The relationship between Shore hardness of elastomeric dental materials and Young's modulus.
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.
Meththananda
Iranthi M
IM
IRC in Biomedical Materials, Dental Physical Sciences, Barts and the London School of Medicine and Dentistry, Queen Mary, University of London, London, UK.
Parker
Sandra
S
Patel
Mangala P
MP
Braden
Michael
M
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
D003760:Dental Impression Materials; C022821:Impregum; D012117:Resins, Synthetic; D012826:Silicone Elastomers