Dental pulp

It is that highly specialized delicate connective tissue

structure occupying the center of each tooth

Development;

The name of tooth pulp is designated only after dentin formation around it. The tooth pulp in early stage of development is named dental papillae

the dental papilla controls early tooth formation and tooth morphology.

It is responsible for the invagination of the bud structure at the early stage of tooth development

the dental papilla is highly vascular and highly innervated with differentiated cells, odontoblasts and fibroblasts,

Sympathetic and parasympathetic nerves enter and follow the blood vessels.

Morphology of the pulp;

Pulp constitutes two anatomical portions;

1-Coronal pulp; it occupy the pulp chamber and its shape following the outer surface of the crown dentin extending from it pulp horns. By continuous deposition of secondary dentin , the pulp horn disappear.

2-Radicular pulp; it is that part occupying the root canal and its shape follow the dentinocemental junction. At the early time of root development , the epithelial diaphragm limited the apical part of radicular pulp as a wider opening . After root completion the radicular pulp become narrow and tapered to be continuous with the periodontal ligament through the apical foramen. The diameter of this foramen not exceed 0.3-0.4 mm

3-Accessory root canal; The radicular pulp may extend laterally in lateral small canals (Accessory root canal) toward the periodontal ligaments, they are mostly seen near to its apical portion. The actual cause of this canals

4- Apical foramen

PULP VOLUME

Histological structure :

The dental pulp is formed of specialize loose connective tissue. It is formed of cells, fibers, intercellular substances, blood vessels and nerves. The intercellular substance is dense and gel like in consistency and varies in appearance from finely granular to fibrillar. It is formed of acid mucopolysaccharides and glycoproteins.

Odontogenic zones

I-Cellular components:

The cells of the pulp may be divided into:

1-Progenitor cells: Undifferentiated mesenchymal cells.

2-Synthetic cells (formative cells): odontobtasts and fibroblasts.

3-Defensive cells: histiocytes (macrophages) small lymphocytes, eosinophils, mast cells and plasma cells.

II-fibers; collagen and elastic fibers

III-Ground substances

IV-Blood vessels

V- Nerves

VI- Lymphatics

VII- Functions

VIII- Age changes.

Peripheral zone

(odontogenic zone 3).

Central zone

(pulp core 1).

Zones of the pulp

Dentin

The odontogenic zone is composed of

1. Odontoblasts,

2. The cell free zone

3. The cell rich zone.

odontogenic zone:

B- cell free zone (the zone of Weil) The cell-free zone is a space in which the

odontoblast may move pulpward during tooth development and later to a limited extent in functioning teeth. This may be why the zone is inconspicuous during early stages of rapid dentinogenesis since odontoblast migration would be greatest at that time. The cell-free zone contains subodontoblastic plexus of nerves and vessels.

C- cell rich zone: The cell-rich layer

composed principally of

fibroblasts and undifferentiated

mesenchymal cells is restricted

to the coronal regions, as it is

formed during the pre-eruptive

phase of the tooth. During early

dentinogenesis

there are also many young

collagen fibers in this zone.

odontogenic zone:

A- odontoblasts:

1- Synthetic cells:

a-Odontoblasts: the odontoblasts are found adjacent to the predentin with the cells bodies in the pulp and cell processes in the dentinal tubules. They arc approximately 5-7u in diameter and about 25-40u in length. The shape and arrangement of the cell bodies vary with the stage of tooth development. It consists of a single layer of cells in the early stage of dentin formation where the cells are regularly arranged and of moderate length. In the later stages of development, the odontoblastic layer is much broader, the cells are less columnar and tend to be pyriform where the broadest pan of the cell contains the nucleus.

The length of the odontoblasts varies in different parts of the tooth. They are longer in the crown and then become cuboidal root wise, until the crown and then become cuboidal rootwise until the root apex, where they may be almost flattened. The odontoblasts lie very close to each other and the plasma membranes of adjacent cells exhibit junctional complexes. The clear terminal part of the cell body and the adjacent intercellular junction is shown as terminal bars. At this zone the cell enters the dentinal tubule.

During active dentinogenesis, the cell bodies contain well developed Golgi apparatus, the rough surfaced endoplasmic reticulum is more abundant and numerous mitochondria appear throughout the odontoblast and its process. Also a great number of vesicles are seen along the periphery of the process. While near the pulpal predentin junction the cell cytoplasm is devoid of organelles.

Immediately beneath the odontoblastic layer a cell free zone can often be demonstrated, Some believe that the cell free zone is the area of mobilization and replacement of odontoblasts. and this may explain why this zone is not clear during early stages of rapid dentinogenesis. Beneath the cell free zone, if present, there is a narrow zone of pulp tissue, this is a rich cell zone. The cell rich zone is composed mainly of fibroblasts and undiffemtiated mesenchymal cells. The odontogenic zone is composed of the odontoblasts, the cell free zone and the cell rich zone.

b- Fibroblasts:

These are the most numerous type of cells. They are spindle in shape with elongated processes which are widely separated and link up with those of other pulpal fibroblasts by gap junction. These processes give the cells a stellate appearance. The nucleus stains deep with basic dye and the cytoplasm is highly stained and homogenous.

