1. Anticaries Mechanism of Fluoride
DENT 5302 TOPICS IN DENTAL BIOCHEMISTRY
6 April 2007
Anticaries Mechanism of Fluoride
The Effect on De/Remineralization
Objectives:
Role of structural-bound vs topical fluoride
The effect of fluoride on demineralization
The effect of fluoride on remineralization

2. Outline Caries resistance concept vs Current philosophy
Why it was believed that structurally-bound F was important?
What are the conflicting evidences?
How fluoride inhibits demineralization
How fluoride enhances remineralization

3. Historical perspective
Fluoride presented during tooth formation provided 'caries resistance'
Current philosophy
Caries-reducing effect of fluoride is from its presence during active caries development to alter the dynamics of de- and remineralization
Why do we want to know how fluoride prevents dental caries?
Basis to develop effective ways of using fluoride
Systemic F for the maximum benefit
(less soluble enamel )
Risk of developing (mild) fluorosis
Posteruptive effect
Topical fluoride application

4. Caries Resistance Concept
Historical perspective: Fluoride & Caries Resistance
Caries Resistance Concept
Fluoride present during tooth formation provided 'caries resistance'
Systemic incorporation of fluoride into enamel during development
‘More perfect’ enamel crystals Less acid soluble
Structurally-bound fluoride is life-long protection.
The more fluoride incorporated, the better the cariostatic effect.
Treatment strategy according to this concept:
Systemic F for the maximum benefit (less soluble enamel )
Consequence
Risk of developing (mild) fluorosis

5. Is that true? Water fluoridation (10 years) reduced DMF
Fluoride incorporated in tooth structure increases caries-resistance
Is that true?

6. Lower caries prevalence
Why was fluoride believed to make teeth more resistant to caries attack?
Fluoridated area
Non- fluoridated area
F in water supplies
Lower caries prevalence
2.5 ppm
Teeth formed in fluoridated area
Increased F content in surface enamel
But….2000 vs 3000 ppm F is too small for 50% reduction in DMF!
Comm Dent Oral Epid 1985;13:65-7.
No correlation between DMFT and enamel fluoride concentration

7. F in tooth structure is not crucial
Shark enamel (almost pure fluorapatite; 30,000 ppm F) developed caries lesions in an in situ model (4 wks), although less severe
Human enamel + 0.2% NaF rinse (daily, 4 wks) ~ Shark enamel
Human
Shark
Ögaard B et al.
Scand J Dent Res 1991;99:
Human
+ rinse
FAP has only a moderate caries protective potential, ~ daily F-rinse.

8. does not provide enough Ca? (Ca is firmly bound)
Human
Shark
+ Rinse
Shark enamel % NaF rinse was not as good as human enamel % NaF rinse
Human enamel:
CaF2-like globules
Shark enamel:
Nothing observed
does not provide enough Ca? (Ca is firmly bound) 1
CaF2-like material: caries inhibition effect of topical fluoride
Ögaard B et al. Scand J Dent Res 1991;99: & 1988;96:

9. x Unwanted Calcium fluoride-like material
Forms on tooth surface exposed to high level of fluoride
Slightly soluble in water, dissolves in strong mineral acids and KOH
high level F : >300 ppm at pH or >100 ppm at pH 5 x
Rapidly dissolve
Retain on enamel > 2 weeks
Unwanted
phosphate
Oral
environment
Tooth surface + high level F CaF2 F-
pH 4-5
Phosphate 'shell' reduces solubility
Fluoride reservoir; releases F in acidic environment
pH more soluble release F
ten Cate. Eur J Oral Sci 1997;105:461-5.

10. Clinical evidence: F in tooth structure is not crucial
Okinawa study
No difference in caries status in young adults (18-22 years old) who received fluoridated water only until about 5-8 years old (13 years discontinued) vs those who never received fluoridated water.
DMFT
Fluoridated
water
Nonfluoridated water NS
Kobayashi et al, Comm Dent Oral Epid 1992
Fluoride in the tooth structure cannot give a life-long protection.

11. Discussion: (group of 6-8)
From this Okinawa study, although DMFT between 2 groups were not different which is the main conclusion of the study, DMFS were significantly different. How can you explain the result?
DMFT
DMFS
Fluoridated
water
Nonfluoridated water NS
P < 0.05
Kobayashi et al, Comm Dent Oral Epid 1992

12. Clinical evidence: F in tooth structure is not crucial
Children that had water fluoridation started at age 12 (teeth already formed; no extra structural F) showed significant reduction in caries prevalence.
Harwick et al. Br Dent J 1982
= 20 %
= 26 %
= 27 %
Low level topical F is more important than F in the tooth structure.

