title: Suitability of a shear punch test for dental restorative materials.
abstract: OBJECTIVE
  The aim of the study was to evaluate the suitability of a shear punch test for determining the mechanical properties of dental restorative materials. The method was evaluated by measuring and comparing the shear punch strength of seven different restorative materials, that is amalgam, composite resin, compomer, composite containing pre-reacted glass ionomer filler, resin modified glass ionomer, glass ionomer and polycarboxylate cement.
  
  
  METHODS
  The effects of specimen restraining conditions, specimen thickness and test speed on the shear punch strength were evaluated using polycarboxylate cement and two different equipment set-ups. Using the preferred testing regime as determined in the preliminary experiments, the shear punch strength of seven different materials were measured and compared. Twenty disc specimens, 0.5mm thick and 10mm diameter, were prepared for each material, restrained within the test equipment and tested at a speed of 1.0mm/min.
  
  
  RESULTS
  The shear punch strength increased as the torque used for restraining a specimen was increased. There was no difference in shear punch strength for specimens of different thickness. The greatest shear punch strength was obtained at the test speed of 1.0mm/min. The shear punch strength values decreased in the order composite>composite containing pre-reacted glass ionomer filler>amalgam>compomer>resin-modified glass ionomer>glass ionomer>polycarboxylate. A difference in the shear punch strength for seven different kinds of restorative materials clearly emerged. Specimen fracture occurred by circumferential cracking for the shear-punch test. However, for some glass ionomer and amalgam specimens radial cracking was also observed.
  
  
  CONCLUSIONS
  This study suggests that the simple test described is suitable for standardization purposes.
authors.affiliation: Dental Materials Science Unit, Department of Restorative Dentistry, The Dental School, University of Newcastle upon Tyne, Framlington Place, Newcastle upon Tyne NE2 4BW, UK.
authors.forename: R
authors.initials: R
authors.lastname: Nomoto
authors.forename: T E
authors.initials: TE
authors.lastname: Carrick
authors.forename: J F
authors.initials: JF
authors.lastname: McCabe
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry; D016001:Confidence Intervals; D003723:Dental Amalgam / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis / Q000295:instrumentation / Q000379:methods; D005899:Glass Ionomer Cements / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D010865:Pilot Projects; D011076:Polycarboxylate Cement / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013499:Surface Properties; D019415:Torque
chemical_list: D003188:Composite Resins; D003764:Dental Materials; D005899:Glass Ionomer Cements; D011076:Polycarboxylate Cement; D019279:Resin Cements; D003723:Dental Amalgam