title: Force systems yielded by different designs of T-loop.
abstract: OBJECTIVE
  To determine the mechanical characteristics of beta-titanium T-loops with and without helices, with 0 and 180 degree gable bends and constructed from 0.017 inch x 0.025 inch and 0.019 inch x 0.025 inch wire.
  
  
  METHODS
  Forty beta-titanium T-loops were centrally positioned in a universal testing machine. The horizontal force and the moment/force ratios during activation were recorded at 1 mm intervals, up to a maximum of 7 mm. The data were analysed with analysis of variance complemented by the Tukey test for multiple comparisons.
  
  
  RESULTS
  The results demonstrated that the transverse section of the wire had the greatest effect on the horizontal force produced by the loops. Significantly lower levels of horizontal force were obtained with loops made with the smaller 0.017 inch x 0.025 inch wire. Loops with gable bends yielded high moment/force ratios, whereas loops without gable bends had low moment/force ratios. In general, T-loops with helices yielded lower magnitudes of horizontal force and moment/force ratios than plain T-loops.
  
  
  CONCLUSIONS
  The horizontal forces and moment/force ratios generated by plain T-loops with 180 degree gable bends yielded more adequate force systems. Incorporation of helices in the design of T-loops seems to be unnecessary.
authors.affiliation: UNISUL Dental School, Florianópolis, SC, Brazil. guilhermethiesen@yahoo.com.br
authors.forename: Guilherme
authors.initials: G
authors.lastname: Thiesen
authors.forename: Marcus Vinicius Neiva Nunes
authors.initials: MV
authors.lastname: do Rego
authors.forename: Luciane Macedo
authors.initials: LM
authors.lastname: de Menezes
authors.forename: Roberto Hideo
authors.initials: RH
authors.lastname: Shimizu
mesh_terms: D001696:Biomechanical Phenomena; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D016382:Orthodontic Appliance Design; D019516:Orthodontic Space Closure / Q000295:instrumentation*; D009969:Orthodontic Wires; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry
chemical_list: D014025:Titanium