SALIVARY GLANDS AND SALIVA INTRODUCTION : Saliva is a most valuable oral fluid that often is taken for granted. It is critical in the preservation and maintenance of oral health. Saliva has also become useful as a noninvasive systemic sampling measure for medical diagnosis and research. Consequently, it is necessary for clinicians to have a good knowledge base, concerning the norm of salivary flow and function.
SALIVARY GLANDS DEVELOPMENT OF SALIVARY GLANDS The 3 major sets of salivary glands-the parotid, the submandibular and the sublingual-originate in a uniform manner by oral ectodermal epithelial buds invading the underlying mesenchyme. The parotid glands are the first to appear at the 6 th week of intrauterine life and the inner cheek near the angles of the mouth and grow back towards the ear. In the para-otid, or ear region, the epithelial cord of cell branches and canalize 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 become encapsulated. The submandibular salivary gland buds also appear in the 6 th week as a grouped series forming epithelial 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 ducts of the submandibular gland. The mesenchymal stroma separates off the paranchymal lobules and provides the capsule of the gland.
The sublingual glands arise in the 8 th week of intrauterine, as a series of about ten epithelial buds just lateral to the submandibular 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.
SALIVARY GLANDS - GROSS MORPHOLOGY PAROTID GLANDS Parotid glands provide 60-65% of total salivary volume. Each parotid gland is pyramidal in shape. The base of the pyramid being rhomboidal and lying immediately beneath the skin. Each gland weighs 25g. A dense fibrous capsule separates the gland from other structures. The superficial surface of the parotid gland (The base of the pyramid) is defined by the zygomatic arch, the external antitory meatus, and just behind and below the angle of the mandible. The gland extends into the groove between the mandibular ramus and sternocleidomastoid muscle to reach the styloid process and associated muscles which separate the gland from the internal carotid artery and jugular vein. The external carotid artery enters the glands and divides into its terminal branches. The facial nerve also passes through the gland, dividing close to the anterior border. The main parotid duct (Stensen’s duct) leaves the mesial angle of the gland to traverse over the masseter muscle and turn abruptly to enter the buccinator muscle prior to opening into the oral cavity in a small papilla close to the buccal surface of the maxillary first molar tooth.
SUBMANDIBULAR GLAND : The submandibular gland produces about 20-30% of the total salivary volume. The glands are irregular, walnut in shape, with the superficial inferior portion in contact with the skin and platysma muscle. Laterally, the gland is in contact with the mandibular body and medially with the extrinsic tongue and mylohyoid muscles. There may be a small, deeper portion of the gland between the mylohyoid, hyoglossus and styloglossus, muscles. This part of the gland extends forwards and inwards above the posterior edge of the sublingual gland. After leaving the superficial part of the gland, the duct (Wharton’s duct) passes beneath the deep part, between the mylohyoid and hyoglossus muscles and between the sublingual gland and genioglossus muscle to end at the summit of the sublingual papilla at the side of the lingual frenulum. The tortuous duct is approximately 5 cm long. SUBLINGUAL GLAND : The sublingual glands are the smallest of the major salivary glands; the produce 2-5% of the total salivary volume. Each is of the size and shape of an almond and weighs 3-4 gms. The glands lie immediately beneath the oral mucosal lining of the mouth floor, raising a small fold on either side of the tongue. The glands rest on the mylohyoid muscle, with the mandible lateral and genioglossus muscle medial. This gland has a series of small ducts (Bartholins ducts) that open on the surface of the sublingual folds on either side of the tongue.
MINOR GLANDS (Accessory glands) Anterior Lingual Glands These two irregular glandular groups lie on either side of the frenulum on the under-surface of the tongue, with several ducts piercing the overlying mucosa. Serons glands of von Ebner These are small glands whose ducts open into the sulci of the circumvallate papillae. Lingual, buccal, labial and palatal glands : Small glands with short ducts, producing a secretion rich in mucoproteins are found scattered over the surface of the tongue, the inside of the lips and cheeks, and in the mucosa covering the hard and the soft palate. Blood supply : The blood supply to the parotid is derived from the facial and external carotid arteries, with a richer vascular supply to the ductal than the acinar system. In fact the blood flow is parallel, but in opposite direction to the salivary flow. The facial and lingual arteries supply the submandibular gland, whereas the submental and sublingual arteries supply the sublingual gland. Venous drainage of all the glands is mainly through the external jungular vein. Nerve supply : The parasympathetic nerve-supply, carrying the secretomotor fibers to the parolid gland travels in a branch of the glossopharyngeal nerve to which synapses in the otic ganglion and passes from three with the auriculotemporal nerve to the gland.
