title: Force system evaluation of symmetrical beta-titanium T-loop springs preactivated by curvature and concentrated bends.
abstract: BACKGROUND
  The objective of this research was to compare the effect of preactivation on the force system of beta-titanium T-loop springs (TLSs).
  
  
  METHODS
  Twenty TLSs with dimensions of 6 × 10 mm, of 0.017 × 0.025-in beta-titanium alloy, were randomly divided into 2 groups according to their preactivation. By using a moment transducer coupled to a digital extensometer indicator adapted to a testing machine, the amounts of horizontal force and moment produced were recorded at every 0.5 mm of deactivation from 5 mm of the initial activation in an interbracket distance of 23 mm. The moment-to-force ratio, the "neutral position" and the load-deflection ratio were also calculated.
  
  
  RESULTS
  TLSs preactivated by curvature delivered horizontal forces significantly lower than those preactivated by concentrated bends. No differences were found in relation to the moments produced throughout the deactivation of both groups. The moment-to-force ratios were systematically higher on the TLSs preactivated by curvature than those preactivated by concentrated bends, except on 5 mm of activation. Significant differences were found in the load-deflection rates and "neutral position."
  
  
  CONCLUSIONS
  The TLSs preactivated by curvature delivered lower horizontal forces and higher moment-to-force and load-deflection ratios than did those preactivated by concentrated bends.
authors.affiliation: Department of Orthodontics and Pediatric Dentistry, UNESP, São Paulo State University, Araraquara School of Dentistry, Araraquara, São Paulo, Brazil. sergeirabelo@uol.com.br
authors.forename: Sergei Godeiro Fernandes Rabelo
authors.initials: SG
authors.lastname: Caldas
authors.forename: Renato Parsekian
authors.initials: RP
authors.lastname: Martins
authors.forename: Marília Regalado
authors.initials: MR
authors.lastname: Galvão
authors.forename: Camilla Ivini Viana
authors.initials: CI
authors.lastname: Vieira
authors.forename: Lídia Parsekian
authors.initials: LP
authors.lastname: Martins
mesh_terms: D003722:Dental Alloys; D003799:Dental Stress Analysis; D008422:Materials Testing; D016382:Orthodontic Appliance Design; D019516:Orthodontic Space Closure / Q000295:instrumentation*; D009969:Orthodontic Wires; D011897:Random Allocation; D013314:Stress, Mechanical; D014025:Titanium
chemical_list: D003722:Dental Alloys; C023988:beta titanium; D014025:Titanium