Saliva

• SALIVA & SALIVARY GLANDS

• INTRODUCTION

The mouth is the gateway for food and drink destined for the gastro-intestinal tract. SALIVARY Gland secretions perform a considerable number of protective functions due to their complex physical and chemical composition.

SALIVA is a unique defensive system present in the mouth which helps to ensure the integrity of the Oral Tissues.

Definition

SALIVA: It is a watery film/liquid produced by glands in the mouth comprising of organic and inorganic constituents which helps in chewing, swallowing and digestion. ( Tencate’s)

It is a clear liquid secreted into the mouth by salivary glands and mucous glands of the mouth; it moistens the mouth and starts the digestion of starches ( WEBSTER’S Dictionary)

J About 90% of total Salivary flow is from Parotid And Submaxillary Glands, 5% from Sublingual Glands and 5% from Minor Salivary Gland

J Daily Secretion of Saliva ranges between 500 and 1500 mls.

J Normal stimulated secretion rate in adults is 1-2 ml/min

J Saliva constitutes one of the largest secretions of the human body

J As saliva is secreted by salivary glands we need to first to discuss the salivary glands.

• Overview of Salivary Glands

• CLASSIFICATION OF SALIVARY GLANDS

SALIVARY GLANDS

MAJOR SALIVARY GLANDS

LOCATED OUTSIDE THE ORAL

CAVITY WITH EXTENDED DUCT

SYSTEM THROUGH WHICH THE GLAND

SECRETIONS REACH THE MOUTH.

MINOR SALIVARY GLANDS

LOCATED IN THE SUBMUCOSAL

LAYER WITH SHORT DUCTS

OPENING DIRECTLY ONTO THE

MUCOSAL SURFACE.

• DEVELOPMENT OF SALIVARY GLANDS

• The salivary glands develop as outgrowths of the buccal epithelium.

• During fetal life each salivary gland is formed at a specific location in the oral cavity through the growth of a bud of oral epithelium into the underlying mesenchyme.

• The promodia of the parotid and submandibular glands of humans appear during 6th week and that of sublingual gland appear after 7th week. The minor salivary glands begin their development during third month.

These outgrowths are at first solid and later they canalize and branch repeatedly to form the duct system.

The terminal parts of the duct system develop into secretory acini.

As the salivary glands develop near the junctional area between the ectoderm of the stomatodaeum and the endoderm of the foregut, it is difficult to determine whether they are ectodermal or endodermal.

major salivary glands

• PAROTID GLAND

(PARA-AROUND, OTIC-EAR)

LARGEST OF THE SALIVARY GLANDS.

WEIGHS ABOUT 15-28g.

IRREGULAR, LOBULATED, YELLOWISH MASS.

SHAPE- WEDGE SHAPED.

SITUATED BELOW THE EXTERNAL ACOUSTIC MEATUS BETWEEN THE RAMUS OF THE MANDIBLE AND STERNOMASTOID.

THE ACCESSORY PAROTID LIES BETWEEN THE ZYGOMATIC ARCH AND THE PAROTID DUCT.

• Parotid capsule

INVESTING LAYER OF DEEP CERVICAL FASCIA SPLITS BETWEEN THE

ANGLE OF MANDIBLE AND THE MASTOID PROCESS TO FORM TWO

LAMINAS WHICH ENCLOSES THE GLAND.

SUPERFICIAL LAMINA.

DEEP LAMINA.

A PORTION OF DEEP LAMINA EXTENDING BETWEEN THE STYLOID

PROCESS AND THE MANDIBLE THICKENS TO FORM

STYLOMANDIBULAR LIGAMENT WHICH SEPERATES THE PAROTID

FROM THE SUBMANDIBULAR SALIVARY GLAND.

• RELATIONS OF PAROTID GLAND

PAROTID GLAND HAS FOUR SURFACES:

a) SUPERIOR SURFACE.

b) SUPERFICIAL SURFACE.

c) ANTEROMEDIAL SURFACE.

d) POSTEROMEDIAL SURFACE.

APEX:

CERVICAL BRANCH OF FACIAL NERVE AND TWO DIVISIONS OF RETROMANDIBULAR VEIN EMERGE THROUGH IT.

SUPERIOR SURFACE:

CARTILAGENOUS PART OF EXTERNAL ACOUSTIC MEATUS.

POSTERIOR SURFACE OF TMJ

SUPERFICIAL TEMPORAL VESSELS

AURICULOTEMPORAL NERVE.

SUPERFICIAL SURFACE:

LARGEST OF THE FOUR SURFACES.

COVERED BY:

A) SKIN

B) SUPERFICIAL FASCIA CONTAINING ANTERIOR BRANCHES OF GREATER

AURICULAR NERVE.

C) PAROTID FASCIA.

D) A FEW DEEP PAROTID LYMPH NODES.

ANTEROMEDIAL SURFACE:

A) MASSETER.

B) LATERAL SURFACE OF TMJ.

C) POSTERIOR BORDER OF RAMUS OF MANDIBLE.

D) MEDIAL PTERYGOID.

E) EMERGING BRANCHES OF FACIAL NERVE.

