Forces and Influences Involved in Dentofacial Development

Muscles of the lips, cheek and tongue along with the muscles used in chewing are the natural forces involved in our dentofacial growth and development. When we chew, swallow and breathe in a normal fashion, the muscular forces are balanced providing for a normal arrangement and alignment of the teeth and jaws. These normal forces play an important role in our dentofacial growth and occlusal physiology. When this muscle force deviates from normal, as in a habitual mouth breather or thumb sucker, the deviate muscle forces can cause enough imbalance to the growth pattern of the child to produce a malocclusion and/or dentofacial abnormality. Muscle forces strong enough to cause a malocclusion or dentofacial abnormality are considered abnormal forces.

Developmental abnormalities is one major causes of imbalance to the natural muscular forces. Developmental abnormalities can be from disturbances during embryonic development such as genetic disorders, or possibly environmental insults such as illnesses contracted during pregnancy or possibly chemical agents taken while pregnant.

Congenitally missing, malformed or supernumary (extra) teeth are some examples of developmental abnormalities. Disturbances in the normal exfoliation and eruption of teeth can be a problem. An example of this would be with the early loss of a primary tooth resulting in inadequate space for the permanent tooth to erupt.

Trauma is another major cause of muscular imbalance leading to malocclusion and dentofacial abnormalities. Childhood fractures of the lower jaw is not uncommon. One study at the University of North Carolina reported that approximately 5% of patients who need surgical correction for severe mandibular deficiencies had had a history of an earlier fracture of the jaw.

Tooth trauma or an injury to the primary teeth can result in damage to permanent tooth buds. Tooth trauma can also result in direct injury to the permanent tooth with fracture or exfoliation being one of the major consequences. Drifting of permanent teeth can also occur after the premature loss of a primary tooth.

            Mouth breathing and habits such as thumb-sucking are examples of functional causes of muscular imbalances that may result in malocclusions and abnormal dentofacial growth. Just as desired normal habits play an important role in craniofacial growth and occlusal physiology, abnormal habits may interfere with the regular and desired pattern of facial growth. Certain abnormal habits are known to be involved in the etiology of malocclusion and/or dentofacial development.

Thumb sucking is commonly associated with flared and protruding upper anterior teeth. This results in a greater potential for accidents such as fractures and/or avulsions of these teeth. Pushed back lower anterior teeth and an anterior open bite are also associated with thumb sucking, along with tooth crowding, a narrow upper arch and a high palatal vault.

Tongue thrusting is believed to be the result of an anterior open bite. The open space must be sealed with the tongue in order to swallow effectively resulting in a tongue thrusting habit that perpetuates the open bite by not permitting the anterior teeth to close.

Lip sucking and biting is also a well documented habit leading to an abnormal growth pattern. The force of the lower lip continually held beneath the upper teeth can cause the upper teeth to flair and protrude forward. In extreme cases the lower front teeth may be pushed back and an open bite may also develop.

Mouth breathers have an unusually high incidence of malocclusion. Humans are primarily nasal breathers. Mouth breathing usually results from a nasal obstruction. Polyps, enlarged turbinates or underdeveloped nasal passages are all causes of nasal obstruction. Deviated septums, allergic edema and enlarged tonsils and adenoids are also common causes of nasal obstruction that should be corrected earlier rather than later.

The open mouth breathing position tends to alter muscle function effecting the growth of the face, often resulting in an unusually long narrow appearance. In order to breath through the mouth the lower jaw is dropped, the head is tilted back and the tongue is lowered from contact with the palate and protruded to provide a greater oral airway. Tooth crowding, narrow palate, high palatal vault, asymmetrical growth of the upper and lower jaws and/or an abnormal swallowing pattern are often noted results.