An orthodontic force mechanism according to the invention includes an elongated jack screw having at a pair of end portions, at least one of which is threaded, and a
central spindle section between the end portions, which spindle section has at least two intersecting radial through-holes therein. A pair of nut housings are mounted on the end portions of the jack screw, at least one of which is threadedly coupled to a threaded end portion of the jack screw. A lock mechanism is mounted on the
central spindle section, which lock mechanism includes a spring-loaded
detent configured to engage an end opening of each of the through holes in the spindle section when such through hole is in alignment with the
detent, such that the spindle cannot rotate relative to the lock mechanism when the
detent is inserted into a through-hole, and is free to rotate relative to the lock mechanism when the detent is clear of a through hole. The detent can be moved out of engagement with a through hole using a tool inserted into that through hole from its opposite end, such that a distal end of the tool pushes the detent out of the through-hole, and the same tool can then be used to rotate the jack screw.