The Importance of Saliva in Oral Health
بسم الله الرحمن
الرحيم
صدق الله العلي العظيم
Saliva and dental caries
Dr. Rihab Abdul Hussein Ali
B.D.S , M.Sc. , PhD.
•
Saliva
is the glandular secretion which constantly
bathes the
teeth
and the
oral mucosa
. Pure saliva
secreted by the oral glands is
sterile
until it is
discharged
onto the mouth.
•
Salivary glands are
exocrine
glands and are classified
according to the nature of their
secretion
or their
duct
system. Of the
major
salivary glands,
parotid
glands are the
largest
; the
submandibular
gland is
smaller
than the parotid glands. The
sublingual
gland is composed of
several smaller
glands.
•
The
minor
glands situated on the
tongue, palate
and
buccal and labial
mucosa. These glands produce
10%
of the total volume of saliva.
•
The function of the
minor
salivary glands is also
important since about
70 %
of the total volume
of salivary
proteins
is secreted by them. They
also contribute
fluoride
that bathes the teeth and
enhances caries resistance
.
•
The
parotid
glands are
serous
glands; upon
stimulation, they produce
watery
saliva with
high
content of
enzymes
like
amylase and
lipase
, while the secretions of
sublingual
glands
are predominantly
mucous
,
mucin-rich
fluids, as
same as of
minor
salivary glands. While the
secretions of
submandibular
glands are a
mixture of
mucous and serous
fluids.
•
The
word saliva
is synonymous with
spittle
,
whole saliva
,
mixed
saliva and
oral fluid
.
•
Oral fluid
which include
all
the fluid present in
the
mouth
and it is made by secretion of
salivary
glands, gingival crevicular fluid, food debris,
microorganisms, human cells, desquamated
oral epithelia, transudate
of the
mucous
membrane and mucous
from
nasal cavity and
pharynx
, sometimes it may include
acid
from the
stomach
in cases of
gastric reflux
.
Function of saliva:
-
Lubrication
(
Coats
mucosa and helps to
protect
against
mechanical, thermal and chemical
irritation. Assists
speech and swallowing
).
-
Digestion
(The presence of
amylase
enzyme in
saliva which aid in
breaking
down of
starchy
food).
-
Ion reservoir
(Solution
supersaturated
with
ions
facilitate
remineralization
of the teeth).
-
Taste
(saliva acts as
solvent
for
substances
thus
allowing
interaction
of
foodstuffs
with
taste buds
to facilitate taste).
-
Clearance
(clears
food
and facilitates
swallowing
).
-
Maintenance
of healthy
oral tissues
.
-
Buffer
capacity (helps to
neutralize plaque pH
after
eating, thus
reducing
time for
demineralization
).
-
Route
of
excretion
for many substances (This is a very
inefficient
excretory pathway as
reabsorption
may occurs
further
down
the
intestinal tract
).
-
Antimicrobial
actions (help control the
oral microflora
by
specific
and
non-specific
immune components).
-
Agglutination
(
Aggregation and accelerated
clearance of
bacterial
cells).
-
Water balance
.
Oral clearance
•
The oral cavity is frequently
exposed
to
substances
with potentially
harmful
properties.
Some of these substances have a
direct
influence
on the
caries
process.
•
An
important function
of saliva is therefore to
dilute and eliminate
substances. This is a
physiological
process usually referred to as
salivary clearance
. The
total volume
of saliva
spread out in a
thin film
on teeth and mucosa
varies
depending on several
factors, but is
usually
small, 0.8–1.2
ml.
•
Since the
mucosal surface area
of the oral cavity is
approximately
200 cm2
, the saliva film is
only
about
100 μm thick
and
varies
between
sites
in the oral
cavity. For example, the film is only about
10 μm
in
the
palate
and it has been shown that
individuals
experiencing
xerostomia
often have a saliva film
less
than that.
•
The saliva film is
moving slowly
towards the
throat
with a
speed
varying from about
1 to 8
mm/min, the
slowest
movement is in the
front
of the
upper jaw
and the
fastest
in the
lower jaw
. The
main stream
of
saliva goes
over
the
floor
of the
mouth
at
each side
of the
tongue
with
little exchange
between the
two
streams
.
Composition of saliva
•
The
composition
of saliva
varies
, depending on
whether it is
stimulated or unstimulated
(
resting
).
Stimulated
saliva is
secreted
in
response
to
masticatory or gustatory
stimulation, or to other
less common
stimuli such
as
vomiting center
.
