Saliva

SALIVAPresented by Dr. ASLAM TARIQ MOHAMMEDIst Yr PGDept.Of Orthodontics

Contents IntroductionHistorySalivary gland structure (macroscopic and microscopic) and developmentMechanism of secretion of salivaNerve distribution in glandsComposition and functions of salivaIncreased salivation/sialorrheaDecreased salivation/xerostomia

Applied aspects Saliva and friction Saliva and bonding Salivary clearance rate Experimental salivary pellicles and orthodontic materials Salivary ph and elastomers Saliva and corrosionConclusion References

Introduction:

Neglected by dentists and ignored by physicians, saliva is the least known and the least appreciated of all the body fluids. Yet, this lowly secretion plays a vital role in the integrity of the oral tissues; in the selection, ingestion and preparation of the food for digestion and in our ability to communicate with one another.

Hence it is justified for us to know the physiology of the secretion namely saliva in depth so that when circumstances encounter us regarding its undersecretion or oversecretion can suitably alter our modality of treatment so that best possible treatment is rendered to our patients

History Dwell on the past and you will lose an eye, forget the past and you will lose both eyesOrabasius (325-403 AD)- described submandibular salivary glands on each side of the tongueThomas Wharton (1614-1673)- Whartons duct. Dane Neils Stenson- parotid gland duct stensons duct.Antonius Nuck (1650-1692)-injected coloured wax into the ducts and studied their pattern.Ivan Pavlov-under took a classical study on reflex salivary secretion in dogs. He concluded that different stimulus to the mouth produced qualitative and quantitative differences in reflex salivary secretion.

Major salivary glandsThe salivary glands of humans are considered the cyto- architectural replica of salivary glands of rats, hence we find a number of literature where in experiments on rat salivary glands are correlated to that of human beings. Salivary glands are defined as compound, tubuloacinar, merocrine , exocrine glands whose ducts open into oral cavity.

Salivary glands are classified : According to size of the glands as : Major : ex parotid, submandibular, sublingual Minor : lingual salivary glands (vonebners glands), labial glands, palatal glands in postero lateral aspect, buccal glands in cheek. According to histochemical nature of secretion: Serous - parotid gland, vonebners gland. Mucous palatine, glossopalatine and glands in post part of tongue. Mixed sub mandibular (predominently serous , mixed). sub lingual (predominently mucous, mixed).

According to position:Extra oral : ex parotid, submandibular, sublingual Intral oral : vonebners gland, labial, palatine, buccal glandsIn humans saliva secretion from parotid, submandibular, sublingual glands contribute abut 90% of saliva volume and minor salivary glands contribute 10% Submandibular gland contributes : 65% of total saliva secretion.Parotid 25%,Sublingual 10% .

MAJOR SALIVARY GLANDS (macroscopic view)Parotid salivary gland: are enclosed within a well formed connective tissue capsule with its superficial portion lying in front of the external ear and its deeper portion lying in the retromandibular fossa.On the surface of the masseter, small detached part lies b/w zygomatic arch and parotid duct-accessory parotid gland or socia parotidis

External FeaturesResembles an inverted 3 sided pyramid

Four surfacesSuperior(Base of the Pyramid)SuperficialAnteromedialPosteromedial

Separated by three bordersAnteriorPosteriorMedial

RelationsSuperior Surface ConcaveRelated to Cartilaginous part of ext acoustic meatusPost. Aspect of temperomandibular jointAuriculotemporal NerveSup. Temporal vesselsApexOverlaps posterior belly of digastric and adjoining part of carotid triangle

Superficial SurfaceCovered by SkinSuperficial fascia containing facial branches of great auricular NSuperficial parotid lymph nodes and post fibers of platysma

Anteromedial SurfaceGrooved by posterior border of ramus of mandible

Related toMasseterLateral Surface of temperomandibular jointMedial pterygoid musclesEmerging branches of Facial N

Posteromedial Surface

Related to mastoid process with sternomastoid and posterior belly of digastric.

Styloid process with structures attached to it.

External Carotid A. which enters the gland through the surface

Internal Carotid A. which lies deep to styloid process

BORDERS:Anterior border:

Separates superficial surface from anteromedial surface.

Structures which emerge at this border

Parotid DuctTerminal Branches of facial nerveTransverse facial vessels

Posterior Border:

Separates superficial surface from posteromedial surface.Overlaps sternomastoid.

Medial Border:

Separates anteromedial surface from posteromedial surfaceRelated to lateral wall of pharynx

Parotid Duct:

Ductus parotideus; Stensens duct

5 cm in length

Appears in the anterior border of the gland

Runs anteriorly and downwards on the masseter b/w the upper and lower buccal branches of facial N.

At the anterior border of masseter it piercesBuccal pad of fatBuccopharyngeal fasciaBuccinator Muscle

It opens into the vestibule of mouth opposite to the 2nd upper molarSurface anatomy of parotid duct Corresponds to middle third of a line drawn from lower border of tragus to a point midway b/w nasal ala and upper labial margin.

