title: Investigating failure behavior and origins under supposed "shear bond" loading.
abstract: OBJECTIVE
  This study evaluated failure behavior when resin-composite cylinders bonded to dentin fractured under traditional "shear" testing. Failure was assessed by scaling of failure loads to changes in cylinder radii and fracture surface analysis. Three stress models were examined including failure by: bonded area; flat-on-cylinder contact; and, uniformly-loaded, cantilevered-beam.
  
  
  METHODS
  Nine 2-mm dentin occlusal dentin discs for each radii tested were embedded in resin and bonded to resin-composite cylinders; radii (mm)=0.79375; 1.5875; 2.38125; 3.175. Samples were "shear" tested at 1.0mm/min. Following testing, disks were finished with silicone carbide paper (240-600grit) to remove residual composite debris and tested again using different radii. Failure stresses were calculated for: "shear"; flat-on-cylinder contact; and, bending of a uniformly-loaded cantilevered beam. Stress equations and constants were evaluated for each model. Fracture-surface analysis was performed.
  
  
  RESULTS
  Failure stresses calculated as flat-on-cylinder contact scaled best with its radii relationship. Stress equation constants were constant for failure from the outside surface of the loaded cylinders and not with the bonded surface area or cantilevered beam. Contact failure stresses were constant over all specimen sizes. Fractography reinforced that failures originated from loaded cylinder surface and were unrelated to the bonded surface area.
  
  
  CONCLUSIONS
  "Shear bond" testing does not appear to test the bonded interface. Load/area "stress" calculations have no physical meaning. While failure is related to contact stresses, the mechanism(s) likely involve non-linear damage accumulation, which may only indirectly be influenced by the interface.
authors.affiliation: School of Dental Medicine University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030-1615, United States.
authors.forename: Hassam
authors.initials: H
authors.lastname: Sultan
authors.affiliation: School of Dental Medicine University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030-1615, United States. Electronic address: Kelly@uchc.edu.
authors.forename: J Robert
authors.initials: JR
authors.lastname: Kelly
authors.affiliation: School of Dental Medicine University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030-1615, United States.
authors.forename: Reza B
authors.initials: RB
authors.lastname: Kazemi
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D001840:Dental Bonding; D003799:Dental Stress Analysis / Q000379:methods*; D003804:Dentin / Q000737:chemistry*; D017220:Dentin-Bonding Agents / Q000737:chemistry*; D008422:Materials Testing; D009716:Numerical Analysis, Computer-Assisted; D033081:Shear Strength; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D003188:Composite Resins; D017220:Dentin-Bonding Agents
keywords: Bond testing; Dentin; Resin-based composite; Shear stress