Evaluation of force systems from a “free-end” force system

Introduction: The purpose of this study was to investigate the biomechanical characteristics of a V-bend wire configuration in a free-end system, ie, with 1 end mounted in an orthodontic tube and the other loosely ligated to a bracket. The effects of V-bend position and size, wire dimension, method of ligation, and the inclusion of a second wire in the system were examined. Methods: Samples of various wire configurations were mounted in a bench testing machine to measure moments and forces at both ends in a standardized configuration resembling a 2-premolar extraction clinical case incorporating a special bracket with a second, frictionless slot. The position of the V-bend was altered in 1.0-mm intervals. Results: Moments were created at the posterior end, resulting in intrusive forces anteriorly that induced moments on the anterior block. The sizes of the moments and forces were increased in connection with posterior positioning of the V-bend, increase in the wire dimension and the V-bend sizes, although they were reduced and stabilized by the inclusion of a second nickel-titanium wire. The double wire system created clinically revelant moments and forces. Conclusions: The V-bend in a free-end system can create variable moments and forces that can be used clinically in intrusion and space-closing procedures but should be measured and monitored closely.