'No firm evidence' over dental floss health benefits
There is little proof that using dental floss every day prevents gum disease and cavities, the US federal government has admitted.
The acknowledgement came after a US Freedom of Information request was made to the American health, human services and agriculture departments regarding evidence for the health benefits of flossing.
In response, the US federal government admitted to Associated Press reporters that the effectiveness of flossing has never been researched, as required by law for public health recommendations.
The US federal government has recommended flossing since 1979, first in a surgeon general's report and later in the Dietary Guidelines for Americans, which are issued every five years. The guidelines must be based on scientific evidence, under US law.
Last year, the Associated Press (AP) asked the departments of Health and Human Services and Agriculture for their evidence, and followed up with written requests under the US 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.
Reporters looked at the most rigorous research conducted over the past decade, focusing on 25 studies which generally compared the use of a toothbrush with the combination of toothbrushes and floss.
The research found that evidence for flossing is "weak, very unreliable", of "very low" quality, and carries "a moderate to large potential for bias".
One review conducted last year said: "The majority of available studies fail to demonstrate that flossing is generally effective in plaque removal."
Another 2015 review cites "inconsistent/weak evidence" for flossing and a "lack of efficacy".
The two leading professional groups - the American Dental Association (ADA) and the American Academy of Periodontology, for specialists in gum disease and implants - cited other studies as proof of their claims that flossing prevents the build-up of plaque, gingivitis and tooth decay.
However, most of these studies used outdated methods or tested few people. Some tests 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.
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 which measured bacteria and did not even consider gum disease.
The ADA later said flossing "removes plaque" and "is proven to help remove" debris from between teeth.
Even companies with a big market share of the worldwide £1.5 billion dental floss industry struggled to provide convincing evidence of their claims that floss reduces plaque or gingivitis - despite the industry having paid for most studies and sometimes even designing and conducting the research.
Procter & Gamble, which claims that its floss fights plaque and gingivitis, pointed to a two-week study, which was discounted as irrelevant in the 2011 research review.
Johnson & Johnson spokesman Marc Boston said floss helps remove plaque. When reporters sent him a list of contradicting studies, he declined to comment.
The floss-making companies partner with the ADA through its Seal of Acceptance programme. The ADA promotes the seal to companies as something that "directly affects the purchase decisions of consumers". Each manufacturer is charged 14,500 dollars (£10,970) for this evaluation. If it approves the product, the ADA then charges an additional annual fee of 3,500 dollars (£2,648).
The ADA said it rigorously evaluates products and makes no profit from the programme. However, floss companies themselves are allowed to design the studies.