Just 23 of New Zealand's 67 local authorities use it in their water supplies.
Otago University senior lecturer on dental decay Jonathan Broadbent said Northland's dental woes wouldn't be solved until fluoridation was the norm.
Dr Broadbent said Northland's situation was worse than in some Third World countries. He said in parts of Papua New Guinea where they fluoridate their water they now have lower rates of dental decay than Northland.
"You are having a lot of young children having to have dental treatment under general anaesthetic, which shows there is something seriously wrong.
"Fluoride is a safe and effective way of treating the problem and improving the dental health of your children. The Ministry of Health supports it, as does the Dental Council, the Maori dental group and the vast majority of scientists and dental experts."
He said it was a shame that Northland councils had rejected fluoridation as two-year fluoride trials in the Kaitaia and Kaikohe water supplies had led to a drop in tooth decay in children there.
But Whangarei dentist Lawrie Brett from the Fluoride Action Network said the Dental Council, Ministry of Health and others promoting fluoridation were wrong and there was a growing body of research that showed it was a toxin that should not be put into water supplies.
"And the people of Northland are saying they don't want it. We've had referenda in Whangarei and the Far North where people listened to the debate and made an informed decision not to accept it," Dr Brett said.