Controlled retraction of maxillary incisors.

The force characteristics inherent in the prefabricated PG retraction spring have been shown to be efficient for controlled movement of canines. In the present investigation, this spring was analyzed with regard to its applicability for controlled retraction of the maxillary incisors. A description of the required system of moments and horizontal and vertical forces, acting at both the active (alpha) and reactive (beta) units, is presented. The three-dimensional force system generated by specific modifications of the spring was registered in a bench testing device mounted with strain gauges, and the resultant data presented in a graphic. It is concluded that the PG retraction spring can be used as a module for controlled retraction of both canines and incisors. The magnitude of horizontal and vertical forces is kept within the anticipated physiologic limits and can be identified by the shape of the activated spring. Variability of the distance between the anterior and the posterior points of force attack has no significant influence on the horizontal and vertical forces produced. Only minor clinical adjustments are needed to modify the retraction spring from canine-to-incisor retraction.