The British Dental Association warned the NHS dentistry service "has effectively ceased to exist for millions".
It comes a few days after the Government rolled out 700,000 extra urgent dentist appointments in 'dental deserts' where patients struggle to access dental care.
Figures from the NHS Business Services Authority, an arm's length body of the Department of Health and Social Care, show there were 262 dentists working in the NHS Somerset Integrated Care Board area in 2023-24.
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It means there were 45 dentists per 100,000 people in the area – down slightly from 50 the year before, and from 58 in 2019-20.
Across England, there was an average 42 dentists per 100,000 people in 2023-24, which was in line with the previous year, but down from a rate of 44 in 2019-20.
There were also significant disparities in access to dental care across the country – Norfolk and Waveney counted 31 dentists per 100,000 population last year, compared to 67 per 100,000 people in North West London.
BDA chair Eddie Crouch said: "Access to NHS dentistry has always been a postcode lottery, but the chances of your numbers coming up are now more remote than ever.
"This reality is this service has effectively ceased to exist for millions."
Mr Crouch urged the Government to fund its pledge to rebuild the NHS dentistry service, which includes the roll out of extra urgent dentist appointments as well as supervised toothbrushing in schools.
"Only then will this service have a future," he added.
Rachel Power, chief executive of the Patients Association, warned NHS dentistry is "leaving patients struggling to get the care they need".
She said dental care appointments are "simply out of reach" in certain areas, leading to "serious consequences" for people's dental health.
Separate NHS BSA figures show only 32% of adults in Somerset saw a dentist in the past two years, and just 43% of children in the area had a dental appointment in the last 12 months.
In England, around 41% of adults had an appointment in the past two years, and about 56% of children did so in the last year.
NHS England's guideline states most adults should see a dentist every two years, and children should go no longer than a year without a dental check-up.
Dr Nigel Carter, CEO of the Oral Health Foundation, said regional inequalities in access to NHS dental services are "shocking" as dental care should be "available at the point of need".
He explained dental conditions such as rotting teeth could be prevented with more regular check-ups but warned "it is not something which can now be fixed overnight".
Dr Carter added: "Currently the NHS contract is not fit for purpose for either the public or profession leading to a crumbling system."
An NHS spokesperson said: "The NHS is determined to improve access to dental care, and that’s why we are working to incentivise dentists to work in underserved areas to ensure people in all areas of the country can receive the care they need.
"But there is more to do and we are working with local systems to provide 700,000 additional urgent dental appointments and with the Government to reform the dental contract and shape the upcoming 10-year plan to improve our services for patients."