• Role of structural-bound vs topical fluoride

• The effect of fluoride on demineralization

• The effect of fluoride on remineralization

Objectives:

DENT 5302 TOPICS IN DENTAL BIOCHEMISTRY

6 April 2007

Outline

Caries resistance concept vs Current philosophy

Why it was believed that structurally-bound F was important?

How fluoride inhibits demineralization

What are the conflicting evidences?

How fluoride enhances remineralization

Systemic F for the maximum benefit

(less soluble enamel )

Risk of developing (mild) fluorosis

Historical perspective

Caries-reducing effect of fluoride is from its presence during active

caries development to alter the dynamics of de- and remineralization

Current philosophy

Fluoride presented during tooth formation provided 'caries resistance'

Why do we want to know how fluoride prevents dental caries?

Basis to develop effective ways of using fluoride

Posteruptive effect

Topical fluoride application

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.

Fluoride present during tooth formation provided 'caries resistance'

Systemic F for the maximum benefit (less soluble enamel )

Risk of developing (mild) fluorosis

Consequence

Caries Resistance ConceptCaries Resistance Concept

Treatment strategy according to this concept:

Water fluoridation (10 years) reduced DMF

Fluoride incorporated in tooth structure increases caries-resistance

Teeth formed in fluoridated area

Increased F content in surface enamel

F in water supplies

Lower caries prevalence

Fluoridated area

Non- fluoridated area

2.5 ppm

But….2000 vs 3000 ppm F is too

small for 50% reduction in DMF!

Why was fluoride believed to make teeth more resistant to caries attack?

Comm Dent Oral Epid 1985;13:65-7.

No correlation between DMFT and enamel fluoride

concentration

Shark enamel (almost pure fluorapatite; 30,000 ppm F) developed

caries lesions in an in situ model (4 wks), although less severe

0

300

600

900

1200

1500

1800

Human Shark Human +Rinse

Shark + Rinse

Min

era

l lo

ss

Human Shark Human+ rinse

Human enamel + 0.2% NaF rinse (daily, 4 wks) ~ Shark enamel

F in tooth structure is not crucialF in tooth structure is not crucial

Ögaard B et al.

Scand J Dent Res 1991;99:372-377

FAP has only a moderate caries protective potential, ~ daily F-rinse.

1

Human enamel:CaF2-like globules

Shark enamel:Nothing observed

does not provide enough Ca? (Ca is firmly bound)

CaF2-like material:

caries inhibition effect

of topical fluoride

Ögaard B et al. Scand J Dent Res 1991;99:372-377 & 1988;96:209-211.

Shark enamel +

0.2% NaF rinse

was not as good

as human enamel

+ 0.2% NaF rinse0

300

600

900

1200

1500

1800

Human Shark Human +Rinse

Shark + Rinse

Min

era

l lo

ss

Human Shark SharkHuman+ Rinse + Rinse

Calcium fluoride-like material

Tooth surface + high level F CaF2

Oral environment

Phosphate 'shell' reduces solubility

Fluoride reservoir; releases F in acidic environment

phosphate

pH 4-5

F-

ten Cate. Eur J Oral Sci 1997;105:461-5.

pH 4-5 more soluble release F

Rapidly dissolvex

Forms on tooth surface exposed to high level of fluoride

Slightly soluble in water, dissolves in strong mineral acids and KOH

Retain on enamel > 2 weeks

high level F : >300 ppm at pH 7.2 or >100 ppm at pH 5

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.

Kobayashi et al, Comm Dent Oral Epid 1992

DMFT

Fluoridated water

8.92 + 4.79

Nonfluoridated water

10.73 + 5.48 NS

Fluoride in the tooth structure cannot give a life-long protection.

Clinical evidence: F in tooth structure is not crucialClinical evidence: F in tooth structure is not crucial

Okinawa study

Kobayashi et al, Comm Dent Oral Epid 1992

DMFT

DMFS

Fluoridated water

8.92 + 4.79

15.02 + 9.14

Nonfluoridated water

10.73 + 5.48

20.36 + 13.43

NS

P < 0.05

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?

