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 their evidence, and followed up with written requests under the Freedom of Information Act.
“The majority of available studies fail to demonstrate that flossing is generally effective in plaque removal,” said one review conducted last year. Another 2015 review cites “inconsistent/weak evidence” for flossing and a “lack of efficacy.”
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.” A commentary in adental magazine stated that any benefit would be so minute it might not be noticed by users.
Wayne Aldredge, president of the periodontists’ group, acknowledged the weak scientific evidence and the brief duration of many studies. In an interview at his private practice in New Jersey, 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.”
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 in the United States, according to publisher MarketSizeInfo.com — struggled to provide convincing evidence of their claims that floss reduces plaque or gingivitis. Yet the industry has paid for most studies and sometimes designed and conducted the research.
The ADA says it rigorously evaluates products and makes no profit from the program. However, floss companies themselves are allowed to design the studies.
“The funding can come from companies — no problem at all,” said dentist Marcelo W.B. Araujo, vice president of the ADA’s Science Institute, who joined the organization after serving as an executive for Johnson & Johnson. “The design can start from the company.”
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 applicant noted that dentists were widely recommending its use.
National Institutes of Health dentist Tim Iafolla acknowledged that if the highest standards of science were applied in keeping with the flossing reviews of the past decade, “then it would be appropriate to drop the floss guidelines.”
Regardless, he added, Americans should still floss.
“It’s low risk, low cost,” he said. “We know there’s a possibility that it works, so we feel comfortable telling people to go ahead and do it.”