SALIVA

Saliva is not one of the popular bodily fluids. It lacks the drama of

blood, the sincerity of sweat and the emotional appeal of tears. Despite the

absence of charisma, however it is becoming increasingly apparent to

investigators and clinicians in a variety of disciplines that saliva has many

diagnostic uses and is especially valuable is the young, the old and infirm.

DEFINITION

Stanlay Jablonski’s dictionary of dentistry.

Clear, slightly acid, sometimes viscid mixture of secretions of the

salivary glands and gingival fluid exudates.

Stedman’s medical dictionary 26th edition.

Saliva is a clean, tasteless, odorless slightly acidic viscous fluid,

consisting of secretions from the paratid, sublingual, submandibular

salivary glands and the mucous glands of oral cavity.

Digestive juices

There are five digestive juices in all namely Saliva, gastric juice pancreatic

juice, succus entericus (intestinal juice) bile.

The necessity for so many digestive juices is that.

1) one juice does not contain all the enzymes necessary for digesting all the

different types of food stuffs.

E.g. Saliva contains only carbohydrate splitting enzymes. Gastric

juice contains both fat and protein splitting enzymes but none acting on

carbohydrates.

2) one particular juice cannot digest a particular type of food up to

completion.

Composition and function :

Human saliva

Total amount : - 1,200 – 1500 ml in 24 hrs. A large proportion of this

24 vol is secreted at meal time when the secretory rate is highest.

Consistency – slightly cloudy because of the presence of cells and

mucin.

Reaction – usually slightly acidic (PH 6.02 – 7.05). on standing or

boiling it loses CO2 and becomes alkaline. This alkaline reaction

causes precipitation of salivary constituents, as tartar on the teeth or

calculus in salivary ducts.

Specific gravity – 1.002 –1.02.

Freezing point – 0.07 – 0.340C

Composition

99.6% Water & 0.5% Solids.

1. Cellular constituents – Yeast cells, bacteria, protozoa,

polymorphonucler leucocytes, desquamated epithelial cells etc.

2. Inorganic salts – About 0.2% consists of NaCl, KCl, acid & Alkaline

sodium phosphate, CaCO3, Calcium phosphate, K thiocyanate.

(Smoker’s Saliva rich in thiocyanate)

3. Organic 0.3%

a) Enzymes – Ptyaline (salivary amylase) lipase, carbonic

anhydrase, phosphatase and a bacteriolytic enzyme, lysozome.

b) Mucin.

c) Urea, Amino acids, cholestrol and vitamins.

d) Soluble specific blood group substances. A, B, O – 10 to 20

mgm / lit.

4. Gases – 1ml of oxygen, 2.5 ml nitrogen and 50 ml of CO2 per 100

ml.

Bicarbonates, phosphates and the proteins act as buffers. An enzyme

kallikrein is present in saliva which acts upon plasma protein to produce a

substance known as Kallidin or brady kinin. This produces vasodilation of

salivary gland during secretion.

FUNCTIONS

I Mechanical function

1. It keep the mouth moist & helps speech

2. It helps in the process of mastication of the food stuff and in

preparing it into a bolus, suitable for deglutination. Here saliva also

acts as a lubricant.

3. It dilutes hot and irritant substances and thus prevents injury to

OMM.

4. Constant flow of saliva washes down the food debris and thereby

does not allow the bacteria to grow.

The mechanical functions of saliva are its chief functions and is

mainly contributed by mucin.

II Digestive function :

Saliva contains 2 enzymes.

a) Ptyalin – which splits starch upto maltose .

b) Maltose – (in traces ) converts maltose into glucose.

III Excretory functions :

Saliva excretes urea, heavy metals, thiocyanates, certain drugs like

iodide etc. alkaloids, such as morphine, antibiotics, such as pernicillin,

streptomycin etc.

IV Helps in the sensation of taste – Taste is a chemical sensation. Unless

the substances be in solution, the taste buds cannot be stimulated. Saliva

acts as a solvent and is thus essential for taste.

V Helps water balance – Saliva keeps the mouth moist. When moisture is

reduced in the mouth, certain nerve endings at the back of the tongue are

stimulated and the sensation of thirst arises.

VI Helps heat loss – This is mainly found in animals. When they become

hot and excited more saliva is secreted causing greater heat loss.

VII Buffering action – Mainly bicarbonate and to a lesser extent phosphate

and mucin present in saliva act as buffers.

VIII Bacteriolytic action - Cell membrane of different varieties of bacteria

contains polysaccharides, lyzozoyme, the enzyme present in the saliva is

poly saccharidise, thus it dissolves the cell wall of many bacteria and finally

kills them.

DEVELOPMENT OF THE SALIVARY GLANDS

The 3 major sets of salivary gland – the parotid, the submandibular,

and the sublingual – originate in a uniform manner by oral ectodermal

epithelial buds invading the underlying mesenchyma.

The parotid gland buds are the first to appear at the 6th week intra

uterin on the inner cheek near the angles of the mouth, and grow back

towards the ear. In the “par-otid, or ear region, the epithelial cord of cells

branches and canalizes to provide the acini and ducts of the gland. The duct

and acinar system is embedded in a mesenchymal stroma that is organized,

into lobules and becomes encapsulated. The parotid duct, although

repositioned traces the path of the embryonic epithelial cord in the adult.

