[The computer-aided development of orthodontic treatment elements made from NiTi memory alloys exemplified by a pseudoelastic retraction spring].

Employing the segmented arch technique, specifically designed loops are employed to bring about sufficient force and turning moments to achieve a purely translatory retraction. Most importantly, the moment to force ration (M/F) is determined by the occluso-gingival height, but, as there are intraoral limitations to the spring height, the maximum possible M/F is also limited. Consequently the M/F is no longer constant and activation of the loop to achieve a specific M/F can become critical. This potential problem can be overcome by the use of highly flexible wires, particularly those made of the superelastic alloy nickel titanium. The data presented in this study result from calculations arrived at with the help of a plane numerical model of pseudoelasticity which in turn is based on the finite element method. The calculations are compared with those resulting from experimentations using the orthodontic measurement and simulation system. A variation in the different parameters led to the design of a T-loop with a height and an apical length of 10 mm each. A T-segment made of superelastic NiTi alloy Sentalloy (0.016" x 0.022") was joined to steel horizontal arms. This loop produces a constant M/F ratio of -7 mm and requires no uprighting bends. The range of activation is approximately 15 mm. A superelastic plateau was calculated between an activation of 10.5 mm and 2.5 mm, with a distalizing force from 0.9 N to 0.5 N. The experimental values corresponded to the numerical data. The clinical application of the superelastic T-loop is thus demonstrated.