An MP has called NHS bosses to parliament after the closure of three dental surgeries left thousands of people in Portsmouth without a dentist.
The city has no availability for new NHS patients after Colosseum Dental announced the practices would close in mid-July due to a shortage of dentists.
Portsmouth South MP Stephen Morgan fears 9,000 to 20,000 people could be left without access to dental care.
NHS England said patients were being offered help to find alternative care.
Mr Morgan said: "The consequences of this latest development will be detrimental to local residents. Portsmouth people shouldn't have to travel long distances to receive vital treatment.
"The time for complacency is over. I look forward to discussions with NHS England, the health secretary and others in order to safeguard dental services for the people of Portsmouth."
Colosseum - a Europe-wide company owned by Switzerland-based investment group Jacobs Holding - took over the surgeries in Southsea, Paulsgrove and Portsea when it acquired Southern Dental in 2017.
The nearest availability is now in Havant, or a ferry ride away in Gosport.
A company spokeswoman said: "It was with regret and disappointment that Colosseum Dental UK has made the very difficult decision to close a small number of practices in the south east.
"This is due to long-standing and ongoing challenges in dentist recruitment which make it increasingly difficult to continue to provide the very highest standard of care to our patients, to which the company aspires.
"We've been informed by the NHS that they have agreed provision for the 9,000 patients affected."
Last week, the Local Democracy Reporting Service said one patient was told her care would be provided by another surgery but when she contacted them she was told 20,000 people were affected and she would have to join a waiting list.
An NHS England South East spokesman said: "There are more than 20 dental practices open in the Portsmouth area and patients in nine in 10 dental surgeries will not be affected by these changes, while support is being offered for people to find alternative care where that's needed."