Benefits of Fluoride and Understanding Dental Caries

Objectives: Participants will...

• Understand the role of fluoride in inhibiting demineralization and enhancing remineralization of enamel tooth structure, thus preventing decay.
• Learn the newly recommended schedule for dietary fluoride supplementation.
• Understand that frequency of eating is the significant factor in caries development.

Over a century ago, in 1892, Sir James Crichton suggested that the specific cause of an increase in dental caries was a change in the type of bread eaten – i.e., a deficiency in the fluorine present in the bran or husk parts of wheat. Numerous studies demonstrate effectiveness of fluoride in caries prevention and decline of dental health on cessation of water fluoridation.

Fluoride has played a major role in the marked reduction in caries incidence and prevalence. Under normal conditions there is a constant exchange of ions between the enamel surface and the surrounding saliva, resulting in a dynamic equilibrium. This equilibrium is disturbed when organic acids are produced by bacterial metabolism of fermentable carbohydrates. The acids lower the ph of plaque fluid on the enamel surface, penetrate the enamel subsurface, and then cause enamel crystals to dissolve and leave the enamel. This process is called demineralization.

Today, scientists agree that maintaining fluoride at and within the enamel surface of the teeth is an important factor in determining whether an early carious lesion, i.e., a demineralized area of the tooth, will progress to a cavity or will be remineralized.

The frequency of eating has a more significant effect on the development of caries than what is eaten. Because of this, the habit of infant nursing throughout the night or sleeping with a bottle without preventive techniques puts the infant at risk for ECC.

In the United States, community water fluoridation is recommended at a concentration ranging from 0.7 to 1.2 parts per million (ppm) of fluoride, depending upon the community’s mean maximum daily temperature. New York City water is fluoridated at 1.0 ppm.

Fluoridated drinking water acts both systemically and topically. Other forms of topically applied fluoride include professionally applied and self applied fluoride treatments, fluoride dentifrices, fluoride mouthrinses, and fluoride varnishes.

Dietary fluoride supplements are prescribed by practitioners for children living in areas with a suboptimal level of fluoride in the drinking water. They are administered either as drops or tablets with or without vitamins. However, before prescribing a fluoride supplement, a physician or dentist should know the child’s age and the concentration of fluoride in the child’s “primary” source of drinking water. (Note: the “primary” water source is often not the child’s “home” water source).

ADA/AAPD Recommended Supplemental Fluoride Dosage Schedule

Improper use of dietary fluoride supplements and ingestion of fluoride dentifrices by small children, particularly in fluoridated communities, may result in dental fluorosis. Dental fluorosis is defined as hypoplasia or hypomaturation of tooth enamel produced by chronic ingestion of excessive amounts of fluoride as the teeth are developing, and are manifested as whitish opacities on the teeth. In severe cases, mottled enamel may occur.

Although fluoride ingested by mother can cross the placenta, for lack of conclusive evidence that it will reduce dental caries in her offspring, prenatal fluoride supplementation for the expectant mother is not recommended.

Fluoride varnishes have been used in Europe for more than 30 years, and have recently been approved for use in the United States. It is a most promising product for the prevention of tooth decay due to its unique properties of remaining in contact with tooth surfaces for extended periods of time and setting to a hard coating on tooth enamel even in the presence of moisture.

There are 4 fluoride varnishes available for use in the United States.  Most commonly they contain 5% sodium fluoride. When applied, the varnish forms a sticky layer on the tooth, which hardens on contact with saliva.  Fluoride is then absorbed into the enamel of the tooth.  It is recommended that the varnish be allowed to remain on the teeth for up to four hours for optimal absorption.

Most studies have shown 25-45% reductions in the decay rate with the use of fluoride varnish.  Of special note is the reduction of decay in pits and fissures (the biting surfaces of molars), as well as on smooth surfaces of teeth.  A two-year study by Holm resulted in a 44% caries reduction rate following semi-annual varnish applications.

Although the concentration of fluoride in varnishes is much higher than that of APF gels or other topical fluorides, due to the sticky form of the varnish and the small amount used per application, risk of ingestion and toxicity is very low. This most promising fluoride product will become the preferred method of application of topical fluoride in the years to come.