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SALIVA IMPLICATIONS IN PROSTHODONTICS

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1 SALIVA IMPLICATIONS IN PROSTHODONTICS

2 1.Introduction 2.Source composition & Properties. 3.Functions.
4.Anatomy & Histology of Salivary Glands. 5.Control of salivation. 6.Salivary flow rate. 7.Salivary flow and ageing. 8.Mastication, Oesophageal Function & Saliva 9.Xerostomia and its management. 10.Sialorrhea. 11.Prosthodontic considerations. 12.Saliva as a diagnostic tool. 13.Conclusion. 14.Bibliography.

3 INTRODUCTION Saliva is largely an unheralded ,unsung and ignored secretion. Is saliva important? There”s an old axiom which states “you never miss the water till the well runs dry”. How true this is, especially for saliva. The fact is, a world without saliva is a world without pleasure….like living with a drought….. Saliva is most valuable oral fluid that is often taken for granted. It is critical for the preservation and maintenance of oral health, yet it receives little attention until quality or quantity is diminished. Consequently it is necessary for clinicians to have a good knowledge base concerning the norm of salivary flow and function

4 SOURCE Saliva is a clear and slightly alkaline mucoserous exocrine secretion. It is a complex mixture of fluids, with contributions from major salivary glands ,parotid submandibular and sublingual, the minor or accessory glands and the gingival crevicular fluid. Additionally, it contains a high population of bacteria normally resident in the mouth , desquamated epithelial cells , and transient residues of food or drink following their Ingestion.

5 Secretions enter into the oral cavity by way of:
When referring to the fluid normally present in the mouth the term “whole saliva” is commonly used, as distinct from “duct saliva” which is that flowing from the individual glands. Secretions enter into the oral cavity by way of: Parotid –stensens duct- orifice in the cheek above the molar teeth.

6 Submandibular gland-whartons duct-sublingual caruncle situated to the lingual side of the mandible in the submandibular fossa. Sublingual gland- Bartholins duct- empties along the sublingual fold in the floor of the mouth. Accessory salivary glands empty through individual ducts at their respective locations.

7 COMPOSITION Organic constituents:
99.5%water and balance made of solid substances- inorganic 0.2%,organic 0.3%. The concentration of which are characterized by wide variation , both between individuals and with a single individual. Organic constituents: Protein: 200mg/100ml(only 3% of the protein concentration in plasma) Enzymes ,immunoglobulins, mucous glycoprotiens , traces of albumin , poly peptides etc.

8 Major digestive enzyme. Parotid-60to120mg/100ml.
Alpha amylase : Major digestive enzyme. Parotid-60to120mg/100ml. Submandibular-25mg/100ml. Hydrolysis of alpha 1:4 glycoside bond- end product is maltose. Immunoglobulins: Secretary IgA- predominant-20 mg /100ml IgG-1.5mg/100ML IgM-0.2mg/100ml,arising from gingival crevice.

9 Antibacterial Proteins
Lysozyme-attacks components of the cell wall of certain bacteria leading to lysis. Lactoferrin-iron binding protein- removes free iron from saliva –depleting the supply of iron needed for bacterial growth. Sialoperoxidase- oxidizes salivary thiocyanate ion to hypothiocyanate- potent antibacterial substance using hydrogen peroxide produced by oral bacteria as an oxidant.

10 Sialin- helps to regulate the Ph of plaque.
Glycoprotiens : MG1 and MG2- submandibular and sublingual saliva & a group of Proline rich glycoprotiens (PRPs)-parotid saliva Other poly peptides: Statherin- rich in tyrosine and proline- inhibits the hydroxyapatite crystal growth- inhibitor of calculus formation both in glands and on the teeth. Sialin- helps to regulate the Ph of plaque.

11 Other Organic Compounds
Many free amino acids are present at low concentration. While saliva can be used by some oral bacteria as a sole source of nutrient ,the amino acid content is too low to provide a rich growth medium. Urea - hydrolyzed by many bacteria with release of ammonia – increase in pH. Glucose- 0.5mg/100ml- are too low to support extensive growth, but may be raised in diabetics.

