The pulp
I-Definition :
The pulp is the specialized loose connective tissue, derived from the mesenchymal papilla occupying the central zone of the tooth; the pulp is surrounded at the coronal and radicular levels by mineralized dentin, it communicates with the periodontal structures at the apical orifices.
II-pulp formation:
The development of the pulp chronologically follows the mesenchymal papilla of the dental germ.
The papilla-pulp transition occurs at the end of the dental bell stage when the peripheral cells of the dental papilla differentiate to form primary odontoblasts, which deposit the first layer of pre-dentin.
At this stage, the differentiation into fibroblasts of the ectomesenchymal cells of the central papilla, the progressive increase in the density of collagen fibers in the extracellular matrix and penetration of nerve fibers into the pulp. The pulp will be surrounded at the coronal then radicular level by dentin.
The mature pulp is thus confined in an almost totally closed, inextensible space divided into a large portion inside the crown: the pulp chamber, and a portion located inside the root: the root canal.
III-Pulp morphology:
It is made up of two essential elements:
– the pulp chamber
– the different root canals.
A- The pulp chamber or the coronal portion
It reflects the shape of the tooth.
The tubercles and grooves that we see on the surface of the enamel have their correspondence at the pulp level: pulp horns and concavities.
It is limited at the top by the pulp ceiling; which reproduces the external shape of the occlusal face; and at the bottom by the pulp floor which only exists at the level of multi-rooted teeth.
B- The canal system or canal portion
This system is complex because if it is a root that has a single cylindro-conical canal and a single apical foramen, it is only an exception.
according to the DE DEUS classification of 1975 we distinguish: the main canal, the lateral canal, the secondary canal and the Accessory canal.
1-The main channel
It starts from the pulp floor and goes towards the end of the root, following its axis. It contains most of the pulp parenchyma.
Its caliber decreases from its origin to the level of the cemento-dentin limit where the “apical delta” exists as demonstrated by KUTTLER.
It is described as the superposition of two cones inverted with respect to each other:
– a long dentinal cone,
– a small cement cone
2-The lateral canal
It is an emanation of the main canal connecting the endodontium and the desmodontium at the level of the two coronal thirds.
Its axis is often perpendicular to the axis of the main channel.
3-The secondary channel
It arises from the main canal at the level of the apical third.
Its axis is oblique towards the apex compared to that of the main canal.
4- The accessory channel
It is a side branch of the secondary canal.
The accessory canals represent as many exit doors from the canal and as many pathways for the propagation of pulp inflammation.
I V-HISTOLOGY:
The pulp is made up of cells, an extracellular matrix, and vessels and nerves.
A-THE CELLS
They are dispersed in the low-density hydrated extracellular matrix, their distribution is not uniform: we distinguish a peripheral region called dentinogenetic and a central region.
Aa-The dentinogenic region
It is divided into three zones:
1-the peripheral zone made up of odontoblasts:
It is responsible for the synthesis of dentin during dental development, and its repair throughout the life of the pulp organ.
2-the acellular layer of WEIL (subodontoblastic zone or cell-poor layer) : it is approximately 40 µm thick, apparent especially at the level of the pulp horns, it contains some branched cytoplasmic extensions emitted by the underlying cells, it also contains the major part of the subodontoblastic capillary plexus and the terminal branches of the sensory and autonomic nerve fibers (RASCHKOW plexus).
3-The subodontoblastic layer of HOhL (zone rich in SCHOUR cells) : this is a thin zone rich in cells:
-fibroblasts with rounded or ovoid morphology.
– undifferentiated mesenchymal cells called HOhL cells found most often near vessels and having the potential to differentiate into odontoblasts if necessary.
-Dendritic immune cells.
This layer of HOhL is continuous with the central zone of the pulp.
Ab-The central region of the pulp
It consists of fibroblasts, undifferentiated mesenchymal cells and immunocompetent cells.
1-Fibroblasts: spindle-shaped or spiny cells, non-polarized, rich in intra-cytoplasmic organelles, and also containing a cilium whose base is located in the Golgi region.
Role: development and remodeling of the extracellular matrix of the pulp.
This renewal is ensured by the synthesis of type I and III collagen fibers, proteoglycans and glycoproteins. During aging they are transformed into fibrocytes which are cells with reduced activity, therefore containing fewer cellular organelles.
Fibroblasts can synthesize cytokines in response to various stimuli after insult, they are involved in the healing of pulp lesions.
2-Undifferentiated mesenchymal cells:
Large, polyhedral cells, with a large central nucleus and abundant cytoplasm and peripheral cytoplasmic extensions.
They are located in the subodontoblastic layer of HOhL and in the central pulp area always close to the blood vessels, they are in a latent state.
Role: depending on the stimulus, they could differentiate into odontoblasts or fibroblasts.
