Almost half of Birmingham's dentists have failed to sign new contracts allowing them to carry on providing NHS treatment.
A new funding regime comes into force on Saturday, and only those who have agreed to revised terms and conditions will be able to continue treating NHS patients. Just 261 of the 481 dentists and practices working within the health service had signed contracts by Wednesday.
Birmingham and the Black Country Strategic Health Authority said it was confident of a last-minute rush which would see more sign up before the deadline. Only 13 had said they were definitely leaving the NHS, the health authority said.
The new contracts provide dentists with a fixed income, instead of paying them for every piece of work they do.
But dentists claim the changes will leave them worse off, and will damage patient care by removing incentives to do more than the bare minimum.
The contracts can be agreed either with individuals or with practices, depending on working arrangements.
Birmingham MP Steve McCabe (Lab Hall Green) urged dentists to agree to the new terms.
He said: "The Government supports working with dentists who are committed to providing a good service in the NHS. If there are issues with the contract arrangements, I hope the Department of Health can talk to dentists and resolve those."
Mr McCabe criticised dentists who were leaving the NHS and attempting to sell patients private health care.
"It is wrong to persuade, cajole or con people into taking out private insurance when they don't need it."
A spokeswoman for Birmingham and the Black Country Strategic Health Authority said the new contracts "will secure for the dentists a guaranteed NHS income for the next three years and enable the Primary Care Trusts to maintain the current level of NHS dentistry."
Ministers say dentists can expect to earn £80,000 a year under the new contracts. New ones will be recruited to replace any who left the NHS.
Almost half of British adults and two thirds of children are currently registered with one of the country's 19,300 NHS dentists.
A report last year found that two million patients are unable to find an NHS dentist. ..SUPL: