title: Self-corrective T-loop design for differential space closure.
abstract: BACKGROUND
  The current approach to measuring T-loop force systems in patients requiring differential anchorage does not consider active unit angulations and steps during space closure. The angulations and steps during movement introduced by rotation can considerably modify the force system acting on the teeth.
  
  
  METHODS
  In this study, geometric modifications were determined during controlled tipping of the 6 anterior teeth, where there was no movement of the posterior teeth, thus configuring a type A anchorage situation.
  
  
  RESULTS
  An optimal beta-titanium alloy 0.017 x 0.025-in T-loop spring was designed by using a simulation performed with LOOP software (dHAL Orthodontic Software, Athens, Greece) to allow compensation for anterior unit-position effect on the final force system. The force systems produced by this T-loop spring with and without geometric correction of the brackets have significant differences that should be considered in the segmented arch approach to space closure.
  
  
  CONCLUSIONS
  The effects of steps, angles, and vertical forces were combined to produce an ideal T-loop design that would provide a more determinate force system. The effects and force systems are estimates based on simplified locations of the centers of resistance, assuming relatively constant behavior of the centers of rotation. These simplifications might differ slightly from what happens in vivo. The finite element method or an accurate spring tester capable of reproducing the geometric corrections should be used to ensure a precise force system.
authors.affiliation: Department of Oral Facial Development, Orthodontics Section, Indiana University School of Dentistry, Indianapolis, IN 46202, USA. rviecill@iupui.edu [corrected]
authors.forename: Rodrigo F
authors.initials: RF
authors.lastname: Viecilli
mesh_terms: D001696:Biomechanical Phenomena; D003198:Computer Simulation; D003481:Cuspid / Q000473:pathology; D003722:Dental Alloys / Q000737:chemistry; D006801:Humans; D007180:Incisor / Q000473:pathology; D008954:Models, Biological; D016382:Orthodontic Appliance Design; D016910:Orthodontic Brackets; D019516:Orthodontic Space Closure / Q000295:instrumentation*; D009969:Orthodontic Wires; D012399:Rotation; D013314:Stress, Mechanical; D014025:Titanium / Q000737:chemistry
chemical_list: D003722:Dental Alloys; C023988:beta titanium; D014025:Titanium