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What causes mouth-breathing and why does it matter?

For children, one of the biggest causes of crowding of teeth is habitually breathing through the mouth rather than the nose.

We routinely screen for correct breathing and tongue position during our regular 6-monthly preventative examinations. For children, one of the biggest causes of crowding of teeth is habitually breathing through the mouth rather than the nose. For adults, the changes to the airway introduced by mouth-breathing give rise to snoring and sleep apnoea, which steals quality of life and can be life-threatening.

When children don’t breathe through the nose:

  • The tongue sits over the bottom teeth to keep the airway open, rather than sitting on the palate – hence the upper jaw doesn’t expand and grow properly. This causes a narrow, high palate and narrow dental arch with insufficient room to accommodate all the teeth, causing crowding. In turn this leads to crowding in the lower jaw too, as the growth of the upper jaw limits the growth of the lower jaw.

  • The face also grows in a vertical direction resulting in the long, narrow face and flattened checks of a mouth-breather. In studies done on identical twins where one has no nasal obstruction and the other is a chronic mouth breather their faces grow quite differently and no longer appear identical due to the mouth-breathing and change tongue position affecting the growth of the facial bones and dental arches.

What causes mouth-breathing in adults and children?

  • A chronically blocked nose due to allergies to foods, dust mites, pollens, and mucous-producing foods such as dairy

  • Chronic colds and sinus infections

  • Enlarged adenoids and tonsils

  • Polyps or swollen nasal lining

  • Deflected nasal septum  (congenital or from trauma, often needing surgery to correct it)

With mouth-breathing the breathing mechanics change and you get used to a higher volume of air (“over-breathing”). As a result you may feel you are not getting enough air when breathing through your nose. This can maintain the habit, even if the nose is not blocked. To switch to nasal breathing you may need to do breath retraining and oral muscle exercises to correct the tongue position and become more comfortable breathing through your nose.

A blocked airway and mouth-breathing can also contribute to snoring and sleep apnoea which can have serious health consequences in both children and adults.

Treatment and dental help for mouth-breathing

Mouth-breathing is best treated with an integrative approach depending on the primary issue:

  • Assessment of the airway (nasal blockage, tonsils and adenoids), working with an ENT specialist

  • Management of chronic allergies and infections

  • Retraining the breathing mechanics and muscles


  • We can expand the upper arch to allow the tongue to sit properly on the palate and correct the crowding teeth.

  • In some cases the lower jaw can also be brought forward to improve the airway, particularly if you suffer from sleep apnoea.

Two important things to know

Orthodontic treatment is more stable and successful if the patient converts to nose-breathing and the tongue posture is corrected.

For adults, where facial changes have occurred during childhood, the teeth can be straightened and upper jaw expanded but the appearance of the long face cannot be changed very much. Hence it is very important to recognise mouth-breathing in children and treat as early as possible, ideally before the age of 7 when most of the facial growth pattern is established.

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