Abstract: The expander fits into the upper region of the patient's palatal cavity, and has a longitudinally extending screw which can be given prescribed turns by the patient over a predetermined timetable in order to spread his palate. The screw has forward and rear segments which threadably receive nuts oppositely threaded with respect to one another so that rotation of the screw causes movement of the nuts toward and away from one another. Laterally outwardly movable linkages are pivotally supported on these nuts so that the device operates in the manner of a scissors jack, and orthodontic wires are provided to connect the linkages to orthodontic bands which fit onto the patient's teeth so that the mechanical force and moment achieved in the scissors jack construction can be used to spread the patient's palatine bone segments.