EVALUATION OF FRICTION BETWEEN EDGEWISE STAINLESS-STEEL BRACKETS AND ORTHODONTIC WIRES OF 4 ALLOYS

This investigation was designed to determine the effects of wire size and alloy on frictional force generated between bracket and wire during in vitro translatory displacement of bracket relative to wire. Stainless steel (SS), cobalt-chromium (Co-Cr), nickel-titanium (NiTi), and β-titanium (β-Ti) wires of several sizes were tested in narrow single (0.050-inch), medium twin (0.130-inch) and wide twin (0.180-inch) stainless steel brackets in both 0.018- and 0.022-inch slots. The wires were ligated into the brackets with elastomeric ligatures. Bracket movement along the wire was implemented by means of a mechanical testing instrument, and frictional forces were measured by a compression cell and recorded on an X-Y recorder. β-Ti and NiTi wires generated greater amounts of frictional forces than SS or Co-Cr wires did for most wire sizes. Increase in wire size generally resulted in increased bracket-wire friction. The wire size-alloy interaction on the magnitude of bracket-wire friction was statistically significant (p < 0.005). With most wire sizes and alloys, narrow single brackets were associated with lower amounts of friction than wider brackets were. The levels of frictional forces in 0.018-inch brackets ranged from 49 gm with 0.016-inch SS wires in narrow single brackets to 336 gm with 0.017 × 0.025-inch β-Ti wires in wide twin brackets. Similarly for 0.022-inch brackets, frictional forces ranged from 40 gm with 0.018-inch SS wires in narrow single brackets to 222 gm with 0.019 × 0.025-inch NiTi wires in wide twin brackets.aFormer Resident and Clinical Instructor, Department of Orthodontics, University of Oklahoma, College of Dentistry; presently Adjunct Assistant Professor and Doctoral Student at University of California, San Francisco.bVisiting Assistant Professor, Department of Orthodontics, University of Oklahoma.cProfessor and Chairman, Department of Dental Materials, University of Oklahoma, College of Dentistry.dProfessor and Chairman, Department of Orthodontics and Division of Developmental Dentistry, University of Oklahoma, College of Dentistry. © 1990 Mosby-Year Book, Inc.