; Fluoride_ Human Health and Caries Prevention - 09Dent
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Fluoride_ Human Health and Caries Prevention - 09Dent


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Arwa Owais
Fluoride: Human Health and
Caries Prevention
nFluoride ranks as a primary influence in
better oral health because it demonstrated
that caries and subsequent tooth loss were
not inevitable.

nJustas important, it helped dentists to
reshape their attitudes toward tooth
conservation and retention.

n   Fluorine is one of the most reactive elements and
    therefore is never found naturally in its elemental

n    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

 – F's ubiquity in soil and water means that
   all plants and animals contain F to some
 – 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.
n   Humans absorb F from air, food, and water.

n    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.
n   F's abundance in soils and plants means that
    everyone consumes some F.
n    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 area
n   Estimates 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.
n   For 2-year-olds in the same cities, the range was
    0.41 to 0.61 mg F/day

n    For infants, The Iowa studies documented
    the F exposures of new­ orn infants at
    periodic intervals through extensive
    interviews about all likely sources of F
n   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.
n   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.
n   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.
n   For most people, water and other
    beverages provide 75% of F intake,
    whether or not the drinking water is

n   This can occur because many soft
    drinks and fruit juices are processed in
    fluoridated cities.

n   Although 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

n   Everyone in dentistry should
    understand how the human body
    handles ingested F so that the material
    can be used safely and efficiently.
Absorption, Retention, and Excretion

n   Ingested F is absorbed mainly from the upper
    gastrointestinal tract.
n   About 80% of F in food is absorbed, as is 85% to
    97% of F in water.
n   Absorbed F is transported in the plasma, and is
    either excreted or deposited in the calcified tissues.
n   Most absorbed F is excreted in the urine;
n    F ingested on an empty stomach produces a peak
    plasma level within 30 minutes.
n   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.
n   When F absorption is inhibited this way, fecal
    excretion of F increases.
The Body Burden of F
n   Studies 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.
n   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.
The Body Burden of F
n   Urinary concentrations can vary
    considerably with fluid intake during the
    period of F exposure and require a 24 ­ our
    sample to be accurate.
n   Accurate monitoring of plasma levels in
    individuals also requires frequent measures
    because of normal hour-to-hour
n   Plasma F concentrations are more closely
    correlated with urinary flow rates than with
    urinary F concentrations.
The Body Burden of F

n   Although there is no absolute measure
    of lifetime F intake, even theoretically,
    the nearest measure of long-term F
    intake would come from bone F
n    For research purposes, however, this
    is a theoretical concept only; people
    don't volunteer to give a bone sample!
Fluoride Balance

n   Fluoride 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.
Fluoride Physiology
n   F has an affinity for calcified tissues (i.e.,
    bone and developing teeth).
n   F that is not excreted is deposited in these
    hard tissues, al­hough storage is dynamic
    rather than inert.
n   Bone F levels (from postmortem assays)
    range from 800 to 10,000 ppm, depending on
    many factors, including age and F intake.
n   F levels in the outer few microns of dental
    enamel range from 400 to 3000 ppm and
    decrease rapidly with greater enamel depth.
Fluoride Physiology
n   F 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.

n    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
    "Optimum Fluoride Intake"

n   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.

n      C
    Mc­ lure's estimate somehow came to be interpreted
    as the lower limit of the range of "opti­ um" F

n   A widely quoted 1974 reports suggested 0.06 mg
    F/kg body weight/day as "optimum,"
"Optimum Fluoride Intake"
n   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.

n    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

n   For 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.
"Optimum Fluoride Intake“??
n   Fluoride was classified as beneficial and not essential

n   The 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.

n   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.
 Early Studies

n   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.

n   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.
n   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.

n   For the United States as a whole, no differences
    could be found in 1949-1950 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.

n   Mortality rates were similar for cancer, heart
    disease, intracranial lesions, nephritis, and cirrhosis
    of the liver.

n   Similar findings were reported later in 1979.

n   A 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.

