An open bite is when, with the back teeth closed together, the upper teeth do not overlap the lower teeth and a gap remains between the upper and lower teeth. It can cause problems such as being unable to bite through noodles with the front teeth, difficulty closing the mouth, mouth breathing, or a lisp. If left untreated, the face may lengthen into an underbite-like shape, and the mouth may stay open all the time.

Causes of an open bite include genetic factors and degenerative changes in the lower jaw due to jaw joint disorders, and it can also develop from habits that persist through adolescence, such as thumb sucking, mouth breathing, tongue thrusting, and resting the chin on the hand.