Misrepresenting fluoride science – an open letter to Paul Connett

A poster for Connett’s Blenheim meeting – scaremongering because there is no proposal for mandatory fluoridation in New Zealand.

A new year and a new speaking tour of New Zealand by US anti-fluoride campaigner Paul Connett. Looking over the presentation he is giving at his New Zealand meetings I find he has absolutely nothing new to say. It’s all been said before – and all his claims have been debunked before.

His visit this year is slightly unusual – the first time I am aware he has visited in winter. Perhaps the local anti-fluoride movement has decided they need to get him early because of the impending introduction of new legislation on community water fluoridation (CWF).

In this open letter to Paul, I respond briefly to the points he makes in his current presentation and will link to a fuller discussion of each point in earlier posts. Many of these links will be to my debate with Paul Connett 3 years ago. You can download the full debate (Connett & Perrott, The Fluoride debate – 2014) or find the individual posts at Fluoride Debate.

Finally, I have offered Paul the right of reply here. I believe that participation in a good-faith discussion is the most scientifically ethical response to my open letter.

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Dear Paul,

I wish to challenge claims you made in your 2016 New Zealand speaking tour. Most of these claims were refuted in our 2013/2014 debate but it is worth itemising some of them here because you are continuing to rely on them.

I, of course, offer you the right of reply and access to an open good faith discussion here if you feel I have misrepresented you in any way.

Fraudulent charges of scientific fraud

From Connett’s 2016 New Zealand presentation

Scientific fraud is an extremely serious offence and accusations should not be made lightly. Yet you have accused New Zealand scientists involved in the Hastings trial of scientific fraud without even citing the study’s reports or publications. You have relied simply on an out-of-context sentence in a letter from a departmental official and unsubstantiated claims about changes in methodology. I pointed this out to you in our 2013/2014 debate  yet you are persisting in this defamation of researchers who are no longer here to defend themselves. You have even gone as far as producing an internationally distributed newsletter entitled “New Zealand Fluoridation Fraud” which was promoted by Fluoride Free NZ activists in this country.

You base your charge of “fraud'” on:

1. An out of context quote from an internal letter by a director,
2. Abandonment of Napier as the planned control city at the beginning of the study, and
3. Alleged changes in the diagnostic procedures used during the course of the trial.

1: A letter from a divisional director expressing his frustration at developing a description “with meaning to a layman” is not evidence of “fraud,” or an attempt to distort the evidence. Scientists are always being urged by officials to make their findings more accessible and understandable to the public.   Your presentation of it as such is equivalent to the 2009/2010 “climategate” misinformation campaign launched by climate change deniers using out-of-context quotes from scientists emails. In that case, we know the real fraud was carried out by those attempting to deny the science and discredit the scientists.

2: Yes, the original plan was to use Napier as a control non-fluoridated city alongside the fluoridated city of Hastings. This was abandoned when data showed a lower incidence of tooth decay in Napier and it was judged unsuitable as a control because of differing soil chemistry which would have introduced an extra confounding factor. While this reduced the Hastings experiment to a longitudinal study, comparisons were made with other non-fluoridated New Zealand cities.

Surely this was a sensible solution to a problem? – and these are always occurring in long-term studies as any researcher familiar with such studies will confirm. Yet, in our debate, you irresponsibly described these reasons as “bogus.” As I said in our debate:

“That is the problem with conspiracy theories – they paint the world black and white which is very unrealistic. I expected far more professionalism from Paul than this.”

This is not the sort of rational assessment expected from a scientific review but sounds more like the declaration of a biased political campaigner.

3:  The diagnostic procedure used in the Hastings experiment were described in the first paper of the series reporting results (Ludwig 1958). Subsequent papers (Ludwig and Ludwig, et al., 1959, 1962, 1963, 1965, 1971) refer to this description and confirm it continued to be used. So where is the evidence for a change in diagnostic procedure?

Yes, there were changes in tooth filling procedures used by New Zealand dental nurses around the time this trial started. But even the anti-fluoride  Colquhoun & Wilson (1999) confirm attempts were made to use a consistent filling procedure in the trial – quoting from a file they received from their Official Information Act request:

“At the commencement of the Hastings fluoridation project steps were taken to ensure that the practice of preparing prophylactic type fillings by dental nurses was discontinued.

Of course, longer term trial like this always have a possibility of technician (or dental nurse) differences and good trial managers attempt to reduced such differences.

