A crossbite occurs when the cusps of the upper and lower jaws do not coincide and do not bite into each other. This causes an incorrect alignment of the jaws.
In a normal dentition, the cusps of the lower teeth bite centrally between the cusps of the upper teeth. Crossbite is a malocclusion in which the cusps of one or more upper teeth do not occlude properly on the sides with the opposite lower teeth.