Please note the update below*
Some people claim both supporters and opponents of fluoridation agree on one thing. That the benfits of fluroide come from topical application and not via systemic intake or ingestion of fluoridated water.
Well, that’s not quite correct. There is a semantic confusion. Researchers aret talking about mechanisms – that once teeth have erupted they are protected by the presence of fluoride in saliva and the biofilm on the teeth. A topical mechanism of protection. This can come from procedures not involving ingestion – fuoridated toothpaste, fluoride varnishes and other dental applications, but also from fluoridated water passing the teeth during drinking. Some ingested fluoride can also contribute to salivary fluoride after metabolism.
Yet the anti-fluoridation activists commonly assert fluoridation of water does not work because, they claim, it doesn’t contribute to this topical mechanism. Effectively they are choosing to interpret the topical mechanism as meaning a topical method of application or delievery is required.
Here’s the claim from the local Fluoride Action Network (FANNZ) (see 1. New science proves there is no benefit from swallowing fluoride):
The basic premise that swallowing fluoride prevents tooth decay has been disproved. When water fluoridation was first introduced en masse in the 1950s, dentists argued that fluoride needed to be ingested by children — while their teeth were developing — in order to be effective. The theory was that by swallowing fluoride it would accumulate in the teeth and make the enamel stronger and less susceptible to decay. However, since 1999 this theory has been rejected by all dental researchers (Featherstone 2000; Fejerskov 2004) and now the belief is that the primary benefit from fluoride is topical rather than systemic. That means it has to be applied to the teeth, not swallowed.
Well, we should all know that scientific knowledge is provisional and therefore changes as we accumulate more evidence. And we should be happy with that fact. But notice the word “applied. The awareness of a topical mechanism of action does not mean that fluoridated water is ineffective because it is drunk and ingested.
What researchers actually say
What did these researcher actually say? For example, FANNZ cite Featherston (2000). The paper is The science and practice of caries prevention, – here is a quote from the abstract which I think is sufficient to make my point:
“Fluoride, the key agent in battling caries, works primarily via topical mechanisms: inhibition of demineralization, enhancement of remineralization and inhibition of bacterial enzymes. . . . . . Fluoride in drinking water and in fluoride-containing products reduces caries via these topical mechanisms. “
Far from a topical mechanism excluding a protective effect from fluoride in drinking water it actually provides a mechanism for fluoridated water to be effective becdause it is incorporated into the saliva and biofilms during drinking..
The review article Mechanisms of Action of Fluoride for Caries Control by Buzalaf, Pessan, Honório, and ten Cate JM (2011) shows the context for the topical mechanism in the diagram below.
Dynamics of minerals in saliva and enamel under neutral (a, b) and acidic conditions (c, d). (Buzalaf et al. 2011).
Read the review for the details, but basically it involves fluoride present in saliva and the biofilm on the tooth surface reacting with calcium and phosphate dissolved during acid attack and producing an insoluble F containing bioapitate which is incorporated into the tooth structure because it has a lower solublilty than the bioapate which doesn’t contain substituted F.
The frequent drinking of the fluoridated water supplies F at an appropriate concentration to the tooth suraces, biofilms and saliva. So the review concludes
“More than 60 years of intensive research attest to the safety and effectiveness of this measure to control caries. In this case, however, it should be emphasized that despite being classified as a ‘systemic’ method of fluoride delivery (as it involves ingestion of fluoride), the mechanism of action of fluoridated water to control caries is mainly through its topical contact with the teeth while in the oral cavity or when redistributed to the oral environment by means of saliva. Since fluoridated water is consumed many times a day, the high frequency of contact of fluoride present in the water with the tooth structure or intraoral fluoride reservoirs helps to explain why water fluoridation is so effective in controlling caries, despite having fluoride concentrations much lower than fluoride toothpastes, for example. This general concept can be applied to all methods of fluoride use traditionally classified as ‘systemic’. In the light of the current knowledge regarding the mechanisms by which fluoride control caries, this system of classification is in fact misleading.”
As well as this topical mechanism for protecting exisiting teeth the current research still indicates some health benefits from ingestion:
“Evidence also supports fluoride’s systemic mechanism of caries inhibition in pit and fissure surfaces of permanent first molars when it is incorporated into these teeth pre- eruptively.”
Ingested fluoride can also benefits bones – see my article Is fluoride an essential dietary mineral? for more on this.
