People using some dentists operating in private practice faced charges four times as high as those for similar treatment elsewhere, the office of fair trading said yesterday.
It found that many surgeries did not detail costs before treatment, nor ensure that patients knew whether they were being charged under the NHS or privately.
Dentists were also not following professional rules that they should not persuade people to accept private treatment by giving incorrect information.
A 14-month investigation concluded that private dentistry costing 7 million people more than £1bn a year was "not working well for consumers". Business was expanding rapidly although only around 200 of Britain's 11,000 dental practices were wholly private. But around a fifth of practices' work nationwide was now done privately, with cosmetic and innovative treatments not available on the NHS fuelling the boom.
The OFT report, the first under a fast-track procedure known as a "supercomplaint", was welcomed by the Consumers' Association which had prompted the investigation after finding huge differences in costs round the country.
The association's principal policy adviser, Frances Blunden, said it was a warning for private dentists. "They must drag themselves into the 21st century ... Patients are not being well served either by the NHS or private care and the Department of Health needs to take a comprehensive approach to dental care."
The OFT inquiry found that only a third of patients were given information about prices before treatment. Many patients were given no information on which work had been done on the NHS and which privately.
A private examination typically cost £20.07 but some dentists charged under £10 and others £40. An amalgam filling cost on average £28.15 but at some dentists this would cost £10 and at others over £54.
John Vickers, director general of fair trading at the OFT, said: "There can be cost and quality differences and to assume every kind of treatment is exactly the same would not be true. But when you see variations on this scale it poses some very serious questions and underlines the need for better treatment ...
"Private dentistry is a young mass market that is not yet properly consumer-oriented. In particular, poor information to many consumers, a lack of price transparency and inadequate self-regulation is limiting competition and choice."
The OFT found that in some cases 40% of the patients who had stayed with a practice when they converted from NHS to private work had done so because they thought there were no NHS alternatives, although this was not necessarily the case.
It wanted better policing of existing rules, a new complaints procedure for private practice, and changes to rules which prevent other dental health professionals such as hygienists and technicians directly offering their services to the public.
Nairn Wilson, president of the General Dental Council which regulates the profession, said it was reviewing its guidance to dentists.