POSTEROMEDIAL SURFACE:

MASTOID PROCESS,STERNOMASTOID, POSTERIOR BELLY OF DIGASTRIC.

STYLOID PROCESS.

EXTERNAL CAROTID ARTERY ENTERS THE

GLAND THROUGH THIS SURFACE.

FROM MEDIAL TO LATERAL SIDE , THESE ARE:

ARTERIES:

THE EXTERNAL CAROTID ARTERY.

MAXILLARY ARTERY

SUPERFICIAL TEMPORAL VESSELS.

POSTERIOR AURICULAR ARTERY.

VEINS:

THE RETROMANDIBULAR IS FORMED WITHIN THE GLAND BY THE UNION OF

SUPERFICIAL TEMPORAL AND MAXILLARY VEINS.

IN THE LOWER PART OF THE GLAND,THE VEIN DIVIDES INTO ANTERIOR AND

POSTERIOR DIVISIONS WHICH EMERGE AT THE APEX OF THE GLAND.

NERVE:

FACIAL NERVE ENTERS THE GLAND THROUGH ITS POSTEROMEDIAL

SURFACE.

THE TERMINAL BRANCHES LEAVE THE GLAND THROUGH ITS

ANTEROMEDIAL SURFACE.

• Parotid duct(stensons duct)

Thick walled.

5 cm long.

Emerges from the middle of the anterior border of the gland.

runs forwards and downwards on the MASSETER.

The duct opens into the vestibule of the mouth

opposite the crown of the second molar tooth.

• Relations of parotid duct

The parotid duct can be felt on the face and rolled on the anterior border of the masseter by pressing the finger backwards on it ( with teeth clenched to make the muscle tense).

• The parotid glands secrete entirely the serous type of salivary secretion. About 90% of the total salivary flow is from the parotid gland.

• Resting flow of saliva from this gland is 0.4 ml/min and on stimulation is 1.0-2.0 ml/min.

BLOOD SUPPLY:

Parotid gland is supplied by EXTERNAL CAROTID ARTERY.(transverse facial

and maxillary)

Veins drain into EXTERNAL JUGULAR VEIN.

LYMPHATIC DRAINAGE:

Lymph drains SUPERFICIAL and to the UPPER DEEP

CERVICAL NODES FROM PREAURICULAR GROUP.

• NERVE SUPPLY

SYMPATHETIC NERVES:

Are vasomotor and derived from plexus around the EXTERNAL

CAROTID ARTERY.

PARASYMPATHETIC NERVES:

Are secretomotor.

PREGANGLIONIC FIBERS :

INFERIOR SALIVATORY NUCLEUS

↓

GLOSSOPHARYNGEAL NERVE

↓

TYMPANIC BRANCH

↓

TYMPANIC PLEXUS

↓

LESSER PETROSAL NERVE

↓

OTIC GANGLION

postganglionic fibers from

OTIC GANGLION

↓

AURICULOTEMPORAL NERVE

↓

PAROTID GLAND

SENSORY FIBERS:

To the gland: AURICULOTEMPORAL NERVE.

To parotid fascia: SENSORY FIBERS OF GREATER AURICULAR

NERVE

• SUBMANDIBULAR SALIVARY GLAND

Irregular, size of a walnut.

Situated in anterior part of digastric triangle.

Divided by posterior border of mylohyoid into a larger part superficial to the muscle and a smaller part lying deep to the muscle.

enclosed between two layers of deep cervical fascia.

a)superficial

b)deep

SUPERFICIAL PART:

fills the digastric triangle.

reaches to the anterior belly

of digastric and back to the

stylomandibular ligament.

extends upwards upto the

mylohyoid line.

3 surfaces:

INFERIOR, LATERAL,

MEDIAL.

• Relations of submandibular gland

a)INFERIOR SURFACE

a)skin.

b)platysma.

c)cervical branch of the facial nerve.

d)deep fascia.

e)facial vein.

f)submandibular lymph nodes.

b)LATERAL SURFACE

a)submandibular fossa on the mandible.

b)insertion of the medial pterygoid.

c)facial artery.

c)MEDIAL SURFACE

a)anterior part: mylohyoid muscle,nerve and vessels.

b)middle part: hyoglossus,styloglossus,the lingual nerve,the submandibular ganglion and the hypoglossal nerve.

c)posterior part: the styloglossus, the stylohyoid ligament, the ninth nerve, and the wall of the pharynx. Inferiorly it overlaps the stylohyoid and the postererior belly Of the digastric.

•

SUBMANDIBULAR DUCT

Thin walled.

About 5 cm long.

Emerges at the anterior end of deep part of the gland.

Runs forward on the hyoglossus between lingual and the hypoglossal nerve.

Opens on the floor of the mouth, on the summit of the sublingual papilla,

at the side of the frenulum of the

tongue.

BLOOD SUPPLY:

Supplied by FACIAL ARTERY.

Veins drain into COMMON FACIAL and LINGUAL VEIN.

LYMPHATIC DRAINAGE:

TO SUBMANDIBULAR LYMPH NODES.

