Dental fillings are needed when a cavity or other type of tooth decay has occurred. Cavities are caused by bacteria in the mouth that produce acid that erodes the enamel on the tooth. This can result in a small hole, or cavity, in the tooth that needs to be filled in to prevent further decay and restore the tooth’s function and appearance. In addition to cavities, dental fillings can also be used to repair cracks, chips, or other types of damage to the tooth. Fillings can also improve the appearance of a discolored or misshapen tooth.