Last year, some British tabloids starting passing around the story that flossing didn’t work. It was a total ploy for journalistic clickbait: nobody likes flossing, even though their dentist says it’s an essential part of oral hygiene. Everybody wants to be told that they don’t have to do it anymore. The story even got picked up by the BBC because it wasn’t quite as tabloid as Bat Boy or the latest antics on Celebrity Big Brother. There was a little kerfuffle, but, by and large, the story was forgotten.
Then this year, the US government decided to drop flossing from its dietary guidelines, where it had been a common element since 1979. Why did it drop the recommendation? Because the evidence supporting flossing was not very strong. The Associated Press ran with the story and it has given many people the excuse they needed to stop flossing. But you should keep flossing, and here’s why.
Government Guidelines: A Solid Floor, Not a Comfortable Ceiling
Dropping flossing from the recommendations is not as big a deal as you might think. Sure, it seems like a major blow to the legitimacy of flossing, but it’s not. That’s because, contrary to some propaganda, government recommendations are intended to be minimal, and based only on the strongest science available. They are intended to be the bare minimum of what has been proven to be effective, not the maximum of what we think is effective.
In other words, consider the government guidelines as, literally the least you need to do to maintain your health, not as a comprehensive list of healthy habits or even what you should be doing to stay healthy.
But the fact that we don’t have strong scientific evidence to support flossing still gives some people pause. But there are many good reasons why scientific studies don’t show the effectiveness of flossing.
People Don’t Floss Correctly
Most people don’t know how to floss properly. If they’re asked to floss for a study or not floss, the benefits of flossing might be lost because people don’t know how to do it right. Again, flossing is unpopular, and people just want to get it done quickly.
We have some evidence that support this theory. The first is a study cited in the AP piece, which ostensibly showed that flossing didn’t help. This study looked at two groups of children. The first is a group of adolescents who were asked to floss their own teeth for two years. These children got no benefit from flossing.
But the second group was younger children who had their teeth flossed by professionals every school day for 1.7 years. These children experienced a 40% reduction in their cavities between teeth. This doesn’t prove that flossing doesn’t work, just that teenagers don’t know how to do it properly (like driving, amiright?)
And the challenge of flossing properly might be why flossing doesn’t do as well as interdental brushes in clinical studies. It might be easier to use the brushes to clean between teeth than it is to floss properly.
People Lie about Flossing
But one of the big problems with studying flossing is that people hate flossing, and they lie about it. In fact, studies show that 27% of people admit to lying to their dentist about flossing. Dentists say the actual number is likely much, much higher.
In studies, researchers don’t (usually) floss people’s teeth or watch them floss. It’s on the honor system, so if people are lying to researchers about flossing, it would obscure the benefits of flossing. With rigorous statistical standards, it wouldn’t take even 27% of people lying about it to obscure the benefits of flossing.
Our Studies Aren’t Designed Properly
But the problem might not lie with the study subjects, but with the studies themselves. The biggest benefits of flossing are likely reduction in gum disease and cavity risk. We’ve already noted how difficult it was to get a cavity risk survey that showed benefit. Gum disease is even worse. It’s strongly mediated by genetic factors that were poorly understood at the time of most flossing studies, which are almost all before 2010. The potential benefits of flossing might have been hidden by underappreciated confounders.
Another problem with flossing studies might be that they’re not long enough. Long studies are expensive, and there’s not a lot of money in flossing. Besides, with everyone essentially assuming the benefits of flossing, there was no reason for government agencies like the National Institute for Dental and Craniofacial Research (NIDCR) to sponsor studies about flossing.
It’s possible that will change now that flossing has been removed from recommended guidelines. That, and the conversation we can now have about flossing, might be the silver linings in this otherwise dark cloud seeded by the AP.