•
While
unstimulated
saliva is the
mixture
of
secretions
which enter the mouth in the
absence
of
exogenous stimuli
. The
submandibular
gland
secretes the
greatest
proportion of the
unstimulated saliva (
69%
) followed by the
parotid, sublingual
and
minor glands
.
•
Saliva is composed of about
99.5%
water
and
0.5% solid
of which about
half
is
inorganic
(
chloride, bicarbonate,
phosphate, sodium, calcium, potassium,
trace elements, and dissolved carbon
dioxide, oxygen, and nitrogen
) and about
half
is
organic
(
proteins, vitamins, lipids,
hormone
like substances,
free amino acids,
urea
, as well as
microbial and shed cells
,
and
antimicrobial
substances).
•
Calcium
is distributed in saliva as
ionized
calcium and
bound
calcium. At
pH
values
close
to normal
the
ionized
calcium comprises
approximately
50%
of the
total
calcium
concentration.
•
The
most important
ions for maintaining the
ionic strength
of saliva are
sodium, potassium
and chloride
.
Sodium and chloride
are
reabsorbed
to an extent that
depends
on the
salivary flow rate
during the
passage
of the saliva
down the salivary
duct
. The
higher
the salivary
flow rate, the
fewer
ions are
reabsorbed
.
Factors influencing salivary composition
1- Flow rate:
It is the
main
factor affecting the composition
of saliva. The c
oncentration
of constituents
varies
between
stimulated and unstimulated
flow rate of saliva. As the
flow
rate
increases
, the
pH
and other constituents like
protein,
sodium, calcium, chloride and bicarbonate rise
. While
other constituents
fall
(
magnesium, potassium and
phosphate
).
2- Glandular source:
The
parotid
glands normally
contribute
20%
of the total volume of
unstimulated
saliva,
while at
high flow
rate the parotid glands contribute
50%
of
the whole saliva.
3- Duration of stimulation:
The saliva collected for
two
minutes
will have a
different
composition from saliva
collected for
10-15 minutes
.
Bicarbonate, protein and
calcium
concentration
increases
with
duration
of
stimulation whereas
decreased chloride
.
4- Nature of stimulus:
The taste of
salts
stimulated
much
higher protein
content.
Acid
is the
most potent
stimulus for salivary secretion and leads to production
of
an alkaline
saliva. The
pH
of saliva is
dependent
mainly on the
flow rate
and is
independent
of the
nature of the
stimulus
. The
secretion
of salivary glands
is mainly controlled by
parasympathetic
impulses
from the
salivary nuclei
.
Sympathetic
impulses are
more likely to
influence salivary composition
by
increasing exocytosis
from certain cells.
5- Others
like
medications
(
Antidepressants,
diuretics, antihistamines and narcotics
), various
diseases
(
Autoimmune diseases, diabetes mellitus,
salivary glands stones, malnutrition
) and
exercises
.
Salivary flow rate
•
Flow rate is the
most important clinical
parameter of saliva affecting
dental caries
susceptibility. A
reduced
salivary flow rate results
in
reduced defense
capacity and
increased
susceptibility
to
oral diseases
. A
low
flow rate
can affect
oral sugar clearance negatively
,
reducing salivary pH
, and influencing the
concentrations
of various salivary components
in
particular
the
antimicrobial factors
. A
total
volume of about
0.5 - 1
liters of saliva is
secreted
daily
.
•
Hyposalivation
is
not
the
same
thing as
xerostomia
.
Hyposalivation
describing a
condition
where the
flow rates of saliva are
abnormally low
. The
cut-off
value for
unstimulated
whole saliva flow rate is
0.1
ml/min
and that of
paraffin-chewing stimulated
whole saliva is
0.5–0.7 ml/min
(for
women and men
,
respectively).
•
These flow rates are
significantly lower
than the
generally accepted ‘
normal values
’ in
healthy
individuals of around
0.3 ml/min
for the
unstimulated
whole saliva flow rate and
1.5 ml/min
for the
chewing stimulated
one.
Both
rates showed a
wide
range. It should be noted that
taste stimulation
,
especially
sour taste
, results in
much higher flow
rates.
•
Xerostomia
may
exist without
the patient fulfilling the
criteria
for the
diagnosis
of hyposalivation and
hyposalivation
may be
symptomless
, although
xerostomia
most often is
associated
with
low saliva flow
rates. In general,
healthy
individuals with a
normal
salivary flow
rate can experience
xerostomia
, like those
breathing through the mouth
.
