The biting surfaces of back teeth are shaped like "hills and valleys' known as cusps and fissures. Toothbrush bristles are unable to get into the narrow fissures to remove plaque and bacteria which produce acid when sugar is eaten, causing decay. To help prevent decay, the fissures are sealed over with a fissure sealant, which is a plastic coating. This means your back teeth (molars) will be less likely to need fillings at a later date.
Placing a fissure sealant is a painless procedure as there is no cutting away of tooth tissue - no drilling.