title: Effect of time and pH on physical-chemical properties of orthodontic brackets and wires.
abstract: OBJECTIVE
  To test the hypothesis that treatment time, debris/biofilm, and oral pH have an influence on the physical-chemical properties of orthodontic brackets and arch wires.
  
  
  METHODS
  One hundred twenty metal brackets were evaluated. They were divided into four groups (n  =  30) according to treatment time: group C (control) and groups T12, T24, and T36 (brackets recovered after 12, 24, and 36 months of treatment, respectively). Rectangular stainless-steel arch wires that remained in the oral cavity for 12 to 24 months were also analyzed. Dimensional stability, surface morphology, composition of brackets, resistance to sliding of the bracket-wire set, surface roughness of wires, and oral pH were analyzed. One-way analysis of variance, followed by a Tukey multiple comparisons test, was used for statistical analysis (P < .05).
  
  
  RESULTS
  Carbon and oxygen were shown to be elements that increased expressively and in direct proportion to time, and there was a progressive increase in the coefficient of friction and roughness of wires as a function of time of clinical use after 36 months. Oral pH showed a significant difference between group T36 and its control (P  =  .014).
  
  
  CONCLUSIONS
  The hypothesis was partially accepted: treatment time and biofilm and debris accumulation in bracket slots were shown to have more influence on the degradation process and frictional force of these devices than did oral pH.
authors.affiliation: a Master's student, Graduate Program in Dentistry, Federal University of Paraíba, João Pessoa, PB, Brazil.
authors.forename: Aretha Aliny Ramos
authors.initials: AA
authors.lastname: Dos Santos
authors.forename: Matheus Melo
authors.initials: MM
authors.lastname: Pithon
authors.forename: Fabíola Galbiatti Carvalho
authors.initials: FG
authors.lastname: Carlo
authors.forename: Hugo Lemes
authors.initials: HL
authors.lastname: Carlo
authors.forename: Bruno Alessandro Silva Guedes
authors.initials: BA
authors.lastname: de Lima
authors.forename: Tibério Andrade
authors.initials: TA
authors.lastname: Dos Passos
authors.forename: Rogério
authors.initials: R
authors.lastname: Lacerda-Santos
mesh_terms: D000293:Adolescent; D000328:Adult; D018441:Biofilms; D002244:Carbon / Q000032:analysis; D055598:Chemical Phenomena; D003722:Dental Alloys / Q000737:chemistry*; D003741:Dental Deposits / Q000737:chemistry; D004577:Electron Probe Microanalysis; D017276:Friction; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D016910:Orthodontic Brackets / Q000382:microbiology; D009969:Orthodontic Wires / Q000382:microbiology; D010100:Oxygen / Q000032:analysis; D012463:Saliva / Q000502:physiology; D013193:Stainless Steel / Q000737:chemistry; D013499:Surface Properties; D013997:Time Factors; D055815:Young Adult
chemical_list: D003722:Dental Alloys; D013193:Stainless Steel; D002244:Carbon; D010100:Oxygen
keywords: Brackets; Orthodontic wires; Properties