Fillings are placed in teeth in order to restore them after the decay has been removed. There are several materials that can be used for this purpose.
Amalgam or silver fillings are made of a mixture of mercury with several different metals including silver, copper and zinc. They are mixed and placed into the hole left by the cavity when still soft, and are held in place with undercuts prepared in the tooth after they harden.
Composite or white fillings are made of glass particles embedded in a resin matrix. They are tooth colored and are held in place with a sophisticated bonding method. They are therefore more conservative in size and more natural in appearance than amalgams.
Porcelain fillings are made of pure porcelain. They are stronger and more natural than either amalgam or composites. They also have the advantage of being bonded to the tooth, but require two visits for completion.