Both the submandibular and sublingual glands are served by parasympathetic secretomotor fibers originating in the facial nerve, lining in the middle ear and passing as the chordaympani to join the lingual nerve. These fibers synapse in the submandibular ganglion and the postganglionic fibers pass to the glands. Symathetic fibers pass from the superior cervical ganglion with the blood vessels to all the glands.
SALIVARY GLANDS – MICROSTRUCTURE The structure of the salivary glands is similar to other exocrine glands, comprising a series of secretory units (acinar cells) clustered around a central lumen. These acini comprise the terminal or secretory end-piece of the gland, situated fasthest from the oral cavity. They are supported by the myoepithelial cells and a basement membrane. From each acinus the secretions pass to a series of interconnected ducts before passing out through the major salivary duct into the oral cavity. Each acinus consists comprises a series of polygonal cells on a basement membrane central around a central ductal lumen. The acinar cells are classified histologically into two types – serous cells and mucous cells according to their appearance after staining with eosin and heamatoxylin i.e this in a histochemical term rather than a functional description.
Serous Cells They stain blue these cells make up most of the acini of the parotid gland and of von ebner. They are large and polygonal in shape. They are characterized by a nucleus lying towards the basement membrane. The cells contain extensive endoplasmic reticulum and many mitochondria in the luminal portion of the cells are granules and vacuoles which fill up during resting periods but discharge by exocytosis on stimulation some of these can be shown to contain amylase.
The cells produce a secretion much less viscous or more serous than the secretion of the other glands. Hence the term serous cells.
Mucous cells Predominantly pink – staining cells. Since their staining properties resemble those of other cells elsewhere which produce mucoid substances, and since the secretions of these cells are viscous and rich in protein – carbohydrate complex, they have been referred to as mucous cells. The acinar cells of the submandibular and sublingual glands are said to comprise mucous cells. The general form and appearance of mucous cells is not dissimilar to that of serous cells. Mucous cells show more areas of smooth parallel cisternae and have larger secretory vacuoles.
DUCTS Intercalated duct cells The secretions pass from the acinus to a short intercalated duct: the duct cells tend to by cuboidal, they have large central nucleus and many mitochondria and little endoplasmic reticulum. The duct lining cells are closely interdigitated. The contain zymogen granules, which may contribute to stable changes in salivary composition.
Striated duct cells The intercalated duct then pass abrupt into another short but wide, striated duct, the striated duct are lined by cells which are much more columnar than the cells of the intercalated duct. The cells have marked cellular membrane interdigitations projecting towards the lumen. the striated ducts actively resorb sodium ions from the primary acinar secretion, with the associated capillaries then transporting the ions away from the glands into systemic circulation.
These striated ducts then pass abruptly into two epithelial cell layered excretory ducts and finally to the stratified squamous epithelial cell lined terminal duct. Although these latter excretory ducts resorb electrolytes from the primary secretion, they are probably less efficient than the stratified duct lining cells. Myoepithelial cells These cells constrict the acini and ducts to falicitate salivary secretory flow. In myoepithelial cells the nucleus lies in a broader part of the cell and is surrounded by mitochondria and strands of endoplasmic reticulum. The remainder of the cells consists of longitudinally arranged myofibrils.
MECHANISM OF SALIVARY SECRETION Stimulation of secretomotor nerves results in the release of neurotransmitter substances i.e., acetylcoline from the parasympathetic nerves
and
noradrenalinc
from
the
sympathetic
nerves.
These
neurotransmitters act on membrane receptor sites on the acinar cells to stimulate secretion. Formation of the acinar fluid The acinar fluid consists of water, ions, small molecules, synthesized by the cells. This fluid arises from the interstitial fluid, which in turn arises from the blood in the capillaries. The capillaries behave in a similar manner as capillaries else were : hydrostatic pressure causes an outflow of water, and small ions and molecules diffuse from the plasma. The acinar cells behave as if freely permeable to lipid-soluble substances and water, but much less permeable to other molecules. Entry of glucose and amino–acids probably occurs by active transport, their concentration in acinar fluid is low.
