title: In-vivo and in-vitro comparison of bond strengths of orthodontic brackets bonded to enamel and debonded at various times.
abstract: BACKGROUND
  The purpose of this study was to measure and compare in-vivo and in-vitro bond strengths of orthodontic brackets bonded to human enamel and debonded at various times. An in-vivo debonding device was validated and used to measure bond strengths in the oral environment.
  
  
  METHODS
  For the in-vitro study, mini-twin metallic premolar brackets (Opti-mesh XRT, Oromco Corp, Glendora, Calif) precoated with Transbond XT composite resin (3M Unitek, Monrovia, Calif) were bonded to 60 extracted premolars. The teeth were divided into 4 groups of 15, and shear bond strength was tested on a universal testing machine at 4 time periods: 10 minutes, 24 hours, 1 week, and 4 weeks. For the in-vivo test, 60 premolars in 22 volunteers (dental students) from King Saud University were bonded with Mini-Twin metallic premolar brackets and divided into 4 groups; bond strengths were measured at 10 minutes, 24 hours, 1 week, and 4 weeks.
  
  
  RESULTS
  Statistical analysis with 1-way ANOVA at P <.05 showed no significant differences among the in-vitro or the in-vivo groups. Two-way ANOVA at P <.05 was used to compare the in-vitro results with the in-vivo results; the in-vivo group had significantly lower mean bond strength values. In addition, survival analysis, used to calculate the probability of bond failure at P <.05, confirmed the significant difference between in-vitro and in-vivo environments.
  
  
  CONCLUSIONS
  Reported bond strength values are not time dependent.
authors.affiliation: Orthodontists Division, King Saud University, Riyad; specialist in orthodontics, Ministry of Health, King Fahad Hospital, Jeddah, Saudi Arabia. manars2@yahoo.com
authors.forename: Manar K A
authors.initials: MK
authors.lastname: Hajrassie
authors.forename: Salwa E
authors.initials: SE
authors.lastname: Khier
mesh_terms: D000704:Analysis of Variance; D001641:Bicuspid; D001840:Dental Bonding / Q000379:methods*; D017005:Dental Debonding / Q000295:instrumentation / Q000379:methods*; D003764:Dental Materials / Q000737:chemistry*; D006801:Humans; D016910:Orthodontic Brackets; D015203:Reproducibility of Results; D019279:Resin Cements / Q000737:chemistry*; D033081:Shear Strength; D016019:Survival Analysis; D013997:Time Factors
chemical_list: D003764:Dental Materials; D019279:Resin Cements; C477790:Transbond XT