Amalgam restorations are very strong and typically last for a long period of time. They are only used in the posterior because they are not as esthetically pleasing as a tooth colored restoration, like a composite or veneer. The composite and veneer match the color of the natural teeth but usually are not as durable as the amalgam.
Nikki to Group: "Our first patient is Mr. Brian Smith. He has scheduled an amalgam procedure on tooth #3. We explained to him that this would be the strongest type of restoration for that area. He was pleased with that, although he was concerned about the look of a "silver" filling. He also will be having a composite restoration in the anterior on #8."