The submandibular salivary gland buds also appear in the 6 th week as

a grouped series forming epeithelial ridges on either side of the midline in

the floor of the mouth. The epithelial cord proliferates back into the

mesenchyme beneath the developing mandible, to branch and canalize,

forming the acini and duct of the submandibular gland. The mesenchymal

stroma separates off the parenchymal lobules, and provides the capsule of

the gland.

The sublingual glands arise in the 8th week intra uterine, as a series of

about ten epithelial buds just lateral to the submandibular gland anagen.

These branch and canalize to provide a number of ducts opening

independently beneath the tongue.

A great number of smaller salivary glands arise from the oral

ectodermal and endodermal epithelium, and remain as discrete acini and

ducts scattered throughout the mouth.

“ Some of the major salivary glands building from the oral cavity”

SALIVARY CONTROL

AFFERENT PATHWAYS

The rate of salivary gland secretion may be affected by 3 principal

factors.

a) Local factors – Whenever the sensation of taste is stimulated, the

salivary flow rate increases. The fibres carrying taste sensation pass

along the chorda tympani in the lingual nerve and the

glosopharyngeal nerve. Glassophyryngeal nerve stimulation results

mainly in increase parotid salivary flow. Acid stimuli are the most

effective salivary flow stimulants, salt and sweet less so, and bitter

the least effective.

Olfactory irritants similarly cause increase salivary flow. There is

however, uncertainty as to whether non-irritating olfactory stimuli

also have a similar effect or whether the salivary response is a

conditioned reflex.

Irritation of the oral mucosa can also result in increased salivation,

this feature is most pronounced following new denture on orthodontic

appliance insertion.

b) Emotional (psydric) stimuli – The sight of food, taking about food, on

the noise of food preparation are sufficient to activate the conditioned

reflexes leading to increase salivation. Sight, thought or discussion of

disliked food – decrease salivation.

c) Stimulation from other organs - Oesophageal irritation causes reflex

salivation, although gastric irritation leads to increase salivation as a

component of the nausea / vomiting reflex.

CENTRAL CONTROL

The afferent stimuli are finally integrated in the cell bodies of

preganglionic secretomotor neurons. The cell bodies of the sympathetic

nerous system appear to lie in the lateral columns of the first five thoracic

nerves, with the spinal reflex centers being influence by the medulla and

higher centers eg. Hypothalamus. This area, the nucleus salivations,

comprise a neuronal cluster in the reticular formation extending from the

facial nucleus to the nucleus ambigues.

Nucleus salivations

1) Nucleus salivatorius superior –

stimulation causes secretion from the

ipsilateral subsmandibular gland

2) Nucleus salivatorius inferior –

stimulation causes secretion from the

ipsilateral parotid gland.

EFFERENT PATHWAY

The control of salivation is mainly under parasympathetic control,

although there may be a sympathetic component.

Passing through the facial nerve, parasympathetic fibres pass via the

chorda tympani to reach the lingual nerve and then, synapsing in the small

ganglia around the submandibular and sublingual nerves, short post-

ganglionic fibres pass into the glands.

The glossopharyngeal fibres pass through the tympanic and lesser

superficial petrosal nerves to reach the otic ganglion where they synapse

with the post ganglionic fibres of the auriculotemporal nerve which supplies

the parotid gland.

AUTONOMIC CONTROL

The sympathetic fibres synapse in the superior cervical ganglion with

postganglionic fibres then passing to all the salivary glands.

The parasympathetic post ganglionic neurotransmitter is

acetylcholine, whereas that of the sympathetic postganglionic terminals is

nonepinephrine (noradrenaline), in addition to salivary secretion, the

Autonomic Nervous System also exerts control even the glandular

vasculature, excretory duct activity and myoepithelial cells.

FUNCTIONS OF SALIVA

1) DIGESTIVE FUNCTION

The only important digestive enzyme present in saliva is PTYALIN

(or salivary amylase) it digests starch provided it has been previously

cooled.

It is clear that food remains in the mouth for too a short time to allow

much digestion of starch to occur. However after a large meal, the PH of the

food which enters the stomach last remains nearly 30 mins or more, during

which amylase activity may continue. Once the gastric HCl soaks into the

food and lowers the PH amylase is activated and is eventually digested by

pepsin, like any other protein.

It is possible that the main action of salivary amylase is to digest

starch from food residues which remain in the mouth after meals, rather than

to contribute to digestion as a whole.

2) ANTIBACTERIAL FUNCTION OF SALIVA

Although bacteria are always present, wounds in the mouth rarely

become infected. This fact suggests that saliva contains some means of

keeping in cheek harmful bacteria and that the organisms normally present

in the mouth are those which have become resistant to salivary inhibition.

Dog saliva inhibits many bacteria more powerfully than does human,

hence dogs are free from dental caries.

Saliva has some mechanical action in removing bacteria form the

mouth and converting them to the stomach where most of them are killed

and digested by gastric juice. Although bacterial growth on some surfaces of

the mouth is greatly restricted by this means, it probably has little effect on

the bacteria in sheltered places such as the crevices between the teeth.

a) LEUCOTAIN & OPSONINS

Two properties of saliva have been described which may be related to

its antibacterial power.

