Leading dentists have called for health officials take back some of the responsibilities currently provided by outsourcing firm Capita.
Capita was commissioned to run NHS England's Primary Care Support England service, which provides support services to NHS GP practices, pharmacies, dentists and opticians.
But the British Dental Association (BDA) said that hundreds of dentists have not been able to perform NHS work because of delays with the service.
It said NHS dentists have had to wait - in some cases for up to a year - to get their National Performer Number required to provide NHS services.
The BDA has written to NHS England boss Simon Stevens requesting that the administration of all Performer List applications should be "taken back in house".
Henrik Overgaard-Nielsen, the BDA's chairman of general dental practice, said: "Continuity of care now requires that these contracts are taken back in-house by the NHS, so dentists can get back to work."
Last week Capita saw its shares plunge to a 15-year low after warning over profits and announcing an investor cash-call as part of a major overhaul.