[The practical aspects of using "superelastic" arch wires in the edgewise technic]

Effect of archwire qualities and bracket designs on the force systems during leveling of malaligned teeth

OBJECTIVES

The force systems during multiband treatment are influenced by the selection of the bracket-archwire combinations. Resin models replicated from casts reflecting the pretreatment intraoral situation of a patient's mandible were used to explore how different bracket systems and archwire qualities would affect the force systems developing during simulated orthodontic leveling of several malaligned teeth.

MATERIALS AND METHODS

Leveling movements of the malaligned teeth 32, 33, and 34 were simulated using the orthodontic measurement and simulation system (OMSS). Two bracket types and three archwire qualities were compared, the former featuring a slot width of 0.022" (0.56 mm) and including one conventional (Freedom MIM Roth by ODS) and one passive self-ligating (Carriere MBT by ODS) design. Both were combined with three NiTi round 0.014" (0.36 mm) archwire products, two of them standard products (CuNiTi by Ormco; EuroArch by ODS) and one being a low-cost (NiTi Superelastic by Modern Arch) product. Measured parameters included force, torque, translation, and rotation.

RESULTS

Archwire qualities are critical to the force systems developing in the leveling stage. On the other hand, the finding that lower force/torque values result in less tooth movement is not primarily due to wire selection. Our most striking result was that the ODS EuroArch wire resulted in very low force and torque values both with the conventional and with the self-ligating brackets. Almost identical patterns with these two bracket designs were found, and none of the measured parameters revealed a significant advantage for any of the bracket-archwire combinations over the others.

CONCLUSION

In our experimental simulations of tooth leveling, wire-quality selection was found to be a key modifier of force, torque, translation, and rotation. Clearly, however, neither the wire qualities nor the bracket designs made a decisive difference to the amounts of leveling movement induced to malaligned teeth; other factors like tooth class or nature of the malalignment seem to be more important in this regard. A therapeutic benefit of self-ligating over conventional brackets was not demonstrable.