What Are the Functions and Zones of Dental Pulp?
The crown of a human tooth consists of three sections. The outermost layer is called enamel, the layer beneath it is called the dentin, and the innermost layer is called the pulp.The dental pulp can be termed a vascular yet soft connective tissue present in the tooth and the reason for the perception of the tactile stimulus of the tooth. It acts as a support to the dentinal tooth layer. The various functions of the pulp are listed below:
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The Formation of the Dentin Layer and Its Nutrition Supply - This is provided by the vascular pulp region. Dentin formation remains the most critical function of the pulp, for which it also acts as a support system.
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Defensive Functions - The pulp mainly forms new dentin, creating a barrier between the various decay lesions, bacterial ingress, external harmful foreign bodies, or irritants.
What Are the Different Zones of the Pulp?
According to histological analysis, the pulp can be mainly divided further into the zones listed below:
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Odontoblastic Zone - The odontoblast cells present primarily in the outer peripheral region of the pulp are involved in dentin formation.
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Weils Zone or Cell Free Zone - This layer is next to the odontoblast layer of the pulp and contains very few cells, nerves, capillaries, etc. This is the area where the odontoblasts get constantly replaced and undergo mobilization as well.
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Cell Rich Zone - As the name suggests, this zone is composed of various types of cells like fibroblasts, undifferentiated mesenchymal stem cells, immune defense cells, accessory cells, etc. This layer is highly vascular not only because of these cells but because it is innervated by blood capillaries and the subododontoblastic neural plexus.
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The Pulp Core - This comprises the bulk structure of the pulp, with the central region integrated by blood vessels and nerves.
What Are the Different Types of Pulp Cells and Their Functions?
The functions of each type of pulp cell found in these zones are as follows:
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Odontoblast Cells - The odontoblasts, the most representative or distinguished dental pulp cells, are usually present in layers. These layers of odontoblast cells can be visualized histologically along the interface between the dental pulp tissue and the dentin. Odontoblast acts as a natural barrier between the mineralized tissues, the dentin, as well as the soft tissue layers of the dental pulp, which is the main source of tooth vitality. The odontoblasts, due to their presence within the periphery of the dental pulp, exhibit certain unique morphological characteristics essential for the functions of the pulp. The cytoplasmic processes extending from the odontoblast processes into the dentinal tubules have a significant role in sensory communication between these two layers of pulp and dentin.
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Fibroblasts - Fibroblasts are the most abundant cells in dental pulp tissue. They are responsible for carrying out the physiologic functions of the pulp. The fibroblasts being much more numerous, usually within the coronal pulp region, are part of the cell-rich zone of the pulp. The main functionality of the fibroblast cell layer is not only formative in nature but also beneficial in maintaining the extracellular matrix region in the pulp. It is composed of collagen and a ground matrix substance. In younger individuals, the pulp region has a comparatively higher fibroblast activity, and hence the matrix synthesis is more. This fibroblast activity diminishes as age progresses. This can also be attributed according to histopathological research that suggests the effect of aging on fibroblast cells of the dental pulp. While in younger individuals, the fibroblasts are oval-shaped with a pale stained nucleus possessing fine granular chromatin and abundant cytoplasm, in contrast, in aged individuals, the fibroblasts tend to morphologically alter as flattened spindle-shaped cells with the cytoplasm content much reduced with a flattened nucleus alongside condensed chromatin as per histologic observations. With aging, which is a normal physiological process, the main ability of the fibroblasts to synthesize various mediators of inflammation, such as IL (interleukin)-6, IL-8, vascular endothelial growth factor (VEGF), etc. Usually, in response to various attacks or bacterial invasions as immune defense, these reduce naturally.
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Undifferentiated Mesenchymal Cells - These are the cells of the dental pulp which play a crucial role in the regenerative processes of the pulp.
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Accessory Immune Cells - Macrophages, lymphocytes, antigen-presenting cells (dendritic cells), mast cells, and plasma cells are highly pivotal in their functions for the phenomenon of phagocytosis as maintaining immune defense.
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Other Immune Cells - In the healthy dental pulp, other cells also exist, such as a very small number of T lymphocytes, B lymphocytes, plasma cells, etc. For example, in inflammatory disease conditions of the dental pulp, the number of lymphocytes and plasma cells naturally tend to increase. A minor count of leukocytes or white blood cells, especially neutrophilic and eosinophilic granulocyte cells, increases substantially as part of the oral immune defense of the tooth to protect against bacterial ingress or to prevent the infectious process of pulp from aggravation. Similarly, the mast cells are important immune cells found in most connective tissue types of the oral cavity. It is not only present in the dental pulp but also plays a role in immune defense mechanisms and is present in the periodontal ligament and gingiva as well.
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Dental Pulp Stem Cells - These are mesenchymally derived cells that can be isolated from the dental pulp of both adult and deciduous dentition. These stem cells, especially within the postnatal dental pulp, not only have a good capacity for self-regulation, but given the appropriate environmental conditions, these stem cells can further have the potential for differentiation into odontoblasts, adipocytes, chondrocytes, neurons, etc. Recent research shows that these cells also have a marked ability to differentiate into osteoblasts. This is representative of the fact that dental pulp stem cells can indeed hold a promising future in the field of bone regeneration.
Conclusion
To conclude, the pulp occupies the center of each tooth and is composed of soft connective tissue. The pulp is present in the pulp chamber within the crown and the root canal of the root. The pulp present in the crown is called the coronal pulp, and the pulp present in the root is called the radicular pulp. The cell population is varied and of great functionality in the human dental pulp. Apart from preserving the tooth's vitality and functions, the cells of the pulp are also involved in immune defense, protection, and the tactile response of the tooth to any stimulus.
