Around six million people currently have fluoridated water in England, in areas where councils have opted into the scheme.
A report found that where fluoride has been added to water, such as Scunthorpe in Lincolnshire where supplies have been treated for decades, fewer children needed fillings.
Britain’s ten million children had around 3.5 million fillings last year, and experts believe youngsters in socially deprived areas may benefit most from mass fluoridation.
But critics of adding fluoride to the water supply suggest it could be putting children at risk of developing dementia when they get older.
Philippe Grandjean, professor of environmental health at Harvard University, told the Daily Mail: "The possible effects on degenerative brain diseases are uncertain.
"We recommend further research to clarify what role fluoride exposure levels may play in possible adverse effects on brain development so that future risk assessments can properly take into regard this possible hazard.”
It is thought adding fluoride could create mottled teeth as well as cause aluminium to move around the body from the stomach to the brain, increasing the risk of dementia. In England councils are allowed to choose to opt into the scheme to add fluoride to the water supply, but campaigners are calling for a measure where people have to give explicit consent for their water supply to be added to.
The NHS report records the number of fillings carried out on children per Primary Care Trust area, before they were abolished under the health reforms.
Of the areas in the top five for fewest number of fillings, three of these – North Lincolnshire, Walsall and Warwickshire – were areas where supplies had been treated with the enamel protecting chemical.
Areas where wholesale fluoridisation carried out had seven per cent less fillings compared with the rest of the country.
Susan Hodgkiss, from the British Fluoridation Society, said reviews of fluoridation had found dental health benefits. She added: “Socially deprived children suffering the highest levels of decay may be among those who stand to benefit most."