12 Inorganic constituents of whole saliva(mg/100ml)

13 Calcium and phosphate in saliva
Major ions –main contributors to the osmolarity of saliva. Bicarbonate –principal buffer in saliva. Fluoride- anticaries action. Calcium and phosphate in saliva Saliva is super saturated w.r.t hydroxyapatite at normal intraoral Ph, submandibular saliva to a greater extent than parotid saliva. CA10(PO4)6(OH) CA2+ + 6PO H- ph Decreases- Dissolution pH Increases- Rimenarilisation

14 PROPERTIES pH 6.7 TO 7.4 - whole saliva
parotid saliva varies over a greater range Depends on the bicarbonate concentration- concentration of which increase with increase in salivary flow. Initially saliva is isotonic as is formed in the acini but it becomes hypotonic as it travels through the duct network .Hypo tonicity of unstimulated saliva allows the taste buds to perceive different taste and during low flow periods allows for expansion and hydration of mucin glycoprotiens which protectively blanket the tissues of the mouth.

15 Lower levels of glucose ,bicarbonate and urea in unstimulated saliva augment the hypotonic environment to enhance taste. Viscosity Viscosity of saliva is non newtonian. It exhibits different viscosities at different rates of shear , and has visco elastic properties. Viscous behaviour changes with time after secretion because of its non newtonian properties and post-secretory degradation of mucous glycoprotiens by bacterial enzymes.

16 Volume: Mean daily salivary output -500ml-1500ml.
Average volume of saliva present in the oral cavity is approximately– 1 ml. Contribution to the Total unstimulated volume of saliva- Parotid-20% Submandibular -60% Sublingual-5%

17 Factors influencing the composition of saliva
Flow rate Increased flow rate-increase concentration of proteins, sodium chloride and bicarbonate, decreased phosphate & magnesium. Differential gland contributions In unstimulated whole saliva parotid glands contribute only 20% of fluid volume whereas in stimulated saliva they become predominant. Thus the composition of the mixed fluid reaches that of parotid saliva at high flow rates.

18 Duration of stimulus At a constant rate of flow the composition may vary with the duration of stimulation. Nature of stimulus Not biologically significant though salt stimulates- increase in protein content , sugar- increase amylase content.

19 FUNCTIONS Digestion: Salivary amylase initiates digestion of starch- inactivated in stomach- low ph and proteolytic activity. Starch digestion in the mouth may be either beneficial in aiding starch clearance, or detrimental in liberating maltose for fermentation by oral bacteria to form acid- overall effect on caries is still undecided. Lubrication: Aids in speech, mastication, swallowing and for general oral health and comfort- property –water & mucous gylcoproteins.

20 Glycoprotiens- high – minor & sublingual secretions,
Intermediate – submandibular ; low in parotid saliva. Dilution and clearance: Effect of water content of saliva is the dilution of substances into the mouth and their subsequent removal by swallowing or spitting. Clearance is more rapid in some parts of the mouth than others. Unstimulated saliva is present as a thin film covering the hard and soft tissues of the mouth & the velocity with which this film moves over the surface determines the rate of clearance of a substance from different sites,rapid clearance eg lower anteriors and upper posterior teeth.

21 Neutralisation and Buffering:
Saliva is alkaline and is an effective buffer system. Reduces the drop in plaque ph- cariogenic potential of foods. Saturation: Saliva is supersaturated w.r.t tooth mineral- responsible for growth of hydroxyapatite crystals during the remineralisation phase of the caries process. Inhibitors of precipitation- statherin & proline prevents the excessive calcification in the mouth, however they cannot penetrate the plaque due to large molecular size - unable to prevent seeding and calculus formation.

22 Bacterial competition:
Saliva plays a role in the control of the bacterial flora by acting as a selective growth medium. Antibacterial effects Pellicle and plaque formation

23 CONTROL OF SALIVATION The salivary glands are unusual among the glands of the digestive tract in being under purely nervous control. Hormonal influences can alter the composition of saliva but are not responsible for its secretion. Salivary glands are strongly stimulated by the parasympathetic nervous system, the sympathetic system has little or no direct effect on salivation. The indirect effect , a reduction in the rate of secretion from sympathetic stimulation is a result of vasoconstriction of blood vessels to the gland.

24 parasympathetic fibres from-
Stimulation of submaxillary & sublingual glands is by –superior salivary nuclei. Parotid – inferior salivary nuclei. parasympathetic fibres from- 7th nerve - submandibular; 9th nerve-parotid- are secretomotor and vasodilator.

