About 2500 Auckland children have not had a dental check-up since 2016.
Dentists worry many could be in pain, while others could be on track for a lifetime of problems with their teeth.
Every child was meant to be seen by the school dental service once a year.
NZ Dental Association president Dr Katie Ayers said the number who had not been seen for four years was surprising and worrying.
If the children had been developing tooth decay it could now be very, very advanced, she said.
"When children have significant dental problems it affects their ability to eat and their ability to sleep, and their ability to do well at school.
"And it also impacts on the whole family, so if a child's not sleeping well then the parents aren't going to be sleeping well either."
If children were living with pain and infection in any other part of their body it would be regarded as unacceptable, so it was frustrating that long dental care delays persisted, she said.
"We need politicians and leaders to understand that oral health is just as important as general health, and these children need access to the appropriate treatment."
In a report to the Waitematā DHB, Auckland Regional Dental Service said it was making good progress in providing care for the children who had not been seen since 2016.
The number had more than halved since October last year.
Some of the children had not attended their last two scheduled appointments and work was continuing to try to understand the barriers to them attending, a spokesperson said.
It had introduced weekend and mobile clinics to try to make dental care more accessible.
But the service was facing new delays because of Covid 19, with about half of all Auckland children overdue for their routine check-up.
Ayers said the problem was echoed in many other parts of the country.
The Government should consider transferring children to the adolescent dental service at intermediate, rather than high school, she said.
Children would then be seen for free in private clinics, with the school dental services freed up to clear backlogs more quickly.
Delays now could cause many more problems down the track, with poor oral health in childhood likely to lead to problems in adulthood, she said.