Role of Zinc in Silver Amalgam
Zinc as such does not participate in the amalgamation process or in the setting reaction of silver amalgam alloy with mercury during and after the completion of the restoration process.
It is used during the silver alloy manufacturing process to scavenge the impurities that are produced during production process. It acts as a scavenging material. After its function is finished, it remains in the silver alloy powder without any function.
It does not produce any effect on set silver amalgam filling as such the isolation is poor and the dentist does not take proper care to prevent moisture contamination. So, when moisture enters the mixed silver amalgam alloy during condensation process, it reacts with zinc slowly and starts creating gas. This gas starts causing expansion of the set mass and the filling tends to extrude from the confines of the prepared cavity.
Therefore, the manufacturers now have adopted newer techniques for scavenging purpose and produce silver powders without adding zinc. These alloys are known as zinc free alloys.