Fluoride Action Network

Dental Products

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Fluoride Gels

“Fluoride Gels” are acidic, highly concentrated fluoride products that dentists topically apply to a patient’s teeth about two times a year. Of all the fluoride products currently utilized in dentistry, these fluoride gels are – without question – the most hazardous. While fluoride gels are designed to be applied “topically” (i.e., directly to teeth), very large quantities of fluoride are absorbed into the body during the treatment.

Due to the high exposure to fluoride during gel treatment,, many patients – particularly children – will experience nausea, gastrointestinal pain, or vomiting within an hour of the treatment.  Gastric distress is not the only risk. Fluoride gels produce an enormous spike in blood fluoride levels for up to 14 hours, exposing every tissue in the body to fluoride concentrations that have been found to damage, in short-term exposures, the kidney, the male reproductive system, and glucose metabolism.

Although the dental community has taken steps to reduce the amount of fluoride that gets into the blood, the extent of fluoride exposure from fluoride gels continues to remain excessive and toxic. Due to the conspicuous absence of any meaningful safety studies, however, the public health consequences from widespread fluoride gel use remain a disturbing mystery.

What Are Fluoride Gels?

Fluoride Gels are often referred to as “1.23% APF” gels. This refers to the concentration of fluoride (1.23% fluoride ion, or 12,300 ppm) and the chemical compound (“APF,” or acidulated phosphate fluoride). A 1.23% concentration of fluoride equates to 12,300 parts per million, or 12.3 mg of fluoride for every milliliter of the gel. The gel is placed in two trays (one tray for the upper teeth, and one tray for the bottom teeth), which are then placed in the patient’s mouth. The patient is then asked to bite down on the trays for 4 minutes. Due to the high acidity of the gel (pH 3.5), saliva flow is markedly increased during the course of the treatment, thus increasing the percentage of the gel that is ingested. The high acidity also enables the fluoride to cross directly through the gum membrane. (Whitford 1982). Thus, patients can be exposed to significant amounts of systemic fluoride even when no fluoride is actually swallowed. Read More.

When scientists discovered in the 1980s the enormous spikes in blood fluoride levels that occur after fluoride gel treatment (see below), the dental community implemented measures to reduce the amount of fluoride ingested from the gel. These measures include: (a) ensuring that the patient is sitting upright; (b) reducing the amount of gel used for young children; (c) placing a suction device in the mouth during the course of the treatment to vacuum out the excess saliva; and (d) encouraging the patient to spit (i.e., expectorate) for up to one minute when the trays are removed from the mouth. (Hawkins 2003; LeCompte 1987). Even when dentists comply with these recommendations (the rate of professional compliance is unknown), significant ingestion of fluoride can still occur. Indeed, when preventive measures are used, it is estimated that children ingest an average of 7.7 mg of fluoride per treatment, while adults ingest an average of 10.3 mg. (Hawkins 2003; Johnston 1994). As discussed below, these doses are sufficient to produce toxic spikes in the blood fluoride level.

Gastric Pain, Nausea, and Vomiting

Gastric pain and nausea are common side effects from fluoride gel treatment. It is not uncommon, for example, for a child to vomit on the way home from the dental office after receiving a fluoride gel. Fluoride causes the gastric symptoms by combining with gastric acid in the stomach to form hydrofluoric acid, which exerts a direct toxic effect on the gastric mucosa. Scientists have found that a single dose of just 3 mg fluoride is sufficient to damage the gastric mucosa, and that tissue damage can occur in the absence of gastric symptoms. (Spak 1990). Most children receiving fluoride gel treatment will ingest doses that far exceed 3 mg. Thus, even if no gastric symptoms are experienced, tissue damage to the gastric mucosa will occur. The long-term significance of this effect has yet to be investigated. Read More.

Toxic Spikes in Blood Fluoride Levels

Fluoride gels were introduced in the 1960s without any clinical evidence of safety or effectiveness. (Ekstrand 1987). As with other fluoride products, the dental community assumed that the fluoride gels were safe, and thus took no measures to reduce the amount of fluoride that patients ingested. It wasn’t until the early 1980s that researchers first discovered that both children and adults were absorbing enormous quantities of fluoride from the gels, as evident by the staggering spike in blood fluoride levels that occurred following treatment. In relatively small studies, researchers found that children’s blood contained up to 1,450 parts per billion (ppb) of fluoride after treatment, and that adults’ blood contained up to 980 ppb—a near 100-fold increase from the baseline level. (Ekstrand 1980, 1981). Researchers found that the peak concentration was normally reached within 1 to 2 hours of treatment, and remained significantly elevated for up to 14 hours. (Ekstrand 1980). According to the leading researcher in the field: “It is concluded that following the use of topical fluoride products, variable amounts of fluoride are swallowed and absorbed into the systemic circulation–amounts which may be sufficient to produce acute or chronic side-effects.” (Ekstrand 1987).