Submandibular salivary glands : Are enveloped by a well defined capsule and is located in submandibular triangle below floor of mouth and mylohyoid. The main excretory duct, Whartons duct opens on either side of lingual frenum in the floor of the mouth.Consists of both mucous and serous acini. Blood supply Artery : facial artery Vein : common facial vein Lymphnodes : submandibular group of lymphnodes Nerve supply : branches from submandibular ganglion, Secretomotor pathway begins in superior salivatory nucleus ,

preganglionic fibres pass through the sensory root of facial nerve, geniculate ganglion, facial nerve, chorda tympani and lingual nerve. Sublingual Salivary glands : lies above mylohyoid but below floor of the mouth. Contains both serous and mucous acini but predominantly mucous acini. Blood supply Artery : lingual and submental arteries Nerve supply : from submandibular ganglion the main duct (Bartholins duct) opens with the submandibular duct and several smaller ducts (ducts of Rivinous) open independently along sublingual fold.

Development of salivary glands Three major pairs of salivary glands originate uniformly as oral epithelial buds involving the underlying mesenchyme. All parenchymal (secretory) tissue of the glands arises from the proliferation of oral epithelium, which is either ectodermal or endodermal in origin. The stroma (Capsule and septa) of the gland originates from the mesenchyme that may be of either mesodermal or neural crest origin. Failure of the bud to canalize to form ducts before acinar cells starts secretion cammernces results in retention type of cysts.

We find initiation of salivary gland formation during the following mentioned period of intra-uterine life of the developing fetus. Parotid 6 week intra-uterine Submandibular -6 weeks intra-uterine Sublingual 8 weeks intra-uterine

Mechanism of secretion of salivaSaliva is first secreted in the acinar cells. They determine the type of secretion.Serous cells produce a watery seromucous secretion and mucous cells produce a viscous mucin rich secretion.Saliva is formed in two stages: a primary secretion occurs in the acini, then modified as it passes through the ducts. The primary secretion is formed actively by the movement of sodium and chloride ions into the lumen, creating an osmotic gradient which leads to passive movement of water

Other acinar components are added here, before the fluid enters the duct, where sodium ions are actively reabsorbed (chloride ions follow passively to maintain electrical equilibrium) and potassium and bicarbonate ions secreted.The macromolecular components (amylase, mucous glycoproteins etc) are formed in the usual way in the acinar cell endoplasmic reticulum, processed into secretory vesicles in the golgi apparatus and are exported from the cell by exocytosis.

SIGNAL TRANSDUCTION: When a nerve to the salivary gland is stimulated, the transduction of this signal to increase the formation of saliva is first brought about by the release of a neurotransmitter substance. These include noradrenalin (sympathetics) and acetyl choline, substance P and vasointestinal polypeptide (parasympathetics). When the neurotransmitter arrives at a secretory cell membrane it binds to and activates a receptor (which may be stimulatory or inhibitory) on the external surface of the membrane.

This activates an intermediate guanine nucleotide-dependent membrane protein known as a G protein, which in turn activates a regulatory enzyme on the inner, cytoplasmic surface of the cell. The regulatory enzyme may be either phospholipase C or adenyl cyclase. PHOSPHOLIPASE C PATHWAY: Phospholipase C enzyme (PLC) is activated on binding of acetyl choline at muscarinic receptors, substance P at peptidergic receptors, or noradrenaline at adrenergic receptors on the acinar cell membrane. It controls the intracellular pathway leading to the secretion of water and electrolytes. The pathway is rather complex.

PLC is responsible for hydrolyzing a membrane phospholipid (phosphatidyl inositol biphosphate, PIP2) to form diacylglycerol (DAG) and inositol triphosphate (IP3). The latter stimulates the release of calcium ions from the endoplasmic reticulum. This increased cytoplasmic calcium ion concentration causes the opening of potassium channels in the acinar cell membrane, which allow potassium ions to diffuse out of the cell down a concentration gradient established by a Na/K membrane pump.The second is a sodium/potassium exchange pump in the membranes of the intercellular canaliculi. Thus, the extrusion of potassium triggers the entry of sodium and chloride ions into the intercellular canaliculi.The chloride ions which entered the cell with the sodium then diffuse across the luminal membrane via a calcium - sensitive channel.

The arrival of chloride ions in the lumen triggers the movement of sodium ions from the intercellular canaliculi across the tight junction between the cells, thus establishing the osmotic gradient for the movement of water into the lumen.ADENYL CYCLASE PATHWAY: Adenyl cyclase (AC) is activated when noradrenaline binds to beta adrenergic acinar receptors, or vasoactive intestinal peptide (VIP) binds to peptidergic receptors. Activation leads to exocytosis of secretory proteins.AC causes the intracellular formation of 3, 5- cyclic AMP from ATP. Cyclic AMP (cAMP) activates a second enzyme, cAMP dependent protein kinase (cA-PK) which exists in four subunits.

Two subunits are receptor molecules which bind with cAMP (2R cAMP), thereby liberating the other two catalytic subunits (2C) to activate effector proteins (Pr) by phophorylation (Pr-P). The activated effector proteins then stimulate exocytosis. Diacylglycerol (from the phospholipase C pathway) also promotes exocytosis.

CompositionVolume 1/5th the plasma volume Specific gravity 1.002 -- 1.012 Osmolality saliva is hypotonic to plasma Salivary flow rates, differ at different times of the day lowest rate of saliva flow is observed in the early hours of the morning (4-6 o clock) and peak flow rates are seen in the evening (16:00-20:00hrs).Inorganic components : Most important cations are Na+ and K+The major osmotically active anions are Cl- and HCO3- Water and ionic constituents of saliva are derived by translocation from blood plasma.

Although salivary electrolytes are derived from the blood supply, their ionic concentrations are not identical to plasma . So that saliva is not merely on ultra filtrate of plasma.

