Teeth have many pits and crevices along their surface that collect food and bacteria.
For a young person, especially, these areas can be hard to brush and sections can be missed that have trapped food which leads to a cavity and a future filling.
Dental sealants are coatings that are applied by a dentist to the surface of teeth. These coatings are designed to fill these pits and crevices so that food cannot be trapped. This reduces greatly the opportunity for tooth decay and subsequent drilling and filling. The great thing about sealants is that there is no drilling, no needles for anesthesia and are done in a single visit.