Transcript Slide 1

DENT 5302 TOPICS IN DENTAL BIOCHEMISTRY
6 April 2007
Objectives:
• Role of structural-bound vs topical fluoride
• The effect of fluoride on demineralization
• The effect of fluoride on remineralization
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
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 )
Posteruptive effect
Topical fluoride application
Risk of developing (mild) fluorosis
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
Water fluoridation (10 years) reduced DMF
Fluoride incorporated in tooth structure increases caries-resistance
Why was fluoride believed to make teeth more resistant to caries attack?
Fluoridated
area
Nonfluoridated
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
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
1800
Ögaard B et al.
Scand J Dent Res 1991;99:372-377
Mineral loss
1500
1200
900
600
300
0
Human
Hum an
Shark
Shark
Human
Hum an
+ rinse
Rinse
+
Shark + Rinse
FAP has only a moderate caries protective potential, ~ daily F-rinse.
Mineral loss
1800
1500
Shark enamel +
1200
0.2% NaF rinse
900
was not as good
600
as human enamel
300
+ 0.2% NaF rinse
0
Human
Hum an
Shark
Shark
Human enamel:
CaF2-like globules
Human
Hum
an +
+ Rinse
Rinse
Shark
Shark
+ Rinse
+ Rinse
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;99:372-377 & 1988;96:209-211.
Calcium fluoride-like material
Forms on tooth surface exposed to high level of fluoride
high level F : >300 ppm at pH 7.2 or >100 ppm at pH 5
Slightly soluble in water, dissolves in strong mineral acids and KOH
x
Rapidly dissolve
Retain on enamel > 2 weeks
phosphate
Oral
environment
Tooth surface + high level F
F-
CaF2
pH 4-5
Phosphate 'shell' reduces solubility
Fluoride reservoir; releases F in acidic environment
pH 4-5
more soluble
release F
ten Cate. Eur J Oral Sci 1997;105:461-5.
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
8.92 + 4.79
10.73 + 5.48
NS
Kobayashi et al, Comm Dent Oral Epid 1992
Fluoride in the tooth structure cannot give a life-long protection.
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?
Fluoridated
water
Nonfluoridated
water
DMFT
8.92 + 4.79
10.73 + 5.48
NS
DMFS
15.02 + 9.14
20.36 + 13.43
P < 0.05
Kobayashi et al, Comm Dent Oral Epid 1992
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.
10
Harwick et al. Br Dent J 1982
= 27 %
DMFS
8
6
= 26 %
4
= 20 %
Control
2
Fluoride
0
0
1
2
3
4
5
Year
Low level topical F is more important than F in the tooth structure.
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
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;131:887-899
Fluoride in the solution inhibits demineralization
Dissolution of 3 wt% carbonated
3 wt %
apatite
in presence of fluoride
Initial dissolution
rate of CAP
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
Initial dissolution
rate of HAP
3 ppmF in acid buffer
No measurable reduction in
solubility of 3% CAP (~ enamel)
with 1000 ppmF incorporated
F in the aqueous phase
Adsorbed to the crystal surface
Protect against acid dissolution
Featherstone JDB et al. J Dent Res 1990;69:620-5
Fluoride in the solution inhibits demineralization
Mineral loss (Calcium)
Enamel samples subjected to solutions varying in pH and F conc.
Fluoride (even low
concentration)
reduces rate of
mineral dissolution
ten Cate JM, van Loveren C. Fluroide Mechanisms. Dent Clin N Am 1999;43:713-742.
Fluoride enhances remineralization
Enamel
crystal
(Carbonated
apatite)
Partially demineralized crystals = nucleators
Fluoride ions adsorb to the crystal surface
Acid
Demin
Attract Ca, P new mineral formation
Partially
dissolved
crystal
The newly formed FAP-like ‘veneer’
Ca, P, F
Remin
Exclude carbonate
Composition between HAP and FAP
FAP-like
‘veneer’
Adapted from Featherstone JDB
JADA 2000;131:887-99.
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
Remineralized area has higher acid resistance
Arrested
enamel
caries
Arrested
enamel
caries
Arrested enamel lesion had higher
resistance to acid challenge
than the adjacent area
Koulourides T, Cameron B
J Oral Pathol 1980;9:255-269
Lesion surface
Higher F content
Fluoride has greater effect on lesion progression than initiation
Culemborg
(n=436)
(no water F; 0.1 ppm)
Tiel
(n=406)
(Fluoridation; 1 ppm)
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
26
1
64
34
27
14
8
0
49
Backer Dirks O.
J Dent Res
1966;43:503
Cavity
13
4
7
22
12
45
0
2
1
2
0
5
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)
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
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?