title: Effect of activation and preactivation on the mechanical behavior and neutral position of stainless steel and beta-titanium T-loops.
abstract: OBJECTIVE
  To quantify, for each activation, the effect of preactivations of differing distribution and intensity on the neutral position of T-loops (7-mm height), specifically the horizontal force, moment to force (M/F) ratio, and load to deflection ratio.
  
  
  METHODS
  A total 100 loops measuring 0.017 × 0.025 inches in cross-section were divided into two groups (n = 50 each) according to composition, either stainless steel or beta-titanium. The two groups were further divided into five subgroups, 10 loops each, corresponding to the five preactivations tested: preactivations with occlusal distribution (0°, 20°, and 40°), gingival distribution (20°), and occlusal-gingival distribution (40°). The loops were subjected to a total activation of 6-mm with 0.5-mm iterations. Statistical analysis was performed using comprised ANOVA and Bonferoni multiple comparison tests, with a significance level of 5%.
  
  
  RESULTS
  The location and intensity of preactivation influenced the force intensity. For the M/F ratio, the highest value achieved without preactivation was lower than the height of the loop. Without preactivation, the M/F ratio increased with activation, while the opposite effect was observed with preactivation. The increase in the M/F ratio was greater when the preactivation distribution was partially or fully gingival.
  
  
  CONCLUSIONS
  Depending on the preactivation distribution, displacement of uprights is higher or lower than the activation, which is a factor to consider in clinical practice.
authors.affiliation: Department of Orthodontics, Faculty of Dental Medicine, University of Porto, Porto, Portugal.
authors.forename: Saúl Matos
authors.initials: SM
authors.lastname: de Castro
authors.affiliation: Department of Mechanical Engineering, University of Aveiro, Aveiro, Portugal.
authors.forename: Rui
authors.initials: R
authors.lastname: Moreira
authors.affiliation: Department of Production and Systems Engineering, School of Engineering, University of Minho, Braga, Portugal.
authors.forename: Ana Cristina
authors.initials: AC
authors.lastname: Braga
authors.affiliation: Department of Orthodontics, Faculty of Dental Medicine, University of Porto, Porto, Portugal.
authors.forename: Afonso Pinhão
authors.initials: AP
authors.lastname: Ferreira
authors.affiliation: Department of Orthodontics, Faculty of Dental Medicine, University of Porto, Porto, Portugal.
authors.forename: Maria Cristina
authors.initials: MC
authors.lastname: Pollmann
keywords: Neutral position; Preactivation; T-loop