The ions of the acinar fluid are broadly similar to those of interstitial fluid. Sodium and chloride concentration are similar to those of plasma and it is probably that active transport of these two ions at the luminal membrane is the major factor producing an osmotic forces to speed water movement through the acinar cells. Potassium is lost from the acinar cells to the acinar fluid on stimulation and high acinar potassium level may arise from a cell membrane permeability when exposed to acetyle coline. Synthesis of salivary proteins occurs at the ribosomes and the proteins pass into the cisternae of the endoplasmic reticulum ; to be secreted from the cell surface by exocytosis. MODIFICATIONS OF THE ACINAR FLUID Modification in the intercalated duct : Physiological evidence from the animal studies suggests that the intercalated ducts are also involved in the initial secretion which is added to the acinar fluid ; through histologically they do not resemble cells normally considered to show secretory activity. It is possible that the loss of potassium from the gland which occurs on stimulation may take place here as well as in the acinar cells. Modification in the striated duct : The duct system, from the beginning of the striated ducts, plays an active part in the modification of saliva, in this area, the acinar fluid is transformed from an isotonic, or slightly, hypertonic fluid, with ionic concentration similar to plasma, to a hypotonic fluid, with low sodium and chloride concentration. The sodium pump mechanism of the membrane operate in a polarized fashion, since the massive infolding of the baeal wall of the cells increases the pump capacity in the side. As a result, sodium is actively transported across the cell and the concentration gradiant in thus
enhanced between the cells and the luminal fluid, resulting in diffusion of sodium into the cells from the lumen. The active transport of sodium is linked with active transport of potassium in the opposite direction and also with passive diffusion of chloride to maintain the electrochemical balance. Bicarbonate is actively secreted to the lumen in this part of the gland. The cells behave as if largely impermeable to water, so that although salts are conserved in the area, water is not resorbed and a hypotonic secretion results. Stimulation either of sympathetic or parasympathetic nerves causes activation of the duct cells. The resting transmembrane potential of the cells of the striated ducts is around – 80 mv with the inside of the cell negative. On stimulation of the glands, the transmembrane potential on the luminal side of the cells becomes much less negative (around – 20 mv). Modification in the distal excretory ducts : In the distal part of the excretory ducts partial re-equilibration of saliva with plasma occurs and concentration of ions return from extreme values to more plasma like concentrations.
SALIVARY CONTROL The secretion of saliva is controlled by a salivary center composed of nuclei in the medulla but there are specific triggers for this secretion.
Afferent pathways (stimuli) The triggers or stimuli for secretion are
Local factors The act of chewing, the sensation of taste, the irritation of the mucous membrane of the mouth all these act as sensory stimuli which reflexly
produce salivation. The fibers carrying sensations of taste and touch are carried in the same nerves carrying the secretomotor fibers – i.e., the chorda tympani fibers in the lingual nerve (which originate in the facial nerve) from the anterior 2/3rd of the tounge and glossophargneal nerve from the poterior 1/3 and the tounge. The sensation of small and sight from the nose and eyes are carried by the 1st and 2nd cramial nerves respectively.
Psychic stimuli The sight of food, talking about or the noise of food preparation are sufficient to activate the conditioned reflexes for salivary secretion. This indicates
that
salivation
can
be
influenced
by
higher
centers,
ex: hypothalamus.
Stimulation from other organs Esophageal irritation causes reflex salivation, although gastric irritation leads to increased salivation as a component of the nausea / vomiting reflex.
Central control The afferent stimuli reach the brain and spinal cord and are finally integrated in the cell bodies of the preganglionic secretomotor neurons. Where efferent secretomotor impulses are generated. The cell bodies of the parasympathetic neurons are in the nuclei of the facial and the glossophsyngeal nerves. The area which gives salivary response on stimulation is termed. ‘nucleus salivatorius’. The nucleus salivatorius has been divided into two components. Superior salivary nucleus : stimulations of which causes secretion of submandibular and sublingual glands.
Inferior salivary nucleus : stimulation causes secretion of parotid glands. The cell bodies of the sympathetic nervous system lie in the lateral columns of the first fine thoracic nerves. The secretomotor cell-bodies, in addition receive inputs, both excitatory and inhibitory, from other parts of the brain. Hypothalamic activity is also associated with salivary responses.
