What Interdental Cleaning Actually Does. And Why Floss Isn't the Only Option.

Aug 31

3 min read

By Dr John Barclay | DRJB Smile Clinic, Ruabon, North Wales

A toothbrush cleans three of the five surfaces of each tooth. The two surfaces that face the adjacent teeth — the contact points — are inaccessible to any toothbrush, manual or electric, however well it's used. If you're only brushing, forty percent of each tooth's surface is being left unclean twice a day.

Interdental cleaning is the only way to reach those surfaces. Here's what it does, why it matters, and why the method matters less than most people think.

What Happens in the Spaces Between Teeth

Plaque accumulates wherever it isn't disrupted. Between teeth — in the embrasure spaces, along the contact point, below the gum margin — it accumulates undisturbed unless something is actively put into that space to remove it.

Plaque left between teeth for long enough calcifies into calculus. Calculus cannot be removed by brushing or interdental cleaning at home — it requires professional instrumentation. Calculus at and below the gum margin is one of the primary drivers of periodontal disease.

The gum disease and decay that begin between teeth are often entirely invisible until they've progressed significantly. Interproximal decay is consistently detected later than buccal or lingual decay because patients can't see it and don't clean it. The first sign is often sensitivity, or a filling at a check-up when the patient thought everything was fine.

Floss: The Right Tool for Some Mouths

Floss is effective where the contact point is tight — where teeth are closely approximated and there is minimal space between them. In that situation, floss is the right tool because it can pass through the contact and clean the proximal surfaces below it.

Floss is the wrong tool, or an insufficient tool, where there is any space between the teeth. If an interdental brush fits in the space, it will clean the surface more effectively than floss because it contacts more of the proximal surface and the adjacent root. Using floss in a space that can accommodate an interdental brush is using the less effective tool by habit.

Interdental Brushes: Better for Most Adults

For the majority of adult patients — particularly those with any history of gum disease, recession, or tooth movement — interdental brushes are more effective than floss. They come in a range of sizes from very fine to quite wide, and the right size for each space is the one that fits snugly without forcing.

The sizing matters. An interdental brush that's too small slides through without contacting the root surface properly. One that's too large damages the papilla. Getting the right size — which varies between different spaces in the same mouth — is worth spending a few minutes on at a hygiene appointment.

Water Flossers: A Useful Adjunct

Water flossers are not a replacement for mechanical interdental cleaning but are a useful adjunct, particularly for patients who struggle with dexterity, have fixed orthodontic appliances, or are managing gum disease.

The evidence for water flossers as a standalone interdental cleaning tool is less strong than for interdental brushes. The evidence for them improving outcomes when used alongside brushing and interdental brushing is more positive. They're worth recommending to patients who will actually use them, rather than the theoretically superior option that stays in the bathroom cabinet.

The Honest Summary

The best interdental cleaning tool is the one you'll use consistently. A method you find manageable and sustainable will always outperform the technically superior method you use three times a week.

That said, if you're currently using floss in spaces that could accommodate an interdental brush — ask at your next hygiene appointment which size is right for you. It's likely you'll clean more effectively with less effort.

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References & Further Reading

1. Chapple ILC et al. Primary prevention of periodontitis: managing gingivitis. Journal of Clinical Periodontology, 2015. → Supports interdental cleaning as essential for gingivitis prevention and management.

2. Slot DE et al. The efficacy of interdental brushes on plaque and parameters of periodontal inflammation. International Journal of Dental Hygiene, 2008. → Primary evidence base for interdental brush efficacy compared to floss.

3. Worthington HV et al. Home use of interdental cleaning devices. Cochrane Database of Systematic Reviews, 2019. → Cochrane-level review of interdental cleaning device efficacy.

4. Goyal CR et al. Evaluation of the plaque removal efficacy of a water flosser compared to string floss. Journal of Clinical Dentistry, 2013. → Supports water flosser use as an adjunct to mechanical cleaning.

5. Public Health England / OHID. Delivering Better Oral Health. 4th ed. OHID, 2021. → Underpins the interdental cleaning recommendations in clinical practice.