The government has been told there are major savings to be made in extending fluoridation but that controversy surrounding the issue will not go away.
Health Minister Jonathan Coleman announced last month that district health boards rather than local authorities will decide which community water supplies are fluoridated.
Information and research provided to Cabinet's social policy committee backgrounding the decision was released by the Ministry of Health yesterday.
In the release, Dr Coleman and Associate Health Minister Peter Dunne say although New Zealand's oral health outcomes have improved dramatically over the past 30 to 40 years, the country still has high rates of preventable tooth decay.
"In 2013, for example, more than 40 percent of all five year olds and more than 60 percent of Māori and Pacific five-year-olds already had tooth decay.
"These same children, and children in high deprivation areas, are also likely to have significantly lower levels of newborn enrolment with primary care services, contact with Well Child services, enrolment with child oral health services and completion of the B4 School Check."
Fluoridation has benefits for all age groups, the information states.
"Reductions of tooth decay are reported to be around 20 percent among adults aged 18 to 44 years and 30 percent among adults aged 45 years and over. Among children and adolescents, there is a 40 percent lower lifetime incidence of tooth decay."
The World Health Organisation has endorsed fluoridation as the most effective public health measure for preventing tooth decay and the research provided to the Committee says some evidence suggests poor oral health is also linked to other health problems.
Currently 27 out of 67 territorial local authorities fluoridate their drinking-water supply, meaning 54 percent of New Zealanders receive fluoridated water.
"The level of coverage has not increased over the last 15 years. A number of local authorities have decided not to fluoridate or have introduced fluoridation and then reversed their decision."
The papers provided to Cabinet said fluoridation had become "an increasingly contentious issue" for local bodies, because of active lobbying and court action against councils by anti-fluoridation groups, and controversy at local body elections and referendums.
"The view of Local Government New Zealand is that fluoridation decisions should be made in the health sector, rather than by local government which is simply the owner and operator of water assets and does not have fluoridation expertise."
They said it was possible that fluoridated water supplies could be extended to cover an extra 1.45 million people. Net savings of more than $600 million over 20 years would result, with most savings to consumers and a small amount to Vote Health.
A report by the Sapere Research Group, which was also released, estimates the total capital and operating costs of extending fluoridation, to areas not currently receiving it, to be $144 million over 20 years.
Sapere said dental decay accounts for approximately one percent of all health loss in New Zealand, due to early death, illness or disability.
The research said there had been a number of court challenges over fluoridation, notably involving South Taranaki District Council and Hamilton City Council.
"Because none of the High Court's decisions finally rule on the substantive merits of fluoridation, the issue remains open to challenge by opponents of fluoridation. Councils find that they cannot make a decision "once and for all" but face the prospect of having to undertake further public consultations and to revisit decisions to fluoridate."
The government decided DHB decision-making was the best of several future options considered - but added it came with risks.
These included that "the boards of DHBs would face the same scrutiny that territorial local authorities have experienced at election time over fluoridation. The election of anti-fluoride advocates could lead to a stalemate or a reversal of fluoridation, as has happened with some local authorities."
The research says that in order to help manage these risks, the ministry would develop a regulatory framework to support DHBs to take a structured and nationally consistent approach.
Local bodies will retain the direct operating and capital costs of fluoridation, but DHBs are likely to incure some additional costs, relating to consultation and accessing technical expertise, and to costs in the event of judicial review of their decisions.
These costs, expected to be in the range of $100,000 to $200,000 (per challenge and excluding GST), potentially could pose "a substantial burden on smaller DHBs. In this case the Ministry may need to provide additional financial support to DHBs."
A bill and other measures are expected to give effect to the changes later this year.