Fluoride reduces dental caries through multiple mechanisms including: 1) Incorporation into tooth enamel and dentin during development and after eruption, making the tooth structure less soluble in acid. 2) Interacting with the bacterial enzymes and metabolic processes that produce acid in dental plaque, reducing acid production. 3) Promoting remineralization of enamel and dentin that have been demineralized by acid from plaque bacteria.

1. Mechanism Of Action of Fluoride in dental
caries.

2. Mechanism of action of
fluoride
• Florine is the most electronegative
element and therefore highly reactive. It
does not occur in the elemental state (F2)
in nature but is widespread in nature,
occurring in fresh water, vegitables, blood,
milk and organic compounds.
• Since fluoride can affect both the
inorganic tooth structure & the bacterial
metaboloims in plaque, several mechanism
of action have been proposed.

3. • Reduced enamel, solubility, improved
crystallinity, promotion of reminerlization,
lower free surface energy, desorption of
protein and bacteria, reduced cariogenic
flora & inhibition of bacterial enzymes
systems.
• Many of these mechanisms probably work
simultaneously depending on the
cnsentration and form of fluoride but the
exact contribution of any one of the total
careis reduction is unknown.

4. Systemic Effect of
Fluoride
• The main in organic constituent of tooth and bone is
hydroxy apatite (HAP)
• Hydroxy apatite on addition of fluorine results in the
formation of flour apatite (FAP) or fluoridated
hydroxy apatite becaue not all the hydroxyl groups
are replaced by fluorides.
• A pure fluorapatite crystal would contain 38,000 ppm
F but enamel form a fluoridated area contain only 500
to 2000 ppm.
• And this leads to speculation on several possible
mechanims of action of systemically ingested
fluoride improved crystalinity, the void theory, FAP
V/s HAP solubility in acid & iproved tooth morphology.

5. • Improved crystallinity :-
This theory is
explained by x-ray diffraction method -
Fluoride increases the crystal size and
less produces, less strain in crystal lattice.
This takes place through conversion of
amorphous calcium phosphate into
crystalline hydroxy phosphate.

6. • Void theory :- void in the crystals
decreases the stability and increases
chemical reactivity. If fluoride fills
these void in the hydroxy apetite
crystals it will attain stable from with
formation of more and stronger
hydrogen bonds. Greater stability will
leads to lower solubility and hence
greater resistance to dissolution in
acids.

7. • Acid Solubility (FAP V/s HAP) The simplest
explanation for the decreased solubility of fluoridated
enamel is that fluorapatite (with a solubility product
constant of 10-60) is less soluble than hydroxyapatite
(whose solubility product is constant between 10-55 and
10-60) 46 However, the amount of fluoride in surface
enamel from the teeth of persons living in a
fluoridated area is only 500 to 2000 ppm F-. This is
but a fraction of the theoretie amount of fluoride in
fluorapatite (38000 ppm F in enamel). Obviously little
of the enamel is composed of fluorapatite.
However the actual difference in the
amount dissolving is usually so small that it is not likely
to be factor in cariostasis.

8. • Tooth Morphology:-
Quantitative studies on
the influence of fluoride in the morphology
of human teeth showed that person living
in a high fluoride areas shows smaller cusp
height and less convexity
According to Wallensus, tooth in a high
fluoride area were 1.7% wider then
control.

9. Topical Effect Of
Fluoride
• Topical effect of fluoride may be due to
either low or high concentration of
fluoride and frequent or sporadic
exposure.
• Bacterial Metabolism & fluoride:-
Once the teeth
erupt into oral cavity, the systemic
effects of fluoride on enamel ceases
fluoride is relieved to have an effect on
the glycolates pathway of oral micro
organism.

10. • Enzyme Inhibition

11. • Fluoride has enolase inhibition effect and it also
inhibits glucose transport, enolase is a metallo
enzyme that requires adjavalent cation for tis
activity., fluoride due to its increased reactivity
forms a complex with this cation. Thus inhibiting
the enzyme. It also inhibits non-metallo enzyme
like phosphatage thus leading to reduce acid
production.
• Suppression of flora :- Stanous fluoride is a
potent suppressor of the bacterial growth
because it oxidizes the thiol group present in
bacteria thus inhibiting bacterial matabolism.

12. • Antibacterial action:- The concentration of
fluoride above 2 ppm in solution progressively
decrease the transport of uptake of glucose into
Cells of streptococci and also reduces ATP
synthesis.
Action of fluoride on tooth surface
• Fluoride incorporation in enamel – Incorporation
of fluoride into enamel through out development
is not a principal mechanism of cario static's
effect. It is believed that pre eruptive exposure
to fluoride may produce teeth more resistance
to caries by making pits and fissures shallower.

13. • Pre-eruptive in corporation – fluoride gets
incorporated in the fluid filled sac, which
surrounds the developing tooth. It then
enters the developing enamel. Highest
concentration of fluoride is seen in enamle
crown located at or near the tooth
surface.
• Post eruptive incorporation – fluoride
continuous to enter the enamel surface,
causing crystal to change from
predominatly carbonated apatite and
hydroxy apatite to flour apatite (FAP) and
flour hydroxy apatite (FHAP) crystals.
These fluoride rich crystals are less acid
soluble then the original enamel apatite.

15. Remenerilization of Acid Dissolved enamel
Minerals of tooth enamel are continuously in
exchange with the minerals of saliva and thus
the balance is maintained. This Equilibrium
can get disturbed with the organic acid
produced by the metabolism of fermentable
carbohydrates by the microorganism. This
leads to drop in PH. of the plaque on the
enamel surface and in the sub surface.
Minerals, particularly calcium and phosphate
leave the dissolved enamel in their ionic form
an entrace the plaque fluid. This process is
called deminerilization this get reverrse with
the factor like fluoride and is terms
reminerilization.

16. Specific Plaque
Hypothesis
• The use of topical fluoride as a cure for
infection has been termed the specific plaque
hypothesis by hoesche. The primary
assumption in this theory is that dental caries
results from a specific pathogen, S. mutans.
Thus the elimination or reduction of this
pathogen with provide a lasting cariostatic
effect. Thus the specific palque hypothesis
explains a persistant anticaries action of
topical fluorides that is not seen with water
fluoridation or fluoride dentifrices.

17. • References:
• Shobha Tondon
Text book of pedodontics