The My Dentist practice in Dolgellau will close on 31 March and the town's other practice is private.
A spokesman for the NHS practice said it had been unable to recruit a permanent dentist in the last two years
The deputy mayor of Dolgellau, Delwyn Evans, told BBC Radio Cymru's Post Cyntaf programme more needed to be done to get dentists into rural areas.
My Dentist clinical director Steve Williams said: "There is a shortage of dentists in parts of rural Wales where long-term unfilled vacancies persist over a significant period of time.
"We have tried unsuccessfully to recruit a dentist for the last two years and, regretfully, can no longer provide services at the Mervinian House Family Dental Practice."
A spokesman for Betsi Cadwaladr Health Board said it intended to re-commission dental services in the area as soon as possible.
"However, there is likely to be a gap between the date of termination of the existing services and the completion of the tender exercise and the re-establishment of new services," he said.
"We are therefore making arrangements for the provision of dental services on a cover basis until a permanent solution can be put in place.
"This will include exploring options for short-term support from the other nearest practices, as well as a dental out-of-hours clinic to operate from Dolgellau Community Hospital for patients requiring urgent unscheduled care."
A Welsh Government spokesman said: "When a dentist decides to reduce or end their NHS commitment, the associated funding remains with the health board to re-commission the service.
"Betsi Cadwaladr UHB has invited applications from dental contractors to help ensure there are NHS services available in the area.
"We expect the health board to continue to review and improve access to NHS primary care dental services through the targets set within its 2016-17 Operational Plan."
Nearly 4,500 patients will lose their only NHS dentist in a Gwynedd town from the end of the month.