The union, which represents dentists working in the public sector, said some people might have to wait more than two years to get in.
The North Metropolitan Health Service said Westfield Park in Camillo had a waiting time of 16.2 months.
“Waiting lists at some of the clinics continue to be unacceptably high and unfortunately many people on the long-term lists will give up and not receive much-needed dental treatment,” CPSU/CSA branch secretary Toni Walkington said.
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READ NOWA spokesman from the North Metropolitan Health Service said dental health services staffing levels were currently adequate and it was experiencing low staff turnover rates.