Please explain why does my amalgam (filling) hurt?

Filling sensitivity: Drilling out the decay on a tooth and restoring it with a filling is a surgical procedure on the tooth and it is not uncommon to have some post-op sensitivity. It could be related to the bite being high or the the nerve being inflamed. Call the dentist who treated you for advice on this matter. It might go away on its own or require further treatment. Your own dentist will know best.

Why amalgam hurt?: A tooth may be sensitive to cold or hot for several weeks after you get a silver amalgam filling. The reason is metal is an excellent conductor of hot and cold and an amalgam filling is metal. However, the sensitivity to temperature normally goes away after a while (4-8 weeks). Be patient.