Fluoride

1
Fluoride

• Arwa Owais

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Fluoride 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.

3
ENVIRONMENTAL 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

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ENVIRONMENTAL 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.

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SOURCES 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.

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SOURCES 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
  area
• 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.
• For 2-year-olds in the same cities, the range was
  0.41 to 0.61 mg F/day

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SOURCES 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.

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SOURCES 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.

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SOURCES 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.

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FLUORIDE PHYSIOLOGY

• 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
  respect.
• Everyone in dentistry should understand how the
  human body handles ingested F so that the
  material can be used safely and efficiently.

11
Absorption, 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.

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The Body Burden of F

• 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.
• 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.

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The Body Burden of F

• Urinary 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.

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The Body Burden of F

• 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
  content.
• For research purposes, however, this is a
  theoretical concept only people don't volunteer
  to give a bone sample!

15
Fluoride Balance

• 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.

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Fluoride Physiology

• F 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.

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Fluoride Physiology

• 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.
• 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.

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"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,"

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"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 kg
• 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.

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"Optimum Fluoride Intake??

• Fluoride was classified as beneficial and not
  essential nutrient
• 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.
• 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.

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FLUORIDE 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.

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FLUORIDE 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.

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Mortality

• 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.
• Mortality rates were similar for cancer, heart
  disease, intracranial lesions, nephritis, and
  cirrhosis of the liver.
• Similar findings were reported later in 1979.

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Cancer

• 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.
• A special committee appointed by the US Public
  Health Service, reached the following conclusion
  on cancer risk

25
Cancer

• Optimal 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.

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Down Syndrome

• A 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.

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Bone 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.

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Bone 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, 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.

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Bone 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.

30
Child 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.

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FLUORIDE TOXICITY

• There 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.

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FLUORIDE TOXICITY

• 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.
• 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.

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FLUORIDE TOXICITY

• 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.

34
Dental Fluorosis

• 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.

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FLUORIDE 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. Fs 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.

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FLUORIDE 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.

37
Fluoride and Plaque

• 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.
• 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.

38
Fluoride and Plaque

• 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.
• 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.

39
Fluoride and Plaque

• High 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.

40
Fluoride and Enamel

• 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 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.

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Fluoride and Plaque

• Perhaps 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.

42
Fluoride and Saliva

• Salivary 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 0.016 ppm in a nonfluoridated area,
  they were 0.006 ppm.
• After toothbrushing with an F toothpaste or
  mouthrinsing with an F solution, salivary F
  levels can rise 100- to 1000-fold.

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Effects on Different Tooth Surfaces

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

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EFFECTIVE 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.