INTRODUCTION
Underbite refers to an abnormal protrusion (jutting out) of the lower jaw, leading to a malocclusion, or bad bite. To get an idea of what an underbite looks and feels like, stand in front of a mirror stick out your chin and bottom teeth so they are positioned in front of your upper teeth.

Between 5 and 10 percent of the general population has an underbite. The frequency of underbite is higher among Asians.

What Causes an Underbite?
An underbite is predominately hereditary in nature, usually involving malformations of both the teeth and the underlying jawbone. Poor chewing habits can sometimes contribute to an underbite.

Aside from Aesthetic Concerns, Why Is It Important to Treat an Underbite?
Uncorrected, an underbite can potentially lead to temporo-mandibular joint disorder (TMJ)-- a misalignment or malfunction that causes excess pressure on the jaw joint. TMJ can lead to head and cheek pain, a clicking or popping sound each time you open and close your mouth, limited range of motion of the jaw joint, and other symptoms.

Additionally, many years of living with an underbite can cause the teeth to wear down prematurely or unevenly.

What Is the Best Age to Treat an Underbite?
Historically, the procedure was to wait until the child stopped growing and then realign the jaws surgically. Today, the goal is to avoid surgery whenever possible by intervening when the patients are still growing, as young as age 5.

How Is an Underbite Treated?
If the patient is an adult, and the underbite is skeletal, surgery is usually required. Braces are worn for about a year before surgery and for 6 to 9 months afterward.

During the operation, the surgeon pushes back the lower jaw, pulls the upper jaw forward, or both.

If the underbite is confined to the teeth and there is no skeletal involvement, the malocclusion can potentially be corrected with braces alone.

If the patient is under age 8, and if the lower jaw is outgrowing the upper jaw, surgery may be avoided. The treatment typically begins with an upper jaw expander. This molded plastic and wire device is fixed to the roof of the mouth for about a year. Each night for the first few months, the parent uses a key to open the expander slightly. Once the proper jaw width is achieved, the expander remains in place for several more months before being replaced with a retainer. This helps ensure that the upper jaw hardens in its new position.

At around age 8 or 9, the child is fitted with a "reverse-pull face mask," which resembles a catcher's mask and is worn after school and at night. The mask is anchored to the mouth with rubber bands, which are attached metal bands around the top back molars. The gentle but steady pressure exerted by the rubber bands on the upper jaw encourages bone growth. In effect, the upper jaw is "pulled out" like a dresser drawer.

If the underbite is mild or moderate, the lower jaw is left alone. In severe cases where growth of the lower jaw needs to be restrained, the child will also wear a chin cap. The cap wraps around the chin and the top of the head. How long the child wears the face mask and chin cap depend on the severity of the overbite; a year is fairly typical.

While the reverse-pull face mask treatment obviates the need for surgery in the majority of cases, sometimes the discrepancy between the lower and upper jaws is so great that surgery is still needed.

After treatment with the face mask or surgery, the child may still need to wear standard braces for 1 to 3 years, followed by a retainer for another 2 years or longer, to achieve and maintain an ideal bite.

What Is the Long-Term Success Rate for Correcting an Underbite?
The success rate of surgical and nonsurgical correction of an underbite is both extremely high. Parents who have undergone surgery for their underbite are usually thrilled to learn that their children can avoid surgery if orthodontic treatment begins early.

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