Over the 2017-18 financial year 48,982 free courses of treatment were given to adults, including check ups, fillings and urgent extractions, according to NHS Digital figures.
However this was a 23 per cent drop on 2013-14, when 14,998 more free courses of treatment were offered.
Across England the number of free dental treatments has decreased by almost a quarter.
The British Dental Association claims low income patients are “turning away from NHS dentistry in droves”, due to the Government’s aggressive approach to stop ineligible patients.
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It believes people who should receive free dental care are not seeking treatment over fears they will be fined for a wrongful claim.
The Government’s advertising campaign uses the slogan “don’t assume you’re entitled”.
Adults are eligible for free dental care if they are pregnant or on low income benefits.
The BDA says many patients have received £100 fines for simply ticking the wrong box on the form.
It claims the number of fines issued in England has increased by more than 12 times, from 33,887 in 2012-13 to 428,000 in 2017-18.
The BDA’s chairman of general dental practice Henrik Overgaard-Nielsen said: “This huge fall in NHS attendance amongst patients exempt from NHS charges is the logical outcome of failed government policy.
“Ministers have created a hostile environment for vulnerable groups and those on low incomes who have a right to free dentistry. These patients, often with complex needs, require early intervention not the ever-present threat of fines.
“Sadly the Government has shown no interest in getting hard to reach families to attend, when prevention could save our NHS millions.”
The type of procedures with the largest drop in Wakefield were urgent and occasional treatments, which decreased by 31 per cent.
These are treatments for when oral health has deteriorated rapidly, such as several fillings and extractions.
A Department for Health and Social Care spokesman said: “We want every child and adult to have access to free NHS dental care if they are eligible and we are looking at ways of simplifying the process for vulnerable people.
“But it is absolutely right that we recoup money from patients who incorrectly claim free services so it can be reinvested back into the NHS.”