Adding fluoride to water in deprived areas of the north-east of England will reduce dental decay among children, the country's chief medical officer claims.
Sir Liam Donaldson says children in deprived parts of the region have levels of dental decay more than three times worse than in others.
Research in his annual report focussed on dental health among five-year-olds.
It showed areas with fluoridated water had low levels of decay - even though some had high levels of deprivation.
His report shows the number of decayed, missing and filled teeth varies from 0.86 per child in Hartlepool, to 2.82 per child in South West Durham.
Sir Liam said: "Local studies have shown that fluoridation can nullify the effects of deprivation.
"On Teesside, for example, the most deprived wards in fluoridated Hartlepool still have less dental decay than the least deprived wards of non-fluoridated Middlesbrough.
"Extending the provision of fluoridated water remains a priority in tackling inequality."
The research also highlights a historic irony in some of the earliest work identifying the benefits of fluoride which compared dental decay in two similar populations in North and South Shields.
Those in South Shields - which then drew its water from naturally fluoridated wells - had much lower rates of decay.
But because these have now been replaced by a non-fluoridated supply and most of North Shields now receives fluoridated water, the positions in the two towns have been completely reversed.