Although most dentists now use measures to prevent fluoride from getting into the bloodstream, children still swallow an average of 7.7 mg of fluoride per treatment, while adults swallow an average of 10.3 mg. (Johnston 1994). Based on prior research of fluoride’s pharmacokinetics, the blood fluoride levels resulting from these doses are still strikingly high. (Ekstrand 1983).

A) Kidney Damage

When scientists first discovered the high blood fluoride levels resulting from treatment with fluoride gels, little was known about the blood fluoride levels that could cause harm to human health. The only thing that scientists knew was that short-term exposures to high levels of fluoride (as occurred from the fluorinated anesthetic methoxylflurane) damaged the kidney, by impairing the kidney’s ability to concentrate urine and thereby producing a diabetes insipidus-type condition marked by excessive urination. (Mazze 1977). It is estimated that the threshold blood level that causes this effect during short exposures is 570 ppb. (Whitford 1987). While this defect is believed to be reversible (i.e., it ends when the fluoride clears from the blood), no research has yet been conducted to determine the long-term kidney health of those who have repeatedly experienced short-term toxic exposures to fluoride. Read More.

B) Danger for Diabetics

In 1986 and 1987, scientists funded by the National Institutes of Health (NIH) reported that the toxic effects from short-term spikes in blood fluoride levels are not limited to the kidney.  (Shahed 1986; Whitford 1987).  In studies on rats, the scientists reported that a blood fluoride level of just 234 ppb (the lowest level they examined) caused significant impairment in glucose metabolism, as evident by sharp rises in blood glucose and decreases in insulin. (Whitford 1987). An impairment in glucose metabolism and insulin production are hallmarks of diabetes. As the authors noted, this was the “first time” that a single, acute exposure to fluoride could reduce insulin levels in blood, which was striking because the dose that caused the effect was well within “the range of fluoride ingestion observed following a topical application of APF gel.” (Shahed 1986). The authors concluded, therefore, that “it is conceivable that normal ingestion of F following an APF application could alter several metabolic processes.” (Shahed 1986).

Subsequent research has demonstrated that the NIH study’s findings were not a fluke. Indeed, not only have researchers confirmed that spikes in blood fluoride levels increase glucose levels, but they have found that the effect occurs at just 95 ppb – less than 10 times the fluoride level that can enter blood after fluoride-gel treatment, and exceeded on a daily basis by some children using fluoride toothpaste. (Menoyo 2005; de la Sota 1997; Rigalli 1995, 1990). Despite these findings, neither the NIH nor the dental community have conducted any research to determine the effect of fluoride gels on glucose metabolism in children or adults.

C) Damage to Sperm

In 2002 and 2006, Polish researchers reported that low levels of fluoride can damage sperm in ways that could impair male fertility. (Zakrzewska 2002, 2006). In the studies, the researchers exposed ram semen to 380 ppb of fluoride. After just five hours of exposure, the researchers found significant decreases in sperm motility (the ability of the sperm to move) and the number of intact acrosomes (the part of the sperm that produces enzymes necessary for egg penetration). According to the authors, such changes “undoubtedly affect the physiological function of the sperm.” (Zakrzewska 2002).

Although no research has ever been conducted to determine the impact of fluoride gel treatment on human reproductive function, the blood fluoride concentrations that result from such treatments can exceed, for over five hours, the concentrations found to damage ram semen. Nevertheless, manufacturers make no mention of these findings in the product insert for fluoride gels. The product insert simply states: “Potential adverse reproductive effects of fluoride exposure in humans have not been adequately evaluated. Adverse reproductive effects of fluoride have been reported in animal studies, but at high concentrations sufficient to produce other manifestations of toxicity.”

Other Effects from Fluoride Gels

In 2008, researchers reported that fluoride gels damage the oral mucosa. (Tsai 2008). The researchers found that a single application of fluoride gel to the oral mucosa of rabbits for 4 minutes caused cell damage (e.g., DNA strand breaks) that did not disappear, but actually increased, during the 8 days of follow-up examinations. Based on their findings, the authors suggest that dentists take precautions to prevent the fluoride gels from contacting the gums.

In addition to damaging the oral mucosa, fluoride gels have also been found to damage tooth restorations, such as porcelain or ceramic vaneers. As noted by Johnston, the “APF gel releases hydrofluoric acid which may etch and dull these restorative materials after several applications.” (Johnston 1994).

