Three-dimensional force systems from vertically activated orthodontic loops.

When both vertical alignment and first-order rotation of teeth are to occur simultaneously, a 3-dimensional force system is required. This numerical study evaluated several appliances (rectangular loops and L-loops) used to vertically align teeth. Consideration was given to how these designs might be modified to produce the appropriate force system to allow both movements to occur simultaneously. It was found that the rectangular loop was the most appropriate choice for first-order corrections. For the rectangular loops studied, the in-plane force system was shown to be essentially independent of the out-of-plane effects, which allowed the 2 corrections to be controlled separately.