A study has found two-fifths of pre-schoolers in Northland and Auckland have dental cavities.
Dental exams of five-year-olds from 2014 and 2015 show about 40 percent had one or more decayed, missing or filled teeth.
The prevalence was higher in Maori and Pacific children - around three-fifths - and those from the most-deprived neighbourhoods or communities where the water isn't fluoridated.
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"More effort is necessary to reduce the burden of early childhood caries in Auckland and Northland," the researchers said.
"Healthy public policies, such as community water fluoridation, and strategies to reduce sugary drink consumption, such as the implementation of a sugar-sweetened beverage tax, regulating the promotion of sugary foods and drinks, and health warnings on product labels similar to tobacco products, are necessary to address oral health problems in New Zealand children.
"Innovative health promotion, such as health messaging through culturally relevant and interactive platforms of videos, songs, television and tooth brushing demonstration, may also be considered.'
Children are eligible for free dental care up until the age of 17.
The latest study was carried out by the University of Auckland and Waitemata District Health Board, and published in the New Zealand Medical Journal on Friday.