ELECTRICAL PROPERTIES
Two electrical properties of interest are galvanism and corrosion. Galvanism results from the presence of dissimilar metals in the mouth. Metals placed in an electrolyte (a liquid that contains ions) have various tendencies to go into solution.
Aluminium, alloys of whichare sometimes used as temporary crows, has a strong tendency to go to into solution an has an electrode potential 0f + 1.33 volts. Gold on the other hand, has a little tendency to go into solution, as indicated by an electrode potential of - 1.36 volts. The oral fluids function as the electrolyte, and the system is similar to that of an electrical cell. When the two restoration touch, current flows because the potential difference is 2.69 volts, and the patient experiences pain and fraquently complains of a metallic taste. The some effect can be experienced if a piece of aluminium foil from a baked potato becomes wedged between two teeth and contacts a gold restoration. Temporary plastic crown are used to prevent this problem because they are poor electrical conductors.
Corrosion also can result from this same condition when adjacent restorations are of dissimilar metals. As a result of the galvanic action, material goes into solution, and roughness and pitting occur. This effect also may occur if a gold alloy is contaminated with a metal such as iron during handling in the dental laboratory or because of variations in concentaration of elements from one part of the restoration to another. Corrosion also may result from chemical attack of metals by components in food or saliva. Dental amalgam, for exapmle, reacts with sulfides and chlorides in the mouth, as shown by polished amalgams becoming dull and discolored with time. This effect sometimes is reffered to as tarnish.
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