anticaries mechanism of fluoride
DESCRIPTION
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. Outline. - PowerPoint PPT PresentationTRANSCRIPT
• 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?