Crossbite is a condition in which teeth are in a reversed alignment. There are two forms of crossbite, rostral and caudal.
In the “normal” carnivore mouth the incisors (front teeth) are arranged in a scissors bite: the upper incisors are just in front of the lower incisors when the mouth is in a closed position. Rostral crossbite is the misalignment of one or more of the incisors. Either the upper incisors are positioned too far backward, the lower incisors are positioned too far forward, or a combination of both. The end result is the upper incisors sit behind the lower incisors.
In the example of the “normal” carnivore mouth, the large chewing teeth toward the back of the mouth (carnassial teeth) are arranged in a sectorial dentition: the upper fourth premolars are positioned lateral (to the outside) to the lower first molar when the mouth is in a closed position. This allows the teeth to shear against one another during biting motion, and creates the slicing action that carnassial teeth are famous for. Caudal crossbite is the misalignment of these teeth in which the upper tooth is angled to far inward, the lower tooth is angled too far outward, or a combination of both. The end result is reversed positioning of the carnassial teeth – the upper tooth sits to the inside of the lower tooth.
Clinical problems don’t always result and sometimes crossbites are a cosmetic problem only. However in some cases, tooth-on-tooth wear (attrition), soft tissue trauma, dental inflammation (pulpitis), or periodontal disease can occur. With caudal crossbite, the normal chewing action of the carnassials can be affected.
Treatment may not always be necessary. When needed however, treatment options for rostral crossbite include application of an orthodontic appliance or strategic extraction(s). For caudal crossbite, extraction of one or more of the carnassial teeth is usually performed, especially when significant wear attrition or trauma are present.