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Underbite (Mandibular Prognathism)

 It looks cute on a bulldog, but people with underbites may be a little more self-conscious about their appearance. While much less common than its doppleganger, the overbite, an underbite can cause major problems for those who suffer from them.

Also known as a prognathism, an underbite is a type of malocclusion, or “bad bite.” Most orthodontic problems result from an abnormal protrusion of the jaw or alignment of the teeth. An underbite is specifically characterized by the lower jaw (mandibule) protruding beyond the upper jaw (maxilla), causing the lower front teeth to overlap those on top. This may be formed through a malformation of the jawbone (skeletal), a misalignment of the teeth (dental), or both.

What Causes a Prognathism?

Although far less common than overbites, underbites still affect 5-10 percent of the population. Underbites are usually hereditary, meaning most people are born with it. In this case, the overbite is usually the result of a larger lower jaw or smaller upper jaw, although overcrowding and malformed teeth can also be the cause.

Interestly, some ethnic groups may be more prone to developing an underbite. For instance, people of Asian decent have a higher percentage of mandibular prognathism than the rest of the population, a sign that underbites may be the result of a genetic trait. One such example of how genetics play into the development of an underbite is the “Habsburg jaw,” where many generations of the European Royal Habsburg Family displayed this trait.

An underbite can also be caused by environmental factors: Tongue thrusting and mouth breathing tend to position the tongue against the lower front teeth, pushing the jaw forward in early childhood development. Poor eating habits can also contribute to an underbite. Children who suffer from allergies and nasal congestion tend to breathe more often through their mouths, forcing the tongue to rest against the lower jaw and increasing their chances of developing a prognathism as well.

Complications From an Underbite

An extreme underbite can cause a facial abnormality, resulting in an extended chin. Besides the aesthetic problem, underbites can also cause other problems, including difficulty with chewing, swallowing and speaking. Bite problems caused by a prognathism can wear down tooth enamel, increasing your chance of developing tooth decay or other dental problems. Underbites have also been known to cause TMJ, a painful disorder of the jaw joint.

Underbite Treatment for Children

When it comes to underbite treatment, intervention is the best medicine. The earlier an underbite is treated, the better chances you’ll have of avoiding dental surgery in the future. Ideally, treatment for an underbite should begin before the age of 8. During this time, childrens’ jaws are still forming, making them easier to reshape.

If you’re not sure whether your child has a prognathism, take him or her to an orthodontist for an evaluation. The American Dental Association recommends that every child should visit an orthodontist by the age of 7, leaving you plenty of time to intervene should your child be diagnosed with an orthodontic problem.

The following procedures are common underbite treatments for young children:

– An upper jaw expander is a molded plastic and wire device fixed to the roof of the mouth. A key is used to widen the expander on an nightly basis until treatment is complete, which usually takes about one year. Once the desired width is achieved, the expander is replaced with an orthodontic retainer.
– A reverse-pull face mask wraps around the head and attaches to metal bands on the upper back teeth to pull the upper jaw into place.
– Unlike the previous two treatments for underbites, which encourage the growth of the upper jaw, a chin cap restrains the growth of the lower jaw. It wraps from the chin to the top of the head and can be combined with reverse-pull face mask.

Not every treatment will completely eliminate the need for surgery later in life. But if the underbite is mild or dental (totally pertaining to the teeth), your dentist may choose to do nothing and treat it with dental braces as a teenager or adult. Regardless of what type of procedure is used early on, braces are usually needed later to complete treatment.

Adult treatment for underbites is more limited. Once the jaws have fully formed, expanders and masks will not help. If the underbite is skeletal in nature, dental surgery is typically needed to reposition the jaw. During this surgery, the lower jaw is pushed back or upper jaw is moved forward into a more desirable position. This type of surgery is usually done in a hospital setting under general anesthesia. Braces may be needed before and after the surgery as part of your treatment.

If the underbite is dental in nature, you may be able to avoid surgery. Tooth extractions may still be necessary to relieve overcrowding and dental braces are necessary to move underbite teeth into the proper position.

It’s never too late to correct your underbite.

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