A filling is a substance that dentists use to replace a decayed or broken portion of a tooth. Commonly used substances for fillings include metal, alloy, plastic, porcelain, or a combination of materials (composite).

Composite resins are made from plastic materials (glass and resin) and are usually similar to tooth color. They are often used on the front teeth where a natural appearance is important. Composite resins can sometimes also be used on the back teeth.