What is Saliva?

Saliva Composition

• The majority of saliva is water, making up 99% of its composition.
• Organic and inorganic substances constitute the remaining 1%.
• Saliva composition is difficult to assess due to a food stimulus differing from a wax stimulus, affecting saliva production.

Whole vs Pure Saliva

• "Whole" or "mixed" saliva in the mouth differs from "pure" saliva produced in the glands.
• Crevicular fluid secreted from inflamed gingival pockets is part of "whole" saliva when periodontal disease exists.
• Food debris, epithelial cells, and bacteria from the oral cavity are present in saliva.

pH of Saliva

• Resting pH varies among individuals, typically ranging from 6.7 to 7.4.
• pH can vary based on diet and time of day.
• Low pH is associated with caries, while higher pH is linked to calculus formation.

Organic Components of Saliva

• Saliva contains several hundred different proteins, many with antibacterial properties.
• Mucin and enzymes are both proteins.
• Immunoglobulins (IgA, IgG, and IgM) aid in bacteria disposal by clumping them together, preventing adherence to oral cavity surfaces.
• This clumping process, termed agglutination, works with serous saliva to wash away bacteria.
• Lysozyme destroys harmful bacteria through lysis of the cell wall.
• Lactoferrin binds free iron, inhibiting bacterial metabolism.
• Lactoperoxidase also inhibits bacterial metabolism.
• Amylase initiates the breakdown of cooked starches.
• Ribonuclease catalyzes the endonucleolytic cleavage of RNA.
• Phosphatase is involved in calculus formation and caries remineralization.
• Mucin proteins provide saliva with its viscous/sticky consistency.
• Muco-proteins contain more than 4% carbohydrate derivatives.
• Glyco-proteins contain less than 4% carbohydrate derivatives.
• Urea neutralizes acids.
• Uric acid is also present.
• Ammonia, formed from urea, raises pH.
• Waste products are by-products of cell metabolism.
• Desquamated epithelial cells are constantly replaced as worn/dead cells.
• White blood cells from the gingival crevice contribute to the body's defense mechanism during inflammation.
• Commensal bacterial cells exist in a symbiotic equilibrium with the host, preventing pathogenic bacteria from gaining a foothold.
• Hormones such as oestrogen and progesterone are present.

Inorganic Components of Saliva

• Inorganic components consist mainly of mineral salts, known as ions in solution.
• Ions buffer saliva, maintaining pH levels.
• Calcium phosphate ions play a significant role in caries incidence and calculus formation.
• Other ions present include sodium, potassium, magnesium, chloride, fluoride, bicarbonate, sulphate, and hydrogen.
• Fluoride aids in remineralization, provides antibacterial action, has a topical effect resulting in teeth being more resistant to decay.
• Bicarbonate acts as a buffer.

Gas Components

• Saliva contains oxygen and nitrogen.
• Carbon dioxide levels are higher in the salivary glands, and its release may be related to calculus formation.

Functions of Saliva

• Glyco-proteins lubricate and waterproof soft tissues, protecting against abrasion, aiding speech, and maintaining a healthy mucosa.
• Saliva forms the salivary pellicle, protecting enamel by acting as a barrier to acid attacks.
• Serous saliva cleanses, removing food and bacterial debris.
• Ions maintain pH, preventing bacterial colonization and neutralizing acids and alkalis.
• Bicarbonate ions increase during higher salivary flow when eating.
• Salivary amylase initiates the breakdown of cooked starches and helps form the bolus.
• Taste sensation requires substances to be in solution.
• Proteins and Ig's destroy or prevent colonization by harmful bacteria.
• Ions aid maturation of immature enamel in newly erupted teeth and assist in repair from acid attacks.
• Saliva generally has a protective function.
• Patients with impaired saliva flow often experience rapid plaque deposition, rampant caries, and severe periodontal disease.

Saliva and Caries

• The salivary pellicle, formed by glyco-proteins, protects against acid but can encourage adherence of harmful plaque bacteria.
• Supersaturation of inorganic ions acts as a buffer, continuously aiding control of demineralization and remineralization.
• Serous saliva's cleansing effect may reduce fermentable carbohydrate available for conversion to acid.
• Saliva quantity changes from day to night (1-1.5 liters during the day, 10ml at night), on stimulation, and as affected by drugs, illness, and radiation.

