Severely disabled children and adults have been unable to get routine appointments at a special dental practice for nine months.

NHS England has launched an investigation after a report from patient group Healthwatch Hackney (HWH) revealed patients have only been able to book emergency appointments at the clinic in St Leonard’s Hospital in Nuttall Street since it was taken over by a new provider last year.

Parents of autistic children with communication and learning disabilities, who used to have appointments every few months, have been told by staff at the Community Dental Service they will not be seen “for the foreseeable future”, and that there was “a backlog of over 100 patients”.

Kent Community Health NHS Trust – which this week apologised “for any inconvenience” – took over running the service from Barts NHS Trust in April.

It is thought Kent undercut what Barts NHS Trust had been charging when NHS England put the contract out to tender – but the health body would not reveal how much the new deal was worth, saying procurement bids are “commercial in confidence”.

The special dental service has nearly 500 disabled children and young people on its books who have a social, psychological or physical disability and require dental care to be adapted for them.

A spokeswoman for HWH described the situation as “an unacceptable state of affairs”.

“These patients are children with the most complex needs, who cannot articulate pain or distress to their care-givers in a typical way,” she said.

“Without access to adequate dental care, these children are likely to experience long term problems with their oral health on top of their existing health challenges. Poor oral health can have a significant impact on their behaviour and communication at home and at school.”

She said it was important to know whether money had been cut from the previous contract.

“I think this wouldn’t be happening if they hadn’t sucked loads of money out of it. There’s no transparency to it and there is no accountability,” she said.

No parent approached by HWH had received an appointment letter, reminder or communication of any kind from the service since Kent took over.

One parent said they used to see the hygienist and specialist dentist every six weeks. “It was to get them used to going to the dentist and sitting on the chair at first,” they said. “As time went by it became more familiar and safe. Then they were finally able to work on his teeth. This has to be more regular for our kids.”

Kent’s dental clinical director Nicola Pearson said her trust takes the “quality and timely care” of patients “very seriously”.

“Since April we have seen an increase in the number of patient referrals for treatment from our paediatric and special care community dental services,” she said.

“We are working very hard to meet the needs of our patients. Through partnership working with local high street dentists, we have significantly reduced our waiting list and have improved access to care for patients. We are also working with special schools in Hackney to provide school-based dental prevention programmes. We are in contact with NHS England about the number of patients seen, the complexity of treatment provided and waiting times.”

A spokesman for NHS England (London) said bosses were “sorry” to hear patients couldn’t access the special dentistry service, and would investigate the matter.