Cavities between teeth are among the hardest to prevent because the tight contact points where teeth touch create sheltered pockets that your toothbrush can’t reach. Bacteria thrive in these gaps, feeding on sugar and producing acid that eats into enamel. The good news: with the right cleaning tools and a few habit changes, you can dramatically cut your risk.
Why Cavities Form Between Teeth
Bacteria in your mouth build a sticky film called biofilm (plaque) on every tooth surface. Between teeth, this film is especially dangerous. The bacteria produce a protective matrix that acts like a shield, letting sugar diffuse in easily while blocking your saliva from neutralizing the acid inside. Your saliva is your mouth’s natural defense system, but it literally cannot reach the acids produced deep within this plaque layer.
When you eat or drink something sugary, the pH inside interdental plaque drops to around 4.3 within ten minutes. That’s acidic enough to dissolve enamel, which starts breaking down below a pH of about 5.5. What makes the spaces between teeth worse than smooth, exposed surfaces is that the acid lingers. Studies measuring plaque acidity between teeth after a simple sugar rinse show “immediate, pronounced, and long lasting acidification.” On a flat tooth surface, saliva can wash over and buffer the acid relatively quickly. In the crevice between two teeth, it stays trapped.
Over time, repeated acid attacks pull calcium and phosphate out of the enamel. This creates a white spot lesion, the earliest visible sign of a cavity. At this stage, the damage is still reversible. Once the decay punches through enamel and into the softer layer underneath, a filling becomes necessary.
Interdental Brushes vs. Floss
The single most effective thing you can do is physically remove plaque from between your teeth every day. Toothbrushing alone misses these surfaces entirely. The two main tools are string floss and interdental brushes (the small, bottle-brush-shaped picks you thread between teeth), and they are not equally effective.
Head-to-head clinical trials consistently favor interdental brushes. A 2018 analysis ranked them as the tool most likely to produce the best reduction in gum inflammation, while floss had a near-zero probability of ranking first. In a 12-week trial, interdental brushes produced significantly greater improvements in plaque removal and gum pocket depth compared to floss. Multiple studies from the 1990s through the 2000s confirm the pattern: final plaque scores between teeth tend to be markedly lower after using an interdental brush than after flossing.
The catch is that interdental brushes need enough space to fit. If your teeth are very tightly packed, a brush may not slide through without forcing. In those spots, floss is your best option. Many people benefit from using both: interdental brushes where they fit comfortably, and floss for tighter contacts. The key is using whichever tool you’ll actually use consistently. When people use floss or interdental brushes unsupervised at home, the improvements in gum inflammation end up similar (around 2.6 to 2.8%), likely because technique and consistency matter as much as the tool itself.
How to Use Each Tool Well
For floss, curve it into a C-shape against each tooth and slide it gently below the gumline, then scrape up and down rather than sawing back and forth. For interdental brushes, choose the largest size that fits snugly without forcing. Push straight through from one side, then pull back. You don’t need toothpaste on either tool. Do this once a day, ideally before brushing so the fluoride from your toothpaste can reach the freshly cleaned surfaces.
How Fluoride Protects These Surfaces
Fluoride works in two ways between teeth. It helps rebuild enamel that’s started to weaken (remineralization), and it makes the rebuilt enamel more acid-resistant than the original. For this to work, fluoride needs to actually contact those interproximal surfaces.
Brushing with fluoride toothpaste is the baseline. After you clean between your teeth, brush normally and let the toothpaste foam work its way into the gaps. Spit but don’t rinse with water afterward. This leaves a thin layer of fluoride on your teeth, including the freshly exposed surfaces between them.
Professional fluoride varnish, applied by a dentist, delivers a much higher concentration (about 22,600 parts per million of fluoride, compared to roughly 1,000 to 1,500 ppm in regular toothpaste). This is particularly useful if you already have early white spot lesions between teeth. The varnish sticks to enamel and releases fluoride over several hours, giving those vulnerable spots sustained exposure. For people at higher cavity risk, dentists may apply varnish every three to six months.
Silver diamine fluoride is another option for early lesions that haven’t yet broken through the enamel surface. In one clinical study, it arrested 100% of non-cavitated interproximal lesions, compared to 80% with standard fluoride. The tradeoff is that it stains decayed areas black, which matters less between back teeth where the stain isn’t visible.
What You Eat and Drink Matters
Every time sugar enters your mouth, bacteria between your teeth start producing acid within seconds, and the pH stays dangerously low for an extended period. The frequency of sugar exposure matters more than the total amount. Sipping a sugary coffee over two hours creates a near-continuous acid bath between your teeth. Drinking it in ten minutes gives your saliva a chance to recover.
Sticky and chewy foods are worse for interproximal cavities because they lodge in the gaps and feed bacteria for longer. Dried fruit, caramel, gummy candies, and even granola bars pack sugar directly into the spaces between teeth where it’s hardest to clear. If you eat these foods, cleaning between your teeth afterward (or at least rinsing with water) helps limit the damage.
Foods that stimulate saliva production help counteract acid. Cheese, nuts, and crunchy vegetables all increase saliva flow. Cheese in particular raises the pH in your mouth and delivers calcium and phosphate that support remineralization. Finishing a meal with a piece of cheese is a surprisingly effective habit for cavity prevention.
Can Mouthwash Reach Between Teeth?
Mouthwash can help, but it’s not a replacement for physically removing plaque. The biofilm between teeth has a structured matrix that many rinses simply can’t penetrate. Lab studies show that some common antiseptic ingredients, including hydrogen peroxide and sodium hypochlorite, kill bacteria on contact but fail to break through the biofilm’s protective structure. They reduce the bacteria floating in your mouth without touching the colonies embedded between your teeth.
Chlorhexidine-based rinses perform better, significantly reducing both the mass and thickness of biofilm in lab tests. Essential oil rinses (like those in Listerine-type products) also show antibiofilm activity. However, these rinses work best as a supplement after you’ve already disrupted the plaque mechanically. Think of it this way: flossing or brushing between teeth breaks up the biofilm’s protective shell, and a rinse afterward can help kill the bacteria you’ve exposed.
Dental Sealants for Adults
Most people associate sealants with children’s molars, but some dentists now apply resin coatings to adult teeth with deep grooves or particularly cavity-prone contacts. For interproximal surfaces specifically, sealants are less commonly used than on biting surfaces, but resin infiltration is a newer technique worth knowing about. A dentist applies a thin resin that soaks into early enamel lesions between teeth, essentially plugging the pores that acid has created. This can halt the progression of white spot lesions without drilling.
Putting It All Together
A realistic daily routine for preventing cavities between teeth looks like this: clean between your teeth once a day with interdental brushes (where they fit) or floss (where they don’t), then brush with fluoride toothpaste and spit without rinsing. Limit sugary snacks and drinks to mealtimes rather than grazing throughout the day. If you’re going to have something sweet, eat it in one sitting and follow it with water or cheese.
At dental visits, ask whether you have any early lesions between teeth showing up on X-rays. These are invisible to the naked eye and painless, but catching them at this stage means they can often be reversed with fluoride treatment or resin infiltration rather than a filling. If your dentist identifies you as high-risk for interproximal cavities, professional fluoride varnish or silver diamine fluoride can provide an extra layer of protection that home care alone can’t match.