Fluoridation of Drinking Water to Prevent Dental Caries

Journal article

By: Centers for Disease Control and Prevention

Date: October 22, 1999

Source: Division of Oral Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention. "Achievements in Public Health, 1900–1999: Fluoridation of Drinking Water to Prevent Dental Caries." Morbidity and Mortality Weekly Report 48 (October 22, 1999): 933-940.

About the Author: The Centers for Disease Control and Prevention (CDC) is part of the U.S. Department of Health and Human Services. It was founded in 1946 to help control malaria. Today, its mission is to improve public health by preventing, investigating, documenting, and controlling chronic and emergent disease, injuries, workplace hazards, disabilities, and environmental health threats.

INTRODUCTION

Campaigns to improve the health of the public, instituted by organizations such as the CDC and the World Health Organization (WHO), can take many forms. They may seek to educate and inform, or they may offer a specific service, such as vaccination against smallpox or measles. Sometimes campaigns lead to a change in the law. For example, many countries have moved beyond merely advising people to quit smoking towards banning it in public places.

To be successful, a public health campaign must be supported by sound science and it must have broad support among the population. The latter is vital, given that some public health measures may involve a certain amount of intrusion on people's individual liberties. For instance, many people who smoke feel their rights are violated by anti-smoking legislation and remain unconvinced of the dangers of secondary smoke.

In the journal article that follows, the CDC describes the fall in tooth decay due to the fluoridation of drinking water and the accompanying improvement in public health as one of the biggest public health success stories of the twentieth century. The under-pinning science appears convincing and fluoridation won the support of most doctors, dentists, and policy makers.

PRIMARY SOURCE

Fluoridation of community drinking water is a major factor responsible for the decline in dental caries (tooth decay) during the second half of the 20th century. The history of water fluoridation is a classic example of clinical observation leading to epidemiologic investigation and community-based public health intervention. Although other fluoride-containing products are available, water fluoridation remains the most equitable and cost-effective method of delivering fluoride to all members of most communities, regardless of age, educational attainment, or income level.

DENTAL CARIES

Dental caries is an infectious, communicable, multi-factorial disease in which bacteria dissolve the enamel surface of a tooth. Unchecked, the bacteria then may penetrate the underlying dentin and progress into the soft pulp tissue. Dental caries can result in loss of tooth structure and discomfort. Untreated caries can lead to incapacitating pain, a bacterial infection that leads to pulpal necrosis, tooth extraction and loss of dental function, and may progress to an acute systemic infection….

At the beginning of the 20th century, extensive dental caries was common in the United States and in most developed countries. No effective measures existed for preventing this disease, and the most frequent treatment was tooth extraction….

HISTORY OF WATER FLUORIDATION

The identification of a possible etiologic agent for mottled enamel led to the establishment in 1931 of the Dental Hygiene Unit at the National Institute of Health headed by Dr. H. Trendley Dean. Dean's primary responsibility was to investigate the association between fluoride and mottled enamel….

The hypothesis that dental caries could be prevented by adjusting the fluoride level of community water supplies from negligible levels to 1.0-1.2 ppm was tested in a prospective field study conducted in four pairs of cities (intervention and control) starting in 1945: Grand Rapids and Muskegon, Michigan; Newburgh and Kingston, New York; Evanston and Oak Park, Illinois; and Brantford and Sarnia, Ontario, Canada. After conducting sequential cross-sectional surveys in these communities over 13-15 years, caries was reduced 50%-70% among children in the communities with fluoridated water….

The effectiveness of community water fluoridation in preventing dental caries prompted rapid adoption of this public health measure in cities throughout the United States. As a result, dental caries declined precipitously during the second half of the 20th century. For example, the mean DMFT among persons aged 12 years in the United States declined 68%, from 4.0 in 1966–1970 to 1.3 in 1988–1994 (CDC, unpublished data, 1999) The American Dental Association, the American Medical Association, the World Health Organization, and other professional and scientific organizations quickly endorsed water fluoridation. Knowledge about the benefits of water fluoridation led to the development of other modalities for delivery of fluoride, such as toothpastes, gels, mouth rinses, tablets, and drops. Several countries in Europe and Latin America have added fluoride to table salt.

