It’s definitely bad if you do it like this fellow. Credit: Gregory Gill / Flickr

Since a New Orleans dentist began advising his patients to use a thin silk thread to clean between their teeth in 1815, dental flossing has steadily caught on. Nowadays, most dentists advise patients they floss their teeth, and the whole dental floss industry has grown to $2 billion. But although most dental health care professionals will tell you flossing is good for fighting plaque, cavities, and gum disease, an investigation carried out by reporters from the Associated Press found the actual science says otherwise.

Little evidence that flossing does anything to keep gums and teeth healthy

The AP reporters found the studies which back the claim of dentists that flossing is good for oral health are outdated and only surveyed a small number of people, hence inconclusive. When 25 studies published over the past decade which compared the outcomes between people who only brushed or brushed and flossed were scrutinized, the evidence in favor of flossing was found to be “weak, very unreliable,” of “very low” quality, and carries “a moderate to large potential for bias.”

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

“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.”

Despite this evidence or lack thereof, depending on how you look at things, the American Dental Association (ADA) and the American Academy of Periodontology (AAP) still actively advises patients to floss. One of the studies they cite to back their claim was published in 2011 and credits flossing with a slight reduction in gum inflammation. However, the same study’s reviewers found the evidence was “very unreliable,” while a dental health scholar said: “any benefit would be so minute it might not be noticed by users.”

When AP reporters confronted Matthew J. Messina, an ADA spokesman, with this issue, Messina acknowledged weak evidence but blamed research participants who didn’t floss correctly.

Another serious flaw in flossing science the AP uncovered was that leading floss manufacturers like Procter & Gamble or Johnson & Johnson are allowed to conduct or fund their own studies, despite the obvious risk of bias and conflicting interest. For instance, P&G used to claim that its flossing products fight plaque and gingivitis, citing a two-week study which the company funded. This study was discounted as irrelevant in a 2011 research review.

All in all, this investigation suggests that research about flossing is severely lacking. However, that doesn’t mean that flossing doesn’t, in fact, fight plaque or gingivitis. We just need better research.

At the same time, flossing could even do harm, as it can cause damage to gums, teeth, and dental work when done improperly. Bleeding can leach harmful bacteria in the bloodstream.

By now, most of you — including yours truly — must be confused. Is flossing good or bad? Considering millions of people floss with no particular detrimental health outcome, I would say that the risks of flossing are very small. By flossing you might even reap some oral hygiene rewards — maybe. Don’t throw out your floss just yet.