NHS dentistry in Wales could disappear, the British Dental Association has warned.
Dentists have described being on the brink of handing back NHS contracts due to stress and concerns about patients' care after changes in Wales.
Welsh government reforms aim to make 112,000 appointments for new patients.
It said it was "always disappointing" when a dentist returned their contract and it was investing £2m annually to improve access to dentists in Wales.
A Senedd committee expressed fears earlier this month that too many people were unable to access an NHS dentist in Wales.
Announced in July 2022, Wales' Chief Dental Officer Andrew Dickenson said the changes to check-ups from six months to 12 months would allow practices to take on up to 112,000 new NHS patients a year.
The British Dental Association (BDA) said the system had left dentists fearing for the survival of NHS practices, with many dentists considering quitting their contracts due to threats of fines.
Out of a recent survey of 250 high street dentists in Wales, conducted by the BDA, more than a third said they would reduce their NHS contract this year, while 13% said they would hand back their contract entirely by March 2023.
Russell Gidney, chairman of the BDA's Welsh General Committee, said the targets were impossible to hit when new patients could take far longer to treat than existing patients who mostly needed check-ups, and that many patients were already only seen once a year.
Combined with a backlog of patients due to Covid, he said the breaking point for the service was "about six weeks ago" and warned it was "going to disappear".
"We've a very real possibility that NHS dentistry as we know it will not in exist in a year or two's time, three months' time," he said.
Mr Gidney anticipated many practices quitting the NHS when the new financial year begins, and accused the Welsh government of refusing to engage.
"We're really expecting to see a snowball effect of practices [quitting] as they deal with the repercussions of this year in six weeks' time.
"If you're trying to make that input and make that change and just not getting listened to, soul-sucking is probably the word I would use," he added.
Dentist Lowri Leeke, who manages Hapus Dental surgery in Merthyr Tydfil, said staff were under huge pressure due to backlogs caused by the Covid-19 pandemic and contract changes.
She said trying to tell people who were used to six-monthly check-ups they would not be seen for a year was "stressful" and she feared health problems - including gum disease and tooth decay - were going unnoticed for months due to less regular routine appointments.
"We are in my practice seeing first hand a big rise in possible oral cancer patients," she said.
"We are constantly just playing catch-up.
"Morale is very low; we are all very tired and very stressed."
Ms Leeke said she knew of dentists who had already handed back their NHS contracts, and many others, including herself, were considering it.
"I'm a practice owner and I'm losing money on a daily basis on my NHS patients," she said.
"The time and the stress that the admin is causing me, I'm spending more of my time ticking boxes and doing paperwork than treating people."
Helen Briscoe, 51, moved to Llanidloes in Powys from Telford, Shropshire, in February 2022 and five members of her family are currently on the waiting list for an NHS dentist.
She has hereditary gum disease which requires her to be seen by a dental hygienist every three months in order to keep her teeth.
But she has not seen a dentist for a year, and said her gums have since "deteriorated".
"I'm very conscious and because I know they've got worse over the year, I don't smile, I don't show my teeth at work, I don't laugh," she said.
Helen used to pay for her treatment through the NHS, which she said made it affordable but she was "worried" how she would cope with the cost of private treatment.
"You manage to save up money, save for a holiday, I'll be saving to have my teeth done every three months," she said.
What does the Welsh government say?
The Welsh government said, while it was "always disappointing" when a dentist reduced or terminated their NHS contract, "less than 20 out of over 400 contracts have been handed back this year [and] most have been re-procured or are in the process of being so".
"We continue to work the BDA to explore how the reform of the national dental contract can encourage dental practices to collaborate and best respond to the dental and oral health needs of their communities," it said.
"The £2m annual funding to improve access to NHS dentistry across Wales will allow health boards to fund dental services based on local needs and issues."