Half of people in England do not have a NHS dentist, Department of Health figures reveal.
Hundreds queued to join a new NHS dentist in Scarborough this week
They show just 44% of adults and 60% of children were registered with a NHS dentist last year.
The figures come just days after hundreds of people in Scarborough queued for hours to join a new NHS dentist.
The Department of Health has rejected opposition claims that NHS dentistry is in crisis. Ministers say they are spending millions improving services.
The figures were published in response to questions tabled by the Liberal Democrats in parliament.
They show that the proportion of people who are registered with a NHS dentist has hardly changed since 1999.
They also reveal huge variations across the country. For instance, just 36% of adults in south west London were registered with a NHS dentist last year. This compares to 65% of adults in north and east Yorkshire and northern Lincolnshire.
Similarly, just 37% of children in Kent and Medway are registered with a NHS dentist compared to 67% in Avon, Gloucestershire and Wiltshire.
Liberal Democrat health spokesman Paul Burstow said the figures were low because NHS dentists are refusing to take on new patients.
He said just 10,700 of the 16,649 dentists in England were accepting new children as patients while just 8,830 were offering free treatment to adults.
"With so few dentists accepting NHS patients it is little wonder that the levels of people registering with the NHS are so low.
"As NHS dental cover declines so too is dental health. The government must get to grips with the crisis in dental health."
There is anecdotal evidence that many people have difficulty finding a NHS dentist.
In recent months, the arrival of new NHS dentists in some towns and cities has been followed by huge queues of people trying to register before they get too full.
Health officials in Scarborough say they will now appoint a second NHS dentist after this week's queues.
John Renshaw, a dentist in Scarborough and chairman of the British Dental Association, urged ministers to take action.
"We get 3,000 inquiries a year at our surgery alone from people wanting to register as new NHS patients and if you multiply that you can see just how big the problem is," he said.
"Is the government making any attempt to stop the problem getting worse?
"What they are doing here is putting a sticking plaster over the haemorrhage and everything's spilling out from under the plaster."
Health Minister Rosie Winterton said the government was committed to improving the service.
"We are increasing the number of graduates coming through dental schools and in the longer term we are changing the way dentists are paid, which will ensure that they are encouraged to stay with the NHS," she told the BBC.
Conservative health spokesman Andrew Lansley accused the government of breaking promises.
"Tony Blair pledged in his 1999 party conference speech that everyone would be able to see an NHS dentist within two years. This promise was repeated in the government's NHS Plan in July 2000.
"The people queuing to register for the NHS dentist in Scarborough know only too well that this is yet another promise that the Government has made but failed to deliver."