An orthodontic expansion screw comprising at least two bodies (1, 2) arranged at a mutual distance that can be changed by means of a spindle, which engages both bodies (1, 2), wherein the spindle comprises an activating part, from which at least one threaded part (7, 8) proceeds into a threaded hole in one of the two bodies (1, 2), so that the spindle and the threaded hole have a shared longitudinal axis, at least one guide pin (5, 6), which engages both bodies (1, 2) and guides them while preventing a relative rotation of the bodies (1, 2) upon a change in their distance relative to each other, wherein the shared longitudinal axis runs parallel to the guide pin (5, 6), wherein in order to prevent or impede an inadvertent twisting of the spindle relative to the bodies (1, 2), the outer periphery of the activating part has a lateral surface, whose configuration differs from a lateral surface of a circular cylinder in such a way that there is at least one first position of the spindle in which the activating part contacts the guide pin (5, 6) with a pressure that causes an elastic deformation of the guide pin (5, 6), and that there is at least one second position of the spindle in which the activating part does not contact the guide pin (5, 6) or contacts them with no pressure or so little pressure that no guide pin (5, 6) is deformed, wherein the configuration of the lateral surface of the activating part differs from the lateral surface of a circular cylinder in such a way that characterized in that the lateral surface of the activating part is flattened in two locations lying diametrically opposite each other in order to form two second positions. at least two bodies (1, 2) arranged at a mutual distance that can be changed by means of a spindle, which engages both bodies (1, 2), wherein the spindle comprises an activating part, from which at least one threaded part (7, 8) proceeds into a threaded hole in one of the two bodies (1, 2), so that the spindle and the threaded hole have a shared longitudinal axis, at least one guide pin (5, 6), which engages both bodies (1, 2) and guides them while preventing a relative rotation of the bodies (1, 2) upon a change in their distance relative to each other, wherein the shared longitudinal axis runs parallel to the guide pin (5, 6), wherein in order to prevent or impede an inadvertent twisting of the spindle relative to the bodies (1, 2), the outer periphery of the activating part has a lateral surface, whose configuration differs from a lateral surface of a circular cylinder in such a way that there is at least one first position of the spindle in which the activating part contacts the guide pin (5, 6) with a pressure that causes an elastic deformation of the guide pin (5, 6), and that there is at least one second position of the spindle in which the activating part does not contact the guide pin (5, 6) or contacts them with no pressure or so little pressure that no guide pin (5, 6) is deformed, wherein the configuration of the lateral surface of the activating part differs from the lateral surface of a circular cylinder in such a way that characterized in that the lateral surface of the activating part is flattened in two locations lying diametrically opposite each other in order to form two second positions.