Cavities are a common dental issue. They affect millions of people, children and adults alike. They form as a result of tooth decay, which occurs when the acids produced by plaque and bacteria erode your tooth enamel. Once cavities form, they only continue to grow larger over time. Fillings are a common treatment for cavities. Made from amalgam or composite resin, they fill in the spaces in your teeth left behind by cavities, preventing further damage and protecting the health of your teeth and your mouth.