Organic components : They have different function such as enzymatic action, coating of tissue surfaces, protection of dental tissues, control of tissue growth. The digestive enzyme salivary amylase or ptyalin is the organic component found in highest concentration in saliva. Amylase consists of two families of isoenzymes glycosylated - non glycosylated

Doubt has always existed concerning the function of salivary amylase, since there is little time for the enzyme to be active before the food bolus is swallowed and exposed to stomach pH that would inactivate the enzyme. Lipase from van ebners gland has significant role in digestion of fat and is active in stomach pH also. Mucous glycoproteins secreted in saliva have a high molecular weight and consist of multiple oligosaccharide chains attachment to a peptide core. All oral soft tissues are coated with mucous glycoproteins which are thought to act as trap for bacteria and a regulator of interaction and interchange between surface epithelial cells and oral environment.

Some of these glycoproteins bind strongly to the tooth surface and are therefore an important constituent of enamel pellicle. There are 2 types of proline rich glycoproteins Basic glycoprotein binds lipids and may preferentially adsorb to membranes. Acidic glycoproteins comprises of calcium binding proteins and attaches to the tooth surface. These factors have role in stabilizing the tooth surface and promote remineralization.Tyrosine rich peptide called statherin may play a role in stabilizing supersaturated solution of Ca and phosphate and prevent calcium precipitation from saliva thus prevents demineralization.

Secretory IgA is synthesized by plasma cells, Functions of secretory IgAIt has 2 functions - mucosal defense - dental defense Perhaps compliment activating IgG antibodies are more potent with regard to elimination of noncolonized bacteria than IgA antibodies that do not engage this lytic system efficiently. Periodontal disease secretory IgA is responsible for host resistance to periodontal disease. hence secretory IgA antibodies have little or no effect in an established dental plaque.

Functions:PROTECTION : The glycoprotein content, which makes saliva mucinous protects the lining mucosa by forming is barrier against noxius stimulus, microbial toxins and minor trauma. Its fluid consistency also provides a mechnical washing action which flushes away nonadherent bacterial and cellular debris from mouth. In particular, the clearance of sugars from mouth by salivary washing action limits their availability to acidogenic plaque microorganisms. The calcium binding proteins in saliva helps in formation of salivary pellicle, which behaves as a protein membrane.

BUFFERING ACTION : protects oral cavity in 2 ways : It prevents potential pathogens from colonizing in the mouth by denying then optimal environmental conditions. Plaque microorganisms can produce acid from sugar, which if not rapidly buffered and cleared by saliva, can demineralize enamel. Much of buffering capacity of saliva lies in HCO3 and phosphate ions .Negatively charged residues on salivary proteins are also thought to serve as buffers, a salivary peptide, sialin, plays a significant role in raising the pH of dental plaque after exposure to fermentable carbohydrate.

If access of saliva to the plaque is prevented there is a dramatic fall in plaque pH, whereas unrestricted salivary flow to plaque results in little alteration of plaque pH. Saliva is therefore able to prevent acidification of plaque. Resting parotid saliva has a pH of 5.82 and bicarbonate conc. of 0.6m Eq/L. Whereas at high flow rates the pH rises to 7.67 and bicarbonate conc increases to almost 30 mEq/L. It can be hypothesized that to increase the buffering power of saliva it is necessary to increase the saliva flow.

DIGESTION : Saliva provides taste acuity, neutralizes esophageal contents, dilutes gastric chyme, forms the food bolus. Amylase content in saliva breaks down starch into oligosaccharides such as maltose, maltotriose, thus occurs best at a pH of 6.7. Further digestion of oligosaccharides takes place in small intestine by pancreatic amylases. TASTE : Although it enables the pleasurable sensations of food to be experienced, its primary role is protection in that it permits the recognition of noxious substances.

Saliva is required to dissolve substances to be tasted and to carry them to the taste buds. It also contains a protein called Gustin that is thought to be necessary for growth and maturation of taste buds. ANTIMICROBIAL ACTION : Saliva has a major ecologic influence on the microorganisms that attempt to colonize in oral tissues. In addition to the barrier effect of its mucus content, it contains a spectrum of proteins with antimicrobial properties such as Histatin. Lysozyme is an enzyme that can hydrolyze the cell walls of some bacteria. The essential element secretory IgA has the capacity to clump or agglutamate microorganisms.

MAINTENANCE OF TOOTH INTEGRITY : Saliva is saturated with Calcium and phosphate ions. The high concentration of these ions ensures that ionic exchange with the tooth surface is directed to the tooth. This exchange begins as soon as the tooth erupts because, although the crown is fully formed morphologically when it erupts it is crystalographically incomplete. Interaction with saliva results in post eruptive maturation through diffusion of ions such as Cal, phosphorus, magnesium, chloride into the surface apatite enamel crystals. This maturation increases surface hardness, decreases permeability, heightens the resistance of enamel to caries.

Remineralization is achieved, largely through the availability of phosphate and calcium ions in the saliva. If fluoride is also present remineralization occurs, the repaired lesion thus is less susceptible to future decay.TISSUE REPAIR : Presence of epidermal growth factor in the saliva produced by the submandibular glands helps in wound healing.SALIVA AS A DIAGNOSTIC TOOL :Flow rates of minor salivary gland as well as the calcium levels in saliva have diagnostic importance in Cystic Fibrosis. Status of Bells Palsy can be measured by monitoring flow rate of submandibular gland.

