THE INORGANIC COMPONENTS OF SALIVA

1
THE INORGANIC COMPONENTS OF SALIVA
2nd Year BChD Orofacial Biology
Professor J Kirkham Division of Oral Biology
2
THE BIOCHEMISTRY OF SALIVA
To describe the role played by saliva in
maintaining the healthy oral environment
AIM
OBJECTIVES

• To examine the clinical significance of saliva by
  describing
• specific protective functions.
• 2. To examine the causes underlying salivary
  complexity.
• 3. To evaluate the role of oral
  compartmentalisation in oral disease
• processes.
• 4. To describe the inorganic components of saliva
  and their specific
• functions in maintaining oral health.
• 5. To describe the organic components of saliva
  and their specific
• functions in maintaining oral health

3
HYDROGEN IONS
-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
4
EFFECT OF CARBOHYDRATE CONSUMPTION ON PLAQUE pH
The Stephan Curve Stephan, RM, J Am Dent Ass.
27 718-723, 1940
CHO
CHO
8
7
pH
6
Mineral dissolves
5
4
0
40
80
Time (min)
5
EFFECT OF SUCROSE ON PLAQUE pH
Telemetric data from Imfeldt, 1977
3 UREA
3 UREA
Sucrose 0.025
Sucrose 1.25
Sucrose 2.5
Sucrose 5
Sucrose 10
Chew wax 3 min
Chew wax 3 min
Chew wax 3 min
Chew wax 3 min
Chew wax 3 min
Chew wax 3 min
7
6
pH
5
4
0
113
Time (min)
6
pH of SALIVA (cont)
The pH of saliva varies with flow rate
Higher flow rates increase salivary buffering
In general
Flow rate
pH

7
EFFECT OF FLOW RATE ON pH OF SALIVA
1 mL/min
stimulation begun
7.4
0.5 mL/min
7.0
pH
0.25 mL/min
unstimulated
6.6
6.2
5.8
0
5
10
15
20
25
Time (min)
8
2. BICARBONATE IONS
Important BUFFER at high flow rates
Produced by the striated epithelium of the
salivary gland ducts
Concentration in saliva varies with salivary flow
as bicarbonate content of saliva increases with
metabolic acitivity of the salivary glands
Range lt 1 mM (unstimulated) to 60 mM (highest
flow rates)
Concentration in mechanically stimulated saliva
typically around 15 mM
9
EFFECT OF FLOW RATE ON BICARBONATE CONCENTRATION
IN SALIVA
32
stimulation begun
1 mL/min
24
HCO3 (mM)
0.5 mL/min
16
unstimulated
0.25 mL/min
8
0
0
5
10
15
20
25
Time (min)
10
BUFFERING OF PROTONS BY BICARBONATE
Carbonic anhydrase
-
H HCO3
H2CO3
H2O CO2
pKa 6.1
Carbonic anhydrase is present in salivary glands
(and also in saliva)
11
BICARBONATE PRODUCTION IN SALIVA
CATABOLISM IN GLAND
SALIVARY GLAND
H2CO3
H2O CO2
H
-
Excess in saliva
HCO3
-
HCO3
PLASMA
H
H2CO3
H2O CO2
LUNGS
12
3. POTASSIUM AND SODIUM IONS
Both present as counter ions to preserve
electrical neutrality
Sodium is the counter ion for bicarbonate
Potassium is the counter ion for phosphate
Concentration range Sodium 6 26 mM
Potassium 14 32 mM
In general
Flow rate
Na

but K
13
EFFECT OF FLOW RATE ON SODIUM AND POTASSIUM
CONCENTRATIONS IN SALIVA
Na
60
m eq / L
40
20
Concentration
K
1
2
3
Rate of secretion mL / 6 min
14
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
In general
Flow rate
Mg

15
4. CALCIUM AND MAGNESIUM IONS (cont)
Ca
Actively secreted by major salivary glands
Forms complexes with calcium-binding salivary
proteins
Important role in maintenance of ionic product
for hydroxyapatite (see later)
Concentration range in saliva 1 2 mM
Behaviour with flow rate variable due to protein
binding
In general

Flow rate
Ca
( protein)
16
EFFECT OF FLOW RATE ON Ca AND Mg
CONCENTRATIONS IN SALIVA
stimulation begun
1.00 mL/min
1.5
120
1.3
Ca
80
Ca (mM)
Mg (µM)
1.1
40
unstimulated
Mg
0.9
0.04 mL/min
0
0
5
10
15
20
25
Time (min)
17
EFFECT OF FLOW RATE ON CONCENTRATION OF PROTEIN
IN SALIVA
1 mL/min
stimulation begun
350
270
Protein (mg)
0.5 mL/min
190
0.25 mL/min
unstimulated
110
5
10
15
20
25
Time (min)
18
5. PHOSPHATE IONS
Acts as a buffer, especially in unstimulated
saliva
Important in maintenance of ionic product for
hydroxyapatite
Concentration range in saliva 2 -23 mM
In general
Flow rate
H2PO4- / HPO4

19
EFFECT OF FLOW RATE ON INORGANIC ORTHOPHOSPHATE
CONCENTRATION IN SALIVA
Time (min)
20
HYDROXYAPATITE
The 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 Ca10 x PO46 x OH2
21
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
22
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, PO43-
(and OH-) in saliva.
Protonation of the phosphate group is pH dependent
H
H
H
PO43-
HPO42-
H2PO4-
H3PO4
-H
-H
-H
pKa 12.7
pKa 7.2
pKa 2.12
23
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
Brushite / Dicalcium phosphate
CaHPO4 / CaHPO4.2H2O
DCPD
Tricalcium phosphate
TCP
Ca3(PO4)2
24
6. CHLORIDE IONS
Preserves electrical neutrality
Activates salivary amylase
Concentration range in saliva 17 29 mM
In general
Flow rate
Cl-

25
6. FLUORIDE ION
See later lecture Prof Robinson
Fluoride ion is normally present at very low
concentrations in whole saliva (range 0.001
0.005 mM)
Fluoride accumulates in porous enamel (and
dentine), including caries lesions
Fluoride concentrations in plaque are higher than
those in saliva
Fluoride replaces (OH) in the HAP lattice
structure, increasing its stability and
inhibiting acid dissolution
Fluoride facilitates HAP precipitation and
therefore promotes remineralisation.
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.