title: Effect of adhesive resin flexibility on enamel fracture during metal bracket debonding: an ex vivo study.
abstract: OBJECTIVE
  To test the null hypothesis that neither the flexural properties of orthodontic adhesive resins nor the enamel pre-treatment methods would affect metal bracket debonding behaviours, including enamel fracture.
  
  
  METHODS
  A dimethacrylate-based resin (Transbond XT, TX) and two methyl methacrylate (MMA)-based resins (Super-Bond C&B, SB; an experimental light-cured resin, EXP) were tested. Flexural strength and flexural modulus for each resin were measured by a three-point-bending test. Metal brackets were bonded to human enamel pretreated with total-etch (TE) or self-etch adhesive using one of the three resins (a total of six groups, n = 15). After 24 hours of storage in water at 37°C, a shear bond strength (SBS) test was performed using the wire loop method. After debonding, remaining resin on the enamel surfaces and occurrence of enamel fracture were assessed. Statistical significance was set at P < 0.05.
  
  
  RESULTS
  The two MMA resins exhibited substantially lower flexural strength and modulus values than the TX resin. The mean SBS values of all groups (10.15-11.09MPa) were statistically equivalent to one another (P > 0.05), except for the TE-TX group (13.51MPa, P < 0.05). The two EXP groups showed less resin remnant. Only in the two TX groups were enamel fractures observed (three cases for each group).
  
  
  CONCLUSIONS
  The results were drawn only from ex vivo experiments.
  
  
  CONCLUSIONS
  The hypothesis is rejected. This study suggests that a more flexible MMA resin is favourable for avoiding enamel fracture during metal bracket debonding.
authors.affiliation: Departments of *Conservative Dentistry.
authors.forename: Young Kyung
authors.initials: YK
authors.lastname: Kim
authors.affiliation: Orthodontics, and.
authors.forename: Hyo-Sang
authors.initials: HS
authors.lastname: Park
authors.affiliation: Dental Biomaterials, School of Dentistry, Kyungpook National University, Daegu, Korea.
authors.forename: Kyo-Han
authors.initials: KH
authors.lastname: Kim
authors.affiliation: Dental Biomaterials, School of Dentistry, Kyungpook National University, Daegu, Korea tykwon@knu.ac.kr.
authors.forename: Tae-Yub
authors.initials: TY
authors.lastname: Kwon
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods; D001896:Boron Compounds / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D003722:Dental Alloys / Q000737:chemistry; D017005:Dental Debonding / Q000009:adverse effects*; D003743:Dental Enamel / Q000293:injuries*; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D006801:Humans; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D008768:Methylmethacrylates / Q000737:chemistry; D016910:Orthodontic Brackets; D018583:Pliability; D019904:Polymethyl Methacrylate / Q000737:chemistry; D011897:Random Allocation; D019279:Resin Cements / Q000737:chemistry*; D033081:Shear Strength; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014082:Tooth Fractures / Q000209:etiology*; D014867:Water / Q000737:chemistry
chemical_list: D001896:Boron Compounds; D003188:Composite Resins; D003722:Dental Alloys; D008689:Methacrylates; D008768:Methylmethacrylates; D019279:Resin Cements; C429625:Transbond Plus Self-Etching Primer; C477790:Transbond XT; C516047:Transbond XT Light Cure Adhesive Primer; D014867:Water; D019904:Polymethyl Methacrylate; C049495:Super-bond