Flossing Back Molars

Why the back teeth get skipped

The molars at the very back sit where your fingers, lips and cheeks all get in the way. The floss has to travel farther, your view is poor, and the angle feels strange, so many people quietly stop at the premolars. Those teeth still have surfaces that touch their neighbors, which is where food and plaque collect.

Dental organizations commonly advise cleaning between all your teeth once a day, and that includes the ones you cannot easily see. Treat the back of the mouth as part of the routine rather than an optional extra.

Setting up your grip and your jaw

Start with a length of floss wrapped around the middle fingers, leaving a short working span between your thumb and forefinger. For the top back teeth, use your thumb and forefinger to steer. For the bottom, two forefingers often feel more natural.

Open your mouth only about halfway. It sounds backward, but a wide opening pulls the cheek tight against the molars and leaves less room. A slightly relaxed jaw gives your fingers more space to reach the last tooth.

Sliding the floss in without snapping it

Back molars often sit tightly against each other, so the floss may resist at the contact point. Use a slow, short sawing motion to ease it through, and stop pushing the moment it passes. Snapping it down can bruise the gum tissue between the teeth.

Once it is through, curve the floss against one tooth in a C shape and move it up and down along that surface. Then lift it, curve it the other way, and clean the neighboring tooth. Each gap has two sides, and both count.

Do not forget the far side of the last tooth

The very last molar has no neighbor behind it, so people assume there is nothing to clean. In fact, the rear surface of that tooth can trap plaque just like any other. Hook the floss around the back of it and wipe gently in a C shape.

This can feel awkward on the first few tries. A small mirror or good light helps you see what your hands are doing, and a slow pace matters more than speed.

When your hands will not reach

Some people have limited grip, small mouths or a strong gag reflex, and flossing the back teeth by hand just does not work well. That does not mean you should give up on cleaning there.

Several tools can fill in. Ask your dental team which suits your spaces and your gums, because the right size matters.

• A floss holder or pick with a handle
• A small interdental brush sized to the gap
• A water flosser, if your dentist agrees it suits you
• Floss threaders if you have bridges or braces

A note on supplements

Some readers wonder whether an oral probiotic could take the place of this effort. It cannot. As one example, the seller of ProDentim describes it as a chewable oral probiotic and lists three strains: Lactobacillus paracasei, Bifidobacterium lactis BL-04 and Lactobacillus reuteri. Those are the seller's claims, not verified here, and research on oral probiotics is still early and mixed.

Anyone who is pregnant or breastfeeding, takes medicines, has a medical condition or has allergies should ask a dentist, doctor or pharmacist before using any supplement.

Questions readers ask