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The plane strain short-rod fracture toughness of six dental amalgams after having been aged in air or exposed to 0.1% sodium chloride for 2 years was investigated. Amalgams were also corroded by polarization. Their fractured chevron surfaces were characterized by scanning electron microscopy. Results revealed an effect from sample diameter. The 6.35 mm diameter high-copper amalgams had a fracture toughness 20-37% higher than that for 11.28 mm diameter size. Only one amalgam, one with indium revealed significantly higher toughness, this being 16% after immersion, whereas the other amalgams showed no significant differences between air and solution conditioning. Increases in toughness were also obtained by polarization-induced corrosion, which after excessive charge transfer, decreased toughness. Chlorine was detected within regions of the fractured chevron planes indicating diffusion to a depth of 300 μm and more. It was thought that chlorides were deposited along Ag-Hg matrix phase grain boundaries inhibiting their decohesive rupturing thereby enhancing toughness.
plane strain, fracture toughness, short-rod, chevron notch, crack jump, smooth crack advance, load versus mouth opening displacement, fractography, microstructure, dental amalgam, corrosion, polarization
Research Associate, Council on Dental Materials, Instruments and Equipment, American Dental Association, Chicago, IL