A health board says it has been unable to find a dentist to provide NHS treatment for around 4,000 people.
The NHS dentist in Adpar, near Newcastle Emlyn, Ceredigion, retired in February and an interim replacement service was set up in Cardigan.
Hywel Dda Health Board says the interim service has since been withdrawn due to "recruitment issues".
Many areas of Wales have suffered from a dentist shortage, with hundreds queueing for hours to register.
Carmarthen East & Dinefwr MP Jonathan Edwards called for a "permanent solution".
In March, the Patients Association said "innovative" NHS management had helped improve the situation for many.
The charity noted the Hywel Dda Local Health Board had seen 40,000 extra patients register with an NHS dentist since 2006.
The health board has now said the interim NHS dental service begun in April at the Integrated Dental Holdings practice in Cardigan had been withdrawn.
It said it was working to reinstate dental services as close to Adpar as possible since the previous practitioner retired and closed the practice.
It added that no-one should be in dental pain as additional practice sessions had been put on in Cardigan and Whitland while a permanent replacement was sought.
Mr Edwards said his predecessor as MP, Adam Price, as well as local AM Rhodri Glyn Thomas, had been campaigning on the issue.
He said: "We just need some clarity. The situation arose because the dental practitioner in that part retired.
"There were interim arrangements but they seem to have fallen by the wayside.
"You are talking about a pretty large catchment area and the authorities need to provide some detail about what's going to happen from here on in.
"We expect a permanent solution for the communities of the Teifi valley."
Hywel Dda Health Board said in a statement: "Unfortunately, we regret that despite great efforts, Integrated Dental Holdings has been unable to recruit an additional dentist to provide the temporary service for former Adpar patients.
"The health board has been working extremely hard to put in place alternative arrangements, whilst a long-term solution is put in place. There is no need for any patient to be in dental pain, as urgent care will be provided.
"Patients have been advised that the health board has bolstered emergency access sessions each day at Feidr Fair Practice, in Cardigan, and Hendy Gwyn in Whitland. "
The health board said there was also capacity in some Carmarthen dental practices for those patients who live closer to the town and were willing to travel.
Any patients who need urgent dental care are asked to contact NHS Direct Wales on 0845 6010128, where they will be triaged by a dental nurse.