title: The influence of cyclic shear fatigue on the bracket-adhesive-enamel complex: an in vitro study.
abstract: OBJECTIVE
  To describe the effect of fatigue on the strength of the bracket-adhesive-enamel complex and characterize the fatigue behavior of the materials tested.
  
  
  METHODS
  Upper central incisor brackets (Discovery(®), Dentaurum) were bonded with a light-curing (Transbond XT™, 3M Unitek) and a chemically-curing adhesive (Concise™, 3M Unitek) on bovine teeth embedded in cylindrical resign bases and stored in water at 37(±2)°C for 24 (±2)h. The first 15 specimens were tested with a universal testing machine ZMART.PRO(®) (Zwick GmbH & Co. KG, Ulm, Germany) for ultimate shear bond strength according to the DIN-13990-2-standard. The remaining three groups of 20 specimens underwent fatigue staircase testing of 100, 1000 and 3000 cycles at 1Hz with a self-made testing machine. The survived specimens were subjected to shear strength testing.
  
  
  RESULTS
  The fatigued specimens showed decreased shear strength with both adhesives at all cycle levels. The shear strength after fatigue for 100, 1000 and 3000 cycles was in the Concise™-groups 34.8%, 59.0%, 47.3% and in the Transbond™ XT-groups 33.6%, 23.1%, 27.3% relative to the ultimate shear strength. The fatigue life of the Concise™-groups decreased with increasing stress and Transbond™ XT showed lower fatigue ratio with no obvious trend. The specimens bonded with Transbond™ XT showed typically favorable fracture modes in contrary to Concise™.
  
  
  CONCLUSIONS
  Fatigue of the bracket-adhesive-enamel complex decreased its shear strength. The staircase method can provide a standardized experimental protocol for fatigue studies, however testing at various cycle numbers is recommended.
authors.affiliation: Department of Orthodontics, University of Bonn, Germany. nikolaos.daratsianos@uni-bonn.de
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Daratsianos
authors.forename: Ena
authors.initials: E
authors.lastname: Musabegovic
authors.forename: Susanne
authors.initials: S
authors.lastname: Reimann
authors.forename: Manfred
authors.initials: M
authors.lastname: Grüner
authors.forename: Andreas
authors.initials: A
authors.lastname: Jäger
authors.forename: Christoph
authors.initials: C
authors.lastname: Bourauel
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002417:Cattle; D001840:Dental Bonding / Q000379:methods*; D003738:Dental Cements / Q000737:chemistry*; D003743:Dental Enamel / Q000737:chemistry*; D003799:Dental Stress Analysis; D019544:Equipment Failure Analysis; D008422:Materials Testing; D016910:Orthodontic Brackets; D033081:Shear Strength
chemical_list: D003738:Dental Cements