View source for Chemistry:Water fluoridation

{{Short description|Addition of fluoride to a water supply to reduce tooth decay}}
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[[File:Glass-half-full.jpeg|thumb|300px|upright=0.7|alt=Clear water pours from a spout into a drinking glass.|Fluoridation does not affect the appearance, taste or smell of drinking water.<ref name=Lamberg/>]]
<!-- Definition -->
'''Water fluoridation''' is the controlled adjustment of [[Chemistry:Fluoride|fluoride]] to a public water supply solely to reduce [[Medicine:Tooth decay|tooth decay]].<!-- <ref name=FWRG/> --> Fluoridated water contains fluoride at a level that is effective for preventing cavities; this can occur naturally or by adding fluoride.<ref name=FRWG/> Fluoridated water operates on tooth surfaces: in the mouth, it creates low levels of fluoride in [[Biology:Saliva|saliva]], which reduces the rate at which [[Biology:Tooth enamel|tooth enamel]] demineralizes and increases the rate at which it [[Medicine:Remineralisation of teeth|remineralizes]] in the early stages of cavities.<ref name=Pizzo/> Typically a fluoridated compound is added to drinking water, a process that in the U.S. costs an average of about ${{inflation|US|0.72|1999|r=2}} per person-year.<ref name=FRWG/>{{Inflation/fn|US}} [[Chemistry:Defluoridation|Defluoridation]] is needed when the naturally occurring fluoride level exceeds recommended limits.<ref name=Taricska/> In 2011, the [[Organization:World Health Organization|World Health Organization]] suggested a level of fluoride from 0.5 to 1.5&nbsp;mg/L (milligrams per litre), depending on [[Earth:Climate|climate]], local environment, and other sources of fluoride.<ref name=WHO2011/>  Bottled water typically has unknown fluoride levels.<ref name=Hobson/>

<!-- Health effects -->
Tooth decay remains a major public health concern in most industrialized countries, affecting 60–90% of schoolchildren and the vast majority of adults.<ref name=Petersen-2004/> Water fluoridation reduces cavities in children, while efficacy in adults is less clear.<ref name=Cochrane2015>{{cite journal | vauthors = Iheozor-Ejiofor Z, Worthington HV, Walsh T, et al |  title = Water fluoridation for the prevention of dental caries | journal = The Cochrane Database of Systematic Reviews | volume = 6 | issue = 6 | pages = CD010856 | date = June 2015 | pmid = 26092033 | pmc = 6953324 | doi = 10.1002/14651858.CD010856.pub2 }}</ref><ref name=Scher2011/> A [[Organization:Cochrane (organisation)|Cochrane]] review estimates 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.<ref name=Cochrane2015/> Most European countries have experienced substantial declines in tooth decay, though milk and salt fluoridation is widespread in lieu of water fluoridation.<ref>{{cite web |url=https://www.wda.org/wp_super_faq/european-countries-have-rejected-fluoridation-so-why-should-we-fluoridate-water |title=Question: European countries have rejected fluoridation, so why should we fluoridate water? |author=<!--Not stated--> |date= 8 March 2013 |website=www.wda.org |publisher=Wisconsin Dental Association |access-date=6 February 2018 |archive-url=https://web.archive.org/web/20190801044237/https://www.wda.org/wp_super_faq/european-countries-have-rejected-fluoridation-so-why-should-we-fluoridate-water |archive-date=1 August 2019 |url-status=dead}}</ref> Some studies suggest that water fluoridation, particularly in industrialized nations, may be unnecessary because [[Chemistry:Topical fluoride|topical fluorides]] (such as in [[Medicine:Toothpaste|toothpaste]]) are widely used, and [[Medicine:Tooth decay|caries]] rates have become low.<ref name=Pizzo/>

<!-- Side effects -->
Although fluoridation can cause dental fluorosis, which can alter the appearance of [[Medicine:Human tooth development|developing teeth]] or [[Biology:Tooth enamel|enamel fluorosis]];<ref name=Pizzo/> the differences are mild and usually not an aesthetic or public health concern.<ref name=NHMRC/> There is no clear evidence of other [[Medicine:Side effect|side effect]]s from water fluoridation.<ref name=YorkReview2000/> Fluoride's effects depend on the total daily intake of fluoride from all sources. Drinking water is typically the largest source;<ref name=Fawell/> other methods of [[Medicine:Fluoride therapy|fluoride therapy]] include fluoridation of toothpaste, salt, and milk.<ref name=Jones-PH/> The views on the most efficient method for community prevention of tooth decay are mixed. The Australian government states that water fluoridation is the most effective way to achieve fluoride exposure that is community-wide.<ref name=NHMRC/> The World Health Organization reports that water fluoridation, when feasible and culturally acceptable, has substantial advantages, especially for subgroups at high risk,<ref name=Petersen-2004/> while the European Commission finds no benefit to water fluoridation compared with topical use.<ref name=EU2011/>

<!-- Usage and positions-->
Public water fluoridation was first practiced in the U.S.<ref name=Sellers/> As of 2012, 25 countries have artificial water fluoridation to varying degrees, 11 of them have more than 50% of their population drinking fluoridated water. A further 28 countries have water that is naturally fluoridated, though in many of them the fluoride is above the optimal level.<ref name=extent2012/> As of 2012, about 435&nbsp;million people worldwide received water fluoridated at the recommended level (i.e., about 5.4% of the global population).<ref name=extent2012/>{{Rp|56}} About 214 million of them live in the United States.<ref name=US-CDC-WF-Stats-2012>{{cite web |url=https://www.cdc.gov/fluoridation/statistics/2014stats.htm |title=Community Water Fluoridation … 2014 Water Fluoridation Statistics |work=www.cdc.gov |access-date=19 April 2016}}</ref> Major health organizations such as the [[Organization:World Health Organization|World Health Organization]] and [[Organization:FDI World Dental Federation|FDI World Dental Federation]] supported water fluoridation as safe and effective.<ref>{{cite web|title=Support for Water Fluoridation|url=http://www.bfsweb.org/onemillion/11%20One%20in%20a%20Million%20-%20Support%20for%20Fluoridation.pdf|website=British Fluoridation Society|access-date=19 April 2016|date=2012|url-status=dead|archive-url=https://web.archive.org/web/20160306034706/http://bfsweb.org/onemillion/11%20One%20in%20a%20Million%20-%20Support%20for%20Fluoridation.pdf|archive-date=6 March 2016}}</ref> The Centers for Disease Control and Prevention lists water fluoridation as one of the ten great public health achievements of the 20th century in the U.S.<ref name=Ten-great>{{cite journal | vauthors = CDC | title = Ten great public health achievements – United States, 1900–1999 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 48 | issue = 12 | pages = 241–243 | date = April 1999 | pmid = 10220250 | url = http://cdc.gov/mmwr/preview/mmwrhtml/00056796.htm }}</ref> Despite this, the practice is controversial as a public health measure. Some countries and communities have discontinued fluoridation, while others have expanded it.<ref name=Scher2011>{{cite web|title=Introduction to the SCHER opinion on Fluoridation|url=http://ec.europa.eu/health/scientific_committees/opinions_layman/fluoridation/en/l-3/1.htm#0|publisher=European Commission Scientific Committee on Health and Environmental Risks (SCHER)|access-date=18 April 2016|date=2011}}</ref><ref name=Tienman2013>{{cite web|last1=Tiemann|first1=Mary|title=Fluoride in Drinking Water: A Review of Fluoridation and Regulation Issues|url=https://www.fas.org/sgp/crs/misc/RL33280.pdf|access-date=19 April 2016|date=5 April 2013|pages= 1–4}}</ref> Opponents of the practice argue that neither the benefits nor the risks have been studied adequately, and debate the conflict between what might be considered mass medication and individual liberties.<ref name=Tienman2013/><ref name="ChengChalmers2007">{{cite journal | vauthors = Cheng KK, Chalmers I, Sheldon TA | title = Adding fluoride to water supplies | journal = BMJ | volume = 335 | issue = 7622 | pages = 699–702 | date = October 2007 | pmid = 17916854 | pmc = 2001050 | doi = 10.1136/bmj.39318.562951.BE }}</ref>

== Goal ==
[[File:Dental caries.jpg|thumb|alt=Molar viewed from the top, with a cavity in the central pit, and a small amount of blood in nearby fissures.|A cavity starts in a tooth's outer enamel and spreads to the dentin and pulp inside.]]

The goal of water fluoridation is to prevent tooth decay by adjusting the concentration of fluoride in public water supplies.<ref name=FRWG/> Tooth decay (dental caries) is one of the most prevalent chronic diseases worldwide.<ref name=Selwitz/> Although it is rarely life-threatening, tooth decay can cause pain and impair [[Biology:Eating|eating]], speaking, facial appearance, and acceptance into society,<ref>{{cite journal |vauthors=Gibson-Moore H |title=Water fluoridation for some—should it be for all? |journal=Nutr Bull |date=2009 |volume=34 |issue=3 |pages=291–295 |doi=10.1111/j.1467-3010.2009.01762.x }}</ref> and it greatly affects the [[Philosophy:Quality of life|quality of life]] of children, particularly those of low [[Social:Socioeconomic status|socioeconomic status]].<ref name=Selwitz/> 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.<ref name=Petersen-2004/> In the U.S., minorities and the poor both have higher rates of decayed and missing teeth,<ref>{{cite journal | vauthors = Hudson K, Stockard J, Ramberg Z |title=The impact of socioeconomic status and race-ethnicity on dental health |journal=Sociol Perspect |volume=50 |issue=1 |pages=7–25 |year=2007 |doi=10.1525/sop.2007.50.1.7 |s2cid=30565431 |url=https://scholarsbank.uoregon.edu/xmlui/handle/1794/28139 }}</ref> and their children have less dental care.<ref>{{cite journal | vauthors = Vargas CM, Ronzio CR | title = Disparities in early childhood caries | journal = BMC Oral Health | volume = 6 | issue = Suppl 1 | pages = S3 | date = June 2006 | pmid = 16934120 | pmc = 2147596 | doi = 10.1186/1472-6831-6-S1-S3 | doi-access = free }}</ref> Once a cavity occurs, the tooth's fate is that of repeated [[Medicine:Dental restoration|restorations]], with estimates for the median life of an [[Chemistry:Amalgam (dentistry)|amalgam]] tooth filling ranging from 9 to 14 years.<ref name=Griffin-econ/> Oral disease is the fourth most expensive disease to treat.<ref name=WHA-2007>{{cite journal | vauthors = Petersen PE | title = World Health Organization global policy for improvement of oral health--World Health Assembly 2007 | journal = International Dental Journal | volume = 58 | issue = 3 | pages = 115–121 | date = June 2008 | pmid = 18630105 | doi = 10.1111/j.1875-595x.2008.tb00185.x | doi-access = free }}</ref> The motivation for fluoridation of salt or water is similar to that of iodized salt for the prevention of congenital hypothyroidism and goiter.<ref name=Horowitz>{{cite journal | vauthors = Horowitz HS | title = Decision-making for national programs of community fluoride use | journal = Community Dentistry and Oral Epidemiology | volume = 28 | issue = 5 | pages = 321–329 | date = October 2000 | pmid = 11014508 | doi = 10.1034/j.1600-0528.2000.028005321.x }}</ref>

The goal of water fluoridation is to prevent a chronic disease whose burdens particularly fall on children and the poor.<ref name=Selwitz/> Another of the goals was to bridge inequalities in dental health and [[Medicine:Dentistry|dental care]].<ref name=Burt/> Some studies suggest that fluoridation reduces oral health [[Social:Economic inequality|inequalities between the rich and poor]], but the evidence is limited.<ref name=Pizzo/> There is anecdotal but not scientific evidence that fluoride allows more time for dental treatment by slowing the progression of tooth decay, and that it simplifies treatment by causing most cavities to occur in pits and fissures of teeth.<ref name=Kumar2008/> Other reviews have found not enough evidence to determine if water fluoridation reduces oral-health social disparities.<ref name=Cochrane2015/><!-- Quote = There is insufficient information to determine whether initiation of a water fluoridation programme results in a change in disparities in caries across socioeconomic status (SES) levels. -->

