The prevalence of untreated tooth decay in kids is higher in Australia than in comparable countries, says a new Adelaide University survey.

One quarter of Australian children under 10 have untreated tooth decay while one in nine kids up to the age of 14 have never been to a dentist, says a new survey.

"The prevalence of tooth decay was similar to other comparable countries, such as the United States and New Zealand, but the prevalence of untreated decay was somewhat higher in Australia," says co-researcher Associate Professor Loc Do.

The National Child Oral Health Survey 2012-2014, led by the University of Adelaide, involved data from more than 24,000 children aged 5-14 years in each state and territory.

"We found that tooth decay affected a significant proportion of children: over 40 per cent of children aged 5-10 years had decay in their primary (baby) teeth," he said.

One quarter of children in that age group had never received treatment for their tooth decay.

On average kids aged 5-10 had 1.5 primary teeth with decay.

"More than one third of children aged 9-14 years had decay in their permanent teeth, and one in seven children in this age group had not previously been treated for decay in permanent teeth."

Children from Queensland and from the Northern Territory had the highest prevalence and severity of tooth decay.

The Queensland data was collected at the start of the expansion of water fluoridation, so it was too early to see its impact, Prof Do said.

"Children of low socio-economic background and indigenous children had significantly higher rates of dental decay, unfavourable dental and general health behaviours, and unfavourable dental visiting patterns."

Although the National Oral Health Plans target was for all children to see a dentist, the study showed one in nine had never been to one.