Perhaps one way to confirm that such “teething problems” (pardon the pun) did not have an overriding effect is to see that the improvements in oral health measured as differences from the 1954 start were also observed if 1957 was taken as the start (and also for later dates). In our debate I showed this to be a fact using the graphs below.

Hastings data shows similar improvement in oral health even if the project had started in 1957. Plots are for different ages.

Paul, you description of honest research, no matter what its limitations, as fraudulent is irresponsible. Considering your motives for this description and the way you have distorted the situation I would even describe your behavior itself as fraudulent.

Misrepresenting WHO data.

You repeat the same misleading interpretation of the World Health Organisation (WHO) data that we discussed in our debate where you attempted to avoid my criticisms and in the end did not have a sensible response. Despite the refutation, you continue to promote the following misleading graph every chance you get (see also Fluoridation: Connett’s naive use of WHO data debunked):

Slide from Connett’s 2016 New Zealand presentation

These data do not support your claim of no difference between the rates of improvement of oral health in fluoridated and unfluoridated countries because there is no attempt to account for all the different factors influencing dental health. Robyn Whyman pointed this out in his report for the National Fluoridation Information Service – “Does delayed tooth eruption negate the effect of water fluoridation?“:

“Inter-country comparisons of health status, including oral health status, are notoriously difficult to interpret for cause and effect, because there are so many environmental, social and contextual differences that need to be considered.”

It is far more rational to compare regions within countries and you have purposely omitted the WHO data where fluoridated and unfluoridated areas within individual countries were compared.

Here is that WHO data for Ireland which shows a clear benefit in fluoridated areas.

As I said in my post Fluoridation: Connett’s naive use of WHO data debunked:

“I showed this graph to Connett at the beginning of our debate on fluoridation. throughout the next few months he continued to confuse the issue and I kept coming back to it. Finally, he said in his closing statement, “My apologies. I should have checked back.”

An acknowledgment, of sorts, that his use of the WHO data is wrong in his graphs – but he continues to misrepresent it in this way!”

Isn’t it about time you stopped promoting this invalid and misleading use of the WHO data?

Nexo and ChildSmile are complimentary to CWF – not alternatives

From Paul Connett’s 2016 New Zealand presentation.

You are being disingenuous in promoting oral health programmes like the Danish Nexo and Scottish ChildSmile programmes, as “alternatives” to community water fluoridation (CWF). Health authorities do not see them as alternatives – more as possible complimentary social programmes. The British Dental Association supports both the Scottish ChildSmile programme and CWF. In Scotland it has come out publicly called for communities to move towards introducing water fluoridation. In the absence of CWF, UK health professionals see ChildSmile as “the next best thing – a rather expensive substitute for the fluoridation schemes that have never been introduced.”

I discussed the ChildSmile programme in my article ChildSmile dental health – its pros and cons and in our debate (see Fluoride debate: Ken Perrott’s closing response to Paul Connett?). It, and the Nexo programme, use approaches of child and parent education, toothbrushing supervision and programmes, and  health education initiatives based principally on public health nurses and health visitors attaching themselves to particular schools in order to give oral health advice to children and parents. Subject to parental consent, they also arrange for children who are not registered with a dentist to undergo check-ups and, if necessary, treatment.

Both programmes also provide regular fluoride varnishes for children’s teeth (so much for being an alternative to fluoride).

The point is that elements of these programmes are probably already incorporated into the social health policies of many countries. They certainly are in New Zealand. The introduction of a social health policy like CWF does not mean that programmes like the Nexo and Childsmile, or elements of them, are abandoned by health authorities. The research still shows that CWF reduces tooth decay even when other programmes like this, the use of fluoridated toothpaste and restriction of sugar consumption are practiced (see for example Blinkhiorn et al., 2015).

Interestingly, though, because sometimes programmes like tooth varnishes are targeted at the more vulnerable children in non-fluoridated areas these may lead to difficulties in drawing conclusions from simple comparison of fluoridated and unfluoridated areas. I discussed this in my article on mistakes in one of John Colquhoun’s  papers – Fluoridation: what about reports it is ineffective? – where children from non-fluoridated areas received preferential fluoride varnishing.

There is no single “silver bullet,” for solving the problem of tooth decay so why not use programmes like CWF and Childsmile/Nexo, or elements of the these, together?

In fact, that is exactly what is happening in New Zealand.

Asserting CWF out of step with the science

You claim:

“A better guide as to what nature thinks about the safety of fluoride is the level found in mother’s milk.”

This is simply weird, a naive example of the naturalistic fallacy.

