Mouth Breathing, Nasal Breathing and Orthodontics

How does mouth breathing affect the jaw and teeth?

Nasal breathing keeps the tongue resting against the palate, and this steady tongue pressure shapes the upper arch from the inside as a child grows. Mouth breathing removes that supporting force, so the cheek muscles push inward unopposed. Over time this produces a narrower upper arch, a higher vaulted palate, an increased tendency towards an open bite because the tongue drops and lets the jaws separate, flared or spaced upper front teeth from the loss of lip seal and pressure, and a downward-rotating "long face" growth pattern caused by the open mouth posture itself.

How does nasal breathing differ from mouth breathing?

Nasal breathing is the normal pattern. With the lips sealed and the tongue resting on the palate, the tongue pushes outward from inside while the lips and cheeks balance it from outside, and the upper arch develops to its full width. During mouth breathing the tongue drops to the floor of the mouth and the lips part, so both forces are lost. Through the growth years this altered balance lets the upper arch develop narrower and higher, and the lower arch often follows the restricted upper arch.

Why is mouth breathing linked to open bite?

A mouth breather's tongue often sits low and forward, and a forward tongue thrust can stop the front teeth erupting fully so they do not meet when the back teeth are together. The open mouth posture also lets the jaws rotate downward and backward, which opens the bite at the front. An open bite linked to breathing is harder to hold after treatment, because the bite can reopen if the tongue posture and breathing pattern are not also addressed.

What is adenoid facies or long face syndrome?

Children who breathe through their mouth for years can develop a recognisable facial pattern, often called adenoid facies or long face syndrome. Features include a longer lower third of the face, narrow nostrils, parted lips at rest with a short-looking upper lip, dark circles under the eyes and a chin that sits further back. Some of these changes can be partly modified in early adolescence with nasal treatment and orthodontics, but established skeletal changes in adults respond less to orthodontics alone.

What causes mouth breathing in children?

The most common cause in children is enlarged adenoids and tonsils that physically obstruct the nasal airway. Allergic rhinitis causing a chronically blocked nose is also very common, alongside a deviated nasal septum or nasal polyps in some children. In a smaller number of cases, mouth breathing persists as a habitual or learned pattern even after the original nasal obstruction has been treated and resolved, which is why breathing pattern should be reassessed after any medical treatment.

What signs should a parent look out for?

Parents typically notice an open mouth at rest, dry or chapped lips from constant air exposure, snoring or noisy breathing during sleep, poor sleep quality with daytime tiredness or irritability, dental crowding developing earlier than expected, a narrow V-shaped upper arch visible on inspection, and dark circles under the eyes linked to disrupted sleep. Any combination of these signs is a reasonable trigger to seek an assessment rather than waiting to see if the pattern resolves on its own.

Does mouth breathing affect orthodontic treatment outcomes?

Yes. Active mouth breathing can limit how stable orthodontic results are over time. If the upper arch is expanded but the airway problem and the breathing pattern are not addressed, the arch is more likely to relapse afterwards because the same muscle imbalance that narrowed it in the first place is still acting on the teeth. Orthodontists commonly include an airway assessment in their records, using CBCT imaging where clinically relevant, because palate expansion itself can improve airway dimensions in some patients — making it both a dental and a breathing intervention. Because the palate forms the floor of the nose, widening it can increase nasal airway volume and reduce resistance to airflow, which helps most when a narrow nasal passage, rather than enlarged adenoids, is the cause.

How do dentists spot mouth breathing?

At examination, a narrow high-arched palate with crowded upper front teeth is the most consistent finding. Dry, reddened gums around the upper front teeth, a reduced overbite or open bite not explained by thumb sucking, and lips that rest apart are further clues. If mouth breathing is suspected, the dentist or orthodontist will ask about snoring, a blocked nose, daytime tiredness and sleep quality, and may suggest a GP or ENT referral to check adenoid and tonsil size.

When should a mouth-breathing child be assessed?

A child who consistently breathes through their mouth at rest should be assessed rather than monitored indefinitely. The recommended pathway starts with a GP referral to address adenoids, tonsils, or allergies and treat any physical obstruction first, followed by an orthodontic assessment of arch width, bite, and IOTN score. Age seven to ten is the prime window for early intervention, because palate expansion is most effective while a child is still growing and before the mid-palatal suture fuses.

What are the treatment options for mouth breathing?

Treatment depends on the underlying cause and how much dental effect has already occurred. Palate expansion — either rapid maxillary expansion or a removable expansion plate — widens the upper arch and can improve airway space at the same time. Myofunctional therapy uses lip and tongue exercises to retrain correct muscle function and resting posture. Medical treatment such as adenotonsillectomy or allergy management addresses the root cause of the obstruction. Functional appliances for jaw repositioning are used in selected cases where the jaw relationship itself has been affected by the long-standing breathing pattern.

Can orthodontics cure mouth breathing?

No. Orthodontic treatment corrects the dental and some of the skeletal effects of mouth breathing, such as narrowing, crowding and open bite, but it does not cure the breathing habit itself. If a blocked nasal airway, habitual open mouth posture or low tongue position is left untreated, results are less stable and relapse is more likely. Treatment is usually part of a wider plan that may involve the GP, ENT, myofunctional therapy and sometimes speech therapy.

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This guide is for general information only. It is not a diagnosis, treatment plan, or substitute for advice from a registered dentist or orthodontist.