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2. Anatomical and histological features of the teeth’ structure. Age-related changes in them. The concept of periodontium, its functions. Saliva, oral fluid: composition, properties, functions.

 

DEVELOPMENT OF THE TOOTH GERM

The tooth germ develops in three stages: bud, cap and bell (Fig. 1).

Bud

At 8 weeks of intrauterine life, clumps of mesenchymal cells induce the dental lamina to form swellings known as enamel organs. Each enamel organ will be responsible for the development of each tooth (Fig. 1 a).

Cap

As the enamel organs grow and increase in size, the inner aspect becomes concave, resembling skull caps. By the late cap stage, at 12 weeks of intrauterine life, cells on the inner aspect of the enamel organ change from cuboidal to columnar, forming the inner enamel epithelium. The outer layer of cells remains cuboidal and is known as the outer enamel epithelium (Fig. 1 b).

Beneath the inner enamel epithelium the condensation of mesenchymal cells is termed the dental papilla; this will eventually become the pulp. A fibrous capsule surrounds each enamel organ and this is termed the dental follicle; this will eventually become the periodontal ligament.

Bell

By 14 weeks of intrauterine life (Fig. 1 c) the enamel organ consists of the following:

■ Inner enamel epithelium: cells lining the inner surface of the enamel organ which, at the bell stage, are columnar in shape. The inner enamel epithelium defines the shape of the crown and eventually the cells differentiate into enamel-forming cells (ameloblasts).

■ Stratum intermedium: this lies over the inner enamel epithelium and consists of two to three layers of cells. It transports nutrients to and from the ameloblasts.

■ Stellate reticulum: this lies between the stratum intermedium and the outer enamel epithelium. It consists of star-shaped cells which protect the underlying dental tissues; it also maintains the shape of the tooth.

■ Outer enamel epithelium: these cells line the outer surface of the enamel organ. They are cuboidal in shape and maintain the shape of the enamel organ. The outer enamel epithelium meets with the internal enamel epithelium at the cervical loop. Eventually the inner and outer enamel epithelium grows downwards at the cervical loop forming Hertwig’s root sheath which maps out the shape of the root. At the late bell stage the dental lamina disintegrates and is ready for the formation of dental hard tissue. Dentine formation always precedes enamel formation.

 

 

 

DEVELOPMENT OF THE DENTAL TISSUES

Dentine formation (dentinogenesis)

Differentiation of odontoblast cells

At the late bell stage the inner enamel epithelium induces cells at the periphery of the dental papilla to differentiate into columnar odontoblast cells.

Secretion of dentine matrix

The odontoblast cells begin to secrete an unmineralised dentine matrix. As more dentine matrix is deposited, the odontoblast cells retreat in the direction of the pulp leaving an elongated process known as the odontoblast process. The dentine matrix formed prior to mineralisation is termed predentine. A narrow layer of predentine is always present on the surface of the pulp.

Mineralisation of dentine

Mineralisation of dentine begins when the predentine is approximately 5 µm thick. Spherical zones of hydroxyapatite called calcospherites are formed within the dentine matrix. Mineralisation of the dentine matrix starts at random points and eventually these calcospherites fuse together to form mineralised dentine. Dentinal tubules form around each odontoblast process. The odontoblasts retreat in S-shaped curves towards the dental papilla. The first layer of mineralised dentine is called mantle dentine and the remaining bulk of the mineralised dentine is known as circumpulpal dentine.

Enamel formation (amelogenesis)

Differentiation of ameloblast cells

Immediately after the first layer of dentine is formed, the inner enamel epithelium differentiates into ameloblast cells. The ameloblast cell is columnar in shape with its base attached to cells of the stratum intermedium; at the secretory end there is a pyramidal extension called the Tomes’ process.

Secretion of enamel matrix

The enamel matrix is secreted through the Tomes’ process at the amelo-dentinal junction.

