis but only to a level that was of no medical or aesthetic concern. Other studies found no other significant adverse effects even in areas with fluoride levels as high as 8 mg/L.[38] To test the hypothesis that adding fluoride would prevent cavities, Dean and his colleagues conducted a controlled experiment by fluoridating the water in Grand Rapids, Michigan starting on January 29, 1945. The results, published in 1950, showed significant reduction of cavities.[39] By present-day standards this and other pioneering studies were crude, but their large reductions in cavities convinced public health professionals of the benefits of fluoridation.[20]

Fluoridation became an official policy of the U.S. Public Health Service by 1951, and by 1960 water fluoridation had become widely used in the U.S., reaching about 50 million people.[38] By 2006, 69.2% of the U.S. population on public water systems were receiving fluoridated water, amounting to 61.5% of the total U.S. population; 3.0% of the population on public water systems were receiving naturally occuring fluoride.[30]

McKay's work had established that fluorosis occurred before tooth eruption. Dean and his colleagues assumed that fluoride's protection against cavities was also pre-eruptive, and this incorrect assumption was accepted for years. By 2000, however, the topical effects of fluoride (in both water and toothpaste) was well understood, and it had become known that a constant low level of fluoride in the mouth works best to prevent cavities.[20]

[edit] References

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  2. ^ a b Ripa LW (1993). "A half-century of community water fluoridation in the United States: review and commentary" (PDF). J Public Health Dent 53 (1): 17–44. PMID 8474047. http://aaphd.org/docs/position%20papers/A%20Half-Century%20of%20Community%20Water1993.pdf. Retrieved on 1 January 2009. 
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  4. ^ a b c d McDonagh MS, Whiting PF, Wilson PM et al. (2000). "Systematic review of water fluoridation" (PDF). BMJ 321 (7265): 855–9. doi:10.1136/bmj.321.7265.855. PMID 11021861. PMC: 27492. http://www.bmj.com/cgi/reprint/321/7265/855.pdf.  The full report is at: McDonagh MS, Whiting PF, Bradley M et al. (2000). "A systematic review of water fluoridation" (PDF). CRD Report 18. NHS Centre for Reviews and Dissemination.
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  19. ^ Top 10 U.S. public health achievements in 20th century:
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  32. ^ Ingram, Colin. (2006). The Drinking Water Book. pp. 15-16
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    • Peterson J (1997). "Solving the mystery of the Colorado Brown Stain". J Hist Dent 45 (2): 57–61. PMID 9468893. 
    • "The discovery of fluoride". Colorado Springs Dental Society (2004). Retrieved on 2009-01-08.
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