Like other metals, the volume of metal amalgam fillings is highly temperature-sensitive. This means that when hot food or liquid contacts a metal amalgam filling, the filling will expand, and it will expand more rapidly than the tooth material surrounding it. When this happens, the filling will put pressure on your tooth nerve, causing pain.The opposite happens when you eat cold foods and liquids. The metal amalgam will contract, causing a pulling stress on your tooth that may also lead to sensitivity.