Dental sealants are thin plastic coatings that are applied to the grooves (called pits and fissures) on the chewing surfaces of the back teeth and act as a barrier to prevent cavities. The majority of tooth decay occurs on these surfaces because brushing and flossing can't always get into all of the nooks and crannies of the back teeth. Sealants protect the chewing surfaces from tooth decay by keeping germs and food particles out of these grooves.
The likelihood of developing pit and fissure decay begins early in life, so children and teenagers are obvious candidates. However, adults can benefit from sealants as well.