Water fluoridation

ABSTRACT

The safety and efficacy of water fluoridation has been a topic of great controversy throughout America’s communities. Scientific evidence has shown that ingesting low to moderate levels of fluoride can benefit the dental health of a community, especially those populations in a community that may be classified as having low socioeconomic status. Children in all areas, but especially those with low SES, are at greatest risk for developing dental caries and having a community water fluoridation program (CWFP) will help them reduce their dental caries. Moderation of fluoride ingestion for individuals is the key. Low to moderate daily ingestion of fluoride, averaging 1.0 mg/liter per day is optimum. Dental and skeletal fluorosis can occur if ingestion levels are greater than 3.0 mg/liter per day for long periods of time. This is a discussion on the safety and efficacy of water fluoridation.

INTRODUCTION

This commentary presents the on-going controversy on community water fluoridation in the United States, and I will attempt to analyze science-based evidence in support of water fluoridation. There have always been questions on the safety and efficacy of fluoride in drinking water, some school of thought believes that fluoridation has some adverse effects to exposed human populations, especially in infants and children. Another school of thought believes that water fluoridation is essential in preventing tooth decay, and therefore the practice should be sustained. According to the Center for Disease Control and prevention (CDC) water fluoridation is one of the 10 great public health achievements of the 20th century in the United States (CDC, 1999), which is attributable for increased lifespan of Americans by 25 years ( Bunker et al., 1994). This paper will discuss science-based evidence that proves the efficacy and safety of water fluoridation among children as well as offer some recommendations to the various stakeholders.

POSITION STATEMENT

Water fluoridation is the adjustment of the concentration level to the optimally regulated level of which the naturally occurring fluoride presents in public or community drinking water supplies. In most cases, deflouridation is needed when the naturally occurring fluoride level exceeds recommended limits. The recommended fluoride concentration in drinking water by the U.S. Public Health Service (PHS) is 0.7-1.2mg/L, to effectively prevent dental caries and minimize the occurrence of dental fluorosis (NRC, 2006). Low decay rates were found to be associated with continuous use of water with fluoride content of 1ppm (Meskin, 1995). There has been serious questions as to the efficacy of fluoride intervention in preventing both tooth decay, as it benefit is said to be merely cosmetic or topical (CDC, 1999). Such topical effect of fluoride can be achieved by the use tooth without the risking the overexposure from ingested fluoride (NRC, 2006). However, it has also been reported that fluoride exposure provides both systemic and topical protection. Ingested fluoride deposited on tooth surface during tooth formation, and fluoride contained in saliva provides long-lasting systemic protection against booth tooth decay than topical application using tooth paste or fluoride foams (CDC, 2001).

WHAT IS FLUORIDE

Fluoride is a naturally occurring element. It is found in rocks and soil everywhere. Fluoride can be found in fresh water and ocean water. Naturally occurring fluoride levels ranges from 0.1ppm to over 12ppm (NRC, 2006).Fluoride is present in the customary diets of people and in most portable water sources. The average dietary intake of fluoride is approximately 0.5mg daily from either naturally occurring fluoride in the water or the fluoride found in produce. It is also a normal component of tooth enamel and bone studies have shown that the calcified tissues of both enamel and bone are made up of a combination of hydroxyl- and fluor-apatites of varying composition depending on the abundance of fluoride at the site of formation. These tissues are the principal sites of deposition of fluoride (NRC, 2006).

