By Nick Triggle BBC News health reporter

However, many more put pen to paper, but remain in dispute. Could more dentists opt out?

Piers Lambert has signed the contract, but is unhappy with the terms

Essex dentist Piers Lambert hands out leaflets to his patients explaining the new government reforms.

Reading it, patients will not be left in any doubt that he is not happy.

He points out for treatments such as fillings and x-rays the fee has doubled, while more complex care has gone up by �100 to �189.

And the leaflet quickly adds: "Please remember that these increased charges will not increase the revenue to the practice.

"We will be collecting the indirect "tooth tax" on behalf of the government."

We do not know what is going to happen, but dentists could end up leaving the NHS Lester Ellman, of the British Dental Association

Unsurprisingly, Mr Lambert is one of thousands of dentists who signed the contract "in dispute", meaning they only agreed to put pen to paper to ensure services keep running while continuing to negotiate on the terms.

Mr Lambert, who has a practice in Brightlingsea near Chelmsford, said: "I feel I was coerced into signing it. It was rushed in and is untried and untested.

"I am very concerned that the patients themselves are paying more for a basic treatment."

It is unclear how many of England's 21,000 dentists are in the same boat - the British Dental Association says 60%, the government 30%.

However, unless carefully managed the dentistry crisis could get a whole lot worse. Some 500 dentists have already written to the NHS Litigation Authority lodging their displeasure with the contract.

BDA chief Lester Ellman said: "Dentists are challenging the terms of the deal on a variety of grounds - pay, fees, the deamnds being placed on them, the way it was introduced.

"We do not know what is going to happen, but dentists could end up leaving the NHS."

Deal

The contract signed was for three years, and at this stage it is unclear whether dentists could cut it short.

But with many calling for it to be reviewed in a year, it is clear the government is in for a bumpy ride.

Acting chief dental officer Dr Barry Cockcroft said it was "utterly unlikely" that the contracts in dispute would end up being rejected by dentists and added he remained confident patients would get better access to dentists in the future.

But he acknowledged there had been a degree of anxiety about the new contract but said some of it was due to "misleading and inaccurate impressions of what we are doing".

On the ground, local heath chiefs who are responsible for commissiong services for dentists remain confident things will improve.

NEW DENTAL FEES �15.50 - Will cover a check up, diagnosis and preventative care such as scale and polish �42.40 - Covers all treatment in �15.50 pay band plus fillings, root canal treatment and extractions �189 - Includes treatment in first two pay bands and also more complex procedures such as crowns, dentures and bridges

Clair Raybould, dental lead at Redditch and Bromsgrove Primary Care Trust, said her area had seen some contracts rejected, but had actually ended up with more provision of services than before.

In the past, if dentists had opted out, NHS trusts had no opporutinity to buy in extra services, but under the reforms they can buy in services when contracts are not taken up.

"We have used the money left over to pay dentists who did sign the contract to take on more patients. We have more services than we did before."

But campaigners remain unconvinced such success can be sustained across the country.

Sarah Apps, from consumers association Which?, said: "We are not sure what is going to happen. We know many are in dispute and they may yet jump out of NHS dentistry.

"The other think to bear in mind is that we have a shortage of dentists already."