We fill cavities with a tooth-colored resin, rather than the traditional metal fillings. The metal restorations, besides being unattractive, react to temperature and over time can crack from the stress of the metal expanding and contracting, just as roadways crack and create potholes from water expanding to ice.
The tooth-colored resin is chemically bonded to the tooth, rather than simply applied to the tooth. This chemical bond fills in cracks and keeps food, liquids, and bacteria out.
As defined by the American Dental Association (ADA), composite, tooth-colored fillings are a more conservative solution because more of the tooth can be left intact, resulting in a smaller filling.