The document discusses the functions of saliva, highlighting its role in oral physiology, including the production of saliva by major and minor salivary glands, its protective and digestive functions, as well as its immunologic properties. It details the anti-cariogenic function of saliva and its components, such as statherin, which forms a protective biofilm on teeth, alongside various immune molecules that protect against oral diseases. Additionally, it explores the significance of salivary proteins and enzymes in microbial clearance and the development of innovative oral care products that leverage these properties.

1. Oral Physiology-Functions of Saliva
Dr Muhammad Danial Khalid
BDS, MSc (UK), MFGDP (UK)
Assistant Professor
Department of Oral Biology

2. Introduction to Functions of Saliva
• Every day, an estimated 0.5 to 1.5 liters of saliva is produced and secreted in the oral
cavity by the paired major (parotid, sublingual, and submandibular) and the numerous
minor salivary glands throughout the mouth.
• Salivary secretions include inorganic components like (electrolytes, such as chloride,
potassium, sodium, and bicarbonate).
• Saliva forms a protective layer on the surfaces of teeth.
• Salivary enzymes aid in digestion such as salivary amylase and lipase.
• Saliva also contains other organic components such as mucous glycoproteins, acidic
proline-rich, tyrosine-rich proteins, and numerous other proteins which have two
functions:
1. Anti-cariogenic function (salivary protein: Statherin)
2. Immunologic functions (various salivary proteins like Histatin, cystatin, lactoferrin etc)

3. Anti-cariogenic function of saliva
• The anti-cariogenic function means “prevention of caries
development”.
• The main salivary protein exerting this function is called Statherin.
• Statherin binds to hydroxyapatite (HAP) or fluoro-hydroxyapatite
(FAP) on the surface enamel (tooth surface).
• Along with Statherin, other salivary proteins also bind onto the tooth
surface.
• This results in the formation of a “BIOFILM”.
This salivary bio-film on the tooth surface is also called “acquired
pellicle”.

4. Anti-cariogenic function of saliva-
Statherin

5. Anti-cariogenic function of saliva-
formation of acquired pellicle

6. Introduction to Oral Immunology
• The physical and functional integrity of the oral mucosa is important both for
oral and systemic health.
• Both soft-shedding mucosal surfaces (desquamation) and the hard non-shedding
tooth surfaces are protected by innate and adaptive immune mechanisms.
• The immune mechanisms and molecules of the oral cavity derive either from the
secretory or systemic immune system
• The secretory immune system mainly comprises the secretions of the major and
minor salivary glands
• The systemic immune system mainly acts through the gingival crevicular fluid.
• GCF is a serum exudate that originates in the gingival capillaries and flows into the
gingival crevice carrying locally produced mediators of innate and adaptive immunity.
The immune mechanisms operating in the specific areas of oral cavity are peculiar in
nature and may co-exist.

7. Oral Immunology-An Overview

8. Immunologic functions of saliva
• Salivary glands secrete mucins and other innate microbial factors that protect against
oral disease.
• Mucins are of two types, A and B, both of which form a protective lining over the
entire oral mucosa.
• The IgA secreted in saliva is also called ‘‘sIgA”.
• Anti-microbial peptides are also present in saliva.
• Examples of such antimicrobial peptides include Beta-defensins and calprotectin.
Lymphocytes present in the oral connective tissue (lamina propria) can also produce anti-
microbial peptides and cytokines after they have been chemotactically recruited.

9. Immunologic functions of saliva

10. Immunologic functions of saliva-sIgA
• sIgA stands for “secretory
immunoglobulin A”.
• It is the main immunoglobulin
found in saliva as well as other
secretions such as lacrimal,
mammary etc.
• It is not derived from blood like IgE
(in the gingival crevice).
• Produced by B-lymphocytes and
not by salivary gland cells.
• sIgA exhibits a diurnal rhythm,
with the most concentration seen
at morning time.
• Along with salivary mucins,
salivary sIgA forms a protective
barrier over the oral mucous
membranes.
• The bio-chemical structure of sIgA
is such that it binds to pathogens.

11. Immunologic functions of saliva
• The array of innate Anti-microbial proteins found in saliva have antibacterial,
antifungal as well as antiviral properties.
• The mechanism of action of salivary proteins is generally two-fold:
1. Promoting microbial adherence by acting as receptors.
2. Promoting microbial clearance through agglutination and swallowing.
• High Molecular Weight glycoproteins are also present in saliva such as mucin types A
and B, salivary agglutinin, surfactant protein-A, PRPs and fibronectin are adhesive
proteins mediating bacterial agglutination (promoting microbial clearance)
• Other proteins have been categorized into cationic Anti-microbial peptides, metal ion
chelators such as lactoferrin and calprotectin, protease inhibitors and enzymes.
• Both mechanisms (microbial adherence and clearance) co-exist.

