Fluoride

Fluorine is the member of the halogen family with a relative atomic weight of 19 and an atomic number 9. The word fluorine is derived from the latin term “Fluore” meaning “to flow”. At room temperature fluorine is a pale yellow green gas. It is the most electronegative and reactive of all elements and thus, in nature, is rarely found in its elemental form. The WHO expert committee on trace elements has included fluorine as one among the 14 physiologically essential elements for normal growth and development of human beings.

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Cerium(IV) fluoride

Sodium fluoride tablets

Historical Evolution of Fluoridation

The history of fluoridation is more than 70 years old. It started with the arrival of Dr Fredrick Mckay in Colorado springs, Colorado, USA in 1901, the year following his graduation from the University of Pennsylvania Dental School. He soon noticed that many of his patients had an apparently permanent stain on their teeth, which was known to the local inhabitants as “Colorado brown stain”.

• 1902: The first systematic endeavor to investigate this lesion was made by the Colorado Springs Dental Society.
• 1905: Mckay moved to St. Louis to practice orthodontics. There he never saw a case of mottled enamel and when he returned in 1908, the stain problem struck him with more force than ever.
• 1908: El Paso county Odontological Society sent him, together with the patients to the annual meeting for the state Dental Association in Boulder. Here he learned of similar conditions in several other towns. The dentists here had not bothered to report the stain. Dr Mckay approached Dr. G.V.Black for help

and he agreed to attend the Colorado state Dental Association meeting in July 1909 and promised to spend some time in Colorado Springs. In preparation for this visit and a first step in mapping out the entire endemic area, Mckay and a fellow townsman, Dr Isaac Binton, examined the children in the public schools. 2945 children were examined. 87.5% of the children native to the area had mottled teeth. For the first time the investigator had statistical data. This information was given to Dr. Black when he arrived.

• 1912: Mckay found an article written by Dr J.M Eager in 1902 reporting the unusual occurrence of brownish colored stains among majority of the residents in Naples. Eager had termed these brownish discolorations as “denti di chiaie”.
• 1916: Mckay and Dr Black conducted studies on individuals living in 26 different communities in various parts of USA and they concluded that an unidentified factor was responsible for the mottling of enamel. They assumed that this unknown factor might has been present in the water consumed by the individuals during the period of tooth calcification. They based this assumption from the observation that the water supply of Britton was changed from shallow wells to deep wells after 1898 and those people who were born prior to 1898 had normal appearance of teeth while those born after 1898 had enamel mottling.
• 1918: Mckay confirmed the presence of an unknown element in the water supply to be the definite causative factor for enamel mottling. Similar findings were reported in Bauxite with regard to change in water supply. In Oakley and Idaho, Mckay found, the children living on the outskirts of the city, using water from a private spring, were free of mottling. He advised the people of Oakley to abandon their old water supply and tap their spring for a new source, which the community did in 1925. Children born in Oakley, subsequent to the change were free of mottled enamel.
• 1928: Mckay observed that in areas where the mottled enamel conditions were found, the prevalence of dental caries appeared lower than would be expected.
• 1931: Mckay sent several samples of suspected water to Churchill H V, a chemist employed with an aluminum company Alcoa. Spectrographic analysis was done. The mysterious factor responsible for mottled enamel was thus identified as “Fluoride”. The fluoride levels ranged from 13–17 ppm. Other important studies carried out were the “21 city study” and the “Shoe Leather survey”.
• 1931: US National Institute of Health appointed Dr, H. Trendly Dean, the first dentist to study the fluoride-caries-mottled enamel relation. The term “mottled enamel” was replaced to “Fluorosis”. Dean conducted a survey among 22 cities in ten states of USA on a total population sample of 5824 children and gave the following report on mottling of enamel at various concentration of fluoride:

1. A high concentration of fluoride in water is directly related to the severity of enamel mottling
2. Enamel mottling was widespread in areas with water having fluoride content of 3 ppm.
3. Mottling with discrete pitting of enamel was noticed at fluoride levels of 4 ppm
4. Mottling was less in case of fluoride levels of 2.5–3 ppm with a dull chalky white appearance of teeth.
5. No mottling or any other enamel changes were observed in areas with water containing 1 ppm fluoride.
6. Dental caries experience in different communities dropped sharply as fluoride concentration rose towards 1 ppm and then leveled off.

