Experts have called for an end to the "woeful" neglect of Kiwi kids' dental health, with a major new study revealing one in seven of our 4-year-olds are suffering tooth decay.

The study, drawing on data from 275,000 children, pointed to a heightened risk among Māori and Pacific kids, those living in deprived areas - and those without access to fluoridated drinking water.

Published this morning in high-ranking journal JAMA Paediatrics, the study explored data collected under the B4 School Check screening programme between 2011 and 2016, revealing more than 41,000 kids - almost 30 per cent - had severe cavities.

Once data were adjusted for factors like age, sex, ethnicity and wealth, and location, the researchers found that children living in areas without fluoridated community water had 20 per cent higher odds of severe cavities, compared with those living within fluoridated areas.

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They also found that even children in wealthier areas weren't immune from dental problems: about seven per cent of Pākehā children and children living in the least deprived areas still had severe tooth decay.

"Modern dentistry can only do so much to tackle this issue and by the time children receive dental care it's often too late to save their baby teeth, which then affects the development of adult teeth," said study co-author Dr Martin Lee, Canterbury's Community Dental Service clinical director.

"Community water fluoridation is the safest and most cost-effective preventative strategy we have to protect the teeth of all Kiwi kids, and the teeth of all New Zealanders generally."

New Zealand had a long-term national policy supporting community water fluoridation, yet only 54 per cent of the population currently received it.

A bill proposing moving responsibility for this from councils to district health boards, introduced in 2016 - yet it hasn't been progressed since a health select committee report in 2017.

The study's lead author, Professor Philip Schluter of the University of Canterbury, said the burden on the dental health of Kiwi kids was not shared equally across the country.

"The research shows the current lack of widespread community water fluoridation disproportionately affects children living in the most deprived areas, with Māori and Pacific children more likely to experience worse oral health than pākehā, even after accounting for key sociodemographic factors," he said.

"We hope that the real-world evidence provided in this research will be used in evidence-based policy-making to combat the woeful oral health burdens and neglect carried unnecessarily by so many children in New Zealand."

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The new findings weren't surprising to prominent dental researcher Dr Jonathan Broadbent, who wrote about the need for more investment in prevention this month in the New Zealand Medical Journal.

Along with progressing the bill on fluoridation, the Otago University researcher said other Government intervention was needed to tackle rates of tooth decay.

"[The bill would be] effective – but it's not enough."

Earlier this month, New Zealand researchers reported that nearly one in five of Canterbury's 5-year-olds have tooth decay – Christchurch is New Zealand's only major metropolitan centre without a fluoridated water supply – and that children in our most deprived areas benefit from fluoridation.

Health Minister Chris Hipkins last night told the Herald the benefits for oral health of fluoride in drinking water were "clear".

"My expectation is that local authorities recognise the science, listen to the medical advice, and act accordingly as many already do."

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Hipkins said the Health (Fluoridation of Drinking Water) Amendment Bill remained part of the Government's legislative agenda, which had more recently been increasingly busy with Covid-19-related legislation.

Broadbent noted with interest that the new study happened to be published in the same journal that last year featured a controversial paper that suggested children exposed to more fluoride at very young ages had lower IQs.

Scientists around the world were quick to criticise that paper – which prompted billboards in Auckland by anti-fluoride campaigners – with one calling the reported link "false" and another calling the findings "pretty weak and borderline".

A high-level review carried out in 2014, and commissioned by then-chief science adviser Sir Peter Gluckman and Royal Society Te Aparangi, found fluoride levels used in New Zealand created no health risks and provided protection against tooth decay.