Abstract
The distribution of hardness was determined in sectioned amalgam restorations prepared with four alloys with different particle shape and copper content, and were condensed into the prepared cavity as in usual clinical practice. The high copper amalgams were apparently harder than the low copper amalgams, the single compositional high copper amalgam being the hardest among them. The hardness of amalgam adjacent to the lateral cavity wall was obviously smaller than that of the center, and the low copper lathe-cut amalgam had an extremely small hardness. The top of the restoration had a remarkably smaller hardness which was especially apparent with single compositional high copper amalgam. Therefore, the hardness at the margin of an restoration was not the same as that of the center but in considerably smaller, regardless of the alloy type used. Accordingly, the mechanical properties of the marginal region of a high copper amalgam restoration is considered not as favorable as expected from the result of commonly used mechanical tests, compared with low copper amalgams.