Salivary eletrolyte levels have been used as adjuncts in diagnosing and monitoring Hyperaldosteronism and in diagnosis Digitalis toxicity. Analysis of Hexosaminidase A in saliva has been reported to be useful in identifying individuals with Tay-Sachs disease as well as carriers. Heavy metal toxicity such as mercurism (acrodynia, Pinks disease} can also be monitored. In Pinks disease there will be drooling of saliva, loss of hair in patches, mucosal erythema and ulcerations. LINGUAL LIPASE : Secreted by Van Ebners gland splits fats into fatty acids. Helps in articulation of words thus enhancing proficiency of speech.

Exerts thirst mechanism thereby controlling bodys hydration requirements. ANTIFUNGUAL ACTIVITY : Saliva has antifungal factors which prevent a healthy person with good immunity from developing candidiasis.

Increased salivation/sialorrhea

Causes of PTYALISM (Sialorrhoea) Local reflexes. Oral infections (acute necrotizing ulcerative gingivitis) Oral wounds Dental procedures New dentures, appliances. Systemic : Nausea Acid regurgitation (GERD) Toxic : Heavy metal poisoning mercury - Pinks disease (Acrodynia}.

False ptyalism : (drooling) Pychogenic Bells palsy Parkinsons diseases Stroke Management : Adrenergic drugs such as atropine are used. Newer drugs like Banthine, Probanthine, Scopalamine can also be used. Patient is instructed not to wear contact lens during the period while on treatment with adrenergic drugs.

Decreased salivation/xerostomia

Xerostomia or dryness of the mouth is a clinical manifestation of salivary gland. But does not itself represent a disease entity. Xerostomia decrease in salivation, Sialorrhea increased salvation, Aptyalism absence of salivation. However the subjective complaint of dry mouth does not correlate reliably with the objective finding of decreased salivary flow rates.

Clinical evaluation of xerostomia. If tongue blade sticks to buccal mucosa xerostomia

Flow chart to depict patients at risk of developing salivary gland hypo functionChief compliant : does pt complian of dry mouth?YESNODRY MOUTH QUESTIONAIRE: 1.)Does the amount of saliva in your mouth seem too little or too much or you dont notice it? 2.)Do you have any difficulty in swallowing ? 3.)Does your mouth feel dry when eating a meal? 4.)Do you sip liquids to aid in swallowing dry food?YESNOMEDICAL HISTORY AND REVIEW OF SYSTEMS: Does patient have any known risk factors??CLINICAL EVALUATION: Does patient manifest any of the following symptoms??Major salivary gland : Enlarged?Tender?No saliva pool?Saliva contaminated with pus and blood?LIPS:Dry?Chapped?Fissured? ErythematousMUCOSA:Dry?Erythematous?Lobulated?Fissured?DENTITION:Extensive?Restorative?Rampant Caries?Caries Involving Incisal Edge,root ?CONSIDER FURTHER DIAGNOSTIC WORKUP: Sialometric evaluation,Serologic evaluation,Microbial analysis,Imaging, histological examination,medical consultation,psychological evaluation.

Xerostomia can be due to: Non salivary circumstances Salivary gland hypofunction / dysfunction

Non-salivary circumstances including changes in patient, during psychological distress, mouth breathing, sensory alterations in the oral cavity that may lead to perception of dry mouth. Therefore it is important to determine if salivary function is actually decreased using objective measurement techniques in patient complaining of xerostomia .

CAUSES OF XEROSTOMIA DUE TO SALIVARY GLAND HYPOFUNCTION Clinical features : Patient usually complains of dry or burning sensation in mouth.

In partial xerostomia mucosa appears normal. In severe cases mucosa will appear dry and atrophic sometimes inflammed, pale and translucent. Tongue has atrophy of papillae. Fissuring, inflammation, cracking of lips may be seen.

CAUSES OF SALIVARY GLAND HYPOFUNCTIONDrugsExternal beam irradiation to the head and neckOncologic chemotherapySystemic diseases sjogrens syndrome primary and secondary Granulomatous diseases(sarcodiasis , tuberculosis) graft versus host disease cystic fibrosis bells palsy diabetes amyliodosis HIV infectionLate stage liver diseaseThyroid disease (both hypo and hyperthyroidism)Psychological factorsIdiopathic

1) Medication or pharmaceutical usage: ex : Antisialogogues. It is the most common cause of decreased salivary gland function. Several antisialogogues are used in dentistry, such as atropine, banthine, Bellafoline, probanthine, scopolamine. Cholinergic agents are potent stimulants for salivary secretion. Therefore anticholinergic medications, such as antihistamines are most likely to cause hypofunction. Anti cholinergic drug Atropine. Indications as pre anesthetic mediation to decrease secretions - in bronchial asthma to relieve congestion.

-causes mydriasis, used to check refraction in ophthalmologic examination. - An article of relavenceBrandt S, Servoss JM, Perslly KB, in 1981 conducted a studyto evaluate antisialogogue effects of atropine sulphate injected submucosally to the base of the tongue. 1cc of atropine sulfate (0.4 mg / cc) was injected submucosally at the base of the tongue adjacent to lingual frenum with help of a tuberculin syringe. After 5 minutes collection period of saliva began, usually in first 5-15 minute interval there was increase in salivation due to anxiety but after 20 minutes salivation reduced drastically and the effect was noticed upto 2 hours.

