What is the best appliance to correct a unilateral posterior crossbite caused by a constricted maxillary arch in a child?

A unilateral posterior crossbite from a narrow maxilla is treated by widening the maxilla with a palatal expander, correcting the transverse discrepancy.Other options: Headgear addresses anteroposterior growth; a lingual holding arch is a space maintainer; a Hawley retainer maintains, not expands.Key exam takeaway: Constricted-maxilla posterior crossbite in a child: palatal expander.