Health and dental organizations worldwide have endorsed its safety and effectiveness.<ref name=Pizzo/> Its use began in 1945, following studies of children in a region where higher levels of fluoride occur naturally in the water.<ref name=NICDR/> Further research showed that moderate fluoridation prevents tooth decay.<ref name=Ripa/>

== Implementation ==
[[File:Fluoride-monitor-Anderson-1987.jpeg|thumb|alt=Large water pipes next to monitoring equipment.|Fluoride monitor (at left) in a community water tower pumphouse, Minnesota, 1987]]

Fluoridation does not affect the appearance, taste, or smell of drinking water.<ref name=Lamberg>{{cite journal | vauthors = Lamberg M, Hausen H, Vartiainen T | title = Symptoms experienced during periods of actual and supposed water fluoridation | journal = Community Dentistry and Oral Epidemiology | volume = 25 | issue = 4 | pages = 291–295 | date = August 1997 | pmid = 9332806 | doi = 10.1111/j.1600-0528.1997.tb00942.x }}</ref> It is normally accomplished by adding one of three compounds to the water: sodium fluoride, fluorosilicic acid, or sodium fluorosilicate.
* [[Chemistry:Sodium fluoride|Sodium fluoride]] (NaF) was the first compound used and is the reference standard.<ref name=Reeves/> It is a white, odorless powder or crystal; the crystalline form is preferred if manual handling is used, as it minimizes dust.<ref name=WFPP-theory/> It is more expensive than the other compounds, but is easily handled and is usually used by smaller utility companies.<ref>{{cite book |chapter=Fluoride in dentistry and dental restoratives | vauthors = Nicholson JW, Czarnecka B |title=Fluorine and Health |veditors=Tressaud A, Haufe G |year=2008 |publisher=Elsevier |isbn=978-0444530868 |pages=333–378 }}</ref> It is toxic in gram quantities by ingestion or inhalation.<ref>[http://hazard.com/msds/mf/baker/baker/files/s3722.htm NaF MSDS]. hazard.com</ref>
* Fluorosilicic acid (H<sub>2</sub>SiF<sub>6</sub>) is the most commonly used additive for water fluoridation in the United States.<ref>{{cite web|title=Water Fluoridation Additives Fact Sheet|url=https://www.cdc.gov/fluoridation/factsheets/engineering/wfadditives.htm|website=cdc.gov|access-date=27 January 2015|url-status=dead|archive-url=https://web.archive.org/web/20150221093801/http://www.cdc.gov/fluoridation/factsheets/engineering/wfadditives.htm|archive-date=21 February 2015}}</ref> It is an inexpensive liquid by-product of phosphate fertilizer manufacture.<ref name=Reeves/> It comes in varying strengths, typically 23–25%; because it contains so much water, shipping can be expensive.<ref name=WFPP-theory/> It is also known as hexafluorosilicic, hexafluosilicic, hydrofluosilicic, and silicofluoric acid.<ref name=Reeves/>
* [[Chemistry:Sodium fluorosilicate|Sodium fluorosilicate]] (Na<sub>2</sub>SiF<sub>6</sub>) is the sodium salt of fluorosilicic acid. It is a powder or very fine crystal that is easier to ship than fluorosilicic acid. It is also known as sodium silicofluoride.<ref name=WFPP-theory>{{cite book |title=Water Fluoridation Principles and Practices |publisher=American Water Works Association |date=2004 |edition=5th |series=Manual of Water Supply Practices |volume=M4 |chapter=History, theory, and chemicals |pages=1–14 |isbn=1583213112 | vauthors = Lauer WC }}</ref>

These compounds were chosen for their [[Chemistry:Solubility|solubility]], safety, availability, and low cost.<ref name=Reeves>{{cite web |title=Water fluoridation: a manual for engineers and technicians | vauthors = Reeves TG |url=http://www.cdph.ca.gov/certlic/drinkingwater/Documents/Fluoridation/CDC-FluoridationManual-1986.pdf |access-date=10 December 2008 |publisher=Centers for Disease Control |year=1986 |url-status=dead|archive-url=https://web.archive.org/web/20081007233737/http://www.cdph.ca.gov/certlic/drinkingwater/Documents/Fluoridation/CDC-FluoridationManual-1986.pdf |archive-date=7 October 2008 }}</ref> 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 fluorosilicic acid, 28% with sodium fluorosilicate, and 9% with sodium fluoride.<ref>{{cite report |url=http://cdc.gov/fluoridation/pdf/statistics/1992.pdf |title=Fluoridation census 1992 |publisher=Division of Oral Health, National Center for Prevention Services, CDC |year=1993 |access-date=29 December 2008 }}</ref>

===Recommendations===
The Centers for Disease Control and Prevention developed recommendations for water fluoridation that specify requirements for personnel, reporting, training, inspection, monitoring, surveillance, and actions in case of overfeed, along with technical requirements for each major compound used.<ref>{{cite journal | title = Engineering and administrative recommendations for water fluoridation, 1995. Centers for Disease Control and Prevention | journal = MMWR. Recommendations and Reports | volume = 44 | issue = RR-13 | pages = 1–40 | date = September 1995 | pmid = 7565542 | url = http://cdc.gov/mmwr/preview/mmwrhtml/00039178.htm }}</ref>

Although fluoride was once considered an essential nutrient, the U.S. National Research Council has since removed this designation due to the lack of studies showing it is essential for human growth, though still considering fluoride a "beneficial element" due to its positive impact on oral health.<ref>{{cite journal | vauthors = Burt BA | title = The changing patterns of systemic fluoride intake | journal = Journal of Dental Research | volume = 71 | issue = 5 | pages = 1228–1237 | date = May 1992 | pmid = 1607439 | doi = 10.1177/00220345920710051601 | url = https://deepblue.lib.umich.edu/bitstream/2027.42/67895/2/10.1177_00220345920710051601.pdf | hdl = 2027.42/67895 | s2cid = 8491518 }}</ref> 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 [[Chemistry:Dietary Reference Intake|Adequate Intake]] (AI) value for it. The AI of fluoride from all sources (including non-dietary sources) is 0.05&nbsp;mg/kg body weight per day for both children and adults, including pregnant and lactating women.<ref>{{cite journal|title=Scientific Opinion on Dietary Reference Values for fluoride |author=European Food Safety Authority|journal=EFSA Journal|date=2013|page=46|doi=10.2903/j.efsa.2013.3332|url=http://www.efsa.europa.eu/en/efsajournal/pub/3332|access-date=19 April 2015|volume=11|issue=8|doi-access=free}}</ref>

In 2011, the U.S. Department of Health and Human Services (HHS) and the U.S. Environmental Protection Agency (EPA) lowered the recommended level of fluoride to 0.7&nbsp;mg/L.<ref name=HHSEPA2011>{{cite web|url=http://yosemite.epa.gov/opa/admpress.nsf/6427a6b7538955c585257359003f0230/86964af577c37ab285257811005a8417!OpenDocument|year=2011|title=HHS and EPA announce new scientific assessments and actions on fluoride|author=U.S. Department of Health & Human Services}}</ref> In 2015, the U.S. Food and Drug Administration (FDA), based on the recommendation of the U.S. Public Health Service (PHS) for fluoridation of community water systems, recommended that bottled water manufacturers limit fluoride in bottled water to no more than 0.7 milligrams per liter (mg/L; equivalent to [[Parts per million|parts per million]]).<ref>{{cite web|title=FDA Issues a Letter for Manufacturers with Recommendations on Fluoride Added to Bottled Water|website=[[Organization:Food and Drug Administration|Food and Drug Administration]]|url=https://www.fda.gov/Food/NewsEvents/ConstituentUpdates/ucm444401.htm|access-date=6 May 2015|date=27 April 2015}}</ref>

Previous recommendations were based on  evaluations from 1962, when the U.S. specified the optimal level of fluoride to range from 0.7 to 1.2&nbsp;mg/L, 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.<ref name=CDC-1992-2006>{{cite journal | vauthors = Bailey W, Barker L, Duchon K, Maas W | title = Populations receiving optimally fluoridated public drinking water--United States, 1992-2006 | journal = MMWR. Morbidity and Mortality Weekly Report | volume = 57 | issue = 27 | pages = 737–741 | date = July 2008 | pmid = 18614991 | url = http://cdc.gov/mmwr/preview/mmwrhtml/mm5727a1.htm }}</ref>

These standards are not appropriate for all parts of the world, where fluoride levels might be excessive and fluoride should be removed from water, and is based on assumptions that have become obsolete with the rise of [[Physics:Air conditioning|air conditioning]] and increased use of soft drinks, ultra-processed food, [[Medicine:Toothpaste#Fluorides|fluoridated toothpaste]], and other sources of fluorides.<ref name=WHO2011/> In 2011, the World Health Organization stated that 1.5&nbsp;mg/L should be an absolute upper bound  and that 0.5&nbsp;mg/L may be an appropriate lower limit.<ref name=WHO2011>[http://apps.who.int/iris/bitstream/10665/44584/1/9789241548151_eng.pdf Guidelines for Drinking-water Quality, 4th Edition] WHO, 2011. {{ISBN|978-9241548151}}. p. 168, 175, 372 and see also pp 370–373.  See also J. Fawell, et al  [http://apps.who.int/iris/bitstream/10665/43514/1/9241563192_eng.pdf?ua=1 Fluoride in Drinking-water].  WHO, 2006. p. 32. Quote: "Concentrations in drinking-water of about 1 mg l–1 are associated with a lower incidence of dental caries, particularly in children, whereas excess intake of fluoride can result in dental fluorosis. In severe cases this can result in erosion of enamel. The margin between the beneficial effects of fluoride and the occurrence of dental fluorosis is small and public health programmes seek to retain a suitable balance between the two"</ref> A 2007 Australian systematic review recommended a range from 0.6 to 1.1&nbsp;mg/L.<ref name=NHMRC>{{cite book |url=http://nhmrc.gov.au/_files_nhmrc/file/publications/synopses/Eh41_Flouridation_PART_A.pdf |access-date=13 October 2009 |year=2007 |title=A systematic review of the efficacy and safety of fluoridation |author=National Health and Medical Research Council (Australia) |isbn=978-1864964158 |archive-date=14 October 2009 |archive-url=https://web.archive.org/web/20091014191758/http://www.nhmrc.gov.au/_files_nhmrc/file/publications/synopses/Eh41_Flouridation_PART_A.pdf |url-status=dead }} Summary: {{cite journal | vauthors = Yeung CA | title = A systematic review of the efficacy and safety of fluoridation | journal = Evidence-Based Dentistry | volume = 9 | issue = 2 | pages = 39–43 | year = 2008 | pmid = 18584000 | doi = 10.1038/sj.ebd.6400578 | doi-access = free}} See also [http://nhmrc.gov.au/_files_nhmrc/file/media/media/rel07/Fluoride_Flyer.pdf lay summary] from NHMRC, 2007.</ref>

[[File:Groundwater-fluoride-world.svg|thumb|300px|alt=World map with several land areas highlighted, especially in China, India, east Africa, southwest U.S., and Argentina.|Geographical areas associated with [[Earth:Groundwater|groundwater]] having over 1.5&nbsp;mg/L of naturally occurring fluoride, which is above recommended levels<ref name=NHMRC/>]]
[[File:Southern-Arizona-fluoride-groundwater.jpeg|thumb|alt=Southern Arizona map with a jumble of regions colored gray, white, and blues of various shades.|Detail of southern Arizona. Areas in darker blues have groundwater with over 2&nbsp;mg/L of naturally occurring fluoride.]]