Nature doesn’t think – such an arguments could be used against everything humanity has done to ensure that we have a better quality and length of life than “offered by nature.” As I pointed out in our debate, we are used to other elements being deficient in mothers milk and therefore requiring supplementation (see also Iron and fluoride in human milk for discussion of an evolutionary perspective vs a naive appeal to nature).

Your assertion:

“in mammals not one single biochemical process has been shown to need fluoride to function properly”

is simply deceptive – knowingly so. Fluoride may not play a biochemical role but it does play a chemical one. It is a normal and natural component of bioapatites – bones and teeth. And when present in optimum amounts confers strength and low solubility. Surely as a chemist you are familiar with the fact that minerals like apatite usually do not occur in the ideal form, as end members of a chemical series. In practice, no bioapatites are “fluoride-free.”

I demonstrated the difference between real world apatites and the ideal end members in our 2013/2014 debate using this figure. As a chemist this should be obvious to you.

In the real world bioapatites like bones and teeth always contain fluoride as a normal and natural constituent. The end members hydroxylapatite and fluoroapatite are not real models for natural bioapatites.

You claim that:

“With fluoridation: the chemicals used are not pharmaceutical grade but contaminated waste products from the phosphate fertilizer industry.”

But none of the chemicals used in water treatment, or the water itself, are of  “pharmaceutical grade.” Water plants and water treatment have their own grading system for the chemicals used.

In fact, comparing the certificated concentrations of contaminant elements in fluoridating chemicals used with the same contaminants already in the source water, we find that fluoridating chemicals are not a real source of contamination. We should be more concerned about the source water itself. I presented data to show this in my article Chemophobic scaremongering: Much ado about absolutely nothing. In most cases contamination from the fluoridating chemical is less than 1% of the contaminant concentration already in the source water.

Your reference to “contaminated waste products” is simply naive (or dishonest since you have chemical training) chemophobic scaremongering

Misrepresenting facts on dental fluorosis

Paul Connett cites an irrelevant figure in his 2016 New Zealand presentation.

Your claims regarding dental fluorosis are presented as an argument against CWF and in that context are very misleading:

1: The deceit of not identifying contribution from CWF.

Your slide refers to all forms of dental fluorosis and to all areas – fluoridated and fluoridated. It is very misleading to infer that CWF is responsible for a dental fluorosis prevalence of 41%  of dental fluorosis. In fact, CWF makes only a small contribution – often not detectable as was the case with the New Zealand Oral Health survey illustrated below (see Dental fluorosis: badly misrepresented by FANNZ).

Unfortunately, even the recent Cochrane Fluoridation Review (Iheozor-Ejiofor et al., 2015) mistakenly presented the dental fluorosis data without differentiation between fluoridated and non-fluoridated areas. My calculations from their data indicated tyhe prevalence of dental fluorosis due to CWF is more like 7% – much less than your 41% (see  Cochrane fluoridation review. III: Misleading section on dental fluorosis).

2:  Scaremongering by not differentiating between mild and severe forms.

Your 41% sounds scary – especially with the implication it is caused by CWF. But at least your acknowledge that the prevalence of more severe forms is much less. That is obvious from my figure above and from your later slide acknowledging a 3.6% prevalence of moderate and severe dental fluorosis in American teens.

This figure from the National Research Council review shows that CWF (which usually uses a concentration of 0.7 ppm) does not contribute at all to severe dental fluorosis.

Usually only the moderate and severe forms of dental fluorosis are considered of aesthetic concern – and the milder forms are often judged favourably by parents and teenagers.

What you did not say is that CWF does not contribute at all to moderate and severe forms. These forms are completely irrelevant to the discussion of CWF and it is dishonest to use it as an argument against CWF. Again, my calculation from the Cochrane data indicates the contribution of CWF to dental fluorosis of aesthetic concern was within the measurement error.

If you are really concerned about dental fluorosis, and especially the more severe forms of aesthetic concern, you should be paying attention to high natural sources of fluoride in some regions, industrial pollution and the possibility of obsessive consumption of toothpaste by children.

Brain damage?

Wild claim by Connett in 2016 New Zealand presentation. There is absolutely no evidence that CWF is harmful to the brain.

Paul, you have been uncritically dredging the scientific literature for articles you can use to imply fluoride is toxic or a neurotoxicant. Of course you will find studies supporting your bias that you can cherry-pick. A similar uncritical dredging will produce far more articles showing water is toxic! Such confirmation bias is scientifically unethical. We should always read the scientific literature intelligently and critically.