NERVE SUPPLY:

SENSORY- from lingual nerve.

SYMPATHETIC- from the plexus on FACIAL ARTERY.

PARASYMPATHETIC- preganglionic fibers from

Superior Salivatory Nucleus

↓

sensory root of the facial nerve

↓

↓

the Geniculate ganglion

↓

Facial Nerve

↓

Chorda Tympani

↓

Lingual Nerve

↓

SUBMANDIBULAR GANGLION

↓

postganglionic fibers to the gland

• APPLIED ANATOMY

• MOST COMMON TO BE AFFECTED BY CALCULUS.

• INCISION TO BE PLACED AN INCH BELOW THE ANGLE TO

PRESERVE MANDIBULAR BRANCH OF FACIAL NERVE.

•

SUBLINGUAL SALIVARY GLAND

Smallest of the three salivary glands.

Almond shaped.

Weighs 3-4 gm.

Lies above the mylohyoid, below the mucosa of the floor of the mouth, medial to the sublingual fossa of the mandible and lateral to the genioglossus.

DUCTS:

most of the ducts open directly into the floor of the mouth on the summit of the sublingual fold. A few of them joins submandibular duct.

• SECRETION OF SALIVA

• The daily secretion of saliva normally ranges between about 800-1500ml. Saliva contains two major types of protein secretion:

a) serous secretion: that contains PTYALIN (an α-amylase),which is an enzyme for digesting starches.

b) mucous secretion: that contains mucin for lubricating and for surface protective purposes.

• Nervous regulation of salivary secretion:

• Saliva is continuously secreted in the mouth.

• Salivary glands are controlled mainly by parasympathetic nervous signals from the superior and the inferior salivatory nuclei in the brainstem.

• Salivation can also be stimulated or inhibited by nervous signals arriving in the salivatory nuclei from higher centers of the CNS, e.g., when a person smells or eats favorite foods

• Sympathetic stimulation can also increase salivation a moderate amount but much less so than does parasympathetic stimulation. The sympathetic nerves originate from superior cervical ganglia and then travel along blood vessels to the salivary glands.

• STRUCTURE OF THE SALIVARY GLAND

A SALIVARY GLAND CONSISTS OF

SERIES OF BRANCHED DUCTS

TERMINATING IN

SECRETORY END PIECES OR ACINI.

THE MAIN EXCRETORY DUCT DIVIDES

INTO SMALLER INTERLOBULAR AND

INTRALOBULAR EXCRETORY DUCTS

THAT ENTER THE LOBES

AND LOBULES OF THE GLAND.

THE PREDOMINANT INTRALOBULAR DUCTAL COMPONENT IS THE STRIATED DUCT.

INTERCALATED DUCT JOINS SECRETORY DUCT TO THE SECRETORY END PIECES.

STRIATED DUCT PLAYS A MAJOR ROLE IN THE

MODIFICATION OF SALIVA PRODUCED BY THE

SECRETORY END PIECES.

• SECRETORY CELLS

• TWO MAIN TYPES OF SECRETORY CELLS ARE PRESENT:

i) SEROUS CELLS.

II) MUCOUS CELLS.

• SEROUS CELLS

• Secretory end pieces that are composed of serous cells are typically spherical and consist of 8 to 12 cells surrounding a central lumen.

1) Structure:

• The cells are pyramidal, with a broad base adjacent to the connective tissue stroma and a narrow apex forming part of the lumen of the end piece.

• Numerous secretory granules, in which macromolecular components of the saliva are stored, are present in the apical cytoplasm

2) Function:

• These cells which secrete a watery fluid, essentially devoid of mucus and produce proteins and glycoproteins which have well defined enzymatic, antimicrobial and calcium binding activities.

• These proteins are modified by the addition of sugar residues (glycosylation) and thus are called glycoproteins. Typically serous glycoproteins have N-linked oligosaccharide side chains.

• Structure of serous cells

• MUCOUS CELLS

• Secretory end pieces that are composed of mucous cells typically have a tubular configuration; when cut in cross section, these tubules appear as round profiles with mucous cells surrounding a central lumen of larger size than that of serous end pieces.

1) Structure:

• The most prominent feature of mucous cells is the accumulation in the apical cytoplasm of large amounts of secretory product (mucus), which compresses the nucleus and endoplasmic reticulum against the basal cell membrane.

2) Function:

• These cells produce mucins which have a protein core (apomucins).

• Mucins function mainly to lubricate and forms a barrier on surfaces and to bind and aggregate microorganisms.

• Structure of mucous cells

Myoepithelial cells

• These are contractile cells associated with the secretory end pieces and intercalated ducts of the salivary glands.

• They are located between the basal lamina and the secretory or duct cells and are joined to the cells by desmosomes.

1) Structure:

• Myoepithelial cells present around the secretory end pieces have a stellate shape; numerous branching processes extend from the cell body to surround and embrace the end piece.

2) Function:

• Contraction of the myoepithelial cells is thought to provide support for the end pieces during active secretion of saliva.

• The cells may help to expel the primary saliva from the end piece into the duct system.

