[Optimization of arch guided tooth movement by the use of powerhooks].

Arch guided tooth movement is today still the most often used technique to move teeth bodily in mesiodistal direction. One of the most important disadvantage of this method, however, is friction between bracket and arch wire, which impairs tooth movement and may result in dangerous overload of the anchorage units. Powerhooks are used to accomplish a more effective orthodontic tooth movement by reduction of the tipping and rotating moments. This investigation answers the question which mechanical dimensions powerhooks should have in order to minimize friction. If the point of force application lies coronally to the center of resistance (CR) and rotatory moments are eliminated, friction can be reduced by as much as 90%. Concerning length, powerhooks must not be extended beyond. Otherwise, if the point of force application lies apically to CR, friction increases dramatically. In the horizontal direction, a unilateral powerhook should not be extended to more than the half of its length.