•
Xerostomia
is a
common condition
in population. It’s
reported that
25 %
of
general population
complain of
xerostomia
or
symptoms
associated with it. For
elderly
,
the
incidence
is as high as
40 %
.
•
Xerostomia
patients
should be
instructed
to observe a
variety of
caries preventive
procedures, including
oral
hygiene instruction, plaque control, low sugar dietary
advice,
daily
use of
topical fluoride
(
0.05 %
),
professional
applied of
fluoride
,
antimicrobial mouth
rinses
, uses of
artificial saliva
and
placement of sealants
.
Factors influencing salivary flow rate
1- Age:
The flow rate
increases
gradually with
age
.
2- Gland size:
Flow rate is
less
in
females
than for males due
to a
larger size
of glands among
males
.
3- Nature of stimulus: Mechanical
stimulation leads to
increase salivation
.
4- Medications
like
antidepressants, antihypertensive
reduce
salivary
flow rate
.
5- Other factors
like
circadian
(
Sodium and chloride
levels
peak
in the early
morning
while the
peak protein
is in the
late afternoon
) and
circannual rhythms
(flow is
lower
in
warm
weather and
higher
in
cold
),
body position
; a person
when
standing
will have a
higher
flow rate than
sitting
and
when a person is
lying down
. It’s almost
zero during sleep
.
Influence of saliva on dental caries
•
The presence of saliva is
important
for the
health
of
both
oral
soft and hard
tissues. The
complexity
of
physical and chemical
composition of salivary
secretions performs a
considerable number
of
protective
functions
in addition
to
other
functions.
The
influence
of saliva on the
caries
process is
fundamental
; the
anti-caries
effects of saliva can
be categorized as
static or dynamic
.
•
The
static
effects are those which may be assumed
to be
exerted continuously
, throughout the
day
and
include effects on
bacterial
composition of plaque
through
antibacterial or metabolic
factors,
protective
effects of
pellicle
formation, and effects
of
salivary ions
in maintaining a
supersaturated
environment for the
tooth mineral
.
•
Dynamic
effects, on the other hand, are those that
are
mobilized
over the
time-course
of the
Stephan
curve. These include the
clearance
of
the
carbohydrate
challenge and of the
acid
products of
plaque metabolism
, and the
alkalinity
and
buffering
power
to restore
plaque
pH
towards
neutrality
.
•
These
dynamic
effects are
related
to the
level
of
salivary
stimulation
, and are thus
activated
during
eating or drinking
, i.e., approximately
when their
action is required
.
1.
Saliva
enhances
the
clearance
of
cariogenic
microorganisms
from the mouth,
not only
by
its
flushing
effect, but also by
bacteria
agglutination
.
2.
Saliva may
remineralize
early carious
lesion
by its
calcium and phosphate
ions.
Remineralization
is remarkably
enhanced
by
the
presence of fluoride
.
3.
Inorganic
components of saliva (
calcium,
phosphate, fluoride
)
increase
the
resistance
of
hydroxyapatite
against
cariogenic
challenge and
enhance
the
saturation
of
plaque fluid
with respect to the
tooth surface
structure.
4. Salivary
buffering
effect (
bicarbonate,
phosphate
and some
protein
systems which
not
only
have a
buffer
effect but
also provide ideal
conditions for
automatically eliminating
certain
bacterial
components that require a
very low pH
to
survive).
•
The
buffering
systems in saliva (
buffer
is a
solution that tend to
maintain constant pH
) have
different pH
ranges of
maximal buffering
capacity, the
phosphate and bicarbonate
systems have
pH
of
6.8 - 7.0
and
6.1 - 6.3
respectively
.
•
Bicarbonate
may buffer against
pH fall
, thus plays an
important
role in the
protection
against
dental caries
.
The bicarbonate found in saliva is present as a
result
of
carbohydrate metabolism
, through
anaerobic
glycolysis
and the
citric acid
cycle.
•
When an
acid is added
bicarbonate
release
a
weak
carbonic acid
, which rapidly
decompose
to
water and
carbon dioxide
that
leave
the solution.
•
The
increase
in the
carbonic acid
concentration lead to
more carbon dioxide escape
from saliva making it
possible for
more bicarbonate
to
bind to hydrogen
ions
(
H+
), which will
end
in the removal of the
acid
.