• Contraction of the myoepithelial cells of the intercalated ducts may shorten and widen the ducts, helping to maintain their patency.

• DUCTS

3 CLASSES OF DUCTS:

INTERCALATED DUCTS.

STRIATED DUCTS.

EXCRETORY DUCTS.

Intercalated ducts

• The overall diameter of the intercalated ducts is smaller than that of the end pieces, and their lumina are larger.

• A few small secretory granules may be found in apical cytoplasm, especially in cells located near the end pieces.

2) Function:

• The intercalated ducts contribute macromolecular components which are stored in their secretory granules to the saliva. These include lactoferrin and lysozyme a portion of the fluid component of the primary saliva likely is added in the intercalated duct region.

• Undifferentiated cells believed to be present in the intercalated ducts also may proliferate and undergo differentiation to replace damaged or dying cells in the end pieces and striated ducts.

Striated ducts

• The striated ducts, which receive the primary saliva from the intercalated ducts, constitute the largest portion of the duct system.

1) Structure:

• Striated duct cells are columnar, with a centrally placed nucleus and a pale, acidophilic cytoplasm.

2) Function:

• An important function of striated duct cells is modification of the primary saliva by reabsorption and secretion of electrolytes.

• The granules contain kallilrein, and other secretory proteins.

• The presence of vesicles suggests that the cells may participate in endocytosis of the substances from the lumen.

Excretory ducts

• The excretory ducts are located in the connective tissue septa between the lobules of the gland that is, in an extralobular or interlobular location.

1) Structure:

• They are larger in diameter than striated ducts and have a pseudostratified epithelium

2) Function:

• It is main duct through which saliva is secreted in the oral cavity.

SALIVA

DEFINITION

• A clear liquid secreted into the mouth by the salivary glands and mucous glands of the mouth; it moistens the mouth and starts the digestion of starches. (WEBSTER’S DICTIONARY)

• Watery film/liquid produced by glands in the mouth comprising of organic and inorganic constituents which helps in chewing, swallowing and digestion.

AMOUNT OF DAILY SALIVA SECRETION:

• The daily secretion of saliva ranges normally between 500 and 1500 milliliters.

• Normal stimulated secretion rate in adults is 1 – 2 ml per minute. It may be reduced to less than 0.1ml per min in severe salivary gland malfunction (xerostomia / dry mouth).

Circadian variation:

• Unstimulated flow peaks at approx 5 pm in most individuals, with a minimum flow at night (0.05ml/min) during sleep allowing populations of bacteria to build up in mouth - result is a dragon breath in morning.

PROPERTIES

• Saliva is a merocrine secretion. In man, the saliva is a more or less turbid and slightly viscid fluid and generally of an alkaline reaction.

• The ability to draw out a thread of saliva is known as ‘Spinnbarkelt’.

ph of saliva: Saliva has a pH between 6.0 and 7.4 (with the higher pH exhibited upon increased secretion).

FORMATION OF SALIVA

• Saliva is formed in two stages

1) Primary secretion is formed actively by movement of sodium & chloride ions into lumen of the acini, creating an osmotic gradient, which leads to passive movement of water. This ‘primary isotonic saliva’ has plasma like concentration of Na, Cl & HCO3

2) Secondary secretion - the primary saliva is modified as it flows down the duct system. Sodium ions are actively reabsorbed & potassium and bicarbonate ions are secreted.

CONTROL OF SALIVATION

Salivary glands are unusual among the glands of the digestive tract in being purely under control of the autonomic nervous system, which controls both the volume and type of saliva secreted.

• Stimulation of Para-sympathetic fibers of 7th and 9th nerve produce an increase in volume of saliva, making it thin and watery

• Stimulation of the sympathetic fibers result in secretion small in amount containing high concentration of mucin and ptyalin

COMPOSITION OF SALIVA

• - 99% WATER

• - 1% SOLIDS

* ORGANIC 60%

* INORGANIC 40%

ORGANIC

• Proteins of acinar cell origin

●Amylase – (found in highest concentration in saliva. Parotid saliva : 60-120mg/100ml. Submandibular saliva : 25mg/100ml)

●Lipase

●Mucous glycoproteins (MG1 & MG2 found in submandibular & sublingual saliva)

●Proline rich glycoprotein's (found in parotid saliva ; stabilize tooth surface +aid remineralization)

– Basic glycoprotein (adsorbs to membranes)

– Acidic protein (attaches to tooth surface)

●Tyrosine-rich protein (prevent Ca precipitation from saliva)

●Histadine-rich protein (help in pellicle formation)

●Peroxidase (inhibits bacterial glycolysis & adherence of S.mutans to saliva coated hydroxyapatite, reduces bacterial aggregation)

• Proteins of nonacinar cell origin

●Lysozyme (helps in oral protective functions)

●Secretary IgA (synthesized by plasma cells, neutralizes surface charge of bacteria, inhibits bacterial adherence, prevents adverse effects of bacterial toxins & enzymes)

●Growth factors

●Regulatory peptides

Other polypeptides

• Statherin – is a small phosphoprotein which inhibits hydroxyapatite crystal growth. It also prevents precipitation of calcium phosphates from supersaturated solutions & favors remineralization. It is important as an inhibitor of calculus formation, both in the glands & on the teeth.