• 1934: Trendly H Dean introduced the mottling index which is popularly known as Dean’s Index of fluorosis.
• 1942: The important milestone discovery was made by Dean et al that at 1 ppm fluoride in water, 60% reduction in caries experience was observed.
• 1945: World’s first artificial fluoridaton plant at Grand Rapids, USA began and thus started water fluoridation.

Fluorine in the Environment

Lithosphere

Fluoride is widely distributed in the earth’s crust where it averages to 300 ppm. Concentration of fluoride is increased in highly siliceous igneous rocks, alkali rocks in geothermal waters and hot springs and volcanic gases. Examples of minerals containing fluoride are:

• Fluorspar (principle fluoride containing mineral) Fluorapatite and Cryolite.

Biosphere

The normal level of fluoride in plants is about 2–20 mg/gm of dry weight. Leafy vegetables such as cabbages, lettuce and Brussel sprouts contain about 11–26 mg fluoride on dry weight basis. Tea plants have found to accumulate high concentration of fluoride. Washing leafy vegetables reduces fluoride by about 1/3 to 1/2. Plants growing in acidic solids, in vicinity of industries show elevated fluoride concentration. The concentration of fluoride in various animal products is approximately in the same range as the plants, e.g. sardines, salmon, mackerel and other fishes contain 20 ppm of fluoride (High fluoride level in fish is attributed to skin and bones).

Hydrosphere

Water contains fluoride in varying concentration. Highest of about 2800 ppm is found in Lake Nakura in Kenya. Surface water has less fluoride compared to ground water.

Atmosphere

Fluoride emissions are heaviest in the vicinity of industries in the production of aluminum from cryolite, fertilizers, fluorinated hydrocarbons, etc.

Pharmacokinetics of Fluoride

• The absorptive process occurs by passive diffusion from both the stomach (mainly) and the intestine (GI tract). The ionic fluoride which enters the acidic environment of the stomach is largely converted into HF (undissociated weak acid hydrogen fluoride) which readily passes through the biologic membrane of the stomach. (H+ + F¯ → HF)
• The fluoride which is not absorbed from the stomach will be readily absorbed through the microvilli in the intestine. The plasma peak usually occurs in 30 mins. Half life is 4–10 hours.

Distribution to Mineralized Tissue

Bone

Approximately 99% of all the fluoride in the human body is found in calcified tissues. Mature bones take up less fluoride compared to younger ones. Cancellous bone incorporates more than cortical bone. Fluoride is reversibly bound to the bone.

Enamel

The enamel which is porous absorbs fluoride. The accumulation of fluoride by enamel seems largely restricted to the surface than the interior.

Dentin

Dentin is like bone and cementum, it is a mesenchymal derivative unlike enamel which is ectodermal in origin. Mesenchymal tissues have collageneous matrix, increased surface area of the crystals, tubular structure and high degree of tissue hydration which succumb to high fluoride absorption (fluoride concentration is highest towards the pulpal surface).

Cementum

Greater tissue porosity and poor crystallinity facilitate increased fluoride uptake in cementum. Absorption of fluoride in ascending order: Cementum > bone > dentine > enamel

Distribution to the Fetus

Some authors have said that placenta acts as a complete barrier to fluoride, while others have said that the placenta barrier is partial (Primary dentition exhibits less severe degree of dental fluorosis, then permanent dentition).

Excretion of Fluoride

Fluoride is excreted in urine, feces and is lost through sweat. It also occurs in traces, in breast milk, saliva, hair and tears. About 10–25% of the daily intake of fluoride is excreted. Renal clearance is 35 ml/min and it is pH dependent.

Trace Elements in Tissues and Biologic Systems

Aluminum	Copper	Nickel
Antimony	Fluorine	Rubidium
Barium	Iodine	Selenium
Boron	Lead	Silver
Bromine	Lithium	Strontium
Cadmium	Manganese	Tin
Chromium	Mercury	Vanadium
Cobalt	Molybdenum	Zinc

• Dailymed label info on Fluoride
• FDA Fluoride

Fluoride Resources
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