By Nick Triggle
Health reporter, BBC News
There are fears that younger dentists are turning their backs on the NHS.
The government has been struggling with NHS dentistry for years
NHS Information Centre data suggests older dentists now focus on NHS work more than young colleagues - a reversal of the situation over five years.
The British Dental Association said older dentists may feel more loyalty to the NHS, and patient groups warned the trend could harm NHS care.
The government said cosmetic work was being embraced by young dentists, but there was still enough for NHS care.
The amount of private work dentists have been doing has been rising since the early 1990s due to dissatisfaction with NHS pay rates.
But it is the big rises in the amount of private work young dentists are doing that is causing most concern.
In 2000-1, 65% of the income of dentists under the age of 35 came from the NHS, but by 2005-6 that had nearly halved to 36%.
This compares to dentists in the older age groups who have seen a much smaller change.
Dentists aged 55 and over received 58% of their income from the NHS in 2000-1, but by 2005-6 it had fallen to 47%. Dentists aged 45 to 54 saw a shift from 55% to 44%.
However, the data, from the NHS Information Centre, did include some small sample sizes.
Dr Anthony Halperin, a dentist and chairman of the Patients Association, said: "These figures are worrying.
"My fear is that we will lose more and more dentist time to the private sector and this will mean NHS care will be reduced to little more than a basic core service."
Lester Ellman, of the British Dental Association, said he believed younger dentists did not have such a strong feeling of responsibility to the NHS as older professionals.
"Dentists who qualified in the 1960s and 1970s were entering a profession that was all about the NHS. There was really no private practice.
"That only started taking off in the 1990s and, coupled with the growth of cosmetic dentistry, it means newly qualified dentists are coming into a profession which is no longer dominated by the NHS. That seems to be making a difference."
But Professor Chris Franklin, of the Committee of Postgraduate Dental Deans and Directors, which oversees the training of dental school graduates, said: "I don't think young dentists are any less committed to the NHS.
"The profession has changed but they still see the NHS as a key part of their work."
The warnings come after Labour has struggled for years to tackle the problems with accessing NHS dentistry.
Tony Blair promised in 1999 that everyone would have access to an NHS dentists within two years, but latest figures suggest the situation is getting worse, not better.
A new contract was introduced in April 2006, but there was a lukewarm response to the changes among the profession.
Barry Cockcroft, the chief dental officer for England, said: "The growth in private practice over the last few years has mainly been within modern cosmetic practice, which has been embraced more by younger dentists.
"This empowers patients to get the treatment they need on the NHS with the option of getting the dental procedure they want where there's no clinical need."
But he added: "There is no shortage of dentists bidding to provide local NHS dental services."
New NHS training places will be made available to dentistry graduates in areas of highest patient need the government has announced.
The initial 40 extra training places coming through in 2009 will be located in Yorkshire, the North West, the South West and the South Central and the 170 dentists graduating every year from 2010 will also be allocated places according to oral health need or where demand is greatest.