===Occurrences===
Fluoride naturally occurring in water can be above, at, or below recommended levels. Rivers and lakes generally contain fluoride levels less than 0.5&nbsp;mg/L, but groundwater, particularly in volcanic or mountainous areas, can contain as much as 50&nbsp;mg/L.<ref name=Fawell>{{cite book |chapter=Environmental occurrence, geochemistry and exposure |title=Fluoride in Drinking-water | vauthors = Fawell J, Bailey K, Chilton J, Dahi E, Fewtrell L, Magara Y |publisher=World Health Organization |isbn=9241563192 |year=2006 |url=https://www.who.int/water_sanitation_health/publications/fluoride_drinking_water_full.pdf |pages=5–27 }}</ref> Higher concentrations of [[Chemistry:Fluorine|fluorine]] are found in [[Chemistry:Alkaline|alkaline]] [[Earth:Volcanic rock|volcanic]], [[Earth:Hydrothermal circulation#Hydrothermal ore deposits|hydrothermal]], sedimentary, and other [[Earth:Rock (geology)|rocks]] derived from highly evolved [[Biology:Magma|magma]]s and [[Chemistry:Ore genesis#Hydrothermal processes|hydrothermal solutions]], and this fluorine [[Chemistry:Solvation|dissolves]] into nearby water as fluoride. In most drinking waters, over 95% of total fluoride is the F<sup>−</sup> [[Physics:Ion|ion]], with the [[Chemistry:Magnesium|magnesium]]–fluoride [[Chemistry:Complex|complex]] (MgF<sup>+</sup>) being the next most common. Because fluoride levels in water are usually controlled by the solubility of [[Chemistry:Fluorite|fluorite]] (CaF<sub>2</sub>), high natural fluoride levels are associated with [[Chemistry:Calcium|calcium]]-deficient, alkaline, and [[Chemistry:Soft water|soft water]]s.<ref>{{cite journal | vauthors = Ozsvath DL |title=Fluoride and environmental health: a review |journal=Rev Environ Sci Biotechnol |year=2009 |volume=8 |issue=1 |pages=59–79 |doi=10.1007/s11157-008-9136-9 |bibcode=2009RESBT...8...59O |s2cid=85052718 }}</ref> Defluoridation is needed when the naturally occurring fluoride level exceeds recommended limits. It can be accomplished by percolating water through granular beds of [[Chemistry:Activated alumina|activated alumina]], [[Chemistry:Bone meal|bone meal]], bone char, or [[Chemistry:Tricalcium phosphate|tricalcium phosphate]]; by coagulation with [[Chemistry:Alum|alum]]; or by [[Chemistry:Precipitation|precipitation]] with lime.<ref name=Taricska>{{cite book | vauthors = Taricska JR, Wang LK, Hung YT, Li KH | chapter = Fluoridation and Defluoridation |title=Advanced Physicochemical Treatment Processes |veditors=Wang LK, Hung YT, Shammas NK |series=Handbook of Environmental Engineering 4 |doi=10.1007/978-1-59745-029-4_9 |isbn=978-1597450294 |publisher=Humana Press |year=2006 |pages=293–315 }}</ref>

Pitcher or faucet-mounted water filters do not alter fluoride content; the more-expensive [[Chemistry:Reverse osmosis|reverse osmosis]] filters remove 65–95% of fluoride, and [[Distillation|distillation]] removes all fluoride.<ref name=Hobson>{{cite journal | vauthors = Hobson WL, Knochel ML, Byington CL, Young PC, Hoff CJ, Buchi KF | title = Bottled, filtered, and tap water use in Latino and non-Latino children | journal = Archives of Pediatrics & Adolescent Medicine | volume = 161 | issue = 5 | pages = 457–461 | date = May 2007 | pmid = 17485621 | doi = 10.1001/archpedi.161.5.457 | url = http://archpedi.ama-assn.org/cgi/content/full/161/5/457 | doi-access = free }}</ref> Some bottled waters contain undeclared fluoride, which can be present naturally in source waters, or if water is sourced from a [[Earth:Tap water|public supply]] which has been fluoridated.<ref name=CDCBottle/>  The FDA states that bottled water products labeled as de-ionized, purified, demineralized, or distilled have been treated in such a way that they contain no or only trace amounts of fluoride, unless they specifically list fluoride as an added ingredient.<ref name=CDCBottle>{{cite web|title=CDC – Bottled Water and Fluoride – Fact Sheets – General – Community Water Fluoridation – Oral Health|url=https://www.cdc.gov/fluoridation/faqs/bottled_water.htm|website=www.cdc.gov|access-date=28 April 2016}}</ref>

== Evidence ==
Existing [[Medicine:Evidence-based medicine|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.<ref name=Cochrane2015/><ref name=NHMRC/> No clear evidence of other adverse effects exists, though almost all research thereof has been of poor quality.<ref name=YorkReview2000/>

=== Effectiveness ===
Reviews have shown that water fluoridation reduces cavities in children.<ref name=Cochrane2015/><ref name=EU2011>{{cite web|title=What role does fluoride play in preventing tooth decay?|url=http://ec.europa.eu/health/scientific_committees/opinions_layman/fluoridation/en/l-3/5.htm#0|year=2011|access-date=18 April 2016}}</ref><ref name=Parnell>{{cite journal | vauthors = Parnell C, Whelton H, O'Mullane D | title = Water fluoridation | journal = European Archives of Paediatric Dentistry | volume = 10 | issue = 3 | pages = 141–148 | date = September 2009 | pmid = 19772843 | doi = 10.1007/bf03262675 | s2cid = 5442458 }}</ref> A conclusion for the efficacy in adults is less clear with some reviews finding benefit and others not.<ref name=Cochrane2015/><ref name=Parnell/> 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.<ref name=FRWG/>

A 2000 UK [[Systematic review|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 [[Medicine:Dental restoration|filled]] primary teeth (average decreases was 2.25&nbsp;teeth). The review found that the evidence was of moderate quality: few studies attempted to reduce [[Observer bias|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.<ref name=YorkReview2000>{{cite web | vauthors = McDonagh M, Whiting P, Bradley M, et al |title=A systematic review of public water fluoridation |url=http://www.york.ac.uk/media/crd/crdreport18.pdf |year=2000 }} Report website: {{cite web |title=Fluoridation of drinking water: a systematic review of its efficacy and safety |publisher=NHS Centre for Reviews and Dissemination |date=2000 |url=http://www.york.ac.uk/inst/crd/fluorid.htm |access-date=26 May 2009 }} Authors' summary: {{cite journal | vauthors = McDonagh MS, Whiting PF, Wilson PM, et al | title = Systematic review of water fluoridation | journal = BMJ | volume = 321 | issue = 7265 | pages = 855–859 | date = October 2000 | pmid = 11021861 | pmc = 27492 | doi = 10.1136/bmj.321.7265.855 | url = }} Authors' commentary: {{cite journal | vauthors = Treasure ET, Chestnutt IG, Whiting P, McDonagh M, Wilson P, Kleijnen J | title = The York review – a systematic review of public water fluoridation: a commentary | journal = British Dental Journal | volume = 192 | issue = 9 | pages = 495–497 | date = May 2002 | pmid = 12047121 | doi = 10.1038/sj.bdj.4801410a | doi-access = free }}</ref> A 2007 Australian systematic review  used the same inclusion criteria as York's, plus one additional study. This did not affect the York conclusions.<ref>{{cite journal | vauthors = Richards D | title = Fluoridation | journal = Evidence-Based Dentistry | volume = 9 | issue = 2 | page = 34 | date = 1 January 2008 | pmid = 18583997 | doi = 10.1038/sj.ebd.6400575 | doi-access = free }}</ref> A 2011 European Commission systematic review based its efficacy on York's review conclusion.<ref name=Scher2011/> A 2015 [[Organization:Cochrane (organisation)|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.<ref name=Cochrane2015/> The evidence was of poor quality.<ref name=Cochrane2015/> A 2020 study in the ''[[Finance:Journal of Political Economy|Journal of Political Economy]]'' found that water fluoridation significantly improved dental health and labor market outcomes, but had non-significant effects on cognitive ability.<ref>{{Cite journal|last1=Aggeborn|first1=Linuz|last2=Öhman|first2=Mattias|date=2020-10-01|title=The Effects of Fluoride in the Drinking Water|url=https://www.journals.uchicago.edu/doi/abs/10.1086/711915|journal=Journal of Political Economy|volume=129|issue=2|pages=465–491|doi=10.1086/711915|s2cid=52267424|issn=0022-3808|hdl=10419/201430|hdl-access=free}}</ref>

Fluoride may also prevent cavities in adults of all ages. A 2007 [[Meta-analysis|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).<ref name=Griffin>{{cite journal | vauthors = Griffin SO, Regnier E, Griffin PM, Huntley V | title = Effectiveness of fluoride in preventing caries in adults | journal = Journal of Dental Research | volume = 86 | issue = 5 | pages = 410–415 | date = May 2007 | pmid = 17452559 | doi = 10.1177/154405910708600504 | s2cid = 58958881 | url = http://jdr.sagepub.com/cgi/content/full/86/5/410 | access-date = 13 February 2009 | archive-date = 19 April 2010 | archive-url = https://web.archive.org/web/20100419024226/http://jdr.sagepub.com/cgi/content/full/86/5/410 | url-status = dead }} Summary: {{cite journal | vauthors = Yeung CA | title = Fluoride prevents caries among adults of all ages | journal = Evidence-Based Dentistry | volume = 8 | issue = 3 | pages = 72–73 | year = 2007 | pmid = 17891121 | doi = 10.1038/sj.ebd.6400506 | doi-access = free }}</ref> A 2011 European Commission review found that the benefits of water fluoridation for adult in terms of reductions in decay are limited.<ref name=EU2011/> A 2015 Cochrane review found no conclusive research regarding the effectiveness of water fluoridation in adults.<ref name=Cochrane2015/> A 2016 review found variable quality evidence that, overall, stopping of community water fluoridation programs was typically followed by an increase in cavities.<ref>{{cite journal | vauthors = McLaren L, Singhal S | title = Does cessation of community water fluoridation lead to an increase in tooth decay? A systematic review of published studies | journal = Journal of Epidemiology and Community Health | volume = 70 | issue = 9 | pages = 934–940 | date = September 2016 | pmid = 27177581 | doi = 10.1136/jech-2015-206502 | pmc = 5013153 | doi-access = free }}</ref>

Most countries in Europe have experienced substantial declines in cavities without the use of water fluoridation due to the introduction of fluoridated toothpaste and the large use of other fluoride-containing products, including mouthrinse, dietary supplements, and professionally applied or prescribed gel, foam, or varnish.<ref name=Pizzo/> For example, in Finland and Germany, tooth decay rates remained stable or continued to decline after water fluoridation stopped in communities with widespread fluoride exposure from other sources. Fluoridation is however still clearly necessary in the U.S. because unlike most European countries, the U.S. does not have school-based dental care, many children do not visit a dentist regularly, and for many U.S. children water fluoridation is the primary source of exposure to fluoride.<ref name=Burt>{{cite book | vauthors = Burt BA, Tomar SL |chapter=Changing the face of America: water fluoridation and oral health |pages=307–322 |title=Silent Victories: The History and Practice of Public Health in Twentieth-century America |editor=Ward JW, Warren C |publisher=Oxford University Press |year=2007 |isbn=978-0195150698 }}</ref> The effectiveness of water fluoridation can vary according to circumstances such as whether preventive dental care is free to all children.<ref>{{cite journal | vauthors = Hausen HW | title = Fluoridation, fractures, and teeth | journal = BMJ | volume = 321 | issue = 7265 | pages = 844–845 | date = October 2000 | pmid = 11021844 | pmc = 1118662 | doi = 10.1136/bmj.321.7265.844 }}</ref>

=== Fluorosis ===
[[File:MildFluorosis02-24-09.jpg|thumb|alt=Closeup of a smiling mouth with teeth showing minor white streaks on one tooth.|A mild case of dental fluorosis, visible as white streaks on the subject's upper right central incisor]]

