Sealants are used to fill in narrow grooves in a tooth that cannot be adequately cleaned by brushing. In some cases, the tooth structure has fine grooves or pits which accumulate plaque, not because the person doesn't brush, but because they're too narrow to allow even one bristle into them. These will develop cavities over time, and you don't want that. So, the dentist or hygienist will place a coating that seals the grooves and pits, making it possible to brush off all the plaque and keep your teeth healthy. Typically, sealants are placed on children/young adults to help get them through the “high sugar” years and perfect their oral hygiene routines.