Fluoride varnish is a highly concentrated form of fluoride which is applied to the tooth's surface, by a dentist, as a type of topical fluoride therapy. It is not a permanent varnish but due to its adherent nature it is able to stay in contact with the tooth surface for several hours. It may be applied to the enamel, dentine or cementum of the tooth and can be used to help prevent decay, remineralise the tooth surface and to treat dentine hypersensitivity. The American association of Pediatric Dentistry recommends topical fluoride application in children on a bi-annual basis to help strengthening of teeth and to prevent decay.