1) Saliva increases capillary permeability

2) Mixed saliva possesses leucotaclic activity i.e. the power of attracting

polymorphonuclear leucocytes, but this is absent from the saliva

collected from the ducts and is greatly reduced after thorough

brushing of the teeth and the dorsum of the tongue. The activity

returns within 1-3 hrs in different individuals. Whether the leucotoxin

in saliva play any part in the normal supply of leucocyes in the mouth

is not known, but if the tissues are injured it would gain access to the

damaged area and by its dual action may promote the accumulation of

leucocytes.

The substances in plasma which make bacteria more palatable to

leucocytes are called opsonins now thought to be IgG. IgM and

certain constituents of complement saliva contains opsonins, but

being Ig, they are much less active than in plasma, saliva from caries

– free individuals has been stated to show more opsonic activity than

caries – active saliva.

b) THE NATURE OF THE ANTIBACTERIAL SUBSTANCES IN

SALIVA.

In the year 1922 Flemming discovered in tears, nasal secretion,

saliva, eggwhite and in most tissues and body fluids a substance which

dramatically kills and dissolves some strain of organisms.

The substance is called lysozyme on muranidase, an enzyme which

splits a link present in the walls of certain bacteria, the splitting of which

causes their death and disintegration.

The effectiveness of lysozyme in saliva is probably reduced by the

presence of mucin which inhibits its action.

C) BACTERIAL ANTAGONISMS

Some organisms are unable to survive in the mouth because they are

killed in the presence of other salivary organisms.

Effect demonstrated by pouring a suspension in agar of one species of

organisms over previously grown colonies of other organisms killed by UV

light on further incubations those organism may fail to grow in the vicinity

of the dead colonies.

Unidentified factors, H2O2 and lactic acid are products of salivary

bacteria which antagonizes other species in the oral flora.

D) SALIVA & BLOOD COAGULATION

When freshly – shed blood is diluted with saliva its clotting time is

reduced.

This property of saliva has been studied quantitatively by Soku

(1960) whose main finding were as follows

i) If blood is diluted with saline, the clotting time is reduced to about

40% of normal but when diluted with saliva it is reduced to 10% of

normal the effect being similar whether the blood saliva ratio was 4:1

or 1:1

ii) Saliva from all 3 glands as well as both supernatant and sedement

from whole saliva all contained the coagulation factors normally

present in serum.

iii)Whole saliva contains factors which act like tissue thromboplastine

iv) Whole saliva could replace the platelet factor in experimental clotting

but parotid r submandibular saliva could only do so partially.

v) Saliva as secreted from the ducts dose not contain factor V but whole

saliva and its sediments did contain some of the factor

3. BUFFERING POWER OF SALIVA

4. SALIVA AS A LUBRICANT

Glycoproteins – main protein of saliva. Have the important property

of giving saliva its slimy nature. The moistening of the food is important for

bolus formation and its lubrication of mouth is necessary for clean speech.

Accurate positioning of the tongue in relation to teeth is difficult when the

mouth is dry. These glycoproteins are at high concentrations in the minor

mucous gland and sublingual gland secretions, intermediate in

submandibular and very low in parotid.

The lubricating function of saliva is perhaps best appreciated when

salivary flow is inhibited during nervousness or embracement.

5. SALIVA AND WATER BALANCE

Common (1937) first observed that the drying of the month due to

excessive evaporation of saliva, as during prolonged talking, acted as a

stimulus to salivary flow, the “dry mouth reflex” and its existence has been

thoroughly confirmed. One of the theories of nature of thirst is that it results

from drying of the mucous membrane in the pharynx . If the mouth is dry,

and dry mouth reflex operates salivary flow is stimulated which prevents

drying of the pharynx and according to this theory thirst is avoided if the

body tissues are short of water, the reflex does not occur and in these

circumstances thirst follows any drying.

6. SALIVA AND TASTE

The sensation of taste is produced only by substances in solution.

Some foods, such as fruits, contain such a high proportion of H2O that

probably all the substances which have a taste are already in solution and

their taste may be received as soon as they are released by mastication.

Other foods, biscuits for eg. Contain relatively little water and before their

taste becomes apparent saliva must dissolve out the favorite constituents. By

this means saliva not only makes eating more pleasurable but may assist in

the detection of unwholesome contaminants of food.

7. SALIVA AS A ROUTE OF EXCRETION

It is frequently stated that the saliva is a solute by which certain

substances are excreted. It seems doubtful whether this can apply to any of

the normal constituents of saliva since they would be absorbed from the

intestine after the saliva was swallowed. Saliva can only be an effective

route of excretion for substances that are either destroyed or rendered

insoluble during their passing through the gut after swallowing, for eg. The

mercury and lead are present in traces in the saliva of people suffering from

poisoning by these. However the amount of excretion through the saliva

would seem to be insignificant compared with that via the kidney.

8. Reported functions of uncertain status.

a) The nerve growth factor.

b) Epidermal growth factor.

c) Parotin, a harmone – like subs isolated from the parotid gland.

d) Iodine metabolism.

