title: Determination of the force systems produced by different configurations of tear drop orthodontic loops.
abstract: OBJECTIVE
  To determine the mechanical characteristics of teardrop loop with and without helix fabricated using different metal alloy compositions (stainless steel and beta-titanium), submitted to different intensities of bends preactivation (0° and 40°), and with different cross-sectional dimension of the wire used to build these loops (0.017 x 0.025-in and 0.019 x 0.025-in).
  
  
  METHODS
  Eighty loops used to close spaces were submitted to mechanical tests. The magnitudes of horizontal force, the moment/force ratio, and the load/deflection ratio produced by the specimens were quantified. Loops were submitted to a total activation of 5.0 mm and the values were registered for each 1.0 mm of activation. For statistic data analysis, a analysis of variance was performed and a Tukey's Multiple Comparison test was used as supplement, considering a 5% level of significance.
  
  
  RESULTS
  In general, teardrop loops with helix produced lower magnitudes of horizontal force and load/deflection ratio, and higher moment/force ratio than teardrop loops without helix. Among all analyzed variables, metal alloy composition presented greater influence in the horizontal force and in the load/deflection ratio. The moment/force ratio showed to be more influenced by the preactivation of loops for space closure.
authors.affiliation: UNISUL-SC, Brazil. guilhermethiesen@yahoo.com.br
authors.forename: Guilherme
authors.initials: G
authors.lastname: Thiesen
authors.forename: Roberto Hideo
authors.initials: RH
authors.lastname: Shimizu
authors.forename: Caio Vinicius Martins
authors.initials: CV
authors.lastname: do Valle
authors.forename: Karyna Martins
authors.initials: KM
authors.lastname: do Valle-Corotti
authors.forename: Jefferson Ricardo
authors.initials: JR
authors.lastname: Pereira
authors.forename: Paulo Cesar Rodrigues
authors.initials: PC
authors.lastname: Conti
mesh_terms: D000704:Analysis of Variance; D003722:Dental Alloys; D008422:Materials Testing / Q000379:methods; D016382:Orthodontic Appliance Design; D019516:Orthodontic Space Closure / Q000295:instrumentation* / Q000379:methods; D009969:Orthodontic Wires; D009971:Orthodontics, Corrective / Q000295:instrumentation* / Q000379:methods; D013314:Stress, Mechanical
chemical_list: D003722:Dental Alloys
keywords: Biomechanics; Orthodontic space closure; Orthodontics; Tooth extraction