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Dentists Have Been Telling You to Floss for 100 Years — But the Science Never Actually Caught Up

By Myth Clarified Health
Dentists Have Been Telling You to Floss for 100 Years — But the Science Never Actually Caught Up

Every six months, the routine plays out in dental offices across America. You sit in that tilted chair, mouth full of metal instruments, while your hygienist asks the question you're dreading: "Have you been flossing regularly?"

Most of us lie. We mumble something about "trying to do better" while our bleeding gums betray the truth. We've been conditioned to feel guilty about our flossing habits since childhood, told repeatedly that this thin piece of string is the difference between healthy teeth and dental disaster.

But what if the guilt is misplaced? What if the practice that's been drilled into our heads for generations is based on surprisingly shaky ground?

The Investigation That Shook Dental Orthodoxy

In 2016, the Associated Press decided to do something unusual: they actually looked at the research behind flossing recommendations. What they found was startling.

Associated Press Photo: Associated Press, via logos-world.net

After reviewing dozens of studies conducted over the past decade, the AP concluded that the evidence supporting flossing was "weak" and "very unreliable." Most studies were short-term, involved small groups, and used methods that wouldn't meet today's standards for rigorous clinical trials.

Even more telling was what happened next. When the AP pressed the Department of Health and Human Services for evidence supporting their flossing guidelines, the agency couldn't provide it. Shortly after, flossing quietly disappeared from the federal dietary guidelines — a document that had recommended the practice for nearly four decades.

How Flossing Became Dental Gospel

So how did a practice with such thin evidence become universal dental wisdom?

The answer lies in the early 20th century, when dental hygiene was still a developing field. Flossing was first promoted in 1908 by a New Orleans dentist named Levi Spear Parmly, who recommended using silk thread to clean between teeth. The idea seemed logical: if brushing cleans the surfaces of teeth, surely something should clean the spaces between them.

Dental professionals embraced the concept long before anyone conducted proper studies to test it. By the time rigorous clinical research became the standard in medicine, flossing was already deeply embedded in dental practice. It became one of those "common sense" recommendations that seemed too obvious to question.

The American Dental Association has promoted flossing since 1908, but their recommendations have always been based more on theoretical benefits than hard evidence. Even today, the ADA acknowledges that "the majority of available studies fail to demonstrate that flossing is generally effective in plaque removal."

What the Research Actually Shows

This doesn't mean flossing is completely useless. Some studies have found modest benefits for certain people, particularly those with specific types of gum disease or large gaps between their teeth. The problem is that these benefits are far smaller and less consistent than most people believe.

A comprehensive review published in the Journal of Clinical Periodontology found that flossing might reduce gum inflammation slightly, but the effect was so small it might not be clinically meaningful. Another analysis found that flossing plus brushing was only marginally better than brushing alone for preventing cavities.

Interestingly, some research suggests that other tools might be more effective. Water flossers (like Waterpiks) and interdental brushes have shown more promising results in clinical trials than traditional string floss.

Why Dentists Still Recommend It

If the evidence is so weak, why do dentists continue to push flossing?

Part of it is institutional inertia. Dental schools still teach flossing as standard practice, and changing long-held professional recommendations requires overwhelming evidence — not just an absence of evidence.

There's also the "it can't hurt" mentality. Most dentists genuinely believe that flossing is better than doing nothing, even if they can't point to solid studies proving it. From their perspective, recommending flossing is a low-risk way to encourage patients to pay attention to their oral health.

Finally, there's the practical reality that proving flossing doesn't work would require expensive, long-term studies that no one wants to fund. It's easier to maintain the status quo than to definitively settle the question.

The Real Keys to Oral Health

While the flossing debate continues, researchers have identified factors that definitely do affect oral health:

The Takeaway

This doesn't mean you should throw away your dental floss tomorrow. If flossing makes you feel better about your oral hygiene routine, and your dentist sees improvements in your gum health, there's no harm in continuing.

But you can probably stop feeling guilty about those nights when you skip it. The decades of dental guilt might be based more on tradition than science. Sometimes the most surprising truth is that the experts don't always have the evidence to back up their certainty.

The next time your dentist asks about your flossing habits, you might want to ask them about the research behind their recommendation. You might be surprised by their answer.