title: Effect of multiple debonding sequences on shear bond strength of new stainless steel brackets.
abstract: OBJECTIVE
  This in-vitro study aimed at evaluating the effect of three debonding sequences on the shear bond strength (SBS) of new stainless steel (SS) brackets.
  
  
  METHODS
  Stainless steel twin brackets (0.022-inch, American Orthodontics, Sheboygan, WI, USA) were bonded with light cure adhesive (Transbond XT, 3M Unitek, St. Paul, MN, USA) to 80 newly extracted human premolars after acid etching with 37% phosphoric acid (30 s). Brackets were debonded with a universal testing machine, and new brackets were bonded to teeth using the same adhesive and same manner. This process was repeated twice, and brackets were debonded within 24 h after bonding. The longitudinal changes of average SBS were assessed with the repeated measures ANOVA. Post-hoc tests using the Bonferroni correction were also used to compare the average SBS at three debonding sequences.
  
  
  RESULTS
  The mean SBS decreased significantly after each debonding sequence (P < 0.01). The corresponding mean values (standard deviation, 95% CI) after the first, second, and third debonding sequences were 22.88 MPa (4.08, 21.97-22.79), 19.36 MPa (4.54, 18.62-20.64), and 16.67 MPa (4.27, 15.72-17.62), respectively. There was no significant difference among the adhesive remnant index (ARI) scores of three debonding sequences (χ(2)= 5.067, df = 6, P = 0.53).
  
  
  CONCLUSIONS
  Average SBS after three debonding sequences was significantly decreased, but was above the recommended 5.9-7.8 MPa. In-vivo studies are required to validate the finding of this study.
authors.affiliation: Department of Orthodontics and Dentofacial Deformities Research Center, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Ladan
authors.initials: L
authors.lastname: Eslamian
authors.affiliation: Warwick Dentistry, Warwick Medical School, University of Warwick, Coventry, UK ; NHS England (Locum Orthodontic Consultant), UK.
authors.forename: Ali
authors.initials: A
authors.lastname: Borzabadi-Farahani
authors.affiliation: Private Practice of Orthodontics, Tehran, Iran.
authors.forename: Pegah
authors.initials: P
authors.lastname: Tavakol
authors.affiliation: Private Practice of Orthodontics, Tehran, Iran.
authors.forename: Ali
authors.initials: A
authors.lastname: Tavakol
authors.affiliation: Private Practice of Orthodontics, Tehran, Iran.
authors.forename: Nazila
authors.initials: N
authors.lastname: Amini
authors.affiliation: Warwick Dentistry, Warwick Medical School, University of Warwick, Coventry, UK.
authors.forename: Edward
authors.initials: E
authors.lastname: Lynch
keywords: Adhesive remnant index; enamel; multiple debonding; orthodontic brackets; shear bond strength