0

2

4

6

8

10

0 1 2 3 4 5Year

DM

FS

Control

Fluoride

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 %

Clinical evidence: F in tooth structure is not crucialClinical evidence: F in tooth structure is not crucial

Low level topical F is more important than F in the tooth structure.

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.

Maximize benefit (throughout life) with minimal adverse effects

Caries Controlled ConceptCaries Controlled Concept

Treatment (preventive) strategy according to this concept:

Primary mode of action of fluoride is post-eruptive topical effect.

Topical fluoride; low level, frequent exposure, life-long

3. Enhancing remineralization

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

Form a layer of fluorapatite-like material on the crystal surfaces

Featherstone JDB. The science and practice of caries prevention. JADA 2000;131:887-899

Fluoride in the solution inhibits demineralizationFluoride 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)

No measurable reduction in

solubility of 3% CAP (~ enamel)

with 1000 ppmF incorporated

3 ppm F reduces ~ 40% (log)1 ppmF in acid buffer

3 ppmF in acid buffer

F in the aqueous phase

Adsorbed to the crystal surface

Protect against acid dissolution

Fluoride (even low

concentration)

reduces rate of

mineral dissolution

pH ~ caries formation

Min

eral

loss

(C

alci

um

)

Fluoride, 1-10 ppm

Enamel samples subjected to solutions varying in pH and F

conc.

ten Cate JM, van Loveren C. Fluroide Mechanisms. Dent Clin N Am 1999;43:713-742.

Fluoride in the solution inhibits demineralizationFluoride in the solution inhibits demineralization

Enamel crystal

(Carbonated apatite)

Partially dissolved

crystal

Acid

FAP-like‘veneer’

Ca, P, F Remin

Demin

Adapted from Featherstone JDB JADA 2000;131:887-99.

This FAP-like coating precipitated in the crystal surface, not F incorporated

during tooth formation, is the major contribution to reduce enamel solubility

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

Fluoride enhances remineralizationFluoride enhances remineralization

Arrested enamel lesion had higher

resistance to acid challenge

than the adjacent area

Koulourides T, Cameron BJ Oral Pathol 1980;9:255-269

Arrested enamel caries

Arrested enamel caries

2nd Demin

2nd Demin

Lesion surface

Higher F content

Remineralized area has higher acid resistanceRemineralized area has higher acid resistance

Sound

White spot(arrested)

White spot(active)

Cavity

Culemborg(no water F; 0.1 ppm)

Tiel(Fluoridation; 1 ppm)

Age 9 Age 15

241

59

123

13

263

64

64

45

318

54

34

0

271

81

49

5

Total

1862354

251821

2611261

12

47

22

2441710

452214

271480

0

212

(n=436) (n=406)Backer Dirks O.

J Dent Res

1966;43:503Age 9 Age 15 Total

Fluoride has greater effect on lesion progression than initiationFluoride has greater effect on lesion progression than initiation

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)

F incorporated into the mineral during

tooth development has only minor effect

Delivery methods that bring F to the tooth surface,

saliva, plaque fluid

The frequency of fluoride exposure

To optimize clinical effects of fluoride:

Discussion: (group of 3-4)

Give some examples of topical source that can provide low

level of F continuously.

Recommended references

1. Ten Cate JM, van Loveren C. Fluoride Mechanisms. Dent Clin North Am 1999;43(4):713-742.

2. Featherstone JD. The science and practice of caries prevention. J Am Dent Assoc 2000;131:887-899.

3. Ten Cate JM. Current concepts on the theories of the mechanism of action of fluoride. Acta Odontol Scand 1995:57:325-329.

4. Fejerskov O. Changing paradigms in concepts on dental caries: Consequences for oral health care. Caries Res 2004;38:182-191.

5. ADA Reports. Position of the American Dietetic Association: The impact of fluoride on health. 2005;105:1620-1628.

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?