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 [[Medicine:Human tooth development|tooth development]]; this is mostly mild and is unlikely to represent any real effect on aesthetic appearance or on public health.<ref name=NHMRC/> In April 2015, recommended fluoride levels in the United States were changed to 0.7 ppm from 0.7–1.2 ppm to reduce the risk of dental fluorosis.<ref name=US2015CDC/> 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%.<ref name=Cochrane2015/> This increases to 40% when considering fluorosis of any level not of aesthetic concern.<ref name=Cochrane2015/> 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%.<ref name=US2015CDC>{{cite web|access-date=9 May 2015|url=http://www.publichealthreports.org/documents/PHS_2015_Fluoride_Guidelines.pdf|title=U.S. Public Health Service Recommendation for Fluoride Concentration in Drinking Water for the Prevention of Dental Caries|publisher=CDC|archive-date=18 May 2015|archive-url=https://web.archive.org/web/20150518095539/http://www.publichealthreports.org/documents/PHS_2015_Fluoride_Guidelines.pdf|url-status=dead}}</ref>

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%.<ref>{{cite journal | vauthors = Abanto Alvarez J, Rezende KM, Marocho SM, Alves FB, Celiberti P, Ciamponi AL | title = Dental fluorosis: exposure, prevention and management | journal = Medicina Oral, Patologia Oral y Cirugia Bucal | volume = 14 | issue = 2 | pages = E103–E107 | date = February 2009 | pmid = 19179949 | url = http://medicinaoral.com/medoralfree01/v14i2/medoralv14i2p103.pdf }}</ref> Compared to water naturally fluoridated at 0.4&nbsp;mg/L, fluoridation to 1&nbsp;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 aesthetic concern in one of every 22 people (95% CI 13.6–∞ people). Here, ''aesthetic concern'' is a term used in a standardized scale based on what adolescents would find unacceptable, as measured by a 1996 study of British 14-year-olds.<ref name=YorkReview2000/> In many industrialized countries the [[Prevalence|prevalence]] of fluorosis is increasing even in unfluoridated communities, mostly because of fluoride from swallowed toothpaste.<ref name=Sheiham>{{cite journal | vauthors = Sheiham A | title = Dietary effects on dental diseases | journal = Public Health Nutrition | volume = 4 | issue = 2B | pages = 569–591 | date = April 2001 | pmid = 11683551 | doi = 10.1079/PHN2001142 | doi-access = free }}</ref> A 2009 systematic review indicated that fluorosis is associated with consumption of infant formula or of water added to reconstitute the formula, that the evidence was distorted by [[Publication bias|publication bias]], and that the evidence that the formula's fluoride caused the fluorosis was weak.<ref>{{cite journal | vauthors = Hujoel PP, Zina LG, Moimaz SA, Cunha-Cruz J | title = Infant formula and enamel fluorosis: a systematic review | journal = Journal of the American Dental Association | volume = 140 | issue = 7 | pages = 841–854 | date = July 2009 | pmid = 19571048 | doi = 10.14219/jada.archive.2009.0278 }}</ref> In the U.S. 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.<ref name=Kumar2008/>

=== Safety ===
Fluoridation has little effect on risk of [[Medicine:Bone fracture|bone fracture]] (broken bones); it may result in slightly lower fracture risk than either excessively high levels of fluoridation or no fluoridation.<ref name=NHMRC/>

There is no clear association between water fluoridation and [[Medicine:Cancer|cancer]] or deaths due to cancer, both for cancer in general and also specifically for bone cancer and osteosarcoma.<ref>{{cite book |url=http://nhmrc.gov.au/_files_nhmrc/file/publications/synopses/Eh41_Flouridation_PART_A.pdf |access-date=2009-10-13 |year=2007 |title=A systematic review of the efficacy and safety of fluoridation |author=National Health and Medical Research Council (Australia) |isbn=978-1864964158 |archive-url=https://web.archive.org/web/20091014191758/http://www.nhmrc.gov.au/_files_nhmrc/file/publications/synopses/Eh41_Flouridation_PART_A.pdf |archive-date=2009-10-14 |url-status=dead }}</ref> Series of research concluded that concentration of fluoride in water does not associate with osteosarcoma. The beliefs regarding association of fluoride exposure and osteosarcoma stem from a study of US National Toxicology program in 1990, which showed uncertain evidence of association of fluoride and osteosarcoma in male rats. But there is still no solid evidence of cancer-causing tendency of fluoride in mice.<ref>[http://www.cancer.org/cancer/cancercauses/othercarcinogens/athome/water-fluoridation-and-cancer-risk "Water Fluoridation and Cancer Risk"], ''American Cancer Society'', 6 June 2013.</ref> Fluoridation of water has been practiced around the world to improve citizens' dental health. It is also deemed as major health success.<ref>[https://www.cancerwa.asn.au/resources/cancermyths/fluoride-cancer-myth/ "Cancer myth: Fluoride and cancer"], ''Cancer Council Western Australia''.</ref> Fluoride concentration levels in water supplies are regulated, such as United States Environmental Protection Agency regulates fluoride levels to not be greater than 4 milligrams per liter.<ref>[http://water.epa.gov/drink/contaminants/basicinformation/fluoride.cfm "Basic Information about Fluoride in Drinking Water"], ''United States Environmental Protection Agency''.</ref> Actually, water supplies already have natural occurring fluoride, but many communities chose to add more fluoride to the point that it can reduce tooth decay.<ref>[https://www.cdc.gov/fluoridation/faqs/ "Community Water Fluoridation"], ''Centers of disease control and prevention''.</ref> Fluoride is also known for its ability to cause new bone formation.<ref>[https://www.nrv.gov.au/nutrients/fluoride "Fluoride"], ''Australian government national health and medical research council''.</ref>  Yet, further research shows no osteosarcoma risks from fluoridated water in humans.<ref>[http://www.cancer.gov/cancertopics/factsheet/Risk/fluoridated-water "Fluoridated Water"], ''National Cancer Institute''.</ref> Most of the research involved counting number of osteosarcoma patients cases in particular areas which has difference concentrations of fluoride in drinking water.<ref>{{cite journal|vauthors=Blakey K, Feltbower RG, Parslow RC, James PW, ((Gómez Pozo B)), Stiller C, Vincent TJ, Norman P, McKinney PA, Murphy MF, Craft AW, McNally RJ|title=Is fluoride a risk factor for bone cancer? Small area analysis of osteosarcoma and Ewing sarcoma diagnosed among 0–49-year-olds in Great Britain, 1980–2005|journal=International Journal of Epidemiology|date=14 January 2014|volume=43|issue=1|pages=224–234|doi=10.1093/ije/dyt259|pmc=3937980|pmid=24425828}}</ref> The statistic analysis of the data shows no significant difference in occurrences of osteosarcoma cases in different fluoridated regions.<ref>{{cite journal|vauthors=Mahoney MC, Nasca PC, Burnett WS, Melius JM|title=Bone cancer incidence rates in New York State: time trends and fluoridated drinking water|journal=American Journal of Public Health|date=April 1991|volume=81|issue=4|pages=475–479|doi=10.2105/AJPH.81.4.475|pmc=1405037|pmid=2003628}}</ref> Another important research involved collecting bone samples from osteosarcoma patients to measure fluoride concentration and compare them to bone samples of newly diagnosed malignant bone tumors. The result is that the median fluoride concentrations in bone samples of osteosarcoma patients and tumor controls are not significantly different.<ref>{{cite journal|vauthors=Kim FM, Hayes C, Williams PL, Whitford GM, Joshipura KJ, Hoover RN, Douglass CW, ((National Osteosarcoma Etiology Group))|title=An assessment of bone fluoride and osteosarcoma|journal=Journal of Dental Research|date=October 2011|volume=90|issue=10|pages=1171–1176|doi=10.1177/0022034511418828|pmc=3173011|pmid=21799046}}</ref> Not only fluoride concentration in bones, Fluoride exposures of osteosarcoma patients are also proven to be not significantly different from healthy people.<ref>{{cite journal|vauthors=Gelberg KH, Fitzgerald EF, Hwang SA, Dubrow R|title=Fluoride exposure and childhood osteosarcoma: a case-control study|journal=American Journal of Public Health|date=December 1995|volume=85|issue=12|pages=1678–1683|doi=10.2105/AJPH.85.12.1678|pmc=1615731|pmid=7503344}}</ref> More recent studies have disputed any relationship to consumption of fluoridated drinking water during childhood.<ref>{{Cite journal|last1=Lindsey|first1=Brock A.|last2=Markel|first2=Justin E.|last3=Kleinerman|first3=Eugenie S.|date=2016-12-08|title=Osteosarcoma Overview|journal=Rheumatology and Therapy|volume=4|issue=1|pages=25–43|doi=10.1007/s40744-016-0050-2|issn=2198-6576|pmc=5443719|pmid=27933467}}</ref>

Fluoride can occur naturally in water in concentrations well above recommended levels, which can have several long-term adverse effects, including severe dental fluorosis, [[Medicine:Skeletal fluorosis|skeletal fluorosis]], and weakened bones; water utilities in the developed world reduce fluoride levels to regulated maximum levels in regions where natural levels are high, and the WHO and other groups work with countries and regions in the developing world with naturally excessive fluoride levels to achieve safe levels.<ref name=Hhe>{{cite book |chapter=Human health effects |title=Fluoride in Drinking-water | vauthors = Fawell J, Bailey K, Chilton J, Dahi E, Fewtrell L, Magara Y |publisher=World Health Organization |isbn=9241563192 |year=2006 |url=https://www.who.int/water_sanitation_health/publications/fluoride_drinking_water_full.pdf |pages=29–36 }}</ref> The World Health Organization recommends a guideline maximum fluoride value of 1.5&nbsp;mg/L as a level at which fluorosis should be minimal.<ref>{{cite book |chapter=Guidelines and standards |title=Fluoride in Drinking-water | vauthors = Fawell J, Bailey K, Chilton J, Dahi E, Fewtrell L, Magara Y |publisher=World Health Organization |isbn=9241563192 |year=2006 |url=https://www.who.int/water_sanitation_health/publications/fluoride_drinking_water_full.pdf |pages=37–39 }}</ref>

In rare cases improper implementation of water fluoridation can result in overfluoridation that causes outbreaks of acute fluoride poisoning, with symptoms that include nausea, [[Medicine:Vomiting|vomiting]], and [[Medicine:Diarrhea|diarrhea]]. Three such outbreaks were reported in the U.S. between 1991 and 1998, caused by fluoride concentrations as high as 220&nbsp;mg/L; in the 1992 Alaska outbreak, 262 people became ill and one person died.<ref>{{cite journal | vauthors = Balbus JM, Lang ME | title = Is the water safe for my baby? | journal = Pediatric Clinics of North America | volume = 48 | issue = 5 | pages = 1129–1152, viii | date = October 2001 | pmid = 11579665 | doi = 10.1016/S0031-3955(05)70365-5 }}</ref> In 2010, approximately 60 gallons of fluoride were released into the water supply in Asheboro, North Carolina in 90 minutes—an amount that was intended to be released in a 24-hour period.<ref>{{cite news |publisher= Fox 8 |title= Asheboro notifies residents of over-fluoridation of water |date= 29 June 2010 |url= http://www.myfox8.com/news/wghp-asheboro-fluoride-release-100629,0,2164002.story |url-status= dead|archive-url= https://web.archive.org/web/20100704054308/http://www.myfox8.com/news/wghp-asheboro-fluoride-release-100629,0,2164002.story |archive-date= 4 July 2010 }}</ref>

