Category Archives: The Dental pulp

Age changes of the pulp

Posted by on February 8, 2012 1 comment

 

 Age changes of the pulp

 

 

1- Change in the size of the pulp cavity ;

The continuous secondary dentin deposition on the pulpal wall (especially the floor of the pulp chamber) leads to its gradual reduction in size and its irregularity by age.

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The apical foramen becomes also narrowed by cementum deposition. 

2-  Cellular changes:

By age, the cells of the pulp decrease in number. These cells are characterized by a decrease in size and number of various cytoplasmic organelles.

3-  Fibrosis:

In the aging pulp, there is gradual increase in the bundles of collagen fibers. These bundles may appear arranged longitudinally in the radical pulp and in a random diffuse arrangement in the coronal area. Some investigators suggested that this is an apparent increase of the fibers which is attributed to the decreased pulp size by age. Therefore, there is an increased fibers number per unit area, but their total over all volume is the same.

4-  Vascular changes:

In old pulp, the blood vessels and nerve bundles are also decreased. The diameter of the vessel walls becomes greater as collagen fibers increase on the medial and adventitial layers. Calcifications may appear in and around the walls of the blood vessels which is most apparent in the region near the apical foramen.

5. Pulp calcification.

Pulp stones or denticles are nodular calcified masses appearing in the pulp organ. They are classified according to their structure

as;                 

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-True denticles:

Its structure is similar to dentin. They exhibit dentinal tubules containing the processes of the odontoblasts that exist on their surface. They are rare and are usually located near the apical foramen.

It has been postulated that remnants of epithelial root sheath have become enclosed in the pulp as a result of local disturbance at the root apex during development. These epithelial remnants induce the cells of the pulp to differentiate into odontoblasts that form dentin masses of the true pulp stones. -False denticles :

These denticles do not exhibit dentinal tubules but appear as concentric layers of calcified tissue. Remnants of necrotic and calcified cells and calcification of thrombi in blood vessels may serve as nidus for the deposition of concentric layers in typical calcospherite form giving rise to small nodules, these nodules increase in size by incremental growth in their surface.

The surrounding pulp tissue may appear quite normal. They are seen more frequently in the coronal pulp.

 

 

-Diffuse calcifications:

They appear as amorphous irregular calcific deposits in the pulp tissue, usually following collagen fiber bundles or blood vessels. They are usually found in root canals and less often in the coronal area.

Diffuse pulp calcification commonly occurs on top of hyaline degeneration. They may develop into larger masses but usually persist as fine spicules.

Pulp stones are also classified according to their location in relation to the surrounding dentinal wall into free, attached, and embedded.

 

The free denticles are entirely surrounded by pulp tissue. The attached denticles are partly fused with the dentin. The embedded denticles are entirely surrounded by dentin.

 

All are believed to be formed free in the pulp and become attached or embedded as dentin formation progresses.

The incidence as well as the size of the pulp stones increase with age. 90% of teeth of persons after 50 years of age may show calcifications of some type.

Structure Of The Dental pulp 2

Posted by on February 7, 2012 No comments

Structure Of The Dental pulp 1

Structure Of The Dental pulp 2

 

• They are found usually in association with blood vessels.

• Mast cells are primarily involved in inflammation and immune mechanisms.

c) Plasma Cells :

It originates from plasmablast cells which develop from B-lymphocytes. These B- lymphocytes should be activated previously by specific antigens before their transformation into plasma cells.

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• They are small rounded cells with basophilic cytoplasm rich with organelles.

• The nucleus is eccentrically found and show cart-wheel arranged chromatin material.

• The cytoplasm also show rounded acidophilic bodies (Russell bodies) which represent the immunoglobulin granules and are secreted by the Golgi apparatus.

• They secrete specific antibody.

d) Leucocytes :

Blood leucocytes may appear in the pulp

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• Lymphocytes : increase in chronic inflammation.

• Eosinophils : increase in allergic conditions. They have large ovoid specific membrane-bound granules contain hydrolytic enzymes include histaminase.

• Neutrophils : migrate from blood vessels to the pulp
connective tissue in case of acute infections to phagocytose
micro organisms. -,,

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B. The Intercellular substance

(1) The ground substance

It is amorphous flexible gel like in form through which nutritive materials and metabolites may diffuse.

It is composed of:

a) Glycosaminoglycans (GAG) formerly called mucopolys­accharides. All normally occurring connective tissue GAG are demonstrated in the pulp. These are chondroitin-4- sulphate, chondroitin-6- sulphate, dermatan sulphate, heparan sulphate, keratan sulphate, and hyaluranan (the only without sulphate side).

) Proteoglycans (formerly known as mucoproteins). These are large macromolecules consist of a protein core with side chain of GAG and oligosaccharides. It constitutes 90-95% carbohydrate. During the active phase of dentinogenesis, chondroitin sulphate accouts for most GAG. In mature pulp, hyaluranan is the most predominant (60%).

(2) Fibers of the pulp

The fibers are of collagen type. These are the most predominent fibers. They are wavy branched bundles formed of fibrils which run parallel to each other in the fiber. 60% of the collagen fibers is present as type 1 collagen, while the remainder is type III collagen.