EFFECTIVENESS OF WATER FLUORIDATION

Early studies reported that caries reduction attributable to fluoridation ranged from 50% to 70%, but by the mid-1980s the mean DMFS scores in the permanent dentition of children who lived in communities with fluoridated water were only 18% lower than among those living in communities without fluoridated water. A review of studies on the effectiveness of water fluoridation conducted in the United States during 1979–1989 found that caries reduction was 8%-37% among adolescents (mean: 26.5%).

Since the early days of community water fluoridation, the prevalence of dental caries has declined in both communities with and communities without fluoridated water in the United States. This trend has been attributed largely to the diffusion of fluoridated water to areas without fluoridated water through bottling and processing of foods and beverages in areas with fluoridated water and widespread use of fluoride toothpaste. Fluoride toothpaste is efficacious in preventing dental caries, but its effectiveness depends on frequency of use by persons or their caregivers. In contrast, water fluoridation reaches all residents of communities and generally is not dependent on individual behavior.

Although early studies focused mostly on children, water fluoridation also is effective in preventing dental caries among adults. Fluoridation reduces enamel caries in adults by 20%-40% and prevents caries on the exposed root surfaces of teeth, a condition that particularly affects older adults.

Water fluoridation is especially beneficial for communities of low socioeconomic status. These communities have a disproportionate burden of dental caries and have less access than higher income communities to dental-care services and other sources of fluoride. Water fluoridation may help reduce such dental health disparities.

BIOLOGIC MECHANISM

Fluoride's caries-preventive properties initially were attributed to changes in enamel during tooth development because of the association between fluoride and cosmetic changes in enamel and a belief that fluoride incorporated into enamel during tooth development would result in a more acid-resistant mineral. However, laboratory and epidemiologic research suggests that fluoride prevents dental caries predominately after eruption of the tooth into the mouth, and its actions primarily are topical for both adults and children. These mechanisms include 1) inhibition of demineralization, 2) enhancement of remineralization, and 3) inhibition of bacterial activity in dental plaque.

Enamel and dentin are composed of mineral crystals (primarily calcium and phosphate) embedded in an organic protein/lipid matrix. Dental mineral is dissolved readily by acid produced by cariogenic bacteria when they metabolize fermentable carbohydrates. Fluoride present in solution at low levels, which becomes concentrated in dental plaque, can substantially inhibit dissolution of tooth mineral by acid.

Fluoride enhances remineralization by adsorbing to the tooth surface and attracting calcium ions present in saliva. Fluoride also acts to bring the calcium and phosphate ions together and is included in the chemical reaction that takes place, producing a crystal surface that is much less soluble in acid than the original tooth mineral.

Fluoride from topical sources such as fluoridated drinking water is taken up by cariogenic bacteria when they produce acid. Once inside the cells, fluoride interferes with enzyme activity of the bacteria and the control of intracellular pH. This reduces bacterial acid production, which directly reduces the dissolution rate of tooth mineral.

POPULATION SERVED BY WATER FLUORIDATION

By the end of 1992, 10,567 public water systems serving 135 million persons in 8573 U.S. communities had instituted water fluoridation. Approximately 70% of all U.S. cities with populations of greater than 100,000 used fluoridated water. In addition, 3784 public water systems serving 10 million persons in 1924 communities had natural fluoride levels greater than or equal to 0.7 ppm. In total, 144 million persons in the United States (56% of the population) were receiving fluoridated water in 1992, including 62% of those served by public water systems. However, approximately 42,000 public water systems and 153 U.S. cities with populations greater than or equal to 50,000 have not instituted fluoridation….

SAFETY OF WATER FLUORIDATION

Early investigations into the physiologic effects of fluoride in drinking water predated the first community field trials. Since 1950, opponents of water fluoridation have claimed it increased the risk for cancer, Down syndrome, heart disease, osteoporosis and bone fracture, acquired immunodeficiency syndrome, low intelligence, Alzheimer disease, allergic reactions, and other health conditions. The safety and effectiveness of water fluoridation have been re-evaluated frequently, and no credible evidence supports an association between fluoridation and any of these conditions.

21ST CENTURY CHALLENGES

Despite the substantial decline in the prevalence and severity of dental caries in the United States during the 20th century, this largely preventable disease is still common. National data indicate that 67% of persons aged 12-17 years and 94% of persons aged greater than or equal to 18 years have experienced caries in their permanent teeth.

