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Dentists’ claims that flossing is beneficial aren’t backed up with good evidence

It appears there’s no good evidence that flossing works at reducing gingivitis or cavities.

We’ve been told for decades that flossing daily will prevent gum disease and cavities.

Indeed, not only will you find the “flossing is an essential part of taking care of your teeth and gums” message on the American Dental Association (ADA) website, it’s also been featured in repeated editions of the federal government’s Dietary Guidelines for Americans.

But what, exactly, is the evidence to back up that advice?

Last year, the Associated Press (AP) decided to ask that question of experts at the departments of Health and Human Services and Agriculture. What they found may make you, well, do a spit take. Apparently, the evidence for flossing is nonexistent or (if you want to be charitable) extremely weak.

That discovery may explain why, as AP reporter Jeff Donn wrote on Tuesday, “the flossing recommendation was removed, without notice” from the federal government’s latest dietary guidelines issued earlier this year.

“The guidelines must be based on scientific evidence, under the law,” writes Donn. Yet, as government officials acknowledged in a letter to the AP, the effectiveness of flossing has never actually been proven.

That’s also what the AP found, as Donn reports:

The AP looked at the most rigorous research conducted over the past decade, focusing on 25 studies that generally compared the use of a toothbrush with the combination of toothbrushes and floss. The findings? The evidence for flossing is “weak, very unreliable,” of “very low” quality, and carries “a moderate to large potential for bias.”

“The majority of available studies fail to demonstrate that flossing is generally effective in plaque removal,” said one review conducted last year. Another 2015 review cites “inconsistent/weak evidence” for flossing and a “lack of efficacy.”

Problematic studies

In 2011, Cochrane, a highly respected global independent network of researchers, published its review of 12 flossing-related randomized controlled studies (considered the “gold standard” by scientists). That review found that flossing plus toothbrushing slightly reduces plaque and gum inflammation (gingivitis — a potential forerunner to full-fledged gum disease). But it also concluded that even that evidence was “weak” and “very unreliable.”

A major problem with flossing-related research, the Cochrane reviewers pointed out, is that few studies have lasted for more than three months.

“Ideally, trials would run for 12 months or longer, which would also be important in any study that considered dental caries as an outcome, since it takes longer for caries to develop to a stage that can be detected by any of the methods currently available,” they wrote.

The ADA and the American Academy of Periodontology provided the Donn and his AP colleagues with other studies, which they claimed proved flossing’s benefits. “However, most of these studies used outdated methods or tested few people,” writes Donn.

“Some lasted only two weeks, far too brief for a cavity or dental disease to develop,” he explains. “One tested 25 people after only a single use of floss. Such research, like the reviewed studies, focused on warning signs like bleeding and inflammation, barely dealing with gum disease or cavities.”

As Donn also reports, most flossing-related studies have been funded — and sometimes designed and conducted — by the $2 billion-a-year flossing industry.

Yet even their researchers have failed to come up with positive results.

“Procter & Gamble, which claims that its floss fights plaque and gingivitis, pointed to a two-week study, which was discounted as irrelevant in the 2011 research review,” Donn writes. “Johnson & Johnson spokesman Marc Boston said floss helps remove plaque. [But] when the AP sent him a list of contradicting studies, he declined comment.”

Needed: solid research

What’s the bottom line for consumers? It appears there’s no good evidence that flossing works at reducing gingivitis or cavities. Yet, there’s some evidence that flossing, if done incorrectly, can do some harm.

“Careless flossing can damage gums, teeth and dental work,” writes Donn. “Though frequency is unclear, floss can dislodge bad bacteria that invade the bloodstream and cause dangerous infections, especially in people with weak immunity, according to the medical literature.”

Still, if well-designed, long-term independent studies were conducted, flossing might be proven to be beneficial. Right now, though, no one has the evidence to make such a statement with any certainty.

Half of American adults over the age of 30 have gum disease, and people with prolonged gum disease are 46 times more likely to lose their teeth.

It seems time — long past time, actually — to conduct those studies. Or, if no one is willing to spend the money to do that research (and such studies would be very expensive), it’s time that dentists and public health officials be more up front with people about what the research on flossing actually says.

FMI: You can read the AP’s article online.

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Comments (6)

  1. Submitted by Jim Halonen on 08/03/2016 - 09:01 am.

    Articles like this

    Are an attempt to see what nonsense people will believe. Other professional groups are jealous what politicians have been able to achieve.

  2. Submitted by William Stahl on 08/03/2016 - 09:38 am.


    When good scientific evidence isn’t available, one would do well to go with what is known as common sense. If food is stuck between teeth, then it should be removed before bacteria start doing bad things. Flossing isn’t the only way to do this but it probably increases the odds of timely removal.

  3. Submitted by Pat Thompson on 08/03/2016 - 10:02 am.

    Doing it wrong

    While I believe there are no studies that prove (or disprove) flossing’s effectiveness, I never thought it was about preventing decay, as much as preventing gum disease.

    If a study could be designed (though it probably can’t be placebo controlled) of flossing *correctly* vs. not flossing over a long enough period (like decades) I would be willing to bet money it would show the flossers are significantly less likely to have periodontal disease.

    Proper flossing means going below the gum line on each tooth, both sides, multiple times, with the floss pulled tightly against the tooth. Not just popping it down between the teeth once, like you might if you are removing a piece of corn or chicken.

    Also… the plastic floss-holders like the one shown in this article’s photo make it impossible to floss the way that we should. Can’t reach well, not enough pressure on the floss against the tooth… completely useless.

  4. Submitted by Gerald Abrahamson on 08/03/2016 - 10:20 am.

    No reason to floss–do something better.

    Nobody really carries floss to clean between their teeth. A toothpick is usually adequate during the day to get out food that gets stuck when eating. However, a good cleaning at night is what is really needed. As floss does not work well, that leaves small appliances such as a WaterPik. They remove food particles caught between teeth and also many bacteria in the mouth.

  5. Submitted by Susan Lesch on 08/03/2016 - 11:16 am.

    Short studies

    The AP article cited ends with an NIH dentist telling people to floss anyway.

  6. Submitted by Pat Berg on 08/03/2016 - 11:35 am.

    Flossing difficulties

    I’m one of those people whose teeth are so tightly spaced that flossing is extremely difficult. My fingers literally turn purple and go numb as I attempt to get the floss held securely enough to make it between the nonexistent spaces separating my teeth. And then half the time the floss breaks en-route and it takes a second piece (and more winding and cutting off of circulation) to dislodge the floss piece!

    But alarmed by the pocket depth measurements recorded by my dental hygienist at my visit last spring, I became re-determined to do a better job and decided to take a try with a Sonicare Air Floss device (a more recent product introduction akin to the Water Pik).

    Even THAT little technological marvel has some difficulty driving the water between some of my dental spaces, but I’ve kept at it, and – lo and behold – my gum pocket depth measurements (which are supposed to be diagnostic of impending gum disease) did see an improvement at my most recent visit.

    So I’m not sure what to make of this study. But as Susan notes, “Still, if well-designed, long-term independent studies were conducted, flossing might be proven to be beneficial”. So I guess I’m willing to keep on with the Air Floss and hope I don’t start noticing any loose teeth!

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