First we were told that we should avoid food that is high in cholesterol; then we were told that such food doesn’t get into the blood so it doesn’t matter. We were told to avoid eating fat; now we are told that fat can be good for us. Sometimes coffee has been described as harmful and sometimes as helpful. Drinking alcohol used to be considered unhealthy; now we are told it’s good for the heart.
But there has always been an eternal healthcare verity: Be sure to floss.
Now that maxim too is under assault: Researchers are now saying that there is little to no evidence that flossing actually works.
Read the story excerpted and linked to after the jump, and then consider what I say afterwards, how this may reflect a bigger intellectual issue: the difference between valid deductive reasoning and empirical proof.
From Jeff Donn, Medical benefits of dental floss unproven (AP) | News OK:
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 their patients; the American Dental Association insists on its website 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 their 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 over 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 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 a dental magazine stated that any benefit would be so minute it might not be noticed by users.
Now “there is no evidence that flossing works” is not the same as saying that “flossing does not work.”
The case for flossing seems to be largely grounded in reason and common-sense. Flossing does remove stuff between the teeth. So this is presumably a good thing.
But this is deductive reasoning. It goes from the general principle that gunk on the teeth is bad to approving the technique for removing gunk from between the teeth.
Modern science, though, by the rules it assigns itself, is inductive. Empirical evidence, the result of controlled experimentation, is the only basis for argumentation that is allowed.
Sometimes empirical evidence is hard to come by. If only because some experiments have not been conducted yet.
There have apparently been no large-scale, long-term longitudinal studies, involving control groups, of the effect on teeth of regular flossing. Those need to be conducted and probably will be, now that the dental profession has been called out on the issue.
But those results will take time. In matters of medicine, empirical evidence does trump deductive “common sense.” But in the meantime, it is still reasonable to follow your deductions. And it is a logical deduction to keep flossing your teeth.