Preventive Dentistry Lecture (4)
2022-2022 5th stage
Assist. Professor Dr. Nada Jafer Radhi B.D.S., M.Sc., Ph.D. College of Dentistry/ University of Baghdad
Fluoride in dentistry
The history of fluorides in dentistry is over 100 years old. Fluoride was
isolated from water supplies in 1931 and has been incorporated into water, milk,
salt, tablets, and drops. It has also been included as an active agent for the
prevention of dental caries. The use of fluorides for dental purposes began in the
nineteenth century. The detrimental effects of fluoride on the appearance of tooth
enamel (dental fluorosis) that prompted the initial detailed investigations and
ultimately the discovery of its anticaries benefits. Water is by far the most common
natural source of fluoride, but even in areas with levels of fluoride in the drinking
water less than 0.5–0.7 mg/l, importation of commercially prepared beverages and
other foods, from areas where water supplies contain higher levels, can add
substantially to the amount of fluoride ingested.
Fluorine is the lightest member of the halogen group and is one of the most
reactive of all chemical elements (form salts of almost of all metals). It is not,
therefore, found as fluorine in the environment (which is derived from a Latin
word fluore that is to flow). It is the most electronegative of all the elements.
Fluoride thus forms mineral complexes with a number of cations and some fairly
common mineral species of low solubility contain fluoride.
Fluorine in the environment is therefore found as fluorides which together
represent about 0.06–0.09 per cent of the earth’s crust. Fluorides are found at
significant levels in a wide variety of minerals, including fluorspar (CaF2), rock
phosphate, cryolite (Na3AlF6), apatite (Ca10(po4)6F2) and others.
In atmosphere; Fluoride is commonly associated with volcanic activity and their
gases. It is originating from dusts of fluoride containing soils, gaseous industrial
wastes.
In sea water, the fluoride concentration ranged 0.8-1.4 ppm. While the
concentration in vegetation is range from 2-20 ppm dry weight according to
species of the plant, age of leafs, soils, fertilizers and pollution. Fluoride is return
to soils through plant wastes or it may enter the food chain and be returned as
animal’s waste. Thermal waters, especially those of high pH, are also rich in
fluoride. The fluoride salt cryolite is used for the production of aluminium and as a
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pesticide. Rock phosphates are converted into phosphate fertilizers by the removal
of up to 4.2 percent fluoride; the removed and purified fluoride (as fluorosilicates)
is a source of fluoride that in some countries is added to drinking water in order to
protect against dental caries.
Fluoride:
- has beneficial effects on teeth at low concentrations in drinking-water.
- excessive exposure to fluoride in drinking-water, or in combination with
exposure to fluoride from other sources, can give rise to a number of adverse
effects. These range from mild dental fluorosis to crippling skeletal fluorosis
as the level and period of exposure increases. Crippling skeletal fluorosis is a
significant cause of morbidity in a number of regions of the world.
- The caries preventive effect was demonstrated since 1930. Some studies
reported that water fluoridation reduce dental caries by 50%.
- Fluoride is expressed as part per million (ppm) which equal to 1 mg fluoride
per liter of water (kilogram).
- Sources of fluoride in man involving water, food (breast milk F= 6-
12mg/ml; cow’s milk F <0.019ppm; tea F= 0.5-4ppm; fish and shell fish),
drugs (diuretics and anesthetics) and dental products (as dentifrices and
mouth rinses).
Fluoride metabolism
Fluoride ingestion is particularly important in infants as dental fluorosis can only
occur when teeth are developing. Fluoride is poorly transported from plasma to
milk, even when the mother or animal has a high intake of fluoride
- Absorption
Approximately 75–90 per cent of ingested fluoride is absorbed. In an acidic
stomach, fluoride is converted into hydrogen fluoride (HF) and up to about 40 per
cent of the ingested fluoride is absorbed from the stomach as HF. High stomach pH
decreases gastric absorption by decreasing the concentration uptake of HF.
Relative to the amount of fluoride ingested, high concentrations of cations that
form insoluble complexes with fluoride (e.g. calcium, magnesium and aluminium)
can markedly decrease gastrointestinal fluoride absorption (70%) while in food
rich calcium (60%). The time of fluoride ingestion in relation to meals is critical
with respect to how much of the fluoride will become bioavailable
- Distribution
Once absorbed into the blood, fluoride readily distributes throughout the body,
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with approximately 99 per cent of the body burden of fluoride retained in calcium
rich areas such as bone and teeth (dentine and enamel) where it is incorporated into
the crystal lattice. In infants about 80 to 90 per cent of the absorbed fluoride is
retained but in adults this level falls to about 60 per cent. Fluoride crosses the
placenta is about 70% of that of maternal blood and is found in mother’s milk at
low levels essentially equal to those in blood.
Under certain conditions, plasma fluoride levels provide an indication of the level
of fluoride in the drinking-water consumed. Water is the major source of fluoride
intake, fasting plasma fluoride concentrations of healthy young or middle-aged
adults expressed in micromoles per liter are roughly equal to the fluoride
concentrations in drinking water expressed as milligrams per liter”.
