Friday Favorites: Should You Floss Before or After You Brush?

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

“Over the years, it has been generally accepted that [the use of] dental floss has a positive effect,”  removing up to 80% of plaque. How do we know? You can use what’s called a “splitmouth design,” where each person can act as their own control — for example, only flossing one quarter of their mouth. They asked study subjects to stop brushing their lower jaw so that plaque would build up, then they were randomized to floss half, and leave the other half as the non-flossed control. After three weeks, not only did the flossing cut plaque about 60%, more importantly, it cut signs of gingivitis in half — bleeding on probing, and another index of gum inflammation. Note, though, this is comparing flossing to nothing. They weren’t allowed to brush the jaw. So yeah, flossing is better than nothing, but is flossing plus brushing better than just brushing alone?

“The advocacy of floss…hinges, in large part, on common sense.” But common-sense doesn’t go very far as a form of evidence. You don’t really know until you put it to the test. What’s the efficacy of dental floss in addition to a toothbrush? Surprisingly, only three out of the 11 studies they looked at found a significant added benefit.

The anti-flossers were positively giddy, comparing dentists who continued to advocate flossing in the face of the data to flat-earthers. Dentistry was a profession “in denial.” Over 80% of people don’t floss regularly, and it’s just hard for the dental elite to accept that the “great unflossed masses” were right and us doctors were wrong. Flossing doesn’t work — get over it!

So, you’ve heard of the tooth fairy; is flossing just some tooth fairy tale? This review was published back in 2008. Since then, more studies were published, and while the evidence on additional plaque reduction is weak, at least there’s some evidence it helps with gingivitis — which is a primary reason you want to reduce plaque anyway. Why might they have not found stronger evidence? Well, the “[t]rials were of poor quality and [so the] conclusions must be viewed as unreliable.” So, basically, we don’t have good evidence either way, because good studies really haven’t been done.

Why not? Why wouldn’t Big Floss fund the studies? Because it appears that all floss works the same. If you compare unwaxed to woven to shred-resistant floss, they all have about the same plaque-removal efficacy, which it appears all such studies found. So why would a floss company fund a study to show flossing in general is good if they can’t show their product is better? Otherwise, you might just go buy their competitor’s floss.

Where do we stand today? “Although technically the evidence for flossing is weak, more importantly, the methodology…of the studies examining flossing effectiveness are also weak.” For example, they didn’t assess the quality of people’s flossing. This, for example, is not the way to floss (don’t ask—it’s a long story). Bottom line, the American Dental Association continues to recommend brushing and flossing every day.

But what’s the proper sequence? Should you floss before or after you brush? “Some dentists argue that flossing should come first, because you stir up the particles and plaque that the toothbrush can [then] brush” away, and then the fluoride from the toothpaste might get in there better. But others recommend brushing first, thinking that would “remove…the bulk of the particles” first, then the floss could like floss some of the fluoride from the residual toothpaste in there.

You don’t know until you put it to the test. “The effect of toothbrushing and flossing sequence on [between-tooth] plaque reduction and fluoride retention: A randomized controlled clinical trial” — and flossing first won, in terms of getting rid of significantly more plaque, and getting more of the fluoride in there. When we floss after brushing, much of the particles that are being pushed out by dental floss may stay in place on our teeth. The bottom line is flossing, followed by brushing, is preferred.

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Motion graphics by Avocado Video