title: Force characteristics of nickel-titanium open-coil springs.
abstract: BACKGROUND
  The objective of this study was to quantify the properties of commercially available nickel-titanium open-coil springs.
  
  
  METHODS
  Eleven springs from 3 manufacturers were tested 5 times over a 12-week period. A universal testing machine was used to measure the force generated when open-coil springs were compressed to half of their original length and then gradually allowed to decompress.
  
  
  RESULTS
  The average forces generated at the initial recording session for uniformly wound springs from GAC International (Bohemia, NY) and 3M Unitek (Monrovia, Calif) were 19.3% to 42.7% and 9.7% to 38.8% below the manufacturers' labeled force levels, respectively. GAC's 100-, 150-, and 200-g stop-wound coils demonstrated statistically and clinically significant stepwise force degradation over the 12-week experimental period (P <0.0001). GAC's uniformly wound light (100 g) coils generated the lowest load-deflection ratios (23.7 g/mm).
  
  
  CONCLUSIONS
  Open coils might need to be compressed by more than one-third of their original length to produce the labeled forces. Uniformly wound coils generally produce lower load-deflection ratios and maximum forces, which are generally more acceptable for tooth movement.
authors.affiliation: Department of Orthodontics, University of Toronto,Toronto, Ontario, Canada. allysonbourke@hotmail.com
authors.forename: Allyson
authors.initials: A
authors.lastname: Bourke
authors.forename: John
authors.initials: J
authors.lastname: Daskalogiannakis
authors.forename: Bryan
authors.initials: B
authors.lastname: Tompson
authors.forename: Philip
authors.initials: P
authors.lastname: Watson
mesh_terms: D019245:Compressive Strength; D003722:Dental Alloys / Q000737:chemistry*; D003799:Dental Stress Analysis; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry; D016382:Orthodontic Appliance Design; D009967:Orthodontic Appliances; D013314:Stress, Mechanical; D014025:Titanium / Q000737:chemistry; D014072:Tooth Abrasion; D014087:Tooth Movement Techniques / Q000295:instrumentation*
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium