Interdental Brushes: How to Choose a Size and Use Them

Interdental brushes are small brushes made to fit between your teeth. They clean the sides of each tooth and the gumline inside the gaps a toothbrush misses. They are often easier to use than string floss, especially in wider gaps, and where a brush fits the gap, the research comparing cleaning tools tends to favor it.

This guide covers what the evidence says, how sizing works, a step-by-step method, braces and dental work, and when bleeding needs attention. It is general information. Your dentist or hygienist can size your gaps and check your technique in a few minutes.

What an interdental brush is

Most interdental brushes have nylon bristles twisted into a thin wire, set in a small handle. Rubber and silicone versions also exist. Heads come straight, or angled (often sold as L-shaped) to reach the back teeth. Some are sold as single-use and others are made to be rinsed and reused until they wear, so check the packet.

The Oral Health Foundation says interdental brushes are often easier to use than floss, especially where the spaces between teeth are larger. The NHS says you can use them instead of flossing, especially if you have gaps between your teeth, and that the brush should fit snugly.

Are interdental brushes better than floss?

Where they fit, the evidence leans their way, but it is not strong. Here is what the main reviews found, with their limits.

The practical rule that follows is simple: use a brush in every gap it fits without force, and use floss for contacts too tight for any brush. Water flossers ranked close behind brushes in the 2018 analysis, although the Cochrane review found their evidence limited and inconsistent. If you are weighing one up, our guides to water flossers versus string floss and how to use a water flosser cover the trade-offs.

Interdental brush sizes

A brush size describes the gap it fits. The international standard for manual interdental brushes, ISO 16409, sizes them by passage hole diameter: the smallest hole the brush can pass through without its wire bending. Packets usually print it as a size number, a diameter in millimeters, or both.

These bands come from a public summary of the standard, and editions differ at the smallest and largest sizes. The standard does not set colors or wire thickness, so a pink brush from one brand may not match a pink brush from another. Go by the size on the packet when you reorder.

To find your sizes:

• Ask your dentist or hygienist to show you the right size for each gap. The Oral Health Foundation recommends this, and it saves buying packs that do not fit.
• Start with the smallest size and work up. The brush should pass through without force and feel snug.
• If the wire bends or the bristles splay as you push, try a smaller size.
• If a brush slides through without touching the teeth at all, that gap may need a larger size.
• Expect to need more than one size, because gaps vary around the mouth. A mixed pack makes it easier to test before you buy refills.
• Where no brush passes without force, use floss for that gap instead.

How to use an interdental brush

This method follows the Oral Health Foundation and NHS guidance. If your dental team has shown you a different technique for your mouth, follow theirs.

1. Pick a time once a day. The Oral Health Foundation suggests cleaning between your teeth before brushing, so fluoride toothpaste can then reach between the teeth.
2. Choose the size for the gap. Use the sizes you have tested or been given for each area.
3. Hold the brush gently between your thumb and forefinger, close to the head.
4. Guide it into the gap at the gumline. Ease it in without forcing it. An angled head can make the back gaps easier to reach.
5. Move it gently in and out a few times, then take it out and move to the next gap. Work in the same order every time, such as the top teeth from left to right and then the bottom, so you do not miss a space.
6. Rinse the brush as you go to clear debris, then rinse it well at the end and let it dry.
7. Replace it when it wears. Flattened or splayed bristles, or a bent or kinked wire, mean it is time for a new one.

Mistakes that cause most problems:

• Forcing a brush that is too big. It hurts, it can damage the gum, and it bends the wire.
• Pressing hard or scrubbing. Gentle movement cleans the gap.
• Sharing brushes, even within a household.
• Reaching for a wooden toothpick instead. The NHS advises against using toothpicks to remove trapped food, because they can damage the gums.
• Stopping because the gums bleed in the first few days. See the bleeding section below for what is common and what needs a dentist.

Interdental brushes for braces, bridges and implants

Braces add brackets and a wire that trap food and plaque. An interdental brush can clean between the wire and the teeth and around the base of each bracket, which string floss reaches only with a threader or special floss. The space under the wire is not the same as the gap between teeth, so ask your orthodontist which size and shape to use there. Our guide to water flossers for braces explains how brushes, threaders and a water flosser fit into one routine.

Bridges, implants and gum recession change the shape of the spaces you are cleaning. Your dental team may recommend a particular brush type or size for those areas. Do not force a brush under a bridge or around an implant, and follow any aftercare instructions from recent dental work before a general guide like this one.

Bleeding and soreness: when to get advice

The Oral Health Foundation says mild bleeding is common when you start cleaning between your teeth, and that it usually improves with regular cleaning. If it continues, speak to your dental team. Forcing a brush that is too big can also injure the gum, so check the size for any gap that bleeds or hurts.

The NHS gum disease guidance says to see a dentist if your gums bleed when you brush or eat hard foods, or are painful and swollen. It advises asking for an urgent appointment for very sore and swollen gums or teeth that are becoming loose. Our bleeding gums guide lists what to tell the dental practice and when to seek urgent care.

How often to use them and when to replace them

Once a day is the common advice. The Oral Health Foundation says to use interdental brushes once a day, the NHS recommends cleaning between your teeth every day with floss or interdental brushes, and the 2015 European consensus recommends once-daily cleaning between teeth for people with gum inflammation.

How long a brush lasts depends on the brand and on how tight your gaps are. Follow the packet, rinse the brush after each use, and replace it when the bristles flatten or splay or the wire bends. Keep your own brushes separate from anyone else’s.

A store example, clearly labeled

Two interdental brush listings in our owner’s store are relevant here. We have not tested either product, and FlosserGuide and Oral Cove share an owner.

• The Threadpik L-shaped and 7-shaped interdental brushes are listed with stainless-steel wire, L-shaped and 7-shaped heads, adult use, and color-coded wire diameters from 0.6 mm (pink) to 1.2 to 1.5 mm (orange). The listing gives these as wire diameters, which is a different measure from the ISO passage hole size above, and it has a single purchase option. Confirm which sizes the pack contains before ordering.
• The Braceglide orthodontic interdental brushes are listed as disposable manual brushes for cleaning around orthodontic braces, 60 per box, for adults. The listing does not state a brush size, so ask your orthodontist which size you need before buying.

Sources and limits

• Worthington HV and colleagues, home use of interdental cleaning devices, in addition to toothbrushing, Cochrane Database of Systematic Reviews, 2019.
• Kotsakis GA and colleagues, a network meta-analysis of interproximal oral hygiene methods, Journal of Periodontology, 2018.
• Chapple ILC and colleagues, primary prevention of periodontitis: European Workshop on Periodontology consensus, Journal of Clinical Periodontology, 2015.
• Slot DE and colleagues, the efficacy of interdental brushes: a systematic review, International Journal of Dental Hygiene, 2008.
• Oral Health Foundation: cleaning between your teeth, technique and sizing advice.
• NHS: how to keep your teeth clean and NHS: gum disease.
• ADA MouthHealthy: flossing, tools for cleaning between teeth.
• Wikipedia: toothbrush, interdental brushes, public summary of ISO 16409 sizes. The standard itself is sold by ISO.
• Oral Cove product listings, checked September 27, 2026.

This guide summarizes published guidance and research. We have not run trials or tested brushes ourselves, and nothing here is a diagnosis or personal dental advice. Size bands and product details can change, so check the packet and ask your dental team about your own gaps.