Displaying a mouthful of healthy white teeth shows that you're either a friendly person or nightmarish toothpaste spokesman Mr. Smile. Get a beautiful grin with this Groupon.

The Deal

$49 for a kid's dental package with exam, x-rays, cleaning and fluoride ($275 value)

Fluoride is a key substance in protecting teeth from decay. To learn why dentists love it, read on.

Fluoride: Something Smiling in the Water

In the early 1900s, when the most common cavity treatment was still extraction, two dentists in different parts of the country—one in Colorado and one in Arkansas—noticed a new phenomenon in their patients. Despite their mottled stains, the children’s teeth showed a remarkable resistance to decay. Looking to dispel the rumor that kids had simply evolved mouths filled with rocks, scientists soon found an explanation: the two locations’ drinking water contained remarkably high levels of fluoride. As it turns out, fluoride—an ion of fluorine—naturally protects teeth by adsorbing onto their surface, fortifying the enamel by attracting calcium ions in the saliva. When bacteria try to dissolve the minerals of the enamel, the film of fluoride and calcium protects it, like armor shielding a knight from sunburn.

The highly fluoridated water in Colorado and Arkansas was a bit of an anomaly; although fluoride is almost always present in soil and water, its concentrations are usually so low that it is of little benefit to teeth. In what the Centers for Disease Control and Prevention named as one of the 10 Great Public Health Achievements in the 20th Century, local governments began artificially fluorinating water supplies that had insufficient amounts, starting with Grand Rapids, Michigan, on January 25, 1945. Since then, the incidence of tooth decay has decreased—by up to 70% in children alone—and fluoride is found in virtually every dental product from whitening toothpaste to swear-absolving mouthwash.