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Description : The structure of the dentin-pulp complex

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Published on : Dec 10, 2023 | Views : 948 | Downloads : 0

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The structure of the dentin-pulp complex Made by a student: Таклу мохаммед халил 4th year, 18th group (34)
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The structure of the pulp Тhe dental pulp is formed by cells which are implicated in the secretion and reorganization of a collagen-rich extracellular matrix (ECM). Pulp cells play a crucial role in the synthesis and in the ECM molecules remodeling: In the dental pulp, a series of characteristic cells have been identified. The pulp stromal fibroblasts, also named pulpoblasts by Baume , constitute the most abundant pulp cell population. In addition, other cell lineages have been recognized in the pulp: specifically progenitors (also named stem cells, or side population) and neuronal, vascular, and immune system cells. Resident structural cells are permanently subjected to renewal and apoptosis. This cell population includes stem cells, which are acting as progenitors. According to some researchers, in the dental pulp, a ~9 % positivity was found for STRO-1, a stem cell marker, whereas according to Kenmotsu et al. between 0.11 and 0.40 % of the pulp cells are stem cells
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ZONES OF THE PULP: Odontoblast Layer Subodontoblastic Area: Cell-Poor Zone Cell-Rich Zone Central Layer - Pulp Proper CELLS OF THE PULP: Odontoblast Pulp Fibroblast Macrophages Dendritic cells Lymphocyte Mast Cell
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The peripheral aspect of dental pulp, referred to as the odontogenic zone (1), differentiates into a layer of dentin-forming odontoblasts (A). Immediately subjacent to the odontoblast layer is the cell-free zone (of Weil). This region (2) contains numerous bundles of reticular (Korff's) fibers (B). These fibers pass from the central pulp region, across the cell-free zone and between the odontoblasts, their distal ends incorporated into the matrix of the dentin layer. Numerous capillaries (C) and nerves (D) are also found in this zone. Just under the cell-free zone is the cell-rich zone (3) containing numerous fibroblasts (E) - the predominant cell type of pulp. Fibroblasts of the pulp have demonstrated the ability to degrade collagen as well as form it. Perivascular cells (undifferentiated mesenchymal cells) are present in the pulp and can give rise to odontoblasts, fibroblasts or macrophages. Since odontoblasts themselves are incapable of cell division, any dental procedure that relies on the formation of new dentin (F) after destruction of odontoblasts, depends on the differentiation of new odontoblasts from these multipotential cells of the pulp. Lymphocytes, plasma cells and eosinophils are other cell types also common in dental pulp. Medial to the cell-rich zone is the deep pulp cavity (4) that contains subodontoblastic plexus (of Raschkow; parietal layer) of nerves (G).
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Innervation: The existence of peripheral “nociceptive” (pain-detecting) sensory neurons forms the basis for pain, and pain sensations of varying qualities and intensities are evoked by activation of the intradental nerves innervating teeth. Noxious stimuli in teeth are transmitted in primary afferent neurons located in the trigeminal ganglion via second-order neurons in the brain stem to the brainز Regardless of the nature of the sensory stimulus (i.e., thermal, mechanical, chemical, electric [e.g., pulp tester]), almost all afferent impulses generated from pulp tissue result in the sensation of pain. The innervation of the pulp includes: afferent neurons, which conduct sensory impulses, autonomic or efferent neurons, which provide neurogenic modulation of the microcirculation, inflammatory reactions, and perhaps regulate dentinogenesis.
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With the exception of the innervation of dentinal tubules, the bulk of dentin is devoid of sensory nerve fibers. Some fibers were found running from the subodontoblastic nerve plexus toward the odontoblast layer. However, these fibers do not reach the predentin; they terminate in extracellular spaces in the cell-rich zone, the cell-poor zone, or the odontoblast layer. Other fibers extend into the predentin and run through a dentinal tubule in close association with an odontoblast process. Most of these intratubular fibers extend into the dentinal tubules for only a few micrometers, but a few may penetrate as far as 100 μm. The area covered by a single such terminal complex often reaches thousands of square micrometers Intratubular nerve endings are most numerous in the area of the pulp horns, where as many as 40% of the tubules may contain fibers. The number of intratubular fibers decreases in other parts of the dentin, and in root dentin only about 1% of dentinal tubules contain fiber.
