Is Flossing Actually Necessary?

In 2016, a news story reported that the benefits of flossing were unproven, and the claim still comes up in searches today. If you find flossing tedious, that headline sounded like permission to stop. So is flossing necessary, or was it oversold all along?

The short answer: the spaces between your teeth need a daily clean, and floss is only one of several tools that can reach them. The studies behind floss really were weak. Weak studies mean the benefit is not proven, which is a different finding from proof that floss does nothing.

What did the 2016 AP story on flossing find?

The Associated Press story, published in August 2016, examined 25 studies that compared brushing on its own against brushing with floss. Its verdict on that evidence was "weak, very unreliable" and of "very low" quality (AP, August 2016). The federal dietary guidelines issued that year had also quietly removed the flossing recommendation.

The research reviews say much the same, before and after the story. A 2011 Cochrane review of 12 trials found that adding floss to brushing reduced gum inflammation by a small amount. None of those trials reported on cavities at all (Sambunjak et al., 2011). A broader 2019 Cochrane review covered every kind of between-teeth cleaner across 35 trials. Its authors still found the evidence low or very low in certainty (Worthington et al., 2019).

Also in August 2016, the U.S. Department of Health and Human Services told ADA News, the American Dental Association's newsroom, that flossing remains "an important oral hygiene practice" (ADA).

Weak studies aside, is flossing necessary?

Yes, because a short study can miss a real benefit, and most flossing studies were too short to see the outcomes that matter.

Bone loss from gum disease and new cavities between teeth both develop slowly. In the 2019 review, results were mostly measured over one to three months (ADA). AP found some studies that lasted two weeks, a span it said was far too brief for decay or gum disease to develop. In that window, a researcher can measure bleeding and plaque, but not lost bone or new cavities. The 2019 review asks for future trials long enough to measure exactly those two things.

In most of the studies, the volunteers' gums were only mildly inflamed to begin with, which leaves a trial little room to show improvement. And a volunteer always knows if they are flossing, so no flossing trial can be blinded, which weakens any trial of a habit.

The clearest test of cavities comes from children. In school trials, professionals flossed children's teeth every school day for roughly 1.7 years. Most of those teeth were baby teeth, and the risk of new cavities between them dropped by 40%. A professional floss once a quarter for three years did not help. Neither did two years of young teens flossing for themselves (Hujoel et al., 2006).

The authors caution against applying the result to everyday flossers too directly. What it does show is that floss can prevent cavities between teeth. The trials where it failed differed in how often it was used and who was using it.

Where does a toothbrush miss?

Where two neighboring teeth meet, they touch at a point dentists call the contact point. Below that spot, the gum rises into a small triangle that fills the space between the teeth. Bristles clean the cheek side and the tongue side of each tooth well, but they cannot pass through the contact. They hardly touch the side walls of the teeth beneath it either.

The ADA says it directly: "Toothbrush bristles alone cannot clean effectively between these tight spaces" (ADA). So plaque, the soft bacterial layer that builds up on teeth each day, sits there undisturbed.

What happens if you never clean between your teeth?

The first problem that starts in that hidden strip is gum disease, which often begins in the triangle of gum between the teeth. Plaque left against it makes the gum swell and bleed, which is gingivitis. Left longer, plaque hardens into tartar, the gum pulls away from the root, and the bone around the tooth starts to go. Our post Can Gum Disease Be Reversed? covers the point where that damage stops being reversible.

The second is a cavity between two teeth, which usually starts on the side wall just under the contact point. You cannot see that spot in a mirror, and decay there does not hurt at first. An X-ray can show it before you notice anything. Our post on how cavities form explains why decay stays quiet for so long.

Which works best: interdental brushes, floss or a water flosser?

Interdental brushes are tiny bristle brushes on a thin wire, sold in different sizes. Where the space between two teeth is wide enough to fit one, they have the strongest evidence. A 2015 review of reviews found "moderate evidence" that they reduce both plaque and gum inflammation. It called them "the most effective method" for removing plaque between teeth (Sälzer et al., 2015). The 2019 Cochrane review also put them ahead of floss for calming gum inflammation, though on low-certainty evidence.

Floss is the tool that fits where teeth touch tightly and a brush cannot pass, and technique decides what it does. Curve it into a C around one tooth, slide it just under the gumline, then do the same against the neighboring tooth (ADA, MouthHealthy). Snapping it straight down and back up clears the contact but skips the side walls.

Water flossers rinse the space instead of wiping it, and their evidence is thinner. In the 2019 review, water flossers eased gum inflammation after one month, an effect the review did not find at three or six months. The reviewers rated that evidence very low in certainty. They did not clear plaque any better than a toothbrush on its own. The ADA still lists them as one way to clean between teeth (ADA, MouthHealthy).

Does it matter which tool you choose?

It matters less than whether you use one every day. The differences between tools rest on low-certainty evidence. In the 2006 review, by contrast, professional flossing on every school day cut cavity risk, and the same professional flossing done only quarterly did not.

The ADA's own wording is to clean between teeth "with floss (or another interdental cleaner) once a day" (ADA). It also says the timing does not matter, before or after you brush (ADA, MouthHealthy).

If your gums bleed when you start, the gum there is usually already inflamed, which is the gingivitis described above. Keep going gently: the ADA warns that flossing too hard can damage the gum between your teeth (ADA, MouthHealthy). Have the spots checked if the same ones keep bleeding.

What to do

During your next cleaning, find out which spaces between your teeth bleed and which tool suits each one. Interdental brushes are sold in several widths, and a width that fits one space can be too tight or too loose for the next. Our exams and hygiene page explains what that visit includes. If your gums bleed often or you have been told about deep pockets, our periodontics page covers pocket measurement and treatment.

Ready to get started? Schedule a visit with Front Royal Dental Group, or call (540) 636-2003.