Giz Explains: How Fluoride Keeps Bacteria From Eating Your Teeth

Portland, Oregon, made headlines last week, because it became America's largest metropolis to not fluoridate its water supply. Why is a simple ion that's been used for decades still causing such a hubbub? Because, 70 years on, we're still not entirely sure how it works.

What It Is

Fluoride is an ion, the reduced form of fluorine, the 13th most common element in the Earth's crust. Fluoride itself is often found in minerals such as fluorite as well dissolved in food and water — 1.3ppm in seawater and 0.01-0.3ppm in fresh (tap, not bottled). In excessive concentrations, fluoride can cause health problems — mild fluorosis causes disoloration of the enamel — but is filtered down to safe levels by water management in locations where the mineral is overabundant. Many home water filters also effectively remove fluoride from tap water.

“This is the only health condition we’re aware of,” Dr. Barbara Gooch, from the CDC’s oral health division, told FoxNews.com, speaking of flourosis. “It’s a cosmetic condition, and other than that, there are no other documented health conditions in relation to water fluoridation.”

The WHO recommends a concentration of 0.5 to 1.0mg/L.

The practice of adding fluoride to Australian water supplies as a means of preventing tooth decay began in the 1960s and has grown to include more than 70 per cent of Australian households.

How It Works

Flouride's best known as a defender of teeth, and for good reason. Tooth enamel is composed of hydroxyapatite, a strong mineral but one susceptible to acid erosion like that caused by sugar-eating bacterial colonies that live on the surface of the tooth. Normally, brushing will dislodge the bacteria while your saliva neutralises the acid and allows for the tooth to remineralize. However, if more mineral is lost than rematerialised, cavities begin to form. Dental cavities are a major problem, especially in the industrialised nations, affecting up to 90 per cent of school-age children and most adults.

Fluoride helps prevent tooth decay by bonding with tooth enamel and strengthening it against the acid, even helping reverse early-stage cavity damage. We think. Turns out science still isn't quite sure how exactly fluoride confers its benefits, though one research team from Saarland University in Germany believes it might be by acting as a bacterial Teflon coating:

The cavity-preventive effect for teeth is often traced back to effects on demineralization. However, an effect on bacterial adhesion was indicated by indirect macroscopic studies. To characterise adhesion on fluoridated samples on a single bacterial level, we used force spectroscopy with bacterial probes to measure adhesion forces directly. We tested the adhesion of Streptococcus mutans, Streptococcus oralis, and Staphylococcus carnosus on smooth, high-density hydroxyapatite surfaces, pristine and after treatment with fluoride solution. All bacteria species exhibit lower adhesion forces after fluoride treatment of the surfaces. These findings suggest that the decrease of adhesion properties is a further key factor for the cariostatic effect of fluoride besides the decrease of demineralization.

No matter how it works, the fluoride must come in direct contact with the tooth to be effective. It's typically delivered either through the water supply or fluoridated toothpastes and mouthwashes. Water fluoridation is the primary means of delivery — 5.7 per cent of the world population drinks fluoridated water — and appears to be quite effective. Some studies estimate an 18 to 40 per cent reduction in cavities with both fluoridated water and fluoridated toothpaste over those without fluoride on tap. Conversely, the rise of fluoridated toothpastes (and even fluoridated salts) in Europe have proven a viable alternative to drinking it with significant drops in the rate of tooth decay.

No matter how it's delivered, as long as you get fluoride in your mouth, there's a good chance your teeth will stay there too.

[York University, About, Wikipedia, My Health News Daily, Wikipedia, EPA]

Picture: mathom/Shutterstock

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