Bacteria and  food residue can easily get caught in the grooves and fissures on the chewing surfaces of the molars and premolars. The morcels of food provide a perfect protected living environment for millions of bacteria. These undesirable organisms put the chewing surfaces of teeth, particularly for children and young people, extremely at risk of tooth decay, which is why sealing against decay is an integral part of decay prophylaxis for children and young people.
But adults can also avail  of the advantages!

With fissure sealing the chewing surfaces of the teeth are cleaned and polished and the fissures are sealed with a special material. After this treatment the chewing surface is very smooth and therefore provides less opportunity for bacteria and bits of food to take hold.
Once a new tooth has fully broken through a fissure sealing should be carried out immediately, so that decay has no chance of setting in.