title: Thermomechanical properties of nickel-titanium closed-coil springs and their implications for clinical practice.
abstract: BACKGROUND
  The aim was to study nickel-titanium closed-coil springs in a clinically relevant test setting with respect to the accuracy of the "preactivation" for nickel-titanium closed-coil springs application and whether it is possible to keep activation forces constant during the whole time of treatment.
  
  
  METHODS
  We tested 10 types of springs from 5 manufacturers under clinically relevant conditions, allowing us to study the interactions between load and temperature over time. Hystereses were compared using t tests.
  
  
  RESULTS
  Springs with a large mechanical hysteresis also showed a large thermal hysteresis. After heating shock, these springs showed intensive force spikes and persistent high loads. Some springs showed negligible thermal and mechanical hysteresis. Such springs never showed any clinically significant persistent high loads.
  
  
  CONCLUSIONS
  Springs with a large hysteresis were unable to keep activation forces constant during the whole time of treatment even after any preactivation, and they might cause persistently high loads and possibly overloading. Only springs with minor hysteresis, low temperature dependence of force, and a clinically useful plateau have the following clinical advantages: reduced chair time, optimal rates of tooth movement, reproducible clinical results, and conservation of anchorage.
authors.affiliation: Assistant professor, Department of Medical Biophysics, Charles University, Prague, Faculty of Medicine, Hradec Kralove, Czech Republic. Electronic address: bezrouka@lfhk.cuni.cz.
authors.forename: Ales
authors.initials: A
authors.lastname: Bezrouk
authors.affiliation: Private practice, Hradec Kralove, Czech Republic.
authors.forename: Libor
authors.initials: L
authors.lastname: Balsky
authors.affiliation: Postgraduate student, Department of Medical Biophysics, Charles University, Prague, Faculty of Medicine, Hradec Kralove, Czech Republic.
authors.forename: Martin
authors.initials: M
authors.lastname: Smutny
authors.affiliation: Assistant professor, Department of Medical Biophysics, Charles University, Prague, Faculty of Medicine, Hradec Kralove, Czech Republic.
authors.forename: Iva
authors.initials: I
authors.lastname: Selke Krulichova
authors.affiliation: Assistant professor, Department of Medical Biophysics, Charles University, Prague, Faculty of Medicine, Hradec Kralove, Czech Republic.
authors.forename: Jiri
authors.initials: J
authors.lastname: Zahora
authors.affiliation: Associate professor and chair, Department of Medical Biophysics, Charles University, Prague, Faculty of Medicine, Hradec Kralove, Czech Republic.
authors.forename: Josef
authors.initials: J
authors.lastname: Hanus
authors.affiliation: Head, Department of Neurosurgery, National Hospital, Oslo, Norway.
authors.forename: Torstein R
authors.initials: TR
authors.lastname: Meling
mesh_terms: D003080:Cold Temperature; D003722:Dental Alloys / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D004548:Elasticity; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D055595:Mechanical Phenomena; D009532:Nickel / Q000737:chemistry*; D009969:Orthodontic Wires; D013314:Stress, Mechanical; D013816:Thermodynamics; D014025:Titanium / Q000737:chemistry*; D054159:Torsion, Mechanical
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium