Though the government, dental organizations and manufacturers recommend daily floss of teeth, the data from available studies fail to demonstrate that flossing is generally effective in plaque removal," said one review conducted last year. Another 2,015 review cites "inconsistent/weak evidence" for flossing and a "lack of efficacy."
One 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." The two leading professional groups - the American Dental Association and the American Academy of Periodontology - cited other studies as proof of their claims that flossing prevents build up of gunk known as plaque, early gum inflammation called gingivitis, and tooth decay. However, most of these studies used outdated methods or tested few people. Some lasted only two weeks, far too brief for a cavity or dental disease to develop. One tested 25 people after only a single use of floss. Such research, like the reviewed studies, focused on warning signs like bleeding and inflammation, barely dealing with gum disease or cavities.
Wayne Aldredge, president of the periodontists' group, acknowledged the weak scientific evidence and the brief duration of many studies. In an interview, he said that the impact of floss might be clearer if researchers focused on patients at the highest risk of gum disease, such as diabetics and smokers.
Still, he urges his patients to floss to help avoid gum disease. "It's like building a house and not painting two sides of it," he said. "Ultimately those two sides are going to rot away quicker." Aldredge also said many people use floss incorrectly, moving it in a sawing motion instead of up and down the sides of the teeth. Pressed about the origins of his organization's endorsement of flossing, he said it may simply have "taken the ADA's lead."
When the ADA was asked for proof of its claim that flossing helps prevent early gum disease and cavities, the group cited the 2011 review and a 2008 two-week study that measured bacteria and did not even consider gum disease.
In a later statement, the ADA said flossing "removes plaque" and "is proven to help remove" debris from between teeth. A video on its website proclaims that flossing "helps prevent gum disease." When pressed, Matthew J. Messina, a practising dentist and spokesman for the dental association, acknowledged weak evidence, but he blamed research participants who didn't floss correctly.
Even companies with a big market share of the flossing business struggled to provide convincing evidence of their claims that floss reduces plaque or gingivitis.