THE EFFECTS OF REMOVAL OR INACTIVITY OF SALIVARY

GLANDS :

Experiments conducted on rats where in the salivary glands removed

exhibited a most striking feature i.e. there was an increase in the member of

bacteria in the mouth and the incidence of dental caries.

In one experiment, all 3 pairs of salivary glands were removed, dental

caries increased almost 3 times in rats.

Other effects – servere recession of the gingivae around the anterior

teeth resulting in exposure of cementum, which occurs in 14-18 days from

the removal of the glands.

Exposed cementum became carious and debris accumulated which

caused ulceration of the soft tissue and resorption of the alveolar bone.

THE EFFECT OF DESALIVATION OF OTHER ORGANS.

Removal of salivary glands

Salivary flow

Intake of food

Fall in body weight especially in the

Units of adrenals, testis, ovary & uterus.

11. SATURATION

As previously mentioned, saliva is supersaturated with respect to

tooth mineral. This is responsible for the growth of hydroxyapatite crystals

during the remineralisation phase of the caries process. If it were not for this

situation, the teeth would slowly dissolve in saliva.

In addition, salivary calcium and phosphate are the source of minerals

for calculus formation. The presence in saliva of inhibitors of precipitation

such as statherin and the proline rich protein is presumably a major factor

preventing excessive calcification in the mouth. However in plaque, where

these proteins cannot penetrate among the their relatively large molecular

size, they are unable to prevent seeding and growth of calcium phosphate

crystals, and hence calculus formation.

MAINTAINING TOOTH INTEGRITY

Saliva maintains the tooth integrity by demineralization and

remineralization process. Demineralization occurs when acid diffuses

through the plaque and the pellicle into the liquid phase of enamel between

enamel crystals, resulting in crystalline dissolution which occurs at a

pH of 5-5.5, a critical PH range for the development of caries. Dissolved

mineral subsequently diffuses out of the tooth. The buffering capacity of

saliva greatly influences the Ph of plaque surrounding the enamel, thereby

inhibiting caries progression. Remineralization is the process of replacing

lost mineral through the organic matrix of the enamel to crystal.

Supersaturation of minerals in saliva is critical to this process.

The high salivary concentration of the Ca and PO4 which are

maintained by salivary protein may recount for the maturation and

remineralization of enamel. Salivary peptide contribute to the stabilization

of Ca & PO4 salt solution, serves as lubricant to protect tooth from wear and

may initiate the formation of protective pellicle by binding to

hydroxyapatite. Presence of F in saliva speed up the crystal precipitation by

forming fluorapatite viz like coating more resistant to caries.

III. HALITOSIS (Factor aris, bad breath)

This is a condition which is almost universal if the, odor of breath on

waking is included and it increases the intervals between meals and is

reduced by eating, it tends to increase with advancing age.

Unpleasant Odors arise from

- Alimentary canal

- Lungs

- Bacterial activity

Main factors producing mouth odors are

1. Stagnation of food debris or epithelial cells which may arise from

reduced salivary flow or reduced friction in the mouth.

2. Tissue destructions as in periodontal disease or caries.

3. The smell of certain foods such as garlic cling to the mouth.

Saliva it self readily gives rise to bad odor especially during mouth –

breathing, prolonged talking or hunger.

Eating reduces halitosis partly because of increase salivary flow and

friction in the mouth, with the effect of removing the sources of odor and

possibly because if the food contains carbohydrates the growth of acid

producing bacteria is encouraged and bacteria which metabolize proteins

and its derivates are suppressed because they cannot complete for the

limited growth factors in saliva.

Analysis of mouth air by gas chromatography showed that H2S and

methyl mercaptan were responsible for approx 90% of the odor, a 3rd minor

constituent being dimethyl sulphide.

PREVENTION OF HALITOSIS

1. Mouthwash

2. Frequent drinks and means of stimulating saliva

3. Oxidizing agents.

PROPERTIES OF SALIVA

1) Viscosity and spinnbarkeit.

Saliva is a viscous fluid and also show the property of spinnbarkeit

which is the ability to be drawn out into long elastic threads.

Cause of the viscosity of so dilute a solution as saliva is not

understood. Gotts cholk (1961) suggested that the mutual repulsion of the

highly ionized salt groups at the end of the side chains of glycoproteins

would tend to keep the polypeptide core treeched and the molecule

elongated. Molecules of this shape make their solutions viscous by the

considerable friction incurred in the movement relative to one another.

Considerable doubt, however.

Sialate contents of human parotid and submandibular saliva are

similar where as their viscosities are very different.

Schrager and Dates (1971) showed that the side chains and in

sulphate groups which might perform the role originally suggested for

sealate. Large numbers of water molecules become attached to the

glycoproteins and the great bulk of these hydrated molecules may contribute

to the viscosity of saliva, an effect not dependent on highly charged side –

chains.

2) Buffering power of saliva

Its buffering power will vary at different PH values because different

systems of buffers are effective over different parts of the PH range.

Salivary buffer consist of bicarbonates, phosphates and proteins.

Study by Letenthal in 1955 – measured the buffering power of saliva

before and after the removal of bicarbonate by a current of CO2 free air at

PH 5 and before and after dialysis, which removed both phosphates and

bicarbonate but which does not remove the large proteins.