HOW FLUORIDE PREVENTS AND CONTROLS DENTAL CARIES

Dental caries is an infectious, transmissible disease in which bacterial by-products (i.e., acids) dissolve the hard surfaces of teeth. Unchecked, the bacteria can penetrate the dissolved surface, attack the underlying dentin, and reach the soft pulp tissue. Dental caries can result in loss of tooth structure, pain, and tooth loss and can progress to acute systemic infection. Cryogenic bacteria (i.e., bacteria that cause dental caries) reside in dental plaque, a sticky organic matrix of bacteria, food debris, dead mucosal cells, and salivary components that adheres to tooth enamel. Plaque also contains minerals, primarily calcium and phosphorus, as well as proteins, polysaccharides, carbohydrates, and lipids. Cryogenic bacteria colonize on tooth surfaces and produce polysaccharides that enhance adherence of the plaque to enamel. Left undisturbed, plaque will grow and harbor increasing numbers of cryogenic bacteria. An initial step in the formation of a carious lesion takes place when cryogenic bacteria in dental plaque metabolize a substrate from the diet (e.g., sugars and other fermentable carbohydrates) and the acid produced as a metabolic by-product demineralizes (i.e., begins to dissolve) the adjacent enamel crystal surface (CDC,2009). Demineralization involves the loss of calcium, phosphate, and carbonate. These minerals can be captured by surrounding plaque and be available for reuptake by the enamel surface. Fluoride, when present in the mouth, is also retained and concentrated in plaque.

Fluoride works to control early dental caries in several ways. Fluoride concentrated in plaque and saliva inhibits the demineralization of sound enamel and enhances the remineralization (i.e., recovery) of demineralized enamel (Featherstone, 1999 & Koulourides, 1990). As cryogenic bacteria metabolize carbohydrates and produce acid, fluoride is released from dental plaque in response to lowered pH at the tooth-plaque interface. The released fluoride and the fluoride present in saliva are then taken up, along with calcium and phosphate, by de-mineralized enamel to establish an improved enamel crystal structure. This improved structure is more acid resistant and contains more fluoride and less carbonate (Featherstone, 1999). Fluoride is more readily taken up by demineralized enamel than by sound enamel. Cycles of demineralization and remineralization continue throughout the lifetime of the tooth.

Fluoride also inhibits dental caries by affecting the activity of cryogenic bacteria. As fluoride concentrates in dental plaque, it inhibits the process by which cryogenic bacteria metabolize carbohydrates to produce acid and affects bacterial production of adhesive polysaccharides. In laboratory studies, when a low concentration of fluoride is constantly present, one type of cryogenic bacteria, Streptococcus mutans, produces less acid. Whether this reduced acid production reduces the carcinogenicity of these bacteria in humans is unclear (Van Loveren, 1990).

Saliva is a major carrier of topical fluoride. The concentration of fluoride in ductal saliva, as it is secreted from salivary glands, is low — approximately 0.016 parts per million (ppm) in areas where drinking water is fluoridated and 0.006ppm in non fluoridated areas. This concentration of fluoride is not likely to affect cryogenic activity. However, drinking fluoridated water, brushing with fluoride toothpaste, or using other fluoride dental products can raise the concentration of fluoride in saliva present in the mouth 100- to 1,000-fold. The concentration returns to previous levels within 1–2 hours but, during this time, saliva serves as an important source of fluoride for concentration in plaque and for tooth remineralization (Murray,1993).

Applying fluoride gel or other products containing a high concentration of fluoride to the teeth leaves a temporary layer of calcium fluoride-like material on the enamel surface. The fluoride in this material is released when the pH drops in the mouth in response to acid production and is available to remineralize enamel.

In the earliest days of fluoride research, investigators hypothesized that fluoride affects enamel and inhibits dental caries only when incorporated into developing dental enamel (i.e., preeruptively, before the tooth erupts into the mouth) (Murray,1993). Evidence supports this hypothesis, but distinguishing a true preeruptive effect after teeth erupt into a mouth where topical fluoride exposure occurs regularly is difficult. However, a high fluoride concentration in sound enamel cannot alone explain the marked reduction in dental caries that fluoride produces . The prevalence of dental caries in a population is not inversely related to the concentration of fluoride in enamel, and a higher concentration of enamel fluoride is not necessarily more efficacious in preventing dental caries (Mcdonagh etal.,2000).

The laboratory and epidemiologic research that has led to the better understanding of how fluoride prevents dental caries indicates that fluoride’s predominant effect is post eruptive and topical and that the effect depends on fluoride being in the right amount in the right place at the right time. Fluoride works primarily after teeth have erupted, especially when small amounts are maintained constantly in the mouth, specifically in dental plaque and saliva (Mcdonagh etal., 2000). Thus, adults also benefit from fluoride, rather than only children, as was previously assumed.

