Effect of bacterial acids and plaque fluid on the mineral phase of enamel The concept of critical pH...
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Transcript of Effect of bacterial acids and plaque fluid on the mineral phase of enamel The concept of critical pH...
• Effect of bacterial acids and plaque fluid on the mineral phase of enamel
• The concept of critical pH
• Enamel-plaque fluid interaction
Objectives:
DENT 5302 TOPICS IN DENTAL BIOCHEMISTRY
2 April 2007
Outline
Plaque fluid composition
Stephan curve
Erosion
Enamel substrate
Ultrastructure of enamel caries lesion
The concept of critical pH
Enamel – plaque fluid interaction
Extra and intracellular polysaccharides
- Synthesized by bacteria
- Bacterial attachment and cohesion
- Reservoir of fermentable substrates
Plaque Composition
80% water
Critical point: Dental plaque is responsible for the majority of chemical activities
on the tooth surface.
20% solid
Bacterial and salivary protein – 50%
Carbohydrates and lipids – 20-30%
Inorganic components – 25%
Ca, P: several times higher than in saliva
Most Ca is non-ionic. becomes ionized as pH drops
Determine rates of enamel dissolution and remineralization
Other ions: K, Na, Mg, and F.
• Plaque fluid = extracellular aqueous phase of dental plaque
• Provide aqueous medium for diffusion and exchange of substances
between saliva and tooth surface
• Separated from plaque by centrifugation
• 500 g wet weight plaque sample 150 nL plaque fluid
• Changes in ionic composition of plaque fluid cariogenic conditions
Plaque Fluid
Rested plaque fluid: one to several hours after eating
Starved plaque fluid: following overnight fasting
Rested plaque
Starved plaque
Total organic acids
(mmol/L)
56.3 - 102.1
31.9 - 61.5
pH
5.69 - 6.54
6.78 - 7.08
Lactic
0
17.5
Time (min)
7
37.5
15
33.4
23
18.6
Acid(mmol/L)
Lactic acid concentrations in plaque fluid following a 2-min 10% sucrose rinse
Margolis HC, Moreno EC. Composition and cariogenic potential of dental plaque fluid.
Crit Rev Oral Biol Med 1994;5:1-25
Lactic acid: the main acid involved in caries formation
Stephan curve
Stephan RM. JADA 1940;27:718-723Changes in hydrogen-ion concentration on tooth surfaces and in carious lesion.
Stephan RM. JADA 1944; 23:257-266Intra-oral hydrogen-ion concentrations associated with dental caries activity.
?
?
?
Type and amount of CHO available
Bacteria present
Salivary composition and flow
What contributes to the extent of pH drop after glucose challenge?
Other food ingested
Thickness and age of dental plaque
Resting plaque pH:
Constant within each individual, but
differences among groups.
Caries-inactive – resting pH ~ 6.5 - 7
Caries-prone – lower resting pH
Bacterial composition affects metabolic properties of plaque
Storage form of CHO energy source when diet is depleted
What contributes to the differences in resting plaque?
When the host does not ‘eat’, cariogenic bacteria still produce acids
form storage carbohydrates
Margolis HC. Enamel-plaque fluid interaction. Cariology for the Nineties, 1993
What are the differences in plaque fluid between ‘caries-free’ and caries-positive individuals?
Composition
Na+
Mg2+
K+
Calcium
P
Acid
Lactic
Acetic
Propionic
pH
DS (enamel)
14.2 + 3.5
2.0 + 0.4
59.9 + 4.9
16.2 + 5.2
13.9 + 1.9
‘caries-free’ caries-positive
16.5 + 5.4
2.6 + 0.4
71.4 + 11.3
6.9 + 0.4
15.6 + 3.6
1.8 + 0.7
19.9 + 3.5
5.8 + 1.5
2.6 + 1.2
20.3 + 4.6
5.8 + 1.5
7.02 + 0.05 6.79 + 0.12
7.11 + 0.66 5.42 + 0.68
*
*
*
Major mineral component (teeth and bone):
Calcium phosphate crystals ~ Hydroxyapatite Ca10(PO4)6(OH)2
Hydroxyapatite lattice structure
Phosphates fill space
Nikiforuk G. Understanding Dental Caries. Karger 1985
Hydroxyl ions form
columns of parallelogram
Calcium ions form
triangle around hydroxyl ion
Enamel substrate
Enamel: 96% by weight or 87% by volume mineral
13 vol % interprismatic space is diffusion channel
Biological mineral is ‘nonstoichiometric’
Concentration of the chemical components is different from pure HAP
Substitution of three primary constituents with
- carbonate
- other trace elements (impurities): F, Na, Cl, Mg, K, Zn, Si, Sr
≠ Ca10(PO4)6(OH)2
Carbonate (CO3)2- substitute (PO4)3- or 2 (OH)-
Carbonate ions disturb the regular array of ions in the crystal lattice
More soluble in acid than pure HAP
Current concept: Dental mineral is carbonated HAPCurrent concept: Dental mineral is carbonated HAP
Discussion (group of 5-6)
When a tooth is just erupted into the oral cavity, it is
more susceptible to demineralization.
Why?