Although recommended dose for teenagers was 0.75 1.7 mg a 0.4mg dose was considered effective. With the injection the operator need not rely on the patient about ingesting the drug orally 2 hours before the procedure. Sedatives, antipsychotics, anti depressants and diuretics are common drugs which induce xerostomia. Fortunately medication induced xerostomia is usually reversible if medication is discontinued. Irradiation therapy : Salivary glands are often in field of the external beam of radiation. Loss of salivary gland function is dependent on dose. Exposure to radiation greater than 50 Gy usually results in permanent salivary gland destruction.

Usually after irradiation, in a couple of months normal saliva flow rate is regained. Radiation isotope 131I: used as internal radiation for thyroid malignancy also causes reduced salivation. 4) Bone marrow transplant : May lead to Graft V/s host reaction (GVHD) and cause salivary gland hypofunction. 5) SIALOLITHIASIS : is the occurrence of calcareous concentrations in salivary glands or ducts. They from by deposition of calcium salts around a central nidus which may consist of desquamated epithelial cells, bacteria, foreign bodies. They cause xerostomia due to obstruction to flow of saliva. But normal production rate is maintained.

Clinical features : Moderate to severe pain just before, during and after meals associated with swelling of salivary gland. Occasionally there may be firm mass palpable near the orifice. Occurrence : commonly in middle aged adults. Chemical feature of sialolith : may contain a solitary mass or may occur as stones. Composition Calcium phosphate 75% - Cal carbonate 11% - Organic mater - Water.

Investigations : - Occlusal radiographs for submandibular duct stenosis in terminal 2/3rd region of duct.

IOPA film radiograph of Stensons duct is taken if stone is located in terminal 1/3rd region of duct. Increased plasma salivary amylase due to its escape from leaky junctions. Sialography.

Treatment : Surgical extirpation of the gland if stone is present in the gland.Surgical manipulation of the duct to remove the stone if seen superficially. Lithotripsy. SYSTEMIC DISEASES CAUSING XEROSTOMIA : 1) Sjogrens syndrome : It is a chronic autoimmune disease with lymphocyte mediated destruction of the exocrine gland. Sjogren syndrome patients manifest a full gamut of oral problems secondary to salivary dysfunction, often experiencing a dry mouth and needing to sip liquids frequently, difficulty in chewing, swallowing.

They usually present with : xerophthalmia, dysphagia, sinusitis, arthritis, renal tubular defects, neuropathies. Investigations : Include ophthalmologic tests : Schirmers test Rose Bengal dye test. Salivary collection rate to determine flow rate Serological examination for detection of auto antibodies. Histopathology of minor labial glands of lower lip.

Treatment includes : to alleviate dry mouth with help of saliva substitutes -Frequent slips of water Maintain good oral hygiene. Suggest sugar free chewing gum. Chlorhexidine (0.2%) rinses Topical fluoride application. Antifungal mixtures for candidiasis. Ophthalmologic and connective tissue disorders to be investigated by a specialist. Cystic fibrosis : Is a hereditary disease affecting lungs, pancreas and salivary glands. It results from a defective chloride transport protein.

Elevated calcium, phosphorous and proteins are detected in the saliva of Cystic fibrosis patients. Bells palsy : Its the idiopathic disruption of seventh cranial nerve resulting in transient or permanent facial paralysis, paralysis often has abrupt onset and is almost always unilateral. The affected side may have a decreased salivary flow rate. Decreased salivary flow is not due to gland pathology, but is a result of altered neural innervations. Diabetes mellitus (uncontrolled) : decreased saliva flow due to Dehydration from polyuria Neuropathy. Vascular endothelial causes (microangiopathy).

Amyloidosis : Its the extracellular deposition of the fibrous protein amyloid in one or more organs of the body. The etiology and pathogenesis of amyloidosis is unknown, orally it occurs in tongue. The salivary glands maybe effected and cause salivary gland hypofunction. HIV infection : affects salivary glands, influencing its flow rate and saliva composition. They are prone to have an incidence of oral and esophageal candidiasis. Granulomatous disease : TB caused by mycobacterium tuberculosis, cause granuloma formation and also decreased salivary gland function.

Sarcoidosis : It also causes granuloma formation and these granulomas cause destruction of normal tissues and lead to salivary gland hypofunction. Hyperaldosteronism : Sodium potassium ratios in saliva are in excess because due to increased reabsorption of sodium and potassium. Malnutrition : (anorexia, bulimia, dehydration) cause decrease in salivary flow rates.Salivary gland dysfunction and xerostomia in geriatric population :Contrary to early belief, salivary gland function is generally well preserved with age in healthy elderly people. There is general agreement that parotid gland function remains unchanged across the human life span in healthy, non medicated adults.

Xerostomia is a common complaint and may be found in upto 25% of institutionalized adults. This is often caused by systemic disease or its treatments.Management of Xerostomia : It includes use of saliva substitutes - Drugs / pharmaceuticals - Autologous saliva SALIVA SUBSTITUTES : These agents alleviate the patients discomfort mainly by alleviating dryness of mouth, increases articulation of speech, ease in swallowing, decreases burning sensation, prevents atrophy of papilla. hence preserves taste acuity, prevents candidal infections and ulcer formation.