Removal of bicarbonate greatly reduced the buffering power and

dialysis removed the whole of it. He concluded that bicarbonate is the most

important buffers, that phosphate plays some part but that, contrary to

previous views, the proteins can be disregarded as buffers in saliva over the

physiological PH. range , but are the chief buffers of Plaque. Buffers work

by converting any highly ionized acid or alkali which is tending to alter the

Ph of a solution, into a more weakly ionized substance. Bicarbonates release

the weak carbonic acid when an acid is added and once this acid is rapidly

decomposed into H2O & CO2, which leaves the solution, the result is not the

accumulation to a weaker acid (as with most buffers) but the complete

removal of acid. Bicarbonates are very effective buffers against acid and are

important in reducing PH changes in plaque after meals. Unstimulated

saliva which has much lower bicarbonate content, is a less powerful buffer

near neutrality.

Ericssion (1959) studied the diurnal variation in buffering power of

saliva in five subjects. He found that 1) it was high immediately on rising in

the morning but rapidly fell 2) it increases about a quarter of an hour after

meals but usually fell within half to 1 hour after meals. 3) there was an

upward tread in the buffering power through out the day, until wening when

it usually tended to fall.

3) Reducing power of saliva

In any complex biological systems viz saliva with its terming flora,

some chemical reactions in progress will be oxidations and others

reductions. The algebraic sum of these reactions is such that mixed saliva

normally has reducing properties.

In addition to bacterial reductions, saliva contains a complex mix of

substances with reducing properties which have been mistakenly resumed in

the past to be glucose. These reducing substance are present in saliva

collected from the ducts as well as in mouth saliva. They include

carbohydrate split off from glycoproteins, nitrites and some unidentified

subs of low molecular weight.

SALIVARY FLUORIDE

The role of saliva in the mode of action is now well recognized.

Fluoride may reach saliva directly from ingestion or from topical

application treatment, or indirectly from the blood stream via the salivary

glands or gingival – crevicular fluid, or from temporary intra-oral reservoirs

of fluoride, including surface deposition on the teeth of cal- fluoride like

material. It is often stated that it is the persistent elevation of salivary

fluoride from baseline values around 1 mol/L to perhaps 2-5 mol/L which

is true therapeutic factor in caries prevention. It is possible that equilibration

between salivary and plaque fluoride are important in modulating the

cariostatic actions of fluoride. Recent findings by Edgar et al, 1992 shows

that elevations in salivary fluoride of the order stated above are achieved

with the use of 1500 ppm – fluoride dentrifice or in areas with optimally

fluoridated water, these effects were seen more consistently than parallel

elevations in plaque fluoride. Clinical trials and a in situ model data (Dodds

and Edgar 1991) indicate that remineralization by fluoride is not

significantly affected by the presence or absence of plaque.

However since plaque must be present for demineralization to occur,

the accumultion of fluoride in plaque may be more significant in reducing

mineral loss than in enhancing mineral gain.

SALIVARY FLOW

2 types of saliva to be taken into consideration – stimulated

- unstimulated

Resting flow

Under resting conditions, without the exogenous stimulation also with

feeding, there is a slow flow of saliva, which keeps the mouth moist and

lubricates the mucous membranes. This unstimulated flow, which is present

majority of times, is very important for the health and well being of the oral

cavity. The unstimulated flow rates varies considerably during the day, and

is influenced by a number of factors.

Factors influencing unstimulated flow rate

1. Circadian variatjion

unstimulated flow peaks at approx 5 pm is most individuals.

Minimum flow during the might

This variation is independent of eating and sleeping behavior.

2. Light and arousal

If one is blend folded, or in an unlit room, the unstimulated flow rate

falls. This is also probably with the effect of visual input in maintaining a

state of arousal.

Saliva flow is much decreased during sleep.

3. Hydration

A loss of 8% of body water results in a cessation of saliva flow. This

resultant drying of the oral cavity is a feature of thirst. Although thirst and

H2O intake are under hypothalamic control and not dependent upon oral

dryness.

4. Exercise and stress :

A dry mouth is a future of the ‘fight and flight’ response. This is

probably not a direct action of the symptathetic supply to the gland, but

rather is due to inhibitory influence on the salivary nuclei arising from the

hypothalamus.

PSYCHIC FLOW (Stimulated)

A mouth watering sensation is a universal experience on the

anticipation on sight of food, especially if temptingly presented when

hungry. However, although the sensation is sudden flow of saliva into the

mouth, it has not provide possible to demonstrate a large increase in flow

rate in man arising from such a psychic stimuli. This is in contrast to the

well – established conditioned reflex effect in dogs, first demonstrated by

Pavlov, who did that the animals learned to associate the chewing of church

bells with meal times and would salivate on hearing the bells, even if food

was withheld. In man, a small increase in flow can usually be demonstrated

on thinking about food, or seeing it being prepared, but this does not

correspond in amount with the sensation of mouth watering. It has been

suggested that the latter is due to a sudden awareness of saliva already

present in the mouth or a momentary contraction of myoepithelial elements

to express ready – formed saliva into the mouth with out increasing the

overall amount of saliva formed.

Factors affecting flow.

UNCONDITIONAL REFLEXES

The most important stimuli to salivation are those associated with

feeding masticatory movement and especially taste.

