Live Science: Should you floss before or after you brush your teeth?

Brushing your teeth is important for keeping your mouth clean, preventing cavities and avoiding noxious breath. Flossing is equally important for many of the same reasons — but should you floss before or after brushing?

The official stance of the American Dental Association (ADA) is that it doesn't matter. "Either way is acceptable as long as you do a thorough job," the ADA says.

"Flossing will get deeper into your gums than a toothbrush will alone, and it will get any food particles that are where the toothbrush can't reach, so really any order is effective," Dr. Naomi Lane, a board-certified pediatric dentist in Greensboro, North Carolina, told Live Science.

Still, there's an argument to be made for flossing first, before you brush, Dr. Chavala Harris, a dentist in Durham, North Carolina, told Live Science in an email.

"Flossing before brushing will allow removal of any food debris and plaque accumulation between the surfaces of teeth," Harris said. "Brushing after flossing will then remove all remaining food debris and plaque accumulation on the front and back surfaces of teeth." 

However, this is more of an educated guess than scientifically founded advice, Lane noted.

"There haven't been any studies that have looked at doing a different particular order, so we don't have any science proving that," Lane said. "But if you think of it, [flossing before brushing] makes sense, so that you're taking out the bigger food chunks first so that the toothpaste can reach and then the fluoride from your toothpaste can reach into those crevices a little bit easier."

Flossing is also good for the gums; it can help remove plaque from below the gumline and reduce gum soreness and the risk of gingivitis, or gum inflammation.

The ADA recommends brushing twice a day and flossing once per day. But is it better to floss in the morning or at night?

"Another one where it doesn't matter — it can be done at any time of day," Lane said. This is another situation where there isn't scientifically guided advice one way or the other. However,  in general, dentists recommend paying the most attention to your nightly oral hygiene routine, because there's a long length of time between that final brushing and waking up in the morning, she noted. 

"At nighttime, our salivary glands decrease their output, so your mouth is in a drier oral environment," Lane explained. "So if there are any food particles left on during the nighttime, they can have … a higher risk of turning into some decalcifications or potential cavities." "Decalcification" describes when minerals like calcium are lost, leaving white spots on teeth.

The most important thing is to build a routine you can stick with consistently, she said. "If it works better in one particular individual's schedule to do it in the middle of the day at lunchtime … then that is by all means effective." 

And while it might feel like your mouth is clean enough after brushing, you shouldn't skip the flossing. Doing so overlooks important areas that your toothbrush can't reach; that can cause cavities, which can lead to problems far beyond the mouth.

Tooth decay can, of course, cause local issues in the mouth, such as pain, trouble chewing and infections. But "the overall goal of preventing cavities is to ensure that bacteria byproducts of cavities do not travel through the bloodstream, negatively affecting other areas of the body," Harris said.

Flossing is thus important for the health of the gum tissues and "for the health of the entire body," not only teeth and gums, Lane said.