Mineralisation of enamel

Calcium and phosphate ions are secreted into the enamel matrix and mineralisation occurs immediately; hydroxyapatite crystallites are formed. As ameloblasts move away from the amelo-dentinal junction, enamel prisms are formed. Prisms, also known as rods, run from the amelo-dentinal junction to the enamel surface; they contain millions of crystallites.

Enamel maturation

During maturation from pre-enamel to mature enamel, the enamel crystallites increase in size and the organic content is reduced. On completion of enamel formation, the ameloblast cell loses the Tomes’ process, flattens and becomes the reduced enamel epithelium. The reduced enamel epithelium protects the enamel during eruption and will eventually become the junctional epithelium (cuticle – in mature teeth is preserved only in proximal surfaces of crown).

Cementum formation (cementogenesis)

When root dentine has formed, Hertwig’s root sheath degenerates allowing adjacent cells from the dental follicle to come into contact with the root dentine. These cells differentiate into cementoblasts. Cementoblasts are cuboidal in shape and form a single layer on the surface of the root dentine. The cementoblasts secrete cementum matrix consisting of amorphous ground substance and collagen fibres.

Ground substance is composed of glycosaminoglycans (acid mucopolysaccharides), proteoglycans (glycosaminoglycans and protein bound together) and glycoproteins (protein bound with sugars). Crystallites of hydroxyapatite are deposited in this matrix and mineralisation occurs. During formation, a thin layer of unmineralised cementum is always present on the surface; this is known as cementoid. Once cementogenesis has begun, collagen fibres within the dental follicle orientate themselves into bundles forming the principal fibres of the periodontal ligament. The ends of these fibres become embedded in the developing cementum and alveolar bone and are known as Sharpey’s fibres.

Tooth eruption

Tooth eruption is the bodily movement of a tooth from its development position into its functional position in the oral cavity. It can be broken down into two phases: the pre-functional eruptive phase and the functional eruptive phase. (Fig. 2)

Pre-functional phase

During the pre-functional phase, crown formation is completed. As root formation begins, the developing tooth begins to erupt. The overlying alveolar bone is resorbed by osteoclasts and gradually the tooth moves in an axial direction towards the oral cavity. The enamel surface of the tooth is covered by the reduced enamel epithelium which fuses with the oral epithelium. The pressure from the tip of the tooth breaks down the oral epithelium, allowing the tooth to emerge into the oral cavity without any rupturing of blood vessels. Once the tooth has emerged, the reduced enamel epithelium is known as the epithelial attachment. Tooth eruption continues until the tooth contacts (occludes with) the opposing tooth in the opposite jaw.

Functional eruptive phase

The functional eruptive phase continues throughout life due to functional changes. The alveolar bone continuously remodels in response to tooth movement and enamel wear allowing teeth to maintain contact with each other and with opposing teeth.

 

 

Mechanisms of tooth eruption

The eruptive force of tooth eruption is unclear; several theories have been put forward, although there is little evidence to support them. These are:

■ Root growth generates a force beneath the tooth, elevating the tooth towards the oral cavity.

■ Remodelling and deposition of the bone beneath the developing tooth push the tooth upwards.

■ Traction of the periodontal fibres exerts an upward pull on the tooth.

■ Cellular proliferation at the base of the pulp creates pressure that pushes the tooth from the dental follicle.

■ An increase in tissue fluid or blood pressure generates an eruptive force on the tooth.

 

STRUCTURE OF TOOTH.

 

Enamel

Enamel has been studied extensively because it provides the initial major barrier to the caries process. It is composed of 92 per cent mineral and 8 per cent organic material and water, as measured by volume. It is recognized as the hardest human tissue. In spite of its hardness a fluid penetration through the enamel may be demonstrated.

FIGURE 1-5. A 200x SEM of enamel surface indicates the irregularities and porosities that are natural to its surface. (Courtesy of R. Blumershine)

Physical characteristics of enamel

Enamel is highly mineralised and is the hardest tissue in the body. Enamel covers the anatomical crown of the tooth and varies in thickness; it is semi-translucent and its colour can vary from bluish white to hues of yellow.