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1. Autonomic Nerve Fibers. Only sympathetic autonomics fibers are found in the pulp. These fibers extend from the neurons whose cell bodies are found in the superior cervical ganglion at the base of the skull. They are unmyelinated fibers and travel with the blood vessels. They innervate the smooth muscle cells of the arterioles and therefore function in regulation of blood flow in the capillary network. 2. Afferent (Sensory) Fibers. These arise from the maxillary and mandibular branches of the fifth cranial nerve (trigeminal). They are predominantly myelinated fibers and may terminate in the central pulp. From this region some will send out small individual fibers that form the subodontoblastic plexus (of Raschkow) just under the odontoblast layer. From the plexus the fibers extend in an unmyelinated form toward the odontoblasts where they then loose their Schwann cell sheath. The fibers terminate as "free nerve endings" near the odontoblasts, extend up between them or may even extend further up for short distances into the dentinal tubule. They function in transmitting pain stimuli from heat, cold or pressure. The subodontoblastic plexus is primarily located in the roof and lateral walls of the coronal pulp. It is less developed in the root canals. Few nerve endings are found among the odontoblasts of the root.
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Types of Pulp two types of dental pulp are located: 1. Coronal pulp (A) occupies the crown of the tooth and has six surfaces; occlusal, mesial, distal, buccal, lingual and the floor. Pulp horns (B) are protrusions of the pulp that extend up into the cusps of the tooth. With age, pulp horns diminish and the coronal pulp decreases in volume due to continued (secondary) dentin formation - often the result of continued masticatory trauma. At the cervix of the tooth the coronal pulp joins the second type. 2. Radicular pulp (C) extends from the cervix down to the apex of the tooth. Molars and premolars exhibit multiple radicular pulps. This pulp is tapered and conical. In a fashion similar to coronal pulp, it also decreases in volume with age due to continued dentinogenesis. Pulp passing through the apical foramen may be reduced by continued cementum formation.
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The structure of dentin Dentin consists of a basic substance permeated with dentine tubules, in which the processes of odontoblasts are located. Dentine tubules are thin tubes running radially from the pulp of the tooth to the enamel or cement. The lumen of the tubule is filled with an odontoblast process, which is surrounded by dentine fluid. The main substance of dentin is calcified tissue with a large number of collagen fibers. There are peritubular dentin (directly surrounds the dentine tubules) and intertubular dentin (located between the tubules). Peritubular dentin is much more dense. There is also a raincoat (outer) dentin – collagen fibers are located radially in it (Corfe fibers), and near–pulpar (inner) dentin - collagen fibers are located tangentially in it (Ebner fibers). Calcification of dentin is uneven, hydroxyapatite crystals are located in the form of globules (lumps), respectively, interglobular dentin is also distinguished (there are no calcium salts in its composition). Dentin consists of calcified intercellular substance permeated with dentine tubules containing processes of odontoblasts, whose bodies lie on the periphery of the pulp. Intertubular dentin is located between the tubes. The periodicity of dentin growth determines the presence of intercellular substance in it. The intercellular substance of dentin is represented by collagen fibers and the main substance (containing mainly proteoglycans), which are associated with hydroxyapatite crystals. The latter have the form of flattened hexagonal prisms or plates with dimensions of 3-3.5 x 20-60 nm and are much smaller than hydroxyapatite crystals in enamel. Crystals are deposited in the form of grains and lumps, which merge into globular formations – globules or calcospherites.