These cells have a dual function (for both synthesize and degradation of fibers) in the same cell. In the young pulp, when they are producing collagen fibers and ground substances of the pulp they are large cells and have large multiple processes with centrally located oval nucleus, numerous mitochondria, well developed Golgi bodies and rough endoplasmic reticulum (protein secreting cell). Later in periods of less activity and aging these cells appear smaller and round or spindle-shaped with few organelles, they are termed fibrocytes.

Pulpal stem cells

Among the numerous stem cells that have been identified from dental tissues and

characterized, those from the pulpal tissues include dental pulp stem cells (DPSCs) and

stem cells from human exfoliated deciduous teeth (SHED).

The stem cells were shown to undergo proliferation and migrate to the site of injured

odontoblasts and produce dentin.

Growth factors, such as transforming growth factor (TGF-β1) and bone morphogenetic

proteins (BMP-2) were shown to be involved in the proliferation and differentiation, and

endothelial cell injury, in the migration of these stem cells in response to an injury. Though

pulpal stem cells are pluripotent, in that they were shown to develop into adipocytes and

neural cells.

A comparative study of bone marrow and dental pulp stem cells showed that they are

influenced by different regulatory mechanisms to produce osteogenesis and dentinogenesis

respectively. Dentin sialoprotein, a marker for dentin synthesis was observed in dental pulp

stem cell transplants while in bone marrow stem

cell transplants expression of fibro blastic growth factor and matrix metalloproteinase 9 were

observed. The dental pulp stem cells however differed from one another in the rate and

extent of dentin production. Dentonin, a peptide derived from matrix extracellular

phosphoglycoprotein showed its ability to

stimulate dental pulp stem cells.

The pulp tissue of the third molars may serve as a suitable source of stem cells for future

stem cell based therapies as they are found to be viable after cryopreservation.

2- Defensive cells:

a-Histeocyte or tissue macrophage cell: In light microscope, the cells appear irregular in shape with short blunt processes. The nucleus is small, more rounded and darker in staining than that of fibroblast. These cells are usually with small blood vessels and capillaries. Their presence is disclosed by intra-vital dyes such trypan blue. In case of inflammation, it exhibits granules and vacuoles in their cytoplasm and their nuclei, increase in size and exhibit a prominent nucleolus. Invaginations of plasma membrane are noted ultra-structurally with aggregation of vesicles or phagosomes which contain phagocytozed dense irregular bodies.

b-Plasma cells: These cells are seen during inflammation. The nucleus of this cell is small and appears concentric in the cytoplasm. The arrangement of chromatin in the nucleus gives the cell a cart wheel appearance, both mature and immature cells may be found. The mature type exhibits a typical small eccentric nucleus and more abundant cytoplasm. The plasma cells are known to produce antibodies.

c- Lymphocytes and eosinophils: They are found in normal pulp and they increase during inflammation.

d- Mast cells: .May be present, they have a round nucleus and their cytoplasm contains many granules. They are demonstrated by using specific stains as toluidine blue. It produce histamin

I- The fibers and ground substances:

The collagen fibers in an extracellular ground substances surround the cells of the pulp. Both types 1 and II collagen have been found in the pulp, both types are produced by fibroblasts. In young pulp the fibers are relatively sparse and delicate throughout the pulp and gradually the bundles increase in size with advancing age. Where in older pulp two patterns of collagen distribution can be seen, one is a diffuse collagen network with no definite orientation, the other is bundles of collagen. There are no elastic fibers in the pulp except those present in the walls of the larger blood vessels.

The ground substances consist of acid mucopoly saccharides and neutral glycoprotein these substances are the environment that promotes life of the cells.

Ill- Blood vessels and nerves:

The pulp is highly vascularized. It is supplied by the inferior and superior alveolar arteries and drained by the same veins in both mandibular and maxillary regions. The branches of alveolar arteries which enter the tooth and its supporting tissues are different in its structures.

As the vessels enter the tooth, their walls become considerably thinner than those surrounding the tooth. Small arteries which enter the apical canal run in a direct route to the coronal pulp. Along their course they give off numerous branches in the radicular pulp that pass peripherally to form a plexus in the odontogenic region. The pulpal blood flow is more rapid than in most areas of the body.

Structures of blood vessels:

The arteries of the pulp are branched into: arteriole, small arteriole, terminal arteriole and capillaries:

I - Arterioles:

1-The largest arteries of the human pulp are 50-100 microns (u) in diameter, it is formed of three layers.

a- Tunica intima: It consists of one layer of endothelial cells, which contact to each ether They appear overlapped to varying degrees. They are separated from the second layer by a basal lamina.

b- Tunica media: It consists of three layers of smooth muscle cells. A basal lamina surrounds and passes between these muscle cells and separates the muscle cell layer from the intima. Sometimes the endothelial cell wall is in contact with the muscle cells, called myoendothelial junction.

c- Tunica adventitia: It is made up of few collagen fibers forming a network around larger arteries.

