High levels of dental fraud in England prove the system needs overhauling, ministers say.
A review by NHS Protect said some dentists were claiming for work they had not done, or playing the system to get paid more than they should.
The review - based on 5,000 bills - suggested about 3% of the 37.5m claims made each year were inappropriate - equivalent to £73m of payments.
Ministers said the current system was too open to abuse.
A new dental contract was introduced in 2006, and this allows dentists to make claims for each course of treatment they deliver.
The investigation by the anti-fraud watchdog suggested some dentists had used the new system to spread treatment over many visits, allowing them to make multiple claims.
Other inappropriate claims included bills for patients who did not exist, or for courses of treatment that real patients did not have.
In total, as many as a million of the 37.5m claims made each year could be invalid, NHS Protect said.
Dermid McCausland, managing director of the watchdog, said: "Action will be taken against those who attempt to take valuable NHS resources for personal gain."
Health Minister Lord Howe said taxpayers would be rightly "appalled".
"It is a great shame that a minority of dentists have been able to game a complex and confusing contract."
He said it showed why a new system was needed to pay dentists for NHS work.
'Drill and fill'
Pilots are already under way to test a new contract at 62 dental practices.
They involve dentist pay being based on a combination of patient list size, quality of care and the number of courses of treatment.
The aim is to give dentists more incentive to spend time with patients promoting good oral health, rather than just "drilling and filling" to meet treatment targets.
If the pilots prove successful, the new system could be introduced in 2014.
John Milne, of the British Dental Association, said there may be good explanations for some of the seemingly inappropriate claims.
But he added: "Where deliberate fraud occurs, it takes money away from patient care and is indefensible.
"The BDA fully supports the counter-fraud activities undertaken by the NHS to detect and eradicate any such activity."