title: Effects of bracket design on critical contact angle.
abstract: OBJECTIVE
  To explore how the position of the bracket slots relative to the archwire influences the friction between them, and how bracket design affects the critical contact angle (θc).
  
  
  METHODS
  Two kinds of stainless steel archwires (0.016 and 0.019 × 0.025-inch) were tested against four kinds of brackets (Transmission Straight Archwire bracket, Domestic MBT bracket, Tip-Edge Plus bracket, and BioQuick self-ligation bracket) in the dry state. Resistance to sliding (RS) was measured as an increase in contact angle (θ). The value of θc was calculated by two linear regression lines.
  
  
  RESULTS
  Friction remained stable when θ < θc, then increased linearly when θ > θc. The θc values of the Tip-Edge Plus bracket and Transmission Straight Archwire bracket were significantly larger than those for the Domestic MBT bracket and BioQuick self-ligation bracket.
  
  
  CONCLUSIONS
  The relationship between the archwire and bracket slot significantly affects the resistance to sliding. The "edge-off" structure of the Tip-Edge Plus bracket and Transmission Straight Archwire bracket could help to increase the θc value, and to expand the passive configuration range.
authors.affiliation: Department of Orthodontics, Peking University School and Hospital of Stomatology, Beijing, PR China.
authors.forename: Xiaomo
authors.initials: X
authors.lastname: Liu
authors.forename: Peng
authors.initials: P
authors.lastname: Ding
authors.forename: Jiuxiang
authors.initials: J
authors.lastname: Lin
mesh_terms: D017276:Friction; D016014:Linear Models; D008422:Materials Testing; D008962:Models, Theoretical; D016382:Orthodontic Appliance Design / Q000379:methods*; D016910:Orthodontic Brackets; D009969:Orthodontic Wires; D013193:Stainless Steel / Q000737:chemistry*
chemical_list: D013193:Stainless Steel