The number of free NHS dental treatments in St Helens has fallen by more than a quarter over the last five years, new figures reveal.
The British Dental Association says an "aggressive and heavy-handed" policy of automatically fining patients accused of misclaiming free care is fuelling a collapse in attendance among vulnerable groups.
Dentists in the St Helens Clinical Commissioning Group area administered 26,613 courses of treatment in 2018-19 to adults exempt from charges, NHS Digital figures show.
Free treatments, which are offered to low-income groups, elderly people, pregnant women and full-time students, have dropped by 28% since 2013-14.
Across England, the number of free procedures fell by a quarter over the same period.
Without an exemption, adults have to pay a charge to visit the dentist, which varies depending on the type of treatment received.
Band 1 procedures, such as check-ups and examinations, and urgent operations to address severe pain or risk of deterioration both cost £21.60 per treatment.
Band 2 treatments, such as fillings, extractions and root canals, cost £59.10, while Band 3 procedures, such as crowns, dentures and dental bridges, cost £256.50.
In St Helens, dentists did not charge their patients for 23% of the courses of treatment carried out in 2018-19.
Free Band 2 and Band 3 procedures have seen the largest drop, each falling by 33% over the last five years.
And as the number of free treatments declines, more patients are now being charged for their dentist appointments – 86,900 treatments incurred a fee last year, compared with 83,541 in 2013-14. They brought in a total of £3.8 million for the NHS.
Misclaiming free care can lead to automatic fines of up to £100.
The BDA says nearly 400,000 patients a year, including those with learning disabilities, have received fines, some simply for ticking the wrong box on a form.
Charlotte Waite, from the BDA, said: "Vulnerable patients will keep turning away from check-ups as long as ministers refuse to let go of their failed fines policy.
"People will keep falling foul of a confusing system which won't give an inch if you make an honest mistake.
"Sadly, the adults and children now failing to attend are precisely those who could benefit most.
"Ministers should be rolling out the red carpet for these patients, not providing reasons to bottle up oral health problems."
The policy in England is in stark contrast with those in other UK nations – in Scotland and Northern Ireland, patients do not receive fines for mistakenly claiming support for NHS care.
The Department for Health and Social Care maintained that it is right to recoup money lost from people incorrectly claiming exemption from prescription and dental charges.
A spokesperson said: "We want every single person to have access to high quality dental care, and we have a number of clear, unchanged exemptions in place to protect those who cannot pay – including those on low incomes.
"If anyone receives a penalty charge notice incorrectly, there are procedures in place to challenge the decision and have the penalty withdrawn."