title: Effect of specimen gripping device, geometry and fixation method on microtensile bond strength, failure mode and stress distribution: laboratory and finite element analyses.
abstract: OBJECTIVE
  Innumerous modifications have been proposed for the microtensile test since its introduction; however, testing parameters are not often well described and wide variations in bond strength are commonly reported. The aim of this study was to evaluate the effect of the test specimen's gripping device, specimen geometry and fixation method on microtensile bond strength, failure mode, and stress distribution when using an etch-and-rinse 2-step adhesive system bonded to human dentin.
  
  
  METHODS
  Resin-based composite bonded to occlusal dentin from 21 human molars was used to fabricate dumbbell- and stick-shaped test specimens which were divided into three groups: Di - dumbbell-specimens placed in a Dircks device; GeS - stick-specimens gripped in a Geraldeli's device with Superglue; GeZ - stick-specimens gripped in a Geraldeli's device with Zapit. Specimens were tested to failure in tensile mode and the failure mode was examined under stereomicroscopy and fracture initiation sites were verified by scanning electron microscopy and energy dispersive X-ray spectroscopy. Three-dimensional models of each device/specimen were created and finite element calculations were performed.
  
  
  RESULTS
  The effect of the gripping devices on the bond strength was not significant, unless the bond test areas were normalized. The failure mode was influenced by the type of device. Dircks device was less sensitive to human error than Geraldeli's, and produced a more uniform stress distribution at the dumbbell specimen adhesive layer than did the Geraldeli's device at the stick layer.
  
  
  CONCLUSIONS
  Microtensile testing parameters can directly influence the results and consequently inter-study comparisons.
authors.affiliation: Biomechanics Research Group, Department of Operative Dentistry and Dental Materials, School of Dentistry, Federal University of Uberlândia, MG, Brazil.
authors.forename: Luís H A
authors.initials: LH
authors.lastname: Raposo
authors.forename: Steven R
authors.initials: SR
authors.lastname: Armstrong
authors.forename: Rodrigo R
authors.initials: RR
authors.lastname: Maia
authors.forename: Fang
authors.initials: F
authors.lastname: Qian
authors.forename: Saulo
authors.initials: S
authors.lastname: Geraldeli
authors.forename: Carlos J
authors.initials: CJ
authors.lastname: Soares
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods; D000269:Adhesives / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D003487:Cyanoacrylates / Q000737:chemistry; D001840:Dental Bonding; D003738:Dental Cements / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry; D003799:Dental Stress Analysis / Q000295:instrumentation*; D003804:Dentin / Q000648:ultrastructure*; D004867:Equipment Design; D020342:Finite Element Analysis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D021621:Imaging, Three-Dimensional / Q000379:methods; D008422:Materials Testing / Q000295:instrumentation*; D008689:Methacrylates / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D019904:Polymethyl Methacrylate / Q000737:chemistry; D012464:Saliva, Artificial / Q000737:chemistry; D013052:Spectrometry, X-Ray Emission; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013718:Tensile Strength; D013997:Time Factors
chemical_list: D000269:Adhesives; C554641:Adper single bond 2; D003188:Composite Resins; D003487:Cyanoacrylates; D003738:Dental Cements; D003764:Dental Materials; C444701:Filtek Z250; D008689:Methacrylates; D012464:Saliva, Artificial; C073912:Zapit; C558475:poly(ethylcyanoacrylate); C038690:Loctite; D019904:Polymethyl Methacrylate