Fluoride

Fluoride has long been known to influence the activity of various enzymes in vitro. Later it has been demonstrated that many effects primarily attributed to fluoride are caused by synergistic action of fluoride plus aluminum. Aluminofluoride complexes have been widely used as analogues of phosphate groups to study phosphoryl transfer reactions and heterotrimeric G proteins involvement. A number of reports on their use have appeared, with far-reaching consequences for our understanding of fundamental biological processes. Fluoride plus aluminum send false messages, which are amplified by processes of signal transduction. Many investigations of the longterm administration of fluoride to laboratory animals have demonstrated that fluoride and aluminofluoride complexes can elicit impairment of homeostasis, growth, development, cognition, and behavior. Ameliorative effects of calcium, vitamins C, D, and E have been reported. Numerous epidemiological, ecological, and clinical studies have shown the effects of fluoride on humans. Millions of people live in endemic fluorosis areas. A review of fluoride interactions from molecules to disease is necessary for a sound scientific assessment of health risks, which may be linked to the chronic intake of small doses of fluoride and aluminum from environmental and artificial sources.

This report presents the committee’s review of the scientific basis of EPA’s MCLG and SMCL for fluoride, and their adequacy for protecting children and others from adverse health effects.  The committee considers the relative contribution of various sources of fluoride (e.g., drinking water, food, dental-hygiene products) to total exposure, and identifies data gaps and makes recommendations for future research relevant to setting the MCLG and SMCL for fluoride.  Addressing questions of economics, risk-benefit assessment, or water-treatment technology was not part of the committee’s charge.

The aim of this investigation was to determine the influence of fluoride in certain mouthwashes on the risk of corrosion through galvanic coupling of orthodontic wires and brackets. Two titanium alloy wires, nickel-titanium (NiTi) and copper-nickel-titanium (CuNiTi), and the three most commonly used brackets, titanium (Ti), iron-chromium-nickel (FeCrNi) and cobalt-chromium (CoCr), were tested in a reference solution of Fusayama-Meyer artificial saliva and in two commercially available fluoride (250 ppm) mouthwashes, Elmex and Meridol. Corrosion resistance was assessed by inductively coupled plasma-atomic emission spectrometry (ICP-MS), analysis of released metal ions, and a scanning electron microscope (SEM) study of the metal surfaces after immersion of different wire-bracket pairs in the test solutions. The study was completed by an electrochemical analysis. Meridol mouthwash, which contains stannous fluoride, was the solution in which the NiTi wires coupled with the different brackets showed the highest corrosion risk, while in Elmex mouthwash, which contains sodium fluoride, the CuNiTi wires presented the highest corrosion risk. Such corrosion has two consequences: deterioration in mechanical performance of the wire-bracket system, which would negatively affect the final aesthetic result, and the risk of local allergic reactions caused by released Ni ions. The results suggest that mouthwashes should be prescribed according to the orthodontic materials used. A new type of mouthwash for use during orthodontic therapy could be an interesting development in this field.

The treatment comparisons of interest included flossing versus no flossing, or a comparison of different frequencies of flossing use. Studies where the effect of flossing could not be separated from the effects of other treatments were excluded. The primary study outcome was a measure of caries incidence. There were no restrictions with respect to the study population. Study designs were limited to con-trolled clinical trials.

In seven European countries there are national legal regulations, or salt producers have obtained individual authorisations, for the production and marketing of fluoridated edible salt. On the basis of EU mutual recognition rules, there are other countries which import fluoridated edible salt. All European countries practise salt fluoridation on a voluntary basis. In the near future, a European regulation is expected to supersede the national conditions.

Annual examination of selected samples of children continuously resident in Grand Rapids continued for 15 years. Muskegon remained the non-fluoridated control city until July 1951, at which time, in response to the observed effects in Grand Rapids, city officials decided to fluoridate the supply in Muskegon also.

“The dissociation of hexafluorosilicate has been reinvestigated due to recent suggestions that fluorosilicate intermediates may be present in appreciable concentrations in drinking water. 19F NMR spectroscopy has been used to search for intermediates in the hydrolysis of hexafluorosilicate. No intermediates were observable at 10-5 M concentrations under excess fluoride forcing conditions over the pH range of 3.5?5. A single intermediate species, assigned as SiF5- or its hydrate, was detected below pH 3.5. At moderate pH values of 4 and 5 silica oligomerization in the solutions studied made it difficult to directly determine the hexafluorosilicate equilibrium constant. Under more acidic conditions the average pKd, or negative log of the dissociation constant Kd, determined by 19F NMR measurements, was 30.6. We also investigated the behavior of hexafluorosilicate in common biological buffer reagents including phosphate/citrate, veronal/HCl buffers, and Ringer’s solution. The buffer capacity of all of these systems was found to be insufficient to prevent acidic shifts in pH when hexafluorosilicate was added. The pH change is sufficient explanation for the observed inhibition of acetylcholinesterase that was previously attributed to hexafluorosilicate hydrolysis intermediates.”

“The latest estimates suggest that around 200 million people, from among 25 nations the world over, are under the dreadful fate of fluorosis. India and China, the two most populous countries of the world, are the worst affected. India is plagued with numerous water quality problems due to prolific contaminants mainly of geogenic origin and fluoride stands first among them. The weathering of primary rocks and leaching of fluoride-containing minerals in soils yield fluoride rich groundwater in India which is generally associated with low calcium content and high bicarbonate ions. The unfettered ground water tapping exacerbates the failure of drinking water sources and accelerates the entry of fluoride into groundwater. Most of the scientific literature substantiates the benefits of low fluoride concentrations in preventing dental decay. However, as a surprising paradox, incidence of dental, skeletal and crippling skeletal fluorosis was reported in India with average fluoride concentrations as low as 0.5, 0.7 and 2.8 ppm respectively.”

On a farm in Pagosa Springs, Colorado, Quarter horses consuming artificially fluoridated water (up to 1.3 ppm F) for extended periods of time developed classical symptoms of chronic fluoride intoxication including dental fluorosis, crooked legs, hyperostosis and enostosis, hoof deformities, and microscopic evidence of reduced bone resorption. These symptoms began to appear about two years after fluoridation started in 1985 and gradually became more severe. Representative postmortem F concentrations in dry matter bone were: 587 ppm in a 20-year-old gelding drinking F water for the last 10 years; 936 ppm in a 17-year-old gelding on F water for the last 11 years; and 757 ppm in a 21-year-old mare on F water all her life. Blood serum thyroxin in a 19-year old mare (T4) was “very low”, and interference with reproduction was noted after five years. Radiographs of the third metacarpal bone revealed osteomegaly with thick lamellae from both ends extending throughout the medullary space. The levels of F ingestion and the bone F concentrations of these horses are far below those claimed to cause F intoxication in cattle. After fluoridation was terminated on March 29, 2005, colic gradually ceased and other significant improvements have occurred.