25 ANATOMY AND HISTOLOGY OF THE SALIVARY GLANDS CLASSIFICATION OF SALIVARY GLANDS
According to the size: Major-3pairs Parotid Submandibular Sublingual Minor-400 TO Glossopalatine, Buccal , Mucous glands of the cheek etc , spread in the oral cavity except at the gingiva and anterior part of the hard palate.

26 According to the location Glands whose duct open in the vestibule
Lip : superior labial and inferior labial Cheek: parotid and buccal. Glands whose duct open in the oral cavity proper Floor of the mouth: submandibular, sublingual, glossopalatine. Tongue: Body: anterior lingual (of blandin & nuhn) Base: posterior lingual, von ebner. Palate- palatine.

27 According to the type of salivary secretion and duct opening:
a serous secretion (thin watery) containing the enzyme ptyalin for the digestion of starchy foods. a mucous secretion (viscid sticky or adhering) for lubrication.

28 serous- parotid , von ebner. mucous- palatine, posterior lingual
mixed- predominantly serous - submandibular mixed- predominantly mucous-sublingual blandin & nuhn, buccal &labial

29 Location of salivary glands

30 Labial and buccal glands
Parotid superficial portion- in front of the external ear deeper part fills the retromandibular fossa. Submandibular In the submandibular triangle behind and below the free border of the mylohyoid muscle with a small extension lying above mylohyoid. Sublingual Between the floor of the mouth and the mylohyoid muscle- one main gland and several smaller glands. Labial and buccal glands Lips and cheek, although buccal glands are not examined by electron microscopy they are usually described as continuation of the labial glands.

31 Glossopalatine- principally localized in the region of isthmus in glossopalatine fold. Palatine glands- aggregates in the lamina propria of the posterolateral region of the hard palate and in the submucosa of the soft palate and the uvula. Lingual– anteriorlingual -apex of the tongue; Posterior Lingual (mucous): lateral and posterior to the vallate papilla Posterior lingual( serous): between the muscle fibers of the tongue below the valate papilla.

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33 Main features of parenchymal cells of salivary glands:

34 Functions of ducts: The main function of salivary gland ducts is to, convey the primary saliva secreted by the terminal secretory units to the oral cavity. They are not just passive conduits also they actively modify the primary saliva by secretion and reabsorption. Essentially all of the water enters saliva at the level of terminal secretory units, the striated and excretory ducts appear to be relatively impermeable to water

35 SALIVARY FLOW RATE Flow rate= volume (milli litres) of saliva minute
there is great variability in individual salivary flow rate. The accepted range of normal flow ml/min is as follows:

36 Methods of measurement of flow rate:
techniques for assessing salivation & salivary secretion rate has been reviewed and evaluated by many authors. Accurate measures of salivary flow rate are required for a variety of clinical and experimental situations.

37 Two methods- a.measurement of whole saliva
b.measurement of parotid saliva.. Techniques for measurement of whole saliva unstimulated (resting) Draining method Spitting method Suction method Swab method

38 Techniques for collection stimulated whole saliva
Masticatory method (standardized piece of paraffin used) Gustatory method(1% to 6% citric acid used ) The spitting method for estimating resting flow and masticatory method with paraffin chewing for stimulating saliva for measuring flow rates are reliable.

39 SALIVARY FLOW AND AGEING
Flow rate of unstimulated (resting )whole saliva with age: Since 70% of whole resting saliva comes from submandibular and sublingual glands , the decrease in its flow with age must largely be due to decrease in production. Histological findings demonstrate that there is 20 to 30% decrease in volume of salivary acini with age. On the other hand numerous functional studies have failed to show any age related decrease in the flow of parotid saliva as the normal resting flow rates of parotid saliva are extremely small 0.04 to 0.06 ml/min .Therefore often no saliva can be obtained and the frequency of not obtaining it increases with age .

