Dental sealants are the plastic coatings which are placed on the surface of the permanent back teeth (molars and premolars) which is for chewing. It is performed to protect the teeth from decay.
The surface of the molar and premolar teeth has fissures which make them weak to rot. These fissures are very deep and sometimes tough to clean and also can be narrower for a single bristle of the toothbrush to enter the space and clean the tooth. Generally, plaque gathers in these places and attacks the teeth and gives chance to develop cavities.