Fluoride Action Network

Tooth Decay

“The magnitude of [fluoridation's] effect is not large in absolute terms, is often not statistically significant and may not be of clinical significance.” - Ontario Ministry of Health and Long Term Care (1999).

Topical vs. Systemic Effects

When water fluoridation first began in the 1940s, dentists believed that fluoride’s main benefit to teeth came from being swallowed during childhood. When swallowed before the teeth erupted, dentists claimed fluoride would build up in the internal matrix of the teeth and make them more resistant to cavities for the rest of the child’s life. As the U.S. Public Health Service’s chief dentist stated in 1952,”only children born and reared on fluoride water receive its fullest benefits. . . . These benefits are not temporary; they last a lifetime.” (Knutson 1952). As summarized by Danish scientist Ole Fejerskov:

“The hypothesis was that increased intake of fluoride during tooth formation raises the fluoride concentration in enamel and hence increases acid resistance. As a consequence fluoride had to be taken systemically and artificial fluoridation of drinking waters became the ‘optimal’ solution.” (Fejerskov 2004).

Although water fluoridation was launched on this premise, it is now known to be incorrect. Far from making the teeth stronger for life, the July 2000 issue of the Journal of the American Dental Association reported that “fluoride incorporated during tooth development is insufficient to play a significant role in caries protection.” (Featherstone 2000).

“Importantly, this means that fluoride incorporated during tooth mineral development at normal levels of 20 to 100 ppm (even in areas that have fluoridated drinking water or with the use of fluoride supplements) does not measurably alter the acid solubility of the mineral. Even when the outer enamel has higher fluoride levels, such as 1,000 ppm, it does not measurably withstand acid-induced dissolution any better than enamel with lower levels of fluoride.” (Featherstone 2000).

Based on these and other findings, researchers have now overwhelmingly rejected the notion that swallowing fluoride is either necessary or effective for preventing decay. Instead, the current consensus is that fluoride’s benefit (whatever it may be) comes from topical contact with teeth after the teeth have erupted into the mouth. As the Centers for Disease Control (CDC) stated in 1999:

“fluoride prevents dental caries predominately after eruption of the tooth into the mouth, and its actions primarily are topical for both adults and children.”

The CDC repeated this position in 2001, affirming that “fluoride’s predominant effect is posteruptive and topical.”

How does fluoride work topically?

According to the CDC, there are three main mechanisms by which topical fluoride can prevent decay. It can (1) enhance remineralization of carious lesions before they become full-blown cavities, (2) inhibit demineralization, and (3) poison the enzymes in the oral bacteria that produce the acids that erode the teeth. (CDC 2001). Importantly, neither of these three mechanisms depends on teeth having high concentrations of fluoride in their internal matrix. Accordingly, each of the three topical mechanisms can fully occur without a person swallowing a single drop of fluoride their entire life.


The implications of this finding are obvious. If fluoride works topically, there is no need to swallow it, and therefore no need to add it to the water supply. This is especially so when considering that (1) fluoride is not a nutrient, and (2) fluoride’s risks come from ingestion. As noted by Dr. Arvid Carlsson, the 2000 recipient of the Nobel Prize in Medicine/Physiology, upon learning that fluoride works topically (locally):

“In pharmacology, if the effect is local (e.g., topical), it’s of course absolutely awkward to use it in any other way than as a local treatment. I mean this is obvious. You have the teeth there, they’re available for you, why drink the stuff?… I see no reason at all for giving it in any other way than locally.”

It is telling, for example, that fluoride — a powerful poison of enzymes — works topically, in part, by poisoning enzymes in the bacteria. While poisoning enzymes in oral bacteria may lead to a desirable result vis-a-vis teeth, poisoning enzymes elsewhere in the body could lead to a host of undesirable results. This, in fact, is one of the reasons why some of the earliest opponents to fluoridation were biochemists, as they were familiar with the use of fluoride to inhibit enzymes in the laboratory and worried about the potential for fluoride to inhibit enzymes in the body. As noted by Dr. James Sumner, a Nobel Laureate biochemist at Cornell University:

“We ought to go slowly [with water fluoridation]. Everybody knows fluorine and fluorides are very poisonous substances…We use them in enzyme chemistry to poison enzymes, those vital agents in the body. That is the reason things are poisoned; because the enzymes are poisoned and that is why animals and plants die.”

Despite this, many in the public health community continue to advocate for fluoridating water supplies. Unlike their predecessors, today’s advocates insist that fluoridated water provides an effective source of topical fluoride by increasing the fluoride content in both saliva and plaque. Even if true, however, recent studies show that there is virtually no practical difference in tooth decay rates between fluoridated and non-fluoridated areas. Accordingly, if fluoridated water does have a topical effect on teeth, it appears sufficiently miniscule that use of topical fluoride products can readily replace it. Thus, although “it is conceivable” that fluoridated water could produce a topical effect, “it would be more advisable to increase plaque fluoride concentration directly by topical application.” (Hellwig & Lemmon 2004).

As noted by toxicologist, Dr. Vyvyan Howard:

“I don’t think you can justify the fluoridation of drinking water on the lines of a topical treatment to teeth. It’s illogical.”


Centers for Disease Control and Prevention. (2001). Recommendations for using fluoride to prevent and control dental caries in the United States. Mortality and Morbidity Weekly Review 50(RR14):1-42.

Centers for Disease Control and Prevention. 1999. Achievements in Public Health, 1900-1999: Fluoridation of drinking water to prevent dental caries. Mortality and Morbidity Weekly Review 48(41): 933-940.

Featherstone, JDB. (2000). The Science and Practice of Caries Prevention. Journal of the American Dental Association 131: 887-899.

Fejerskov O. (2004). Changing paradigms in concepts on dental caries: consequences for oral health care. Caries Research 38: 182-91.

Hellwig E, Lennon AM. (2004). Systemic versus topical fluoride. Caries Research 38: 258-62.

Knutson JW. (1952). The case for water fluoridation. New England Journal of Medicine 246:737-43.

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