Type 1 collagen 100 nm diameter shows the characteristic 64 nm (640A°) cross striation.

Type III collagen is fine branched filaments 15 nm diameter which predominate in young pulp.

Both types are produced by the pulpal fibroblasts as tropo-collagen and become polymerized extracellularly to form collagen fibers.

There are no elastic fibers in the pulp except for those in the walls of the large blood vessels. It is also synthesized by the

fibroblasts in a precursor form (tropo-elastin) which undergo polymerisation in the extracellular tissue.

Other structural glycoproteteins are also found in the pulp including fibronectin and laminin. They are groups of fiber forming molecules composed of protein chains bound to a branched polysaccharides.

These glycoproteins are known to be associated with surface membranes and play a role in cell adhesion. It is sometimes seen as small (10 nm), non-striated filaments between the larger collagen fibers.

3. Blood Vessels of the pulp:

The pulp is extensively vascularized. It is connected with the vessels of the periodontium through the apical foramen and the accessory canals. As the blood vessels enter the tooth, their wall become thinner, and follow a direct course to the coronal pulp.

Along their course they send off numerous branches that pass peripherally to form a rich subodontoblastic capillary plexus. From this plexus, looping branches pass between the odontoblasts towards the predentin.

Pulpal blood flow is more rapid than in most areas of the body. This is perhaps due to the fact that pulpal pressure is among the highest of the body tissues.

A capillary plexus drains into relatively large thin-walled venules, which in turn are gathered together to form several small veins escaping through each apical foramen. The microscopic appearance of the veins is similar to the arteries except that they have much thinner walls in relation to the size of the lumen.

The presence of lymph vessels in the dental pulp is questioned by some investigators. However, with the EM, the evidence for their existence is largely circumstantial.

Lymph capillaries are described as endothelium- lined tubes that join thin-walled lymph venules or veins in the central pulp.

The lymph vessels draining the pulp and periodontal ligament have a common outlet.

Those draining the anterior teeth pass to the submental lymph nodes, those of the posterior teeth pass to the submandibular and deep cervical lymph nodes.

4. Nerves:

The abundant verve supply in the pulp follows the distribution of the blood vessels.

The majority of the nerve bundles of the myelinated fibers course direct to the pulp chamber where considerable branching takes place resulting in an interlacing network of fibres located adjacent to the cell-rich zone. This is termed the parietal layer of nerves or plexus of Raschkow. Fibres from this plexus ramify around the odontoblasts and may enter the dentinal tubules. More nerve fibers and endings are found in the pulp horns than in other peripheral areas of the pulp.

The nerve bundles of sensory afferents of the trigeminal nerve and sympathetic branches from the superior cervical ganglia. Each bundle contains both myelinated and non-myelinated axons.

The myelinated axons (large diameter) are associated with sharp localized pain, while the non-myelinated axons (small diameters) are associated with diffuse pain.

It was thought that the only sensation appreciated by the dentin-pulp complex is that of pain irrespective of the type of the stimulus. Now, there is evidence that the pulpal afferents can distinguish also mechanical, thermal and tactile stimuli.

Functions of the pulp:

1- Inductive:

The dental papilla (pulp analague) induces the oral epithelium to differentiate the dental lamina and dental organ.

It also determines the identity of the tooth formed, i.e. whether it is anterior or posterior.

2- Formative:

The pulp odontoblasts produce dentin.

3- Nutritive:

The nutritional materials pass from it to the dentin.

4- Sensory:

The pulp contains both sensory and motor nerve fibers. The sensory fibers are responsible for the sensitivity of the pulp and dentin.

5- Defensive:

In case of exposing the pulp to moderate degree of stimuli, it responds by formation of reparative dentin.

Structure Of The Dental pulp 1

Posted by on February 7, 2012 2 comments

Structure Of The Dental pulp 1 

 

The pulp tissue consists of

25%    organic material by weight

75%    water by weight

 

As any connective tissue, the pulp is composed of cells and intercellular substance. The intercellular substance consists of fibers and an amorphous ground substance of gelatinous consistency. In addition, there are blood vessels, nerves and lymphatics.

When the histology of the pulp is examined, different zones could be distinguished,

1.  Peripherally, the pulp is circumscribed by the specialized odontogenic region composed of the odontoblasts followed pulp-ward by,

2.  The cell free zone (zone of Weil) and,

3.  Cell rich zone, followed by

4.  The parietal region.

5.  The core or central region of both coronal and radicular pulp contains large nerve trunks and blood vessels.

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In the cell free zone the odontoblasts may move pulp-ward during tooth development and later to a limited extent in the functioning tooth, so it is inconspicuous during early stages of rapid dentinogenesis.

 

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The cell rich zone is densely packed with undifferentiated mesenchymal cells and fibroblasts. During early development, there are also many young collagen fibers in this zone.

