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Oral Habits and their Effect on the Smile

Thumb Sucking

Thumb sucking causes the upper front teeth to stick out and become spaced, the lower front teeth to tip inwards and become crowded, and the increased cheek muscle activity causes the smile to become narrow.

When the upper front teeth stick out, they are much more likely to be impacted and broken during normal childhood activities. In addition, the incisors also tend to over-erupt.

Teeth naturally erupt until they meet their antagonist in the opposing arch. When the incisors are malpositioned and cannot contact their opposing tooth, they continue to erupt resulting in a gummy smile with too much incisor display. In addition, the lower lip often becomes trapped behind the incisors resulting in what most people refer to as Buck teeth.

Re-intruding teeth to their normal position is a difficult and sometimes risky procedure. In extreme cases, surgery is required to correct the problem.

Mouth Breathing

At rest, we are supposed to breath through the nose with our lips closed. When there is an obstruction in the nasal airway, this is not possible, so a mouth breathing habit develops.

Since the mouth is always open, the top and bottom teeth are rarely in contact (even when swallowing), so the posterior teeth erupt and the lower part of the face becomes elongated and the chin falls backward resulting in a very convex profile. In addition, the tongue rarely contacts the inside of the upper molars, so arch width does not develop resulting in a very narrow smile.

While there are many causes, this is typical of the changes seen when the adenoids are enlarged. Children with “adenoid faces” tend to have long faces with dried, cracked lips and the incisors always showing. They sleep poorly and often snore at night. They have tired eyes and poor appetites.

Tongue Thrust Swallow

During a normal swallow, the teeth clench together and the tongue pushes outward against the upper molars. This is how the width of the smile and lower part on the face develops.

During an anterior tongue thrust swallow, the tongue pushes against the inside of the upper incisors. This prevents the normal overlap of the incisors (termed overbite) from developing so when the teeth are in contact, there is a space between the front teeth (termed openbite). In addition, the incisors are also ofter flared.

Another example occurs when the tongue lies between the posterior teeth during a swallow. This is termed a posterior tongue thrust swallow. This prevents the posterior teeth from erupting and is one of the causes of a “deep bite” when the lower incisors cannot be seen in the smile because they are hidden behind the upper incisors.


Bruxism, or tooth grinding, has many effects and is discussed here.