2- Small arterioles with diameter of 20-30u contain one or two layers of muscle cells are common throughout the coronal pulp.

3- Terminal arterioles or pre-capillary arterioles with diameter l0-15u appear peripherally in the pulp. The ertdothelial cells of these vessels contain numerous micro-vesicles, which function in trans-endothelial fluid movement. These vessels contain single layer of muscle cells. Some times Rouget’s cell or pericyte lies on the surface of these vessels. Pericytes are capillary associated fibroblasts, and their nuclei can be demonstrated as round oval bodies associated with outer surface of these pre-capillaries. These cells are supposed to be modified muscular elements.

4- Blood capillaries are blood endothelial lined tubes with a diameter 8-lOu, the nuclei of these cells are lobulated and have cytoplasmic projecting in to the lumenal surface. The terminal network of the blood capillaries appears nearly perpendicular to the main trunk. This vascular network passes among the odontoblasts and underlies them. These capillaries show fenestration in its endothelial cells. This fenestration is important in rapid transport of metabolites at a time when the odontoblasts are active in the process of dentin matrix formation.

5- Veins and venules are larger than the arteries also appear in the central region of the root pulp. Veins measure 100-150u in diameter and their wall appear less regular and thin.

The endothelial cells, lining these vessels appear more flattened and do not project into the lumen.

The tunica media consists of one or two-layers of muscle cells. The adventitia is lacking or appears as fibroblasts and fibers blend with the surrounding pulp tissues.

6- Lymph vessels: it is endothelium lined tubes that join thin walled lymph venules or veins in the central pulp.

The larger vessels have an irregular-shaped lumen. Lymph vessels draining the pulp and periodontal ligament have a common outlet.

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

Nerves:

The pulp has an abundant nerve supply which follows the distribution of the blood vessels. Two types of nerve fibers are present:

1- The nonmyelinated nerves, which are found in, close association with the blood vessels of the pulp and are sympathetic in nature where they control the contraction of the smooth muscles present in their lumen.

2- Myelinated fibers which are sensory parasympathetic nerves and they carry sensation to the sensory cortex of the brain. The nerve fibers enter the apical foramen and divide into many branches till reaching peripherally the cell rich zone, where they lose their myelin sheath. The peripheral axons form a network of nerves located adjacent to the cell-rich zone. This is termed the “parietal layer of nerves” or plexus of Raschkow. These nerve fibers either terminate among or pass between the odontoblasts where they then terminate adjacent to the odontoblastic processes at the pulp predentin border or in the dentinal tubules. More nerve endings are found in the pulp horns than in other peripheral areas of the coronal or radicular pulp.

Sensory response in the pulp cannot differentiate between heat, touch, pressure, or chemicals. This is because the pulp organs lack those types of receptors. So the sensory nerve ending in the pulp are presumed to function in pain reception only.

Function:

1- Inductive:

Pulp a nlage (dental papilla) induces the enamel organ formation and also determines the morphology of the tooth formed whether an anterior or a posterior tooth.

2- Formative:

Pulp organ produces dentin. The pulpal odontoblasts develop the organic matrix and function in its calcification.

3- Nutritive:

The pulp nourishes the dentin. The nutritional elements are contained in the tissue fluid. Nutrition is mediated to the dentin through the odontoblasts and their processes.

4- Protective:

The sensory nerves in the tooth respond with pain to all stimuli such as heat, cold, pressure, chemical agents and operative cutting procedures. Pain sensation is a useful alarm system of the pulp.

5- Defensive or reparative:

The pulp that responds to irritation by producing reparative dentin and mineralizing any affected dentinal tubules. These reparative or defensive reactions are an attempt to wall off the pulp from the source of irritation. Also the presence of macrophages, lymphocytes and leucocytes aid in the process of repair of the pulp.

Age changes in the pulp

1- the size of the pulp chamber as well as the root canals is reduced. The apical foramen is wide open in the young tooth but becomes narrowed with age and is further constricted by cementum formation

2- the cellular elements are predominant, while with advancing age the pulp, becomes poorer in cells and shows

3- increase in collagenous fibrillar masses which are arranged in bundles, fewer undifferentiated cells available are for emergencies, so the defense and repair processes are slower in getting started.

3- the blood vessels and nerve bundles are also decreased.

4-Reticular atrophy: In these changes the odontoblasts are affected and tend to degenerate, in some areas of the pulp they may have completely disappeared, vacuoles may result. The total effect is the production of a lessened vitality of the pulp tissue and a lessened response to stimulation (reticular atrophy).

5-Pulp calcification : A further change associated with aging is the appearance of deposits of calcium in the pulp. These deposits may be in the form of localized masses known as pulp stones or denticles, sometimes large enough to be seen in an x-ray, or alternatively as diffuse calcification throughout the whole pulp. Denticles as well as diffuse calcification may be found also in young and normal pulp and they tend to increase both in size and number with advance of age. Pulp stones are classified, according to their structure as true and false denticles.

True pulp stone

Faults pulp stone

Free pulp stone

Attached pulp stone

Embeded pulp stone