Dental disease in the form of dental caries is associated with a range of adverse outcomes including substantial pain, reduced sleep capacity, decreased ability to eat some foods, social embarrassment, and lowered self-esteem.1–3
While individual treatment for dental caries is effective, such treatment may be delayed because of financial or other reasons until people are experiencing significant levels of pain and functional impairment. Dental caries is one of the most common diseases in modern societies and carries with it a considerable financial burden.4
The most widely implemented public health intervention for the prevention of dental caries is water fluoridation, a practice that involves the deliberate addition of fluoride to the public water supply. Fluoride improves dental health by being incorporated into the crystalline structure of the tooth to form fluorapatite, which is less soluble than hydroxyapatite, and thereby inhibits the process of demineralization or decay. It also enhances remineralization of the tooth surface, inhibits bacterial metabolism, and inhibits plaque formation.5
Numerous studies have indicated that water fluoridation is effective in reducing dental caries.6
In recognition of this outcome, the Centers for Disease Control and Prevention (CDC) proclaimed water fluoridation as one of the 10 major public health achievements of the 20th century, alongside vaccinations and the control of infectious diseases.7
However, water fluoridation remains relevant in the 21st century, and the U.S. Surgeon General has argued that it “continues to be a vital, cost-effective method of preventing dental caries.”8
Despite the established effectiveness of water fluoridation, many countries have not adopted this public health practice. Indeed, even in those countries with the highest population coverage of fluoridated water, a substantial percentage of people still do not have access to its benefits. In Australia, for example, it was estimated that only 69% of the Australian population in 2006 had access to optimally fluoridated water, with this figure varying across states and territories from 4.7% in Queensland to 100.0% in the Australian Capital Territory.9
The percentage of the population with access to fluoridated water in Australia was similar to that in the U.S. and higher than that of most other countries with water fluoridation.
One reason that some countries have been reluctant to implement water fluoridation is because some decision makers in those countries regard fluoride as an environmental pollutant, a view that has been fostered by lobby groups opposed to water fluoridation.10
However, the argument that water fluoridation is hazardous ignores the importance of fluoride concentration to toxicity. In Australia, for example, although fluoride is officially listed as being both harmful to health and pervasive in the environment, this declaration is qualified by the acknowledgement that it is present “at very low levels that are not believed to be harmful.”11
Water fluoridation is one of numerous public health practices that have generated a degree of controversy at the hands of often small but mobilized groups capable of swaying the views of both politicians and the public. For example, the implementation of water chlorination, compulsory child immunizations, mandatory seatbelt use, free distribution of condoms, and bans on smoking in public places have been criticized as being attacks on personal freedom or downright harmful. Interestingly, other public health policies using fluoride, such as salt or milk fluoridation, have generated less controversy than water fluoridation. Perhaps this dichotomy reflects the fact that salt fluoridation and other such practices are employed much less frequently, and that organized opposition to water fluoridation predominantly stems from the U.S., where water fluoridation is widely implemented but salt fluoridation is not. The continued opposition to water fluoridation can also be attributed to the widespread devolution of political decision-making to local political regions, which are more reactive to outspoken minority and special-interest groups.
Ideally, studies of water fluoridation measure exposure at the individual level, as there may be considerable variation in exposure within a fluoridated or non-fluoridated area as a result of residential mobility (i.e., people moving in and out of fluoridated areas) as well as differences in consumption of public water and fluoride-containing beverages and foods. Studies at the individual level are preferred over studies at the community or population level, which do not take into account individual fluoride exposure or other individual risk factors. However, while community-level studies do not provide good evidence of the efficacy or “actual” effectiveness of fluoridated water consumption, they provide valuable information concerning the effectiveness of water fluoridation in practice, as it is mitigated by a number of other factors. For instance, if very few children are actually consuming adequate quantities of fluoridated public water, the community-level or “practical” effectiveness of water fluoridation may be low, regardless of its efficacy. A pattern of lower decay experience in fluoridated areas compared with non-fluoridated areas would, therefore, be consistent with the argument that a practical benefit is obtained by the addition of fluoride to water supplies.
While a small number of community-level studies have shown water fluoridation to be effective,12–15
some individuals point to studies that show, or allege, either the opposite effect or no effect and have used these studies to dismiss the effectiveness of water fluoridation generally.16
For instance, a study by Yiamouyiannis17
found no caries preventive effect for water fluoridation among U.S. children, although a subsequent study using the same database found significant associations.18
Opponents of water fluoridation make a continued case for the abolition of water fluoridation based on a series of articles from Australia, New Zealand, and elsewhere that argue that water fluoridation is not effective.19–26
Diesendorf has argued that for researchers to either confirm or refute the hypothesis that declines in caries experience are attributable to factors other than water fluoridation, “it is necessary (but not ‘sufficient’) to examine the absolute values of caries prevalence in fluoridated and unfluoridated areas.” He goes on to argue that even if only a small number of non-fluoridated areas have comparable caries experience to that seen in some fluoridated areas, this would provide a strong case for reexamining studies showing the effectiveness of water fluoridation.22
Although such an extreme position is most likely an exercise in sophistry and ignores crucial and obvious variations in dental caries experience resulting from other causes, it is the case that if water fluoridation is effective, we would expect a pattern of results showing reduced caries experience in fluoridated areas after controlling for basic possible confounding factors.
Given the ubiquity of fluoride in the environment where water fluoridation is practiced, it is imperative that we ask whether or not children's caries experience is actually lower in areas with a higher concentration of fluoride in the water. In Australia, descriptive and anecdotal evidence suggests that children's oral health is poor in those areas that have had the least water fluoridation. For example, Queensland, which for many decades remained the only Australian state or territory to have not implemented wide-scale water fluoridation, has consistently ranked among the poorest child oral health in the country.27
In countries such as the U.S., where there are no established school dental programs to provide preventive and restorative treatment to school-aged children, water fluoridation is perhaps even more important and is likely to be even more effective as a population preventive oral health practice.
A report released by the Australian Institute of Health and Welfare in 2007 documented consistently better oral health for children living in fluoridated areas than for children living in non-fluoridated areas.28
However, these differences were not quantified and the socioeconomic circumstances and regional location of the children—factors that have previously been found to be associated with both water fluoridation and children's oral health—were not taken into account in the comparisons. The aim of this study, therefore, was to evaluate whether children living in areas with higher concentrations of fluoride in the public water supply have significantly reduced dental caries compared with children residing in non-fluoridated or low-fluoride areas, after controlling for the possible confounding effects of age, regional location, and area-based socioeconomic status (SES).