Effect of Overheating on Amalgam Hardness

¹ Department of Operative Dentistry, University of Oregon Dental School, Portland, Oregon

The amalgam surface heated to release mercury was examined by indentation hardness. No change in hardness was observed 24 hours after immersion heating and repolishing. This observation was independent of the mercury contents of the amalgam tested, and does not appear to represent a permanent alteration in the resistance of the surface to permanent deformation—a property considered important to the clinical behavior of this material.

The mercury composition of these amalgams (44 percent and 60 percent residual mercury) approximated that shown to allow for restorations manifesting clinically detectable differences in the mouth. The difference in hardness (24 KHN) resulting from these compositions may represent an important change in this test measurement. The deformation of clinically overheated amalgams that might be affected by this difference has been considered.