A sealant is a clear or white plastic coating that is placed on the biting surfaces of back teeth to help prevent tooth decay.
Back teeth have deep grooves and pits that are very difficult to keep clean. Plaque, which is a sticky, colorless film of food and bacteria, collects in these grooves. Plaque is nearly invisible, so to see it, we may stain the plaque with harmless red dye.
Every time you eat, the bacteria in plaque forms acid. Without a protective sealant, this acid attacks the enamel that protects your teeth and causes the enamel to break down. Then, you get a cavity.