Among the most striking results of water fluoridation is the change in public attitudes and expectations regarding dental health. Tooth loss is no longer considered inevitable, and increasingly adults in the United States are retaining most of their teeth for a lifetime. For example, the percentage of persons aged 45-54 years who had lost all their permanent teeth decreased from 20.0% in 1960–1962 to 9.1% in 1988–1994 (CDC, unpublished data, 1999). The oldest post-World War II "baby boomers" will reach age 60 years in the first decade of the 21st century, and more of that birth cohort will have a relatively intact dentition at that age than any generation in history. Thus, more teeth than ever will be at risk for caries among persons aged greater than or equal to 60 years. In the next century, water fluoridation will continue to help prevent caries among these older persons in the United States.

Most persons in the United States support community water fluoridation. Although the proportion of the U.S. population drinking fluoridated water increased fairly quickly from 1945 into the 1970s, the rate of increase has been much lower in recent years. This slowing in the expansion of fluoridation is attributable to several factors: 1) the public, some scientists, and policymakers may perceive that dental caries is no longer a public health problem or that fluoridation is no longer necessary or effective; 2) adoption of water fluoridation can require political processes that make institution of this public health measure difficult; 3) opponents of water fluoridation often make unsubstantiated claims about adverse health effects of fluoridation in attempts to influence public opinion; and 4) many of the U.S. public water systems that are not fluoridated tend to serve small populations, which increases the per capita cost of fluoridation. These barriers present serious challenges to expanding fluoridation in the United States in the 21st century. To overcome the challenges facing this preventive measure, public health professionals at the national, state, and local level will need to enhance their promotion of fluoridation and commit the necessary resources for equipment, personnel, and training.

SIGNIFICANCE

With the widespread availability of fluoride tooth-paste and more awareness of the importance of dental care, tooth decay is no longer such a big issue in oral health. Attention has shifted to the problem of gum disease, which can also lead to tooth loss and which plays a role in other diseases. So, does the fact that fluoridation, despite its success in improving the nation's oral health, is not—and never has been—universal, still matter?

As the American Dental Association (ADA) celebrated sixty years of fluoridation, it also pointed out, with regret, that one-third of the U.S. population still does not have access to a fluoridated public water supply. Along with the ADA, the CDC and many other medical and dental opinion makers still firmly believe that fluoridation of the water supply is the most democratic and cost-effective way of reducing inequities in oral health. Water is a vital part of the diet and the public supply is available to all, whatever their socioeconomic status. People do not necessarily have such equal access to dental care or even fluoride toothpaste.

The global picture echoes the American one, with the World Health Organization pressing for more widespread adoption of fluoridation. Of course, it must be done properly and to the right level, which is between 0.7 to 1.2 parts per million (about one milligram per liter), at a certified water treatment plant. Too much fluoride can mark the teeth, a condition called dental fluorosis. Excess fluoride can also lead to skeletal fluorosis, which may weaken the bones. However, reports that fluoride can cause cancer and other health problems have not been substantiated. And excess fluoride can readily be removed from the water supply.

There remain, however, those who are opposed to fluoridation and many cities have voted not to have their water fluoridated. Partly this arises from a belief that fluoride is truly harmful to health. It is true that the chemicals that are added to the water supply, such as hexafluorosilicic acid, are corrosive and need handling with care. However, they are much diluted in the water. Fluoride in water is odorless, tasteless, and colorless, and only is detectable by specialized tests. The other main reason for opposing fluoridation is that there is a strong belief that water should be "pure"; fluoride is seen as a form of pollution. Furthermore, being forced to take in fluoride in our drinking water because the government thinks it is "good" for us is seen as an invasion of personal liberty and privacy. The same arguments apply to food that is fortified with vitamins or minerals, as well as to the chlorination of drinking water to prevent water-borne diseases. Such public health measures always balance public good against individual freedom. To be credible, they must, of course, be backed by the best scientific studies.

FURTHER RESOURCES

Web sites

American Dental Association. "After 60 Years of Success in Fighting Dental Decay, Water Fluoridation Still Lacking in Many Communities." 〈http://www.ada.org/public/media/presskits/fluoridation/index.asp〉 (accessed November 21, 2005).

World Health Organization. "World Water Day 2001: Oral Health." 〈http://www.who.int/water_sanitation_health/oralhealth/en/〉 (accessed November 21, 2005).