They ensure the regenerative potential of the pulp. With the aging of the pulp their number decreases and the defense potential of the pulp decreases (Piette and Goldberg)
3-Immunocompetent cells:
There are three types: dendritic cells, macrophages and T lymphocytes in a very small percentage.
3-1-Dendritic cells:
They constitute approximately 8% of the total pulp cell population with a dendritic cell/macrophage ratio of 4 to 1.
These are large cells (at least 50 µm), with at least three cytoplasmic extensions (or dendrites), they are connected to each other by the dendrites and form a continuous network throughout the pulp tissue.
Role: They capture antigens and migrate to the lymphatic glands where they present them to lymphocytes; these activated lymphocytes then return to the damaged pulp where they provide immunological monitoring in the event of representation of these same antigens (JONTELL et al 1988).
3-2-Macrophages:
Mainly located in the perivascular areas, they are large cells, oval or star-shaped, whose role in the elimination of dead cells,
phagocytosis, and presentation of antigens to lymphocytes.
3-3-lymphocytes:
T lymphocytes are rare in healthy pulp, and B lymphocytes are exceptionally encountered (Farges, Romeas et al.2003).
B- The extracellular matrix
B-1-The fundamental substance:
It is a colloidal gel, bound to protein-saccharide complexes, it contains glyco-amino-glycans, glycoproteins, elastin and matrix metallo-proteases.
The ground substance supports the cells.
B-2-Collagen
Collagens are the main types of fibrous components present in pulp connective tissue, they represent 34% of the total proteins in human pulp.
The most common is type I (56%), then type III (43%).
B-3-Glycosaminoglycans.
They represent about half of the matrix molecules of the pulp; they are long, unbranched polysaccharide chains composed of repeating disaccharide units.
Role: – their main role is water retention in the pulp.
-they provide mechanical support to tissues, while allowing the rapid diffusion of water-soluble molecules and the migration of cells.
-They provide protection for vascular and nervous elements.
B-4-glycoproteins:
Mainly represented by fibronectin, glycoproteins play a role in the binding of fibroblasts to the collagen fibrillar network.
Fibronectin has binding sites for collagen, glycoaminoglycans, and several adhesion molecules.
In addition, it plays a role in maintaining the specific morphology of odontoblasts, in their terminal differentiation and in the interactions between these cells (SELTZER AND BENDER).
B-5-Elastin:
It is found around the pulp arterioles, with a diameter greater than 100µm, it is responsible for the elasticity of the vascular walls.
B-6-Matrix metalloproteinases (MMPs):
These are zinc- and calcium-dependent enzymes that are involved in the degradation of components of the extracellular matrix of connective tissue, for example: collagenases, gelatinases and stramelysins (degradation of matrix components of pulp connective tissue, they are essential in the pulp remodeling process (physiological or during healing).
B-7-Lipids:
They represent 10 to 15% of the dry pulp weight, mainly represented by cholesterol in free form (30% of total lipids) and phospholipids.
C-Vascularization
C-1-Blood vascularization:
The pulp vascular network is extremely abundant, the main arteries enter the root canal through the apical orifice, then travel into the root canal where they present lateral ramifications which capillarize opposite the subodontoblastic zone where they describe loops and terminal loops.
C-2-Lymphatic vascularization:
The pulp lymphatic network has fine capillaries in the subodontoblastic zone that converge into larger vessels in the central zone. In the apical zone, the pulp lymphatic veins anastomose with the periodontal lymphatic veins. Lymphatic drainage occurs at the submental and submaxillary lymph nodes, then at the cervical lymph nodes.
D-Innervation
The pulp innervation is composed of sensory fibers from the trigeminal system and vasomotor fibers from the sympathetic system.
D-1Sensory fibers:
They enter the pulp through the apical orifices in the form of myelinated bundles. They travel in the root canal parallel to the vascular axes, they subdivide into a fan in the coronal pulp. The terminal ramifications are found in the subodontoblastic layer where they form a dense network: the RASHKOW plexuses. Then the filaments are distributed around the odontoblasts, some of them penetrate the predentin where they form loops by folding back on themselves. Some nerve ramifications penetrate the dentinal tubules, they travel in the pericytoplasmic space, parallel to the odontoblastic extension, then end by winding around the latter.
D-2-Vasomotor fibers
Coming from the sympathetic system, they have close relationships with the arterial and venous muscular bases, they control blood flow by constriction or dilation of the vessels, these fibers are devoid of a myelin sheath.
V-Histo-physiology
1 – the pulp constitutes the organ that produces dentin through the activity of its marginal zone throughout its life.
2-the pulp ensures metabolic exchanges of the entire dentin mass thanks to its rich vascularization.
3-defense role: the pulp ensures the defense role thanks to the activity of the defense cells that it possesses: dendritic cells , macrophages, and lymphocytes.
4-the pulp provides a large part of the dentin sensitivity thanks to the endings
Nervous.
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