Dental Flossing: What Lies Beneath

August 17, 2016

All of a sudden, last month the entire world got highly strung over a report citing a lack of evidence that flossing was effective in preventing dental caries and gum disease. The need to floss is “unproven” said the report. Just as quickly, hundreds of journalists (and patients) concluded that public health officials and the dental profession had been scamming the public for the past 50 or so years.

In reacting to this “revelation,” it would be wise to remember the words of Mark Twain: “There are lies, damned lies and statistics.” He understood the power of using numbers and words to manipulate.

Here’s the background to the story. In 2012 AP reporter Jeff Donn began reviewing research on flossing and asked government health officials for supporting documentation. After some prodding, they responded with a letter indicating there was no research and that the practice was a “general public health recommendation.“

Thus motivated to continue, Donn claims to have looked at numerous studies on the subject and decided that they were based on a “weak amount of evidence”, were “unreliable” and/or “contained bias”. He also implies there is a financial incentive on the part of the American Dental Association to keep pushing the use of dental floss; since manufacturers are required to pay the ADA for both evaluation and their seal of approval.

Indeed Donn is correct on the lack of studies and weak evidence for flossing benefits. However, he has parsed numbers and words to deny the value and credibility of something that is obviously beneficial.

So, why are there a lack of studies, and why are the existing ones weak? Dr. James Wilson, past-president of the Florida Association of Periodontists explains:

They (the studies) were generally short term with a small number of participants due to the cost of running high-quality scientific studies. It makes sense that companies that sell dental floss and dental school universities are not going to pay hundreds of thousands, if not millions, of dollars for large-scale studies lasting many years to prove what most dentists and patients took as truth. Because long-term studies are so expensive, dentists have, for years, extrapolated from shorter-term ones that the buildup of plaque and increased level of inflammation that occurs when patients do not floss can, in a susceptible individual, lead to an increased amount of cavities and gum disease. These extrapolations are reinforced by what we see in our patients daily. Unfortunately, what many take from the article (written by Donn) is that a “lack of evidence” is somehow proof that flossing has no benefit. As in, no flossing is better than flossing if the evidence is not high quality. The bottom line is that a lack of high-quality evidence is not proof of ineffectiveness, especially when there has been little effort to obtain “high-quality” evidence.

There’s a similar example to what we’re discussing here. What if you were basing a decision to jump from a high altitude on whether or not there had been studies to show that doing so without a parachute is harmful to your body? If such a study existed it could conclude that because there had been no long-term clinical trials on the subject, there is a “weak amount of evidence” that parachutes prevented bodily trauma or death when jumping from a plane.

So, what should you, as a dental patient know about flossing? It’s simple: do it because even though the evidence supporting flossing may be weak . . . the evidence that it is not beneficial or harmful is weaker yet.” For some patients, other forms of interdental cleaners or irrigators may be more beneficial than floss. But, in light of its relative low cost, flossing has obvious potential benefits and should remain part of your dental hygiene practices.

There’s more to this story, including an examination of how the credibility of evidence-based studies is rated and accepted. What is the difference between “it is shown that…” and “there are signs that…”? In citing studies, the latter carries far more weight than the former, but that doesn’t mean the former isn’t also correct.

Apparently the reporter, after filing his report, was asked if would still continue to floss his teeth. His answer was “Yes.” That speaks volumes.

Sources: Dr. Scott Froum.

Mun Keat Looi:

Live Science – Flossing: What the experts say.