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What is Amalgam exhibits a Poisson’s ratio of and explain in detail?
Most rigid materials, such as enamel, dentin, amalgam, and dental composite, exhibit a Poisson’s ratio of about 0.3. Brittle substances such as hard gold alloys and dental amalgam show little  permanent reduction in cross section during a tensile test.
More ductile materials such as soft gold alloys, which are high in gold content, show a higher degree of reduction in cross-sectional area and higher Poisson’s ratios. 
Rubber has a Poisson’s ratio of nearly 0.5. 
Cork exhibits little lateral expansion under compression and has a Poisson’s ratio close to 0. 
This property has made cork a common material for sealing wine bottles.
Ref:Craig’s Restorative Dentistry ed 14th pg 36