Pits and fissures are the deep grooves that make up the chewing surfaces of your teeth. Although pits and fissures help you to chew, food can still get stuck in these groove. It's hard to reach these areas with your toothbrush, so food and plaque can remain in place and lead to cavity formation.
A sealant is a protective plastic coating, which is applied to the biting surfaces of the back teeth. The sealant forms a hard shield that keeps food and bacteria from getting into the tiny grooves in the teeth and causing decay. Sealing of pits and fissure is most important in newly erupted teeth to resist decay. Sealants usually last for many years, but your dental team will want to check them regularly to make sure that the seal is still intact. They can wear over time, and sometimes the dental team need to add or replace some sealant to be sure that no decay can start underneath it.