Ask a Dentist

Does Flossing Actually Prevent Cavities?

By Dr. Cynthia Brattesani

A dentist is stranded on a deserted island. Which would she rather have with her, a toothbrush or floss? 

Hands down, she’ll choose floss.


Why? You can use a lot of things to brush your teeth — as long as you’re gentle. But to clean in between your teeth? Only floss can do that job. And it does it well! 

Read on to see why flossing is a top cavity-prevention tool.

Get 100% Clean

Sometimes I ask my patients how much of their tooth surface they think remains unclean if they just brush and don’t floss. They’ll shyly tilt their heads and guess, “Ten percent?” 

Actually, the answer is 35 percent! That means if you only brush (for the full two minutes), you miss more than one-third of the surfaces of your teeth. 

Wow! That’s a lot of uncharted territory! So what does the rest of the job? Floss. 

To get 100 percent clean, you need to both brush and floss.

Prevent the Plaque Attack

Bacteria love to live on the slimy film on your teeth. This sticky, stinky stuff is called “plaque.” The bacteria in plaque produce acids that can eventually burn a hole in your teeth — a cavity. 

But if you floss, you remove that plaque. Remove the plaque and you remove the bacteria, stopping the cavity process altogether.

So yes, flossing prevents cavities.

Bye-Bye, Bits of Broccoli

Flossing also helps you to remove food particles that have gotten stuck between your teeth throughout the day — and can eventually lead to cavities. The higher the acidic or sugar count in those food particles, the more urgently you need to floss! 

Brushing definitely helps remove debris, but even the best brush bristles cannot pull particles from the tight, deep inner surfaces between teeth. You need floss to do the trick.

The Dental Lie Detector

We dentists can clearly see the difference between patients who floss regularly and patients who don’t, even if they start flossing in the days leading up to their appointment. People who floss regularly have taut gums, like an orange peel. 

People who don’t floss regularly have puffy, swollen gums that are full of blood and capillaries. Their gums also probably bleed when they floss — a sign of gum disease

Patients might bend the truth sometimes, but gums don’t lie.

Prescription for Prevention

Now that you know that flossing prevents cavities, what should you do? Ideally, you should floss at least twice a day: in the morning and in the evening, right before you go to bed. If you want to be super diligent, you could also floss after every time you eat, especially if you’ve had sugary treats or acidic foods like meat or dairy. 

This little string does so much not only for your oral health, but for your whole body’s health too. 

It’s simple, just floss.

About the Pro

A San Francisco native, Dr. Cynthia Brattesani, DDS, opened her practice in the City by the Bay in 2002. She has been the recipient of numerous awards, including the American Dental Association’s “Golden Apple” Award for Outstanding New Dentist Leader in 1996, and the U.S. Medal of Merit for outstanding public service for the City of San Francisco Earthquake. She writes for numerous professional publications and frequently lectures at conferences on technology and at San Francisco’s dental schools.

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