Sealants are used to protect healthy teeth that have a high potential for decay. Most often, these are the molars with deep grooves. A PRR, preventive resin restoration, is a type of filling that is placed when a cavity has begun and is infiltrating the grooves in the chewing surface of the tooth.
As dentists, we prefer to protect the enamel and structure of the tooth and avoid decay completely. Sealants and fluoride are two tools that give us a better chance at prevention.