A rapid maxillary expander (also called rapid palatal expander) is used to expand the upper jaw (maxilla) to create space for the teeth, and to correct crossbite. Quite often, after widening, the patient finds it easier to breathe through the nose. That is because the maxilla lies just beneath the bony structures of the nose.
The best time to expand is when the child is in the pre-adolescent years, when the bone is still malleable. In severe cases of narrowed maxillary width, treatment may have to start even earlier.
See also: Transpalatal arch