[The deactivation behavior and effectiveness of different orthodontic leveling arches--a dynamic analysis of the force systems].

Using the orthodontic measuring and simulation system (OMSS), the deactivation behaviour of diverse orthodontic levelling arches was investigated. The vertical forces and uprighting moments, as also the levelling effectiveness for initial malalignments of tooth 21 (1 mm and 2 mm infraocclusion, 20 degrees angulation) were measured, with the influence of various ligatures used in clinical practice being taken into account. The results may be summarized as follows: In the case of a large vertical offset (infraocclusion) the vertical forces can attain values of up to 3.8 N, depending on the type of levelling arch used. On deactivation, we can observe a sharp decrease in force caused by the frictional resistance between bracket and arch wire, which has to be overcome by the wire. The loss of desired force caused by friction may be as much as 50%, and is determined by the arch wire, bracket and mode of ligation. A smaller vertical offset (infraocclusion) (1 mm) is associated with extrusive forces of 0.2 N--0.8 N. Using looped levelling arches made of 0.016" standard steel wire, there is no frictional loss of orthodontic force, so that the highest vertical forces (more than 3.0 N) are observed with these arch wires. With an initial angulation of the tooth of about 20 degrees, uprighting moments of between 3.0 Nmm and 33.0 Nmm are measured, the looped arches again generating the highest moments. To ensure adequate uprighting moments in a combination of vertical offset (infraocclusion) and angulation, very high extrusive forces must be accepted. As a dynamic analysis of the tooth movement with the OMSS shows, the use of a specific arch wire results in a typical levelling defect. There is no general correlation between extrusive force or uprighting moment and the levelling effectiveness of an orthodontic arch. It is not possible to recommend a particular levelling arch.