Topical confusion persists

I got a little leaflet from the Hamilton City Council the other day – with my rate demand. The leaflet tells me the council has stopped adding fluoride to the city’s water supply, gives some advice on alternative sources of fluoride – and then assures me their decision was all for the best. Because:

“Application by toothpaste and other means that directly affect the tooth surface are much more effective at reduing tooth decay than fluoridation of water supplies.”

Trouble is that is just wrong. I shows the council did not learn anything about the mechanism of fluoride protection against tooth decay from their recent hearings . Worse, they are confused – and are passing on their confusion to their citizens.

I discussed this issue of the topical mechanism in my article Fluoridation – topical confusion. But I guess it bears repeating because the Hamilton City Council is not the only group confused about this. And the anti-fluoridation activists are working hard to spread that confusion.

It’s a topical mechanism –  not application

When the word “topical” gets mentioned in this situation we need to understand clearly this refers to the mechanism of inhibiting mineralisation – not to the method of application. The topical mechanism is the major one preventing decay of existing teeth at all ages, it operates at the tooth surface ( and just below) and relies on having a relatively continuous low concentration of F in the saliva and biofilms on the teeth.

Fluoridated water (and fluoride in our food) participates in that mechanism of protection. Some of the fluoride in the drink and food gets transferred directly to saliva, and thence the tooth surface – during consumption.

Anti-fluoridation activists attempt to confuse the issue by talking about fluoride which is ingested, metabolised and then excreted from the salivary duct at a concentration lower than in fluoridated water. That fluoride has little effect at the tooth surface – because of its low concentration.

It is the fluoride transferred directly to saliva during the act of drinking (or consumption of food) that provides a sufficiently high concentration to have a protective effect. That is, F is transferred to the saliva, and then biofilms, during drinking and eating – something we do regularly. The concentration  in saliva spikes and then declines over an hour or so.

The US Center for Disease Control stresses this mechanism in its  report Recommendations for Using Fluoride to Prevent and Control Dental Caries in the United States:

” . . drinking fluoridated water, brushing with fluoride toothpaste, or using other fluoride  dental products can raise the concentration of fluoride in saliva present in the mouth 100-to 1,000-fold. The concentration returns to previous levels within 1–2 hours but, during this time, saliva serves as an important source of fluoride for concentration in plaque and for tooth remineralization.”

The diagram below portrays this – the fluoride is going directly from the drink and food into the saliva:

Mineralisation and remineralisation = tooth decay

Tooth decay occurs because when the pH at the tooth surface is lowered (this happens bacteria decompose sugars) some of the the calcium hydroxy apatite at the tooth  surface dissolves – mineralisation. With time the pH increases and the reaction is reversed – calcium and phosphate ions at the tooth surface reform as the solid hydroxy apatite (remineralisation).

When fluoride is present at the tooth surface a fluorohydroxy apatite is formed. This is “harder” – it doesn’t dissolve as readily. Consequently the incorporation of fluoride into the tooth surface reduces mineralisation – and enhances remineralisation. It inhibits tooth decay.

It turns out that F in fluoridated water and food does this very effectively. And, because we drink and eat often, dietary forms of fluoride help to maintain a useful concentration of saliva fluoride over time.

Topical application methods (toothpastes and dentrifices) are a supplement to fluoridated water and dietary fluoride, but not a substitute – partly because they are not applied as often (if at all). Even here it seems their mode of operation may be by the formation of CaF₂ globules on the tooth surface (because if the high F concentration) which then slowly release their F over time to maintain saliva concentrations at an appropriate level (see the  review article Mechanisms of Action of Fluoride for Caries Control by Buzalaf, Pessan, Honório, and ten Cate JM (2011)).

This topical mechanism which operates with fluoridated water means that the whole population can and does access the “topical mechanism” without thinking about it. Unfortunately the anti-fluoride lobby are spreading a lot of misinformation about the word “topical.” And, now, so is our local City Council.

The dangers of consultation

Hamilton City Councillors came in for a lot of criticism after their shock decision to end fluoridation. In their defence they claim their consultation process (“The Fluoride Tribunal”) gave them then information they needed – and the process was “robust.” (That word “robust” is the latest trendy word at the council these days).

But the fact they are repeating this mistaken description of the topical mode of fluoride protection against tooth decay shows it was far from “robust.” Despite all their efforts – and the large number of submissions, the council got it wrong.

I have watched many of the videos of submissions I know that the group of experts from the Waikato District Health Board and Ministry of Health did explain this topical mechanism. I know they explained it clearly. So why did the “tribunal” get it so wrong?

Here’s a couple of reasons which come to mind:

1. The expert submissions were swamped by the submissions from anti-fluoridation activists (about 90% of the submissions). Many of those repeated the misleading interpretation of the topical mode of action.
2. The Council had set itself up as a “tribunal” (my dictionary describes that as a group “with the authority to judge, adjudicate on, or determine claims or disputes.”) They were assuming they had the power, knowledge and ability to make an authoritative judgement of the scientific evidence set before them.
3. The council appeared to give at least equal credence to “both sides” – councillors often referred to hearing evidence from “eminent experts on both sides.” Apparently an academic title was enough to show credibility in the eyes of these councillors – no attention being paid to the submitters background, specialisation or research experience.
4. Worse, some of the councillors appeared to give more credence to the anti-fluoridation submitters than the District Health Board and Ministry of Health experts. A telling comment from one councillor was his reference to attempting to balance information from “experts who do no research and non-experts who do all the research.” His concept of research seemed to be internet Google searching and listing multiple but unsubstantiated claims. I experienced hostility from several councillors who were very dismissive of any reference to science.

It seems to me the sort of consultation set up by the Hamilton City Council was poorly thought out. It should never have been seen as a “tribunal” set up to make judgments about the science of fluoridation or possible health problems. The council members just do not have the scientific ability – or indeed the necessary skills in critical thinking, to make judgements in such a complex area. They could not produce a decision reflecting the best judgment of the evidence – and indeed they didn’t. Their document purely listed common arguments presented by submitters. There was no assessment of credibility, evidential support or confirmation.

If an assessment of the current science around fluoridation was really required then this should have been done by appropriate professionals – not politicians. The council should have relied on such an expert review, or in its absence, the recommendation of the proper experts. Instead they set themselves up in judgment of the complex science – and took evidence from some of the most inappropriate sources.

In the end, a referendum at the next local boy elections was the only way to resolve the pickle they had got themselves in to. Hopefully the new council will not make the same sort of mistakes about fluoridation advice.

See also:

Making sense of fluoride Facebook page
Other Fluoridation articles