A shake-up in NHS dentistry will come into force next October in a bid to move from "drill and fill" treatments towards more preventative work.

But the National Audit Office (NAO) said dentists may end up cutting their NHS commitments because of scepticism and a lack of detail about the changes.

The government said there were risks but pilot areas had been working well.

The NAO report also highlighted concerns about how the new system would be run.

It said primary care trusts, which will commission services under the deal, did not have the expertise required.

And it added more information was needed on the charging system if patients were to understand the changes.

Risks

The report also warned that the new contract may lead to dentists spending more time with their current patients rather than taking on others, as they are guaranteed a set income over the three years of the deal.

Under the current system, dentists are paid for each individual treatment they carry out, which critics say encourages over-treatment.

Report author Karen Taylor, health director at the NAO, said: "There are clear compelling reasons for why we need change.

"But there are concerns that unless the risks are sorted out quickly, the intended benefits of the new system will not be realised."

Health Minister Rosie Winterton accepted there were risks with the arrangements.

But she said they would make the system more simple for dentists and patients.

She also rejected the criticisms of primary care trusts.

"I understand there are risks with it but PCTs are learning very quickly."

The government is introducing the contract, which will be offered to about 20,000 dentists in England, in a bid to move away from intervention-based working.

It believes dentists have been unable to offer the best service for patients because the payment system is weighted towards treating people rather than addressing why they needed treatment.

The government is also aiming to recruit an extra 1,000 doctors by October 2005.

A review by the Department of Health last year found there was a shortage of 1,850 dentists.

The thinking is that by reducing the amount of time dentists are treating patients and by boosting numbers, more people will be able to get access to dentists.

At the moment just 17m adults and 7m children in England - about half the population - are registered with dentists.

'Ill thought-out'

British Dental Association chief executive Ian Wylie said the government had to get the changes right first time "if it is not to lose what little confidence the dental profession has left in NHS dentistry".

"With less than a year to go until implementation, and still without a draft contract, it's no wonder that many dentists are seriously considering whether or not their future lies within the NHS."

Edward Leigh, chairman of the Commons Public Accounts Committee, to which the NAO reports, said the government had to "step up its efforts".

Shadow Health Secretary Andrew Lansley said it was an "ill thought-out policy".

"Labour has shifted responsibility for dentistry to PCTs without ensuring they have the capacity to deliver."

And Liberal Democrat health spokesman Paul Burstow said: "The new contract is no guarantee that dentists will come rushing back to the NHS.

"There is a real risk that local health trusts will not have the experience to deliver dentistry services, and ministers need to urgently ensure that these trusts have support to provide better access to NHS dentistry."

A spokesman for the NHS Confederation, which represents PCTs, said: "Trusts do already have a full agenda, and the NAO is right to highlight the challenges this new role poses.

"It is vital that over the coming months there is a full programme in place to support implementation and that the necessary resources are available."