Like other common water additives such as [[Chemistry:Water chlorination|chlorine]], hydrofluosilicic acid and sodium silicofluoride decrease pH and cause a small increase of [[Chemistry:Corrosivity|corrosivity]], but this problem is easily addressed by increasing the pH.<ref name=Pollick/> Although it has been hypothesized that hydrofluosilicic acid and sodium silicofluoride might increase human [[Chemistry:Lead|lead]] uptake from water, a 2006 statistical analysis did not support concerns that these chemicals cause higher blood lead concentrations in children.<ref>{{cite journal | vauthors = Macek MD, Matte TD, Sinks T, Malvitz DM | title = Blood lead concentrations in children and method of water fluoridation in the United States, 1988-1994 | journal = Environmental Health Perspectives | volume = 114 | issue = 1 | pages = 130–134 | date = January 2006 | pmid = 16393670 | pmc = 1332668 | doi = 10.1289/ehp.8319 }}</ref> Trace levels of [[Chemistry:Arsenic|arsenic]] and lead may be present in fluoride compounds added to water, but no credible evidence exists that their presence is of concern: [[Chemistry:Concentration|concentration]]s are below measurement limits.<ref name=Pollick/>

The effect of water fluoridation on the natural 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.<ref name=Pollick>{{cite journal | vauthors = Pollick HF | title = Water fluoridation and the environment: current perspective in the United States | journal = International Journal of Occupational and Environmental Health | volume = 10 | issue = 3 | pages = 343–350 | year = 2004 | pmid = 15473093 | doi = 10.1179/oeh.2004.10.3.343 | s2cid = 8577186 | url = http://cdc.gov/FLUORIDATION/pdf/pollick.pdf }}</ref>

== Mechanism ==
Fluoride exerts its major effect by interfering with the demineralization mechanism of tooth decay. Tooth decay is an [[Medicine:Infectious disease|infectious disease]], the key feature of which is an increase within dental plaque of bacteria such as ''[[Biology:Streptococcus mutans|Streptococcus mutans]]'' and ''[[Biology:Lactobacillus|Lactobacillus]]''. These produce organic acids when carbohydrates, especially sugar, are eaten.<ref name=Featherstone/> When enough acid is produced to lower the [[Chemistry:PH|pH]] below 5.5,<ref name=Cury/> the acid dissolves [[Chemistry:Carbonate|carbonate]]d [[Chemistry:Hydroxyapatite|hydroxyapatite]], the main component of tooth enamel, in a process known as ''demineralization''. After the sugar is gone, some of the mineral loss can be recovered—or ''[[Medicine:Remineralisation of teeth|remineralized]]''—from ions dissolved in the saliva. Cavities result when the rate of demineralization exceeds the rate of remineralization, typically in a process that requires many months or years.<ref name=Featherstone/>

[[File:Enamel-fluoride-remineralization.svg|thumb|left|upright|alt=Carbonated hydroxyapatite enamel crystal is demineralized by acid in plaque and becomes partly dissolved crystal. This in turn is remineralized by fluoride in plaque to become fluorapatite-like coating on remineralized crystal|Demineralization and remineralization of dental enamel in the presence of acid and fluoride in saliva and plaque fluid<ref name=Featherstone/>]]
All fluoridation methods, including water fluoridation, create low levels of fluoride ions in saliva and plaque fluid, thus exerting a topical or surface effect. A person living in an area with fluoridated water may experience rises of fluoride concentration in saliva to about 0.04&nbsp;mg/L several times during a day.<ref name=Pizzo>{{cite journal | vauthors = Pizzo G, Piscopo MR, Pizzo I, Giuliana G | title = Community water fluoridation and caries prevention: a critical review | journal = Clinical Oral Investigations | volume = 11 | issue = 3 | pages = 189–193 | date = September 2007 | pmid = 17333303 | doi = 10.1007/s00784-007-0111-6 | s2cid = 13189520 }}</ref> Technically, this fluoride does not prevent cavities but rather controls the rate at which they develop.<ref>{{cite journal | vauthors = Aoba T, Fejerskov O | title = Dental fluorosis: chemistry and biology | journal = Critical Reviews in Oral Biology and Medicine | volume = 13 | issue = 2 | pages = 155–170 | year = 2002 | pmid = 12097358 | doi = 10.1177/154411130201300206 | url = http://cro.sagepub.com/cgi/content/full/13/2/155 | access-date = 13 February 2009 | archive-date = 1 June 2009 | archive-url = https://web.archive.org/web/20090601030650/http://cro.sagepub.com/cgi/content/full/13/2/155 | url-status = dead }}</ref> When fluoride ions are present in plaque fluid along with dissolved hydroxyapatite, and the pH is higher than 4.5,<ref name=Cury>{{cite journal | vauthors = Cury JA, Tenuta LM | title = How to maintain a cariostatic fluoride concentration in the oral environment | journal = Advances in Dental Research | volume = 20 | issue = 1 | pages = 13–16 | date = July 2008 | pmid = 18694871 | doi = 10.1177/154407370802000104 | s2cid = 34423908 | url = http://adr.sagepub.com/cgi/content/full/20/1/13 | access-date = 13 September 2009 | archive-date = 3 June 2009 | archive-url = https://web.archive.org/web/20090603013643/http://adr.sagepub.com/cgi/content/full/20/1/13 | url-status = dead }}</ref> a [[Chemistry:Fluorapatite|fluorapatite]]-like remineralized veneer is formed over the remaining surface of the enamel; this veneer is much more acid-resistant than the original hydroxyapatite, and is formed more quickly than ordinary remineralized enamel would be.<ref name=Featherstone>{{cite journal | vauthors = Featherstone JD | title = Dental caries: a dynamic disease process | journal = Australian Dental Journal | volume = 53 | issue = 3 | pages = 286–291 | date = September 2008 | pmid = 18782377 | doi = 10.1111/j.1834-7819.2008.00064.x }}</ref> The cavity-prevention effect of fluoride is mostly due to these surface effects, which occur during and after [[Medicine:Tooth eruption|tooth eruption]].<ref>{{cite journal | vauthors = Hellwig E, Lennon AM | title = Systemic versus topical fluoride | journal = Caries Research | volume = 38 | issue = 3 | pages = 258–262 | year = 2004 | pmid = 15153698 | doi = 10.1159/000077764 | s2cid = 11339240 | url = http://content.karger.com/ProdukteDB/produkte.asp?Aktion=ShowPDF&ArtikelNr=77764&Ausgabe=230047&ProduktNr=224219&filename=77764.pdf }}</ref> Although some systemic (whole-body) fluoride returns to the saliva via [[Biology:Blood plasma|blood plasma]], and to unerupted teeth via plasma or crypt fluid, there is little data to determine what percentages of fluoride's anticavity effect comes from these systemic mechanisms.<ref>{{cite book |veditors=Berg JH, Slayton RL |title=Early Childhood Oral Health | vauthors = Tinanoff N |chapter=Uses of fluoride |pages=92–109 |isbn=978-0813824161 |publisher=Wiley-Blackwell |year=2009 }}</ref> Also, although fluoride affects the physiology of dental bacteria,<ref>{{cite journal | vauthors = Koo H | title = Strategies to enhance the biological effects of fluoride on dental biofilms | journal = Advances in Dental Research | volume = 20 | issue = 1 | pages = 17–21 | date = July 2008 | pmid = 18694872 | doi = 10.1177/154407370802000105 | s2cid = 40453568 | url = http://adr.sagepub.com/cgi/content/full/20/1/17 | access-date = 13 September 2009 | archive-date = 3 June 2009 | archive-url = https://web.archive.org/web/20090603040601/http://adr.sagepub.com/cgi/content/full/20/1/17 | url-status = dead }}</ref> its effect on [[Biology:Bacterial growth|bacterial growth]] does not seem to be relevant to cavity prevention.<ref name="MarquisClock2003">{{cite journal | vauthors = Marquis RE, Clock SA, Mota-Meira M | title = Fluoride and organic weak acids as modulators of microbial physiology | journal = FEMS Microbiology Reviews | volume = 26 | issue = 5 | pages = 493–510 | date = January 2003 | pmid = 12586392 | doi = 10.1111/j.1574-6976.2003.tb00627.x | doi-access = free }}</ref>

Fluoride's effects depend on the total daily intake of fluoride from all sources.<ref name=Fawell/> About 70–90% of ingested fluoride is absorbed into the blood, where it distributes throughout the body. In infants 80–90% of absorbed fluoride is retained, with the rest excreted, mostly via [[Biology:Urine|urine]]; in adults about 60% is retained. About 99% of retained fluoride is stored in bone, teeth, and other calcium-rich areas, where excess quantities can cause fluorosis.<ref name=Hhe/> Drinking water is typically the largest source of fluoride.<ref name=Fawell/> In many industrialized countries swallowed toothpaste is the main source of fluoride exposure in unfluoridated communities.<ref name=Sheiham/> Other sources include dental products other than toothpaste; air pollution from fluoride-containing [[Earth:Coal|coal]] or from phosphate fertilizers; [[Chemistry:Trona|trona]], used to tenderize meat in Tanzania; and tea leaves, particularly the tea bricks favored in parts of China. High fluoride levels have been found in other foods, including barley, cassava, corn, rice, taro, yams, and fish protein concentrate. The U.S. Institute of Medicine has established [[Chemistry:Dietary Reference Intake|Dietary Reference Intake]]s for fluoride: Adequate Intake values range from 0.01&nbsp;mg/day for infants aged 6&nbsp;months or less, to 4&nbsp;mg/day for men aged 19&nbsp;years and up; and the Tolerable Upper Intake Level is 0.10&nbsp;mg/kg/day for infants and children through age 8&nbsp;years, and 10&nbsp;mg/day thereafter.<ref>{{cite book |title=Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride |author=Institute of Medicine |year=1997 |publisher=National Academy Press |isbn=0309063507 |chapter=Fluoride |chapter-url=http://books.nap.edu/openbook.php?record_id=5776&page=288 |pages=288–313 }}</ref> A rough estimate is that an adult in a temperate climate consumes 0.6&nbsp;mg/day of fluoride without fluoridation, and 2&nbsp;mg/day with fluoridation. However, these values differ greatly among the world's regions: for example, in Sichuan, China the average daily fluoride intake is only 0.1&nbsp;mg/day in drinking water but 8.9&nbsp;mg/day in food and 0.7&nbsp;mg/day directly from the air due to the use of high-fluoride soft coal for cooking and drying foodstuffs indoors.<ref name=Fawell/>

== Alternatives ==
[[File:Toothpasteonbrush.jpg|thumb|left|alt=A tube applying toothpaste to a toothbrush.|Fluoride toothpaste is effective against cavities. It is widely used, but less so among the poor.<ref name=Jones-PH/>]]
[[File:Fluoridiertes Jodsalz.JPG|thumb|left|Fluoridated iodized salt sold in Germany]]
The views on the most effective method for community prevention of tooth decay are mixed. The Australian government review states that water fluoridation is the most effective means of achieving fluoride exposure that is community-wide.<ref name=NHMRC/> The European Commission review states "No obvious advantage appears in favour of water fluoridation compared with topical prevention".<ref name=EU2011/> Other fluoride therapies are also effective in preventing tooth decay;<ref name=Selwitz>{{cite journal | vauthors = Selwitz RH, Ismail AI, Pitts NB | title = Dental caries | journal = Lancet | volume = 369 | issue = 9555 | pages = 51–59 | date = January 2007 | pmid = 17208642 | doi = 10.1016/S0140-6736(07)60031-2 | s2cid = 204616785 }}</ref> they include fluoride toothpaste, [[Medicine:Mouthwash|mouthwash]], gel, and varnish,<ref name=Anusavice/> and fluoridation of salt and milk.<ref name=Jones-PH>{{cite journal | vauthors = Jones S, Burt BA, Petersen PE, Lennon MA | title = The effective use of fluorides in public health | journal = Bulletin of the World Health Organization | volume = 83 | issue = 9 | pages = 670–676 | date = September 2005 | pmid = 16211158 | pmc = 2626340 | url = http://scielosp.org/scielo.php?script=sci_arttext&pid=S0042-96862005000900012 | url-status = dead | archive-url = https://web.archive.org/web/20100314074115/http://www.scielosp.org/scielo.php?pid=S0042-96862005000900012&script=sci_arttext | archive-date = 14 March 2010 }}</ref> [[Medicine:Dental sealant|Dental sealant]]s are effective as well,<ref name=Selwitz/> with estimates of prevented cavities ranging from 33% to 86%, depending on age of sealant and type of study.<ref name=Anusavice/>