40 Flow rate of stimulated whole saliva:
The relationship – SFR and ageing- of whole saliva is mixed. Most studies show no change or only a modest decrease in flow rate even though the histological findings show a significant decline in the volume of salivary acini. The fact that this acinar reduction does not affect the stimulated flow rate of saliva should not be surprising- most organs when stimulated, compensate for the loss of parenchyma. Other factors influencing salivary flow rate: Diurnal variation, drugs, source of saliva, diet, duration and type of stimuli, hormones

41 MASTICATION ,OESOPHAGEAL FUNCTION AND SALIVA Decreased mastication and saliva
Mastication is the exercise of the oral apparatus. Chewing increases ,function and lack of chewing induces atrophy of disuse. Indeed impaired mastication is associated with a reduction in the mass of salivary gland and a decrease in the synthesis & secretion of saliva. Findings indicate that the partial or total loss of teeth, the presence of dentures , the decrease in bite force, TMJ dysfunction , extensive caries , pdl disease , pain , immobilization of jaws and other clinical conditions contribute to in flow of saliva and salivary gland hypofunction. Implicit in these findings is that dentists should place a high priority in restoration of masticatory function.

42 Increased mastication and saliva
Chewing induces an increase in the flow of stimulated whole saliva. This facilitates taste, swallowing and alimentation, enhances clearance, buffers harmful oral and oesophageal acids and aids in the remineralisation of teeth . Given the beneficial effects of stimulated saliva it is not surprising that considerable attention is given to agents which stimulate saliva – eg: chewing of paraffin wax ,sugarless chewing gum can increase flow, diminish the fall in plaque pH & accumulation of harmful acids. Clinical trials have therefore shown that chewing sugarless gums reduces incidence of dental caries .

43 Saliva and oesophageal function
The reflux of gastric acid and food into the lower oesophagus-gastro oesophageal reflux (GERD) is a common condition that is associated with heart burn and nausea. The clearance of acids from the oesophagus, like that of the mouth is a two stage process and saliva plays a significant role in it. Influx of saliva Vmax induces swallowing- initiates first phase of oesophageal clearance (primary peristalsis) This is manifested as a peristaltic wave which clears 90-95% of refluxed acid. A small amount of acid 5% remains, which is diluted and buffered by successive swallows of stimulated saliva . Therefore patients with xerostomia, sjogrens syndrome and rheumatoid arthritis- advised to take chewing gum and sugarless candies and cholinergic agonist like pilocarpine.

44 Clearance , residual saliva and oral dryness
The mouth is a receptacle into which , for about 14 hrs of the day ,there is an influx, distribution and efflux of about 350 ml of resting saliva, additionally about 2hrs of the day variety of solids and liquids and about 250ml of stimulated saliva , enter or placed in the oral cavity. The process whereby substances are removed is known as salivary clearance. Central to this process are the act of swallowing and the flow of saliva.

45 Following deglutition there is progressive influx of unstimulated saliva. This is distributed throughout the mouth, where it mixes with and dilutes it contents, and coats the oral mucous membrane. As the volume of saliva increase it soon reaches a maximum volume, at which point another swallow occurs and the process starts all over again. A small amount of saliva , as well as the substances contained within it remain in the mouth. This is referred to as residual saliva-it sticks as a thin film to the mucous membrane and surfaces of the teeth and flows into the interstices between teeth.

46 Some of the substances dissolved in this residual saliva, enzymes antibacterial peptides, antibodies, are protective to the oral cavity. Others like sugar and carbohydrates are potentially harmful. The clearance process is described as similar to tidal exchange where following the ebb tide, there remains tidal pools and the ecosystem contained within them. Whichever analogy is used ,it should be clear that, with exception of substances wanted to be retained in the mouth-fluoride and chlorhexidine, fast clearance favors health; and slow rates favors disease.

47 Average thickness of the residual saliva film on oral tissues= Vmax
The volume of residual saliva was largely dependent on the max volume V max before swallowing- mean value – 1.07ml and the resting flow rate of whole saliva.The mean volume of residual saliva -0.77ml. Average thickness of the residual saliva film on oral tissues= Vmax total surface area of the oral tissues. =0.036to 0.05mm. Because of the variation in the distribution of saliva the shape of the teeth and their disposition in the maxilla or the mandible the thickness of the film varies.

48 Palate and the upper lip were the driest and covered with least amount of saliva; floor of the mouth and dorsum of the tongue were wettest. Dryness is alleged ,is dependent on the volume of saliva present on the oral mucous membrane and the rate of its evaporation from them. Hard palate – fewer glands, far away from the orifices of major glands and is the area of high evaporation. it is proposed that the thickness of the film of residual saliva on the hard palate is a valid indicator of the degree of oral wetness and xerostomia.

