NHS dentistry is "hanging by a thread" with some patients facing two-year waits for check-ups, the British Dental Association has said.
Department of Health data analysed by the BBC shows almost 1,000 dentists working in 2,500 roles across England and Wales left the NHS last year.
One woman told how she had been in pain for more than a year while waiting to have root canal surgery.
NHS England said patients who most needed care should be prioritised.
Clinical Commissioning Group North Cumbria, which covers the area, lost 4% of its dentists in the last year.
The worst-affected area was NHS Portsmouth CCG, which lost 26% of its NHS dentists over 12 months.
At least 10% of NHS dentists were lost in 28 other English CCGs.
One group of dental practices in Barnsley has failed to attract a single applicant for a number of full-time and part-time NHS dental posts vacant for almost four years.
What's behind the shortage?
The British Dental Association (BDA) and the charity Healthwatch have called for reform of the NHS dental contract.
Until last year, NHS dentists in England and Wales had been using the units of dental activity (UDA) system.
UDAs are used to measure a practice's activity. Courses of treatment - for example, a check-up or a filling, are banded into UDAs.
Practices are set targets of UDAs to achieve, and if that target is missed, the contract holder and the practice can be forced to pay back money.
Critics have claimed the UDA system does not incentivise preventative work and is a key reason for dentists leaving the health service.
Wales moved away from the UDA system in 2021, but it is still in place in England.
What does the British Dental Association say?
The BDA's General Dental Practice Committee chairman Shawn Charlwood wants UDAs scrapped in England.
"NHS dentistry is hanging by a thread," he said.
"Every dentist that is lost or every vacancy for NHS dentists affects thousands of patients.
"Ministers have failed to grasp that we can't have NHS dentistry without NHS dentists."
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Article correct at time of publication 20.1.22.