Mastication

Chewing of flavourless bolus such as wax or chewing gum base leads

to an increase in saliva flow of about 3 folds. This is a reflex response

receptors in the muscles of mastication, TML, and mucosae detect the

presence of a bolus and its mastication, and stimulate the salivary nuclei to

increase the parasympathetic secretomotor discharge.

Gastatory stimuli :

The reflex effects of taste stimuli are more dramatic giving rise to

perhaps a ten – fold increase in saliva flow. Some stimuli are most effective,

followed by sweet, salt and bitter. Most foods also elicit olfactory stimuli

and a reflex response to smell can be demonstrated.

Other stimuli

The inhibitory action of stress on the salivary nuclei has already been

mentioned. On the other hand, there appear to be connections between the

salivary nuclei and the vomiting centre in the medulla, since copious reflex

salivation as well as nausea frequently occur first before vomiting perhaps

as an attempt to dilute or neutralize the irritant which is giving rise to the

nausea.

Hypersalivation (PTY slims) is also described in pregnancy, but the

physiological basis is nuclear, perhaps it seems from morning sickness, or

oesophageal irritation following reflex of gastric contents due to raised

abdominal pressure in late pregnancy. Complaints of excess salivation other

than under the above circumstances are usually associated with motor

disturbances of the oseofacial musculature, and are rarely substantiated by

measurement of flow rates.

POTENTIALLY ANTI – CARIES ACTIONS OF SALIVA

Anticaries effects of saliva can be categorized as

STATIC DYNAMIC

Static effect – are those which may be assumed to be exerted continuously

throughout the day, and include effects on the bacterial composition of

plaque through antibacterial or metabolic factors, protective effects of

pellicle formation, and effects of salivary contents (including F) in

maintaining a supersaturated environment for the tooth mineral.

Dynamic effect – on the other hand, are those which are mobilized over the

time – cause of the Stephen curve. These include the clearance of the

carbohydrate collagen and of the acid products of plaque metabolism, and

the alkalinity and buffering power to restore plaque Ph towards neutrality.

STATIC : 1. Anti bacterial – lysozyme, lactoferin, Ig, Sialoperoxidase

2. Supersaturation – Ca, PO4, OH, F statherin, Proline – rich peptides.

3. Substrates for plaque – sialin, urea, mucous glycoproteins.

4. Pellicle formation – low and high pressure peptides

DINAMIC

1. Buffering power – Bicarbonate ( increases on stimulation)

2. Clearance of sugar, acids – H2O (increases on stimulation)

3. Supersaturation – HCO3 (Alkalinity)

XEROSTOMIA (Dry mouth syndrome)

Xerostomia is a subjective feeling of oral dryness. It is generally

accompanied by salivary gland hypofunction and severe reduction in

secretion of whole saliva.

Oral manifestation

1. Saliva – decreases amount foamy, viscous and ropy.

2. Mucous membrane – appears dry, atrophic influenced and pale or

transluscent. Atrophy of the papilla of tongue.

Inflammation, fissuring, cracking and denudation of the tongue.

Soreness, during, and pain of OMM.

3. Salivary gland – pain and swelling may be present.

Patient suffers from a severe thrust.

Frequent ingestion of fluids

4. Lips – dry and cracked

5. Mastication – difficulty while eating

Material alba accumulates due to lack of self cleansing.

6. Swallowing – difficulty in swallowing

Dysphagia

7. Speech – difficulty in speech and phoneties

Dysphonia

Taste – taste cannot be appreciated

Dysgensia

Systemic Manifestations

- Throat – xerostomia causes dryness, hoarsness and persistent dry

cough

- Nose – dryness of nasal mucous leads to – burning , pain and

inflammation.

- Eyes – Causes, dryness, burning, itching, feeling that eyelids stick

together, blurred vision, sensitivity to light.

- Skin – Dryness and butterfly rashes

- Joints – Pain, swelling and stiffness of the joints.

- GIT = Constipation.

General symptoms

Fatigue, weakness, generalized body ache, weight lose, depression.

Etiology of xerostomia

1. Emotional reaction

2. Blockage of duct by calculus (salivary calculi)

3. Acute or chronic infection of salivary glands.

4. Drugs like atropine, antihistamines.

5. Aplasia

6. Agenesis

7. X – rays

8. Vitamin A, B, Riboflavin, Nicotinic acid diffusion.

9. Sjrons syndrome

10. Pernicious anemia, loss of fluid thru haemorrhaege excessive

sweating, diarhrroea, vomiting , polyurea.

11.Geing.

Clinical Significance

Alteration in the patient’s behaviour

Rampant caries

Difficulty with the dentures.

Pathologic conditions which

Increases salivation Decreases salivation

1. Digestive tract irritants 1. Similar atrophy of salivary glands

2. Peptic ulcers 2. Diabetes Millitus.

3. Pain full affection of oral cavity

which may be due to vitamin

deficiency trauma from surgery. All

3. Diarrhoea

fitting dentures sharp edged

restorations carious teeth mucosal

ulcerations

4.Vitamin deficiency

5. Elevated temperature due to acute

infections.

