Dentists in some parts of England are telling parents they will no longer offer free treatment for children.
The dental reforms start in April
They have said local health bosses are not allowing them to treat adults privately and children on the NHS when a new contract is introduced in April.
Many primary care trusts are insisting on the arrangement as they want to build a family approach to oral health.
Dentists said many may leave the NHS, but the government said it was a matter for local decision-making.
The contract has been designed to allow dentists to spend more time with patients doing preventative work.
It will also lead to an overhaul of the charging system to make it more simple, although patients will find themselves paying more for a basic check up.
The deal has to be signed by the end of February if dentists want to ensure continuity, but the BBC has learnt that many dentists are unhappy with the stance being taken by primary care trusts, which are in charge of implementing the agreement on a local level.
The BBC has found 14 PCTs out of 300 which are not allowing dentists to treat adults and children differently.
Many health chiefs are only making exceptions for those who have been operating a two-tier system for more than three years.
The five PCTs in Leeds are one of a group across the country, including dentists in Birmingham and Bristol, taking a tough stance.
Tracy Cannell, of Leeds PCTs, said she was aware dentists were not happy but believes its better to provide a "universal service" for children and adults.
"We believe it is really important we build a family approach and if dentists treat adults and children differently that will move us away from that aim."
Local dentist Maxine Fairclough said she is frustrated and feels it is unfair on dentists that have stayed loyal to the NHS.
She said her practice would be turning completely private, which will mean cutting list of patients down from about 5,000 to 2,000.
A spokesman for the British Dental Association said: "The BDA is concerned that priority groups could be at risk of losing access where primary care trusts are not prepared to offer dentists contracts to treat children and adults who are exempt from charges.
"In areas where this does happen, it will do nothing to ease health inequalities that exist."
Barry Cockcroft, acting chief dental officer for England, said it was a matter for local decision making.
"PCTs are taking over responsibility for commissioning local dental services in order to address local needs.
"The aim of these reforms is to provide better NHS services to both adults and children.
"However, we do recognise that some practices currently provide NHS treatment for children while also taking on private patients and we have made clear that PCTs can agree that this can continue where it meets local needs.
"However, we have also made clear that dentists cannot provide services on condition of a parent signing up for private treatment."
Meanwhile, the government has ordered PCTs to make sure future dentist registrations are conducted on the phone or via the internet rather than in person.
Pictures of people queuing on the street to join a dental practice have made for embarrassing images for ministers in recent years.
Health Minister Rosie Winterton told The Times: "Of course we want to confine queues to history."