2Fluoride: Human Health and Caries Prevention Fluoride ranks as a primary influence in better oral health because it demonstrated that caries and subsequent tooth loss were not inevitable.Just as important, it helped dentists to reshape their attitudes toward tooth conservation and retention.
3ENVIRONMENTAL FLUORIDE Fluorine is one of the most reactive elements and therefore is never found naturally in its elemental form.The F ion, however, is abundant in nature and occurs almost universally in soils and waters in varying, but generally low, concentrations.Seawater contains 1.2 to 1.4 ppm F.Fresh surface waters, 0.2 ppm F or less,Deep well waters, 29.5 ppm F have been recorded
4ENVIRONMENTAL FLUORIDE F's ubiquity in soil and water means that all plants and animals contain F to some extent.Given this environmental ubiquity, it seems likely that all forms of life must have evolved to thrive with continuous exposure to small amounts of F.
5SOURCES AND AMOUNTS OF FLUORIDE INTAKE Humans absorb F from air, food, and water.Air intake is usually negligible, around 0.04 mg F/day. Exceptions can occur around some industrial plants that work with F-rich material, an issue that has nothing to do with the use of F to control caries.
6SOURCES AND AMOUNTS OF FLUORIDE INTAKE F's abundance in soils and plants means that everyone consumes some F.Estimates for an adult North American male in a fluoridated area fall within the range of 1 to 3 mg F per day from food and beverages, decreasing to 1.0 mg F per day or less in a nonfluoridated areaEstimates from "market basket" analyses are that 6-month-old infants ingest 0.21 to 0.54 mg F/day in 4 American cities with different F concentrations in the drinking water.For 2-year-olds in the same cities, the range was 0.41 to 0.61 mg F/day
7SOURCES AND AMOUNTS OF FLUORIDE INTAKE For infants, The Iowa studies documented the F exposures of newborn infants at periodic intervals through extensive interviews about all likely sources of F exposure.Total F intakes from drinking water alone during the first 9 months of life, either consumed directly or when added to formula and juice, averaged 0.29 to 0.38 mg F/day.
8SOURCES AND AMOUNTS OF FLUORIDE INTAKE Although similar to earlier market basket surveys, there was considerable range of intake with 25% of 9-month old children ingesting 0.49 F/day.Even without swallowing F toothpaste or taking F supplements, the risk of dental fluorosis is likely to be increased in these children because the upper limit of intake for 12-month-old children, beyond which the risk of detectable fluorosis is increased, has been estimated at 0.43 mg F/day.
9SOURCES AND AMOUNTS OF FLUORIDE INTAKE For most people, water and other beverages provide 75% of F intake, whether or not the drinking water is fluoridated.This can occur because many soft drinks and fruit juices are processed in fluoridated cities.
10FLUORIDE PHYSIOLOGYAlthough the use of F is a contribution to the public's health of which dentistry can be proud, F compounds must be handled responsibly and with respect.Everyone in dentistry should understand how the human body handles ingested F so that the material can be used safely and efficiently.
11Absorption, Retention, and Excretion Ingested F is absorbed mainly from the upper gastrointestinal tract.About 80% of F in food is absorbed, as is 85% to 97% of F in water.Absorbed F is transported in the plasma, and is either excreted or deposited in the calcified tissues.Most absorbed F is excreted in the urine;F ingested on an empty stomach produces a peak plasma level within 30 minutes.The time of the plasma peak is extended and the level of the peak reduced, if F is taken with food. This is probably because of the binding of some F with calcium and other cations.When F absorption is inhibited this way, fecal excretion of F increases.
12The Body Burden of FStudies on what is called the body burden of F, meaning how much can be safely absorbed and at what point F absorption becomes a health concern, have mostly relied on urinary volumes and plasma concentrations as the primary measures.Samples of both are relatively simple to obtain, although both measures record only recent F intake (i.e., the previous 3 to 4 weeks) rather than lifetime intakes.