Fluoride [[Medicine:Toothpaste|toothpaste]] is the most widely used and rigorously evaluated fluoride treatment.<ref name=Jones-PH/> Its introduction is considered the main reason for the decline in tooth decay in industrialized countries,<ref name=Pizzo/> and toothpaste appears to be the single common factor in countries where tooth decay has declined.<ref>{{cite journal | vauthors = Milgrom P, Reisine S | title = Oral health in the United States: the post-fluoride generation | journal = Annual Review of Public Health | volume = 21 | pages = 403–436 | year = 2000 | pmid = 10884959 | doi = 10.1146/annurev.publhealth.21.1.403 | doi-access = free }}</ref> Toothpaste is the only realistic fluoride strategy in many low-income countries, where lack of infrastructure renders water or salt fluoridation infeasible.<ref name=Goldman/> It relies on individual and family behavior, and its use is less likely among lower economic classes;<ref name=Jones-PH/> in low-income countries it is unaffordable for the poor.<ref name=Goldman>{{cite journal | vauthors = Goldman AS, Yee R, Holmgren CJ, Benzian H | title = Global affordability of fluoride toothpaste | journal = Globalization and Health | volume = 4 | page = 7 | date = June 2008 | pmid = 18554382 | pmc = 2443131 | doi = 10.1186/1744-8603-4-7 | doi-access = free }}</ref> Fluoride toothpaste prevents about 25% of cavities in young permanent teeth, and its effectiveness is improved if higher concentrations of fluoride are used, or if the toothbrushing is supervised. Fluoride mouthwash and gel are about as effective as fluoride toothpaste; fluoride varnish prevents about 45% of cavities.<ref name=Anusavice/> By comparison, brushing with a nonfluoride toothpaste has little effect on cavities.<ref name=Sheiham/>

The effectiveness of [[Chemistry:Salt|salt]] fluoridation is about the same as that of 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 started fluoridating all salt in 1987, achieving a decline in cavities. Universal salt fluoridation is also practiced in Colombia and the Swiss Canton of Vaud; in Germany fluoridated salt is widely used in households but unfluoridated salt is also available, giving consumers a choice. Concentrations of fluoride in salt range from 90 to 350&nbsp;mg/kg, with studies suggesting an optimal concentration of around 250&nbsp;mg/kg.<ref name=Jones-PH/>

Milk fluoridation is practiced by the Borrow Foundation in some parts of Bulgaria, Chile, Peru, Russia, Macedonia, Thailand and the UK. Depending on location, the fluoride is added to milk, to powdered milk, or to yogurt. For example, milk powder fluoridation is used in rural Chilean areas where water fluoridation is not technically feasible.<ref>{{cite journal |journal=Rev Clin Pesq Odontol |year=2006 |volume=2 |issue=5–6 |pages=415–426 |title=Milk—a vehicle for fluorides: a review |vauthors=Bánóczy J, Rugg-Gunn AJ |url=http://www2.pucpr.br/reol/index.php/RCPO?dd1=1625&dd99=pdf |format=PDF |access-date=3 January 2009 |archive-date=13 February 2009 |archive-url=https://web.archive.org/web/20090213183036/http://www2.pucpr.br/reol/index.php/RCPO?dd1=1625&dd99=pdf |url-status=dead }}</ref> These programs are aimed at children, and have neither targeted nor been evaluated for adults.<ref name=Jones-PH/> A systematic review found low-quality evidence to support the practice, but also concluded that further studies were needed.<ref>{{cite journal | vauthors = Yeung CA, Chong LY, Glenny AM | title = Fluoridated milk for preventing dental caries | journal = The Cochrane Database of Systematic Reviews | issue = 9 | pages = CD003876 | date = September 2015 | volume = 2018 | pmid = 26334643 | doi = 10.1002/14651858.CD003876.pub4 | pmc = 6494533 }}</ref>

Other public-health strategies to control tooth decay, such as education to change behavior and diet, have lacked impressive results.<ref name=Kumar2008>{{cite journal | vauthors = Kumar JV | title = Is water fluoridation still necessary? | journal = Advances in Dental Research | volume = 20 | issue = 1 | pages = 8–12 | date = July 2008 | pmid = 18694870 | doi = 10.1177/154407370802000103 | s2cid = 30121985 | url = http://adr.sagepub.com/cgi/content/full/20/1/8 }}</ref> Although fluoride is the only well-documented agent which controls the rate at which cavities develop, it has been suggested that adding [[Chemistry:Calcium|calcium]] to the water would reduce cavities further.<ref>{{cite journal | vauthors = Bruvo M, Ekstrand K, Arvin E, Spliid H, Moe D, Kirkeby S, Bardow A | title = Optimal drinking water composition for caries control in populations | journal = Journal of Dental Research | volume = 87 | issue = 4 | pages = 340–343 | date = April 2008 | pmid = 18362315 | doi = 10.1177/154405910808700407 | s2cid = 31825557 }}</ref> Other agents to prevent tooth decay include antibacterials such as [[Chemistry:Chlorhexidine|chlorhexidine]] and sugar substitutes such as [[Chemistry:Xylitol|xylitol]].<ref name=Anusavice/> Xylitol-sweetened chewing gum has been recommended as a supplement to fluoride and other conventional treatments if the gum is not too costly.<ref>{{cite journal | vauthors = Zero DT | title = Are sugar substitutes also anticariogenic? | journal = Journal of the American Dental Association | volume = 139 | issue = Suppl 2 | pages = 9S–10S | date = May 2008 | pmid = 18460675 | doi = 10.14219/jada.archive.2008.0349 | doi-access = free }}</ref> Two proposed approaches, bacteria replacement therapy (probiotics) and [[Medicine:Caries vaccine|caries vaccine]], would share water fluoridation's advantage of requiring only minimal patient compliance, but have not been proven safe and effective.<ref name=Anusavice>{{cite journal | vauthors = Anusavice KJ | title = Present and future approaches for the control of caries | journal = Journal of Dental Education | volume = 69 | issue = 5 | pages = 538–554 | date = May 2005 | doi = 10.1002/j.0022-0337.2005.69.5.tb03941.x | pmid = 15897335 | url = http://www.jdentaled.org/cgi/content/full/69/5/538 | access-date = 8 March 2009 | archive-date = 12 March 2011 | archive-url = https://web.archive.org/web/20110312233505/http://www.jdentaled.org/cgi/content/full/69/5/538 | url-status = dead }}</ref> Other experimental approaches include fluoridated sugar, polyphenols, and casein phosphopeptide–amorphous calcium phosphate nanocomplexes.<ref>{{cite journal | vauthors = Whelton H | title = Beyond water fluoridation; the emergence of functional foods for oral health | journal = Community Dental Health | volume = 26 | issue = 4 | pages = 194–195 | date = December 2009 | pmid = 20088215 | doi = 10.1922/CDH_2611Whelton02 }}</ref>

A 2007 Australian review concluded that water fluoridation is the most effective and socially the most equitable way to expose entire communities to fluoride's cavity-prevention effects.<ref name=NHMRC/> A 2002 U.S. review estimated that sealants decreased cavities by about 60% overall, compared to about 18–50% for fluoride.<ref name=Truman>{{cite journal | vauthors = Truman BI, Gooch BF, Sulemana I, et al | title = Reviews of evidence on interventions to prevent dental caries, oral and pharyngeal cancers, and sports-related craniofacial injuries | journal = American Journal of Preventive Medicine | volume = 23 | issue = 1 Suppl | pages = 21–54 | date = July 2002 | pmid = 12091093 | doi = 10.1016/S0749-3797(02)00449-X | url = http://thecommunityguide.org/oral/oral-ajpm-ev-rev.pdf }}</ref> A 2007 Italian review suggested that water fluoridation may not be needed, particularly in the industrialized countries where cavities have become rare, and concluded that toothpaste and other topical fluoride are the best way to prevent cavities worldwide.<ref name=Pizzo/> A 2004 World Health Organization review stated that water fluoridation, when it is culturally acceptable and technically feasible, has substantial advantages in preventing tooth decay, especially for subgroups at high risk.<ref name=Petersen-2004>{{cite journal | vauthors = Petersen PE, Lennon MA | title = Effective use of fluorides for the prevention of dental caries in the 21st century: the WHO approach | journal = Community Dentistry and Oral Epidemiology | volume = 32 | issue = 5 | pages = 319–321 | date = October 2004 | pmid = 15341615 | doi = 10.1111/j.1600-0528.2004.00175.x | url =https://www.who.int/oral_health/media/en/orh_cdoe_319to321.pdf }}</ref>

== Worldwide prevalence ==
[[File:Fluoridated-water-extent-world.svg|350px|thumb|alt=World map showing countries in gray, white and in various shades of red. The U.S. and Australia stand out as bright red (which the caption identifies as the 60–80% color). Brazil and Canada are medium pink (40–60%). China, much of western Europe, and central Africa are light pink (1–20%). Germany, Japan, Nigeria, and Venezuela are white (<1%).|Percentage of population receiving fluoridated water, including both artificial and natural fluoridation, as of 2012:<ref name=extent2012/>{{div col|colwidth=5em}}
{{legend|#aa0000|{{nowrap|80–100%}}|border=1px solid #aaa}}
{{legend|#ff0000|{{nowrap|60–80%}}|border=1px solid #aaa}}
{{legend|#ff8080|{{nowrap|40–60%}}|border=1px solid #aaa}}
{{legend|#ffaaaa|{{nowrap|20–40%}}|border=1px solid #aaa}}
{{legend|#ffd5d5|{{nowrap|1–20%}}|border=1px solid #aaa}}
{{legend|#ffffff|{{nowrap|< 1%}}|border=1px solid #aaa}}
{{legend|#b9b9b9|unknown|border=1px solid #aaa}}{{div col end}}]]
As of November 2012, a total of about 378&nbsp;million people worldwide received artificially fluoridated water.  The majority of those were in the United States.  About 40&nbsp;million worldwide received water that was naturally fluoridated to recommended levels.<ref name=extent2012/>

Much of the early work on establishing the connection between fluoride and dental health was performed by scientists in the U.S. during the early 20th century, and the U.S. was the first country to implement public water fluoridation on a wide scale.<ref name=Sellers>{{cite journal | vauthors = Sellers C | title = The artificial nature of fluoridated water: between nations, knowledge, and material flows | journal = Osiris | volume = 19 | pages = 182–200 | year = 2004 | pmid = 15478274 | doi = 10.1086/649401 | s2cid = 31482952 }}</ref> It has been introduced to varying degrees in many countries and territories outside the U.S., including Argentina, Australia, Brazil, Canada, Chile, Colombia, Hong Kong, Ireland, Israel, Korea, Malaysia, New Zealand, the Philippines, Serbia, Singapore, Spain, the UK, and Vietnam. In 2004, an estimated 13.7&nbsp;million people in western Europe and 194&nbsp;million in the U.S. received artificially fluoridated water.<ref name=extent2012/> In 2010, about 66% of the U.S. population was receiving fluoridated water.<ref>{{cite web | title = 2010 Water Fluoridation Statistics | url = https://www.cdc.gov/fluoridation/statistics/2010stats.htm | publisher = Centers for Disease Control and Prevention | access-date = 30 July 2012}}</ref>

Naturally fluoridated water is used by approximately 4% of the world's population, in countries including Argentina, France, Gabon, Libya, Mexico, Senegal, Sri Lanka, Tanzania, the U.S., and Zimbabwe. In some locations, notably parts of Africa, China, and India, natural fluoridation exceeds recommended levels.<ref name=extent2012>
{{cite book |chapter=The extent of water fluoridation |chapter-url=http://bfsweb.org/onemillion/09%20One%20in%20a%20Million%20-%20The%20Extent%20of%20Fluoridation.pdf |url=http://bfsweb.org/onemillion/onemillion.htm |title=One in a Million: The facts about water fluoridation |edition=3rd |year=2012 |isbn=978-095476840-9 |pages=55–80 |publisher=British Fluoridation Society |location=Manchester |archive-url=https://web.archive.org/web/20081122032013/http://www.bfsweb.org/onemillion/onemillion.htm |archive-date=22 November 2008 |access-date=19 November 2008}} 
</ref>

