By Nick Triggle
BBC News health reporter
Hundreds of dentists could walk away from the NHS before a new contract starts next year, dentist leaders say.
The dental reforms start in April
The British Dental Association warned a significant number of dentists in England were considering going totally private or taking early retirement.
Several dentists have already left, complaining the changes will not end the so-called "drill and fill" culture.
The BDA said the contract, which starts in April, does not give dentists enough time to do preventative work.
The feeling is so strong that in some areas up to three quarters of dentists are threatening to quit the NHS.
The deal states they must carry out 95% of the courses of treatment they currently do to get the same money, which dentists say leaves little time for addressing the causes of bad oral health.
The pilots which have been running across the country did not set any targets for the number of courses of treatment, leading dentists to believe the new contract would be the same.
The BDA's Lester Ellman said the contract was a move "back to the dark ages".
"Dentists feel very disappointed about the contract. It really is not going to make any difference to what we are doing now.
"I expect significant numbers will consider their positions in the next few months."
There are only about 300 dentists out of England's 20,000 workforce who do solely private work.
Most do a mix of private and NHS work - commonly a third private, two thirds NHS.
But the move to more private work has been gathering pace for the last 15 years, with images of long queues for NHS dentists becoming increasingly common.
Last month, Tony Blair admitted he was powerless to stop dentists moving into the private sector, six years after promising within two years everyone would have access to an NHS dentist.
In recent weeks, reports have surfaced of dentists in Oxfordshire, Peterborough and Cumbria opting out of the NHS because of the new contract, which will coincide with a shake-up of the fees system.
Under a new contract in April, dentists will only have to do 95% of the work they are currently doing for the same money, allowing them to spend more time on preventative work
A simpler fees systems with three different bands, instead of over 400 charges, will also be introduced
The Eden Dental Surgery in Carlisle went private two weeks ago, slashing its patient list from 5,500 to just under 3,000.
Principal dentist Elizabeth Mather said: "There was a lot of soul searching, but in the end we wanted time to do more preventative work and the new contract just doesn't allow that."
She said the practice was still hoping to treat children on the NHS, but it was unclear whether local health bosses will fund this.
John Latham, secretary of Manchester's dentist's committee, said a survey had found half of the city's 230 dentists were "seriously considering" going private.
In south Manchester, the figure was as high as 74%.
He said: "Patients will find that NHS dentists will not be available.
"The problem is that it is not easy to measure preventative work, it is only in a generation or two that we will see the benefits."
But Chief Dental Officer Barry Cockcroft denied claims it would not change the treadmill of "drill and fill", whereby the more treatments dentists do, the more they earn.
He said: "These reforms will improve dental services for NHS patients, make NHS dentistry more attractive to dentists and promote a more preventive approach to improve oral health."