49 XEROSTOMIA It is a subjective sensation of a dry mouth, frequently but not always associated with salivary gland hypofunction. Dryness of mouth is one of the oldest symptoms recorded by man. Ancient records describe the use of rice tests to determine guilt or innocence: if innocent-ingestion of rice will stimulate the flow of saliva, if guilty mouth will be dry and swallowing difficult or even impossible.

50 PREVALANCE

51 HOW DOES THE SENSATION OF ORAL DRYNESS CORRELATE WITH THE FLOW OF SALIVA?
Fox et al. Concluded that oral dryness was not a valid indicator of salivary hypofunction. Sreebny &validini also showed that dry mouth per se was not a valid indicator of salivary hypofunction.Their findings –slightly more than half (54%)of the subjects who complained of xerostomia had resting whole saliva flow rates abnormally low (0.1ml/min) Xerostomia is rarely a solitary symptom. Accompanying it is a wide variety of other oral and non oral complaints.

52 CAUSES OF XEROSTOMIA

53 Overall the most common cause of decreased salivary output is the intake of drugs.
A wide variety of medications referred to as Xerogenic drugs induce oral dryness. Prevalence of xerostomia is not only related to drugs that are xerogenic but to the total number of drugs taken. As a general rule the drying and hyposalivatory effects of drugs are transient. Anticholinergic, antidepressants , antihistamines, antipsycotic, antihypertensives, sedatives, diuretics and analgesics.

54 Diagnosis of xerostomia
Clinically Medical history, H/o radiation chemotherapy, oral infections, questionnaire. Dentists should provide the patients with a dry mouth questionnaire- Do you sip liquids to aid the swallowing of foods? Does your mouth feel dry when eating? Do you have difficulties swallowing any foods? Does your mouth usually become dry when you speak? Lab tests: flow rate tests , sialometry ,etc.

55 MANAGEMENT Reassurance, symptomatic and supportive care.
Patient education- to compensate for the oral dryness patient may stop chewing & prefer a liquid or a semisolid diet rich in fermentable carbohydrates. Because decreased mastication worsens the condition , patients should undergo nutritional counseling to limit the harmful effects of reactionary diet modifications.

56 Patient should be reminded to chew , as periodontal mechanoreceptors & mechanical stimulation of the tongue & oral mucosa are vital stimuli for salivation. Sugar free candies & chewing gum are recommended . Use of medication before bed time should be discouraged as this time of the day coincides with lowest salivary flow rate. Should sip cool water throughout the day and drink milk with their meals.

57 sleep on the side to reduce mouth breathing,
Water is a poor mucosal wetting agent, lacks buffering capacity, lubricating mucins. Whole milk may serve as a better substitute. Citrus fruits, caffeine and alcohol, alcohol containing mouth washes cause dehydration & must be avoided. sleep on the side to reduce mouth breathing, Apply petrolatum –based lubricants to lips during the day & bedtime Cool air humidifier be placed in the room. Medication -capable of stimulating salivary glands- pilocarpine -5 to 10 mg ,3 or 4 times daily, 30 min before meals administered.

58 ARTIFICIAL SALIVA SUBSTITUTES Commercially available products contain
Carboxy methylcellulose –lubrication, Animal mucins –to increase viscosity, Parabens- inhibit bacterial growth, Sugar free agents- xylitol, sorbitol- sweetners, mineral salts- simulate electrolyte content, Flouride- reminaralisation. Trade names: salivart(spray), mouthkote (spray), oral balance (gel). The oral mucous and the intaglio surface of prosthesis can be sprayed throughout the day with artificial saliva .

59 Electrical stimulation- SALITRON-
Electrical stimulation- SALITRON-.battery operated devices which deliver an electrical stimulus to the tongue and palate for saliva production. Acupuncture. Future aspects: gene therapy tissue engineering.

60 Therapeutic irradiation of the head and neck
Xerostomia and salivary gland hypofunction are almost inevitably seen in patients whose salivary glands are irradiated for head and neck cancer. Sensation of oral dryness occurs early in the course of radiation. It has been shown that 24 hrs after administration of only 2.25 Gy(225Rads) there is already a 50% decrease in flow of the parotid saliva. When exposure exceeds 50Gy (5000Rads) the reduction in flow is profound &for the most part permanent , the decrease amounts to >90%. Parotid glands are the most sensitive to ionising radiation the other glands in the decreasing order of sensitivity- submandibular, sublingual and the minor glands.

