THE EFFECT OF CROSS-SECTIONAL DIMENSIONAL VARIATIONS OF SQUARE AND RECTANGULAR CHROME-COBALT ARCHWIRES ON TORSION

The purpose of this investigation was to study the control of cross-se ctional dimensions and edge bevel by various manufacturers in the prod uction of chrome-cobalt archwires and its effect on transmitting torqu e through an .018 inch slot bracket system. Twenty-seven different squ are and rectangular chrome-cobalt wires commonly used in the edgewise technique supplied by five different manufacturers were studied with r espect to dimensions, edge bevel, and mechanical properties in torsion . The mechanical study simulated application of torque to an individua l tooth. Standard brackets with .018 inch slot heights were used. The results show that variation in cross-sectional dimension and edge beve l leads to variable torsional play (third-order clearance). As an exam ple, .016 x .016 wires have a mean torsional play of as much as 26.8 d egrees, with a range of 21.0 to 32.3 degrees. When using .016 x .016 w ires, one must apply from 34.8 to 48.6 degrees of twist to get 20 N-mm of torsional moment. This variation is primarily due to the rather wi de range in torsional play. As a result, the prediction by which a pre determined torsional moment can be delivered becomes uncertain. The re sults also show that because the working range in torsion of chrome-co balt wires is somewhat limited due to high torsional stiffness, precis e delivery of torsional moment based on the condition present in the o ral cavity is difficult. The torsional stiffness varies between manufa cturers within the various dimensional groups as a result of differenc es in cross-sectional geometry and material properties.