title: Torque deformation characteristics of plastic brackets: a comparative study.
abstract: OBJECTIVE
  The purpose of this study was to compare the torque deformation characteristics of seven commercially available plastic brackets, both amongst each other and with stainless steel brackets.
  
  
  METHODS
  Ten brackets each of (1) pure polycarbonate, (2) ceramic reinforced polycarbonate, (3) fiberglass reinforced polycarbonate, (4) ceramic reinforced polycarbonate with metal slot, (5) fiberglass reinforced polycarbonate with metal slot, (6) polyurethane, and (7) polyurethane with metal slot were exposed to torsion in a torquemeter, following an aging process according to ISO 10477. Ten stainless steel brackets served as a control group. Torsion was applied continuously using a material testing machine (Zwick Z2.5, Zwick Materialprüfung, Ulm, Germany).
  
  
  RESULTS
  The results showed within the group of plastic brackets that metal slot reinforced brackets were subject to the lowest degree of deformation, followed by the brackets made of pure polyurethane, pure polycarbonate and fiberglass reinforced polycarbonate. The ceramic reinforced polycarbonate brackets showed the highest deformation under torque stress. The plastic deformation of the ceramic reinforced, fiberglass reinforced and pure polycarbonate brackets started even in the recommended torque range of 10-20 Nmm. The additional ceramic and fiberglass in the plastic brackets investigated in this study did not improve the torque stability of the polycarbonate brackets. The pure polyurethane brackets showed no significant difference from the pure polycarbonate brackets at the moment of 15 Nmm which is the optimal torque for a maxillary incisor.
  
  
  CONCLUSIONS
  A comparison with the stainless steel brackets illustrated that plastic brackets are suited for clinical application only if they have a metal slot.
authors.affiliation: Department of Orthodontics, University of Hamburg, Germany. reza.khonsari@med.uni-goettingen.de
authors.forename: Reza
authors.initials: R
authors.lastname: Sadat-Khonsari
authors.forename: Azita
authors.initials: A
authors.lastname: Moshtaghy
authors.forename: Volker
authors.initials: V
authors.lastname: Schlegel
authors.forename: Bärbel
authors.initials: B
authors.lastname: Kahl-Nieke
authors.forename: Mathias
authors.initials: M
authors.lastname: Möller
authors.forename: Oskar
authors.initials: O
authors.lastname: Bauss
mesh_terms: D001696:Biomechanical Phenomena; D002516:Ceramics; D019544:Equipment Failure Analysis; D005898:Glass; D006801:Humans; D016876:Metal Ceramic Alloys; D016382:Orthodontic Appliance Design; D016910:Orthodontic Brackets; D011108:Polymers; D011140:Polyurethanes; D019415:Torque; D014102:Torsion Abnormality
chemical_list: D016876:Metal Ceramic Alloys; D011108:Polymers; D011140:Polyurethanes; C009753:fiberglass; C017902:lexan