RISK FOR DENTAL CARIES

The prevalence and severity of dental caries in the United States have decreased substantially during the preceding 3 decades. National surveys have reported that the prevalence of any dental caries among children aged 12–17 years declined from 90.4% in 1971–1974 to 67% in 1988–1991; severity (measured as the mean number of decayed, missing, or filled teeth) declined from 6.2 to 2.8 during this period (Burt, 1989).

These decreases in caries prevalence and severity have been uneven across the general population; the burden of disease now is concentrated among certain groups and persons. For example, 80% of the dental caries in permanent teeth of U.S. children aged 5–17 years occurs among 25% of those children. Populations believed to be at increased risk for dental caries are those with low socioeconomic status (SES) or low levels of parental education, those who do not seek regular dental care, and those without dental insurance or access to dental services (Meskin,1995). Persons can be at high risk for dental caries even if they do not have these recognized factors.

Children and adults who are at low risk for dental caries can maintain that status through frequent exposure to small amounts of fluoride (e.g., drinking fluoridated water and using fluoride toothpaste). Children and adults at high risk for dental caries might benefit from additional exposure to fluoride (e.g., mouth rinse, dietary supplements, and professionally applied products). All available information on risk factors should be considered before a group or person is identified as being at low or high risk for dental caries. However, when classification is uncertain, treating a person as high risk is prudent until further information or experience allows a more accurate assessment. This assumption increases the immediate cost of caries prevention or treatment and might increase the risk for enamel fluorosis for children aged <6 years, but reduces the risk for dental caries for groups or persons misclassified as low risk. The 1986–1987 National Survey of Dental Caries in U.S. School Children (the most recent national estimates of enamel fluorosis prevalence) indicated that the prevalence of any enamel fluorosis among children was 22%–23% (range: 26% of children aged 9 years to 19% of those aged 17 years) (Brunelle,1987).

NATIONAL GUIDELINES FOR FLUORIDE USE

PHS recommendations for fluoride use include an optimally adjusted concentration of fluoride in community drinking water to maximize caries prevention and limit enamel fluorosis. This concentration ranges from 0.7ppm to 1.2ppm depending on the average maximum daily air temperature of the area (PHS, 1991). In 1991, PHS also issued policy and research recommendations for fluoride use. The U.S. Environmental Protection Agency (EPA), which is responsible for the safety and quality of drinking water in the United States, sets a maximum allowable limit for fluoride in community drinking water at 4ppm and a secondary limit (i.e., non-enforceable guideline) at 2ppm (EPA,1998). The U.S. Food and Drug Administration (FDA) is responsible for approving prescription and over-the-counter fluoride products marketed in the United States and for setting standards for labeling bottled water and over-the-counter fluoride products (e.g., toothpaste and mouth rinse) (ADA,2007).

Nonfederal agencies also have published guidelines on fluoride use. The American Dental Association (ADA) reviews fluoride products for caries prevention through its voluntary Seal of Acceptance program; accepted products are listed in the ADA Guide to Dental Therapeutics (ADA, 2007). A dosage schedule for fluoride supplements for infants and children aged <16 years, which is scaled to the fluoride concentration in the community drinking water, has been jointly recommended by ADA, the American Academy of Pediatric Dentistry (AAPD), and the American Academy of Pediatrics (AAP) (Meskin,1995). In 1997, the Institute of Medicine published age-specific recommendations for total dietary intake of fluoride. These recommendations list adequate intake to prevent dental caries and tolerable upper intake, defined as a level unlikely to pose risk for adverse effects in almost all persons.

