AUDIE CORNISH, HOST:
If you've ever been to the dentist, you've probably heard a spiel like this.
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UNIDENTIFIED WOMAN: When you floss, break off about 18 inches of floss. Wind the floss around your pointer finger. Hold the floss tightly between your thumbs and your fingers. Guide the floss between your teeth using a gentle rubbing motion. Never snap or floss into your gums.
CORNISH: Now, those tips come courtesy of an online video from My Kid's Dentist, a group of pediatric dentists. Since 1979, the federal government has recommended flossing daily, but it quietly dropped that recommendation from its dietary guidelines this year. As NPR's Rae Ellen Bichell reports, the move has surprised some dentists.
RAE ELLEN BICHELL, BYLINE: Flossing has quietly lost its place among American recommendations for daily health. That could be because there's scant evidence that it actually works. Tim Iafolla is a dentist with the National Institute of Dental and Craniofacial Research. It's part of the National Institutes of Health.
TIM IAFOLLA: In large epidemiological studies, the evidence for flossing turns out to be fairly weak.
BICHELL: Iafolla wasn't involved in drafting the government's guidelines, but he's well aware of some of the problems with flossing research.
IAFOLLA: The condition we're trying to prevent, which is gum disease, is something that takes years to develop, and most of the studies only last for a few weeks or a few months.
BICHELL: Flossing first showed up in a report by the surgeon general and then made it into the national dietary guidelines. But when reporters with the Associated Press pushed the government for evidence behind flossing, there wasn't much. And in this year's guidelines, the word floss doesn't show up once.
JOAN OTOMO-CORGEL: It was a surprise because it's almost something that's ingrained in our DNA as dentists.
BICHELL: That's Joan Otomo-Corgel. She's a periodontist with the American Academy of Periodontology who practices in Los Angeles. She remembers learning that a lot of patients lie to their dentists about how much they floss.
OTOMO-CORGEL: It was like 19 percent of patients would rather clean a toilet than floss their teeth. So there is a taboo. And my concern is that the public picks up on this and says, oh, flossing is not a benefit. That means I don't have to do it.
BICHELL: She says based on her own observations during 32 years of practice, flossing does help get rid of films of bacteria that gunk up the space between teeth, causing infections and potentially contributing to bigger health problems.
OTOMO-CORGEL: And biofilms are alive. I mean, you look at it under a microscope, you have swimmers. You have different types of bacteria that form. And the longer they stay, the more virulent they become.
BICHELL: And the higher the odds of impacting overall health. Otomo-Corgel thinks studies on flossing just haven't followed subjects for long enough to show those long-term benefits. Rae Ellen Bichell, NPR News.
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