THE EFFERENT PATHWAY The flow of saliva is controlled entirely by nervous stimuli. Control in exerted mainly by parasympathetic, but also by sympathetic stimuli. The parasympathetic fibers to the submandibular and sublingual glands arise from the superior salivary nucleus in the medulla as nervous intermedins and by – passing the geniculate ganglion descend downwards through the facial (VII cranial) nerve. The chorda tympani nerve descends downwards and reaching the cavity of the mouth meets the lingual nerve. Then the secretory fibers leave the lingual nerve and end in the submandibualar ganglion. From the submandibular ganglion of the post ganglionic fibers arise and reach the submandibular and sublingual glands and supply them with secretory and dialotory fibers. The parasympathetic fibers to the parotid gland arise from the inferior salivary nucleus (dorsal nucleus of the IX nerve) in the medulla and descend downwards through the glossophargneal (IX) nerve and being separated as the tympanic branch pass through the tympanic plexus and then through the lesser superior petrosal nerve end ultimately in the otic ganglion. From this the post ganglionic fibers arise and reach the parotid gland through the auriculotemporal branch of the trigemenal (V nerve) nerve to supply it with secretory and dilator fibers.
The sympathetic fibers to all these glands synapse in the superior cervical ganglion. The postganglionic fibers arising from this ganglion pass along the walls of the arteries and supply all the salivary glands. The sympathetic fibers are believed to end in the serous gland or the serous part of the mixed gland and supply vasoconstrictor fibers to the vessels of the glands and myoepitheilial cells of the ducts.
SALIVA Saliva is a wonderful, marvelously equipped fluid to protect and preserve the oral tissues. According to stedmans medical dictionary 26th edition. Saliva is clean, tasteless, odourless slightly acidic vicious fluid, consisting of secretions from the parotid, sublingual, submandibular salivary glands and the mucous glands of the oral cavity. COMPOSITION OF SALIVA Human saliva : Total amount : 1,200 – 1500 ml in 24 hrs. a large proportion of this volume is secreated at meal time. When the secretory rate is highest. Consistency : slightly cloudy, due to presence of cells and mucin. Reaction : usually slightly acidic (ph 6.02 – 7.05) Specific gravity : 1.002 – 1.02 Feezing point : 0.07 – 0.340c.
COMPOSITION OF SALIVA Saliva consists of 99.5% water and 0.5% of solids
SALIVA Water (99.5%)
Organic (0.3%)
Solids (0.5%)
Inorganic (0.3%)
Îł-globulin Ptyalin
Cations
Mucin
Na+ K+ Ca++ Mg++ Fluoride
Kallikrein Bradykymin Lysosome
Anions ClHCO3PO4Thiocynate
Immunoglobulin IgG Blood group antigen Nerve growth factor Vit C and vit K. Urea and uric acid. Cellular components These component interact in related function in the following general areas. 1) Biocarbonates, phosphates and urea act to modulate Ph and buffering capacity of saliva. 2) Macromolecule proteins, mucins, severe to cleanse aggregate attach oral microorganisms and contribute to dental plaque matabolism. 3) Calcium, phosphate and proteins act together as an antisolubility factor and modulate demineralization and remineralization. 4) Immunoglobulins, proteins, and enzymes provide antibacterial action.
Saliva is not considered as an ultrafiltrate of plasma initially saliva is isotontic as it is formed in the acin, but it becomes hypotomic as it travels through the duct network. The hypotonicity of the unstimulated saliva allows the taste buds to perceive different tastes. Hypotonicity, especially during low flow periods, also allows for expansion and hydration of mucin glycoproteins, which protectively blanket the tissues of the mouth. Factors Affecting The Concentration Of Salivary Constituents Flow rate in salivary glands on individual constituents - Substances whose concentration increase with flow rate increases : Total protein, amylase, Na, HCO3 - Substances whose concentration decreases with the increase in flow rate : Phosphate; Urea, aminoacids, uric acid, serum albumin. - Substances whose concentration Does not change with change in flow rate : Potassium (K), Fluoride - Substances whose concentration decreases at first but increases as flow rate increases : Cl-, Ca++, Protein-bound carbohydrates. Factor affecting flow rate Diurnal variation : Salivary flow rates exhibit diurnal variation. Protein concentrations tend to be high in the afternoon. Na+, Cl- concentrations tend to be high in the early hours K+ - tend to be high in the afternoons Ca++ - tend to be high in the night Nature of stimulus : The stimulus may vary in its affect of different glands. Variations in composition of whole saliva may arise from differing proportion of the major secretions.
