The contract launched in 2006 removed people's ability to permanently register with an NHS dentist, so patients cannot be 'deregistered' as the Healthwatch survey asserts.
Once a patient finishes a course of treatment the next time they see the dentist, under the 2006 contract, they are regarded as a 'new' patient.
Most practices continue to care for their list of patients, but because NHS funding for every practice is fixed, individual practices have limited scope to take on new patients, if at all.
The chair of the BDA's General Dental Practice Committee, John Milne, said: 'The Healthwatch survey is not a particularly representative sample of the population, given the small numbers involved and the fact that its findings are so out of step with the latest NHS patient survey of more than a quarter of a million patients.
'This showed that up to 95% of patients were successful in getting a dental appointment.
'However, the survey does provide an insight into just how badly patients can be let down by an inflexible dental contract.
'It's unacceptable that patients who cannot access NHS care when they need it are then faced with having to be treated privately or not be treated at all.
'It's also frustrating for dentists who want to see more NHS patients but effectively have their hands tied when their allocation of NHS funding runs out.
'It's time the government makes clear what the NHS does and does not provide for patients, and explains simply what the cost is to them.
'We hope the new system that emerges from the pilots will provide patients with access to routine and urgent care when they need it, and improve people's oral health wherever they live.
'The government needs to accelerate the pace of change to ensure patients are not missing out on the care they need now.
'It must invest more in dentistry to ensure access improves, not deteriorates.'