Two forms of fluoride are present; the ionic form (free or in organic fluoride) and
the non-ionic or bounded fluoride. The ionic form in hard and soft tissues is the
most important to health and is directly related to the amount of fluoride intake.
The peak plasma concentration usually occurs within 30-60 minutes then
decreased after distribution in the body.
Levels of fluoride that are found in the bone vary with the part of the bone
examined and with the age and gender of the individual. Bone fluoride is
considered to be a reflection of long-term exposure to fluoride. In long bone, the
higher concentration of fluoride is in the periosteal region with a slight increase in
endosteal region. Cancellous bone has higher concentration of fluoride compared
to compact bone. Thus, bone might be considered a fluoride reservoir that
maintains the fluoride concentration in the body fluids between the periods that
fluoride is not being ingested.
Fluoride in soft tissues depends on the pH of extracellular fluid as higher acidity
increase fluoride ion exchange through tissue plasma. Therefore, alkalization of
body fluid is the useful treatment of fluoride toxicity.
- Excretion
Fluoride is excreted primarily via urine. After entering the renal tubules about 10-
90% of fluoride ions will be reabsorbed and return to the circulatory system.
Urinary fluoride clearance increases with urine pH due to a decrease in the
concentration of HF. Numerous factors (e.g. diet and drugs) can affect urine pH
and thus affect fluoride clearance and retention. About 10% of fluoride is excreted
by feces (either not absorbed or re-excreted into GIT). A few quantities of fluoride
are removed by sweat, saliva, tears.
Fluoride uptake
- Ingestion of fluoride during period of tooth formation (pre-eruptive stage), it may
cause changes in the tooth morphology and composition, as smaller more rounded
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cusps depth of teeth turns the more self-cleansing, also development of shallower
occlusal grooves. Fluoride ion may replace the hydroxyl group of hydroxyl apatite
crystal forming fluorapatite crystal.
Ca10 (Po4)6(OH)2 +2F- → Ca10 (Po4)6F2+2OH
Ingestion of fluoride in the pre-eruptive stage will allow the incorporation of
fluoride in the whole enamel and dentin. This will increase the resistance against
dental caries in addition reduces the progression of dental caries
- In post-eruptive stage, fluoride will react with the outer enamel surface to
enhance remineralization, thus continual topical application of fluoride is needed
from mouth rinses, teeth paste and others. Two types of reaction may develop and
can initiated at any time of person life.
Ca10 (PO4)6(OH)2 +20F- →10CaF2+6PO43-+2 OH-
Ca10 (PO4)6(OH)2 +2F- → Ca10 (PO4)6F2+2OH-
Fluoridated apatite and/or fluorapatite are generally found in the surface layers of
enamel that contains high fluoride concentrations of fluoride. This can arise both
during development and from topical exposure.
Enamel is composed primarily (~95%) of hydroxyapatite (HA) crystals in which
are substituted a number of other ions including fluoride.
Ca10(PO4)6(OH)2 + Mg++ = magnesium whitlockite
Ca10(PO4)6(OH)2 + CO − = carbonated apatite
Fluoride concentrations in teeth
Concentrations of fluoride in all mineralized tissues will vary depending on the
actual fluoride intake and the length of time during which such an intake has taken
place. In general, fluoride levels are greatest at the surface of any tissue since this
part of the tissue has the closest proximity to the surrounding tissue fluid from
which the fluoride is supplied.
The fluoride concentration of the enamel is highest at the surface, but it falls
steeply within the outer 100 Mm. After this point, it remains fairly constant up to
the enamel– dentin junction. The fluoride concentration of dentin is generally
higher than that of bulk enamel and usually increases deeper into the tooth. As
dentin formation continues slowly throughout life, fluoride steadily accumulates at
the dentin–pulp surface. However, the concentration of fluoride at the outermost
surface of the enamel is highly dependent on posteruptive changes and therefore it
may be a poor indicator of fluoride exposure during the developmental period of
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the tooth.
Once the enamel is fully formed and mineralized the fluoride content in human
enamel can only be permanently altered as a result of chemical traumas to the tooth
(dental caries and erosions) or through mechanical abrasion. Unless chemical
interactions take place with substantial fluctuations in pH over a prolonged period
it is not easy to change significantly the fluoride content in the surface enamel even
after several topical fluoride treatments. However, the fluoride concentration in the
surface layers increases whenever demineralization and remineralization processes
are ongoing. This means that in cervical regions, where dental plaque accumulates,
will gradually increase over time. It is also the reason why the surface zone
covering a subsurface caries lesion contains significantly higher amounts of
fluoride than the surrounding normal enamel fluoride concentrations.
Source of fluoride:
The source is water, food, saliva, gingiva in addition to fluoride products. Fluoride
accumulation in enamel is aided by plaque (0.01-50ppm F), which itself
accumulates fluoride that is applied topically.
Low concentration of fluoride is present in saliva 1-2mol/L from water, food,
dentifrices. The concentration of fluoride in saliva is two-third of plasma level.