 

 

Chemical composition of enamel

Enamel consists of 96–97% inorganic material (by weight), the main inorganic component being hydroxyapatite, 1% organic material (by weight), the main organic component being protein and 2–3% water (by weight).

Structure of enamel

Enamel is made up of millions of enamel prisms or rods, which run from the amelo-dentinal junction to the enamel surface. Each prism is made up of a large number of enamel crystallites. When viewed under a light microscope each prism resembles the rounded ‘head’ portion of a keyhole (Fig. 3). The enamel crystallites run parallel to the long axis of the prism and in the ‘tail’ portion the enamel crystallites are inclined away from the long axis of the enamel prism. Enamel is laid down in layers which produce incremental growth lines. After each successive layer the ameloblasts retreat so as not to be trapped within their matrix. Some growth lines mark daily deposits which are about 4 µm thick; these are called cross striations.

Features of enamel

The following features of enamel are significant:

■ Brown striae of Retzius: these are brown lines indicating variations in weekly deposits that run obliquely from the amelo-dentinal junction towards the enamel surface. When the striae emerge on to the enamel surface a series of grooves may be seen; these are termed perikymata grooves.

■ Hunter-Schreger bands: when viewed under a light microscope, broad dark and light bands can be seen running obliquely from the amelo-dentinal junction to two thirds of the thickness of the enamel. They are curved with the convexity of the curve always facing rootwards.

■ Neonatal line: since this line marks the disruption in amelogenesis at birth, it can only be seen in primary teeth and first permanent molars. It can provide an important forensic landmark.

■ Enamel spindles: these are seen where the dentinal tubules extend into the enamel and are found most frequently beneath cusps.

■ Lamellae: these are sheet-like faults that run vertically through the entire thickness of the enamel.

■ Enamel tufts: these are pieces of incomplete mineralised enamel that resemble tufts of grass. They extend from the amelo-dentinal junction and follow the direction of the enamel prisms.

■ Amelo-dentinal junction: the enamel and dentine meet at the amelo-dentinal junction; this junction has a scalloped appearance.

 

 

 

Dentine

Physical characteristics of dentine

Dentine is mineralised tissue forming the bulk of the tooth. It underlies the enamel in the crown area and is covered by the cementum in the root area. Dentine is pale yellow in colour and is harder than bone and cementum but not as hard as enamel.

Chemical composition of dentine

Dentine consists of 70% inorganic material (by weight) of which the main inorganic component is hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂). Organic material constitutes 20% (by weight). The main organic component is collagen fibres embedded in amorphous ground substance. The remaining 10% (by weight) is water.

Structure of dentine

Dentine consists of many dentinal tubules that run parallel to each other, following a double curved course, and extend from the pulp to the amelo-dentinal junction. Each dentinal tubule contains an odontoblast process surrounded by intercellular ground substance composed of fine collagenous fibrils. The odontoblast cells are a layer of closely arranged cells on the pulpal surface of the dentine with their nuclei situated at the basal (pulpal) end of each cell.

Features of dentine

The following features of dentine are significant:

■ Peritubular dentine: this is highly mineralised dentine found within each dentinal tubule surrounding the odontoblast process and can be visualised as similar to ‘furred’ pipes.

■ Interglobular dentine: these are areas of dentine that remain unmineralised.

■ Incremental lines: these are produced due to the rhythmic pattern of dentinogenesis often referred as contour lines of Owen. These lines are seen when dentinogenesis is disrupted (as with amelogenesis).

■ Neonatal line: this is only seen in primary teeth and first permanent molars as a line that marks dentine formation before and after birth.

■ Granular layer of Tomes: this is a narrow layer of granular dentine found in root dentine immediately beneath the cementum.