Contribution from topical methods of delivery
The review I quote above also discusses these other methods of fluoride delivery like fluoridated toothpaste and dental treatments like varnish and fluoride gel applications. In these cases the fluoride is delivered at a much higher concentration and reacts with calcium to form calcium fluoride crystals. These have a low solubility but can release fluoride at the low concentrations suitable for providing protection to teeth by the topical mechanisms discussed above. They effectively act as fluoride reserviors near the teeth.
Despite the effectiveness of these methods of delivery they usually have disadvantages because of the high concentrations of fluoride involved. Problems can arise if they are accidentally or intentionally ingested. Young children are also prone to poison themeselves if such materials are left in unsecure places.
Saliva fluoride from ingested water
FANNZ has also tried to make an issue of the low concentratio of saliva F derived through metabolism of ingested fluoride. In fact, they sometimes claim that advocates of fluoridation still present that as the main method of delivery. The quote from their website above goes on:
“Dentists continue to promote fluoridation as they say there is also a smaller benefit from swallowing fluoride because it gets into peoples saliva and helps to remineralise the teeth.”
FANNZ continues that claim in their criticism of expert evidence presented to the Hamilton City Council hearings on fluoirdation. This then enables them to divert attention away from the delivery of F to tooth surfaces during drinking of fluoridated water. This is what they say about saliva F derived from ingested water. After claiming that saliva F derived from metabolised forms is insufficient to confer a topical benefit they quote from the CDC report Recommendations for Using Fluoride to Prevent and Control Dental Caries in the United States:
“The concentration of fluoride in ductal saliva, as it is secreted from salivary glands, is low — approximately 0.016 parts per million (ppm) in areas where drinking water is fluoridated and 0.006 ppm in nonfluoridated areas. This concentration of fluoride is not likely to affect cariogenic activity.
Looks convincing, eh? But, and this is important, they stop their quote there, omitting the important following sentences:
“However, 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.”
So, in reality, the report they quote, and especially the part they intentionally omit says the complete opposite of what they claim about that report:
“The CDC acknowledges that fluoridated water has no cariostatic effect.”
The complete opposite. The CDC acknowledges nothing of the sort.
Unfortunately I am finding this sort of blatant misrepresentation and distorting is very common in the FANNZ propaganda. I urge readers to approach their literature with caution. To think critically (as one always should) and to actually check their citations by reading the originals.
FANNZ has sort of responded to this article at Misleading claim against FANNZ of misrepresentation.
It’s a confused response relying on a bit of strawmannery, irrelevant chemical assertions and an unjustified assumption that F in fluoridated water can not possible have a topical effect. So I will just make a few points:
1: It is normal to reference and link to an article being criticised. FANNZ didn’t do so – perhaps they want to avoid readers checking out my article?
2: Nowhere did I claim that drinking fluoridated water caused F concentrations in the mouth to magically increase to 16 ppm by a “chemical mechanism by which the saliva “sucked” the Fluoride out of the water in the fraction of a second it passes over the teeth.” Strawmannery.
3: FANNZ assumes that F has no topical effect at concentrations in fluoridated water (0.7 – 1.0 ppm). They justify this by citing 5 cherry-picked papers and ignoring papers which don’t support their assumption. The sources they use refer to studies made at high concentrations (considering topical application methods) or with sugar solutions.
The chemistry of F in saliva and at the tooth surface and subsurfaces is complicated – influenced by both thermodynamic equilibria and kinetic factors. Then influence of F depends on concentrations of Ca and phosphate, pH and organic material present. One should be very careful about extending findings from one situation to other situation.
As well as completely ignoring the conclusions in the CDC report they reference, FANNZ choose to ignore, for example, Featherston (2000)** who says:
“The cariostatic effects of fluoride are, in part, related to the sustained presence of low concentrations of ionic fluoride in the oral environment,derived from foods and beverages, drinking water and fluoride-containing dental products such as toothpaste. Prolonged and slightly elevated low concentrations of fluoride in the saliva and plaque fluid decrease the rate of enamel demineralization and enhance the rate of remineralization. For example, fluoride at 0,04 ppm in saliva can enhance remineralization.” [my emphasis]
**Featherston, JDB (2000). JADA, 131 887-899. “The sciuence and practice of caries prevention.”
debunking anti-fluoridation arguments
Fluoridation and conspiracy theories
Fluoridation – the violation of rights argument.
Poisoning the well with a caricature of science
Fluoridation – it does reduce tooth decay
Getting a grip on the science behind claims about fluoridation
Is fluoride an essential dietary mineral?
Fluoridation – are we dumping toxic metals into our water supplies?
Tactics and common arguments of the anti-fluoridationists