What happens to our teeth when water fluoridation levels change?
To prevent tooth decay, many countries fluoridate their drinking water– not always without controversy. In a recent review, researchers from Malaysia and the UK investigate the relationship between water fluoridation levels and the prevalence of dental fluorosis – a condition associated with excess fluoride intake during infancy.
By Nor Azlida Mohd Nor
Water fluoridation, as a means of preventing dental decay has been acknowledged as one of the 10 great public health achievements by the Centers for Disease Control and Prevention. The World Health Organization has recommended a range of 0.5 to 1 ppm (parts-per-million) for artificial fluoridation.
Numerous studies have shown water fluoridation to be safe, effective and cost saving in preventing dental caries. It is generally accepted that water fluoridation at the recommended level does not pose a threat to general health. The only recognised side effect is dental fluorosis, a condition which appears as white patches on permanent tooth surfaces. Dental fluorosis occurs due to excessive exposure to fluoride during tooth development. The highest risk persists between birth and three years of life for front teeth and eight years of life for other teeth.
Changing fluoridation policies
Over time, a number of countries have reviewed their fluoridation policy, taking into account fluoride exposure from other sources such as toothpastes, dental products as well as foods and beverages. In some areas like Calgary and Comox (Canada); La Salud (Cuba); and Tiel Colemborg (Netherlands), water fluoridation has been ceased permanently.
While some countries have decided to stop water fluoridation, other countries decided to reduce the concentration of fluoride added to the water as a means of mitigating the development of dental fluorosis. For example, in the USA and Ireland, the fluoride concentration in public water supplies has been reduced from 1 ppm to 0.7 ppm. Southeast Asia, Hong Kong, Singapore and Malaysia have lowered the fluoride concentration in their drinking water from 0.7 ppm to 0.5 ppm.
The reasons for the change in fluoride levels vary across studies. These include observed increases in dental fluorosis, a public vote in favour of cessation as well as technical issues. Reasons for reducing fluoride levels in the water are related to an increased prevalence of fluorosis as well as concern over the relationship between water intake and climatic conditions. The connection between climatic conditions and fluid intake also explains why countries in warmer climates have opted for a lower fluoride concentration, the assumption being that people in these areas drink more water than those in colder climates.
Impact of water fluoridation levels on dental fluorosis
To maximise the benefit of fluoride in caries prevention and to minimise fluorosis, it is important to monitor the impact of any changes in fluoride exposure. To date, a number of reviews have been conducted to assess the impact of water fluoridation cessation on dental caries. However, there has not been a comprehensive analysis assessing the impact of stopping the addition or reducing the level of fluoride in public water supplies on dental fluorosis. To understand how changes in fluoride concentration influence the prevalence of dental fluorosis, a group of researchers from Malaysia and the UK identified six corresponding studies and examined them in a review, published in Reviews on Environmental Health.
The evidence suggests a significant decrease in the prevalence of fluorosis after cessation or reduction of fluoride added to the water supply. The majority of the cases remaining were very mild and considered as unlikely to have a negative effect on aesthetic appearance. The results confirmed previous findings of a linear relationship between fluoride concentration in the water and dental fluorosis.
Yet, the authors note the difficulty of assessing water fluoridation in the presence of other fluoride exposures such as toothpaste, which act as confounders. With regard to the methodological limitations of the studies included in the review, they conclude: “More studies are needed with better study design and handling of confounders with statistical analyses.”
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