NHS dentistry is being set back 20 years and patients can expect to have more teeth taken out rather than fixed, dentists claim.
The new NHS Dental contract was introduced in April 2006
They blame a contract brought in by the Welsh Assembly Government in April 2006, an investigation by BBC Wales' Week In Week Out programme revealed.
Some patients found more expensive work was only available privately.
The assembly government said £30m had been spent in 2006 to improve dentistry and a review of the contract launched.
The contract was intended to ensure all patients could access a high street NHS dentist for quality dental treatment.
But patient Rhys Jones, who approached his NHS dentist to fix his root canal, found it would have cost him more than £600. It should cost £39 on the NHS.
He said: "I was told I had to go privately if I wanted to be sure of saving the tooth.
"It hurt so much at the time, I just wanted to get it done but the actual bill they were going to charge me hurt more than the tooth itself."
Some dentists were reluctant to deal with expensive work because of how they are paid under the new contract, said the dentists interviewed.
Under the old contract, dentists were paid for each piece of work, but with more than 400 different charges health managers never knew how much they would have to pay out.
The new contract simplified payments to three bands but Peter Beynon, of the Dental Practitioners Association, said it meant dentists now get paid the same to do one filling on a person as 25 fillings.
He said: "And doing the 25 fillings can take considerably longer. The dentist can do it but he does it out of his own pocket.
"So, for example, if a patient needs two crowns, the second crown is done at the dentist's expense so I don't think he's going to do it is he?"
Howard Rose, a dental technician who makes bridges, crowns and dentures, said his NHS work had dropped by 50% since the new contract.
He said: "In my experience what the patient gets from the dentist now has gone backwards, I would say 20 years because whereas we used to do a great volume of crown work, especially single crowns, those teeth now aren't being crowned, they're being extracted.
"The contract's not working I believe as it ought to work. I believe it's failing a lot of NHS patients."
'Aware of concerns'
The assembly government said overall access to dentistry had improved under the contract.
A statement said: "The health minister, Edwina Hart, is committed to ensuring that access continues to improve. However, the minister is aware of concerns."
A review of the contract, following its first year, had been launched last November by Mrs Hart, it added.
A group set up to look at improving the way it works is due to report later this year.
Week in Week Out is on BBC One Wales on Tuesday at 2235 GMT