• Sialin – is a tetrapeptide which helps to regulate the pH of plaque.

INORGANIC

• Sodium

• Potassium

• Chloride

• Bicarbonate

• Hydrogen ion

• Iodine

• Fluoride

• Thiocynate

• Calcium

• Phosphate

Amylases

• It is an enzyme that metabolizes starch and other polysaccharides

• It is produced by acinar cells of the major salivary glands, particularly those of the serous type.

• Amylase promotes the adherence of oral streptococci to hydroxyapatite. Its ability to bind to the tooth surface as a component of plaque and to metabolize larger polysaccharides into glucose and maltose indicated that is can provide substrate for cariogenic bacteria

Lingual Lipase

• Secreted by von Ebner’s glands of tongue

• Involved in first phase of fat digestion

• Important in digestion of milk fat in new-born

• Unlike other mammalian lipases, it is highly hydrophobic and readily enters fat globules

Mucins

• It is a glycoprotein, which contains large amounts of carbohydrate.

• Its large carbohydrate content means that it binds lots of water, which increases the viscosity of the solution

• Salivary mucin is present at higher concentrations in sublingual saliva than in parotid saliva

Proline-rich Proteins (PRPs)

• Inhibitors of calcium phosphate crystal growth

• Present in the initially formed enamel pellicle and in “mature” pellicles

• Pellicle is formed by selective adsorption of hydroxyapatite-reactive salivary proteins, serum proteins and microbial products such as glucans and glucosyl-transferase

• Pellicle acts as a diffusion barrier, slowing both attacks by bacterial acids and loss of dissolved calcium and phosphate ions

Lysozyme

Lysozyme is an enzymatic protein that has direct antimicrobial effect

• It is positively charged and binds to salivary anions of various types, including bicarbonate, fluoride, iodine, and nitrate. When combined with these anions, the complex binds to the cell wall of bacteria and destabilizes the wall by catalyzing the hydrolysis of glycosidic bonds in the polysaccharide components of the wall and allowing autolysis to take place.

* its ability to bind to hydroxyapatite suggests an antimicrobial role

Secretory Immunoglobulins

Ig A represents the principal immunoglobulin found in saliva, the molecule consisting of two large 30-kD subunits with a connecting polypeptide of approximately 15 kD and a secretory component of approximately 70 kD.

The imunoglobulin exists in saliva in approximately equal amounts of two isoforms, Ig A1 and Ig A2. The secretory component is added to the molecule by the secretory cells and acts as part of the membrane receptor for Ig A.

The Ig A- receptor complex allows IgA to be internalized and transported across the cell.

• Secretory IgA has also been shown to inhibit bacterial adherence to dental enamel

• IgA are been shown to bind to mutans streptococci facilitating bacterial aggregation and removal from the oral cavity.

• Secretory IgA molecules are multivalent antibodies and can prevent the adverse effects of bacterial toxins and enzymes.

Statherins

• Produced by acinar cells in salivary glands

• Supersaturation of calcium phosphates maintain enamel integrity

• Statherins prevent precipitation or crystallization of supersaturated calcium phosphate in ductal saliva and oral fluid

• Also an effective lubricant

Factors Influencing Composition Of Saliva

1. Flow rate:

• With an increase in flow, the composition of saliva changes.

• Sodium and Chloride : Concentration increases with increasing flow.

• Potassium : The potassium concentration of resting saliva is normally considerably higher than plasma but drops a little as the saliva flow rate increases.

• Bicarbonate levels rise dramatically at high flow rates

2. Differential Gland Contribution:

• Stimulated whole saliva contains higher proportion of fluid from parotid gland than does unstimulated saliva (only 10% of fluid volume). Thus composition of mixed saliva approaches that of parotid saliva at high flow rates.

3. Circadian rhythm:

• Levels of Ca & phosphate are low in early morning.

4. Duration of stimulus:

• At a constant rate of flow, composition varies with duration of stimulus.

5. Nature of stimulus:

• Salt stimulates a higher protein content. Sugar stimuli give rise to a higher amylase content in saliva.

6. Fluoride:

• The fluoride concentration in saliva on a moderate fluoride intake is 0.01 – 0.03ppm.

• FUNCTIONS OF SALIVA

1) Protection:

• a) Saliva is capable of considerable antibacterial and antiviral activity by virtue of its content of specific antibodies (secretory IgA) as well as lysozyme, lactoferrin and lactoperoxidase.

• b) Saliva also contains lysozyme, an enzyme that lyses many bacteria and prevents overgrowth of oral microbial populations.

c) Caries and erosion:

• One of the main functions of saliva is to protect teeth against dissolution via either a cariogenic challenge or dental erosion. This is achieved by controlling the pH of the oral cavity by means of secreted bicarbonate ions

2) Digestion:

a) Lubrication and binding:

• The mucus in saliva is extremely effective in binding masticated food into a slippery bolus that slides easily through the esophagus without inflicting damage to the mucosa.

b) Solubilizes dry food:

• In order to be tasted, the molecules in food must be solubilized.

c) Initiates starch & fat digestion and glycogen breakdown:

• Serous acinar cells secrete an alpha-amylase which can begin to digest dietary starch into maltose.