Age changes in dentine

Dentine is a living tissue and with age more dentine continues to form slowly; this dentine is termed secondary dentine. Secondary dentine is laid down at the pulpal end of the primary dentine. As a result of this the pulp chamber reduces in size with age. Peritubular dentine tends to increase with age, reducing the diameter of the dentinal tubules. The tubules may also become completely obliterated and when this happens the dentine becomes more translucent; this is termed translucent or sclerotic dentine.

Reparative dentine

Reparative dentine or irregular secondary dentine is laid down on the pulpal surface of the dentine in response to an external stimulus, e.g. caries, cavity preparation or excessive wear. Following a severe stimulus, the odontoblast process may be destroyed and the contents of the tubule then necrose, leaving the dentinal tubule empty; this is termed a dead tract.

Dentine hypersensitivity

There are many theories for the mechanism of dentine sensitivity. The principal current theories are:

■ Innervation theory: the nerve fibres of the pulp pass into the dentinal tubules.

■ Odontoblast receptor theory: the odontoblasts act as receptors, transmitting nerve impulses.

■ Brannstrom’s hydrodynamic theory: this suggests that there is movement of fluid within the dentinal tubules.

 

 

FIGURE 1-7. A low-power view of dentin and pulp—the odontoblastic layer is healthy and intact. The accumulation of reparative dentin is expected in response to the adjacent cavity preparation.

 

Role of Dentin.

It is apparent then that a number of factors, individually or collectively, may be a source of sensitivity and pulpal irritation in restorative dentistry. It is fortunate that dentin itself provides a certain degree of protection. If the thickness is adequate, it provides thermal insulation, and inhibits penetration of deleterious agents from restorative materials or via microleakage. However, the precarious situation is the deep cavity in which the remaining dentin is in the order of 2 mm or less. As a matter of fact, in the deep preparation, a microscopic pulp exposure may actually be present with no apparent clinical symptoms.

There is yet another facet that must be recognized. Dentin is a dynamic structure with constant fluid exchange throughout the structure. Any changes in the fluid content or the equilibrium of the fluid pressure (the hydrodynamics) can result in a pulpal reaction. This can occur by undue desiccation of the surface or by pressure exerted in the placement of a restoration.

It is timely at this point to note that the instrumentation involved in cutting a cavity preparation produces a tenacious layer of debris, particularly on the dentin. This thin layer, approximately 5 to 10 μm, is referred to as the smear layer, as seen in Figure 1-7. Naturally this debris can prevent bonding of a dental adhesive agent. However, it may provide additional protection to the dentin and the pulp from a potential irritant.

 

Cementum

Physical characteristics of cementum

Cementum is a pale yellow, calcified tissue covering the root dentine. It is softer than dentine and can easily be worn away, resulting in exposure of the dentine. Its thickness varies according to location; it is thickest towards the apical third of the root and thinnest cervically.

Chemical composition of cementum

Cementum is 65% by weight inorganic (mainly hydroxy-apatite), 23% organic (mainly collagen) and 12% water.

Structure of cementum

Cementum has a similar structure to bone. It may be classified by the presence or absence of cells:

■ Acellular cementum: it is the first cementum to form and is sometimes termed primary cementum. It covers the root dentine from the cemento-enamel junction to near the root apex and does not contain cells.

■ Cellular cementum: this is found as a thin layer at the apical third of the tooth. It is sometimes termed secondary cementum. As cellular cementum develops, the cementoblasts which have created the cementum  become embedded within the cementum matrix and become inactivated; these cells are termed cementocytes. Cementocytes are contained in lacunae and their tiny processes spread along canaliculi to join up with other cementocytes. Their processes are directed towards the periodontal ligament, from which they obtain nutrients.

Features of cementum

The following features of cementum are significant:

■ Cemento-enamel junction: this can be variable. In approximately 60% of teeth the cementum overlaps the enamel; in approximately 30% of teeth the cementum and enamel meet exactly; and in approximately 10% of teeth the cementum and enamel do not meet, thus leaving an area of dentine exposed.