13The Body Burden of FUrinary concentrations can vary considerably with fluid intake during the period of F exposure and require a 24 hour sample to be accurate.Accurate monitoring of plasma levels in individuals also requires frequent measures because of normal hour-to-hour fluctuations.Plasma F concentrations are more closely correlated with urinary flow rates than with urinary F concentrations.
14The Body Burden of FAlthough there is no absolute measure of lifetime F intake, even theoretically, the nearest measure of long-term F intake would come from bone F content.For research purposes, however, this is a theoretical concept only; people don't volunteer to give a bone sample!
15Fluoride BalanceFluoride balance is the net result from the accumulated effects of F ingestion, degree of F deposition in bones and teeth, mobilization rate of F from bone, and the efficiency of the kidneys in clearing absorbed F.
16Fluoride PhysiologyF has an affinity for calcified tissues (i.e., bone and developing teeth).F that is not excreted is deposited in these hard tissues, although storage is dynamic rather than inert.Bone F levels (from postmortem assays) range from 800 to 10,000 ppm, depending on many factors, including age and F intake.F levels in the outer few microns of dental enamel range from 400 to 3000 ppm and decrease rapidly with greater enamel depth.
17Fluoride PhysiologyF concentrations in soft tissue rise or fall parallel to plasma F levels, but because healthy excretion and deposition mechanisms operate so rapidly there are negligible concentrations of F in the fluids of soft tissues other than the kidney.A greater proportion of ingested F is excreted in older persons than in the young. It had been suggested that this was because children had lower renal clearance rates than adults, but is now attributed to greater adsorption of F by the young skeleton.
18"Optimum Fluoride Intake" Frank McClure, estimated in 1943 that the "average daily diet" contained 1.0 to 1.5 mg F, or about 0.05 mg F/kg body weight/ day in children up to 12 years of age.McClure's estimate somehow came to be interpreted as the lower limit of the range of "optimum" F intake.A widely quoted 1974 reports suggested 0.06 mg F/kg body weight/day as "optimum,"
19"Optimum Fluoride Intake" The range of 0.05 to 0.07 mg F/kg body weight/day was suggested as "optimum" in 1980, and has even been accepted by opponents of water fluoridation.The estimate of 0.05 to 0.07 mg F/kg/day converts to 3.5 to 4.9 mg F per day for a man weighing 70 kgFor a 10-kg infant , that is a 12- to 18-month-old child, this "optimum" intake converts to 0.45 to 0.64 mg F/day.
20"Optimum Fluoride Intake“?? Fluoride was classified as beneficial and not essential nutrientThe discussions vague about what this intake is "optimum" for. "optimum" for caries resistance, but little of F's action in caries control can be attributed to ingested F.There is no evidence to link this range of F ingestion with caries inhibition, so we suggest that the term "optimum intake" be dropped from common usage.
21FLUORIDE and HUMAN HEALTH Early Studies The first study relating bone fracture experience to the F concentration in home water supplies, a subject revisited in the 1990s, concluded that there was no relationship.McClure then demonstrated the close relationship between urinary F and the F levels of domestic water. His balance studies during World War II, led to the conclusion that the elimination of absorbed F via urine and perspiration is almost complete when the quantity absorbed does not exceed 4 to 5 mg daily. McClure suggested that this may be the F limit that could be ingested without "appreciable hazard" of excessive F storage in the body.
22FLUORIDE and HUMAN HEALTH There was sufficient research evidence to provide reasonable assurance that controlled fluoridation, with up to 1.2 ppm F in the drinking water, could be-instituted in North America without any public health hazard.
23MortalityFor the United States as a whole, no differences could be found in death rates between 32 cities with 0.7 ppm F or more and 32 randomly selected nearby cities with 0.25 ppm F or less in the drinking water.Mortality rates were similar for cancer, heart disease, intracranial lesions, nephritis, and cirrhosis of the liver.Similar findings were reported later in 1979.