n   A special committee appointed by the US
    Public Health Service, reached the follow­ng
    conclusion on cancer risk:
n   Optimal fluoridation of drinking water
    does not pose a detectable cancer risk
    to humans as evidenced by extensive
    human epidemiological data available to
n   No trends in cancer risk, including the
    risk of osteosarcoma, were attributed to
    the introduction of fluoride into drinking
    water in these new stud­es.
Down Syndrome

n   A claim that water fluoridation caused an increase
    in Down syndrome came mid-1950s.

n   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.

n   More rigorous independent studies failed to show
    any correlation between fluoridation and Down
Bone Density, Fracture Experience, and

n   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.

n   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.

n   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.
Bone Density, Fracture Experience, and

n   Recently, ecologic studies to assess the risk
    of bone fracture relative to fluoridated water
    have produced mixed results:
    – decreased risk no association, and
    – increased 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.
Bone Density, Fracture Experience, and

n    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.
    Child Development

n   Newburgh-Kingston fluoridation project,
n   No significant differences in general health or body processes between
    children in the two cities were seen,
n   No radiographic differences in bone density could be demonstrated.
n   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
n   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.
n   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 signifi­ ance could be found between
    the two groups of children.

n   There is difference between a single intake of
    5.0 g F and constant intake of 1 to 3 mg F

n   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 dose­esponse relationship.

n   Ingestion 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.

n   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

n   If an individual is known or suspected to
    have taken a potentially toxic amount of F,
    first aid is to
    – induce vomiting or
    – ingest 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.
Dental Fluorosis

n   Dental 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.

n   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 com­ ination of
    several mechanisms. Three major mechanisms of action have
    been identified, although some possible addi­ional
    mechanisms have been hypothesized.

n   Earlier assumptions: Pre-eruptive F is thought to
    act by being incorporated into the developing
    enamel hydroxyapatite crystal and thus reducing
    enamel sol­ bility.

n   It has been argued that pre-eruptive benefits are
    especially important for reducing pit-and-fissure

n   This is the "pre-eruptive" model for which the
    actual supportive evidence is thin. The evidence for
    posteruptive F action is much stronger.
Fluoride and Plaque

n   F 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.
n    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.
n   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.
Fluoride and Plaque

n   F 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.
n   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.
Fluoride and Plaque

n        c
    High ­ oncentration F gels may have a specific
    bactericidal action on cariogenic bacteria in plaque.
n   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.
n   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.
Fluoride and Enamel

n   It 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

n   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.
    Fluoride and Plaque

n   Perhaps the most revealing study on the action of F in inhibiting
    dental caries came from the Tiel-Culemborg fluoridation study in
    the Netherlands.
n   Although there were considerably fewer dentinal lesions in
    fluoridated Tiel than in nonfluoridated Culemborg after 15 years
    of fluoridation.
n   There was no difference between the two communities in initial
    enamel lesions.
n   This finding means that fewer enamel lesions progress to
    dentinal caries in a fluoridated area than in a nonfluoridated
n                                                        t
    F, therefore, does not prevent the initial carious at­ack, which
    would be expected if its presence in the enamel crystal
    increased enamel resis­ance to acid dissolution.
n   The Tiel-Culemborg findings mean than F in the oral cavity
    inhib­ts further demineralization of the lesion and promotes its
    Fluoride and Saliva

n   Salivary F concentrations are low, although they are
    3 times higher in fluoridated than in nonfluoridated

n   In a fluoridated area, salivary F levels have averaged
    0.016 ppm; in a nonfluoridated area, they were 0.006

n   After toothbrushing with an F toothpaste or
    mouthrinsing with an F solution, salivary F levels can
    rise 100- to 1000-fold.
    Effects on Different Tooth

n   Although F reduces caries on both types
    of surface, the greatest relative effect is
    on smooth and proximal surfaces.

n   Categorizing F compounds into
    systemic fluorides and topical fluorides
    is not easy .

n   The most cost-effective way of reaching
    an entire community with regular, low-
    concentration F is through water

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