However use of water in regular quantity is mandatory to prevent the person from dehydrating. Artificial saliva currently available are

DRUGS : Cholinergic drugs like pilocarpine is used to stimulate the gland in production of saliva. Cevimeline hydrochloride (evoxac) can also be used. Which has lower side effects. Indications of pilocarpine -to Increase secretions,- myasthenia gravis - open angle glaucoma. - to cause miosis, -Alzhimers disease. Contraindications of pilocarpine causes fall in blood pressure. Tachycardia.Dosage 5 mg tablet, thrice a day.

AUTOLOGOUS SALIVA : Before patient undergoes radiotherapy saliva is collected from the patient and subjected to radiation + lyophilisation + chlorhexidin (0.03%) and stored. During radiation therapy the stored saliva was sprayed. Since oral clearance rate in irradiated mouth is less, about 120 ml of saliva would last for 40 days at the rate of spraying 0.3 ml / hour for 10 hours / day. The reason for not using artificial saliva was that it does not pocess protective protein that are present in salivary secretions. Apart from these measures, chlorhexdin 0.12% oral rinse and application of fluoride is essential to prevent dental caries and candidiasis.

SALIVARY GLAND RADIOLOGYDiagnostic imaging of salivary gland disease is undertaken to differentiate between inflammatory and neoplastic disease, distinguish between diffuse and focal suppurative disease, identify and locate stone, demonstrate ductal morphology.

Sialogram of parotid gland in Sjogrens Syndrome

Applied aspects of saliva Saliva and friction Saliva and bonding Salivary clearance rate Experimental salivary pellicles and orthodontic materials Salivary ph and elastomers Saliva and corrosionConclusion References

APPLIED ASPECT OF SALIVA IN RELATION TO ORTHODONTICS :

I) FRICTION : It has been suggested that saliva or a saliva substitute services as an excellent lubricant in the sliding of the bracket along the wire. Here are a few studies relating friction and saliva:1) Frictional changes in force values caused by saliva substitution:Objective of the study was to determine the magnitude of frictional force changes between several sizes of stainless steel orthodontic arch wires i.e. 018, 020, 018 x 025 and edgewise 022 x 028 slot when an artificial saliva medium was introduced.

Yu-Jin Seo et al, European Journal of Orthodontics, 2015, 158163 doi:10.1093/ejo/cju027.

After tabulating results they concluded that :Xero lube, saliva substitute as a lubricant provided a 15% to 19% reduction in force value.They also concluded that saliva medium used has a viscosity of 14.0 centipoise at 370C. They conducted a similar research using glycerine which has viscosity of 325.0 centipose but results obtained did not match to that obtained with xerolube artificial saliva. 2) Frictional resistance of ceramic and stainless steel orthodontic brackets: a similar type of research and found that saliva substitutes increased static friction for all combination tested.

Baker KL,Nieberg LG,Weimer AD,,Hanna M. Am J Orthod Dentofacial Orthop. 2013, 133187.e15187.e24.

Saliva played an insignificant role in lubricating the surface of the wire or bracket slot. The explanation for discrepancy may lie in the significance of loading forces used between the arch wire and the brackets. At low load levels saliva acts as a lubricant, but at high loads saliva may increase friction if its forced out from the contacts between the brackets and the arch wire.

3)The effect of artificial saliva on the frictional forces between orthodontic brackets and archwires: Here the effect of artificial saliva on the static and kinetic frictional forces of stainless steel and polycrystalline ceramic brackets in combination with round end edgewise arch wire and stainless steel, nickel titanium and -titanium arch wire materials under a constant ligature force were investigated. In all the cases artificial saliva had the effect of increasing the frictional force when compared with the dry state. They concluded that artificial saliva played an insignificant role in lubricating the surface of the arch wire in the bracket slot.

The explanation they gave for this study was that arch wire touches the bracket at only 2 points where the pressure is relatively great.The lubricant could be expelled from the areas of contact allowing no lubrication between the arch wire and bracket to exist, hence increasing friction.Use of titanium arch wire produced smallest percentage increase in frictional forces due to; stick and slip phenomenon.

Downing A, McCabe JF, Gordon PH. Br J Orthod.2005 Feb;22(1):41-6

STICK-SLIP PHENOMENONThere are two coefficients of force : 1)static friction 2)kinetic frictionStick-slip can arise when the coefficient of static friction is markedly greater than the coefficient of kinetic friction.During stick phase, the friction force builds up to a certain value, and once a large enough force has been applied to overcome the static friction force, slip occurs at the interface.Usually, a saw tooth pattern in friction force-time curve Friction force as a function of time or distance showing stick-slip phenomenon

II) BONDING AND SALIVA:

A few studies are hereby mentioned to see the ever changing influence of saliva in bonding procedure with advent of new generation of bonding agents, primers. 1) Effect on a New Bonding agent in bond strength to saliva contaminated enamel: The purpose of the study in vitro was to compare bond strengths of brackets applied to contaminated and uncontaminated enamel following pretreatment of contaminated enamel with Scotch MP bonding system.

Sonis AL .J Clin Orthod.2014 Feb;28(2):03-4.

They concluded that bond strength were found to be equal in brackets bonded to saliva contaminated etched enamel treated with Scotch Bond MP primer and bonding agent applied to uncontaminated enamel. Scotch band MP works slightly differently. The primer composed of HEMA and polyalkeonic copolymer behaves similar to the liquid of glass ionomer in that it forms stronger bonds to a moistened enamel or dentin surface.