Dietary factors : Functional salivary glandular activity is influenced by mechanical and gustatory factors eg: copious salivary flow results from the smell of food or new denture insertion. Insufficient salivary flow results in 2 general oral-related effects : 1) Reduced preparation of food for digestion and taste 2) Increased susceptibility of oral structures to diseases. This may be the result of salivary gland hypofunction. Hypofunction of stimulated salivary flow is not a normal age related change. A working knowledge of normal salivary flow is necessary for the clinician, discussing patient home care instructions. - Low flow during sleep, mandates the need to carefully cleanse the mouth before going to bed and after breakfast. - The use of sugarless chewing gum or candy containing Xylitol or sorbitol can be recommended as a mean of stimulating extra salivary flow to aid caries management and lubrication. - Acidic and sweet taste stimuli are better choices as triggers for desired extra flow. - The successful use of removable prostheses by a patient may be affected dramatically by decreased salivary flow.
FUNCTIONS OF SALIVA : Salivary functions can be organized into 5 major categories that serve to maintain oral health and create an appropriate ecological balance. 1) Lubrication and protection. 2) Buffering action and clearance. 3) Maintenance of tooth integrity. 4) Antibacterial activity. 5) Taste and digestion. The
salivary components
work in concert
in overlapping,
multifunctioning roles, which can be simultaneously beneficial and detrimental. 1) Lubrication and protection : As a seromucous coating, saliva lubricates and protects the oral tissues, acting as a barrier against irritants. These irritants include proteolytic and hydrolytic enzymes. Produced in plaque, potential carcinogens from smoking and exogenous chemicals. The best lubricating components of saliva are mucins that are secreted from minor salivary glands. These mucins have the properties of low solubility, high viscosity, high elasticity and strong adhesiveness. Any intraoral contact between soft tissues, between soft tissues and teeth and between soft tissues and prosthesis benefit from the lubricating capability of saliva supplied largely by these mucins. Mastication speech, and swallowing all are aided by the lubricating effects of mucins. Mucins also perform an antibacterial function by selectively modulating the adhesion of micro organisms to oral tissue surfaces, which contributes to the control of bacterial and fungal colonization. Secretions from the submandibular and sublingual glands contain high-molecular weight mucin (MG1) and a low molecular weight mucin (MG2). The importance of these two major mucins has been the focus of
research for the last two decades. MG1 absorbs tightly to the tooth and thereby contributes to the enamel pellicle which protects the tooth from acid challenges. MG2 binds to the enamel but in easily displaced. It promotes the aggregation and clearance of oral bacteria, including streptococci mutans. An important part of the multifunctional role of salivary mucins is preserving mucosal integrity is their ability to regulate intercellular calcium levels. As a part of the enamel pellicle, mucins help initiate bacterial colonization by promoting the growth of benign commensal oral flora, forming, a protective barrier and lubrication against excessive wear, providing a diffusion barrier against acid penetration and limiting mineral aggress from the tooth surface. The results of research clearly indicate that salivary mucins performs a variety of function essential to maintaining a stable oral defense. 2) Buffering action and clearance : Buffering action and clearance are a second function of salvia through the following components : Bicarbonates, phosphate, urea, and amphoteric proteins, and enzymes, bicarbonate is the most important buffering system. It diffuses into plaque and acts as a buffer by neutralizing acids. Moreover, it generates ammonia to form amines, which also serve as a buffer by neutralizing acids; low molecular weight histidine-rich peptides. Present in saliva also act as a buffer. Urea, another buffer releases ammonia after being metabolizaed by plaque and thus increases plaque PH. Buffering action of saliva is more effective during stimulated high flow rates. Phosphate is likely to be important as a buffer only during unstimulated flow. Thus salivary buffering, clearance, and flow rate work in concert to influence intraoral pH. Salivary flow can be augumented by the stimulus of chewing as well as the muscular activity of the tips and tongue. With stimulated additional