Communities have discontinued water fluoridation in some countries, including Finland, Germany, Japan, the Netherlands, and Switzerland.<ref name=Cheng2007/>  Changes have been motivated by political opposition to water fluoridation, but sometimes the need for water fluoridation was met by alternative strategies. The use of fluoride in its various forms is the foundation of tooth decay prevention throughout Europe; several countries have introduced fluoridated salt, with varying success: in Switzerland and Germany, fluoridated salt represents 65% to 70% of the domestic market, while in France the market share reached 60% in 1993 but dwindled to 14% in 2009; Spain, in 1986 the second West European country to introduce fluoridation of table salt, reported a market share in 2006 of only 10%. In three other West European countries, Greece, Austria and the Netherlands, the legal framework for production and marketing of fluoridated edible salt exists. At least six Central European countries (Hungary, Czechia, Slovakia, Croatia, Slovenia, Romania) have shown some interest in salt fluoridation; however, significant usage of approximately 35% was only achieved in the Czech Republic. The Slovak Republic had the equipment to treat salt by 2005; in the other four countries attempts to introduce fluoridated salt were not successful.<ref>{{cite web | vauthors = Marthaler TM, Gillespie GM, Goetzfried F | title = Salt fluoridation in Europe and in Latin America – with potential worldwide | url = https://s3-us-west-2.amazonaws.com/cdhp-fluoridation/Marthaler+%282011%29+Salt+Fluoridation.pdf | publisher = Kali und Steinsalz Heft 3/2011 | access-date = 9 August 2013}}</ref><ref>{{cite web | title = Salt fluoridation in Central and Eastern Europe | url = http://www.sso.ch/doc/doc_download.cfm?uuid=9553209DD9D9424C4C98A160B35CD8DE&&IRACER_AUTOLINK&& | publisher = Schweiz Monatsschr Zahnmed, Vol 115: 8/2005 | access-date = 9 August 2013 }}{{Dead link|date=June 2022 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>  When Israel implemented the 2014 Dental Health Promotion Program, that includes education, medical followup and the use of fluoride-containing products and supplements, it evaluated that mandatory water fluoridation was no longer necessary, stating "supply of fluoridated water forces those who do not so wish to also consume water with added fluoride. This approach is therefore not accepted in most countries in the world.".<ref>{{cite web|type=Press Release|date=17 August 2014|url=http://www.health.gov.il/English/News_and_Events/Spokespersons_Messages/Pages/17082014_1.aspx|title=End of Mandatory Fluoridation in Israel|work=Ministry of Health (Israel)|access-date=29 September 2014|archive-url=https://web.archive.org/web/20141117131814/http://www.health.gov.il/English/News_and_Events/Spokespersons_Messages/Pages/17082014_1.aspx|archive-date=17 November 2014|url-status=dead}}</ref>

== History ==
[[File:McKayandBlackCDC01.jpg|thumb|left|upright|alt=Faded, grainy image of three men in the outdoors, holding up a boy. The man on the left has a short white beard and mustache, a hat, and a three-piece suit.|1909 photograph by Frederick McKay of G.V. Black (left), Isaac Burton and F.Y. Wilson, studying the Colorado brown stain<ref>{{cite book |author=Douglas WA |title=History of Dentistry in Colorado, 1859–1959 |date=1959 |page=199 |location=Denver |publisher=Colorado State Dental Assn |oclc=5015927 }}</ref>]]

The history of water fluoridation can be divided into three periods. The first ({{circa|1801–1933}}) was research into the cause of a form of mottled tooth enamel called the Colorado brown stain. The second ({{circa|1933}}–1945) focused on the relationship between fluoride concentrations, fluorosis, and tooth decay, and established that moderate levels of fluoride prevent cavities. The third period, from 1945 on, focused on adding fluoride to community water supplies.<ref name=Ripa>{{cite journal | vauthors = Ripa LW | title = A half-century of community water fluoridation in the United States: review and commentary | journal = Journal of Public Health Dentistry | volume = 53 | issue = 1 | pages = 17–44 | year = 1993 | pmid = 8474047 | doi = 10.1111/j.1752-7325.1993.tb02666.x | url = http://aaphd.org/docs/position%20papers/A%20Half-Century%20of%20Community%20Water1993.pdf | url-status = dead | archive-url = https://web.archive.org/web/20090304021822/http://aaphd.org/docs/position%20papers/A%20Half-Century%20of%20Community%20Water1993.pdf | archive-date = 4 March 2009 }}</ref>

In the first half of the 19th century, investigators established that fluoride occurs with varying concentrations in teeth, bone, and drinking water. In the second half they speculated that fluoride would protect against tooth decay, proposed supplementing the diet with fluoride, and observed mottled enamel (now called severe dental fluorosis) without knowing the cause.<ref>{{cite book |chapter= Fluorine and dental caries | vauthors = Cox GJ |pages=325–414 |title= A Survey of the Literature of Dental Caries |veditors=Toverud G, Finn SB, Cox GJ, Bodecker CF, Shaw JH |publisher= National Academy of Sciences – National Research Council |location= Washington, DC |oclc=14681626 |year=1952}} Publication 225.</ref> In 1874, the German public health officer Carl Wilhelm Eugen Erhardt recommended [[Chemistry:Potassium fluoride|potassium fluoride]] supplements to preserve teeth.<ref>{{cite journal |author= Eckardt [sic] |title= Kali fluoratum zur Erhaltung der Zähne |language=de |journal= Der Praktische Arzt |volume=15 |issue=3 |pages=69–70 |year=1874}} A followup was translated into English in: {{cite journal |vauthors=Friedrich EG |title= Potassium fluoride as a caries preventive: a report published 80 years ago |journal=J Am Dent Assoc |volume=49 |year=1954 |page=385}}</ref><ref>{{cite web|last1=Meiers|first1=Peter|title=Dr. Erhardts ("Hunter'sche") Fluoridpastillen|url=http://www.fluoride-history.de/Erhardt.pdf|access-date=13 June 2016|date=2016}}</ref> In 1892 the British physician James Crichton-Browne noted in an address that fluoride's absence from diets had resulted in teeth that were "peculiarly liable to decay", and who proposed "the reintroduction into our diet ... of fluorine in some suitable natural form ... to fortify the teeth of the next generation".<ref>{{cite journal |author= Crichton-Browne J |title= An address on tooth culture |journal=Lancet |volume=140 |issue=3592 |pages=6–10 |year=1892 |doi=10.1016/S0140-6736(01)97399-4|pmid= 15117687 |pmc= 1448324 }}</ref>

The foundation of water fluoridation in the U.S. was the research of the dentist Frederick McKay (1874–1959). 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.<ref>Colorado brown stain:
* {{cite journal | vauthors = Peterson J | title = Solving the mystery of the Colorado Brown Stain | journal = Journal of the History of Dentistry | volume = 45 | issue = 2 | pages = 57–61 | date = July 1997 | pmid = 9468893 }}
* {{cite web |url=http://cs-ds.org/history-of-dentistry-in-the-pikes-peak-region.html#fluoride |title=The discovery of fluoride |publisher=Colorado Springs Dental Society |date=2004 |access-date=11 June 2012 |url-status=dead|archive-url=https://web.archive.org/web/20120824210103/http://cs-ds.org/history-of-dentistry-in-the-pikes-peak-region.html#fluoride |archive-date=24 August 2012 }}
</ref> The first report of a statistical association between the stain and lack of tooth decay was made by UK dentist Norman Ainsworth in 1925. In 1931, an [[Company:Alcoa|Alcoa]] chemist, H.V. Churchill, concerned about a possible link between [[Chemistry:Aluminum|aluminum]] and staining, analyzed water from several areas where the staining was common and found that fluoride was the common factor.<ref name=Mullen>{{cite journal | vauthors = Mullen J | title = History of water fluoridation | journal = British Dental Journal | volume = 199 | issue = 7 Suppl | pages = 1–4 | date = October 2005 | pmid = 16215546 | doi = 10.1038/sj.bdj.4812863 | s2cid = 56981 }}</ref>

[[File:H-Trendley-Dean.jpeg|thumb|upright|alt=Head and shoulder of a 60-ish man with a flattop haircut and in a coat and tie, looking directly at camera with head tilted to his right and a slight smile.|H. Trendley Dean set out in 1931 to study fluoride's harm, but by 1950 had demonstrated the cavity-prevention effects of small amounts.<ref name=CDC-1999>{{cite journal |title=Achievements in public health, 1900–1999: Fluoridation of drinking water to prevent dental caries |journal=MMWR Morb Mortal Wkly Rep |volume=48 |issue=41 |pages=933–940 |year=1999 |url=http://cdc.gov/mmwr/preview/mmwrhtml/mm4841a1.htm }} Contains [http://cdc.gov/mmwr/preview/mmwrhtml/mm4841bx.htm H. Trendley Dean, D.D.S.] [http://jama.ama-assn.org/cgi/content/full/283/10/1283 Reprinted] in: {{cite journal | vauthors = <!-- pacify citation bot --> | title = From the Centers for Disease Control and Prevention. Achievements in public health, 1900-1999: fluoridation of drinking water to prevent dental caries | journal = JAMA | volume = 283 | issue = 10 | pages = 1283–1286 | date = March 2000 | pmid = 10714718 | doi = 10.1001/jama.283.10.1283 | doi-access = free }}</ref>]]

In the 1930s and early 1940s, H. Trendley Dean and colleagues at the newly created  U.S. National Institutes of Health published several epidemiological studies suggesting that a fluoride concentration of about 1&nbsp;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.<ref name="Fluoride Wars">{{cite book |last1= Frees |first1= R. Allan |last2= Lehr |first2= Jay H. |date=2009 |title= Fluoride Wars: How a Modest Public Health Measure Became America's Longest-Running Political Melodrama |publisher= Wiley |pages=92–129 |isbn=9780470463673}}</ref>  Other studies found no other significant adverse effects even in areas with fluoride levels as high as 8&nbsp;mg/L.<ref name=Lennon>{{cite journal | vauthors = Lennon MA | title = One in a million: the first community trial of water fluoridation | journal = Bulletin of the World Health Organization | volume = 84 | issue = 9 | pages = 759–760 | date = September 2006 | pmid = 17128347 | pmc = 2627472 | doi = 10.2471/BLT.05.028209 | url = http://scielosp.org/scielo.php?script=sci_arttext&pid=S0042-96862006000900020 | url-status = dead | archive-url = https://web.archive.org/web/20090214022329/http://www.scielosp.org/scielo.php?script=sci_arttext&pid=S0042-96862006000900020 | archive-date = 14 February 2009 }}</ref> 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 25 January 1945. The results, published in 1950, showed significant reduction of cavities.<ref name=NICDR>{{cite web |url=http://www.nidcr.nih.gov/OralHealth/Topics/Fluoride/TheStoryofFluoridation.htm |title=The story of fluoridation |publisher=National Institute of Dental and Craniofacial Research |date=20 December 2008 |access-date=6 February 2010 }}</ref><ref>{{cite journal | vauthors = Dean HT, Arnold FA, Jay P, Knutson JW | title = Studies on mass control of dental caries through fluoridation of the public water supply | journal = Public Health Reports | volume = 65 | issue = 43 | pages = 1403–1408 | date = October 1950 | pmid = 14781280 | pmc = 1997106 | doi = 10.2307/4587515 | jstor = 4587515 }}</ref> Significant reductions in tooth decay were also reported by important early studies outside the U.S., including the Brantford–Sarnia–Stratford study in Canada (1945–1962), the Tiel–Culemborg study in the Netherlands (1953–1969), the Hastings study in New Zealand (1954–1970), and the Department of Health study in the U.K. (1955–1960).<ref name=Mullen/> By present-day standards these and other pioneering studies were crude, but the large reductions in cavities convinced public health professionals of the benefits of fluoridation.<ref name=Burt/>

