Saliva – An Important Factor for a Successful Prosthesis

There’s an old axiom, “you never miss the water till the well runs dry”. How true is that, especially for saliva! The fact is, a world without saliva is like living in a drought. Saliva is important for the preservation and maintenance of oral health, so it is necessary for clinicians to have a good knowledge base concerning the norm of salivary flow and function.

Sources of Saliva

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

Composition

Saliva is composed of 99.5% of water and 0.5% of solid substances, out of which 0.2% are inorganic substances and 0.3% are organic substances. However their concentration is characterised by a wide variation in different individuals.

Properties

• The pH of whole saliva is around 6.7-7.4 whereas that of parotid saliva is 6-7.8
• Volume – Mean daily salivary output is 500 ml-1500 ml
• 20% Parotid
• 60% Submandibular
• 5% Sublingual
• The normal daily production of saliva varies between 0.5 and 1.5 liters. The whole unstimulated saliva flow rate is approximately 0.3-0.4 ml / min. This rate decreases to 0.1 ml / min during sleep and increases to about 4, 0-5, 0 ml / min during eating, chewing and other stimulating activities. 4
• Increased flow rate of saliva causes increased concentration of proteins, sodium chloride and bicarbonate, whereas it causes decreased phosphate and magnesium.

Types of saliva

• Serous / watery
• Mucous / thick
• Mixed

Functions of Saliva

Digestion

• Salivary amylase initiates digestion of starch and proteolytctivity.
• 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 speech, mastication, swallowing and for general oral health and comfort.

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 and 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
• Clearance also depends on the type of saliva. More serous the saliva, higher the rate of clearance

Neutralisation and buffering

• Saliva is alkaline and is an effective buffer system. It reduces the drop in plaque pH reducing cariogenic potential of foods.

Bacterial competition

• Saliva plays a role in the control of the bacterial flora by acting as a selective growth medium. 1

Saturation

• Saliva is supersaturated with respect to tooth mineral which is responsible for growth of hydroxyapatite crystals during the remineralisation phase of the caries process.
• Inhibitors of precipitation – statherin and 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.

Techniques for Collection of Stimulated Whole Saliva

• Masticatory method (standardised piece of paraffin used)
• Gustatory method (1% – 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.

Xerostomia

It is a subjective sensation of a dry mouth, frequently but not always associated with salivary gland hypofunction.

• Overall the most common cause of decreased salivary output is the intake of medications.
• 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 are all xerogenic

Diagnosis of Xerostomia

Clinically

Medical history, H/O radiation chemotherapy, oral infections, questionnaire.

Dentists should provide the patients with a dry mouth questionnaire –

1. Do you sip liquids to aid the swallowing of foods?
2. Does your mouth feel dry when eating?
3. Do you have difficulties swallowing any foods?
4. Does your mouth usually become dry when you speak?

Lab tests: flow rate tests, sialometry, etc.

Management

• Reassurance, symptomatic and supportive care.

Patient education – to compensate for the oral dryness patient may stop chewing and prefer a liquid or a semisolid diet rich in fermentable carbohydrates.

• Because decreased mastication worsens the condition, patients should undergo nutritional counselling to limit the harmful effects of reactionary diet modifications
• Water is a poor mucosal wetting agent, lacks buffering capacity, lubricating mucins. Whole milk may serve as a better substitute. Caffeine and alcohol, alcohol containing mouth washes cause dehydration and must be avoided
• Sleeping on the side to reduce breathing through the mouth
• Apply petrolatum – based lubricants to lips during the day and bedtime
• Cool air humidifier be placed in the room
• Medication – capable of stimulating salivary glands- pilocarpine 5 – 10 mg, 3/4 times daily, administered 30 minutes before food
• Sipping of liquids frequently or use of spray bottles instead

Prosthodontic management

• Thorough case history
• Elastomeric impression materials preferred
• In the partially and fully edentulous patient, there is susceptibility to mucosal ulcerations and fungal infections
• Patient should be made aware of a well fitting dentures and minimise denture use at times when decreased salivary flow is noted.

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.
• Construct a chrome cobalt palatal plate on a duplicate cast cover the palate to the palatal portion of the alveolar process and beginning of the post palatal seal. Post palatal seal not included in the metal to decrease the weight of the denture and to prevent premature loss of the artificial saliva due to leakage between metal and acrylic resin parts of the denture. The metal palate is 0.45 mm thick at the centre and 1 mm thick where it joins the acrylic base.
• Drill two filling holes 1.5 mm 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.
• 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 5 mm palatal to the anterior teeth.

Prosthodontic Considerations

• From the prosthodontists point of view, salivary glands are of great importance both anatomically and physiologically.

Extension of denture base

Stensen's Duct – it is rare for a maxillary denture to cause obstruction to this duct

• Wharton's 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
• Will effect the denture construction process and 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. Advised to swallow instead and prevent pooling of saliva in mouth
• 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
• According to Watt and Macgregor, 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.

References

1. Charles M Hartwell, Textbook of Complete Dentures, 5th Edition
2. Sheldon Winkler, Essentials of Complete Denture Prosthodontics, 2nd Edition
3. S Sachdeva, Role of Saliva in Complete Dentures: An Overview, Annals of Dental Speciality, 2014
4. Gabriela Iorgulescu.Saliva between normal and pathological. Important factors in determining systemic and oral health. J Med Life. 2009 Jul-Sep; 2(3): 303–307.