title: Mechanical behavior and clinical application of nickel-titanium closed-coil springs under different stress levels and mechanical loading cycles.
abstract: BACKGROUND
  The main advantage of superelastic nickel-titanium (NiTi) products is their unique characteristic of force plateaus, which allow for clinically precise control of the force. The aims of this study were to define the mechanical characteristics of several currently available closed-coil retraction springs and to compare these products.
  
  
  METHODS
  A universal test frame was used to acquire force-deflection diagrams of 24 NiTi closed-coil springs at body temperature. Data analysis was performed with the superelastic algorithm. Also, the influence of temperature cycles and mechanical microcycles simulating ingestion of different foods and mastication, respectively, were considered.
  
  
  RESULTS
  Mechanical testing showed significant differences between the various spring types (ANOVA, < or =0.05), but constant intrabatch behavior (t test). Four groups were formed according to the mechanical properties of the springs: strong superelasticity without bias stress, weak superelasticity without bias stress, strong superelasticity with bias stress, and weak superelasticity with bias stress.
  
  
  CONCLUSIONS
  In sliding mechanics, the strongly superelastic closed-coil springs with preactivation are recommended. In addition, we found that the oral environment seems to have only a minor influence on their mechanical properties.
authors.affiliation: Department of Orthodontics, Munich University Medical Center, Munich, Germany. [corrected]
authors.forename: Andrea
authors.initials: A
authors.lastname: Wichelhaus
authors.forename: Lorenz
authors.initials: L
authors.lastname: Brauchli
authors.forename: Judith
authors.initials: J
authors.lastname: Ball
authors.forename: Matthias
authors.initials: M
authors.lastname: Mertmann
mesh_terms: D000465:Algorithms; D000497:Alloys / Q000737:chemistry; D001831:Body Temperature; D003722:Dental Alloys / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D055119:Elastic Modulus; D005502:Food; D006801:Humans; D008409:Mastication; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry*; D016382:Orthodontic Appliance Design; D009969:Orthodontic Wires; D013314:Stress, Mechanical; D013718:Tensile Strength; D014025:Titanium / Q000737:chemistry*
chemical_list: D000497:Alloys; D003722:Dental Alloys; C040654:titanium nickelide; C013616:nitinol; D009532:Nickel; D014025:Titanium