Authors: Iheozor-Ejiofor Z, Walsh T, Lewis SR, Riley P, Boyers D, Clarkson JE, Worthington HV, Glenny A-M, O'Malley L
Does adding fluoride to water supplies prevent tooth decay?*
Key messages
‐ Adding fluoride to water supplies may lead to slightly less tooth decay in children’s baby teeth.
‐ It may also lead to slightly more children being free of tooth decay.
‐ The benefits of fluoride in water supplies may be smaller than they were before the widespread addition of fluoride to toothpaste.
Tooth decay and the use of fluoride
Tooth decay is a worldwide problem affecting most adults and children. Untreated decay may cause pain and lead to teeth having to be removed.
Fluoride is a mineral which occurs naturally in water at different concentrations. It prevents tooth decay. Since 1975, fluoride has been an ingredient in most toothpastes. It is available in some mouth‐rinses, and dentists use treatments that contain fluoride. It is possible to add fluoride to the local water supply. In this case, everyone in a community will have access to fluoride.
If young children swallow too much fluoride while their permanent teeth are forming, marks may develop on those teeth – this is called dental fluorosis. This can be very mild, with barely noticeable white lines or streaks. Rarely, some fluorosis is more noticeable, and people can dislike how their teeth look.
What did we want to find out?
We wanted to find out if water with added fluoride in the local water supply is better than water without added fluoride at:
‐ reducing the number of teeth, or tooth surfaces, with signs of decay;
‐ increasing the number of people who have no tooth decay.
We also wanted to find out about unwanted effects.
What did we do?
We searched for studies comparing communities that had fluoride added to their water supplies with communities that had no additional fluoride in their water.
The last time we published this Cochrane review, we also searched for studies that reported dental fluorosis and the concentration of fluoride in the water. Because the association of fluoridated water with dental fluorosis is widely accepted, we did not update the evidence on this occasion.
What did we find?
We found 21 studies that assessed the effects of adding fluoride to a water supply. We also found one study that assessed the effects of stopping artificially‐added fluoride in a water supply. Studies only measured tooth decay in children.
In the last version of the review – not updated on this occasion – we found 135 studies that assessed the association of fluoridated water with dental fluorosis.
Main results
Studies conducted after 1975 showed that adding fluoride to water may lead to slightly less tooth decay in children’s baby teeth. We could not be sure whether adding fluoride to water reduced tooth decay in children’s permanent teeth or decay on the surfaces of permanent teeth.
Adding fluoride to water may slightly increase the number of children who have no tooth decay in either their baby teeth or permanent teeth. However, these results also included the possibility of little or no difference in tooth decay.
Studies conducted in 1975 or earlier showed a clear and important effect on prevention of tooth decay in children. However, due to the increased availability of fluoride in toothpaste since 1975, it is unlikely that we will see this effect in all populations today.
We were unsure whether there were any effects on tooth decay when fluoride is removed from a water supply.
We were unsure if fluoride reduces differences in tooth decay between richer and poorer people.
In the last version of the review, we found that adding fluoride to water supplies increases the number of people with dental fluorosis. If water contains 0.7 mg/L of fluoride, about 12% of people may have dental fluorosis that causes them to be bothered about how their teeth look, and about 40% of people may have dental fluorosis of any level. We were unsure whether fluoride in water leads to other unwanted effects.
What are the limitations of the evidence?
Our confidence in the evidence is limited because this review included studies in which communities were deliberately selected to have changes to fluoride levels in the water supply. Although a common study approach for this topic, it can mean that there are differences between communities that might affect the results. In addition, the findings in some studies were different from others, and some results included the possibility of benefit and no benefit.
Older studies were conducted before the widespread use of fluoride toothpaste and other improvements in tooth decay prevention. This meant we could not tell if these results were applicable to current times. However, they may still be relevant to countries in which tooth decay is very high and people don't have easy access to fluoride toothpaste and other prevention strategies.
How current is this evidence?
For the effects of water fluoridation on tooth decay, this review updates our previous review and the evidence is current to August 2023.
For the association of fluoridated water with dental fluorosis, the review evidence is current to February 2015.
*This is a plain language summary of a review that is published in the Cochrane Library. You can find the full report of the review here:
https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD010856.pub3/full#CD010856-abs-0002