Abstract: An orthodontic palate expander apparatus comprises an expansion screw assembly having first and second side plates with a threaded member connected between the plates so that its rotation in a first rotational direction about its longitudinal axis causes the plates to move away from one another in a palate expanding manner and rotation of it in the opposite direction causes the side plates to move toward one another for adjustment of the apparatus. A first gear is fixed to central regions of the threaded member and a second gear is mounted in driving relationship therewith. Manual rotation of the second gear thus causes rotation of the threaded member to thereby move the plates toward or away from each other according to the direction in which the second gear is rotated. The second gear is oriented so that with the apparatus installed in a patient's palate portions of the second gear are accessible through the patient's open mouth for turning the gear, for example, with an Allen wrench or screwdriver.