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Does Flossing Help Or Not? The Evidence Is Mixed At Best

Most studies of flossing have been too short to prove the daily practice has long-term health benefits, some dentists say. But conclusive studies aren't cheap or easy.
Klaus Vedfelt
Getty Images
Most studies of flossing have been too short to prove the daily practice has long-term health benefits, some dentists say. But conclusive studies aren't cheap or easy.

Flossing has quietly lost its place among recommendations for daily health, at least as prescribed in the Dietary Guidelines for Americans, which are issued every five years by the U.S. departments of Health and Human Services and Agriculture.

That could be because there's scant evidence that flossing does much to keep teeth and gums healthy.

"In large epidemiological studies, the evidence for flossing turns out to be fairly weak," says Tim Iafolla, a dentist with the National Institute of Dental and Craniofacial Research, which is part of the National Institutes of Health.

Iafolla wasn't involved in drafting the dietary guidelines, but he's well aware of some of the problems with flossing research. Still, he points out, tracking the long-term benefits of flossing isn't cheap or easy.

"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 months," he says. "So the evidence that we gather from these studies is fairly indirect. We can look at bleeding gums, we can look at inflammation, but we have to extrapolate from that evidence to gum disease."

A 2011 Cochrane "oral health" review of 12 studies on the effects of flossing found that they "were of poor quality and conclusions must be viewed as unreliable." The review concluded that there was some evidence that flossing and brushing regularly did appear to reduce gingivitis, compared to tooth brushing alone, but that evidence was weak on how much it reduced plaque. Most trials were too short to determine if flossing could have long-term impacts on things like tooth decay, the researchers who conducted that review concluded.

Federal recommendations in favor of flossing showed up in a report by the surgeon general in 1979, and later made it into the national dietary guidelines. But when reporters with The Associated Press recently pushed the government for evidence that supports flossing, there wasn't much.

And in this year's guidelines, the word floss doesn't show up once.

A spokesperson with the U.S. Department of Health and Human Services tells Shots that the most recent committees reviewing the guidelines focused more on the impact of sugars on dental health, and did not consider flossing.

"Since neither the 2010 nor 2015 Advisory Committees reviewed evidence on brushing and flossing teeth, the authors of the current edition decided not to carry forward the information on brushing and flossing included in past editions of the guidelines," she says. But non-flossers shouldn't claim victory yet. The committee hasn't ditched flossing entirely.

"They were not implying that this is not an important oral hygiene practice," the spokesperson cautions. "It is also important to note that, although dental floss was mentioned in past editions of the guidelines, it was most likely identified as a supporting recommendation along with brushing teeth, with the primary emphasis being on the nutrition-based recommendation to reduce added sugars."

Still, the move to delete flossing from the health guidelines isn't sitting well with some dentists.

"It was a surprise because it's almost something that's ingrained in our DNA as dentists," says Joan Otomo-Corgel, 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.

And a survey by the academy found that almost 15 percent of adults 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,' " says Otomo-Corgel.

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.

"Biofilms are live," she says. "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."

And that does not bode well for a person's overall health, says Otomo-Corgel.

It may be, she says, that studies on flossing just haven't followed subjects for long enough to notice long-term benefits.

Copyright 2021 NPR. To see more, visit https://www.npr.org.

Rae Ellen Bichell is a reporter for NPR's Science Desk. She first came to NPR in 2013 as a Kroc fellow and has since reported Web and radio stories on biomedical research, global health, and basic science. She won a 2016 Michael E. DeBakey Journalism Award from the Foundation for Biomedical Research. After graduating from Yale University, she spent two years in Helsinki, Finland, as a freelance reporter and Fulbright grantee.