Management of Xerostomia

Management of xerostomia depends on the cause of its condition. If a

drug is suspected to be the cause, consulting with patient’s physicians may

result in the alternate drug therapy. Saliva substitutes are available but

unfortunately have not proven to be acceptable to many patients and are

more expensive also.

Milk has been proposed as a salivary substitute milk not only aids in

lubrication and increases pressure in eating but also has a buffering

capacity. Due to the presence of protein, calcium and phosphorus, milk

prevents enamel demineralization and promotes reminiralization.

Sialogoues (agents which stimulate salivary flow)

- Such as sugar free gums, lozenzes or sugar free candies containing

citric acid may be recommended.

- Sorbitol / xyletol secreting agents / products well decreases the risk of

candiasis.

- An ethanol free rinse containing aloe or landing or water soluble

lubricating jelly can be used.

- Additional recommendations include beverages that may produce

more saliva such as water with slice of lemon / lemonades.

THE ROLE OF SALIVA IN PROSTHODONTICS

Salvia plays an important role in the normal functioning of the

complete denture prosthesis. A moderate amount of saliva is needed to act

as a lubricant buffer between the prosthesis and the mucosa, (to help protect

this sensitive tissue against scuffing as the prosthesis slides over and against

it in function. In addition a thin film of saliva is indispensable in creating

adhesion between the denture base and the mucosa).

Regarding the role played by the intermediate fluid between the base

plate and the mucosa, saliva has generally been compared with that of

water, and it has been taken for granted, especially in experimental

investigations, that the power of fixation attained by the adhesion, cohesion

and surface tension of water is equivalent to that of the saliva.

In order to simply the decision about the influence that saliva might

have on the adhesion between and upper denture and the mucosa, we may

consider the adhesion mechanism between two glass plates with a thin layer

of fluid between them. Let us take H2O as the fluid.

If plates are held horizontally, the intermediate layer of fluid in the

periphery of the plate will be limited by a free layer of fluid. Layer of fluid,

the so called “meniscus”. The form of this meniscus depends on the pressure

within the fluid at the time of examination.

Plates are closer to one another (greater pressure in the

fluid>atmospheric pressure) – meniscus will bulge out, attempts to separate

the plates will cause an inward bulge of the fluid meniscus (decrease

pressure)

Measurement of the force necessary to separate two glass plates with

an intermediate layer of water and from mixed saliva, respectively, will

show that separation requires a greater force if the intermediate layer

consists of saliva.

The meniscus created by the surface tension will act as a spring all

around the edges of the plates, and the tension of that spring will be directly

correlated to the coefficient of the surface tension. This is a very important

factor that holds the plates together.

When a separating force exceeds the elasticity modulus of the fluid

meniscus, the meniscus breaks and an intense flow in the intermediate layer

of fluid will occur. This divides the layer of fluid into two parts, each of

which adheres to the glass plates.

The flow of the fluid is however, diminished by an increased

viscosity. This explains why fresh saliva, despite its lower surface tension,

gives stronger adhesion between the glass plates i.e. the rate of flow is

lowered by the high viscosity of the saliva among to its mucoid content. The

higher the viscosity, the lower the rate of flow and the greater the fixation

power.

b) The amount and viscosity of the saliva is important as it serves two very

important functions a moderate amount of saliva is needed to act as a

lubricant and also to help protect this sensitive tissue against scuffing as the

prosthesi slides over and against it in function.

In addition a thin film if saliva is indispensable in creating adhesion

between the denture base and the mucosa.

Too much Too little

An overly profuse supply of saliva

will not increase the retention and

may complicate the impression

procedure to a degree.

Xerostomea or a ptyalism may be a

systemic disorder such as diabetes

or nephritis.

Excessive sol can be controlled by

having the patient rinse with water

just before the impression tray is

inserted into the mouth, in order to

close the orifices of the salivary

glands partially

It may also be induced by regular

use of certain of the tranquilizing

drugs and may be associated with

nutritional deficiency.

In some cases antisialogogus such

as pamine may be increased.

Thick viscous type of saliva Thick Mucinous type of saliva

This type of saliva sometimes

reduces retention by interfering

with intimate contact between the

denture and the mucosa. It may

also interfere with obtaining an

accurate impression of fine tissue

detail, by filling in and bridging

over fine grooves and depressions

so that they are not registered with

complete fidelity in the impression

material. This type of saliva can

usually be controlled for

impression registration with an oral

rinse administered just before

making the impression.

This type of saliva is usually

associated with the patient who has

a marked tendency to gag. `

More than 350 palatine glands are

located in the post 2/3rd of the

palate. In some mouths these

glands secrete a profuse supply of a

thick mucinous type of saliva that

can interfere with the registration

of an accurate impression (a

mucosa which feels exceptionally

slippery indicates that it is coated

with a layer of thick mucosa)

The mucinous type of saliva can

usually be controlled by means of

mouth wash. Consisting of ½

teaspoon of bicarbonate of soda in

a half of a glass of water this pre

impression rinse has a thinning

effect on the saliva that it is much

less likely to obliterate tissue detail

by intervening at the impression –

tissue interface. If a mouth wash is

not at hand the tandem impression

technique is employed. Where 1st

impression is taken to soak up the

bubbles and mucinous saliva,

followed by a 2nd impression which

will record the tissue in a relatively

saliva free state.

