What Causes Crooked Teeth

The majority of children now have crooked teeth, which is evident from five years of age and is often attributed to hereditary factors. However, rather than blame genetics for crooked teeth and poor jaw development, modern research has produced evidence that points to other causes.

Mouth breathing, tongue thrusting, reverse swallowing and thumb sucking (known as incorrect myofunctional habits) are the real causes.

Allergies, asthma and an open mouth posture also contribute to incorrect jaw development. Growing up, most of us have had one or more of these myofunctional problems, which may have been the cause of incorrect dental and facial development.

Myofunctional habits


When a child breathes through the mouth, the jaws become narrow and develop downwards rather than forwards. This means there is not enough room for the teeth and the face can become narrow.


An incorrect (reverse) swallowing pattern takes place when the tongue pushes forward and the lips push back. This habit restricts forward growth of the jaws, preventing the face developing to its genetic potential.

Tongue Position

The tongue resting position determines the shape and size of the upper jaw and should always rest in the roof of the mouth. If the child habitually has a low tongue position, the upper teeth will not have enough space and the lower jaw is forced back and down.

Lip Function

Poor muscle tone or incorrect control of the lip and cheek muscles can make it difficult for the child to seal their lips and increases over-activity when swallowing. These incorrect lip habits cause the lower teeth to be crowded and restrict forward jaw growth.

Understanding the causes

Hereditary factors or big teeth in small jaws are not responsible for crowded teeth or incorrect jaw development. The real culprits are mouth breathing, tongue thrusting, reverse swallowing and thumb sucking, which are known as incorrect myofunctional habits.

Allergies, asthma and open mouth posture compound the issue and most children have at least one of these myofunctional problems contributing to incorrect dental and facial development.

If the tongue and lips are not functioning correctly, crowded teeth and underdeveloped jaws are the result. These are called incorrect myofunctional habits. If function and jaw shape are correct, there is plenty of room for the teeth.

The Myobrace®System is preventive pre-orthodontic treatment that focuses on addressing the underlying causes of crooked teeth, often without the need for braces or extraction of teeth, unlocking natural growth and development.

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