61 Prosthodontic management:
In Preventive therapy: maintain impeccable oral hygiene, schedule frequent recalls , use topical flouride regime. Prosthodontic management: Thorough case history Elastomeric impression materials preferred. In the partially and fully edentulous patient, susceptibility to mucosal ulcerations & fungal infections- patient should be made aware of the well fitting denture & minimize denture use at times when salivary flow is noted. Patient should be made aware of a well fitting denture and minimize denture use at times when decreaesed salivary flow is noted.

62 Artificial saliva reservoir Fabrication of intra oral reservoirs
Construct the maxillary denture with an accepted technique. provide the maximum inter arch space possible with an acceptable vertical dimension of occlusion. thicken the external palatal surface of the trial denture with wax. soften the wax and contour its surface with functional movements of the tongue (swallowing, speech , mastication). Complete the wax up, ,invest it , and boil out the wax.

63 Glue the metal base to the flasked cast.
Construct a chrome cobalt palatal plate on a duplicate cast cover the palate to the palatal portion of the alveolar process & beginning of the post palatal seal. Post palatal seal not included in the metal to decrease the weight of the denture & to prevent premature loss of the artificial saliva due to leakage between metal and acrylic resin parts of the denture. The metal palate is 0.45mm thick at the center & 1mm thick where it joins the acrylic base. Drill two filling holes 1.5mm in the metal base one anterior and one posterior to the midline. Glue the metal base to the flasked cast. Fill the maximum space available for the reservoir with optosil which is then glued to the metal base .

64 Pack and cure the acrylic resins into the flask in the usual manner.
space for acrylic resin must remain between the filler and the investment Pack and cure the acrylic resins into the flask in the usual manner. Remove the metal base and the filler from the denture and reattach the metal base into the denture. The border of the metal base interlocks with the acrylic resins internal surface of the palate . Drill a saliva release hole (0.1 to 0.2) in the reservoir at the midline of the denture 5mm palatal to the anterior teeth.

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67 SIALORRHEA Excessive salivation often experienced by the individual
and experienced by the individual & noticed by the operator. Prosthodontic management Impression making: mouth irrigated with an astringent. Mouth washed prior to investing impression material. Fast setting impression material is used. Anti sialagogues administered 1to 2 days before treatment Dummy dentures are fabricated & given.

68 Prosthodontic Considerations
From the prosthodontists point of view, salivary glands are of great importance both anatomically and physiologically. Extension of denture base: Stensens duct- it is rare for a maxillary denture to cause obstruction to this duct. whartons duct-extension of the lingual flange in this region can lead to obstruction – patient complains of swelling under the tongue while eating. Sublingual- it is rare for a denture to cause any significant obstruction.

69 Excess saliva- complicates denture construction- impression making.
Amount of saliva Will effect the denture construction process & quality of the final product. If a mouth is dry . Retention of the denture –affected+ increased potential for soreness. Excess saliva- complicates denture construction- impression making. When new dentures are first inserted increased salivation due to temporary increase in salivary flow is a natural response to foreign object & in time will subside. Patients need assurance about this. Deglutition will be necessary to evacuate the excess - advised not to rinse and spit as this – unsettling of the denture bases.

70 Best to work with a serous type of saliva.
Consistency Best to work with a serous type of saliva. Presence of thick saliva may create a problem for maxillary complete denture retention,-create hydrostatic pressure in the area anterior to the post palatal seal area- downward dislodging force exerted upon the denture base. In an effort to alleviate this problem, a cupids bow can be scribed on the master cast . Watt and macgregor feel that 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.

71 Thick saliva also complicates impression making by forming voids in the impression surface while the impression sets- palatal surface should be wiped free of saliva & the mucous glands massaged with a piece of gauze just before the final impression is made to eliminate as much as mucous as possible. It may also be factor for the patient to gag while impressions are made and after the placement of new dentures.

72 Role of saliva in denture retention
Saliva is considered as a major factor in evaluating the physical influences that contribute to the denture retention . The physical forces in which saliva is involved are: Adhesion cohesion atmospheric pressure capillary attraction peripheral seal Viscosity of saliva & Surface tension.