COST-EFFECTIVENESS OF FLUORIDE MODALITIES

Documented effectiveness is the most basic requirement for providing a health-care service and an important prerequisite for preventive services (e.g., caries-preventive modalities). However, effectiveness alone is not a sufficient reason to initiate a service. Other factors, including cost, must be considered. A modality is more cost-effective when deemed a less expensive way, from among competing alternatives, of meeting a stated objective (Garcia,1989). In public health planning, determination of the most cost-effective alternative for prevention is essential to using scarce resources efficiently. Dental-insurance carriers are also interested in cost-effectiveness so they can help purchasers use funds efficiently. Because half of dental expenditures are out of pocket (Garcia, 1989), this topic interests patients and their dentists as well. Potential improvement to quality of life is also a consideration. The contribution of a healthy dentition to quality of life at any age has not been quantified, but is probably valued by most persons.

Although solid data on the cost-effectiveness of fluoride modalities alone and in combination are needed, this information is scarce. In 1989, the Cost Effectiveness of Caries Prevention in Dental Public Health workshop, which was attended by health economists, epidemiologists, and dental public health professionals, attempted to assess the cost-effectiveness of caries-preventive approaches available in the United States (Downer et al., 1981).

Community Water Fluoridation

Health economists at the 1989 workshop on cost-effectiveness of caries prevention calculated that the average annual cost of water fluoridation in the United States was $0.51 per person (range: $0.12–$5.41) (Burt, 1989). In 1999 dollars, this cost would be $0.72 per person (range: $0.17–$7.62). Factors reported to influence the per capita cost included:

  • size of the community (the larger the population reached, the lower the per capita cost);
  • number of fluoride injection points in the water supply system;
  • amount and type of system feeder and monitoring equipment used;
  • amount and type of fluoride chemical used, its price, and its costs of transportation and storage; and
  • expertise of personnel at the water plant.

When the effects of caries are repaired, the price of the restoration is based on the number of tooth surfaces affected. A tooth can have caries at >1 location (i.e., surface), so the number of surfaces saved is a more appropriate measure in calculating cost-effectiveness than the number of teeth with caries. The 1989 workshop participants concluded that water fluoridation is one of the few public health measures that results in true cost savings (i.e., the measure saves more money than it costs to operate); in the United States, water fluoridation cost an estimated average of $3.35 per carious surface saved ($4.71 in 1999 dollars). Even under the least favorable assumptions in 1989 (i.e., cities with populations <10,000, higher operating costs, and effectiveness projected at the low end of the range), the cost of a carious surface saved because of community water fluoridation ranged from $8 to $12 ($11–$17 in 1999 dollars),which is still lower than the fee for a one-surface restoration ($54 in 1995 or $65 in 1999 dollars) (ADA, 2005).

A Scottish study conducted in 1980 reported that community water fluoridation resulted in a 49% saving in dental treatment costs for children aged 4–5 years and a 54% saving for children aged 11–12 years (Downer et al., 1981). These savings were maintained even after the secular decline in the prevalence of dental caries was recognized. The effect of community water fluoridation on the costs of dental care for adults is less clear. This topic cannot be fully explored until the generations who grew up drinking optimally fluoridated water are older.

School Water Fluoridation

Costs for school water fluoridation are similar to those of any public water supply system serving a small population (i.e., <1,000 persons). In 1988, the average annual cost of school water fluoridation was $4.52 per student per year (range: $0.81–$9.72) (Garcia,1989). In 1999 dollars, this cost would be $6.37 per person (range: $1.14–$13.69). Use of this modality must be carefully weighed in the current environment of low caries prevalence, widespread use of fluoride toothpaste, and availability of other fluoride modalities that can be delivered in the school setting (Garcia, 1989).