Fluoride Gels: Only Recommended for “High-Risk” Patients

Considering the serious hazards involved with fluoride-gel treatments, one would think the treatments must provide a very convincing, irreplaceable benefit. Amazingly, however, that is not the case. Due to the glut of over-the-counter topical fluoride products, even gel proponents note that “there seems little reason for dental professionals to apply topical fluorides for patients with a low defs/DMFS count.” (Johnston 1994).

A Failure to Investigate

Fluoride gels were introduced onto the market in the 1960s in the absence of “evidence of clinical efficacy.”  (Ekstrand 1987). Despite the staggeringly high levels of fluoride that enter the bloodstream after fluoride gel treatment, there has been virtually no research since that time to determine the occurrence of side effects among patients receiving fluoride gel treatment. This shocking omission was confirmed in 2009, when scientists at the Cochrane Library reviewed all available human trials on fluoride gels and reported that “there is little information” on “adverse effects.” Of the 25 clinical trials that have tested fluoride gels, only two trials bothered looking for side effects, and of these two studies, only nausea and vomiting were considered (in a very limited fashion).  The Cochrane review thus concluded that “more research is needed on adverse effects” because the “lack of evidence about adverse effects makes it more difficult for clinicians and policy makers to weigh the benefits of fluoride gels in preventing caries against possible side effects.”

The lack of research on side effects from fluoride gel treatment is largely a result of the NIH’s failure to fund such research. Indeed, after NIH-funded researchers reported in 1986 that fluoride gels produced sufficient fluoride levels in blood to impair glucose metabolism, the NIH has not funded a single study, let alone a clinical trial, to further investigate the matter.


— de la Sota M, Puche R, Rigalli A, et al. 1997. [Changes in bone mass and glucose homeostasis in subjects with high spontaneous fluoride intake] (Article in Spanish). Medicina 57(4): 417-20.
— Ekstrand J. (1987). Pharmacokinetic aspects of topical fluorides. J Dent Res. 66(5):1061-5.
— Ekstrand J, et al. (1983). Plasma fluoride concentrations in pre-school children after ingestion of fluoride tablets and toothpaste. Caries Res. 17(4):379-84.
— Ekstrand J, et al. 1981. Pharmacokinetics of fluoride gels in children and adults. Caries Research 15(3):213-20.
— Ekstrand J, Koch G. (1980). Systemic fluoride absorption following fluoride gel application. J Dent Res. 59(6):1067.
— Hawkins R, et al. (2003). Prevention. Part 7: professionally applied topical fluorides for caries prevention. Br Dent J. 195(6):313-7.
— Johnston DW. (1994). Current status of professionally applied topical fluorides. Community Dent Oral Epidemiol. 22(3):159-63.
— Lecompte EJ. (1987). Clinical application of topical fluoride products–risks, benefits, and recommendations. J Dent Res. 66(5):1066-71.
— Mazze RI, et al. (1977). Inorganic fluoride nephrotoxicity: prolonged enflurane and halothane anesthesia in volunteers. Anesthesiology. 46(4):265-71.
— Menoyo I, et al. (2005). Effect of fluoride on the secretion of insulin in the rat. Drug Res 55(5):455-60.
— Rigalli A, et al. (1995). Comparative study of the effect of sodium fluoride and sodium monofluorophosphate on glucose homeostasis in the rat. Drug Res 45(3):289-92.
— Rigalli A, et al. (1990). Inhibitory effect of fluoride on the secretion of insulin. Calcif Tissue Int 46:333-8.
— Shahed AR, et al. (1986). Effect of F on rat serum insulin levels in vivo. Journal of Dental Research 65:756.
— Spak CJ, et al. (1990). Studies of human gastric mucosa after application of 0.42% fluoride gel. Journal of Dental Research 69(2):426-9.
— Tsai CL, et al. (2008). Induction of apoptosis in rabbit oral mucosa by 1.23% acidulated phosphate fluoride gel. Arch Toxicol. 82(2):81-87.
— Whitford GM, et al. (1987). Topical fluorides: effects on physiologic and biochemical processes. J Dent Res. 66(5):1072-8.
— Whitford GM, et al. (1982). Fluoride absorption through the hamster cheek pouch: a pH-dependent event. J Appl Toxicol. 1982 Dec;2(6):303-6.
— Zakrzewska H, Udala J. (2006). [In vitro influence of sodium fluoride on adenosine triphosphate (ATP) content in ram semen]. [Article in Polish]. Ann Acad Med Stetin. 52 Suppl 1:109-11.
— Zakrzewska H, et al. (2002). In vitro influence of sodium fluoride on ram semen quality and enzyme activities. Fluoride 35: 153-160.

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