title: Moment-to-force characteristics of preactivated nickel-titanium and titanium-molybdenum alloy symmetrical T-loops.
abstract: BACKGROUND
  This in-vitro study investigated the loads (forces), moments, and moment-to-force ratios (M:F) generated during the activation and deactivation of T closing loops made of rectangular nickel-titanium (NiTi) and titanium-molybdenum alloy (TMA) wires incorporating either 0 degrees, 15 degrees, or 30 degrees of preactivation.
  
  
  METHODS
  T-loop designs were formed in the wires by using a standard template, and, for the NiTi alloys, a temperature of 510 degrees C for 9 minutes was used. Forces and moments of the T-loops were measured at 35.6 degrees C +/- 0.5 degrees C, and these were used to calculate the M:F ratio. Analysis of covariance was used to identify statistical differences between wire alloy and preactivation.
  
  
  RESULTS
  Nonpreactivated (0 degrees) closing loops failed to produce an optimum M:F ratio for translational tooth movement. With increasing preactivation, the M:F ratio increased over the deactivation range for both alloys. The NiTi T-loops produced an M:F ratio of greater than 10:1 over a larger deactivation range (while still delivering a force of 50-150 g) than for the equivalent TMA T-loop. The difference in M:F between the 0 degrees and 30 degrees TMA loops was statistically significant (P <0.000) but not between the equivalent NiTi loops (P <0.136). There was no statistical difference between the NiTi wire alloys at any preactivation angulation.
  
  
  CONCLUSIONS
  Optimum M:F ratios for orthodontic translation can be achieved by using preactivated NiTi and TMA T-loops, with NiTi loops maintaining the optimum M:F ratio over a greater range of deactivation.
authors.affiliation: Discipline of Orthodontics, School of Dentistry, University of Otago, Dunedin, New Zealand.
authors.forename: Darnell
authors.initials: D
authors.lastname: Rose
authors.forename: Andrew
authors.initials: A
authors.lastname: Quick
authors.forename: Michael
authors.initials: M
authors.lastname: Swain
authors.forename: Peter
authors.initials: P
authors.lastname: Herbison
mesh_terms: D000497:Alloys / Q000737:chemistry*; D001696:Biomechanical Phenomena; D003722:Dental Alloys / Q000737:chemistry*; D004548:Elasticity; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry*; D016382:Orthodontic Appliance Design; D016910:Orthodontic Brackets; D009969:Orthodontic Wires; D013193:Stainless Steel / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D014025:Titanium / Q000737:chemistry*; D014087:Tooth Movement Techniques / Q000295:instrumentation; D014159:Transducers
chemical_list: D000497:Alloys; D003722:Dental Alloys; C525450:titanium molybdenum alloy; C040654:titanium nickelide; D013193:Stainless Steel; D009532:Nickel; D014025:Titanium