24CancerA number of independent analyses of the same data, in both Britain and the United States, however, used more detailed age-sex-race adjustments; none could find a link between cancer incidence and consumption of fluoridated water.A special committee appointed by the US Public Health Service, reached the following conclusion on cancer risk:
25CancerOptimal fluoridation of drinking water does not pose a detectable cancer risk to humans as evidenced by extensive human epidemiological data available to date.No trends in cancer risk, including the risk of osteosarcoma, were attributed to the introduction of fluoride into drinking water in these new studies.
26Down SyndromeA claim that water fluoridation caused an increase in Down syndrome came mid-1950s.The studies had errors in the research design. The most serious error was to assume that the city of birth was the place of residence of the mother, which is clearly not the case for hospitals serving a large rural population.More rigorous independent studies failed to show any correlation between fluoridation and Down syndrome.
27Bone Density, Fracture Experience, and Osteoporosis Bone fragility conditions (e.g., spontaneous vertebral fracture in the elderly as a result of osteoporosis) have been treated for years with high does of F combined with calcium, estrogen, and vitamin D.Controlled clinical trials have shown that high doses of- F (30 to 60 mg/day), administered under medical supervision, can increase vertebral bone mass and reduce the vertebral fracture rate.These favorable changes do not come without problems, however, for the new bone can be imperfectly mineralized and a good proportion of patients do not respond to treatment.
28Bone Density, Fracture Experience, and Osteoporosis Recently, ecologic studies to assess the risk of bone fracture relative to fluoridated water have produced mixed results:decreased risk no association, andincreased risk, with relative risks in the range of 1.08 to 1.41.Extensive reviews of literature have also reached the conclusion that no relationship can be discerned between bone fracture experience and water with 1.0 ppm F.
29Bone Density, Fracture Experience, and Osteoporosis In summary, although there does not appear to be any protective effect from fluoridated water, neither is there evidence that bone fracture experience is associated with drinking water containing 1.0 ppm F.
30Child Development Newburgh-Kingston fluoridation project, No significant differences in general health or body processes between children in the two cities were seen,No radiographic differences in bone density could be demonstrated.Essential similarity in vision and hearing tests and in findings for skeletal maturation, hemoglobin level, erythrocyte and leukocyte counts, and quantity of sugar, albumin, red blood cells, and casts in urine.At the final examination, 19 of 476 children in Newburgh (4.0%) and 20 of 405 children in Kingston (4.9%) were referred to the family physician for conditions including such minor ailments as a plantar wart or ringworm.Long-term downward trends in stillbirth and maternal and infant mortality rates continued in each of the cities. The overall conclusion was that no differences of medical significance could be found between the two groups of children.
31FLUORIDE TOXICITYThere is difference between a single intake of 5.0 g F and constant intake of 1 to 3 mg F daily.F is like many other nutrients: beneficial in small amounts, toxic in high amounts. This gradation in response with variations in dose is a common pharmaceutical phenomenon and is known as a doseresponse relationship.
32FLUORIDE TOXICITYIngestion of a single dose of 5 to 10 g of sodium fluoride by an adult male (32 to 64 mg F/kg body weight) results in a rather unpleasant death in 2 to 4 hours if first aid is not applied immediately.From that lower limit of 32 mg F/kg body weight, the estimated equivalent dose for a 10-kg child (12 to 18 months old) is 320 mg F.
33FLUORIDE TOXICITYIf an individual is known or suspected to have taken a potentially toxic amount of F, first aid is toinduce vomiting oringest a material to bind F. Milk is usually the most readily available.The ADA recommends, as a safety precaution, that F materials for home use contain no more than 264 mg F if packaged in a bulk container (tablets, mouthwash) or up to 300 mg F if the F material is individually packaged.
34Dental FluorosisDental fluorosis is a permanent hypomineralization of enamel, characterized by greater surface and subsurface porosity than in normal enamel. It results from excess F reaching the developing tooth during developmental stages.
