by Cochrane

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The dental health benefits of adding fluoride to drinking water may be smaller now than before fluoride toothpaste was widely available, an updated Cochrane review has found.

The team of researchers from the Universities of Manchester, Dundee and Aberdeen reviewed the evidence from 157 studies which compared communities that had fluoride added to their water supplies with communities that had no additional fluoride in their water. The research was published in Cochrane Database of Systematic Reviews.

They found that the benefit of fluoridation has declined since the 1970s, when fluoride toothpaste became more widely available.

The contemporary studies were conducted in high-income countries. The impact of community water fluoridation in low- and middle-income countries is less clear, due to the absence of recent research.

Fluoride, used in many commercially available toothpastes and varnishes, is known to reduce tooth decay. Governments in many countries have added fluoride to the drinking water supply to improve population oral health, although there are polarized views on whether this is the right action to take.

"When interpreting the evidence, it is important to think about the wider context and how society and health have changed over time," says co-author Anne-Marie Glenny, Professor of Health Sciences Research at the University of Manchester.

"Most of the studies on water fluoridation are over 50 years old, before the availability of fluoride toothpaste. Contemporary studies give us a more relevant picture of what the benefits are now."

Results from studies conducted after 1975 suggest that the initiation of water fluoridation schemes may lead to slightly less tooth decay in children's baby teeth. Analysis of these studies, covering a total of 2,908 children in the UK and Australia, estimates that fluoridation may lead to an average of 0.24 fewer decayed baby teeth per child.

However, the estimate of effect comes with uncertainty, meaning it's possible that the more recent schemes have no benefit. By comparison, an analysis of studies with 5,708 children conducted in 1975 or earlier estimated that fluoridation reduced the number of decayed baby teeth, on average by 2.1 per child.

The same contemporary studies (conducted after 1975) also looked at the number of children with no decay in their baby teeth. The analysis found that fluoridation may increase the number of children with no tooth decay by 3 percentage points, again with the possibility of no benefit.

The review was only able to draw conclusions about the impact on children's teeth, with similar findings across both baby and permanent teeth. There were no studies with adults that met the review's criteria.

"The evidence suggests that water fluoridation may slightly reduce tooth decay in children," says co-author Dr. Lucy O'Malley, Senior Lecturer in Health Services Research at the University of Manchester.

"Given that the benefit has reduced over time, before introducing a new fluoridation scheme, careful thought needs to be given to costs, acceptability, feasibility and ongoing monitoring."

Advocates have suggested that one of the key benefits of water fluoridation is that it reduces oral health inequalities. This updated review sought to examine this question and did not find enough evidence to support this claim, although this doesn't necessarily mean there is no effect.

The review's findings accord with recent observational studies including the LOTUS study, which compared anonymized dental health records with water fluoridation status for 6.4 million adults and adolescents in England between 2010 and 2020. People in fluoridated areas needed slightly fewer invasive dental treatments, with no significant impact on inequalities.

"Contemporary evidence using different research methodologies suggest that the benefits of fluoridating water have declined in recent decades," says Tanya Walsh, Professor of Health Care Evaluation at the University of Manchester, co-author on both the Cochrane review and the LOTUS study. "Oral health inequalities are an urgent public health issue that demands action. Water fluoridation is only one option and not necessarily the most appropriate for all populations."

"While water fluoridation can lead to small improvements in oral health, it does not address the underlying issues such as high sugar consumption and inadequate oral health behaviors," says co-author Janet Clarkson, Professor of Clinical Effectiveness, University of Dundee. "It is likely that any oral health preventive program needs to take a multi-faceted, multi-agency approach."

More information: Water fluoridation for the prevention of dental caries, Cochrane Database of Systematic Reviews (2024). DOI: 10.1002/14651858.CD010856.pub3

Journal information: Cochrane Library 

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