3) Oral hygiene:

• The oraI cavity is almost constantly flushed with saliva, which floats away food debris and keeps the mouth relatively clean. After swallowing the bulk of food or drink, the food residues are cleared by continuing flow of unstimulated saliva.

4) Provides alkaline buffering and fluid:

• Saliva is capable of regulating the pH of oral cavity by virtue of its bicarbonate content + its phosphate and amphoteric protein constituents. Bicarbonate is referred to as the major buffer of saliva it & acts mainly to neutralize acid.

5) Maintains Integrity of teeth because of its calcium and phosphate content.BIt provides minerals that are taken up by incompletely formed enamel surface soon after eruption.

Impotant factors affecting mineralization are:

▪ Statherin - prevents precipitation of calcium phosphates from supersaturated saliva & favors remineralization.

▪ Histatins – They bind to hydroxyapatite & prevent precipitation of calcium phosphates from supersaturated saliva & favor remineralization.

▪ Proline - rich proteins – bind tightly to hydroxyapatite & prevent precipitation of calcium phosphate & thereby protect the enamel surface & prevent demineralization.

▪ Cystatins – inhibit precipitation of calcium phosphate & protect the tooth surface by promoting supersaturation of saliva with calcium & phosphate

▪

• Mucins – MG1 adsorbs tightly to tooth surface contributing to enamel pellicle formation, thereby protecting the teeth from chemical & physical attack including acid challenges. MG2 promotes clearance of oral bacteria by aggregation.

▪ Fluoride - promotes remineralisation of teeth, which have been subjected to a cariogenic challenge. These challenges occur at the base of dental plaque adjacent to the tooth surface.

6) Evaporative cooling:

• This helps in temperature regulation. Clearly of importance in dogs, which have very poorly developed sweat glands. E.g. a dog panting after a long run.

7) Aids in speech by facilitating movements of lips & tongue.

8) Excretion: Certain substances are also excreted through saliva. E.g. aspirin can be tasted second time after being swallowed as salivary glands remove it from blood & secrete it into mouth.

9) Saliva is also an important device for transmitting pathogenic bacteria from host to host.

• SALIVA AND DENTAL HEALTH

1) Role of saliva in post-eruptive maturation

• Saliva is believed to play a key role in the post-eruptive maturation of the tooth in the oral cavity, thus making the tooth less prone to caries.

2) Role of saliva in buffering

• In saliva the reaction is driven by Carbonic Anhydrase

a) A drop in pH:

• When acid is produced within dental plaque, the increase in hydrogen ion concentration will drive the dissociation equation to the left, producing more carbonic acid, which, in turn, produces more carbon dioxide and water.

b) A rise in bicarbonate concentration:

• Concentration of bicarbonate is largely responsible for determining the actual pH of saliva.

• So stimulated saliva contains more bicarbonate than resting saliva which is convenient because it is during eating, when saliva flow is raised, that plaque acid is produced in highest quantities.

c) Importance of saliva pH

• Teeth are bathed by saliva and if the pH were not sufficiently high, they would run the risk of erosion.

3) Pellicle and plaque formation

• Saliva affects the microbial composition, pH lowering & cariogenic potential of dental plaque.

• Both pellicle & plaque matrix contain proteins predominantly derived from saliva.

• Pellicle shields the surface of teeth from saliva and prevents fresh calcium phosphate from being continuously laid down.

4) Calculus formation

• Change in bicarbonate concentration and pH has implications in calculus formation. The stability of calcium phosphate in saliva is directly linked to the pH. Near to the openings of salivary ducts the pH (and bicarbonate concentration) of saliva is at its highest because no bicarbonate has been lost as carbon dioxide.

5) Role of saliva in taste function

• It is difficult to taste food with a dry mouth, therefore, saliva is essential for taste function.

• Saliva not only acts as a solvent for chemical stimuli in food, but also transports these stimuli to taste receptors.

6) Anti-cariogenic actions of saliva

• Flow of saliva can reduce plaque accumulation on tooth surface & increase rate of carbohydrate clearance from the oral cavity.

• Diffusion of salivary components (calcium, phosphate, hydroxyl & fluoride ions) into plaque, reduces solubility of enamel & promotes remineralization of early carious lesions.

• The carbonic acid-bicarbonate buffering system, as well as ammonia and urea constituents of saliva, can buffer & neutralize pH fall that occurs when plaque bacteria metabolize sugar.

• Several non-immunological components of saliva such as lysozyme, lactoperoxidase & lactoferrin have a direct antibacterial action on plaque microflora or may affect their metabolism so that they become less acidogenic.

• Total concentration of IgA in saliva is inversely related to caries experience.

• Salivary proteins increase thickness of acquired pellicle & help in retarding the movement of calcium & phosphate ions out of enamel.

