context: Fluoride is a mineral that occurs naturally in many foods and water. Every day, minerals are added to and lost from a tooth's enamel layer through two processes, demineralization and remineralization. Minerals are lost (demineralization) from a tooth's enamel layer when acids -- formed from plaque bacteria and sugars in the mouth -- attack the enamel. Minerals such as fluoride, calcium, and phosphate are redeposited (remineralization) to the enamel layer from the foods and waters consumed. Too much demineralization without enough remineralization to repair the enamel layer leads to tooth decay. Fluoride helps prevent tooth decay by making the tooth more resistant to acid attacks from plaque bacteria and sugars in the mouth. It also reverses early decay. In children under 6 years of age, fluoride becomes incorporated into the development of permanent teeth, making it difficult for acids to demineralize the teeth. Fluoride also helps speed remineralization as well as disrupts acid production in already erupted teeth of both children and adults. As mentioned, fluoride is found in foods and in water. It can also be directly applied to the teeth through fluoridated toothpastes and mouth rinses. Mouth rinses containing fluoride in lower strengths are available over-the-counter; stronger concentrations require a doctor's prescription. A dentist in his or her office can also apply fluoride to the teeth as a gel, foam, or varnish. These treatments contain a much higher level of fluoride than the amount found in toothpastes and mouth rinses. Varnishes are painted on the teeth; foams are put into a mouth guard, which is applied to the teeth for one to four minutes; gels can be painted on or applied via a mouth guard. Fluoride supplements are also available as liquids and tablets and must be prescribed by your dentist, pediatrician, or family doctor. It is certainly important for infants and children between the ages of 6 months and 16 years to be exposed to fluoride. This is the timeframe during which the primary and permanent teeth come in. However, adults benefit from fluoride, too. New research indicates that topical fluoride -- from toothpastes, mouth rinses, and fluoride treatments -- are as important in fighting tooth decay as in strengthening developing teeth. In addition, people with certain conditions may be at increased risk of tooth decay and would therefore benefit from additional fluoride treatment. They include people with: Dry mouth conditions : Also called xerostomia, dry mouth caused by diseases such as SjÃ¶gren's syndrome, certain medications (such as allergy medications, antihistamines, antianxiety drugs, and high blood pressure drugs), and head and neck radiation treatment makes someone more prone to tooth decay. The lack of saliva makes it harder for food particles to be washed away and acids to be neutralized. Gum disease : Gum disease, also called periodontitis, can expose more of your tooth and tooth roots to bacteria increasing the chance of tooth decay. Gingivitis is an early stage of periodontitis. History of frequent cavities: If you have one cavity every year or every other year, you might benefit from additional fluoride. Presence of crowns and/or bridges or braces: These treatments can put teeth at risk for decay at the point where the crown meets the underlying tooth structure or around the brackets of orthodontic appliances. Ask your dentist if you could benefit from additional fluoride. Fluoride is safe and effective when used as directed but can be hazardous at high doses (the "toxic" dosage level varies based on an individual's weight). For this reason, it's important for parents to carefully supervise their children's use of fluoride-containing products and to keep fluoride products out of reach of children, especially children under the age of 6. In addition, excess fluoride can cause defects in the tooth's enamel that range from barely noticeable white specks or streaks to cosmetically objectionable brown discoloration. These defects are known as fluorosis and occur when the teeth are forming -- usually in children younger than 6 years. Fluorosis, when it occurs, is usually associated with naturally occurring fluoride, such as that found in well water. If you use well water and are uncertain about the mineral (especially fluoride) content, a water sample should be tested. Although tooth staining from fluorosis cannot be removed with normal hygiene, your dentist may be able to lighten or remove these stains with professional-strength abrasives or bleaches. Keep in mind, however, that it's very difficult to reach hazardous levels given the low levels of fluoride in home-based fluoride-containing products. Nonetheless, if you do have concerns or questions about the amount of fluoride you or your child may be receiving, talk to your child's dentist, pediatrician, or family doctor. A few useful reminders about fluoride include: Store fluoride supplements away from young children. Avoid flavored toothpastes because these tend to encourage toothpaste to be swallowed. Use only a pea-sized amount of fluoridated toothpaste on a child's toothbrush. Even though there are no scientific studies to suggest that people who drink bottled water are at increased risk of tooth decay, the American Dental Association ( ADA) says that such people could be missing out on the decay-preventing effects of optimally fluoridated water available from their community water source. The ADA adds that most bottled waters do not contain optimal levels of fluoride, which is 0.7 to 1.2 parts per million (this is the amount that is in public water supplies, in the communities that have fluoridated water). To find out if your brand of bottled water contains any fluoride, check the label on the bottle or contact the bottle water manufacturer. The amount of fluoride you receive in your drinking water depends on the type of home water treatment system used. Steam distillation systems remove 100% of fluoride content. Reverse osmosis systems remove between 65% and 95% of the fluoride. On the other hand, water softeners and charcoal/carbon filters generally do not remove fluoride. One exception: some activated carbon filters contain activated alumina that may remove over 80% of the fluoride. If you use a home water treatment system, have your water tested at least annually to establish the fluoride level your family is receiving in the treated water. Testing is available through local and state public health departments as well as private laboratories. Also, check with the manufacturer of the product you purchased or read the information that came with the water treatment system to determine the product's effects on fluoride in your home water. To find out how much fluoride is in your tap water, ask your local dentist, contact your local or state health department, or contact your local water supplier. Information for contacting your local water supplier should be on your water bill or see the "local government" section of your phone book. Approximately 62% of the U. S. population served by public water supplies has access to adequate levels of fluoride in their water, and 43 of the 50 largest U. S. cities have water fluoridation systems.