Two-couple orthodontic appliance systems: torquing arches.

Twists placed in an arch wire between incisor brackets are often used in an attempt to obtain root torque. This is only partially effective because of the equal and opposite reciprocals acting on the adjacent teeth. Alternatively, a V-bend in a torquing arch, inserted at only the molar and incisor brackets, may use the bending properties of the arch wire to create dissimilar moments in a two-bracket system. If the greater moment is present at the incisors, all of the incisors are rotated en masse in the same direction, with the associated equal and opposite vertical equilibrium forces directed at the incisors and molars. The lesser moment at the molar also usually has equilibrium forces that may reduce or supplement vertical forces at the molar and incisor depending on the magnitude and direction of the moment present. If the arch wire is unrestrained the resulting tooth movement shows rotation of the incisors around the CRes and movement of the CRes in the direction of the vertical equilibrium force present. The alternative use of a single force to rotate incisor crowns facially results in a reciprocal distal force at the posterior teeth and rotation of the incisors with a center of rotation apical to the CRes.