A filling is when a composite material is used to restore a tooth which has been damaged by decay due to bacteria and food. Bacteria and food cause plaque which contains bacteria that feed on sugars in the food you consume. As the bacteria feed, they make acids which eat away at the tooth. The acids can lead to holes in the tooth which creates a cavity. If left untreated, the cavity can cause pain, infection and even can result in losing your tooth.
During a filling procedure your dentist will numb the area with anesthetic, prepare the tooth by removing any decay, clean the tooth, fill the tooth with a tooth coloured composite material the same colour as your tooth and then polish the tooth.