Fillings are among the most common type of restorative treatment and are used to treat tooth decay or wear cavities.
Dental amalgam is the traditional silver-coloured filling we are all familiar with. Although there is mercury in dental amalgam, once it is combined with the other materials in the amalgam filling, its chemical nature is changed, rendering it harmless. Research into the safety of dental amalgam has been carried out for over a century and to date, no trustworthy controlled studies have found a connection between amalgam fillings and any medical problem. That notwithstanding, the use of amalgam is being phased out by many European countries due to its mercury content and the fact that we now have a tooth-coloured durable alternative called composite.
See about composite fillings here.