2) A technique to prevent surface contamination of etched enamel: It has been recommended that a thin layer of primer be applied to the entire etched enamel surface before bonding to seal the enamel, protect it from decay, provide maximal bond strength. If etched surface becomes contaminated by oral fluids before bonding the bond is likely to fail at resin enamel interface.

Greer KS,Lindauer SJ,Darling SG,Browning H,Moon PCJ Clin Orthod.2006 Mar;30(3):145-6

This is most likely to occur when bonding to surgically exposed palatally placed canines or to teeth with short clinical crowns. In such cases its more effective to apply the primer directly to the adhesive resin on the back of orthodontic attachment. Bond strength in this technique was considered best in cases where there is poor visibility or limited exposure.

3) SALIVARY CLEARANCE AND FIXED ORTHODONTIC APPLIANCES : Since fixed ortho appliances have numerous recesses, pits, which entraps the food particles, oral clearance rate is slowed. Here is a study to demonstrate the same. 1) Care- Magnus forsberg, olively A, Jagerlof F in 2012. The study was conducted for the purpose of establishing the possible influence of orthodontic therapy with fixed appliances on salivary clearance of sugar.

Aim to study 1) whether fixed orthodontic appliances increase the residual volume of saliva in mouth. 2) Salivary clearance of sugar. Unstimulated salivary flow rate, RESID, and salivary clearance of sugar was determined on two occasions i.e. before start of treatment and 21 days after fixed appliance was placed in the mouth. In the results, the salivary flow rate before the start of orthodontic treatment was

Care- Magnus forsberg, olively A, Jagerlof F. Am J Orthod Dentofacial Orthop. 2012.

0.46 ml/min, after a wear of appliance for 21 days mean value increased to .57 ml min. Orthodontic appliance had a similar effect on the residual volume of saliva in the mouth after swallowing. It is a well known fact that a foreign body put in the mouth will initially increase the flow of saliva. The present study indicates that fixed appliances does not prolong the salivary clearance of sugar during the first month of treatment.

Further studies with longer duration claimed to have decreased or normal levels of salivary flow and RESID. Since appliance consists of many retentive components that provide numerous recesses and minor pits where food particle may be trapped accounting for delayed clearance of sugars on long term treatment schedules Because of this factor caries and demineralization will continue to be matters of concern during orthodontic treatment.

2) The use of low tack chewing gums for individuals wearing orthodontic appliances A clinical study was carried out to determine the acceptability of a sugar free, low tack chewing gum by orthodontic patients. It was concluded that low tack sugar free chewing gums can be used by orthodontic patients to increase saliva flow with the potential to remineralise and help reduce white spot lesion formation. Gray A,Ferguson MM Aust Dent J.2006 Dec;41(6):373-6

EXPERIMENTAL SALIVARY PELLICLES ON THE SURFACE OF ORTHODONTIC MATERIALS: Conducted a study with a purpose to find out whether composition of salivary pellicles that form on surface of orthodontic materials vary qualitatively in respect to stainless steel, elastomeric ligature ring, bracket bonding resin.They concluded that least amount of salivary pellicle which was cariogenic was found on stainless resin, followed by adhesive resin, highest amount of cariogenic pellicle was found on elastomers.

Lee SJ,Kho HS,Lee SW,Yang WS. Am J Orthod Dentofacial Orthop.2011 Jan;119(1):59-66.

5) EFFECT OF SALIVARY PH ON ORTHODONTIC POLYURETHANE CHAIN ELASTICS:1) The effect of hydrogen ion concentration on forces degradation rate of orthodontic polyurethane chain elastics : The effect of pH on force degradation rates of seven commercial orthodontic polyurethane Chain elastics was evaluated in an in vitro study. The pH values of 4.85 to 7.26 were selected for testing because they represent values closes to the reported extremes of plaque and saliva pH.

FerriterJP,MeyersCE Jr,Lorton L. Am J Orthod Dentofacial Orthop.2009 Nov;198(5):404-10.

All specimens were equally stretched which delivered equal initial force levels. Force degradation rates were recorded after 4 weeks. They concluded that force decay rate of polyurethane orthodontic chain elastics is inversely proportional to the pH of oral environment with a corollary that pH levels above mentioned are more hostile to the polyurethane chain elastics thus increasing their force decay rates.

6) SALIVA AND CORROSION :Saliva acts as an electrolyte and hence aids in causing corrosion of metal components of fixed orthodontic appliances. When metal components of orthodontic appliances are in contact with an electrolyte such as saliva, metals corrode by a complex electrochemical process of oxidation and dissolution known as galvanic corrosion. The generation of an electric cell is simple when different metals are involved, but it can also occur within a single metal.

Atoms at the grain boundary dissolve faster than those within the grain . Impurities, rough surfaces or irregularities can also alter the corrosion resistance of a metal.Corrosion resistant metals are known as noble metals or cathodic metals. Types of corrosion :Uniform corrosion : metal is attacked evenly and throughout, and its mechanical property diminishes proportionately.This type is rarely seen in orthodontics since all the parts of the appliance are not evenly exposed to corrosion agents.

2)Localized or pitting corrosion : most common form seen in orthodontic attachments. Affects the mechanical property of the metal. This type is seen when several different metals are used. 3)Galvanic corrosion : the oral cavity because of saliva, with its salts provides a weak electrolyte. Galvanic corrosion is an important type of electrolyte corrosion which occurs when combination of dissimilar metals lie in direct physical contact with each other. 4)Stress corrosion : if a stressed metal comes in contact with unstressed metals, stressed metal will become the anode of the galvanic cells and will corrode.

