Cavities are the direct result of bacteria, which live in your mouth and feed off sugar from food that's left behind after you eat. Bacteria produce acid, which combines with food particles and saliva to form a sticky film called plaque. Plaque erodes the protective enamel on your teeth and allows cavities to form.
Dental fillings are made of gold, silver combined with other metals, tooth-colored resin, porcelain, or other materials. Sometimes two or more different materials are combined to strengthen the filling.
Before placing a filling, your dentist will remove the decay with special instruments. Then, whichever material you and your dentist choose will be placed into your tooth to fill the cavity.