Simplified formula of tooth mineral
(Ca)10-x(Na)x(PO4)6-y(CO3)z(OH)2-u(F)u
Newly erupted teeth have relatively greater caries susceptibility
During demineralization, carbonate is lost and excluded after remin
Decrease carbonate & increase fluoride in enamel surface
Less susceptible to demineralization
= post-eruptive maturation
Post-eruptive MaturationPost-eruptive Maturation
Ksp is the ionic activity products of substance at saturation
Ksp = Concentrations of the component ions
to the power in saturated solution
e.g., HAP Ca5(PO4)3OH ; Ksp(HAP) = [Ca2+]5[PO43-]3[OH-] = 7.36 x 10-60
Ksp is a constant value
Solubility product (Ksp)
Ksp(carbonated-HAP) = 4.57 x 10-49
Ksp(enamel) = 5.5 x 10-55
When do teeth dissolve?
Teeth dissolve when pH is lower than a critical pH
H+ remove PO43- & OH-
Decrease [PO4] & [OH] in solution
Apatite mineral dissolves
[PO4] & [OH] rise to maintain the saturation level
Acidic solution:
Degree of saturation (DS)
Ratio of the ionic product of a substance in the solution (IAP) to its
ionic product at saturation (Ksp )
DS > 1 : Solution supersaturated WRT mineral
DS < 1 : Solution undersaturated WRT mineral
DS = 1 : Saturation condition
DS =Ksp (ionic activity products at saturation)
IAP (ionic activity products in solution) 1/9
Margolis HC, Moreno EC
Crit Rev Oral Biol Med 1994;5:1-25
e.g., for hydroxyapatite (Ca5(PO4)3OH)
Determined the same way as Ksp, but use the ion concentrations
in the solution.
Ionic Activity Product (IAP)
(WRT = with respect to)
The concept of critical pH
Saliva and plaque fluid are supersaturated WRT tooth enamel
= pH at which a solution is just saturated WRT a particular mineral
If the solution pH > critical pH supersaturated mineral precipitate
If the solution pH < critical pH undersaturated mineral dissolve
Normal condition: Our teeth do not dissolve in saliva or plaque fluid
Critical pH of carious formation in enamel ~ 4.5-5.5Critical pH of carious formation in enamel ~ 4.5-5.5
Coincide with pH when plaque bacteria ferment carbohydrates
HAP is undersaturated & FAP is supersaturated
The tooth will dissolve when the pH of fluid phase is less than critical pH.
pH of saliva & plaque fluid > critical pH
Saliva & plaque fluid contain Ca, P, OH IAP > Ksp tooth enamel
pH 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0
FAP
HAP
deposit caries erosion
demineralization
remineralization
pH 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0
Critical pH
Carious lesion forms at pH 4.5 - 5.5
Erosion lesion forms when pH < 4.5
Endogenous acid: gastric acid, gingival crevicular fluid
Exogenous acid: diet, medicine, industry
3/4 of a bottle of white wine
Every evening for 34 years
Sipping over a 3 hours after dinner
Wine pH ranges about 3-4.
Loss of dental hard tissue through chemical etching and dissolution
by acids of non-bacterial origin
‘acid corrosion'
Frequent and prolonged ingestion
of acidic fruits, fruit juices and
acidic beverages
Gastroesophageal reflux disease, vomiting
Dental consumption due to wine consumption. Mandel L. JADA 2005;136:71-75
0
50
100
150
200
250
300
Cola Sports drink Orangejuice
Drinkingyogurt
Lemon-grass soup
En
am
el H
ard
ne
ss
Before
After
pH 2.74 3.78 3.75 3.83 4.20
S. Wongkhantee et al., J Dent 2006;34:214-220.
Effect of acidic food and drinks on surface hardness of enamel, dentine, and tooth-coloured filling materials.
Enamel samples alternately immersed, 5 sec each, in food or drink and in artificial saliva for 10 cycles.
*
* *
Can acidic food and drinks soften enamel surface?
Solubility isotherm
Current concepts on the theories of the mechanism of action of fluoride.
ten Cate JM. Acta Odontol Scand 1999;57:325-9.
100
10
1
0.1
0.01
0.001
0.0001
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0
HAPHAP
cal
ciu
m (
mo
l/l)
FAPFAP
oral fluid
Critical pH is not a fixed valueCritical pH is not a fixed value
pH
Crystal damage from acid:
- Surface etching
- Central defect or hairpin
Ultrastructure of enamel caries lesion
Larger crystal at prism periphery
from remineralization
• Crystal core has more dislocations or lattice defects
• Higher carbonate content
• Dissolving crystals are smaller
• Increased intercrystalline space
Larger crystals in
surface zone and dark zone
Indication of remineralization
Range of crystal size in each zone of early enamel lesion
1. Surfacezone
2. Body oflesion
3.Dark zone
4.Translucent
zone
Soundenamel
1 2 3 41
2 34
Recommended references
1. Zero DT. Dental Caries Process. Dent Clin North Am 1999;43(4):635-664.
2. Featherstone JD. The science and practice of caries prevention. J Am Dent Assoc 2000;131:887-899.
3. Gordon Nikiforuk. Understanding Dental Caries 1. Etiology and Mechanisms, Basic and Clinical Aspects. Basel; New York: Karger 1985. Chapters 4 &10.
4. Margolis HC, Moreno EC. Composition and cariogenic potential of dental
plaque fluid. Crit Rev Oral Biol Med 1994;5:1-25.
5. Margolis HC. Enamel – plaque fluid interactions. In WH Bowen and LA Tabak (Eds) Cariology for the nineties. University of Rochester Press 1993:173-186.
Diagram showing effect of increase Ca on degree of saturation of plaque
fluid with respect to enamel
Question:
Which line represent
individuals with higher
tendency for caries
formation?