Lever-arm and mini-implant system for anterior torque control during retraction in lingual orthodontic treatment

Abstract

Anterior torque control during retraction is difficult to achieve with lingual orthodontic treatment. This article describes the use of a lever-arm and mini-implant system as absolute anchorage for controlled retraction of the anterior teeth during lingual orthodontic treatment and evaluates 2 protrusion cases treated with this system. Various clinical situations are discussed and analyzed from a biomechanical standpoint. Mini-implants are needed to control the point of force application in the posterior area and produce en masse retraction with no anchorage loss. When the length of the lever-arm is adjusted to the position of the mini-implant, the desired line of action of the retraction force with respect to the center of resistance of the anterior segment is selected. Controlled retraction of the anterior teeth was achieved with no loss of anchorage. The mini-implant, in conjunction with the lever-arm, is useful not only for absolute anchorage but also for anterior torque control during retraction in lingual orthodontic treatment.