12. Salivary proteins of immunologic
significance
CATIONIC ANTIMICROBIAL PEPTIDES
Alpha and beta defensins
Cathelicidin LL-37
Histatins 1 and 3
Adrenomedullin
Statherin
Azurocidin

13. Cationic antimicrobial peptides
• These are small 15-20 amino acid long peptides
• Contain amino acids like arginine, lysine and histidine
MECHANISM OF ACTION:
• About 50%of these amino acids are hydrophobic
• Hydrophobicity allows them to interact with bacterial membranes
• These peptides are collectively active against:
1. Gram positive and gram negative bacteria
2. Fungi (Histatins mainly)
3. Viruses such as HIV, Herpes and vesicular stomatitis etc.
4. Cancerous cells

14. Cationic antimicrobial peptides
APrP, statherins and histatins, Adapted from Schupbach et. al. 2001, Eur J Oral Sci 109:60

15. Cationic Antimicrobial Peptides
Statherins and histatin in the acquired pellicle , Adapted from Schupbach et. al. 2001, Eur J Oral Sci 109:60

16. ADHESIVE PROTEINS CAUSING BACTERIAL AGGLUTINATION
Salivary Agglutinin
Surfactant protein-A
Proline Rich Peptides

17. Surfactant protein-A
• Major protein component of lung surfactants
• But it is also expressed in human saliva
• Causes agglutination of bacteria and neutralization of influenza virus
• Sialic acid residues in the structure of this protien are responsible for its immunlogic
properties
• It has been found that levels of this protein have been elevated in patients with
chronic sialadenitis

18. Proline-rich Peptides
• Produced by parotid and submandibular glands
• 70% of total salivary proteins
• Larger PrPs bind to the tooth surface and promote bacterial adherence
• However smaller PrPs antagonise bacterial adherence and cause
agglutination

19. Metal Ion Chelators
Lactoferrin

20. Lactoferrin
• 80 KDa glycoprotein
• Produced by mucosal epithelial cells and neutrophils
• found in both saliva and GCF
MECHANISM OF ACTION:
• This protein binds iron (Fe3+) and can deprive micro-organisms of this
essential nutrient.
• It is bactericidal (killing bacteria by depriving them of essential nutrients)

21. Protease Inhibitors
Cystatins

22. Cystatins
• Mainly contributed by submandibular and sublingual salivary glands
MECHANISM OF ACTION:
• They inhibit bacterial enzymes.
• The inhibition of bacterial enzymes leads to nutrient deficiency causing inhibition of
bacterial growth

23. Anti-fungal proteins
Histatins

24. Histatins
• They are antifungal proteins
• Are attached to the tooth surface as well as oral mucosa
• Prevent the growth of a common oral opportunistic fungus Candida Albicans thereby
preventing oral candidiasis.
Opportunistic pathogens such as Candida Albicans cause infection in the oral cavity in
patients who are immuno-compromised (low or suppressed immunity). Such patients can
be diabetic, suffering from HIV-AIDS or undergoing chemotherapy for cancer.

25. Salivary Enzymes
LYSOZYME:
• Found in milk, saliva, nasal and bronchial secretions
• Secreted in both saliva and GCF
• It hydrolyses peptidoglycans in the cell wall of gram positive bacteria
• Leads to osmotic breakage of bacterial cell membrane
• Also causes activation of autolysins in the bacterial cell wall
• Agglutination
• It acts synergistically with lactoferrin, peroxidases and sIgA

26. Salivary Peroxidase System
• Peroxidases are found in all mucosal secretions
• In saliva, they include salivary peroxidases
• In GCF, they include myeloperoxidases expressed in neutrophils
MECHANISM OF ACTION:
• They produce hydrogen peroxide which oxidises thiocyanate ions in saliva
to hypothiocyanite which is bactericidal
• Thiocyanate ion is a normal component of both saliva and GCF but needs
to be activated
• Hypothiocyanite also inhibits acid production by cariogenic bacteria, mainly
by oxidising bacterial enzymes.

27. Development of novel products/toothpastes
Most commonly found is the regular fluoride toothpaste (1000 ppm F). Various
newer products have been developed as a result of comprehensive
understanding of salivary biochemistry such as:
1. Synthetic statherins (commercial forms such as STN-21).
2. Toothpastes with added lysozyme, lactoferrin and peroxidases have been
developed e.g. Biotene toothpaste
3. Supplements containing specific protein complexes e.g. GC Tooth Mousse
which contains bovine derived phosphoprotein and mineral calcium.