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Secondary dentin: This is the layer of dentin formed around the pulp after complete root formation but in a slower rate compared to primary dentin and contains less dentinal tubules. Formation of secondary dentin is not uniform; there is more deposition on the floor and roof of the pulp chamber, which causes pulp recession to protect pulp exposure in older teeth.
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Tertiary dentin: This dentin is formed as a reaction to particular stimuli and is subdivided into reparative and reactive dentin. Only the cells that are directly affected by the stimulus form it. The response of these cells depends on the intensity and the duration of the stimulus which in turn defines the quality and quantity of the dentin. 1.Reactionary dentin is formed by preexisting odontoblasts. 2.Reparative dentin is formed by newly differentiated odontoblasts.
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Sclerotic dentin: Particular stimuli during abrasion, erosion, caries, attrition and cavity preparation can cause protective changes in the existing dentin especially in older patients. In this condition, collagen fibers and apatite crystals deposit in the dentinal tubules causing the occlusion of dentinal tubules, which is similar to peritubular dentin. This is a defensive mechanism as it reduces the permeability of the dentin and prolongs the vitality of the pulp. The elasticity of sclerotic dentin is the same as dentin but the fracture toughness is less due to smaller crystals. This type of dentin appears glossy and it is mostly in the apical third of the root and in the crown midway between the DEJ and the surface of the pulp.
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The dentine tubules pass through the so-called dentine tubules. The wall of each dentine tube is formed by the so-called "peritubular dentin", which is characterized by a very high degree of mineralization and the absence of collagen fibers. Between the dentin tubes is the so-called "intertubular dentin", which is characterized by a lower degree of mineralization and a large number of collagen fibers (fibrils). Dentine tubules are hollow inside, and therefore they are often called dentine tubules. From the inside, each tube is covered from the inside with a thin layer of organic matter – this layer contains a high concentration of glycosaminoglycans and is usually called the Neumann membrane. The processes of odontoblasts (Toms fibers) are located in the center of the dentine tubules. The space between the odontoblast process and the wall of the dentine tube is filled with dentine fluid, which is similar in composition to blood plasma. In addition to the processes of odontoblasts and tissue Dentine fluid is a transudate of the peripheral capillaries of the pulp and is similar in protein composition to plasma; it contains. 18. also glycoproteins and fibronectin. This fluid fills the periodontal space (between the process of the odontoblast and the wall of the dentine tube), which is very narrow at the pulpary edge of the tube, and becomes wider in the direction of the dentine periphery
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Denticles are formations of dentine or dentine–like tissue formed as a result of mineralization of the crown and root pulp. The exact causes of their appearance have not been established to date, but with a high degree of probability, the process is triggered as a result of inflammation of the pulp, exposure to external stimuli, against the background of metabolic disorders and chronic diseases. The disease usually proceeds asymptomatically, and the dentures are detected absolutely by chance as a result of X-ray examination. In some cases, they compress the neurovascular bundles of the pulp, leading to the development of concrementous pulpitis, or obliterate the root canal. In this case, the removal of formations is carried out using an ultrasound endodontic device. Denticles (pulp stones, dentinoids, internal odontomas) are dense mineralized areas of pulp. The size of the formations can vary from barely noticeable foci to bodies 2-3 mm in diameter, which tend to merge and further fill the pulp chamber and root canals. Dentikli occur in patients of all ages, including young children. In studies, mineralized areas of pulp were found in embryos and in the rudiments of teeth in newborns. According to statistics, this phenomenon occurs in 39.9—53.9% of patients who go to the dentist. Moreover, in children under the age of 16, this indicator is much lower and is 4.4%. Usually, intact teeth with an erased chewing surface are subjected to the pathological process. Reasons for the appearance of dentures inflammation of the neurovascular bundle; dental injuries; dysfunction of the elements of the dentition; erasing the chewing surface of contact teeth; poor-quality dental treatment associated with the opening of the tooth cavity and excision of carious areas; improper metabolism in tooth tissues; age-related degradation of the pulp.
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Made by a student: Таклу мохаммед халил 4th year, 18th group (34)