Brushing and flossing are the best ways to help prevent cavities, but it's not always easy to clean every nook and cranny of your teeth – especially those back teeth you use to chew (called molars). Molars are rough, uneven and a favorite place for leftover food and cavity-causing bacteria to hide. Still, there's another safety net to help keep those teeth clean. It's called a sealant, and it is a thin, protective coating (made from plastic or other dental materials) that adheres to the chewing surface of your back teeth. They're no substitute for brushing and flossing, but they can keep cavities from forming and may even stop early stages of decay from becoming a full-blown cavity.