A 55 year old male patient returns to your dental office  24 hours after you restored his tooth with amalgam restoration. He complains of sudden sharp pain on biting. Intraoral examination reveals gold inlay with 46. What could be the possible reason for his pain?
An important type of electrochemical reaction occurs when combinations of dissimilar metals are in direct physical contact. Here two adjacent metal restorations where the metal surfaces have different compositions. The alloy combinations that may produce galvanic corrosion or electrogalvanism through the flow of galvanic currents may be in either continuous or intermittent contact. An example would be a dental amalgam restoration placed on the occlusal surface of a tooth directly opposing a gold inlay. Because both restorations are wet with saliva, an electrical circuit exists with a difference in potential between the dissimilar restorations. When the two restorations are brought into contact, there is a sudden short-circuit through the two alloys. This can result in a sharp pain, called galvanic shock.
Ref: Phillips 12 th edition Pg- 43
Chemical corrosion
Galvanic shock
High point on the restoration
Thermal conductivity