title: Mechanical effects of third-order movement in self-ligated brackets by the measurement of torque expression.
abstract: BACKGROUND
  Axial rotation of orthodontic wire produces buccal or lingual root movement and is often referred to as third-order movement or "torque expression." The objective of this study was to quantify torque expression in 3 self-ligation bracket systems (Damon Q, Ormco, Orange, Calif; In-Ovation R, GAC, Bohemia, NY; and Speed, Strite Industries, Cambridge, Ontario, Canada) during loading and unloading.
  
  
  METHODS
  A stepper motor was used to rotate a wire in a fixed bracket slot from -15° to 63° in 3° increments, and then back to -15°. The bracket was mounted on top of a load cell that measured forces and moments in all directions.
  
  
  RESULTS
  Damon's and In-Ovation's maximum average torque values at 63° were 105 and 113 Nmm, respectively. Many Speed brackets experienced premature loss of torque between 48° and 63°, and the average maximum was 82 Nmm at 54°. The torque plays for Damon, In-Ovation, and Speed were 11.3°, 11.9°, and 10.8°, respectively.
  
  
  CONCLUSIONS
  Generally, In-Ovation expressed the most torque at a given angle of twist, followed by Damon and then Speed. However, there was no significant difference between brackets below 34 Nmm of torque. From a clinical perspective, the torque plays between brackets were virtually indistinguishable.
authors.affiliation: Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, Canada. major@ualberta.ca
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Major
authors.forename: Jason P
authors.initials: JP
authors.lastname: Carey
authors.forename: David S
authors.initials: DS
authors.lastname: Nobes
authors.forename: Giseon
authors.initials: G
authors.lastname: Heo
authors.forename: Paul W
authors.initials: PW
authors.lastname: Major
mesh_terms: D003722:Dental Alloys / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D009068:Movement; D016382:Orthodontic Appliance Design; D016910:Orthodontic Brackets; D009969:Orthodontic Wires; D012399:Rotation; D013193:Stainless Steel / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D014087:Tooth Movement Techniques / Q000295:instrumentation; D019415:Torque
chemical_list: D003722:Dental Alloys; D013193:Stainless Steel