What AP Didn’t Mention about Flossing

The recent flurry of news regarding the benefits of dental floss has left out an important point of view: while the evidence of flossing’s medical benefits may be weak, the evidence that it is pointless or harmful is even weaker. What’s more, flossing is an inexpensive oral hygiene practice accessible for people most in need of improved oral health.

But let’s break this down.

The Associated Press reported:

The evidence for flossing is "weak, very unreliable," of "very low" quality, and carries "a moderate to large potential for bias." … One study review in 2011 did credit floss with a slight reduction in gum inflammation — which can sometimes develop over time into full-fledged gum disease. However, the reviewers ranked the evidence as "very unreliable."

But the study review authors actually noted:

There is some evidence from twelve studies that flossing in addition to toothbrushing reduces gingivitis compared to toothbrushing alone. There is weak, very unreliable evidence from 10 studies that flossing plus toothbrushing may be associated with a small reduction in plaque at 1 and 3 months.

What is important to note here is:

1. The "weak, unreliable" language actually references the evidence that flossing specifically reduces plaque, not gum disease. But more importantly, the language used comes from a different lexicon than we use every day. “Weak, unreliable, low quality” all sound like common terminology, but in the research world, this type of language doesn’t indicate the science shouldn’t be believed. The terms actually may reflect that study authors left out some details (such as the exact method of randomizing people) that the study reviewers could not confirm, not that the research is bad. 
2. The fact the review of studies could not prove plaque reduction at 1 and 3 months is very likely because tooth decay and gum disease are slow progressing issues that would require multi-year studies. It may also be because the standard for measuring plaque reduction only scores visible surfaces, so plaque may be reduced on non-visible surfaces such as directly between teeth.
3. In March 2015, the same study review linked above also determined: the very low evidence for the efficacy [of flossing], however, does not preclude the use of floss. For instance, in inter-dental situations that only allow for the penetration of a string of dental floss, floss is the best available tool.

When the U.S. government removed flossing from its 2015-2020 Dietary Guidelines, it did so because the strength of published studies regarding the effectiveness of flossing were admittedly weak, as the AP reports. The studies were generally short-term with a small number of participants due to the cost of running what constitutes high-quality clinical trials. 

Aside from cost, a clinical study comparing patients who did and did not floss would also mean exposing and even encouraging control group patients to worsen their oral health – and watch as it happens without intervention. In the research world, this is considered unethical. We don’t allow people to develop diseases as part of research, and that helps protect every patient in the United States.

According to dental experts including the DentaQuest Institute’s Dr. Brian Nový, Director of Practice Improvement, the lack of long-term clinical trials is also because there is already significant scientific evidence indicating how cavities form and how to prevent them.

Clinical trials don’t investigate how teeth decay, they examine new types of interventions. Oral health experts thus have relied on evidence extrapolated from shorter term studies as well as years of clinical experience and practice standards.

We know the easiest way to prevent cavities is to keep your mouth clean and minimize plaque, and that premise is incorporated into many clinical trials because it is accepted as standard oral hygiene practice. 

In one small study out of the University of North Carolina Chapel Hill, researchers randomized 119 adults who already had gum inflammation. After two weeks, they found the group that only brushed achieved a 35 percent reduction in bleeding sites between teeth, while the other groups who brushed and used floss achieved “dramatic reductions of about 67 percent” – almost double the improvement.

While small, this particular study correlates with the evidence dentists see every day among their patients – flossing creates a healthier mouth and less disease.

“The real problem is that the modern American diet is full of refined carbohydrates, which has changed the type of plaque that forms on our teeth,” Dr. Nový notes. “It is much stickier and more dangerous and everyone should want to keep it off their teeth if they want to avoid dental problems.” 

Tooth decay and gum disease can occur anywhere that food debris and plaque accumulate. The ideal spot is between teeth since it is difficult for the toothbrush bristles to remove or even attempt to remove any of the debris. That is why flossing or use of an inter-dental brush is recommended - to best remove the food debris that would remain between the gums and the teeth where a toothbrush cannot fit.

In response to the AP article, Dr. Robert Compton, Chief Dental Officer, DentaQuest and President, DentaQuest Institute, recalled an observation frequently used by health experts: the evidence to support the effectiveness of parachutes is weak because there has never been a double-blind randomized controlled trial to demonstrate effectiveness. That does not mean that parachutes are not effective. It just means no one has conducted expensive research that compared the effectiveness of somebody jumping with a parachute to a control group jumping without one.

“There's not enough money to conduct research for cancer cures and treatment for heart disease,” said Dr. Compton, adding, “if there isn’t funding for life-saving interventions, there will likely never be funding for the kind of research the AP reports would be required to sanction flossing as a recommended oral health habit.”

While flossing may be a habit that is difficult for people to connect with, it definitely helps remove food debris from hard-to-reach places. It is a low-cost, easy-to-use intervention that has the potential to improve the oral health of many, in particular those already suffering from dental disease.

This, among other reasons, is why oral health clinicians Tim Iafolla of the National Institutes of Health and Wayne Aldredge of the American Academy of Periodontology both told the AP they maintain flossing is important.

And Dr. Nový adds, “It comes down to personal hygiene. Do you want to have bad breath, and puffy bleeding gums, or do you want people to notice your smile because it’s healthy and attractive?  Flossing will improve many aspects of your life and no one has mentioned the research that shows male patients who don’t floss are more likely to experience erectile dysfunction...”