Despite their many possible uses, topical fluorides are used primarily in children. They are most often applied when the premolars erupt, with subsequent treatments declining thereafter.

Unfortunately, the data on the rate of cavities in those over 60 are not positive. A review of five studies that looked at caries incidence among those over 50 found that older people are cavity active group with a rate of decay as high as that found in teenagers. 

The amount of time that the fluoride remains in contact with the tooth is crucial to its effectiveness. Topical fluorides also promote remineralization. Fluoride ions in the presence of calcium and phosphate in teeth enamel readily incorporate into the enamel lattice. This precipitation and growth process is known as remineralization. Furthermore, because of their small size and the electronegative character of fluoride ions, they strongly bind to the enamel lattice and strengthen its stability. 

Finally, topical fluoride adheres to but doses not directly enter the tooth enamel’s crystalline structure, rather, it forms complexes of calcium fluoride that are loosely bound to the enamel surface. These complexes serve as a fluoride reservoir, slowly releasing the ions for the remineralization process. This promotion of remineralization and prevention of demineralization can arrest to the progression of carious lesions, making topical fluoride and effective preventive and treatment agent for caries. 

Fluoride also inhibits the action of plaque bacteria by interfering with the bacteria’s ability to produce the polysaccharides that allow them to stick to teeth, thus forming plaque biofilm. Additionally, Fluoride interferes with the way cariogenic bacteria metabolize carbohydrates and produce acid. In laboratory studies when a low concentration of fluoride is constantly present, streptococcus mutants produce less acid. 

Clinical Effectiveness 

Six fluoride varnish studies and found statistically significant reduction in the number of tooth surface with cavitated lesions and a range of reduction in caries from 30% to 63%. A review of studies comparing fluoride varnish and acidulated phosphate fluoride gel concluded that the varnish wears equally or more effective than the APF gel. 

Dentin Hypersensitivity 

Dentin hypersensitivity is most likely caused by exposed dentinal tubules. The dentinal tubules are often exposed in cases of gingival recession; cervical wear; erosion from diet or conditions such as bulimia; or following periodontal or restorative procedures. The movement of tubule fluid most likely causes dentinal sensitivity. Topical fluorides are among several dental products that occlude and/or create a protective layer over the tubules, preventing movement of the tubules fluid. Fluoride applications have a dual effect on sensitive teeth because the protective layer of calcium fluoride is effective in tooth decay prevention and in eliminating tooth pain. In cases of sensitive teeth, topical fluoride gel can be gently burnished into the sensitive tooth surfaces before scaling and root planning to reduce treatment pain. 

The Recipients 

Low risk patients of any age living in fluoridated communities and using a fluoride dentifrice may not benefit from topical fluoride applications.

High-risk patients (over 6 years) are defined as those with three or more incipient or cavitated lesions in the past 3 years. They should receive fluoride varnish or gel applications four times per year. 

The ADA recommends the application of fluoride varnish for children under 6 semi-annually for moderate risk patients and four times per year for high risk patients. 

Safety 

Topical fluorides have been used for several decades and are safe when used appropriately. Low plasma fluoride levels following the application of fluoride varnish were comparable to plasma fluoride levels experienced after tooth brushing with a fluoridated dentifrice.