ARTIFICIAL SALIVA

From the preceding section it is clear than an adequate amount of

salivary flow is essential in the host’s resistance to dental carries and also of

vital importance in the comfortable and successful mastication and

swallowing of food. It plays a vital role in the comfort of denture wearers.

Where salivary flow reduced, salivary stimulants or artificial salivary

substituted have been proposed. Salivary stimulants are most satisfactory in

the form of a pastille which requires chewing, as chewing also acts as a

stimulant. The active ingredient is usually acidic in nature as this is well

known to provoke salivation. Unfortunately this acidity can cause erosion of

the teeth and there is a need for non-acidic forms to be developed. In the

meantime, patients may be advised to chew and suck pastilles or chewing

gum produced for diabetic. These contain sorbitol rather than sugar, they

also have an acceptable PH.

No Artificial saliva that is fully satisfactory has yet been formulated.

Both carboxymethyl cellulose and hydorxyethyl cellulose in aqueous

solutions are in common use and are used as mouthwash as frequently as

required. Neither of these materials has the visco-elastic properties of

natural saliva and both require frequent use to maintain a moist oral

environment. A possible alternative is high molecular might polyethylene

oxide. Although 2% aqueous solution of polyethylene oxide has similar

viscoelastic properties to natural saliva, this sticky, stringing and viscous

liquid is difficult to handle and transport to the mouth. Wafers of pure

polyethylene oxide placed in the buccal sulcus and activated with warm

water have proved more successful, but not all patients cope well with this

procedure and further developments are awaited with interest.

Many artificial saliva solutions for example those used after

radiotherapy to the jaws (which damages the salivary glands and reduce

saliva flow), contain acid. These should be avoided in dental patients if

possible.

Typical formulae for acid – containing and acid – free artificial saliva

solutions saliva are

Acidic solution (Ph approximately 2)

Citric acid 25g

Chloroform spirit 60 ml

Concentrated anise water 10 ml

Methyl cellulose 20 g

Water upto 1 liter

Non acidic solution (Ph approximately 6)

Calcium chloride 0.5g

Magnesium chloride 0.25 g

Potassium chloride 1.25 g

Sodium chloride 1.75g

Dipotassium hydrogen arthophosphate 2.0g

Potassium dihydrogen orthophosphate 0.65g

Sodium fluoride 0.01g

Lemon spirit 16 ml

Sorbitol 85 ml

Methyl cellulose 100g.

Methyl hyroxy – benxoate 4g

Water to 2 liters

While the above solutions can be made by a pharmacist, a promising

commercial mouth lubricant with a PH of approximately 5.4 is

“glandosane” it contains carboxymethyl cellulose together with calcium and

phosphate ions. Saliva orthane has a PH of 7 and is now available

containing sodium fluorides. Instead of methyl cellulose it contains mucin

extracted from the gastric mucosa of pig to provide the appropriate

viscosity.

Artificial saliva can be classified.

1) Depending upon the treatment approach

a) Extrinsic – topically applied artificial saliva

b) Intrinsic – chemically / drug which stimulates salivary gland.

Extrinsic – divided into groups depending upon the presence or absence of

natural mucin.

i) Synthetic

ii) Animal

2) According to research development

1. Ist generation

2. IInd generation

3. Disease oriented

4. Function oriented

5. Custom designed.

Disadvantages

- Poor taste

- Lack of wettability

- Cannot be selectively targeted to different part of oral site.

- Expensive.

CONCLUSION

The secretion of saliva not only varies in rate between different

individuals but also in its composition. Rather than providing just

lubrication for the oral tissues, it is important for the metabolic health of the

mouth as a whole.

Salivary flow rate is nearly zero in sleep. Maximum cariogenic

activity is likely to occur when people eat carbohydrate at night and then do

not brush their teeth before going to sleep.

LIST OF REFERENCES

C.C.Chatterjee 11th edi. Human physiology

Christopher L.B. Lavelles Applied of the mouth

C.L.B. Lavelle 2nd edition Applied oral physiology.

D.B. Ferquson Physiology for dental study

William F.Gwaong 13th edition Review of medical physiology

CONTENTS

INTRODUCTION

DEFINITION

COMPOSITION

DEVELOPMENT OF THE SALIVARY GLANDS

SALIVARY CONTROL

FUNCTIONS

- DIGESTIVE

- ANTIBACTERIAL

- BUFFERING

- LUBRICATION

- SALIVA AND WATER BALANCE

- SALIVA AND TASTE

- EXCRETION

INACTIVITY OF SALIVARY GLANDS

EFFECT OF DESALIVATION ON OTHER ORGANS

SATURATION

TOOTH INTEGRITY

HALITOSIS

PROPERTIES OF SALIVA

SALIVARY FLUORIDES

SALIVARY FLOW

XEROSTOMIA

ROLE OF SALIVA IN PROSTHODONTICS

CONCLUSION

COLLEGE OF DENTAL SCIENCES

DEPARTMENT OF PROSTHODONTICS

INCLUDING

CROWN & BRIDGE AND IMPLANTOLOGY

SEMINAR

ON

SALIVA SALIVA

PRESENTED BY

DR. MELISSA FERNANDES