An orthodontic force mechanism includes a jack screw having a pair of ends, at least one of which is threaded, and a central spindle between the ends, which spindle has 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 mounted on the central spindle section includes a spring-loaded detent configured to engage an end opening of each of the through holes in the spindle when the 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. The detent can be moved out of engagement with a through hole using a tool inserted into that through hole from its opposite end.