title: Effect of corrosion on the strength of dental silver amalgam.
abstract: OBJECTIVE
  To characterize the effect of crevice corrosion on the strength of dental silver amalgam as determined by the Hertzian 'ball on disc' method, with a view to providing a test method for use in standards compliance testing.
  
  
  METHODS
  Sixteen dental silver amalgam products were tested using the 'ball on disc' protocol at 30 d after setting at 37°C in air or immersed in artificial saliva at pH 6.2. The mixed materials were packed into a tapered steel disc mold (10 mm diameter, 3 mm thick) resting on a glass surface, slightly overfilled and carved level with a sharp edge, then ejected at ∼10 min and placed immediately into an incubator at 37°C. For corrosion specimens, the disc was laid on a flat polystyrene surface, immersed in artificial saliva, to create a spontaneous crevice corrosion cell. Testing was in Hertzian mode, using a 20 mm steel ball, with the specimen resting on a disc of glass-filled polyamide (E=10 GPa) at a cross-head speed of 0.2 mm/min on a universal testing machine (E3000, Instron). The load at first crack was recorded, as was the number of radial cracks produced.
  
  
  RESULTS
  Radial cracking into 2-4 pieces, in a clinically relevant (non-explosive) mode was observed in all cases. On average, corrosion caused a decrease in load at failure of ∼10%, although the interaction with alloy (analysis of variance) was significant (P∼0.03) indicating variation between products. Comparison of the 30 d dry (uncorroded) results with those at 24h obtained earlier showed that there was highly significant increase on average (P∼5×10(-12)), but again a significant variation between products (P∼5×10(-6)), the maximum effect being +22%.
  
  
  CONCLUSIONS
  The ball-on-disc test provides a facile means of ascertaining the sensitivity of dental silver amalgam to corrosion under clinically relevant conditions, and is viable as a standards compliance test.
authors: Dental Materials Science, Dept of Bioclinical Sciences, Faculty of Dentistry, Kuwait University, Kuwait. b.w.darvell@hsc.edu.kw
authors: B W
authors: BW
authors: Darvell
mesh_terms: D000704:Analysis of Variance; D003343:Corrosion; D003723:Dental Amalgam / Q000737:chemistry*; D008422:Materials Testing / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D012464:Saliva, Artificial / Q000737:chemistry*; D012834:Silver / Q000737:chemistry*
chemical_list: D012464:Saliva, Artificial; D012834:Silver; D003723:Dental Amalgam