Locking the screw after rapid palatal expansion: a superfluous procedure?

This prospective clinical trial and theoretical considerations showed that locking the expansion screw of an RPE at the end of active expansion is an unnecessary precaution in most situations. The shallow slope of virtually any expansion-screw threads will prevent relapse of the expansion mechanism. Although our clinical study used a screw coated with a friction agent, it appears from our calculations that such coatings, as well as the ratcheting-type mechanisms incorporated in many screws, may be superfluous