ABNORMAL SALIVARY FLOW

• Few patients complain of a dry mouth. In true xerostomia, the dry mucosa may become tacky & the lips adhere to one another. An examining dental mirror may often stick to the mucosa.

• Causes of Reduced Salivary Flow

• There are numerous systemic conditions which can alter salivary flow:

• Drugs

• Psychological factors

• Anxiety states

• Depression

• Hypochondriasis

• Diseases

– Sjogren’s syndrome

– Sarcoidosis

– HIV infection

– Agenesis

• Hormonal changes (post menopause)

• Dehydration

• Diabetes mellitus

• Diarrhoea & vomiting

• Neurological diseases

• Pancreatic disturbances

• Liver disturbances

• Nutritional deficiencies

• Systemic lupus erythematosus

• Ageing

• Radiotherapy

• GENERAL CONSEQUENCES OF REDUCED SALIVARY FLOW

• Oral mucosa is more prone to traumatic ulceration and infection.

• Mucositis presents as tenderness, pain or burning sensation & is exacerbated by spicy foods, fruits, alcoholic & carbonated beverages, hot drinks & tobacco

• Atrophic changes in mucosa of tongue

• Taste sensation is altered with marked reduction in taste acquity & chewing and swallowing present difficulties.

• Foods requiring great deal of chewing are not well tolerated.

• Speech becomes difficult due to lack of lubrication.

• Individuals suffer from extreme sensitivity of teeth to heat & cold, especially when any dentin is exposed.

• Edentulous patients have problem tolerating dentures because of reduction in surface tension between dry mucosa & fitting surface of denture.

• There is increase in dental plaque accumulation & a modification of plaque flora in favour of candida, S. mutans & lactobacillus. Consequently, candidal infections & gingivitis are frequent and rampant caries is common if no preventive measures are taken.

• Radiation caries

• AMELIORATION OF DRY MOUTH

1. Salivary Stimulants –

These are helpful only if some glandular activity is present.

• Chewing gum or sucking acidic sweets.

• Paraffin wax (1.0 – 1.5 mg) 3 to 5 times a day

• Mouth lubricant and Lemon Mucilage – contain citric acid & have a pH of 2.0 & 2.8 respectively.

• Salivix

• Pilocarpine hydrochloride and Nicotinic acid – these when used systemically have stimulated salivary flow in some cases.

2. Saliva Substitutes –

a) Solutions

• Hypromellose (pH 8.0) – is a combination of hydroxypropryl-methyl cellulose with saccharine.

• V.A. Oralube (pH 7.0) It contains sodium fluoride, calcium, phosphate, potassium & magnesium ions and methyl cellulose, and is designed to remineralize enamel & dentine.

b) Sprays

• Saliva Orthana (pH 7.0) – contains mucin instead of carboxymethyl cellulose to provide viscosity.

• Glandosane (pH 5.1) – is similar to Saliva Orthana except it doesn’t contain fluoride & is formulated with hydroxymethyl cellulose instead of mucin.

c) Lozenges

• Polyox – contains polyethylene oxide, which exhibits similar viscoelastic properties to saliva when dissolved in the mouth.

RECENT ADVANCES

1) NEW DIAGNOSTICS

a) Detection of HIV by the presence of virus-specific antibodies in saliva

b) Experimental salivary assays have already been developed for detecting antibodies for measles, mumps and rubella.

c) Saliva is also reliable in diagnosing viral hepatitis A, B and C in laboratory tests.

d) As an investigational diagnostic aid and potential monitor of disease progression, saliva has been used increasingly in systemic disorders that affect salivary composition and gland function, including Alzheimer’s disease, Sjögren’s syndrome, cystic fibrosis, diabetes & diseases of adrenal cortex.

e) Determination of blood group

Saliva can be used to determine an individual's blood type because some of the glycoproteins in saliva are "blood group active"

f) PCR Technology

• The technology that allows tiny amounts of salivary DNA to be examined in such detail is a procedure called polymerase chain reaction, or PCR. The method is so sensitive that one milliliter of saliva (approximately 1/5 teaspoon) yields enough DNA to do over one hundred separate tests.

g) Gene Transfer Technology

• Scientists have now tricked non-fluid producing ductal cells into making saliva. Unlike acinar cells, ductal cells frequently are not destroyed by irradiation.

h) Salivary proteome: human salivary proteome project

• Human salivary proteome analysis is important for understanding oral health and disease pathogenesis.

• Collectively, 1,166 salivary proteins have been identified: 914 from the parotid fluid and 917 from the combined submandibular and sublingual fluids.

j) Salivary transcriptome

• RNA molecules elevated in oral cancer tissues are also elevated in saliva.

• High-density oligonucleotide microarrays (Affymetrix HG U133A) were used to profile salivary mRNA and revealed that there are approximately 3,000 human mRNAs in the cell-free saliva supernatant of healthy subjects

2) SALIVA AS A DIAGNOSTIC TOOL FOR PERIODONTAL DISEASE

Salivary markers of periodontal Diseases

• Secretions from the major salivary glands (parotid, submandibular and sublingual), which have a large number of proteins and peptides, are responsible for maintaining the integrity of the oral cavity.

