Crossbite

Crossbite at the back and at the front of the mouth

The Glossary of Orthodontic Terms of the American Association of Orthodontists (AAO) defines crossbite by where the teeth meet: “Upper back teeth are in crossbite if they erupt and contact inside or outside of the lower back teeth. Lower front teeth are in crossbite if they erupt in front of the upper front teeth.” At the back, the definition looks at where the upper teeth contact the lower ones, inside or outside them. At the front, it looks at lower teeth that come in ahead of the upper ones. A crossbite, in other words, can sit at the back of the mouth or at the front.

Crossbite or underbite: the AAO’s answer

Underbite is the word a crossbite gets mixed up with, and the AAO’s article on crossbites asks and answers the question in its own words: “Is a crossbite the same as an underbite or overbite? No, not all crossbites are the same.” The AAO’s crossbite article also draws the line at the front of the mouth: “In cases where the front teeth are in a crossbite, one or more top teeth sit behind the bottom teeth. The term underbite is often used when all of the top front teeth or jaw are positioned behind the lower front teeth.” A top front tooth caught behind the bottom teeth is a front crossbite, while underbite is the word often used when all the top front teeth, or the jaw, sit behind.

A single tooth can be in crossbite

A crossbite does not have to involve a whole row of teeth, and the AAO glossary’s entry ends on that point: “A crossbite can be a single tooth or groups of teeth.” Crossbite is the everyday word as well as the clinical one, so the name alone does not say how many teeth are involved or whether they sit at the front or the back.

When a crossbite should be treated is the question behind the crossbite answer page, and underbite, the word the AAO sets it against, can be looked up among the other bite terms in the glossary.