The connective tissue of the pulp composed of: A. The cells      B. The intercellular substance

 

A. The cells of the pulp

 

The cells of the pulp include

1.  The undifferentiated mesenchymal cells

2.  The fibroblasts and fibrocytes

3.  The odontoblasts

4.  Defense cells

 

a)     Macrophages

b)    Mast cell

c)     Plasma cell

d)    Leucocytes (eosinophils, lymphocytes and neutrophils).

1)  The undifferentiated mesenchymal cells :

It is an embryonic branched cell, spindle in shape with large oval nucleus and basophilic cytoplasm. They can differentiate into other ceil types of the connective tissue when necessary (Toti potent cell).

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They are the primary cells, but few are seen in the pulp after tooth eruption. They are found along pulp vessels.

 

2)  The fibroblast and fibrocyte :

The fibroblast is the most numerous cell-type in the pulp.

•   It is stellate shaped branched cell with multiple processes with oval nucleus and basophilic cytoplasm.

•   E. M. examination reveals abundant RER, RNA, mitochondria, Golgi and other organelles which indicate that it is active protein synthetic cell.

•   There is some difference in appearance of these cells depending on the age of the pulp organ.

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• In young pulp, the cells divide and are active in protein synthesis. In the older pulp they appear rounded or spindle

shaped with short processes and exhibit fewer intracellular
organelles and termed fibrocyte.                                       s  .

• The fibroblasts form the pulp fibers and matrix. It also has the capability of ingesting and degrading this same matrix.

 

3) The odontoblasts :

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It is the second most prominent cell in the pulp.

□   They reside adjacent to the predentin with the cell bodies in the pulp and the cell processes in the dentinal tubules.

□   The cells are columnar in shape in the crown, cubiod in the middle of the root, and ovoid or spindle close to the apex.

□   The cell describes long oval nucleus basally situated.

□   The ultrastructural morphology of the active secreting and resting odontoblasts was described before (in the dentin section).

4) Defense cells :

 

a- Histocytes or Macrophages

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•   They are irregularly shaped branched cells with short blunt multiple processes and small round nucleus.

•   They stain with vital stain e. g. trypan blue.

•   In case of inflammation, they exhibit granules and vacuoles in their cytoplasm and their nuclei increase in size.

•   Under EM, they show RER, mitochndia, free ribosomes and the plasma membrane exhibits invaginations. The distinguishing feature of macrophages is aggregates of vesicles, which contain phagocytized bodies.

•   They play an important role in the defense mechanism and can engulf foreign bodies and bacteria.

•   They are usually associated with small blood vessels.

 

 

b) Mast cell:

• They are small round or oval cells that possess irregular

cell membrane.

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• The cytoplasm contains well developed Golgi, but few ER and eccentric nucleus.

 

It is also filled with large basophilic secretary granules. These granules contain sulphated glycosaminoglycans substance which is the precursor of heparin (a potent anticoagulant) and a protein substance which is the precursor of histamine (chemical mediator of inflammation).

The Dental pulp

Posted by on February 7, 2012 No comments

The Dental pulp

 

The dental pulp is a delicate loose connective thissue that occupies the center of each tooth.

It is derived from the dental papilla, of which is the part remaining after the formation of dentin.

In human, the development of the pulp begins at about the 8th week of embryonic life at the location of the incisor and then the more posterior teeth differentiate afterwards.

The cell density of the dental papilla is great and it is higly vascular. The cells appear as undifferentiated mesenchymal cells which gradually appear as stellate fibroblasts. The fibers are mostly fine collagen.

After differentiation of the odontoblasts from the peripheral cells of the dental papilla and dentin formation begins, the tissue is no longer called dental papilla, but designated as the pulp.

Few large myelinated nerves are formed in the pulp until the dentin of the crown is well advanced. The sympathetic nerves follow the blood vessels as the pulp begins to organize.

Form and Relations :

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In the fully formed tooth, the pulp organ is composed of a Coronal pulp located in the crown of the tooth, and a Radicular portion located in its root and is continuous with the periapical connective tissue through the apical foramen.

The shape of the pulp roughly corresponds with the external shape of the tooth. Under the cusps, it is prolonged into narrow projections called pulp horns which are especially prominent under the buccal cusp of premolar and the mesiobuccal cusp of the molar tooth.

During root formation, the apical root end is widely opened limited by an epithelial diaphragm. As growth proceeds, more dentin is formed and the apical end becomes narrower showing clearly defined apicaJ foramen.

The location and shape of the apical foramen may undergo changes as a result of functional influences of the tooth or cementum deposition.

Frequently, there are two or more foramina separated by a portion of dentin and cementum or cementum only.

The apical foramen of the human adult maxillary teeth is about 0.4mm average size, while that of the mandibular is about 0.3 mm.

Accessory canals leading from the radicular pulp laterally through the root dentin to the periodontal tissue may be seen any where along the root, but are most numerous in the apical third of the roots and especially in premolars. These canals contain pulp tissue, blood vessels and periodntal tissue. They are presumed to be caused by localized faiJure in the formation, or premature degeneration of Hertwig’s epithelial root sheath before differentiation of odontoblasts.

They may also occur due to persistence of abnormally placed blood vessel if the vessel is located in the area where dentin is formed, the hard tissue may develop around it making lateral canal.