SALIVA BIOCHEMISTRY Germain INTWALI UR-CMHS School of Dentistry Dental therapy dpt.
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SALIVA BIOCHEMISTRY
Germain INTWALI UR-CMHS
School of DentistryDental therapy dpt.
Intended learning outcomes
Biochemistry of saliva and teeth
14.1. Describe the biochemical composition of saliva
14.2. Describe the biochemical composition of teeth
14.3. Explain the pH changes of saliva
14.4. Describe the functions of saliva
THE BIOCHEMISTRY OF SALIVA
Saliva is produced in and secreted from acinar cells in salivary glands
Secretion volume per day: 1.0-1.5 liters from major s. glands (Parotid, sub mandibular and sublingual)
This include resting flow and stimulated during eating
pH of saliva: 7-8
THE BIOCHEMISTRY OF SALIVA
Composition of saliva: Water 94-99.5% Solid substance range from 0.5% to 6% in unstimulated
and stimulated saliva
Solid substances are: Inorganic constituents: Ca, Mg, F, Na, HCO3, K, Na, Cl and
NH4 ions Organic contituents: Ure, Uric acid, free glucose, free
amino acids, lactate and fatty acids, Organic micromolecules: Proteins, amylase, peroxidase,
thiocyanate, lysozymes, lipids, IgA, IgM, and IgG Elements from oral cavity: Desquamated epithelial cells,
PMNL, and bacteria
Gases: O2, Co2, and N2.
THE BIOCHEMISTRY OF SALIVA
Composition in groups:
Aqueous: water, salivary amylase, lingual lipase, IgA, Kallikrein, Muramidase and Lactoferrin
Electrolytes: Ca, PH, F, K, Na, Cl
Mucus secretion proteins: Mucin, Statherins, Proline rich proteins, antimicrobial proteins such as; Lactoferrin, Histatins, Lysozymes, Cystatins, Peroxidases, Secretory immunoglobins
THE BIOCHEMISTRY OF SALIVA
Saliva is hypotonic to plasma
Na+, Cl- low in saliva than plasma
K+, HCO3- higher in saliva than plasm
pH changes from acidic (6-7) at rest to basic (pH 8) at ultimate stimulation due to Higher HCO3- in the saliva
THE BIOCHEMISTRY OF SALIVA
Functions:
Moistening food
Beggining of digestion
Adjust salt appetite
Contains factors that inhibit adhesion and destroy bacteria (Anti-bacteria)
Antifungal (Histatins)
Antiviral (Cystatins, Mucins)
Buffering
THE BIOCHEMISTRY OF SALIVA
Functions:
Lubrication and visco-elasticity
Mineralizations
Buffering oral environment
HYDROGEN IONS
1. PROTONS (H+)
Concentration dictates pH of the oral environment
pH of saliva varies according to flow rate (young infants also have slightly more alkaline saliva)
Why is pH important in the mouth?
Typical salivary pH (adult) is around 6 – 7.4
-a- Maintaining ionic product for hydroxyapatite (see later)-b- Isoelectric point for salivary protein precipitation on to tooth surfaces-c- Optimal pH for salivary enzymes
EFFECT OF CARBOHYDRATE CONSUMPTION ON PLAQUE pH
Time (min)
pH
4
5
6
7
8
0 40 80
CHO CHO
The Stephan Curve: Stephan, RM, J Am Dent Ass. 27: 718-723, 1940
Mineral dissolves
EFFECT OF SUCROSE ON PLAQUE pH
4
5
6
7
pH
Sucrose0.025%
Sucrose1.25%
Sucrose2.5%
Sucrose5%
Sucrose10%
3% UREA 3% UREA
Time (min)0 113
Chew wax3 min
Chew wax3 min
Chew wax3 min
Chew wax3 min
Chew wax3 min
Chew wax3 min
Telemetric data from: Imfeldt, 1977
pH of SALIVA (cont)
The pH of saliva varies with flow rate
Higher flow rates increase salivary buffering
Flow rate pH
In general:
=
EFFECT OF FLOW RATE ON pH OF SALIVA
0.25 mL/min
0.5 mL/min
1 mL/minstimulation begun
unstimulated
0 5 10 15 20 25
5.8
6.2
6.6
7.0
7.4
pH
Time (min)
2. BICARBONATE IONSImportant BUFFER at high flow rates
Concentration in saliva varies with salivary flow as bicarbonate content of saliva increases with metabolic activity of the salivary glands
Range: < 1 mM (unstimulated) to 60 mM (highest flow rates)
Concentration in mechanically stimulated saliva typically around 15 mM
Produced by the striated epithelium of the salivary gland ducts
EFFECT OF FLOW RATE ON BICARBONATE CONCENTRATION IN
SALIVA
0
8
16
24
32
HC
O3 (
mM
)
stimulation begun
unstimulated
1 mL/min
0.5 mL/min
0.25 mL/min
Time (min)
5 10 15 20 25
0
BUFFERING OF PROTONS BY BICARBONATE
H+ + HCO3 H2CO3 H2O + CO2-
pKa = 6.1
Carbonic anhydrase
Carbonic anhydrase is present in salivary glands (and also in saliva)
BICARBONATE PRODUCTION IN SALIVA
HCO3
H2CO3 H2O + CO2H+
LUNGS
CATABOLISM IN GLAND
HCO3
H2CO3 H2O + CO2H+
Excess in saliva
PLASMA
SALIVARY GLAND
-
-
3. POTASSIUM AND SODIUM IONSBoth present as counter ions to preserve electrical neutrality
Concentration range: Sodium: 6 – 26 mM
Potassium: 14 – 32 mM
Sodium is the counter ion for bicarbonate
Potassium is the counter ion for phosphate
Flow rate Na+
In general:
= but K+
EFFECT OF FLOW RATE ON SODIUM AND POTASSIUM CONCENTRATIONS IN
SALIVA
Rate of secretion mL / 6 min
Con
cen
trati
onm
eq
/ L
20
40
60
1 2 3
Na
K
4. CALCIUM AND MAGNESIUM IONS
Mg++Present in saliva but role and origin unclear.