1) MARKERS AFFECTING THE DENTAL BIOFILM

i) Specific markers

• Immunoglobulins (Ig) are important specific defense factors of saliva. Of the different classes of immunoglobulins, IgA, IgG and IgM influence the oral microbiota by interfering with the adherence of bacteria or by inhibiting bacterial metabolism, with IgA being the predominant immunoglobulin in this respect.

ii) Nonspecific markers

• a) Mucins are glycoproteins produced by submandibular and sublingual salivary glands and numerous minor salivary glands

• The mucin, MG2, affects the aggregation and adherence of bacteria and is known to interact with Aggregatibacter actinomycetemcomitans, and a decreased concentration of MG2 in saliva may increase colonization with this periodontopathogen.

b) Lysozyme is an antimicrobial enzyme with the ability to cleave chemical bonds in the bacterial cell wall.

• It can lyse some bacterial species by hydrolyzing glycosidic linkages in the cell wall peptidoglycan.

• It may also cause lysis of bacterial cells by interacting with monovalent anions and with proteases found in saliva.

c) Lactoferrin is an iron-binding glycoprotein produced by salivary glands, which inhibits microbial growth by sequestering iron from the environment, thus depriving bacteria of this essential element.

• Lactoferrin is strongly up-regulated in mucosal secretions during gingival inflammation

d) Histatin is a salivary protein with antimicrobial properties and is secreted from parotid and submandibular glands.

• It neutralizes the endotoxic lipopolysaccharides located in the membrane of gram-negative bacteria.

• Histatin is also an inhibitor of host and bacterial enzymes involved in the destruction of the periodontium.

e) Peroxidase is a salivary enzyme produced by acinar cells in the salivary glands.

• This enzyme removes toxic hydrogen peroxide produced by oral microorganisms and reduces acid production in the dental biofilm, thereby decreasing plaque accumulation and the establishment of gingivitis and caries.

2) SYSTEMIC MARKERS RELATED TO PERIODONTAL INFECTION

• C-reactive protein is a systemic marker released during the acute phase of an inflammatory response. C-reactive protein is produced by the liver and is stimulated by circulating cytokines, such as tumor necrosis factor-a and interleukin-1, from local or systemic inflammation such as periodontal inflammation.

3) MARKERS OF PERIODONTAL DISEASE FROM WHOLE SALIVA

• Gingival crevicular fluid is both a physiological fluid as well as an inflammatory exudate, originating from the gingival plexus of blood vessels in the gingival corium, subjacent to the epithelium lining of the dentogingival space.

4) MARKERS OF PERIODONTAL SOFT TISSUE INFLAMMATION

• During the initiation of an inflammatory response in the periodontal connective tissue, numerous cytokines, such as prostaglandin E2, interleukin-1beta, interleukin-6 and tumor

necrosis factor-alpha are released from cells of the junctional epithelia and from connective tissue fibroblasts, macrophages and polymorphonuclear leukocytes.

• Subsequently, enzymes such as matrix metalloproteinase (MMP)-8, MMP-9 and MMP-13 are produced by polymorphonuclear leukocytes and osteoclasts, leading to the degradation of connective tissue collagen and alveolar bone.

• During the inflammatory process, intercellular products are synthesized, released and diffuse towards the gingival sulcus or periodontal pocket.

• Prostaglandin E2 acts as a potent vasodilator and increases capillary permeability, which elicits clinical signs of redness and edema.

• Prostaglandin E2 also stimulates fibroblasts and osteoclasts to increase the production of MMPs.

5) MARKERS OF ALVEOLAR BONE LOSS

• Matrix metalloproteinases are host proteinases responsible for both tissue degradation and remodeling. During progressive periodontal breakdown, gingival and periodontal ligament collagens are cleaved by host cell-derived interstitial collagenases.

a) MMP-8:

• MMP-8 is the most prevalent MMP found in diseased periodontal tissue and gingival crevicular fluid.

• The MMP-8 level is also elevated in peri-implant sulcular fluid from periimplantitis lesions

b) Gelatinase (MMP-9),

• It is produced by neutrophils and degrades collagen intercellular ground substance. A twofold increase in mean MMP-9 levels is found in patients with progressive attachment loss.

c) Collagenase-3 (MMP-13)

• MMP-13 has also been implicated in peri-implantitis. It was concluded that elevated levels of both MMP-13 and MMP-8 correlated with irreversible perio-implant vertical bone loss around loosening dental implants.

d) Osteopontin

Osteopontin is highly concentrated at sites where osteoclasts are attached to the underlying mineral surface

6) As an adjunct in forensic odontology

• Forensically significant amounts of saliva are deposited during biting, sucking and traces of salivary evidence can be recovered for identify testing.

• Saliva can collected from saliva by double swab technique.

CONCLUSION

• Saliva often does not receive the attention it deserves. There is hardly any aspect of clinical practice in which the salivary glands and saliva do not play an obvious or hidden role.

• Tacticherefore, a proper understanding of the anatomy, physiology and functioning of salivary glands is essential for a good and successful dental pre.