73 Adhesion Adhesion is the physical attraction of unlike molecules for each other. It acts when saliva sticks and wets to the basal surface of the dentures & at the same time to the mucous membrane of the basal seat. A watery saliva is quite effective , provided the denture base material can be wetted. Saliva that is thick ropy adheres well to both the denture base and the mucosa; but since much of it is produced by the palatal glands under the maxillary denture base it builds up & pushes the denture out of position. The forces of adhesion still act on them but the hydraulic pressure produced by the thick mucus secretion over power them. The amount of retention provided by adhesion is directly proportional to the area covered by the denture

74 Interfacial surface tension
Cohesion Retentive force as it occurs in the layer of saliva between the denture base & the mucosa. Since saliva is a liquid the layer should be thin if it is to be effective. Interfacial surface tension Is the resistance to separation possessed by the film of liquid between two well adapted surfaces. It again found in the thin film of saliva – similar in its action to cohesion and to capillary attraction.

75 Developed with the proper extension of the denture into the vestibule.
Capillary Attraction Is a force that causes the surface of a liquid to become elevated or depressed when it is in contact with a solid. Peripheral Seal: Developed with the proper extension of the denture into the vestibule. Denture border merging against the mucosal border assembled by a thin film of saliva provides border seal as it prevents ingress of air , thus enabling the denture to be in their position.

76 VISCOSITY OF SALIVA: Analogies are usually drawn between the clinical situation & the two circular parallel plates separated by the liquid. Under these conditions Stephens law can be applied :

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78 degree of closeness of fit. Viscosity of the saliva:
Relationship expressed in equation 2 shows that the force required to displace a denture is proportional to the viscosity of saliva fluid film & the square of area of the denture & inversely proportional to the square of the distance separating denture from the supporting tissues & the time of force application . Degree of retention possessed by the denture depends critically on the area of its fitting surface & hence the requirement to extend the denture base to the maximum allowed by the muscle insertion. degree of closeness of fit. Viscosity of the saliva: The glycoprotiens & the proteoglycans dissolved in the saliva not only increase the viscosity but provide it with

79 pseudo plastic properties
pseudo plastic properties. When low shear stress is encountered in the mouth when mastication is not taking place , saliva acts as a semisolid. equation 1. and 2. are valid if we assume that the circular parallel plates are completely immersed in the liquid. In mouth the dentures are not immersed all the time , hence a meniscus can form at the periphery and surface tension can be included as a factor. Laplace formula:

80 Any positive effect that surface tension has must depend on their being an intact saliva/air interface at the periphery of the denture, a condition which could exist only during speech. When eating and drinking the integrity of any peripheral saliva/air interface would be destroyed and the effect of surface tension becomes negligible.Therefore emphasis is placed on close fit and accurate impression technique

81 SALIVA AS A DIAGNOSTIC TOOL
Saliva is not widely used as a indicator of health &. disease. However salivary testing is becoming more common as clinicians have begun to appreciate its advantages & investigators defined its worth. Salivary levels of drugs detected following therapeutic medications. Saliva drug testing kits are commercially available. Included in these are the tests for alcohol, cocaine HLA typing, HIV1 ,HIV2 ,DNA, etc Salivary cortisol is an indicator of hypothalamic pituitary

82 to detect antibodies-hepatitis A, rubella virus, etc
adrenal axis function- used to quantify the human stress & to determine the effect of treatment on it. to detect antibodies-hepatitis A, rubella virus, etc to diagnose systemic disease after salivary gland dysfunction- sjogrens syndrome, alzheimers disease, cystic fibrosis,etc. Forensic odontology Salivary pH assessment using telemetry: Device called telemetry system is incorporated in the denture which has a radiosensitive diode, oscillator, ph sensor, and a computer analyzer.

83 CONCLUSION The multi factorial role of salivary components continue to represent a focused area of dental research. The knowledge of normal salivary composition, flow & function is extremely important on a daily basis when treating patients. Dental health professionals spend untold hours removing this precious natural resource to perform therapy, with little regard to its value until flow is significantly reduced. Whether saliva occurs in quantities large or small , recognition should be given to the many contributions it makes to the preservation & maintenance of oral & systemic health.

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