By now you’ve probably read a few headlines calling flossing a waste of time. According to a recent Associated Press report, there is a striking lack of evidence to show that daily flossing actually prevents gum disease and tooth decay. Could every dentist you’ve ever seen have been wrong?
The federal government had recommended daily flossing as part of its dietary guidelines since 1979. By law, every guideline must be based on scientific research. But when the AP began pressing the feds for their evidence last year, mostly “weak,” “unreliable,” and “very low-quality” results came to the fore. Whether as a direct result or a funny coincidence, the feds quietly dropped the flossing rec from the guidelines issued in early 2016.
But don’t chuck your floss just yet. Although there haven’t been long-term, large-scale clinical studies to show definitively that flossing fends off oral diseases, the American Dental Association, the American Academy of Periodontology, and the National Institutes of Health all stand firmly behind this practice.
“Here’s the thing,” says Dr. Wayne Aldredge, president of the American Academy of Periodontology. “A lack of quality evidence is not indicative of a lack of effectiveness. There is no dispute over whether flossing removes plaque and debris — it does. Since prolonged exposure to the bacteria in plaque may lead to gum disease, removing it is advised.” He says flossing is key to expunging the plaque that often lurks deep between the teeth and beneath the gums — places your toothbrush can’t always reach.
According to Dr. Timothy Iafolla, of the National Institute of Dental and Craniofacial Research, there is decent science to show that removing plaque and debris reduces gum inflammation and bleeding in the short-term. “From there, we just have to extrapolate that flossing may help prevent gum disease,” he says. “Because gum disease can take up to 15 years to develop, it’s nearly impossible to study that as an endpoint.”
For one, Iafolla says it would be hard to track how often and how well study participants flossed versus what they told researchers. “Self-reports are unreliable, so you get weak evidence,” he explains. “And if you had a control group, they’d probably know their gums were being studied, so they might step up their flossing, weakening the study even more.”
It would also be highly unethical to conduct a long-term, randomized, controlled clinical study, says Dr. Scott Tomar, a dentist and oral epidemiologist at the University of Florida’s College of Dentistry. Because there’s good reason to believe flossing can lower your risk of oral issues, researchers couldn’t rightly ask one group of people to floss daily and another group to never floss and then wait to see what happened. “This kind of study wouldn’t get past a university’s institutional review board even if someone put up big money for it,” Tomar says. “Personally, if someone asked me to not floss, I’d opt out of that study.”
Think of it like cigarette smoking. “We know smoking is a risk factor for lung cancer — all stemming from observational studies,” Tomar says. Observational studies are those in which researchers examine the health of a group of people without directing what they eat, which medications they take, how often they exercise, etc. “Nobody would ask participants to smoke or not smoke for 20 years and then sit back and watch who got cancer,” Tomar says. “We have to make public health decisions based on the best available evidence, which may mean data that’s not from randomized, controlled trials.”
The verdict: keep flossing your teeth. Tomar says doing so at least every 24 hours should be sufficient for removing bacteria-laden plaque and lowering your risk of oral diseases. “I recommend flossing at night, not based on any high-level evidence, but because people tend to have more time for oral hygiene at night than in the mornings when they are rushing to get out the door,” he says. “Even with brushing, people usually do better job at night.”
Besides, what do you have to lose? “With flossing, the evidence may be weak, but we think there is a benefit with no real downside,” Iafolla says. “The risk is almost nonexistent and the cost is very low. Keeping your teeth clean is inherently a good thing.”