Assessment of the Adverse Health Effects of fluoride

Evidence of the adverse health effects of prolonged exposure to high concentrations of fluoride are well documented by several peer reviewed studies, which are examined in this paper. Higher concentrations of total ingested fluoride from potential sources like drinking water, food and beverages, dental-hygiene products such as toothpaste, and pesticide residues can have adverse health effects on humans (NRC, 2006). Some of the adverse health effects of fluoride in drinking water are enamel fluorosis, skeletal fluorosis, bone cancer and bone fracture. (NRC, 2006, PHS, 1991). Fluorosis is caused mainly by the ingestion of fluoride in drinking water (Viswanathan et al., 2009). Fluoride has high binding affinity for developing enamel and as such high concentration of cumulative fluoride during tooth formation can lead to enamel fluorosis, a dental condition from mild to severe form characterized by brown stains, enamel loss and surface pitting (DenBesten & Thariani, 1992). These dental effects are believed to be caused by the effects of fluoride on the breakdown rates of early-secreted matrix proteins, and on the rates at which the degraded by-products are withdrawn from the maturing enamel (Aoba & Fejerskov, 2002). Children are much more at risk of enamel fluorosis, especially in their critical period from 6 to 8 years of age, than adults. Fluoride uptake into enamel is possible only as a result of concomitant enamel dissolution, such as caries development (Fejerskov, Larsen, Richards, & Baelum, 1994). There is a 10% prevalence of enamel fluorosis among U.S. children in communities with water fluoride concentrations at or near the EPA’s MCLG of 4 mg/L (NRC, 2006). The CDC estimates that 32% of U.S. children are diagnosed with dental fluorosis (CDC, 2005). Today, there are convincing evidence that enamel fluorosis is a toxic effect of fluoride intake, and that its severe forms can produce adverse dental effects, and not just adverse cosmetic effects in humans (NRC, 2006). Burt and Eklund (1999) states: “The most severe forms of fluorosis manifest as heavily stained, pitted, and friable enamel that can result in loss of dental function”.

Epidemiological data from both observational and clinical studies have been examined. Sowers, Whitford, Clark & Jannausch (2005) investigated prospectively for four years bone fracture in relation to fluoride concentrations in drinking water in a cohort study, by measuring serum fluoride concentrations and bone density of the hip, radius, and spine. The authors reported higher serum fluoride concentrations in the communities with fluoride concentrations at 4 mg/L in drinking water; and higher osteoporotic fracture rates in the high fluoride areas that were similar to those in their previous studies in 1986 and 1991. It is unclear in their recent study whether existing factors in the population like smoking rates, hormone replacement and physical activity were examined as potential cofounders for fractures. Fasting serum fluoride concentrations are considered a good measure of long-term exposure and of bone fluoride concentrations (Whitford, 1994; Clarkson et al., 2000). Findings by the Sowers studies were complemented in several ways by Li et al. (2001) in a retrospective cohort ecologic study. The combined findings of Sowers et al. (2005) and Li et al., (2001) lend support to the biological gradients of exposures and fracture risk between 1 and 4 mg/L of fluoride concentration. Evidently, the physiological effect of fluoride on “bone quality” and the fractures observed in the referenced animal studies are consistent with the effects found in the observational studies.

RECOMMENDATIONS

Before promoting a fluoride modality or combination of modalities, the dental-care or other health-care provider must consider a person’s or group’s risk for dental caries, current use of other fluoride sources, and potential for enamel fluorosis. Although these recommendations are based on assessments of caries risk as low or high, the health-care provider might also differentiate among patients at high risk and provide more intensive interventions as needed. Also, a risk category can change over time; the type and frequency of preventive interventions should be adjusted accordingly.

Continue and Extend Fluoridation of Community Drinking Water

Community water fluoridation is a safe, effective, and inexpensive way to prevent dental caries. This modality benefits persons in all age groups and of all SES, including those difficult to reach through other public health programs and private dental care (CDC, 2001a). Community water fluoridation also is the most cost-effective way to prevent tooth decay among populations living in areas with adequate community water supply systems. Continuation of community water fluoridation for these populations and its adoption in additional U.S. communities are the foundation for sound caries-prevention programs.

In contrast, the appropriateness of fluoridating stand-alone water systems that supply individual schools is limited. Widespread use of fluoride toothpaste, availability of other fluoride modalities that can be delivered in the school setting, and the current environment of low caries prevalence limit the appropriateness of fluoridating school drinking water at 4.5 times the optimal concentration for community drinking water. Decisions to initiate or continue school fluoridation programs should be based on an assessment of present caries risk in the target school(s), alternative preventive modalities that might be available, and periodic evaluation of program effectiveness (CDC, 2001a).

