ORIGINAL ARTICLE Evaluation of friction of stainless steel and esthetic self-ligating brackets in various bracket-archwire combinations Vittorio Cacciafesta, DDS, MSc, PhD, a Maria Francesca Sfondrini, MD, DDS, b Andrea Ricciardi, DDS, c Andrea Scribante, DDS, c Catherine Klersy, MD, MSc, d and Ferdinando Auricchio, MS, PhD e Pavia, Italy, and Aarhus, Denmark This study measured and compared the level of frictional resistance generated between stainless steel self-ligating brackets (Damon SL II, SDS Ormco, Glendora, Calif), polycarbonate self-ligating brackets (Oyster, Gestenco International, Go ¨ thenburg, Sweden), and conventional stainless steel brackets (Victory Series, 3M Unitek, Monrovia, Calif), and 3 different orthodontic wire alloys: stainless steel (Stainless Steel, SDS Ormco), nickel-titanium (Ni-Ti, SDS Ormco), and beta-titanium (TMA, SDS Ormco). All brackets had a .022-in slot, whereas the orthodontic wire alloys were tested in 3 different sections: .016, .017  .025, and .019  0.025 in. Each of the 27 bracket and archwire combinations was tested 10 times, and each test was performed with a new bracket-wire sample. Both static and kinetic friction were measured on a custom- designed apparatus. All data were statistically analyzed (Kruskal-Wallis and Mann Whitney U tests). Stainless steel self-ligating brackets generated significantly lower static and kinetic frictional forces than both conventional stainless steel and polycarbonate self-ligating brackets, which showed no significant differ- ences between them. Beta-titanium archwires had higher frictional resistances than stainless steel and nickel-titanium archwires. No significant differences were found between stainless steel and nickel-titanium archwires. All brackets showed higher static and kinetic frictional forces as the wire size increased. (Am J Orthod Dentofacial Orthop 2003;124:395-402) F riction is the resistance to motion when 1 object moves tangentially against another. A distinc- tion is made between static frictional force—the smallest force needed to start the motion—and kinetic frictional force—the force needed to resist the sliding motion of 1 solid object over another at a constant speed. 1-4 For 1 object to slide against the other, the force application must overcome the frictional force; higher frictional resistance requires greater orthodontic forc- es. 5 Many studies have evaluated the factors that influ- ence frictional resistance: bracket and wire materials, surface conditions of archwires and bracket slot, wire section, torque at the wire-bracket interface, type and force of ligation, use of self-ligating brackets, inter- bracket distance, saliva, and influence of oral func- tions. 6-9 Schumacher et al 10 stated that friction was deter- mined mostly by the nature of ligation. Self-ligating brackets were introduced in the mid-1930s in the form of the Russell attachment, which was intended to reduce ligation times and improve operator efficien- cy. 11,12 Self-ligating brackets are ligatureless bracket systems that have a mechanical device built into the bracket to close off the edgewise slot. From the patient’s perspective, self-ligating brackets are gener- ally smoother, more comfortable, and easier to clean because of the absence of wire ligature. 13 Reduced chair time is another significant advantage. 14 Two types of self-ligating brackets have been developed: those that have a spring clip that presses against the archwire, such as the In-Ovation (GAC International, Bohemia, NY), SPEED (Strite Industries, Cambridge, Ontario, Canada), and Time brackets (Adenta, Gilching/Munich, Germany), and those in which the self-ligating clip does not press against the wire, such as the Activa (“A” Company, San Diego, Calif), the TwinLock (Ormco/ “A” Company, Orange, Calif), and the more recently developed Damon SL I (Ormco/“A” Company) brack- a Assistant clinical professor, Department of Orthodontics, University of Pavia, Italy, and University of Aarhus, Denmark. b Assistant clinical professor, Department of Orthodontics, University of Pavia. c Research fellow, Department of Orthodontics, University of Pavia. d Statistician, Clinical Epidemiology and Biometry Unit, Scientific Direction, IRCCS San Matteo, Pavia. e Professor, Department of Structural Mechanics, University of Pavia. Reprint requests to: Dr Vittorio Cacciafesta, c/o Studio Prof Giuseppe Sfon- drini, Via Liberta ` 17, 27100 Pavia, Italy; e-mail, vcacciafesta@hotmail.com. Submitted, August 2002; revised and accepted, December 2002 Copyright © 2003 by the American Association of Orthodontists. 0889-5406/2003/$30.00 + 0 doi:10.1016/S0889-5406(03)00504-3 395