What are Dental Sealants? Dental sealants are thin plastic coatings placed over the chewing surfaces of back teeth to protect them from food. When left alone, plaque can build up and eventually cause tooth decay. Sealants are usually applied in one quick visit to the dentist. When a dentist places a sealant, the tooth is first cleaned, conditioned, and then a liquid sealant is hardened with a curing light.