Introduction
Dental amalgam is a metallic alloy formed by the reaction of mercury with a powder alloy containing silver (40 – 70%), tin (15 – 30%) and copper (10 – 30%), and sometimes also a small percentage of zinc. The nature of dental amalgam to undergo a corrosion process that can lead to ultimate failure of the restoration particularly is important from a clinical standpoint. This failure usually manifests itself as either a bulk fracture of the restoration or as a progressive breakdown of the amalgam along the marginal angles. The resultant " marginal ditch" provides a nidus for the accumulation of microorganisms that renders the tooth – restoration interface subject to recurrent caries[Holand etal, 1974]. Oral environment is very susceptible to corrosion products formation. Mouth is always moist and is continually subjected to fluctuation in temperature. Food and liquids ingested have wide ranges of pH. Acids are released during the breakdown of foodstuffs. All of these environmental factors contribute to the degrading process known as corrosion. Corrosion in the specific sense is not merely a surface deposit but is an actual deterioration of a metal by reaction with its environment. It causes severe and catastrophic disintegration of the metal body. This disintegration of the metal may occur through the act of moisture, atmosphere, acids, alkalies or certain chemicals [Anusavice, 1996].