Understanding the Causes

Crooked teeth, poor jaw growth.

What are the real 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.

As a child’s face grows forward and downwards, the jaws are influenced and reshaped by facial muscles.

If these muscles are functioning correctly, the tongue is in the proper position and the mouth is predominantly closed, a child has the ability to reach their full genetic potential with enough room for the front and back teeth to fit into their correct position.


If a child is a mouth breather, their tongue is unable to rest in the correct position and the mouth will remain open. This causes the muscles of the jaws and face to restrict correct forward growth, forcing it backwards and downwards, resulting in narrow jaws and an underdeveloped face.

This animation demonstrates how much forward growth is lost and highlights the lack of jaw space, which causes teeth to become crowded and does not allow space for the wisdom teeth to come through.


Fact: The tongue is one of the strongest muscles in our body and can exert up to 500g (17.5oz) of force. To put that in perspective, it only takes 1.7g (0.05oz) of force to move a tooth.

Did you know there is a spot in your mouth where the tongue should naturally rest whenever you are not eating or speaking?

The tongue determines the shape and size of the upper jaw. If the child habitually has a low tongue position (as in mouth breathing), the upper teeth will not have enough space and the lower jaw is forced back and down, affecting the way the face grows.

A normal top jaw grows properly because the tongue rests in the correct position (known as the Correct Tongue Resting Position), which is in the roof of your mouth.

If your tongue does not rest in the roof of your mouth, the top jaw will become too narrow and teeth won’t have enough room to grow straight.


Another thing to watch out for is if you’re swallowing the wrong way, with lots of movement in the bottom lip. Incorrect swallowing is when the tongue pushes forward and the lips push back when swallowing. When this happens your front teeth will be pushed backwards and this also causes your teeth to be crowded. A child swallows twice per minute and if they have an incorrect (reverse) swallowing pattern, the facial muscles will push backwards against the direction of growth, preventing the face from developing to its genetic potential.

The overlay on the second part of this video animation illustrates how much normal growth is lost. The resulting lack of space causes the teeth to be crowded and insufficient room for the wisdom teeth.

Lips and Cheeks

The forces of the lips and cheeks greatly affect the positioning of the teeth and jaws. Poor muscle tone or incorrect control of the lip and cheek muscles make it difficult for the child to seal their lips together and increases overactivity when swallowing.

When swallowing there should be no activity of the lower lip. Incorrect lip habits cause the lower teeth to be crowded and restrict jaw growth.

Genetic Potential

More than 27 years ago, Dr. Chris Farrell founded Myofunctional Research Co. (developers of Myobrace®) and discovered the real causes of orthodontic problems in children. He developed a 10-point evaluation that enabled every child to be screened for signs of poor jaw and facial development. The evaluation looks at the way children breathe, their tongue posture and the way they swallow. These habits greatly affect the way jaws develop and correcting them allows children to grow to their genetic potential and live a healthy lifestyle later in adulthood.

Incorrect facial growth caused by poor oral habits compared to correct facial growth (3D representation only).

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    What is Myobrace®

    Myobrace® treatment focuses on addressing the underlying causes of crooked teeth and correcting the poor oral habits causing orthodontic problems.
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    Treatment Goals

    With good compliance, Myobrace® treatment can offer more than just straighter teeth, allowing children to reach their full genetic potential.
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    Proven Results

    Patients in over 100 countries throughout the world have discovered the benefits of myofunctional orthodontics using The Myobrace® System.

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