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Water treatment helps prevent cavities
Residents in Churchill recently voted in a plebiscite to discontinue adding fluoride to the northern Manitoba community's water supply. Although the vote is not binding on town council, the continued effort in some Canadian communities to ban fluoride has raised concern among health experts. Doug Brothwell is Associate Dean (Academic) at the Faculty of Dentistry, University of Manitoba. He completed his dental public health training at the University of Toronto and has conducted research on the relationship between fluoride consumption and dental fluorosis. He recently took time to explain why adding fluoride to water is good health policy.
What is fluoride?
Fluoride is a naturally occurring element that comprises 0.06 per cent of the earth's crust. As the 13th most abundant element, fluoride is primarily found in inorganic minerals that are present in rocks, soil and water. Being readily soluble, virtually all water sources contain fluoride, but in varying concentrations, dependent on the local environmental conditions.
When did we start adding it to water?
The relationship between water fluoride and tooth decay was first discovered in the 1930s when investigators documented that decay rates were lower in areas with higher natural water fluoride concentration. These observations led to the 1945 community water fluoridation trial in Grand Rapids, Michigan, where it was first shown that fluoride could be added to water to create the same benefit. Since that time, water fluoridation has been the subject of thousands of studies.
How effective is water fluoridation?
The best available evidence to answer questions on the effectiveness of preventive agents comes from a systematic review with meta-analysis. Evidence on the effectiveness of water fluoridation best comes from an extensive systematic review known as the York Report. This report says that when compared with low-fluoride areas, water fluoridation will increase by 15.5 per cent the proportion of children who have never had a cavity (caries-free). Similarly, children in fluoridated areas experience on average 2.23 fewer cavities.
Possibly the two biggest advantages to water fluoridation are its equity and cost-effectiveness. It is equitable because delivery through the water supply ensures that all members of society, including the economically disadvantaged, benefit from healthier teeth. It is also the most cost-effective means of fluoride delivery, with every dollar spent on water fluoridation saving an estimated $38 in treatment costs for tooth decay. All considered, water fluoridation remains a great public health measure in Winnipeg.
Why is adding fluoride to water opposed by some?
Some people oppose water fluoridation due to misconceptions that it does not reduce tooth decay and that it causes serious side-effects. Others are concerned about "mass medication" and losing the freedom of choice about what preventive agents they receive. These individuals can choose to consume reverse-osmosis, distilled, or other low-fluoride bottled waters. Alternatively, people can install reverse-osmosis systems or water distillers. Carbon filtration has also been shown to remove at least some of the fluoride from water, while boiling water is not an effective way to remove fluoride. Using these alternatives, people who wish to avoid consuming fluoridated water can do so, while allowing the rest of the population to benefit from the equity and cost-effectiveness of water fluoridation.
To what concentration is fluoride put in the water?
Traditionally, water fluoride concentration was adjusted and monitored to maintain a concentration of 1.0 parts per million (ppm). In 2007, Health Canada assembled an expert panel to consider the appropriate concentration in a contemporary setting. Based on the advice from the Fluoride Expert Panel, recommended water fluoridation levels were reduced to 0.7 ppm. In response to this recommendation, Winnipeg has now reduced its water fluoride levels to 0.7 ppm.
How does fluoride prevent tooth decay?
Tooth decay is caused when the unique bacteria on our teeth (dental plaque) metabolize dietary sugars to produce organic acids. These acids slowly dissolve the mineral out of tooth enamel, a process known as demineralization. Demineralization is a normal process that occurs in all people. In a healthy mouth, this loss of tooth mineral is balanced by a concurrent process of remineralization where minerals from the saliva re-enter the tooth in periods when dietary sugar is not available. Fluoride exerts its main cavity-fighting effect by upsetting the demineralization - remineralization balance. Fluoride ingested from water is available to the tooth surface on a continuous basis. Fluoride fights previous bouts of demineralization by allowing faster enamel remineralization through the formation of fluorapatite. This increased mineral uptake into the tooth shifts the demineralization - remineralization balance in favour of fewer cavities.
How many Manitobans have access to fluoridated water?
Health Canada informs us that in 2007, 70 per cent of Manitobans lived in areas with fluoridated water. Only Ontario and Alberta had higher fluoridation rates, resulting in about 55 per cent of all Canadians consuming fluoridated water. Water fluoridation is a public health measure used by many other countries including Australia, Brazil, Chile, Ireland, New Zealand, South Korea, Spain, UK, and the United States.
Are there alternative forms of fluoride that help prevent tooth decay?
Yes. Fluoride can exert a beneficial effect with either a systemic application (ingested) or a topical application. Systemic application options include fluoridation of water, salt or milk, or the use of fluoride supplements (drops, tablets or lozenges). Of these, water and salt fluoridation offer the greatest advantages. Fluoride is also effective at reducing cavities when applied topically to the teeth. Toothpaste, dental office fluoride treatments, fluoride varnish, and OTC fluoride rinses are examples of the topical application of fluoride. These products have much higher fluoride concentrations than those used for water fluoridation. While water is fluoridated to 0.7 ppm, toothpaste typically contains 1,000 ppm, fluoride treatments 12,300 ppm, and fluoride varnish 22,600 ppm.
Are there any undesired health effects of water fluoridation?
Like all therapeutic agents, the amount of ingested fluoride needs to be controlled. Excessive fluoride ingestion, such as a child swallowing an entire tube of toothpaste, could be harmful. Luckily, these adverse health risks are very unlikely with the low concentrations found in fluoridated water. In a systematic review of all the available evidence on the potential harms of water fluoridation, the York Report was unable to find evidence that water fluoridation caused an increase in the rate of bone fractures, cancer, Down Syndrome, dementia, mortality, goiter or IQ levels.
What is well known is the fact that water fluoridation is linked with a condition known as dental fluorosis. Dental fluorosis is a relatively minor cosmetic condition where white spots (or rarely brown spots) are present on the teeth due to ingesting too much fluoride during early childhood (prior to age three years). In Canada, the 2009 Canadian Health Measures Survey reported that about 40 per cent of children aged six to 12 had some degree of dental fluorosis, with only 16.4 per cent visible to the untrained eye, and 0.3 per cent of severity above mild. This recent evidence allows additional confidence that water fluoridation is appropriately controlled and administered in Canada.
Are there any special considerations for water fluoridation?
It is important for all health professionals and parents to be aware that water fluoridation creates a unique issue for infant feeding. That issue derives from the fact that most infant formula comes in concentrated liquid or powder form. If parents use tap water to reconstitute powdered formula or to dilute concentrated infant formula, they increase the risk that their child will develop dental fluorosis. This problem is best avoided by breastfeeding for longer duration and by reconstituting powdered or concentrated infant formula with deionized water (reverse-osmosis, distilled, or low-fluoride bottled water). With this precaution, the risk for developing dental fluorosis is significantly reduced
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