title: Physical and chemical properties of orthodontic brackets after 12 and 24 months: in situ study.
abstract: OBJECTIVE
  The aim of this article was to assess how intraoral biodegradation influenced the surface characteristics and friction levels of metallic brackets used during 12 and 24 months of orthodontic treatment and also to compare the static friction generated in these brackets with four different methods of the ligation of orthodontic wires.
  
  
  METHODS
  Seventy premolar brackets as received from the manufacturer and 224 brackets that were used in previous orthodontic treatments were evaluated in this experiment. The surface morphology and the composition of the deposits found in the brackets were evaluated with rugosimetry, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Friction was analyzed by applying tensile tests simulating sliding mechanics with a 0.019x0.025" steel wire. The static friction levels produced by the following ligation methods were evaluated: loosely attached steel ligature around all four bracket wings, steel ligature attached to only two wings, conventional elastomeric ligation around all 4 bracket wings, and non-conventional Slide® elastomeric ligature.
  
  
  RESULTS
  The results demonstrated the presence of biodegradation effects such as corrosion pits, plastic deformation, cracks, and material deposits. The main chemical elements found on these deposits were Carbon and Oxygen. The maximum friction produced by each ligation method changed according to the time of intraoral use. The steel ligature loosely attached to all four bracket wings produced the lowest friction levels in the new brackets. The conventional elastic ligatures generated the highest friction levels. The metallic brackets underwent significant degradation during orthodontic treatment, showing an increase in surface roughness and the deposit of chemical elements on the surface.
  
  
  CONCLUSIONS
  The levels of static friction decreased with use. The non-conventional elastic ligatures were the best alternative to reduce friction.
authors.affiliation: Graduate Program in Orthodontics, Pontifical Catholic University of Minas Gerais, Belo Horizonte, MG, Brazil.
authors.forename: Bernardo de Azevedo Bahia
authors.initials: Bde A
authors.lastname: Mendes
authors.affiliation: Center for Development of Nuclear Technology, National Nuclear Energy Commission CDTN, CNEN, Belo Horizonte, MG, Brazil.
authors.forename: Ricardo Alberto
authors.initials: RA
authors.lastname: Neto Ferreira
authors.affiliation: Department of Orthodontics, Southwest Bahia State University - UESB, Jequié, BA, Brazil.
authors.forename: Matheus Melo
authors.initials: MM
authors.lastname: Pithon
authors.affiliation: Graduate Program in Orthodontics, Pontifical Catholic University of Minas Gerais, Belo Horizonte, MG, Brazil.
authors.forename: Martinho Campolina Rebello
authors.initials: MC
authors.lastname: Horta
authors.affiliation: Graduate Program in Orthodontics, Pontifical Catholic University of Minas Gerais, Belo Horizonte, MG, Brazil.
authors.forename: Dauro Douglas
authors.initials: DD
authors.lastname: Oliveira
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D020724:Elastomers / Q000737:chemistry; D019544:Equipment Failure Analysis / Q000379:methods*; D017276:Friction; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D016382:Orthodontic Appliance Design; D016910:Orthodontic Brackets; D009969:Orthodontic Wires; D013052:Spectrometry, X-Ray Emission; D013193:Stainless Steel / Q000737:chemistry; D018709:Statistics, Nonparametric; D013499:Surface Properties; D013997:Time Factors
chemical_list: D020724:Elastomers; D013193:Stainless Steel