By Ken Perrott 23/01/2019

The latest NZ school dental service data again confirms that community water fluoridation is effective. The data show benefits of up to about 30% improvement in oral health. But, anti-fluoride activists will, once again, reject this evidence and instead cherry-pick the data to support their claims.

The NZ Ministry of Health (MoH) has posted the latest summary of child dental health collected by the dental health service. So it is time for local anti-fluoride activists to indulge in their annual activity of cherry-picking and misrepresentation to claim the data “proves” community water fluoridation (CWF) is ineffective (see my comment on last year’s misrepresentation – Anti-fluoridationists misrepresent New Zealand dental data – an annual event).

I haven’t seen this year’s expected press release from Fluoride Free NZ. I may have missed it or perhaps they haven’t got their A into G yet (although there is a bit of notice on their Facebook page). Nevertheless, I will post here my annual analysis of the data.

My comments are much the same as last year – the data has not really changed. But first an explanation of how the data should be used

Nature of the MoH dental health data

The published spreadsheets are simply records of dental health (% caries free and mean Decayed, Missing and Filled Teeth (DMFT and dmft) for 5-year-olds and year 8  children. There has been no selection of children to give representative data. Distortion due to ethnic and socioeconomic factors has not been taken into account.

Data are presented for all children – (Total), Maori, Pacific Island and “Other.” I have previously explained that the Total data is distorted by ethnic factors – different ethnic groups have differences in oral health, irrespective of fluoridation. In particular, the predominance of Pacific Island children in fluoridated areas distort the “Total” data – 85% live in fluoridated areas. Pacific Island children comprise about 15.1% of children in fluoridated areas but only about 3.2% of children in non-fluoridated areas.

Because Pacific Island children generally have poorer health they increase the value of dmft/DMFT and lower the value of caries-free % in the fluoridated areas in the Total figures. Therefore the “Other” figures are more reliable than the “Total” figures for interpretation.

The 2017 data

You can download the two spreadsheets, and the spreadsheets for earlier years, from the MoH website – Age 5 and Year 8 oral health data from the Community Oral Health Service). I will just give the overall New Zealand data for Māori and “Other” (this is all except Māori and Pacific Island).

As explained above the “Total” data is misleading because of ethnic effects and the data for Pacific Island is poor because only a small number resided in non-fluoridated areas.

5-Year Old Children

Clearly, the overall data suggest a benefit of fluoridation to Maōri and “other” children – about 14% for “Other” and 25% for Māori children (using the data for mean dmft).

Year 8 Children

Again the data suggests that fluoridation has been beneficial to Māori and “Other” children. The DMFT data suggest a benefit of about 30.5% for Māori and 26% for “Other” children.  Even the %Caries free data indicates benefits of about 16% and 11% for Māori and “Other” children respectively.

Changes over time

It’s worth considering more than one year. This overcomes, to some extent, variations in the data. It may also be helpful in assessing if the effectiveness of CWF is changing.

However, there is a proviso. Let’s not forget this is simply raw data from the school dental service. While I have corrected for ethnic differences I have no way of correcting for other differences. Socioeconomic effects may change over time. Another important factor is that, at least in some regions, dental health authorities are targeting children form non-fluoridated areas with extra treatments like fluoride tooth varnishes. Ideally, a controlled experiment would take all these factors into account.

I will just take one example – the DMFT data for year 8 children.

The table shows the mean values of %Caries free and DMFT of year 8 children over the periods 2005-2017 and 2013-2017.

Year 8 Children Māori “Other”
%Caries Free
Mean 2005-2017 24.2 13.4
Mean 2013-2017 15.6 8.8
Mean 2005-2017 31.3 24.7
Mean 2013-2017 30.1 22.2

This data shows that the oral health of both Māori and “Other” children have improved over time irrespective fluoridation. But there is still a difference between fluoridated and unfluoridated areas indicating fluoridation is having a benefit over and above other factors contributing to oral health improvement.

The differences due to fluoridation seem to be diminishing. However, my comments above are relevant here. This could be due to extra fluoride treatments targeting children from non-fluoridated areas.

It’s obviously a factor for health authorities to consider but limitations in this data should be kept in mind and other sources of information also considered.


Once again the MoH school dental service data show benefits from CWF. But don’t expect anti-fluoride activists to accept this. I expect they will indulge in their usual cherry-picking of the data to confirm their biases.