■ Functional changes of cementum: cementum formation continues throughout life. The attachment of the periodontal fibres in cementum can alter according to the functional needs of the tooth. Movement of teeth during orthodontic treatment or eruption can result  in the periodontal fibres becoming rearranged and reattached in a new position.

■ Resorption of cementum: this is not fully understood; it can affect individual or groups of teeth. Resorption of cementum occurs when teeth are placed under excessive masticatory stress or orthodontic loading.

■ Hypercementosis: this is an increased thickening of cellular cementum. Chronic periapical inflammation around the apex of a root or excessive occlusal attrition may give rise to localised hypercementosis. Hypercementosis affecting all the teeth may be associated with Paget’s disease.

■ Ankylosis: this is a term used when the cementum of a tooth is fused with the alveolar bone of the tooth socket.

■ Concresence: this is used to describe when two teeth are fused together by cementum.

 

Dental pulp

The dental pulp is surrounded by dentine and is contained in a rigid compartment.

Functions of pulp

The dental pulp has the following functions:

■ At late bell stage the cells at the periphery of the pulp differentiate into odontoblasts forming dentine.

■ It provides nutrients to the odontoblasts. (trophic function )

■ It acts as a sensory organ especially when dentine is exposed. The pulp rapidly responds to stimuli such  as caries and attrition by laying down reparative or reactionary dentine. (reparative function)

■ It mobilises defence cells when bacteria enter it. (protective function)

■ Cells proliferating in the pulpal tissue create pressure; this is thought to play a part in tooth eruption.

Shape and form

Pulp is a soft vascular connective tissue occupying the centre of the tooth. The shape of the pulp approximately follows the shape of the outer surface of the tooth. The pulp is made up of a pulp chamber in the crown and root canals extending the length of the root. The shape and number of root canals can vary considerably. At the apex of each root is a foramen or foramina through which blood vessels, nerves and lymphatics pass. Small projections of the pulp are found under each cusp; these are known as pulp horns or cornua.

Cellular structure     

The pulp has a gelatinous consistency containing cells and intercellular substances.

Odontoblasts can be found at the periphery of the pulp. At the time of eruption, a cell-free zone known  as the basal layer of Weil often develops beneath the odontoblasts; deep to this zone can be found a cell-rich zone which contains a plexus of capillaries and nerves. Fibroblast cells are very numerous within the pulp and has function to produce collagen. Defence cells (histiocytes) or fixed macrophages are the main defence cells found within the pulp. When the pulp is inflamed, histiocytes become free macrophages. Polymorphonuclear leucocytes can also be found in response to inflammation.

Intercellular substances

The intercellular substances consist of fibres and amorphous ground substance, blood vessels and nerves. Collagen fibres are scattered throughout the pulp and provide support to the pulpal tissue. The amorphous ground substance is a gelatinous substance that gives the pulp its shape. The pulp has a very rich supply of blood. Arterioles enter the pulp through the apical foramen and then ascend towards the crown area, giving off several branches which anastomose (join together) with other arterioles. The arterioles terminate in a dense capillary plexus under the odontoblasts and drain into venules; these leave the pulp through the apical foramen.

Both non-myelinated and myelinated nerve fibres enter the pulp through the apical foramen and generally follow the blood vessels. When the nerve fibres ascend towards the crown area they branch towards the periphery of the pulp and subdivide, forming a network of fibres known as the plexus of Raschkow just beneath the cell-free layer of Weil. Some fibres cross the cell-free layer of Weil, passing through the odontoblasts and pre-dentine layer, and enter the dentinal tubules.

Age changes

The primary changes in ageing are:

■ A reduction in volume due to continuing dentine formation throughout life.

■ A change in content resulting in more collagen, a reduced cellular content and a reduced nerve supply, making the pulp less sensitive. Irregular calcifications (pulp stones) can be found but have little clinical significance except when undertaking root canal therapy.

