Orthodontic rapid palatal expansion. Maxillary expansion. |Rapid palatal expansion is a preliminary treatment procedure that aims at enlarging the maxillary dental arch and the palate (roof of the mouth) to re-establish.cedra rapid jaw crucsher,Rapid Palatal Expander - orthonjThe image at the right shows the type of rapid palatal expander that I use on a model. This appliance is also called a "Hyrax" appliance. It consists of a screw that.