NHS dentists are being charged more than £100m in penalties for underperformance against contracts in 2007-08, a report claims.
Research by private dental plan administrator DPAS showed 5 million "units" of dental activity were recorded as undelivered - a 5 per cent increase on the previous year.
Most primary care trusts told the company they were planning to claw back payments where there was more than a 4 per cent shortfall against contract.
DPAS chair Quentin Skinner said the figures showed dentists were doing more work for less money under the general dental services contract introduced in April 2006.
He said: "We could see this coming and, after our research last year on the 2006-07 outcome, I warned that there was a ratcheted treadmill effect built into the new contract.
"Not only would dentists have to work harder in the second year if they were to keep still, but they also had the matter of year one clawback to address - the situation was always likely to compound itself."
Mr Skinner said dentists who had underperformed would be forced to agree to "a mixture of increased workloads for less money, as their year three revenue is reduced by year two clawback, money already spent on last year's running costs and drawings".
A Department of Health spokesperson said the contract was designed to improve access to NHS dentistry.
He said: "The new dental contract system allows local flexibility and places a duty on primary care trusts to assess the local need for dentistry services and commission dental services to fill those needs.
"Dentists that [have] left the NHS [can] now be replaced. Dentists now also get a financial incentive to do preventative work."