•
HCO- + H+ → H2CO3 → H2O + CO2
•
The
phosphate
buffer plays an
essential
role when
salivary
flow is low
. At a
pH greater
than
6
the
saliva
is
supersaturated
with
phosphate
with regard
to
hydroxyapatite
(
HA
) which
forms
the
dental
enamel
. When the
pH falls below
the
critical
level
(
5.5
) the
HA
begins to
dissolve
,
freeing phosphates
that attempt to
restore
the
pH balance
.
•
Different individuals
may also have
different
critical
pH values owing to
interindividual
variations
in
saliva, total calcium and phosphate
concentrations. Thus, the
critical pH
in saliva is
not
constant
, but more a
dynamic
variable, which
varies
around a
mean pH
value of
5.5
.
Above
this value,
enamel
tends
to
remineralize
.
•
Certain
proteins
, such as
histatins or sialin
, as
well as
certain alkaline
products generated by
the
metabolic activity
of
bacteria
on
amino
acids, peptides, proteins and urea
, are also
important
for
controlling
the
pH
of the saliva.
•
Maintenance of physiological pH
at mucosal
cells and tooth surface is an
important function
of
salivary buffers
.
Hydrogen ion
concentration
is expressed in
pH
units; it is
equal
to the
negative logarithm
of the
hydrogen
ion
concentration. The value of
salivary pH
varies is
in the range of
6.7
and
7.4
.
Saliva plays a crucial role in maintaining oral health by lubricating the mouth, aiding in digestion, serving as an ion reservoir for teeth remineralization, enhancing taste perception, facilitating food clearance, and contributing to the maintenance of healthy oral tissues. Different salivary glands produce varying types of saliva with unique functions, collectively ensuring proper oral hygiene and protecting against dental issues like caries. This comprehensive guide highlights the functions and significance of saliva in oral care.
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Presentation Transcript
Saliva and dental caries Dr. Rihab Abdul Hussein Ali B.D.S , M.Sc. , PhD.
Saliva is the glandular secretion which constantly bathes the teeth and the oral mucosa. Pure saliva secreted by the oral glands is sterile until it is discharged onto the mouth. Salivary glands are exocrine glands and are classified according to the nature of their secretion or their duct system. Of the major salivary glands, parotid glands are the largest; the submandibular gland is smaller than the parotid glands. The sublingual gland is composed of several smaller glands. The minor glands situated on the tongue, palate and buccal and labial mucosa. These glands produce 10% of the total volume of saliva.
The function of the minor salivary glands is also important since about 70 % of the total volume of salivary proteins is secreted by them. They also contribute fluoride that bathes the teeth and enhances caries resistance. The parotid glands are serous glands; upon stimulation, they produce watery saliva with high content of enzymes like amylase and lipase, while the secretions of sublingual glands are predominantly mucous, mucin-rich fluids, as same as of minor salivary glands. While the secretions of submandibular glands are a mixture of mucous and serous fluids.
The word saliva is synonymous with spittle, whole saliva, mixed saliva and oral fluid. Oral fluid which include all the fluid present in the mouth and it is made by secretion of salivary glands, gingival crevicular fluid, food debris, microorganisms, human cells, desquamated oral epithelia, transudate of the mucous membrane and mucous from nasal cavity and pharynx, sometimes it may include acid from the stomach in cases of gastric reflux.
Function of saliva: - Lubrication (Coats mucosa and helps to protect against mechanical, thermal irritation. Assists speech and swallowing). - Digestion (The presence of amylase enzyme in saliva which aid in breaking down of starchy food). - Ion reservoir (Solution supersaturated with ions facilitate remineralization of the teeth). - Taste (saliva acts as solvent for substances thus allowing interaction of foodstuffs with taste buds to facilitate taste). - Clearance (clears food and facilitates swallowing). and chemical
- Maintenance of healthy oral tissues. - Buffer capacity (helps to neutralize plaque pH after eating, thus reducing time for demineralization). - Route of excretion for many substances (This is a very inefficient excretory pathway as reabsorption may occurs further down the intestinal tract). - Antimicrobial actions (help control the oral microflora by specific and non-specific immune components). - Agglutination (Aggregation and accelerated clearance of bacterial cells). - Water balance.
Oral clearance The oral cavity is frequently exposed to substances with potentially harmful properties. Some of these substances have a direct influence on the caries process. An important function of saliva is therefore to dilute and eliminate substances. This is a physiological process usually referred to as salivary clearance. The total volume of saliva spread out in a thin film on teeth and mucosa varies depending on several factors, but is usually small, 0.8 1.2 ml.
