Patients are being given "confusing and inaccurate" information about where they can get dental care on the NHS, a consumer watchdog has warned.
Healthwatch England said that patients are experiencing "increasing frustration" about NHS dentistry as patients struggle to know where to turn.
Some are travelling up to 40 miles to find somewhere that will provide free care while others are so discouraged by their attempts to find a health service dentist that they end up paying for private treatment, it said.
People are also being "deregistered" for missing appointments even if they have valid reasons to do so, the consumer body addded.
Meanwhile the organisation has also accused some NHS dentists of performing more basic treatments - such as tooth extractions rather than fillings.
The organisation, which is a national body representing the 152 Healthwatch's that operate in each local authority region across England, said the situation is "simply not acceptable".
In a statement the organisation added that there are "emerging concerns that dentists are performing more basic treatments on the NHS like tooth extractions rather than fillings, and in some cases forcing patients to have private appointments with a dental hygienist in order to stay on their books."
One surgery near Plymouth in Devon said that it is accepting new NHS patients from as far as 40 miles away in Cornwall, a spokesman said.
The organisation said that in Kirklees, west Yorkshire, a "significant" number of patients have reported struggling to find an NHS dentist.
One patient told Healthwatch Kirklees: "I'm a 65 year old pensioner, I called up my dentist for new dentures. They advised me to call them every month to check if they were taking NHS patients, but they were only taking on private patients.
"In the end I had to go private and pay £760 for new dentures and I am on pension credits. It's degrading ringing up lots of people, I shouldn't have to jump through hoops to get new dentures."
Another said: "I have been looking for a dentist for over three months and have still not found one. I have rung the dentist but they keep advising me to call back after two weeks. I am now in extreme pain.
"I have contacted all local dentists but they are all saying that they will only take on private patients. I don't want to be going to A&E but the problem is getting worse, if I had been seen three months ago then I might not be in the pain that I am in today."
Meanwhile Healthwatch Bolton said that it had been contacted by patients struck off their dentist's register because of missing appointments - even if they had valid reasons to do so.
One woman said she was struck off after missing an appointment due to an issue with domestic violence and another said she was deregistered after missing an appointment to accompany her husband to hospital for cancer care.
And Healthwatch Leicester conducted a survey to discover how many dental surgeries were accepting new NHS patients. The body found that just 18 of 58 were.
Healthwatch England also raised concerns about information provided on the NHS Choices website - saying that many practices listed online do not provide information on whether or not they accept new NHS patients.
Anna Bradley, chairwoman of Healthwatch England, said: "We hear a lot in the news about people struggling to access their GPs but it would seem getting an appointment with an NHS dentist is even more frustrating.
"Patients are constantly being fed confusing and inaccurate information about who is and isn't currently offering NHS treatment, and are feeling like they have to opt for costly private treatments such as hygienist appointments so that they don't get struck off the books.
"It's simply not acceptable and such basic consumer concerns must be addressed when the Dentist Contract comes up for renewal next year."
Dr Barry Cockcroft, NHS England's chief dental officer, said: "Our figures tell us that 93% of people who tried to get an NHS dental appointment in the past two years were successful.
"Of the 6.5% who tried to get an NHS dental appointment at a practice that they had never attended before, 76% were successful.
"Practices cannot deregister patients. Anyone told this should use the practice's complaint system.
"Dental practices update their own information on the NHS Choices website. It can be difficult for practices to do this as the capacity to see new patients might vary from day to day, especially for small practices. We will be looking, with them, at ways that this process can be improved."