Among the many things that are drilled into us as children, one of the most crucial of all is the importance and methodology of oral hygiene: brush your teeth at least twice a day, use floss and maybe even mouthwash in order to combat cavities, gum disease and other mouth-based issues.

There is just one problem, however: dental floss might not even work.

A Brief History Of Floss

Starting in 1979, the U.S. federal government has recommended daily flossing in order to get rid of plaque — a biofilm of bacteria build-up on the teeth that might cause cavities and gum disease if not treated appropriately. Since then, the flossing recommendation has appeared in the Dietary Guidelines for Americans (issued every five years).

Like other things that appear in these guidelines, the importance of flossing needs to be accompanied by supporting evidence. However, a recent investigation by the Associated Press has revealed that the purported benefits of dental floss are largely unproven. In fact, after finding that flossing had been dropped from its dietary guidelines this year, the government acknowledged "the effectiveness of flossing had never been researched, as required."

The Investigation

During the investigation, the AP looked at the best research on the subject within the past decade, focusing on 25 studies in particular. After looking at those studies, it concluded that the evidence for flossing is "weak, very unreliable," of "very low" quality and "carries "a moderate to large potential for bias."

Of course, it's entirely possible that people in the dental industry have a secret they aren't sharing that could shine light on the matter. With that in mind, the AP went to two leading professional groups — the American Dental Association and the American Academy of Periodontology, for specialists in gum disease and implants — to learn what they had to say on the matter.

Both groups cited other studies as proof of the benefits of flossing, but there was one issue with those studies: the majority of them had fatal flaws that should have invalidated them from the get-go, ranging from small sample sizes to brief testing periods. In fact, one such study tested a mere 25 people after only a single use of floss.

Similarly, manufacturers of dental floss were unable to come up with convincing evidence (odd, considering that they fund much of this research). For example, Johnson & Johnson alleged that floss helps remove plaque, but declined to provide further comment when it was presented with a list of contradicting studies. Similarly, Procter & Gamble claimed that flossing fights plaque and gingivitis, but that evidence was rooted in a two-week study that had already been deemed irrelevant in 2011.

For what it's worth, at least one person, Wayne Aldredge, president of the periodontists' group, admitted there is weak scientific evidence supporting flossing, but he still encourages 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."

What This All Means

In the end, it's hard to determine what the results of this study mean for the future of dental floss. As things stand, the global market for dental floss is booming, and is expected to reach almost $2 billion next year (half of which is situated in the United States).

However, at the very least, there is no reason not to floss. As one dentists says: "It's low risk, low cost ... We know there's a possibility that it works, so we feel comfortable telling people to go ahead and do it."

The results by no means suggest that flossing isn't beneficial, just that the science suggesting that it is is quite lacking.