Since the mucosal surface area of the oral cavity is approximately 200 cm2, the saliva film is only about 100 m thick and varies between sites in the oral cavity. For example, the film is only about 10 min the palate and it has been shown that individuals experiencing xerostomia often have a saliva film less than that. The saliva film is moving slowly towards the throat with a speed varying from about 1 to 8 mm/min, the slowest movement is in the front of the upper jaw and the fastest in the lower jaw. The main stream of saliva goes over the floor of the mouth at each side of the tongue with little exchange between the two streams.
Composition of saliva The composition of saliva varies, depending on whether it is stimulated or unstimulated (resting). Stimulated saliva is secreted in response to masticatory or gustatory stimulation, or to other less common stimuli such as vomiting center. While unstimulated saliva is the mixture of secretions which enter the mouth in the absence of exogenous stimuli. The submandibular gland secretes the greatest proportion of the unstimulated saliva (69%) followed by the parotid, sublingual and minor glands.
Saliva is composed of about 99.5%water and 0.5% solid of which about half is inorganic (chloride, bicarbonate, phosphate, sodium, calcium, potassium, trace elements, and dissolved carbon dioxide, oxygen, and nitrogen) and about half is organic (proteins, vitamins, lipids, hormone like substances, free amino acids, urea, as well as microbial and shed cells, and antimicrobial substances).
Calcium is distributed in saliva as ionized calcium and bound calcium. At pH values close to normal the ionized calcium comprises approximately 50% of the total calcium concentration. The most important ions for maintaining the ionic strength of saliva are sodium, potassium and chloride. Sodium and chloride are reabsorbed to an extent that depends on the salivary flow rate during the passage of the saliva down the salivary duct. The higher the salivary flow rate, the fewer ions are reabsorbed.
Factors influencing salivary composition 1- Flow rate: It is the main factor affecting the composition of saliva. The concentration of constituents varies between stimulated and unstimulated flow rate of saliva. As the flow rate increases, the pH and other constituents like protein, sodium, calcium, chloride and bicarbonate rise. While other constituents fall (magnesium, potassium and phosphate). 2- Glandular source: The parotid glands normally contribute 20% of the total volume of unstimulated saliva, while at high flow rate the parotid glands contribute 50% of the whole saliva. 3- Duration of stimulation: The saliva collected for two minutes will have a different composition from saliva collected for 10-15 minutes. Bicarbonate, protein and calcium concentration increases with duration of stimulation whereas decreased chloride.
4- Nature of stimulus: The taste of salts stimulated much higher protein content. Acid is the most potent stimulus for salivary secretion and leads to production of an alkaline saliva. The pH of saliva is dependent mainly on the flow rate and is independent of the nature of the stimulus. The secretion of salivary glands is mainly controlled by parasympathetic impulses from the salivary nuclei. Sympathetic impulses are more likely to influence salivary composition by increasing exocytosis from certain cells. 5- Others like medications (Antidepressants, diuretics, antihistamines and narcotics), various diseases (Autoimmune diseases, diabetes mellitus, salivary glands stones, malnutrition) and exercises.
Salivary flow rate Flow rate is the most important clinical parameter of saliva affecting dental caries susceptibility. A reduced salivary flow rate results in reduced defense capacity and increased susceptibility to oral diseases. A low flow rate can affect oral sugar clearance negatively, reducing salivary pH, and influencing the concentrations of various salivary components in particular the antimicrobial factors. A total volume of about 0.5 - 1 liters of saliva is secreted daily.
Hyposalivation is not the same thing as xerostomia. Hyposalivation describing a condition where the flow rates of saliva are abnormally low. The cut-off value for unstimulated whole saliva flow rate is 0.1 ml/min and that of paraffin-chewing stimulated whole saliva is 0.5 0.7 ml/min (for women and men, respectively). These flow rates are significantly lower than the generally accepted normal values in healthy individuals of around 0.3 ml/min for the unstimulated whole saliva flow rate and 1.5 ml/min for the chewing stimulated one. Both rates showed a wide range. It should be noted that taste stimulation, especially sour taste, results in much higher flow rates.