Applying a bit of objectivity we see that almost all the studies you rely on use exposure levels far greater than the recommended levels for CWF. Many of the animal studies considered exposure 50 to 100 times those levels or more. The quality of many of the research reports you rely on is not good – a point I think you have acknowledged in the past.  The human studies you rely on have, almost without exception, involved regions of endemic fluorosis quite unrepresentative of regions where CWF is used (I discuss the two exceptions below). None of them properly considered relevant confounding factors.

The exceptions

You promote Malin and Till (2015) as evidence that CWF causes attention deficit hyperactivity disorder (ADHD). You have made no critical assessment of that study. If you had you would have found that when relevant confounders like altitude, poverty and home ownership are included there is not statistically significiant relation of ADHD prevalence with CWF. I demonstrated this in my article ADHD linked to elevation not fluoridation. Coincidentally, the importance of altitude was confirmed in another study which you completely ignore. That study is:

Huber, R. S., Kim, T.-S., Kim, N., Kuykendall, M. D., Sherwood, S. N., Renshaw, P. F., & Kondo, D. G. (2015). Association Between Altitude and Regional Variation of ADHD in Youth. Journal of Attention Disorders.

Unfortunately, the scientific literature is full os such inadequate studies where confounding factors are ignored. Great for confirming biases but, by themselves, absolutely useless if we want to get to the truth.

Peckham et al., (2015) is another example you use. They claimed a relationship of hypothyroidism with CWF but refused to include iodine deficiency (a well established cause of hypothyroidism) in their statistical analysis.

Studies from areas of endemic fluorosis

You extract a lot of mileage out of the studies by Xiang and his coauthors (eg Xiang et al., 2003) – and they are probably the better studies in your collection. But even here your confirmation bias leads you to draw unwarranted conclusions. I showed this in my articles Connett fiddles the data on fluoride, Connett & Hirzy do a shonky risk assesment for fluoride and Connett misrepresents the fluoride and IQ data yet again.

For example you claim (correctly) that Xiang found a statistically significant correlation of IQ with urinary fluoride. But a dispassionate consideration of the data shows this relationship explains only 3% of the variance in IQ. I suggest to you that inclusion of some relevant confounders in the statistical analysis would probably cause the correlation with urinary fluoride to be non-significant. This parallels the situation reported by Malin and Till (2015) for ADHD (and here they were able to explain over 20% of the variance in prevalence of ADHD by fluoride – before inclusion of confounders like elevation when the explanatory power of fluoride disappeared).

You have from time to time acknowledged the poor quality of the reports you rely on regarding fluoride and IQ but have said that “there must be something in it” because there are so many reports. There may well “be something in it” but you will not make progress by jumping to your ideologically motivated conclusions favouring chemical toxicity. Just think about it. Those studies occurred in areas of endemic fluorosis – where skeletal fluorosis and severe dental fluorosis are common. It is reasonable to expect such disfiguring and disabling diseases may impact the quality of life, learning ability and IQ of inhabitants. I suggested this mechanism for explaining the data in my article Severe dental fluorosis and cognitive deficits.

CWF is never used in areas of endemic fluorosis so such an effect on cognitive abilities would not occur. And that is consistent with the existing studies which do not show and IQ deficits resulting from CWF (see, for example, Broadbent et al., 2014 and my article IQ not influenced by water fluoridation).

Paul, you are disingenuous to pose the question in your presentations:

“What primary studies (not self-serving government reviews) can you cite that allow you to confidently ignore or dismiss all the evidence of fluoride’s potential to damage the brain?”

We must remember that this is posed in the context of your campaign against CWF and there is no primary study, or review, indicating “potential damage to the brain” from CWF. When you assert “Over 300 studies have found that fluoride is a neurotoxin” you are relying on animal studies where high concentrations of fluoride were used and poor quality studies from areas of endemic fluorosis. None of the studies you rely on are relevant to CWF. It is simply unprofessional scaremongering to promote these sort of political messages:

Scaremongering slide from Connett’s 2016 New Zealand presentation

I demonstrated in my article Approaching scientific literature sensibly how such uncritical dredging of the literature is meaningless. A Google Scholar search for  produced 2,190,000 results for water toxicity but only 234,000 for fluoride toxicity. So let’s paraphrase your question:

“What primary studies (not self-serving government reviews) can you cite that allow you to confidently ignore or dismiss all the evidence of  water’s potential to damage the body?”