13. Caries Controlled Concept
Current philosophy: Fluoride & Caries Control
Caries Controlled Concept
The caries-reducing effect of fluoride is primarily achieved by its presence during active caries development at the plaque/enamel interface where it directly alters the dynamics of mineral dissolution and reprecipitation, and to some extent, affects plaque bacteria.
Primary mode of action of fluoride is post-eruptive topical effect.
Treatment (preventive) strategy according to this concept:
Topical fluoride; low level, frequent exposure, life-long
Maximize benefit (throughout life) with minimal adverse effects

14. Major mechanisms of fluoride on caries process:
1. Affect bacterial metabolism
Require high concentration of fluoride
2. Inhibit demineralization
Fluoride present at the crystal surfaces during acid challenge
3. Enhancing remineralization
Form a layer of fluorapatite-like material on the crystal surfaces
Featherstone JDB. The science and practice of caries prevention. JADA 2000;131:

15. Fluoride in the solution inhibits demineralization
3 wt %
Featherstone JDB et al. J Dent Res 1990;69:620-5
Dissolution of 3 wt% carbonated apatite in presence of fluoride
Initial dissolution rate of CAP
Initial dissolution
rate of HAP
1 ppmF in the acid buffer reduced the dissolution rate ~ 1/3 (to the same level as HAP)
3 ppm F reduces ~ 40% (log)
1 ppmF in acid buffer
No measurable reduction in solubility of 3% CAP (~ enamel) with 1000 ppmF incorporated
3 ppmF in acid buffer
F in the aqueous phase
Adsorbed to the crystal surface
Protect against acid dissolution

16. Fluoride in the solution inhibits demineralization
Enamel samples subjected to solutions varying in pH and F conc.
Fluoride (even low concentration) reduces rate of mineral dissolution
Mineral loss (Calcium)
pH ~ caries formation
Fluoride, 1-10 ppm
ten Cate JM, van Loveren C. Fluroide Mechanisms. Dent Clin N Am 1999;43:

17. Fluoride enhances remineralization
Enamel crystal
(Carbonated apatite)
Partially dissolved crystal
Acid
FAP-like
‘veneer’
Ca, P, F
Remin
Demin
Adapted from Featherstone JDB JADA 2000;131:
Partially demineralized crystals = nucleators
Fluoride ions adsorb to the crystal surface
Attract Ca, P new mineral formation
The newly formed FAP-like ‘veneer’
Exclude carbonate
Composition between HAP and FAP
Low solubility
Crystal surfaces become less soluble
This FAP-like coating precipitated in the crystal surface, not F incorporated during tooth formation, is the major contribution to reduce enamel solubility

18. Remineralized area has higher acid resistance Acquired Acid Resistance
Arrested
enamel
caries
2nd Demin
Arrested
enamel
caries
2nd Demin
Acid challenge
Arrested enamel lesion had higher resistance to acid challenge
than the adjacent area
Lesion surface
Higher F content
Koulourides T, Cameron B
J Oral Pathol 1980;9:

19. Fluoride has greater effect on lesion progression than initiation
Culemborg
(no water F; 0.1 ppm)
Tiel
(Fluoridation; 1 ppm)
Backer Dirks O.
J Dent Res
1966;43:503
(n=436)
(n=406)
Age 9
Age 15
Total
Age 9
Age 15
Total
Sound
241
186 23 54
263
318
244 17 10
271
White spot
(arrested) 59 25 18 21 64 54 45 22 14 81
White spot
(active)
123 26 11 1 64 34 27 14 8 49 4 7 22 2 1
Cavity 13 12 45 5

20. Summary: F & De/Remineralization
Principal mechanisms of fluoride actions rely on
F in saliva
F in the plaque fluid and tooth interface
F in the fluid among the mineral crystals in the lesion
Primary action of fluoride
Topical; after tooth eruption
Benefits continue throughout life
(as long as F is available)

21. Summary: F & De/Remineralization
To optimize clinical effects of fluoride:
Delivery methods that bring F to the tooth surface, saliva, plaque fluid
The frequency of fluoride exposure
F incorporated into the mineral during tooth development has only minor effect

22. Discussion: (group of 3-4)
Give some examples of topical source that can provide low level of F continuously.

23. Recommended references
1. Ten Cate JM, van Loveren C. Fluoride Mechanisms. Dent Clin North Am 1999;43(4):
2. Featherstone JD. The science and practice of caries prevention. J Am Dent Assoc 2000;131:
3. Ten Cate JM. Current concepts on the theories of the mechanism of action of fluoride. Acta Odontol Scand 1995:57:
4. Fejerskov O. Changing paradigms in concepts on dental caries: Consequences for oral health care. Caries Res 2004;38:
5. ADA Reports. Position of the American Dietetic Association: The impact of fluoride on health. 2005;105:

24. Discussion: (group of 6-8)
If structurally bound fluoride is no longer believed to be the major mode of anticaries mechanism of fluoride, why the ADA still recommend children live in non-fluoridated area to have supplement fluoride tablets?