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Authors: Dr Nitesh Shetty, Dr Savita Dandekeri, Dr Vishnudas Prabhu,
Yenepoya University,Mangalore.

Introduction:

Saliva, an amazing body fluid which is neglected and ignored by physicians and dentists. Salivary fluid has a vibrant role in the integrity of the oral tissue; it aids in the ingestion and preparation of food for digestion; and also in speech1. Saliva has myriad of functions in protecting the oral mucosa; helps in clearing the oral cavity of food residue and food debris; gives protection from bacteria and it reduces the harmful effects of strong acids and bases by its buffering action; it also delivers ions for remineralisation of teeth. Additionally it also makes swallowing and speech easy and swift.1

Salivary fluid is an exocrine secretion4,5 consisting mainly 99% of water, comprising a variety of electrolytes (sodium, potassium, calcium, chloride, magnesium, bicarbonate, phosphate) and proteins, represented by enzymes, immunoglobulins and other antimicrobial factors, mucosal glycoproteins, traces of albumin and some polypeptides and oligopeptides of importance to oral health. One of the factor that influence total salivary composition are the relative contribution of the different salivary glands and the type of secretion.2,3

The percentage of contribution by the glands during unstimulated salivary flow is as follows:

• 20% by the parotid glands
• 65%-70% submandibular glands
• 7% to 8% sublingual glands
• <10% by the minor salivary glands,

When salivary flow is stimulated, there is a change in the percentage of contribution of each gland with the parotids contributing over 50% of the total salivary secretion. The salivary secretions may be serous, mucous, or mixed. Serous secretions produced mainly by the parotids, are rich in ions and enzymes. Mucous secretions are rich in mucins (glycoprotein) and present little or no enzymatic activity. They are produced mainly by the smaller glands. In the mixed glands, such as the submandibular and sublingual glands, the salivary content depends on the proportion between the serous and mucous cells.5,6,7
Under normal circumstances dentures do not rest on bare mucous membranes but on an interposed salivary film. This film protects the tissues from forces of the denture base and hydrates these tissues in order that the prosthesis can rest on this layer rather than directly on the oral tissues. The significance of this film is obvious from the multitude of problems associated with denture wear in the xerostomic patient. Soreness and ulceration of the denture bearing tissues, decreased denture retention, burning sensations, alteration in taste perception, and difficulty in mastication and swallowing are among the few problems encountered .8
Saliva is critical for retention of and comfort in wearing removable prostheses.12 In the denture wearing population, salivary wetting mechanics are necessary to create adhesion, cohesion and surface tension that ultimately lead to increased retention of prostheses. An intimate fit of denture bases to supporting tissues and the presence of adequate border seals will provide optimal denture function, provided that saliva is adequate in amount, flow and consistency. Saliva allows for the formation of a vacuum pressure on the seating of dentures and contributes significantly to denture retention and the wearer’s satisfaction with the prosthesis.

Dentures can dislodge during function, and the presence of adequate saliva and swallowing allows for repeated seating of the prosthesis and subsequent retention and denture stabilization. Adhesion, cohesion and surface tension
are interrelated, and they all depend on saliva13.

Factors affecting retention of dentures:
There is a wide-ranging difference in the mechanism of retention in complete denture patient when compared to natural dentition. In a complete denture patient the denture rest on bone with a delicate layer of mucosa between the denture base and the bone, whereas in natural dentition, natural teeth and their embedded roots form an effective arrangement for the mastication of food.
Saliva is one of the physiological factor which plays an important role in the retention of the denture.
The various physical factors which affect retention are

Adhesion:- The physical attraction of unlike molecules to one another .A thin film of saliva is formed between the denture and tissue surface .Thus a thin film helps to hold the denture to the mucosa .The amount of adhesion present is proportional to the denture base area.

Cohesion:-
The physical attraction of like molecules for each other. The cohesive forces act within the film of saliva .Watery serous saliva can form a thinner film and is more cohesive than thick mucous saliva.

Inter-facial surface tension:- The tension or resistance to separation possessed by the film of liquid between two well adapted surfaces. Here a film of saliva tends to resist the displacing forces ,which tends to separate the denture from the tissues .It is totally dependent on the liquid air interface .Surface tension is lost in mandibular denture due to the loss of the air –saliva interface at the denture .
The viscosity of saliva determines retention. Serous saliva which has a moderate flow favourably contributes to retention. Thick ropy saliva often forces the denture out of their position thus proving a detrimental factor for retention.

Some of the detrimental factors of saliva which affect denture retention are:-

  • Excessive saliva ----The new denture may feel like a foreign object and stimulate the flow of saliva .If the flow is excessive, the patient may complain of floating denture.
- Thick saliva also complicates impression making by forming voids in the impression and may cause the patient to gag.9,10

  • Hyposalivation:-
  • -Xerostomia is a condition which reflects a reduction in salivary flow resulting from atrophy of the salivary glands. In this condition dentures are more susceptible to frictional irritation leading to ulceration and soreness.

  • The causes :
    • Sjogren’s syndrome
    • Diabetes Mellitus
    • Renal failure
    • Pharmacotherapy
    • Therapeutic head and neck irradiation

    Prosthodontic management of xerostomia:

    • Consultation with the physician and treatment of the underlying cause.
    • Salivary stimulants like pilocarpine hydrochloride, cevimeline hydrochloride.
    • Dentures which include a reservoir for dispensing artificial saliva like the palatal reservoir helps in reducing the irritation and ulceration caused by hyposalivation.9,11

    References:

    1.FDI Working Group. Int Dent J(1992)42,291-304
    2.Jenkins GN. The physiologic and biochemistry of the mouth. 4th. ed. Oxford: Blackwell Scientific Publications; 1978.
    3. Edgar M, Dawes C, O’Mullane D. Saliva and oral health. 3rd ed. London: BDJ Books; 2004
    4. Berkovitz BKB, Holland GR, Moxham BJ.Oral anatomy, histology and embryology. 3rd ed. New York: Mosby; 2002.
    5. Ferraris MEG, Munõz AC. Histologia e embriologiabucodental. 2. ed. Rio de Janeiro: Guanabara Koogan; 2006.
    6. Tenovuo J, Lagerlöf F. Saliva. In: Thylstrup A, Fejerskov O. Textbook of clinical cariology. 2nd ed.Copenhagen: Munksgaard; 1994
    7.Ten Cate AR. Oral histology: development, structure and function. 5th ed. St. Louis: Mosby; 1998.
    8.Edgerton, Tabak& Levine, 1987; Navazesh, 1989.
    9. Gary.F.Sinclair, Peter.M.Frost .New design for an artificial denture reservoir for the mandibular complete denture by
    10. Katcherine Chiu-Man leung,Hong Kong Dent J Vol.2, No.2 December 2005.
    11. Boucher’s prosthodontic treatment for edentulous patients
    12. Guggenheimer J, Moore PA. Xerostomia: etiology, recognition and treatment. JADA 2003;134(1):61-9.
    13. T Michael, Hyposalivation, xerostomia and the complete denture A systematic review.JADA 2008;139(2):146-50

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