The Ionic See-Saw

• The saliva buffering system can reduce the extent of pH fall when sugars enter the mouth, but prolonged episodes can exhaust the system's ability to contain ion removal.
• A fall in pH increases the free energy of ions at the enamel/plaque interface and the migration of ions from both enamel and plaque.
• As pH falls below 6.0, the solubility limit of the plaque fluid increases, reducing calcium and phosphate ion concentration.
• When the solubility limit of the plaque fluid exceeds the calcium and phosphate ion products, these ions leave the enamel under a concentration gradient.
• This occurs around pH 5.5.
• Below this level, mineral ions (calcium and phosphate) leave enamel to enter plaque, leading to enamel demineralization.
• If buffering action is effective and pH rises, mineral ions return to the enamel under a concentration gradient, causing remineralization.
• Repeated pH fluctuation produces a seesaw of ions across the enamel and plaque fluid interface.

Mechanism of Salivation

• Salivation is a reflex mechanism stimulated by sensory inputs such as sight, smell, and taste.
• Sympathetic and parasympathetic nerve supply to the salivary glands controls salivation.
• Sympathetic and parasympathetic nerves have opposite effects, controlling the output from the salivary glands.
• Sympathetic stimulation reduces salivary flow due to vasoconstriction (e.g., dry mouth in stressful situations).
• Parasympathetic stimulation increases salivary flow due to vasodilation (e.g., mouth waters at the sight/smell/taste of appetizing food).
• Secretomotor supply to the salivary glands results in salivation.

Secretomotor Supply to Salivary Glands

• Glands in the hard & soft palate: Sympathetic Supply from the internal carotid artery to the sphenopalatine ganglion, branches then run with the greater palatine, lesser palatine and pharyngeal nerves of the trigeminal nerve (maxillary division)
• Glands in the hard & soft palate: Parasympathetic Supply from the superior salivary nucleus of the brain with the facial (7th) nerve, via the greater petrosal nerve, then the nerve of the pterygoid canal to the sphenopalatine ganglion (synapse), post-synaptic fibers then run from the ganglion along with branches of the maxillary division of the trigeminal nerve (greater palatine, lesser palatine and pharyngeal nerves) to the hard palate, soft palate and pharyngeal glands
• Submandibular and sublingual glands: Sympathetic - From the facial artery via the submandibular ganglion and the lingual nerve (branch on the mandibular division) to the submandibular and sublingual glands
• Submandibular and sublingual glands: Parasympathetic - From the superior salivary nucleus of the brain via the facial (7th) nerve, via the chorda tympani branch to the submandibular ganglion (synapse), post ganglionic fibres run with the lingual nerve, a branch of the mandibular division of the trigeminal nerve to the submandibular and sublingual glands
• Parotid glands: Sympathetic - From the middler meningeal artery via the otic ganglion and the auriculotemporal nerve (a branch of the mandibular division) to the parotid.
• Parotid glands: Parasympathetic - From the inferior salivary nucleus of the brain via the glossopharyngeal (9th) nerve, via the tympanic plexus of the middle ear and the lesser petrosal nerve to the otic ganglion (synapse), post-ganglionic fibers run with the auriculotemporal branch of the mandibular division of the trigeminal (5th) nerve to the parotid gland
• Taste supply from the anterior two-thirds of the tongue is From the taste buds via the lingual nerve (mandibular division) of the trigeminal nerve) to the submandibular ganglion then travel with the chorda tympani (a branch of the facial nerve) and facial nerve to the nucleus solitarius in the brain
• Taste supply from the posterior third of the tongue is From the tongue via the glossopharyngeal (9th) nerve to the nucleus solitarius in the brain

Salivary Flow Factors

• Increased flow is linked to , mastication, irritants, gingival conditions, hunger, smell/sight of food, and teething in babies
• Reduced flow is due to, drugs, diabetes, alcohol, fear, radiotherapy, and surgery

Medical Conditions Affecting Saliva

• Hypersalivation- is the excess production of saliva
• Xerostomia- dry mouth is due to a reduction or absence of saliva

Saliva in Dentistry

• Cross-Infection Control is important as saliva can be a route of transmission for many viruses, one of many reasons why cross-infection control procedures must be followed.
• The following can be transmitted in saliva: COVID-19, Hep B, Hep C, Herpes simplex (type 1), Epstein-Barr virus, and Tuberculosis