Dental sealants are a dental treatment consisting of applying a plastic material to one or more teeth, for the purpose of preventing dental caries (cavities) or other forms of tooth decay. Since the 1970s, in the United States, the incidence of tooth decay on the smooth surfaces of teeth has declined, in part because of fluoridation becoming widespread in public water supplies as well as improved dental hygiene among the public. However, because the back teeth (molars) have numerous pits and fissures, certain areas of these teeth cannot be properly cleaned of food particles and bacterial plaque even with vigorous tooth-brushing and flossing. As a result, decay among the molars remains nearly unavoidable even with a conscientious dental hygiene program. To remedy this, research into dental sealants began in the 1960s and by the early 1970s; the first generation of sealants became available and were approved by the FDA. When correctly applied, dental sealants are nearly 100% effective in preventing dental caries on treated teeth. Despite this, and the fact that dental sealants have been widely available since the early 1970s, it is estimated currently that fewer than 20% of the population have dental sealants. Dental sealants are usually applied in a dentist's office.