Posterior crossbite is a reverse bite in the back teeth on one or both sides of the mouth. Normally top teeth fit on the outside of the bottom teeth – in a crossbite, the opposite is true.
A posterior crossbite is usually the result of constriction of the top jaw. Constriction usually occurs from an active thumb habit, although there are many cases in which a cross bite is from an unknown origin.
The importance of correcting a crossbite ensures proper alignment and bite of the teeth. An incorrect bite can lead to wear spots, a crooked smile, and malocclusion. If not corrected the permanent teeth will also likely erupt into a cross bite.
Expansion of the upper jaw is needed to correct the crossbite. An appliance called a quad helix can slowly expand the upper jaw to correct the crossbite. Two bands with a small wire are fit on the back molars. This appliance is glued in and cannot be removed by the patient. Usually the crossbite is corrected in approximately 6-8 months with a 4-6 month retention time afterwards. There is no discomfort experienced during this expansion.