35FLUORIDE AND CARIES CONTROL: MECHANISMS OF ACTION F works best to prevent caries when a constant, low ambient level of F is maintained in the oral cavity. Its most important caries-inhibitory action is posteruptive, though a pre-eruptive role continues to be suggested. F’s action in preventing caries is multifactorial; its effect comes from a combination of several mechanisms. Three major mechanisms of action have been identified, although some possible additional mechanisms have been hypothesized.
36FLUORIDE AND CARIES CONTROL: MECHANISMS OF ACTION Earlier assumptions: Pre-eruptive F is thought to act by being incorporated into the developing enamel hydroxyapatite crystal and thus reducing enamel solubility.It has been argued that pre-eruptive benefits are especially important for reducing pit-and-fissure lesions.This is the "pre-eruptive" model for which the actual supportive evidence is thin. The evidence for posteruptive F action is much stronger.
37Fluoride and PlaqueF introduced into the mouth is partly taken up by dental plaque, where 95% of it is held in bound form rather than as ionic F.Plaque contains 5 to 10 mg F/kg wet weight in low F areas and 10 to 20 mg F/kg wet weight in fluoridated areas.The bound F can be released in response to lowered pH, and F is taken up more readily by demineralized enamel than by sound enamel. The availability of plaque F to respond to the acid challenge leads to the gradual establishment of a well-crystallized and more acid-resistant apatite in the enamel surface during demin-remin.
38Fluoride and PlaqueF in plaque also inhibits glycolysis, the process by which fermentable carbohydrate is metabolized by cariogenic bacteria to produce acid. F from drinking water and toothpaste concentrates in plaque, which contains higher levels of F than does saliva.There is also some evidence that plaque F can inhibit the production of extracellular polysaccharide by cariogenic bacteria, a necessary process for plaque adherence to smooth enamel surfaces.
39Fluoride and PlaqueHigh concentration F gels may have a specific bactericidal action on cariogenic bacteria in plaque.These gels also leave a temporary layer of CaF2 on the enamel surface, which is available for release when the pH drops at the enamel surface.At lower concentrations, Streptococcus mutans has been shown, to become less acidogenic through adaptation to an environment where F is constantly present. It is not yet known whether this ecologic adaptation reduces the cariogenicity of acidogenic bacteria in humans.
40Fluoride and EnamelIt became evident to researchers as early as the mid-1970s that a higher concentration of enamel F could not by itself explain the extensive reductions in caries that F produced.The theoretical concentration of F in pure fluorapatite that would reduce its acid solubility is 38,000 ppm, a concentration not even approached in human dental enamel.
41Fluoride and PlaquePerhaps the most revealing study on the action of F in inhibiting dental caries came from the Tiel-Culemborg fluoridation study in the Netherlands.Although there were considerably fewer dentinal lesions in fluoridated Tiel than in nonfluoridated Culemborg after 15 years of fluoridation.There was no difference between the two communities in initial enamel lesions.This finding means that fewer enamel lesions progress to dentinal caries in a fluoridated area than in a nonfluoridated area.F, therefore, does not prevent the initial carious attack, which would be expected if its presence in the enamel crystal increased enamel resistance to acid dissolution.The Tiel-Culemborg findings mean than F in the oral cavity inhibits further demineralization of the lesion and promotes its remineralization.
42Fluoride and SalivaSalivary F concentrations are low, although they are 3 times higher in fluoridated than in nonfluoridated areas.In a fluoridated area, salivary F levels have averaged ppm; in a nonfluoridated area, they were ppm.After toothbrushing with an F toothpaste or mouthrinsing with an F solution, salivary F levels can rise 100- to 1000-fold.
43Effects on Different Tooth Surfaces Although F reduces caries on both types of surface, the greatest relative effect is on smooth and proximal surfaces.
44EFFECTIVE USE OF FLUORIDE Categorizing F compounds into systemic fluorides and topical fluorides is not easy .The most cost-effective way of reaching an entire community with regular, low-concentration F is through water fluoridation.