Frequently Use Small Amounts of Fluoride

All persons should receive frequent exposure to small amounts of fluoride, which minimizes dental caries by inhibiting demineralization of tooth enamel and facilitating tooth remineralization. This exposure can be readily accomplished by drinking water with an optimal fluoride concentration and brushing with fluoride toothpaste twice daily(CDC, 2001a).

Supervise Use of Fluoride Toothpaste among Children Aged <6 Years

Children’s teeth should be cleaned daily from the time the teeth erupt in the mouth. Parents and caregivers should consult a dentist or other health-care provider before introducing a child aged <2 years to fluoride toothpaste. Parents and caregivers of children aged <6 years who use fluoride toothpaste should follow the directions on the label, place no more than a pea-sized amount (0.25 g) of toothpaste on the toothbrush, brush the child’s teeth (recommended particularly for preschool-aged children) or supervise the tooth brushing, and encourage the child to spit excess toothpaste into the sink to minimize the amount swallowed. Indiscriminate use can result in inadvertent swallowing of more fluoride than is recommended (CDC, 2001a).

Use an Alternative Source of Water for Children Aged <8 Years Whose Primary Drinking Water Contains >2 ppm Fluoride

In some regions in the United States, community water supply systems and home wells contain a natural concentration of fluoride >2ppm. At this concentration, children aged <8 years are at increased risk for developing enamel fluorosis, including the moderate and severe forms, and should have an alternative source of drinking water, preferably one containing fluoride at an optimal concentration.

In areas where community water supply systems contain >2ppm but <4ppm fluoride, EPA requires that each household be notified annually of the desirability of using an alternative source of water for children aged <8 years. For families receiving water from home wells, testing is necessary to determine the natural fluoride concentration (CDC, 2001a).

Label the Fluoride Concentration of Bottled Water

Producers of bottled water should label the fluoride concentration of their products. Such labeling will allow consumers to make informed decisions and dentists, dental hygienists, and other health-care professionals to appropriately advise patients regarding fluoride intake and use of fluoride products (CDC, 2001).

CONCLUDING POSITION STATEMENT

When used appropriately, fluoride is a safe and effective agent that can be used to prevent and control dental caries. Fluoride has contributed profoundly to the improved dental health of persons in the United States and other countries. Fluoride is needed regularly throughout life to protect teeth against tooth decay. To ensure additional gains in oral health, water fluoridation should be extended to additional communities, and fluoride toothpaste should be used widely. Adoption of these and other recommendations in this paper could lead to considerable savings in public and private resources without compromising fluoride’s substantial benefit of improved dental health. What is consistent from the literature review is the fact that infants and children are much more at risk of overexposure and the development of adverse health effects. A community water fluoridation program (CWFP) is very safe and efficient, not only in terms of reducing dental caries, but also on the community’s budget (CDC, 2001a). A CWFP can especially help those communities who have populations in the low SES category. These populations have children whose parents or guardians don’t always have access to dental insurance and so regular dental checkups to curb the dental caries is not always an option. Reducing dental caries before they lead into more extreme oral morbidity can be very beneficial to these children. Implementing a fluoridated water program can also be beneficial to a whole community in terms of saving communities thousands and millions of dollars.

Implementing a water program would follow strict guidelines set by the EPA, so the optimum level of fluoride would be followed, staying in the range of 0.7 to 1.2, where people would ingest no more than an average of 1 mg/liter of fluoride per day. Moderation is the key. There are studies confirming that ingestion of fluoride greater than the optimum level could produce dental fluorosis. Though unconfirmed by studies, individual reports have even suggested that ingestion of fluoride >8 mg/liter per day over a long period of time could produce skeletal fluorosis. However, with proper surveillance and reporting of fluoride in water systems, the greater population could be served, increasing the dental health of all individuals, especially the youth and saving dollars from excessive health care costs (ADA, 2009). Remember, a little prevention now can go a long way later.

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