flow, chewing products (such as gum) that contain no fermentable carbohydrates can aid in the modulation of plaque PH. Sugar free gums containing xylitol and sorbitol can be recommended. Indeed research has shown that the use of gum containing xylitol or sorbitol reduces plaque accumulation and gingival inflammation and enhances remineralization potential. 3) Maintenance of tooth integrity : Maintenance of tooth integrity is a third function of saliva, one that facilitates the demineralization and remineralization process. Demineralization occurs when acids diffuse through plaque and the pellicle into the liquid phase of enamel between enamel crystal. Resulting dissolution occurs at a PH of 5 to 5.5, which is the critical PH range for the development of caries. The buffering capacity of the saliva influences the PH of plaque surrounding the enamel, thereby inhibiting caries progression. Remineralization is the process of replacing lost minerals through the organic matrix of the enamel to the crystals. The high salivary concentrations of Ca++ and PO4, may account for the maturation and remineralization of the enamel. Proteins in the pellicle, such as statherin, histamines, and proline rich proteins, aid in controlling crystalline growth of enamel by allowing the penetration of minerals, into the enamel for remineralization and limiting mineral egress. Fluoride in the salivary solution works to inhibit dissolution of apatite crystals. Fluoride speeds up crystal precipitation, forming a fluorapatite-like coating more resistant to caries than the original tooth structure. The
contribution
of
saliva
to
the
demineralization
and
remineralization process points to the importance of monitoring salivary
flow especially in patients taking multiple medications or having systemic entities that decrease salivary flow. For patients with incipient caries fluoride supplements can promote remineralization. Salivary stimulants and substitutes also should be encouraged for patients with salivary hypofunction. Researchers are currently investigating a method to genetically engineer salivary proteins and other salivary components for use in future artificial salivas. 4) Antibacterial activity : A fourth function of saliva in antibacterial activity. Salivary glands are exocrine glands, and as such, secrete fluid containing immunologic and non-immunologic agents for the protection of teeth and mucous surfaces. Immunologic contents of saliva include secretory IgA, IgG and IgM. Non immunologic salivary contents are selected proteins, mucins, peptides and enzymes. (lactoferin, lysosome and peroxidase). MG2 and IgA complex bind mucosal pathogens with great affinity. - Lactoferin, binds to ferric iron in saliva, this process makes ferric iron unavailable as a food source for microbes, such as cariogenic streptococci, that need iron to remain viable. - Lysosomes, split bacterial walls, leading to destruction and inhibition of bacterial growth. - Peroxidase, catalyses bacterial metabolic by-products with thiocynate, which is highly toxic to bacterial systems, peroxidase also protects the mucosa from the strong oxidization effects of hydrogen peroxide produced by oral bacteria.
- Cystatins, have a major role in regulation of salivary calcium. Finally, proteins such as glycoproteins, statherins, agglutinins, histadine-rich protein, proline-rich proteins work to aggregate bacteria, the clumping, inhibits adhereane and colonization on to the hard or soft tissue intraoral surfaces. The concept of saliva’s antibacterial activity highlights the clinical value of stimulating natural saliva especially in patients with decreased function. 5) Taste and Digestion : The fifth and final function of saliva is to enhance taste and begin the digestive process. The hypotonicity of the saliva enhances the tasting capacity of salty foods and nutrient sources. Saliva has an early, limited role in total digestion by beginning the breakdown of starch with amylase, a major component of parotid saliva salivary enzymes also initiate fat digestion. More importantly saliva serves lubricate the food bolus, which aids in swallowing. When one considers the contribution of saliva to taste and early digestion, it becomes clear that artificial supplements would be difficult to develop. ARTIFICIAL SALIVA : From the proceeding section it is clear that an adequate amount of salivary flow is essential in the host’s resistance to dental caries and also to vital importance in the comfortable and successful mastication and swallowing of food. It plays a vital role in the comfort of denture wearers. When salivary flow is reduced, salivary stimulants or artificial salivary substitutes have been proposed. Salivary stimulants are most
satisfactory in the form of pastille, which require chewing, as chewing also acts a stimulant. The active ingradient is acidic in nature as this is well known to provoke salivation. For diabetic patients pastilles containing sorbitol rather than sugar are advised. No artificial saliva that is fully satisfactory has yet been formulated. Both carboxymethyl cellulose and hydroxyethyl cellulose in aqueous solutions are in common use and are used as mouthwash as frequently as required. Neither of these materials have the viso-elastic properties of natural saliva and both require frequent use to maintain a moist oral environment. A possible alternative is high molecular weight polyethylene oxide. Although 2% aqueous solutions has similar viscoelastic properties of natural saliva, this sticky, stringing and viscous liquid is difficult to handle. Many artificial saliva solutions contain acid, for dental patients as the acidic content (usually citric acid) may cause erosion of teeth, acid-free artificial saliva is advised. “Glandosane� a commercial mouth lubricant with a PH of approximately 5.4 which contain carboxymethyl cellulose together with calcium and phosphate ions in a promising product. Saliva orthane which has a pH of 7 and is now available containing sodium fluorides (NaF) instead of methyl cellulose it contains mucin extracted from the gastric mucosa of pig to provide appropriate viscosity.