 

Periodontal ligament

The periodontal ligament is a specialised fibrous connective tissue that surrounds the root area of the tooth. It consists mainly of collagenous fibres.

It has the following functions:

■ It provides a support mechanism for the tooth; it cushions teeth against excessive occlusal  forces, preventing damage to the blood vessels and nerves at the root apex.

■ It maintains the functional position of a tooth by keeping the teeth in contact and prevents the tooth from drifting or tilting.

■ The periodontal fibres undergo continuous change. Its cells form, maintain and repair the alveolar bone and cementum.

■ Sensors in the periodontal ligament provide proprioceptive input, detecting pressures on the tooth.

■ The periodontal ligament has a rich supply of blood, which provides nutrients to the cementoblasts.

Development and structure of the periodontal ligament

At the late bell stage, the Hertwig’s root sheath grows apically, mapping out the shape of the root. When the root dentine has formed, Hertwig’s root sheath degenerates, allowing cells from the dental follicle to come into contact with the root dentine; these cells differentiate into cementoblasts. Once cementum formation has begun, collagen fibres within the dental follicle orientate themselves into bundles and the ends become embedded into the developing surface of the cementum and alveolar bone; these are known as Sharpey’s fibres. The periodontal ligament is made up of two groups of fibres: the gingival fibre groups and the principal fibre groups (Fig. 5).

 The gingival fibre groups of the periodontal ligament include:

■ Dentino-gingival fibres (free gingival fibres) are attached to the cementum and fan out into the gingival tissue.

■ Trans-septal fibres run horizontally from the cervical area of one tooth to the adjacent tooth.

■ Alveolo-gingival fibres arise from the alveolar crest and run coronally into the attached and free gingiva.

■ Circumferential fibres (circular) encircle the neck of the tooth.

■ Alveolar crest fibres run from the cervical cementum to the alveolar crest.

 

 

                                                                     

The principal fibre groups of the periodontal ligament are:

■ Oblique fibres which run obliquely from alveolar bone to tooth.

■ Apical fibres which radiate from the apex of the tooth to the adjacent alveolar bone.

■ Horizontal fibres which run horizontally from the cementum to the adjacent alveolar bone.

■ Inter-radicular fibres which are found between the roots of multi-rooted teeth and run from the root to the adjacent alveolar bone.

The predominant cells found within the periodontal ligament are fibroblasts. Cementoblasts cover the surface of the cementum and osteoblasts and osteoclasts cover the surface of alveolar bone. Remnants of the disintegrated Hertwig’s root sheath remain into adult life and can be found between the collagen fibres of the periodontal ligament. They are known as the epithelial cell rests of Malassez.

The blood supply runs along the long axis of the tooth close to the wall of the socket between the principal fibre bundles. Branches are given off, forming a network of capillaries that encircles the tooth. The nerves follow the pathway of the blood vessels.

Two types of nerve fibres are present: sensory nerve fibres responsible for pain and pressure and autonomic nerve fibres running alongside blood vessels and controlling the blood supply.

 

The normal periodontium

The periodontium (periodontal tissues) hold the teeth in the mouth and surrounds the teeth. The normal periodontium consists of:

 

■ The gingiva. ■ Bone. ■ Cementum. ■ The periodontal ligament.

 

Saliva and salivary glands

 

Saliva and other oral fluids play significant roles in supporting the health of soft and hard tissues in the oral cavity. The protective functions of saliva include maintaining a neutral oral pH, cleaning and remineralizing the dentition, facilitating swallowing and digestion, and protecting oral tissue against dessication and invasion by microorganisms. Dentists are keenly aware that adequate saliva is essential for maintaining oral health, and that reduced salivary secretion (hyposalivation) can contribute to multiple oral problems, such as dental caries, mucositis, fungal infections, and periodontal diseases. Along with protecting oral tissues, saliva has long been considered a “mirror of the body” that generally reflects the state of a patient’s overall health. A wide range of systemic diseases, such as diabetes and Sjögren’s syndrome, have oral manifestations that dentists encounter in patients at various stages of development. Based on these factors, dentists are ideally situated to monitor and treat oral disease progression, impaired salivary status, and various oral complications associated with systemic conditions.

