An interdental brush is a small, narrow brush designed to clean the gaps between your teeth where a regular toothbrush can’t reach. It looks like a tiny bottle brush: a thin wire core surrounded by small bristles, attached to a short handle. You insert it gently into the space between two teeth and move it back and forth to sweep out food debris and plaque. For many people, interdental brushes are easier to use and more effective than traditional floss, especially in wider gaps or around dental work like braces and bridges.
How Interdental Brushes Work
The brush works by physically scrubbing the sides of adjacent teeth and the gum line in between. The bristles fan out to fill the space, making contact with both tooth surfaces at once. This is different from floss, which only contacts one surface at a time and requires more manual dexterity to wrap and slide correctly.
You use them once a day, ideally before brushing your teeth. Gently slide the brush into the gap between two teeth without forcing it. If it doesn’t fit, go down a size. If it slides through without any resistance, go up a size. The brush head should fit snugly but comfortably. Move it back and forth a few times, then pull it out and move to the next gap. Most people need just a minute or two to clean all their interdental spaces.
Why They’re So Effective at Reducing Gum Bleeding
The clinical evidence for interdental brushes is strong, particularly for gum health. In a 2024 multicenter study of people with early gum inflammation, regular interdental brush users saw their bleeding scores drop from a median of 50% at the start to about 11.5% after three months. That’s a dramatic improvement. Occasional users barely budged by comparison, seeing only an 8 percentage point reduction over the same period.
Consistency made a measurable difference. People who used their interdental brushes regularly had bleeding scores 15 to 16 percentage points lower than occasional users at every follow-up point. Even after just one month of daily use, regular users cut their bleeding scores by roughly 38 percentage points, while infrequent users dropped only about 4 points. The takeaway is straightforward: these brushes work well, but only if you actually use them every day.
Choosing the Right Size
Interdental brushes come in standardized sizes ranging from 0 (the smallest) to 8 (the largest), based on an international classification system. The sizes correspond to the diameter of the gap they can pass through:
- Size 0: 0.6 mm or smaller, for very tight spaces
- Size 1: 0.7 to 0.8 mm
- Size 2: 0.9 to 1.0 mm
- Size 3: 1.1 to 1.2 mm
- Size 4: 1.3 to 1.5 mm
- Size 5: 1.6 to 1.8 mm
- Size 6: 1.9 to 2.3 mm
- Size 7: 2.4 to 2.8 mm
- Size 8: 2.9 mm and larger
Most people need more than one size because the gaps between teeth vary throughout the mouth. The spaces between your front teeth are typically narrower than those between your molars. A dentist or hygienist can measure your gaps and recommend the right sizes, but you can also figure it out at home by starting with a smaller brush and working up until you feel gentle resistance. The bristles should touch both teeth as the brush passes through. If the brush slides in with no friction at all, it’s too small to clean effectively.
What About Very Tight Spaces?
Some people have teeth so close together that even the smallest interdental brush won’t fit. In those cases, traditional floss or thin interdental picks remain the better option for those specific gaps. You can still use interdental brushes wherever they fit and floss the rest. There’s no rule that says you have to use only one tool.
Avoiding Gum Damage
The most common mistake is using a brush that’s too large for the gap. Forcing an oversized brush between your teeth can injure the gum tissue and, over time, wear down the hard surfaces of your teeth. This can lead to sensitivity and gum recession.
The other risk comes from the wire core. On straight interdental brushes, you can bend the neck slightly to reach back teeth more easily, but you need to make sure the bristles are doing the cleaning, not the bare wire. If the wire scrapes against the tooth surface, it can cause abrasion. Replace a brush immediately if the wire becomes exposed or bent out of shape.
Some mild bleeding when you first start using interdental brushes is normal and usually stops within a week or two as your gums get healthier. Persistent bleeding or pain means you should check your brush size or technique.
How Long They Last
With daily use, a single interdental brush typically lasts about one to two weeks. Replace it sooner if the bristles look frayed or bent, or if the wire core is damaged. A worn-out brush cleans poorly and is more likely to scratch your gums. Rinse the brush under water after each use and let it air dry.
Interdental Brushes vs. Floss
Both tools accomplish the same basic goal: removing plaque from between teeth. The ADA recommends cleaning between your teeth once daily with floss or another interdental cleaner, placing both options on equal footing. In practice, interdental brushes have some advantages. They’re faster to use, require less coordination, and tend to be easier for people with arthritis, braces, implants, or wide gaps between teeth. Many people who struggle to maintain a flossing habit find interdental brushes more sustainable simply because they’re less fiddly.
Floss still has the edge for very tight contacts where no brush can physically fit. For most adults, though, a combination of both tools, or interdental brushes alone if they fit all your gaps, provides thorough cleaning between the teeth.