Artificial saliva can be classified 1) Depending on treatment approach • Extrinsic – topically applied artificial saliva • Intrinsic – Chemical / drug which stimulates salivary gland. Extrinsic is divided into two groups depending upon the presence or absence of natural mucin. • Synthetic • Animal. 2) According to research development. 1) 1st generation 2) 2nd generation 3) Disease oriented 4) Function oriented 5) Contains design. Disadvantages : - Poor taste - Lack of wettability - Cannot be selectively targeted to different parts of the oral cavity. - Expensive
ROLE OF SALIVA IN PROSTHODONTICS From a prosthodontist point on view, salivary glands are of great importance anatomically and physiologically. The submandibular gland is located in the submandibular fossa on the lingual aspect of the mandible, and a part of the gland is wrapped around the posterior part of the mylohyoid muscle, it is from this position wartons ducts curves forward and open at a papilla in anterior floor of mouth lateral to midline. Extension of the lingual flange of a denture in this region, in such cases patient may complain of developing swellings under the jaws when eating. The orifice of the stensons duct opens on the mucosal fold that is located in the cheek at the level of the crown of the 1 st molar, occasionally a complete denture may obstruct the orifice, however the occurrence is rare. Dentist should examine the duct and orifices to ensure they are open and good salivary flow is evident. Consistency and Amount of saliva : The amount and consistency of saliva will affect the denture construction process and the quality of the final product itself. Consistency of saliva : The consistency of salvia ranges from thin serous type to the thick mucous ropy consistency. It is best to work with the serous type, and fortunately this is more commonly found. The thick, ropy saliva may create a problem for maxillary complete denture rentention. Thick saliva can create hydrostatic pressure in
the area anterior to the posterior palatal seal, resulting in a downward dislodging force exerted upon the denture base. In an effort to alleviate this potential problem, a fine line or cupid’s bow can be scribed on the mastee cast, anterior to the cluster of palatal mucous glands. This extension of the posterior palatal seal line will contain the thick mucous in the posterior part of the denture to provide a seal even if the posterior portion of the denture base is slightly out of contact with the palatal tissues. Amount of salvia : Excess amount of saliva complicates denture conduction especially impression making. During impression making of the maxillary arch. Palatal glands secretion may distort the impression material in the posterior 2/3 of the palate to counteract this 1) Palatal may be massaged to encourage the glands to empty. 2) Mouth may be irrigated with astringent mouthwash just prior to inserting the impression material 3) The palate may be wiped with gauge. Excessive salivation, particularly of submandibular and sublingual glands may present a problem in impression making. Saliva inhibiting drugs like methanthaline bromide and Atropine may be administered.
These drugs are contraindicated in patients with Cardiac disease Prostate hypertrophy Glucoma Saliva should be controlled by mechanical means in these patients by using saliva ejector and cotton swabs. Dry mouth (Xerostomia) It will affect the retention of the denture and increases the potential for soreness in the mouth due to frictional trauma. . Contarary to popular belief, recent studies have shown that salivary flow does not diminish with age. However because of high incidence of elderly patients taking medications, that have an effect on salivary flow, dry mouth (Xerostomia) is not uncommon in the aged. Some of the medications causing xerostomia are. •
Antihistamines
•
Atropine
•
Antihypertensives
•
Nitroglycerine
•
Anti-anxiety drugs.
