Why is tooth sealant only for children?

Sealants are placed on children's permanent back teeth soon after they come into the mouth because they are most at risk for decay at that time. Once a cavity has occurred in a tooth, it must be filled. It cannot be sealed. Also a tooth that has been filled cannot be sealed.

If a person reaches adulthood without getting a cavity in a particular tooth, the likelihood of getting one is substantially reduced, and the benefit of sealing the tooth is very minimal. Adults can have their teeth sealed, but the expense far outweighs the benefit.