Fluoride Notes

Fluoride

  • Since 1930, fluoride (F) has been recognized for its anti-caries effect.
  • Small doses inhibit dental caries; large concentrations can cause dental fluorosis.

What is Fluoride?

  • Formerly known as fluorine, from the Latin "fluore" (to flow).
  • The 17th most frequent element, making up 0.06%-0.09% of the Earth's crust.
  • Found in minerals like:
    • Fluorspar (CaF2CaF_2)
    • Fluoroapatite (Ca<em>10(PO</em>4)<em>6F</em>2Ca<em>{10}(PO</em>4)<em>6F</em>2)
    • Cryolite (Na<em>3AlF</em>6Na<em>3AlF</em>6)

Historical Background

  • 1901: Dr. Frederick McKay identifies “Colorado Stain” (permanent teeth stains).
  • 1912: Mckay links Colorado Stain to a similar condition in Naples, Italy, called denti di chiae.
  • 1931: Churchill discovers high fluoride levels in water supplies caused mottled enamel.
  • 1933: Dean correlates mottled enamel severity with fluoride concentration. Ainsworth reports lower caries in high-fluoride areas.

Artificial Water Fluoridation

  • 1944: Experiment in Grand Rapids (experimental) and Muskegon (control) by Dr. Dean.
  • Sodium fluoride added to Grand Rapids' water.
  • After 6.5 years, Grand Rapids children had half the DMFT (decayed, missing, filled teeth) rate of Muskegon.

Fluoride Intake

  • From:
    • Soils
    • Water
    • Air absorption
    • Atmospheric deposition
    • Rain
  • Sources in humans:
    • Water (0.1-10 ppm)
    • Food (soft drinks, infant/adult food; breast milk: 6-12 mg/ml; tea: 0.5-4ppm; fish/shellfish)
    • Drugs/dental products (diuretics, anesthetics, dentifrices, mouth rinses)
    • Pollution (near metal industries, 25-1000x normal levels)

Metabolism of Fluoride

  • Absorption:
    • Mainly in the GIT (intestine and stomach) at 85-97%.
    • Bioavailability requires ionic form; bonded fluoride is excreted.

Factors Affecting Fluoride Absorption

  • Presence of food.
  • Presence of elements like calcium, magnesium, phosphate, aluminum.
  • Dose and F concentration.
  • Stomach acidity.
  • NaFNaF is more soluble than CaF2CaF_2, hence better absorption.
  • Food retards absorption.
  • Inverse relation between gastric acidity and absorption.
  • Milk may initially retard absorption but later increases it.

Fluoride Distribution

  • Fluoride content in teeth increases rapidly during early mineralization and continues at a slower rate with age.
  • Carious enamel absorbs 10x more fluoride than healthy enamel.
  • Highest concentration near pulp due to blood supply.
  • Distributes in the body within 10 minutes, peaks in plasma within an hour, returns to normal in 11-15 hours.
  • Calcified tissues (bone, teeth) store >99% of F.
  • Bonds to bone reversibly (remodeling), to teeth irreversibly (no remodeling).

Fluoride Excretion

  • Major route: kidneys (renal clearance: 50 ml/minute).
  • 10% removed by feces (unabsorbed).
  • Less quantity via sweat, saliva, gingival exudates, tears.

Fluoride Storage

  • Younger individuals deposit more fluoride in bones.
  • Uptake increases with fluoride concentration in water.
  • Deposition decreases over time, reaching a steady state where intake equals excretion.

Fluoride in Dentin and Enamel

  • Content is lower than in bone.
  • Dentin contains 4x more fluoride than enamel.
  • Highest concentration in dentin is adjacent to the odontoblastic layer.
  • Enamel's outer layer has 4-5x higher fluoride concentration than inner layers.

Chronic Fluoride Toxicity

  • Long-term exposure can lead to skeletal fluorosis (osteosclerosis and exostosis).
  • Severe cases: pain and deformity.
  • During tooth development: dental fluorosis (mottled enamel).
  • High natural fluoride levels can cause crippling bone disease (skeletal fluorosis), especially with nutritional deficiencies.

Acute Fluoride Poisoning

  • Lethal dose: 3-5 gm fluoride (63 mg/kg body weight).
  • Acidulated phosphate fluoride (1.23% F) in 250 ml bottles (~3 gm F) is a potent lethal dose if consumed rapidly.
  • Symptoms: vomiting, excess saliva/mucus, cold/wet skin, convulsions at higher doses.

Dental Fluorosis

  • Developmental enamel disturbance from excessive fluoride during tooth development.
  • Critical ages: 0-6 years; risk decreases after 8 years.
  • Sources: water (up to 1.5mg/day), foods (0.3-1.0mg), swallowed toothpaste (1mg F/day for young children).

Fluoride and General Health

  • No prominent effect on general health from water fluoride at 8 ppm over 37 years.
  • Prolonged high intake (up to 10 ppm) doesn't affect morbidity/mortality.
  • No effect on thyroid gland size or function.
  • No relationship between bone fracture and fluoride exposure in young males from fluoridated areas.
  • No evidence of allergy or intolerance.

Fluoride in Water

  • Optimal concentration: 1 ppm; reduced to 0.7-0.8 ppm in hot climates, increased to 1.2 ppm in cold climates.
  • >1 ppm: dental fluorosis in ~10% of the population.
  • Dean's threshold for endemic fluorosis: 1 ppm.
  • At 2.5 ppm, fluorosis incidence is ~70%.

Theories of Fluoride's Effect on Dental Caries

  • Pre-eruptive theory:
    • Fluoride intake during tooth formation alters composition/morphology.
    • Fluoride replaces hydroxyl in hydroxylapatite, forming fluoroapatite (more stable, less soluble, acid-resistant).
    • Results in rounded cusps and shallower pits/fissures.
  • Post-eruptive theory:
    • Fluoride in saliva/plaque enhances remineralization.
    • Formation of calcium fluoride (temporary) and fluoroapatite.
    • Requires continuous application of fluoridated products.
  • Antibacterial theory:
    • High fluoride concentration (>40 ppm) in plaque affects bacterial growth/fermentation.
    • Interferes with bacterial adherence and inhibits intracellular enzymes.
    • Toxic to bacteria in high concentrations.