Posterior crossbite is one of the most prevalent malocclusions in the mixed
dentition period; it does not have a spontaneous correction and should be treated as
early as possible, after an accurate diagnosis. Maxillary expansion is considered an
effective and reliable method for increasing transverse dimension in patients with
unilateral or bilateral posterior crossbites. Moreover, it seems that this not only
enlarges the constricted maxillae, but also creates additional spaces in the dental arches
to resolve borderline dental crowding in some patients. This chapter addresses the
aetiology, diagnosis and treatment of maxillary transverse discrepancy in the mixed
dentition period.
Keywords: Hyrax appliance, Maxillary expansion, Posterior cross-bite, Quadhelix
appliance.