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&nbsp;million people.<ref name=Lennon/> 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 occurring fluoride.<ref name=US-WF-Stats-2006>{{cite web |publisher=Division of Oral Health, National Center for Chronic Disease Prevention and Health Promotion, CDC |title=Water fluoridation statistics for 2006 |url=http://cdc.gov/fluoridation/statistics/2006stats.htm |date=17 September 2008 |access-date=22 December 2008 }}</ref> In some other countries the pattern was similar. New Zealand, which led the world in per-capita sugar consumption and had the world's worst teeth, began fluoridation in 1953, and by 1968 fluoridation was used by 65% of the population served by a piped water supply.<ref>{{cite journal | vauthors = Akers HF | title = Collaboration, vision and reality: water fluoridation in New Zealand (1952-1968) | journal = The New Zealand Dental Journal | volume = 104 | issue = 4 | pages = 127–133 | date = December 2008 | pmid = 19180863 | url = http://espace.library.uq.edu.au/eserv/UQ:159563/Akers_NZDJ_Dec_2008.pdf }}</ref> Fluoridation was introduced into Brazil in 1953, was regulated by federal law starting in 1974, and by 2004 was used by 71% of the population.<ref>{{cite journal | vauthors = Buzalaf MA, de Almeida BS, Olympio KP, da Cardoso VE, de Peres SH | title = Enamel fluorosis prevalence after a 7-year interruption in water fluoridation in Jaú, São Paulo, Brazil | journal = Journal of Public Health Dentistry | volume = 64 | issue = 4 | pages = 205–208 | year = 2004 | pmid = 15562942 | doi = 10.1111/j.1752-7325.2004.tb02754.x }}</ref> 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;<ref name=Mullen/> fluoridation became required for all sizeable public water systems and by 1996 reached 66% of the population.<ref name=extent2012/> 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 was low, and in [[Place:Basel|Basel]], Switzerland, it was replaced with fluoridated salt.<ref name=Mullen/>

McKay's work had established that fluorosis occurred before [[Medicine:Tooth eruption|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) were well understood, and it had become known that a constant low level of fluoride in the mouth works best to prevent cavities.<ref>{{cite book |vauthors=Burt BA, Tomar SL |chapter= Changing the face of America: water fluoridation and oral health |pages=307–322 |title= Silent Victories: The History and Practice of Public Health in Twentieth-century America |veditors=Ward JW, Warren C |publisher= Oxford University Press |year=2007 |isbn=978-0195150698}}</ref>

== Economics ==
Fluoridation costs an estimated ${{inflation|US|0.72|1999|r=2}} per person-year on the average (range: ${{inflation|US|0.17|1999|r=2}}–${{inflation|US|7.62|1999|r=2}}; all costs in this paragraph are for the U.S.<ref name=FRWG/> and are in {{Inflation-year|US}} dollars, inflation-adjusted from earlier estimates{{Inflation/fn|US}}). 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.<ref name=FRWG/> In affluent countries the cost of salt fluoridation is also negligible; developing countries may find it prohibitively expensive to import the fluoride additive.<ref name=Marthaler>{{cite journal | vauthors = Marthaler TM, Petersen PE | title = Salt fluoridation--an alternative in automatic prevention of dental caries | journal = International Dental Journal | volume = 55 | issue = 6 | pages = 351–358 | date = December 2005 | pmid = 16379137 | doi = 10.1111/j.1875-595x.2005.tb00045.x | url =https://www.who.int/oral_health/publications/orh_IDJ_salt_fluoration.pdf }}</ref> By comparison, fluoride toothpaste costs an estimated ${{inflation|US|6|1999}}–${{inflation|US|12|1999}} per person-year, with the incremental cost being zero for people who already brush their teeth for other reasons; and dental cleaning and application of fluoride varnish or gel costs an estimated ${{inflation|US|66|1999}} per person-year. Assuming the worst case, with the lowest estimated effectiveness and highest estimated operating costs for small cities, fluoridation costs an estimated ${{inflation|US|11|1999}}–${{inflation|US|17|1999}} per saved tooth-decay surface, which is lower than the estimated ${{inflation|US|65|1999}} to restore the surface<ref name=FRWG/> and the estimated ${{inflation|US|100.62|1995}} average [[Finance:Present value|discounted]] lifetime cost of the decayed surface, which includes the cost to maintain the restored tooth surface.<ref name=Griffin-econ>{{cite journal | vauthors = Griffin SO, Jones K, Tomar SL | title = An economic evaluation of community water fluoridation | journal = Journal of Public Health Dentistry | volume = 61 | issue = 2 | pages = 78–86 | year = 2001 | pmid = 11474918 | doi = 10.1111/j.1752-7325.2001.tb03370.x | url = http://cdc.gov/fluoridation/pdf/griffin.pdf }}</ref> It is not known how much is spent in industrial countries to treat dental fluorosis, which is mostly due to fluoride from swallowed toothpaste.<ref name=Sheiham/>

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.<ref name=FRWG>{{cite journal | title = Recommendations for using fluoride to prevent and control dental caries in the United States. Centers for Disease Control and Prevention | journal = MMWR. Recommendations and Reports | volume = 50 | issue = RR-14 | pages = 1–42 | date = August 2001 | pmid = 11521913 | url = http://cdc.gov/mmwr/preview/mmwrhtml/rr5014a1.htm}} See also [http://cdc.gov/fluoridation/guidelines/tooth_decay.htm lay summary] from CDC, 2007-08-09.</ref><ref name=CDC-1992-2006/> Dental sealants are cost-effective only when applied to high-risk children and teeth.<ref name=Reeves2006>{{cite journal | vauthors = Reeves A, Chiappelli F, Cajulis OS | title = Evidence-based recommendations for the use of sealants | journal = Journal of the California Dental Association | volume = 34 | issue = 7 | pages = 540–546 | date = July 2006 | doi = 10.1080/19424396.2006.12222224 | pmid = 16995612 | s2cid = 45728195 }}</ref> A 2002 U.S. review estimated that on average, sealing first permanent molars saves costs when they are decaying faster than 0.47 surfaces per person-year whereas water fluoridation saves costs when total decay [[Medicine:Incidence (epidemiology)|incidence]] exceeds 0.06 surfaces per person-year.<ref name=Truman/> In the U.S., water fluoridation is more cost-effective than other methods to reduce tooth decay in children, and a 2008 review concluded that water fluoridation is the best tool for combating cavities in many countries, particularly among socially disadvantaged groups.<ref name=Kumar2008/> A 2016 review of studies published between 1995 and 2013 found that water fluoridation in the U.S. was cost-effective, and that it was more so in larger communities.<ref name=ran>{{cite journal | vauthors = Ran T, Chattopadhyay SK | title = Economic Evaluation of Community Water Fluoridation: A Community Guide Systematic Review | journal = American Journal of Preventive Medicine | volume = 50 | issue = 6 | pages = 790–796 | date = June 2016 | pmid = 26776927 | doi = 10.1016/j.amepre.2015.10.014 | pmc = 6171335 }}</ref>

U.S. data from 1974 to 1992 indicate that when water fluoridation is introduced into a community, there are significant decreases in the number of employees per dental firm and the number of dental firms. The data suggest that some dentists respond to the [[Finance:Demand shock|demand shock]] by moving to non-fluoridated areas and by retraining as [[Medicine:Dentistry#Specialties|specialists]].<ref>{{cite journal |author=Ho K, Neidell M |year=2009 |title=Equilibrium effects of public goods: the impact of community water fluoridation on dentists |publisher=National Bureau of Economic Research |url=http://www.columbia.edu/~mn2191/w15056.pdf |journal=NBER Working Paper No. 15056 |access-date=13 October 2009 |url-status=dead|archive-url=https://web.archive.org/web/20121023074617/http://www.columbia.edu/~mn2191/w15056.pdf |archive-date=23 October 2012 }}</ref>

== Controversy ==
{{Main|Unsolved:Water fluoridation controversy}}
The [[Unsolved:Water fluoridation controversy|water fluoridation controversy]] arises from political, moral, ethical, economic, and safety concerns regarding the water fluoridation of public water supplies.<ref name=Cheng2007>{{cite journal | vauthors = Cheng KK, Chalmers I, Sheldon TA | title = Adding fluoride to water supplies | journal = BMJ | volume = 335 | issue = 7622 | pages = 699–702 | date = October 2007 | pmid = 17916854 | pmc = 2001050 | doi = 10.1136/bmj.39318.562951.BE | url = http://www.appgaf.org.uk/data/433-water-fluoridation.pdf | access-date = 9 April 2009 | archive-date = 3 March 2016 | archive-url = https://web.archive.org/web/20160303202219/http://www.appgaf.org.uk/data/433-water-fluoridation.pdf | url-status = dead }}</ref><ref name=Armfield>{{cite journal | vauthors = Armfield JM | title = When public action undermines public health: a critical examination of antifluoridationist literature | journal = Australia and New Zealand Health Policy | volume = 4 | page= 25 | date = December 2007 | pmid = 18067684 | pmc = 2222595 | doi = 10.1186/1743-8462-4-25 | doi-access = free }}</ref> For impoverished groups in both developing and developed countries, international and national agencies and dental associations across the world support the safety and effectiveness of water fluoridation.<ref name=Pizzo/> Authorities' views on the most effective [[Medicine:Fluoride therapy|fluoride therapy]] for community prevention of tooth decay are mixed; some state water fluoridation is most effective, while others see no special advantage and prefer topical application strategies.<ref name=NHMRC/><ref name=EU2011/>

Those opposed argue that water fluoridation has no or little cariostatic benefits, may cause serious health problems, is not effective enough to justify the costs, is [[Medicine:Clinical pharmacology|pharmacologically]] obsolete,<ref name=FRWG/><ref name=Thiessen>{{cite journal | vauthors = Ko L, Thiessen KM | title = A critique of recent economic evaluations of community water fluoridation | journal = International Journal of Occupational and Environmental Health | volume = 21 | issue = 2 | pages = 91–120 | date = 3 December 2014 | pmid = 25471729 | pmc = 4457131 | doi = 10.1179/2049396714Y.0000000093 }}</ref><ref name=Hileman>Hileman, Bette (4 November 2006) [http://pubs.acs.org/email/cen/html/090506090615.html Fluoride Risks Are Still A Challenge] Vol 84, Num 36 pp. 34–37, Chemical & Engineering News, Retrieved 14 April 2016</ref><ref name=Kaminsky>[[Biography:Sheldon Krimsky|Sheldon Krimsky]], Book review (16 August 2004) [http://pubs.acs.org/cen/books/8233/8233books.html Is Fluoride Really All That Safe?], Volume 82, Number 33, pp. 35–36 Chemical & Engineering News, Retrieved 19 April 2016</ref> and presents a moral conflict between the [[Philosophy:Common good|common good]] and individual rights.<ref name=ethics>
* {{cite journal | vauthors = McNally M, Downie J | title = The ethics of water fluoridation | journal = Journal | volume = 66 | issue = 11 | pages = 592–593 | date = December 2000 | pmid = 11253350 | url = http://cda-adc.ca/jcda/vol-66/issue-11/592.html }}
* {{cite journal | vauthors = Cohen H, Locker D | title = The science and ethics of water fluoridation | journal = Journal | volume = 67 | issue = 10 | pages = 578–580 | date = November 2001 | pmid = 11737979 | url = http://cda-adc.ca/jcda/vol-67/issue-10/578.html }}</ref>

== See also ==
* Water fluoridation by country
* [[Engineering:History of water supply and sanitation|History of water supply and sanitation]]

== References ==
{{Reflist}}

== External links ==
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[[Category:Water treatment|Fluoridation]]
[[Category:Dentistry]]
[[Category:Medical controversies]]

{{Sourceattribution|Water fluoridation}}