Misrepresentation of evidence supporting CWF

Randomised control trials

Again you raise the red herring of the lack of randomised controlled trials (RTCs) showing CWF effective. As I pointed out to you in our 2013/21014 debate  there is also a lack of RTCs showing CWF not effective – and that must surely tell you something. Simply there are no RTCFs on the subject (although there are on other forms of fluoride delivery like fluoridated milk – see Stephen et al., 1984).

The fact is that such trials are practically impossible with social health measures like CWF. The American Academy of Pediatrics comments in their article on the Cochrane Fluoridation Review:

“it would be a logistical nightmare to try creating a public water system that pumps fluoridated water to the first house on the block, delivers non-fluoridated water to the following two houses and then provides fluoridated water to the 4th and final house on that block.”

This was acknowledged by the Cochrane Reviewers in their discussion. Your mate, and fellow member of the Fluoride Action Network leading body, Bill Osmunson, argues that such an RTC is possible. But his description of how it would be setup shows he is not really serious. He suggests that housing developments be built with several different water reticulation systems and houses be attached to these different systems by flipping coins!

There are some areas of investigation, such as drug efficacy, where RTCs are possible and ethical – but social health measures like CWF is not one of them. That does not prevent an objective analysis of all others sorts of investigation and data which enables health authorities and decision makers to make reliable decisions on such issues.

The Cochrane Fluoridation Review

Paul, I am shocked that with your scientific training you resort to a complete misrepresentation of the recent Cochrane Fluoridation Review (Iheozor-Ejiofor et al., 2015):

Connett misrepresented the findings of the Cochrane Fluoridation Review in his 2016 New Zealand presentations

Surely you are not that naive? The reviewers had selection criteria for inclusion of studies in their calculations. This excluded most modern cross-sectional  studies – on the basis of unavailability of data before CWF was started – not quality as you imply. Those restrictions meant they were unable to draw conclusions on the factors  in your slide – but they were discussed, and the studies cited, in the discussion section of the review. These non-selected studies do show that CWF is beneficial to adults (Griffin et al., 2007, Slade et al., 2013), provides benefits even when fluoridated toothpaste is considered (see Water fluoridation effective – new study and Blinkhorn et al., 2015) and reduces social inequalities (Riley et al., 1999). The research also shows tooth decay increases when CWF is stopped (see Fluoridation cessation studies reviewed – overall increase in tooth decay noted and Mclaren & Singhal 2016).

How is it that you ignore the language in the review referring to limitations imposed by its selection criteria and then present their qualified conclusions as if they were facts. Can you not understand sentences like?:

“Around 70% of these studies were conducted before 1975. Other, more recent studies comparing fluoridated and non-fluoridated communities have been conducted.We excluded them from our review because they did not carry out initial surveys of tooth decay levels around the time fluoridation started so were unable to evaluate changes in those levels since then.”

Why did you persistently ignore the qualifications in their conclusions imposed by their selection criteria expressed in the common phrase?

“We found insufficient information . . . “

And, why did you purposely ignore the specific conclusion:

“Our review found that water fluoridation is effective at reducing levels of tooth decay among children. The introduction of water fluoridation resulted in children having 35% fewer decayed, missing and filled baby teeth and 26% fewer decayed, missing and filled permanent teeth.We also found that fluoridation led to a 15%increase in children with no decay in their baby teeth and a 14%increase in children with no decay in their permanent teeth.”

Yes, that was followed by the disclaimer “These results are based predominantly on old studies and may not be applicable today.” But that only means the reviewers could not draw specific conclusions about today because they had excluded modern studies.

You have purposely ignored the issues around study selection and presented their inability to draw conclusions as evidence that there is no effect. That is not a scientific assessment of the review – it is a blatantly propagandist exercise in cherry picking motivated by an ideological position. An exercise in public relations, not proper scientific assessment.

Topical vs systemic

I think one change that did come out of our debate is that you now tend to qualify you claims about the systemic and topical roles of fluoride in preventing tooth decay. You use words like “primary” and “predominantly.” But you still confuse the issue by arguing that topical action is quite separate from ingestion when you ask”

“If fluoride works primarily on the outside of the tooth why swallow it?”

The fact is that fluoride, calcium and phosphorus in dental plaque and saliva (to which the CDC attributes the topical action of decay prevention) occur through ingestion of these nutrients in food and water. It is naive to separate the reaction at the tooth surface from ingestion of food and beverage.

