Health Secretary Alan Johnson will reopen the debate today on whether fluoride should be added to Britain's water supplies.
He will encourage strategic health authorities to implement measures to add fluoride to water if local people are in favour of the move.
Mr Johnson has argued that fluoridation is an "effective and relatively easy way" to help poorer children by preventing dental problems in later life.
At present about six million people in England, mainly in the north-east and West Midlands, receive water containing fluoride.
Children in non-fluoridated Manchester are twice as likely to have tooth decay as youngsters in Birmingham, where fluoride has been added for over 40 years, according to the Department of Health.
A York University study in 2000 found water fluoridation increased the number of children without tooth decay by 15%.
But critics say adding fluoride can cause fluorosis, where teeth become stained and pitted, and has even been linked to bone cancer.
Mr Johnson said: "I want the NHS to do much more to prevent rather than just treat disease.
"Fluoridation is an effective and relatively easy way to help address health inequalities, giving children from poorer backgrounds a dental health boost that can last a lifetime.
"We have a duty to help the areas with the worst record on tooth decay to discuss this issue and take the necessary steps to improve their dental health."
The extent of water fluoridation varies across primary care trusts (PCTs).
South Worcestershire PCT has 31% of the local population with access to fluoridated water compared with 100% at other PCTs.