Data was provided under the Official Information Act by the Ministry of Health to the New Zealand Herald.
Hospital admissions for dental disease have jumped, especially in poor families.
Toddlers as young as 2 years old are suffering tooth decay so severe all their teeth have to be removed, as child hospitalisations for dental disease soar.
Health data shows the numbers of children admitted for dental treatment in hospital jumped from an annual 4500 to 7500 in the past 15 years.
Worst affected are children from the poorest families, who dentists say struggle to afford toothpaste and sometimes resort to sharing one toothbrush among an entire family.
Those families also rely more heavily on cheaper, high-sugar foods, and are less likely to seek early treatment often because of a lack of transport or time, and may live in non-fluoridated areas - all factors that can lead to huge levels of decay, dentists say.
"For a small subset of children - those living in poverty - it's often not two teeth that are decayed but it's 20 teeth," said pediatric dentist Katie Ayers, from the New Zealand Dental Association.
"And it's more commonly those kids we are seeing in the hospital."
Ayers said some of the children would be counted twice in the statistics, for example those seen at age 2 and then again at age 4. But dentists aimed to only put them under general anaesthetic once if they could help it.
"It's heartbreaking. And parents feel terrible. They feel upset and guilty. I try to relieve their guilt as lots of the factors are beyond their control or they may not have understood the issue. We try to work on prevention," she said. Sometimes health providers also supplied toothbrushes and paste.
The ministry does not record data by socio-economic status, but the Herald was able to analyse it according to the children's address data.
Analysis found admission rates were higher for pre-school children, with 13 in 1000 hospitalised for dental caries (tooth decay) or pulp (nerve decay) last year.
Among 5-14-year-olds, 9 in 100 were hospitalised last year. Admission to hospital was usually only required when a child needed surgery under general anaesthetic, commonly but not always for tooth extraction.
Children from the most deprived areas were more than twice as likely as those from the least deprived to need to go to hospital.
That gap was growing, as admissions increased 10 per cent in the past 10 years among preschoolers from the poorest families.
Professor of Dental Epidemiology and Public Health Murray Thomson, from the University of Otago, linked that to increasingly inequality - particularly during the last National government - which took a toll on those at the bottom.
Thomson said early childhood tooth decay was well known as one of the most sensitive markers of economic stress on households.
"It's easy to blame parents and say they should brush their children's teeth, but this is the precariat - they live hand-to-mouth, they're living in food deserts without fruit and vegetables and with lots of takeaways, where fizzy drink is cheaper than milk," he said.
"Much of that is outside what dentists can do in a clinical setting. But if you improved those people's lives those rates would come down very quickly."
The Ministry of Health said the numbers of children being hospitalised for dental treatment had risen internationally, although overall dental health among children in New Zealand was improving.
Reasons for the increased hospitalisations were many and varied, but they included the re-orientation of the Community Oral Health Service - including $116 million in capital funding and $32 milion operational funding each year - to emphasise early engagement with preschool children. The ministry expected numbers to climb further before they improved.
Neither the government nor the health boards had analysis by deprivation. The last time the data was collated at a socio-economic level was in 2009. Instead, it arranged the data by ethnicity, with Maori and Pacific Island children also having higher rates of decay.
The new health minister, David Clark, did not answer questions about the statistics.
The previous government had also introduced a target of reducing dental hospitalisations by 25 per cent by 2021, but it was unclear if that would remain.
National's health spokesman Jonathan Coleman said hospitalisations had increased because more children were being reached because of more funding in the Community Oral Health Service. He said it was important the child dental health target was continued.
Weekend clinics help numb the shock of tooth removal
When Laura Gray's husband called from the dentist's office to say their 8-year-old needed a tooth removed, it was a "huge shock".
The Manurewa mum-of-two doesn't allow fizzy drink in the house and, after growing up with bad teeth herself, had been making sure her boys brushed every day.
"It was very upsetting," she said. "My husband was very nervous about it but I said we had to do it because he'll be in pain."
Tristan, her son, had the extraction done at the Browns Rd dental clinic under local anaesthetic and has been going back for regular check-ups since, alongside his brother Cody, 10.
Manurewa mum Laura Gray got a shock when her son Tristan, 8, had to have a tooth extracted. She's hoping Cody, 10, will have better luck with his teeth after his appointment. Photo / Brett Phibbs
The clinic was part of a trial in Manurewa, where the Auckland Regional Dental Service introduced weekly Saturday clinics after discovering many families found it hard to attend weekday appointments - largely because of time and transport issues.
Gray was one of those, saying she struggled to take the boys out of school for appointments, but the weekend made it easy and convenient, especially when the children required repeat visits, as Tristan did.
"It means we don't have to worry and when can take him back when he needs another filling."
The dental services says to help more families, planning was now under way to extend Saturday clinics to Otara, Puhinui, Mangere, Kingsland and Glen Innes.
The Government has also committed $2.5 million a year over four years for oral health promotion to improve the oral health of young children. It includes a social marketing campaign and television commercial.
Toothbrushes and fluoride toothpaste will be distributed to families next year.