•
Anti-depressants
Difficulty in denture wearing is often the first sign of Sjogrem syndrome. Although this condition is rare, the dentist must always consider it in an elderly patient with xerostomia. Management of xerostomia depends on the cause of its condition. If a drug is suspected, alternate drug therapy must be discussed with the patients physician if possible. Sialogouges (like pilocarpine) and salivary substituted may be (against stimulating salivary flow) recommended. Petroleum jelly may be applied to the dentures to reduce friction Some of the pathological conditions that decreases salivation are : 1) Senile atrophy of the salivary glands. 2) Irradiation therapy of head and neck tumours 3) Disease of the brain stem that directly depress the salivary nuclei and block salivation. 4) Some types of encephalitis, including poliomyelitis. 5) Diabetes mellitus / Diabetes insipidus. 6) Diarrhea caused by bacteria or frod. 7) Elevated temp caused by acute infectious diseases. 8) Vitamin A deficiency. Pathological conditions that may be accompanied by increased salivation are :
1) Digestive tract irritants 2) Painful afflictions of the oral cavity. RESEARCH APPLICATIONS : Many areas of research involving salivary components and functions are in progress for local and systemic disease diagnosis, treatment and prevention. The value of saliva undoubtedly will continue to increase because it serves as a easily collected, non invasive. Source of information reflective of the status of health in the body, salivary samples can be analysed for 1) Tissue fluid level of naturally, therapeutically, and recreationally introduced substances. 2) Emotional status 3) Hormonal status 4) Immunologic status. 5) Neurologic status 6) Nutritional / metabolic influences. Saliva already is used to aid in the diagnosis of dental disease. Examples include - Caries risk assessment - Identification markers for periodontal disease. - Salivary gland disease and dysfunction. - Candida infections. Salivary collections are used for diagnostic determinants for viral diseases, sarcoidosis, tuberculosis, lymphoma, gastric ulcers and cancers, liver dysfunction and sjogrens syndrome.
Saliva is also being used to monitor levels of polypeptides, steroids, antibodies, alcohol and various other drugs. Research currently is being conducted to determine the value of saliva as a diagnostic aid for cancer and preterm labor. Another area of research involves the possible regenerative properties and functions of growth factors found in saliva. Evidence suggests that these growth factors play a role in wound healing and maintenance of oral and systemic health. The multifunctional roles of salivary components continue to represent a very focused area of dental research. Can the reductant and synergistic effects of the salivary proteins be used to further enhance remineralization ? Could the salivary antibacterial factors be targeted to positively alter the biofilm community in plaque ? Can salivary constituents more selectively control bacterial adherence and aggregation ? Can the buffering system of saliva effectively and selectively be enhanced ? Can salivary components be reproduced or replaced by new development in artificial saliva ? Questions such as these are being addressed through continuing research efforts.
CONCLUSION The knowledge of normal salivary composition, flow and function is extremely important on a daily basis when treating the patients. Recognition should be given to saliva for the many contribution it makes to the preservation and maintenance of oral and systemic health.
REFERENCES : 1) Human Physiology 11th edition : C.C. Chattergee 2) Applied
Physiology
of
the
mouth
3 rd
edition
Christopher L.B. Lavelle 3) Applied Oral Physiology 2nd edition : Christopher L.B. Lavelle 4) Physiology for dental study : D.B. Fergurson 5) Review of Medical Physiology 13th edition : William Gwanong 6) Human Anatomy 10th edition : D.B. Chaurasia 7) JPD 2001 : Vol. 85 ; 162 - 169
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SALIVARY GLANDS AND SALIVA INTRODUCTION SALIVARY GLANDS • Development • Gross Morphology • Blood supply • Microscopic structure • Mechanism of salivary secretion - Formation of acinar fluid - Modification of acinar fluid •
Salivary control
SALIVA • Definition • Composition of Saliva • Factors affecting Salivary flow • Function of saliva • Role of saliva in prosthodontics • Research application CONCLUSION REFERENCES
COLLEGE OF DENTAL SCINECES DEPARTMENT OF PROSTHODONTICS INCLUDING CROWN & BRIDGE AND IMPLANTOLOGY
SEMINAR ON
SALIVARY GLANDS AND SALIVA PRESENTED BY : DR. SUNEEL G. PATIL