Here is a study to indicate corrosion of orthodontic appliance:Nickel ion concentrations in the saliva of patients treated with self-ligating fixed appliances:The aim of the study was to determine salivary Ni2+concentrations in patients undergoing orthodontic treatment with self-ligating fixed appliances.A group of 30 patients between 10 and 13years of age were treated with self-ligating brackets (Smart Clip), molar bands, and nickeltitanium (NiTi) archwires.

Glz L,Knickenberg AC,Keilig L,Reimann S,Papageorgiou SN,Jger A,Bourauel C Nickel ion concentrations in the saliva of patients treated with self-ligating fixed appliances:J Orofac Orthop.2016 Feb 24.

Unstimulated saliva samples were collected after different time points (before treatment, after self-ligating bracket and band placement, before archwire insertion, after archwire insertion, and finally 4 and 8weeks afterwards) and analyzed with an ICP mass spectrometer. And the results stated that Self-ligating orthodontic appliances may affect salivary Ni2+concentrations in vivo over the short term. However, levels resembled those documented in conjunction with conventional bracket use and remained below the daily dietary Ni intake.

Nickel and chromium levels in the saliva and serum of patients with fixed orthodontic appliances:The aim of the study was to evaluate the concentrations of nickel and chromium ions in salivary and serum samples from patients treated with fixed orthodontic appliances. The second aim of the study was to determine any significant changes in these concentrations during any period of the treatment time. Saliva and blood samples were collected.

Aaolu G1,Arun T,Izgi B,Yarat A. Nickel andchromiumlevels in the saliva and serum of patients with fixed orthodontic appliances. Angle Orthod .2014 Oct;71(5):375-9.

The results indicate certain differences in the amount of nickel and chromium released from fixed orthodontic appliances during different periods of treatment. In saliva samples, nickel and chromium reached their highest levels in the first month and decreased to their initial level in the rest of the groups. It can be concluded that fixed orthodontic appliance releases measurable amount of nickel and chromium when placed in the mouth. Most metals used in oral cavity can be expected to undergo this type of corossion. Saliva has a dynamic composition that may be affected by many physiologic variables such as diet, salivary pH, health conditions and salivary flow rate.

7) SALIVA AND DEMINERALIZATION (CARIES) : The pH of saliva acts as a deciding factor, be it demineralization and induction of caries or remineralization. At pH value of 6.8 to 6.0 hydrogen ions reacts with phosphate ions in saliva and plaque. At pH value of 5.5 to 5.0 demineralization occurs wherein hydroxyapatite dissolves but flurapatite forms in the presence of fluoride. At pH of 4.5 to 3.5 (critical pH) both fluropatite and hydroxyapatite dissolves. On the contrary if pH rises to 5.5 from the critical pH and if H+ ion are not exhausted remineralization occurs and fluorapatite forms.

DEMINERALIZATION - REMINERALIZATION CYCLE Critical PH

HA-HYDROXYAPATITE FA- FLOURAPATITE 6.8 to 6.0 5.5 to 5.0 4.5 to 4.0 to 3.5Hydrogen ions reacts with phosphate ions in saliva and plaque Demineralization: HA dissolves, FA forms in presence of fluoride FA and HA dissolve Remineralization FA reforms If H+ ions exhausted or neutralized and all ions retained. 6.8 to 6.0 5.5 to 5.0 4.5 to 4.0 to 3.5

CONCLUSION: With the innumerous number of functions of salivary glands and its secretion namely saliva that we have come across, we can arguably call this secretion namely saliva the champion among the factors that are involved in homeostasis of our body. Since dentistry is basically a material science thorough knowledge is important for us to come out with new innovations so that products we use render maximal service to the patient.

REFERENCES:William G. Shafer., Maynard K. Hine, Barnet M. Levy. A Text Book of Oral Pathology. 4th edition, W.B. Saunders Company. Stuart C. White, Michael J. Paroah. Oral Radiology Principles and Interpretation. 5th Edition. Mosby Yu-Jin Seo et al, European Journal of Orthodontics, 2015, 158163 doi:10.1093/ejo/cju027. Lee SJ,Kho HS,Lee SW,Yang WS. Experimentalsalivarypellicleson the surface of orthodontic materials. Am J Orthod Dentofacial Orthop.2011 Jan;119(1):59-66. Aaolu G1,Arun T,Izgi B,Yarat A. Nickel andchromiumlevels in the saliva and serum of patients with fixed orthodontic appliances.Angle Orthod .2014 Oct;71(5):375-9.

FerriterJP,MeyersCE Jr,Lorton L. Am J Orthod Dentofacial Orthop.2009 Nov;98(5):404-10. Care- Magnus forsberg, olively A, Jagerlof F. Am J Orthod Dentofacial Orthop. 2012. Greer KS,Lindauer SJ,Darling SG,Browning H,Moon PCJ Clin Orthod.2006 Mar;30(3):145-6 Sonis AL .J Clin Orthod.2014 Feb;28(2):03-4. Downing A,McCabe JF,Gordon PH. Br J Orthod.2005 Feb;22(1):41-6Baker KL,Nieberg LG,Weimer AD,,Hanna M. Am J Orthod Dentofacial Orthop. 2013 Apr;91(4):316-20. 13) Gray A,Ferguson MM Aust Dent J.2006 Dec;41(6):373-6