Xerostomia may exist without the patient fulfilling the criteria for the diagnosis of hyposalivation and hyposalivation may be symptomless, although xerostomia most often is associated with low saliva flow rates. In general, healthy individuals with a normal salivary flow rate can experience xerostomia, like those breathing through the mouth. Xerostomia is a common condition in population. It s reported that 25 % of general population complain of xerostomia or symptoms associated with it. For elderly, the incidence is as high as 40 %. Xerostomia patients should be instructed to observe a variety of caries preventive procedures, including oral hygiene instruction, plaque control, low sugar dietary advice, daily use of topical fluoride (0.05 %), professional applied of fluoride, antimicrobial mouth rinses, uses of artificial saliva and placement of sealants.
Factors influencing salivary flow rate 1- Age: The flow rate increases gradually with age. 2- Gland size: Flow rate is less in females than for males due to a larger size of glands among males. 3- Nature of stimulus: Mechanical stimulation leads to increase salivation. 4- Medications like antidepressants, antihypertensive reduce salivary flow rate. 5- Other factors like circadian (Sodium and chloride levels peak in the early morning while the peak protein is in the late afternoon) and circannual rhythms (flow is lower in warm weather and higher in cold), body position; a person when standing will have a higher flow rate than sitting and when a person is lying down. It s almost zero during sleep.
Influence of saliva on dental caries The presence of saliva is important for the health of both oral soft and hard tissues. The complexity of physical and chemical composition of salivary secretions performs a considerable number of protective functions in addition to other functions. The influence of saliva on the caries process is fundamental; the anti-caries effects of saliva can be categorized as static or dynamic. The static effects are those which may be assumed to be exerted continuously, throughout the day and include effects on bacterial composition of plaque through antibacterial or metabolic factors, protective effects of pellicle formation, and effects of salivary ions in maintaining a supersaturated environment for the tooth mineral.
Dynamic effects, on the other hand, are those that are mobilized over the time-course of the Stephan curve. These include the clearance of the carbohydrate challenge and of the acid products of plaque metabolism, and the alkalinity and buffering power to restore plaque pH towards neutrality. These dynamic effects are related to the level of salivary stimulation, and are thus activated during eating or drinking, i.e., approximately when their action is required.
Saliva enhances the clearance of cariogenic microorganisms from the mouth, not only by its flushing effect, but also by bacteria agglutination. Saliva may remineralizeearly carious lesion by its calcium and phosphate ions. Remineralization is remarkably enhanced by the presence of fluoride. Inorganic components of saliva (calcium, phosphate, fluoride) increase the resistance of hydroxyapatite against cariogenic challenge and enhance the saturation of plaque fluid with respect to the tooth surface structure. 1. 2. 3.
4. Salivary buffering effect (bicarbonate, phosphate and some protein systems which not only have a buffer effect but also provide ideal conditions for automatically eliminating certain bacterial components that require a very low pH to survive). The buffering systems in saliva (buffer is a solution that tend to maintain constant pH) have different pH ranges of maximal buffering capacity, the phosphate and bicarbonate systems have pH of 6.8 - 7.0 and 6.1 - 6.3 respectively.
Bicarbonate may buffer against pH fall, thus plays an important role in the protection against dental caries. The bicarbonate found in saliva is present as a result of carbohydrate metabolism, through anaerobic glycolysis and the citric acid cycle. When an acid is added bicarbonate release a weak carbonic acid, which rapidly decompose to water and carbon dioxide that leave the solution. The increase in the carbonic acid concentration lead to more carbon dioxide escape from saliva making it possible for more bicarbonate to bind to hydrogen ions (H+), which will end in the removal of the acid. HCO- + H+ H2CO3 H2O + CO2
The phosphate buffer plays an essential role when salivary flow is low. At a pH greater than 6 the saliva is supersaturated with phosphate with regard to hydroxyapatite (HA) which forms the dental enamel. When the pH falls below the critical level (5.5) the HA begins to dissolve, freeing phosphates that attempt to restore the pH balance. Different individuals may also have different critical pH values owing to interindividual variations in saliva, total calcium and phosphate concentrations. Thus, the critical pH in saliva is not constant, but more a dynamic variable, which varies around a mean pH value of 5.5. Above this value, enamel tends to remineralize.
Certain proteins, such as histatins or sialin, as well as certain alkaline products generated by the metabolic activity of bacteria on amino acids, peptides, proteins and urea, are also important for controlling the pH of the saliva. Maintenance of physiological pH at mucosal cells and tooth surface is an important function of salivary buffers. Hydrogen ion concentration is expressed in pH units; it is equal to the negative logarithm of the hydrogen ion concentration. The value of salivary pH varies is in the range of 6.7 and 7.4.