Possible origins: Cellular degradation (host / bacterial); Early carious attack
(Mg++ rich mineral is first to be removed during acid attack)
Concentration range in saliva: 0.2 – 0.5 mM
Flow rate Mg++
In general:
=
4. CALCIUM AND MAGNESIUM IONS (cont)
Ca++
Actively secreted by major salivary glands
Forms complexes with calcium-binding salivary proteins
Concentration range in saliva: 1 – 2 mM
Flow rate Ca++
In general:
=
Behaviour with flow rate variable due to protein binding
Important role in maintenance of ionic product for hydroxyapatite (see later)
(& protein)
EFFECT OF FLOW RATE ON Ca++ AND Mg++ CONCENTRATIONS IN SALIVA
Ca (
mM
)
0
40
80
120
Mg
(µM
)
stimulation begun
unstimulated
0 5 10 15 20 25
0.9
1.1
1.3
0.04 mL/min
1.00 mL/min
Time (min)
1.5
Ca++
Mg++
EFFECT OF FLOW RATE ON CONCENTRATION OF PROTEIN IN
SALIVA
Time (min)
1 mL/min
0.5 mL/min
0.25 mL/minunstimulated
stimulation begun
Pro
tein
(m
g%
)
110
190
270
350
5 10 15 20 25
5. PHOSPHATE IONS
Flow rate H2PO4- / HPO4
=
In general:
=
Concentration range in saliva: 2 -23 mM
Acts as a buffer, especially in unstimulated saliva
Important in maintenance of ionic product for hydroxyapatite
EFFECT OF FLOW RATE ON INORGANIC ORTHOPHOSPHATE CONCENTRATION IN
SALIVA
Time (min)
4
8
12
Inorg
an
ic p
hosp
hate
(m
M)
unstimulated
stimulation begun
0.25 mL/min0.5 mL/min
1 mL/min
5 10 15 20 250
HYDROXYAPATITEThe mineral component of the mammalian skeletal tissues is a calcium phosphate salt:
HYDROXYAPATITE (HAP; HA, OHA)
Ca10(PO4)6(OH)2
Ionic product for HAP:
Pi = [Ca]10 x [PO4]6 x [OH]2
ROLE OF CALCIUM AND PHOSPHATE IN MAINTAINING TOOTH MINERAL INTEGRITY
AND REMINERALISATION
Saliva is supersaturated with respect to hydroxyapatite
This is essential for:
Maintenance of ionic product
Remineralisation
BUT
Without the presence of inhibitors in saliva, spontaneous precipitation would occur
ROLE OF CALCIUM AND PHOSPHATE IN MAINTAINING TOOTH MINERAL INTEGRITY
AND REMINERALISATION
The mineral component of enamel and dentine is a substituted hydroxyapatite; HAP. Ca10(PO4)6(OH)2
HAP dissolution (and precipitation) therefore depends upon the concentration of Ca++, PO4
3- (and OH-) in saliva.
Protonation of the phosphate group is pH dependent
PO43- HPO4
2- H2PO4- H3PO4
+H+ +H+ +H+
-H+ -H+ -H+
pKa = 12.7 pKa = 7.2 pKa = 2.12
ROLE OF CALCIUM AND PHOSPHATE IN MAINTAINING TOOTH MINERAL INTEGRITY
AND REMINERALISATION
When pH falls, increasing protonation of the phosphate groups results in the formation of salts of greater solubility and vice versa
Ca10(PO4)6(OH)2HAPHydroxyapatite
Brushite / Dicalcium phosphate
CaHPO4 / CaHPO4.2H2ODCPD
Octacalcium phosphate OCP Ca8(PO4)4(HPO4)2.5H2O
Tricalcium phosphate TCP Ca3(PO4)2
Monocalcium phosphateMCP Ca(H2PO4)2
6. CHLORIDE IONS
Preserves electrical neutrality
Activates salivary amylase
Concentration range in saliva: 17 – 29 mM
Flow rate Cl-
In general:
=
6. FLUORIDE ION
Fluoride ion is normally present at very low concentrations in whole saliva (range = 0.001 – 0.005 mM)
Fluoride replaces (OH) in the HAP lattice structure, increasing its stability and inhibiting acid dissolution
Fluoride facilitates HAP precipitation and therefore promotes remineralisation.
Fluoride accumulates in porous enamel (and dentine), including caries lesions
Fluoride concentrations in plaque are higher than those in saliva
Salivary fluoride in patients living in areas of water fluoridation is approx. 2x that of patients living in non-fluoridated regions.
This is a small absolute difference but the benefits in caries reduction are highly significant.
Special thanksTo Dr. Mumena Chrispinus:
A senior lecture and vice Dean of the school of Dentistry at the College of Medicine and Health Sciences- UNIVERSITY OF Rwanda.
Addition: Dean of the OPHTALMOGY DEPT. at UR- CMHS
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