You also ignore completely the evidence that ingested fluoride plays a beneficial systemic role with developing and so far unerupted teeth (see Ingested fluoride is beneficial to dental health and Cho et al., 2014).

And let’s not forget about our bones which benefits from appropriate amounts of fluoride in our diet (see Is fluoride an essential dietary mineral? and  Yiming Li et al., 2001)

Use of PR techniques – You are the guilty party

I have shown here how you have distorted and misrepresented the science around CWF. In doing so you are behaving as an ideologically driven lobbyist – not an objective scientist. You are not intelligently and critically assessing the scientific literature – you are cherry-picking and selectively quoting to promote your own agenda.

Personally, I think this sort of behaviour is unethical for a scientist. Sure, we all have our biases and beliefs and this can influence our interpretation of the literature. But you are consistently misrepresenting the science – and continue to do so even after you have been shown wrong.

Perhaps this is unsurprising considering you are essentially a political lobbyist campaigning against a social health policy. You lead a lobby organisation – the Fluoride Action Network. This organisation receives finance from the “natural”/alternative health industry – most publicly from Mercola. According to tax returns you and other members of your family, personally receive monthly payments from these funds.

It hypocritical for you, then, to disparage honest scientists and their publications in the way you have done regarding the Hastings project. Your bias (and refusal to deal with the science) comes out in your description of scientific reviews and papers as “dummy reviews,” “bogus,” “self-serving government reviews,” etc.

In one of your final slides you claim the alleged PR tactics by scientists:

“Would not be necessary if science was on the promoters’ side – but it is not.”

In fact, it is you that are on the wrong side of the science and that is why you resort to misrepresentation, distortion, fear mongering and slander.

You also claim:

“After 6 years there has been no detailed or documented response to our book The Case Against Fluoride.”

And

“Proponents will very seldom agree to publicly debate either myself or other leading opponents of fluoridation.”

Yet, isn’t that exactly what I did in our Fluoride Debate of 2013/2014? And didn’t I give a platform on my blog for you to make all your points and to present the arguments from your book?

And isn’t it a fact that in most forums where your lobby against CWF you, in fact, lose because the scientific arguments against you prevail? You make a big thing of every single victory you achieve against CWF but are silent about the larger number of losses.

As we are discussing the refusal to debate let’s be honest. Your organisations, internationally and locally, attempt to prevent supporters of science from involvement in their discussion forums. I personally have been banned from all local anti-fluoride forums and from the Fluoride Action Networks Facebook forum.

This suggests to me that neither you nor your supporters are willing to take part in a good-faith discussion of the science around CWF. You are simply behaving like a political and commercial lobbyist – not a scientist for whom such discussion should be welcome.

Nevertheless, once again I offer you a right of reply to my comments in this article. In fact, I would happily welcome such a reply as this would be in the best traditions and interests of the science.

References

I have included only citations where links were not available.

Ludwig, T. G. (1958). The Hastings Fluoridation project I. Dental effects between 1954 and 1957. New Zealand Dental Journal, 54, 165–172.

Ludwig, T. G. (1959). The Hastings fluoridation project: II. Dental effects between 1954 and 1959. New Zealand Dental Journal, 55, 176–179.

Ludwig, T. G. (1962). The Hastings fluoridation project III-Dental effects between 1954 and 1961. New Zealand Dental Journal, 58, 22–24.

Ludwig, T. . (1963). Recent marine soils and resistance to dental caries . Australian Dental Journal, 109–113.

Ludwig, T. G. (1965). The Hastings fluoridation project V- Dental effects between 1954 and 1964. New Zealand Dental Journal, 61, 175–179.

Ludwig, T. G. (1971). Hastings fluoridation project VI-Dental effects between 1954 and 1970. New Zealand Dental Journal, 67, 155–160.

Ludwig, T. G.; Healy, W. B.; Losee, F. L. (1960). An association between dental caries and certain soil conditions in New Zealand. Nature, 4726, 695–696.

Ludwig, T.G.; Healy, W. B. (1962). The production and composition of vegetables in home gardens at Napier and Hastings. New Zealand Dental Journal, 58, 229–233.

Ludwig, T.G.; Pearce, E. I. F. (1963). The Hastings fluoridation project IV – Dental effects between 1954 and 1963. New Zealand Dental Journal, 59, 298–301.

Xiang, Q; Liang, Y; Chen, L; Wang, C; Chen, B; Chen, X; Zhouc, M. (2003). Effect of fluoride in drinking water on children’s intelligence. Fluoride, 36(2), 84–94.

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