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

A team of researchers from the Universities of Manchester, Dundee, and Aberdeen reviewed the evidence from 157 studies comparing communities that had fluoride added to their water supplies with communities that had no additional fluoride in their water. They found that the benefit of fluoridation had 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 the population’s oral health. However, there are polarised views on whether this is the right action to take.

Anne-Marie Glenny, co-author and professor of health sciences research at the University of Manchester, said, “When interpreting the evidence, it is important to think about the wider context and how society and health have changed over time.

“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.”

The results

According to the researchers, 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 0.24 fewer decayed baby teeth per child. However, the estimation is uncertain, 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) examined 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 three 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.

Lucy O’Malley, co-author and senior lecturer in health services research at the University of Manchester, said, “The evidence suggests that water fluoridation may slightly reduce tooth decay in children.

“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 a key benefit of water fluoridation is that it reduces oral health inequalities. The research attempted to examine this question but 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, which compared anonymised dental health records with water fluoridation status for 6.4m 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.

Tanya Walsh, co-author of the Cochrane review and professor of healthcare evaluation at the University of Manchester, said, “Contemporary evidence using different research methodologies suggest that the benefits of fluoridating water have declined in recent decades.

“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.”

Janet Clarkson, co-author and professor of clinical effectiveness at the University of Dundee, said, “Whilst 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 behaviours.

“It is likely that any oral health preventive programme needs to take a multi-faceted, multi-agency approach.”

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