SALIVA

IMPLICATIONS IN PROSTHODONTICS

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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.

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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

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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. www.rxdentistry.net

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.

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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.www.rxdentistry.net

COMPOSITION

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. www.rxdentistry.net

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.www.rxdentistry.net

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.

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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.

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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. www.rxdentistry.net

Inorganic constituents of whole saliva(mg/100ml)

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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)2 10 CA2+ + 6PO43- +20H- ph Decreases- Dissolution pH Increases- Rimenarilisation

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PROPERTIES pH

6.7 TO 7.4 - whole saliva

6.0-7.8 - 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.www.rxdentistry.net

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.www.rxdentistry.net

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%

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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.www.rxdentistry.net

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.

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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. www.rxdentistry.net

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.

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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.

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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

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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. www.rxdentistry.net

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.

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ANATOMY AND HISTOLOGY OF THE SALIVARY GLANDS

CLASSIFICATION OF SALIVARY GLANDS

According to the size:

Major-3pairs

Parotid

Submandibular

Sublingual

Minor-400 TO 500 .- Glossopalatine, Buccal , Mucous glands of the cheek etc , spread in the oral cavity except at the gingiva and anterior part of the hard palate.

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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.www.rxdentistry.net

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.

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serous- parotid , von ebner.

mucous- palatine, posterior lingual

mixed- predominantly serous - submandibular

mixed- predominantly mucous-sublingual

blandin & nuhn,

buccal &labial

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Location of salivary glands

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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.

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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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Main features of parenchymal cells of salivary glands:

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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

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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:

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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.

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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

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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.

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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 . www.rxdentistry.net

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

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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.

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Increased mastication and salivaChewing 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 .www.rxdentistry.net

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.www.rxdentistry.net

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.

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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.

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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.www.rxdentistry.net

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. www.rxdentistry.net

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.

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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.www.rxdentistry.net

PREVALANCE

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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.

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CAUSES OF XEROSTOMIA

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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.www.rxdentistry.net

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.www.rxdentistry.net

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.www.rxdentistry.net

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.

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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.

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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 .

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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.

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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. www.rxdentistry.net

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.www.rxdentistry.net

Artificial saliva reservoirFabrication 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.

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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 . www.rxdentistry.net

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. www.rxdentistry.net

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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.

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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.

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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.

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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.

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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. www.rxdentistry.net

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.

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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

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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.

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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.www.rxdentistry.net

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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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

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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:

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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

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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

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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.

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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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