FRICTIONAL RESISTANCES IN STAINLESS-STEEL BRACKET-WIRE COMBINATIONS WITH EFFECTS OF VERTICAL DEFLECTIONS

This research evaluated the effects of different bracket-wire combinat ions and second-order deflections on kinetic friction. Thirteen differ ent brackets, six with 0.018 x 0.025 inch slots and seven with 0.022 x 0.028-inch slots were evaluated with six different sizes and shapes o f stainless steel orthodontic wire, i.e., 0.016, 0.016 x 0.022, 0.017 x 0.025, 0.018, 0.018 x 0.025 and 0.019 x 0.026 inch for four second o rder deflections of 0.00, 0.25, 0.50, and 0.75 mm. The wires were liga ted into the brackets with elastomeric modules. Bracket movement was i mplemented by means of an Instron universal testing instrument (RMO, D enver, Cole.), and frictional forces were measured by a tension load c ell and recorded on an X-Y recorder (Hewlett-Packard, Anaheim, Calif.) . Second-order deflection was created by a specially designed and mach ined testing apparatus that allowed two alternate pairs of the four to tal brackets to be offset in increments of 0.25 mm. The kinetic fricti onal force increased for every bracket-wire combination tested as the second-order deflection increased. Friction also increased with an inc rease in wire size, whereas rectangular wires produced greater frictio n than round wires. Bracket designs that limited the force of ligation on the wire generated less friction at low second-order deflections ( 0.00 and 0.25 mm).