Dentists also encourage prevention of dental caries through proper hygiene (tooth brushing and flossing), fluoride, and tooth polishing, although excessive brushing can cause damage to the gums. Dental sealants are plastic materials applied to one or more teeth, for the intended purpose of preventing dental caries (cavities) or other forms of tooth decay. Recognized but less conventional preventive agents include xylitol, which is bacteriostatic, casein derivatives, and proprietary products such as Cavistat BasicMints.