HOLMDEL, N.J. — It’s one of the most universal recommendations in all of public health: Floss daily to prevent gum disease and cavities … except there’s little proof that flossing works.
Still, the federal government, dental organizations and manufacturers of floss have pushed the practice for decades. Dentists provide samples to patients. The American Dental Association insists that “flossing is an essential part of taking care of your teeth and gums.”
The federal government has recommended flossing since 1979, first in a surgeon general’s report and later in the Dietary Guidelines for Americans issued every five years. The guidelines must be based on scientific evidence under the law.
Last year, the Associated Press asked the departments of Health and Human Services and Agriculture for the evidence and followed up with written requests under the Freedom of Information Act.
When the federal government issued its latest dietary guidelines this year, the flossing recommendation had been removed, without notice. In a letter to the AP, the government acknowledged the effectiveness of flossing had never been researched, as required.
The AP looked at the most rigorous research conducted in the past decade, focusing on 25 studies that generally compared the use of a toothbrush with the combination of toothbrushes and floss. The findings? The evidence for flossing is “weak, very unreliable,” of “very low” quality and carries “a moderate to large potential for bias.”
“The majority of available studies fail to demonstrate that flossing is generally effective in plaque removal,” said one review last year. Another 2015 review cites “inconsistent/weak evidence” for flossing and a “lack of efficacy.”
One study review in 2011 credited floss with a slight reduction in gum inflammation, which can sometimes develop over time into 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, for specialists in gum disease and implants — cited other studies as proof of their claims that flossing prevents buildup of plaque, gingivitis and tooth decay. However, most of these studies used outdated methods or tested few people. Some studies 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 such as bleeding and inflammation, and barely dealt with gum disease or cavities.
Wayne Aldredge, president of the periodontists group, acknowledged the weak scientific evidence and the brief duration of many studies. He said that the impact of floss might be clearer if researchers focused on patients such those who smoke or those with diabetes, who are at the highest risk of gum disease. 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. Ultimately, those two sides are going to rot away quicker,” he said of the spaces between teeth.
Aldredge also said many people incorrectly use floss, moving it in a sawing motion instead of up and down the sides of the teeth.
Pressed about the origins of his organization’s flossing endorsement, he said it might 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 but did not consider gum disease.
In a later statement to the AP, the ADA said flossing “removes plaque” and “is proven to help remove” debris from between teeth. A video on its website states that flossing “helps prevent gum disease.” When pressed, Matthew Messina, a practicing dentist and an ADA spokesman, acknowledged weak evidence but blamed research participants who didn’t floss correctly.
Even companies with a big market share of the flossing business — by next year, the global market is predicted to reach almost $2 billion, with half of its sales in the U.S., according to MarketSizeInfo.com — struggled to provide convincing evidence of their claims that floss reduces plaque or gingivitis. The industry paid for most of the studies, and sometimes designed and conducted the research.
The floss-making companies partner with the ADA through its Seal of Acceptance program. The ADA promotes the seal as something that “directly affects the purchase decisions of consumers.” Each manufacturer is charged $14,500 for the evaluation. If the ADA approves the product, it charges an additional annual fee of $3,500. The ADA said it evaluates products and makes no profit from the program, and floss companies are allowed to design the studies.
When flossing first gained acceptance, no proof was required of remedies. Dentist Levi Spear Parmly is credited with inventing floss in the early 19th century. By the time the first floss patent was issued in 1874, the application noted that dentists were widely recommending its use.
The ADA has been promoting floss since 1908.
“They just looked into what they did every day in their clinical practice,” said dentist Marcelo W.B. Araujo, vice president of the ADA’s Science Institute and former Johnson & Johnsonexecutive.
Count dentist Damien Walmsley, scientific adviser to the British Dental Association, among the skeptics.
Floss occasionally can cause harm. Careless flossing can damage gums, teeth and dental work. Floss can dislodge bacteria that invade the bloodstream and cause infections, especially in people with weak immunity, according to the medical literature.
National Institutes of Health dentist Tim Iafolla said that if high standards of science were applied in the floss reviews of the past decade, “then it would be appropriate to drop the floss guidelines.”
Regardless, he added, Americans should still floss.
