It may be recommended by your dentist that you have your child's teeth sealed. This is done because when chewing food, small amounts of food and bacteria can become trapped in the deepest portion of our back teeth. These deep grooves are called fissures. If a sealant is placed into the grooves, this will prevent food and bacteria getting caught inside and hence protect that tooth against a cavity.
The pictures below show before and after a white sealant has been applied to a lower left and right first adult molar.