A popular appliance for correcting maxillary arch transverse deficiency is the rapid palatal expander (RPE).
A greater response to RPE therapy has been reported in younger subjects, whereas in older subjects the appliance becomes increasingly less effective.
Four-band RPE is indicated when severe anterior crowding is accompanied by a tapered arch form, and 2-band RPE is recommended in the mixed dentition when mild crowding occurs with posterior constriction.