title: The relationship between Shore hardness of elastomeric dental materials and Young's modulus.
abstract: OBJECTIVE
  Hardness of elastomers can be directly related to Young's modulus, a relationship that was investigated in detail by Gent in a paper in 1958. The aim of this study was to test this relationship for 13 dental elastomers (12 silicone and 1 polyether) using the equation derived by Gent and one from BS 903 (1950) that accounts for departures at low values.
  
  
  METHODS
  The dental elastomers were subjected to tensile testing and Shore A scale hardness measurements. Young's moduli were calculated from the hardness values using the Gent equation and the BS 903 equation. These calculated values were then compared with values derived experimentally from the tensile tests.
  
  
  RESULTS
  Hardness values were in the range 30.2 (+/-0.5)-62.9 (+/-0.8) with the corresponding calculated modulus values in the range 1.1-4.1MPa and 0.9-4.3MPa for the Gent and modified equations, respectively. Young's modulus values derived from the tensile data were in the range 0.8 (+/-0.3)-4.1 (+/-0.3)MPa, showing good agreement with those calculated from the hardness values. Providing viscoelastic creep is minimal during the duration of the test, there is a reasonably well-defined relationship between Shore hardness and Young's modulus in the hardness range studied.
  
  
  CONCLUSIONS
  Simple, non-destructive hardness measurements can be used to determine Young's modulus values. Such values are needed in any calculations of stress distributions in soft lining materials, e.g. by FEA.
authors.affiliation: IRC in Biomedical Materials, Dental Physical Sciences, Barts and the London School of Medicine and Dentistry, Queen Mary, University of London, London, UK.
authors.forename: Iranthi M
authors.initials: IM
authors.lastname: Meththananda
authors.forename: Sandra
authors.initials: S
authors.lastname: Parker
authors.forename: Mangala P
authors.initials: MP
authors.lastname: Patel
authors.forename: Michael
authors.initials: M
authors.lastname: Braden
mesh_terms: D003760:Dental Impression Materials; D003799:Dental Stress Analysis / Q000379:methods*; D003822:Denture Liners; D055119:Elastic Modulus; D006244:Hardness; D008422:Materials Testing; D012117:Resins, Synthetic; D012826:Silicone Elastomers; D013718:Tensile Strength; D014783:Viscosity
chemical_list: D003760:Dental Impression Materials; C022821:Impregum; D012117:Resins, Synthetic; D012826:Silicone Elastomers