Science corrects itself slowly.

In 1819 a dentist in New Orleans recommended flossing to dislodge irritating matter which he claimed was “the real source of disease”. 60 years later, floss became commercially available; 90 years after that flossing became common on the US government’s recommendation:

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.

Jeff Donn, Associated Press

In 2015, the Associated Press filed a Freedom of Information Act request asking for the evidence behind this recommendation – and suddenly the guideline was removed.

A 2011 Cochrane Review used a meta-analysis to compare brushing alone with brushing + flossing with brushing, and found:

  • “some evidence” that flossing reduces gingivitis
  • “weak, very unreliable evidence” that flossing reduces plaque
  • no studies looked at flossing’s effect on cavities

All these studies were short term but the alleged benefits are long term. There’s also a dog that didn’t bark: the industry pays for these studies so the existence of only limited evidence is very underwhelming.

The ADA also immediately put out a press release, in 2016, saying essentially that “absence of evidence is not evidence of absence”. But they went on to say that your dentist knows best and that various branches of government still recommend flossing. This is weak sauce – you can’t just say “well the evidence never mattered since we know what’s best”.

Overall, I think there’s too much we don’t know about the mouth’s microbiome. I floss a few times a week, but I’m not strongly convinced this is helpful. I’m mostly dismayed, again, by the shoddy state of our scientific-social infrastructure, that recommendations can be given moral force on so little evidence, and that institutions correct so slowly.