Underbite

Underbite and its formal name, Class III malocclusion

The Glossary of Orthodontic Terms of the American Association of Orthodontists (AAO) defines underbite and gives its formal name together: “The lower front teeth or jaw sit ahead of the upper front teeth or jaw. Also known as a Class III malocclusion.” Underbite is the everyday word, and Class III malocclusion is the name the same bite carries in clinical terms. The entry’s wording names both possibilities: the lower front teeth or the lower jaw can be what sits ahead.

Dental, skeletal or both: sorting an underbite in treatment

In treatment, an underbite is sorted by where it comes from. The AAO’s article on underbites says “the orthodontist determines whether the underbite is primarily dental, skeletal, or a mix of both. That classification directly shapes which treatment options are most likely to work.” Dental points to the position of the teeth and skeletal to the jaws, the same possibilities the glossary’s definition names. How each kind is treated is the question the underbite answer page sets out to answer.

Uneven jaw growth behind most underbites

The AAO traces most underbites to the growth of the jaws. Its article on common types of bite problems says “An underbite is apparent when the lower jaw sits in front of the upper jaw, causing the lower front teeth to sit in front of the upper front teeth,” and adds “In most cases, underbites are due to differences in the growth rates of the upper and lower jaws.” The words in most cases matter: the jaws are the usual source, not the only one, since the glossary’s definition also names the teeth.

Crowding and open bite, which the same AAO article describes beside underbite, are among the glossary’s bite terms too.