The dental condition involving a vertical gap between the upper and lower teeth when the mouth is closed is an open bite.
In an open bite, some opposing teeth do not meet when the jaws are closed. The most familiar form is an anterior open bite, in which the upper and lower front teeth fail to touch or overlap. A posterior open bite can affect molars or premolars instead. The condition is a type of malocclusion, meaning the teeth or jaws do not align normally.
Open bites may result from prolonged thumb sucking or pacifier use, tongue thrusting, tooth eruption problems, skeletal growth patterns, or a combination of dental and jaw factors. In children, stopping a persistent sucking habit early can sometimes allow the bite to improve naturally, though orthodontic assessment may be needed.
The main mix-up is with overbite, where the upper front teeth vertically overlap the lower teeth. An underbite places the lower teeth in front of the upper teeth, while a crossbite is a sideways mismatch between upper and lower teeth.