Produced in salivary glands, saliva is 98% water, but it contains many important substances, including electrolytes, mucus, antibacterial compounds and various enzymes. The digestive functions of saliva include moistening food, and helping to create a food bolus, so it can be swallowed easily. Saliva contains the enzyme amylase that breaks some starches down into maltose and dextrin. Thus, digestion of food occurs within the mouth, even before food reaches the stomach.

The most important glands of the oral cavity are the salivary glands. The principal salivary glands are the parotid  (situated buccal to the upper molars), submandibular and sublingual, located in the floor of the mouth (Fig. 6). There are, in addition, some minor salivary glands on the surface of the tongue, the internal surfaces of the lips and in the buccal mucosa. The parotid glands produce a serous secretion, the submandibular glands produce a mixture of serous and mucous and the sublingual glands produce a mainly mucous secretion. Secretion is under the control of the autonomic nervous system which controls both the volume and type of saliva produced. Saliva passes through the intercalated ducts, then the striated ducts and finally through the excretory ducts which carry the saliva to the oral cavity.

 

 

 

Saliva has important functions :

1.  Cleanses the mouth due to the bactericidal action of lysozyme and IgA (immunoglobulin A [one of the immune system’s antibodies] ) plus the constant backward flow towards the oesophagus .

2.  Creates a feeling of oral comfort by it’s lubricating action .

3.  Dissolve food chemicals so that they can stimulate the tongue’s taste buds .

4.  Help to form a bolus (ball of food) by the action of mucins thus facilitating swallowing .

5.  Contain a digestive enzyme called salivary amylase (ptyalin) which starts the process of breaking down complex starchy sugars.

The majority of oral secretions are contributed by the sub-mandibular and parotid glands, which equally provide 80 to 90 per cent of the saliva. The remainder is formed by sublingual and minor salivary glands. Secretion of saliva ranges from 500 ml to 2000 ml – daily production. Saliva contributes to the digestion of food and to the maintenance of oral hygiene. Without normal salivary function the frequency of dental caries, gum disease (gingivitis), and other oral problems increases significantly.

 

Fig. 7 Overview of the relationship between the various functions of saliva and the salivary constituents involved. A number of salivary proteins participate in more than one function.

 

Constituents of saliva

The composition of saliva is subject to individual variation. It consists of 99.5% water and 0.5% dissolved substances.

 Salivary proteins. These include:

1.                Glycoproteins (mucoids): lubricate oral tissues; the acquired pellicle provides tooth protection.

2.                 Enzyme amylase: converts starch to maltose.

3.                 Lactoferrins: ferric iron is an essential microbial nutrient; lactoferrins bind to ferric ions, producing an antibacterial effect.

4.                 Lysozomes: attack the cell walls of bacteria, protecting the oral cavity from invading pathogens.

5.                 Sialoperoxidase (lactoperoxidase): controls established oral flora by controlling bacterial metabolism.

6.                 Histatins: inhibit Candida albicans.

7.                 Statherin: inhibits precipitation of calcium phosphates.

8.                 Proline-rich proteins: encourages adhesion of selected bacteria to the tooth surface. They inhibit precipitation of calcium phosphates.

9.                 Salivary immunoglobulins: produce protective antibodies which help to prevent infection.

What is oral fluid?

Oral fluid is the liquid present in the oral cavity. Oral fluid is a mixture of saliva and “oral mucosal transudate”. For opposite, saliva is a pure secrection of salivary glands. Oral mucosal transudate enters the mouth by crossing the buccal mucosa from the capillaries. Oral fluids contain both pathogens and antibodies. It can contain remnants of food as well.

 

 

Information was prepared by Levkiv M.O.