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The procedures were mostly carried out in hospital operating theatres and cost more than $22 million.
RNZ reported last month that thousands of children were waiting months in the public system for serious dental work for often painful conditions.
Much of that was for work under general anaesthetic, with dentists saying that put a strain on the health system as a whole because hospitals had to find space in their theatres.
Figures from the Ministry of Health for the 2017/2018 financial year, showed 8758 people under 18 had dental work under general anaesthetic in the public system.
Of these, more than 7000 of them were 13 and under, a New Zealand Dental Journal study showed.
Dental Association (NZDA) president Bill O'Connor said children needed to go under a general anaesthetic for all sorts of reasons - including disability, anxiety or being too young to sit still in the chair.
He said the vast majority of the work was because of preventable tooth decay.
"It's really frustrating to think that all this money, all this theatre time that's being taken up, all the personnel that have to do those general anaesthetics and work on these things, could be doing other things."
Specialist paediatric dentist Katie Ayers said the procedures were very safe but could cause the children's families a lot of anxiety.
Dr Ayers said If a little more money was spent earlier on preventive care, particularly for pre-schoolers and young children, they wouldn't need to have operations under general anaesthetic as young as four years old.
Professor of dental health Jonathan Broadbent, of Otago University, said it was important the work was done because no one wanted to see children in pain.
But he agreed more funding was needed for prevention, such as fluoridating water supplies and teaching people about the importance of kids avoiding sugary drinks and snacks.