The Memory Expansion Screw has an internal NiTi coil spring that, when adjusted, supplies a continuous positive biologic force of about 500g over a distance of 0.8mm to 1mm. Adjustment typically involves placing three 90Þ turns once every three days. Many practitioners prefer this appliance over the open coil-spring RPEs. Note - The Memory Expansion Screw is also available in a hyrax design.