Dental Pulp and Root Anatomy

• The dental pulp is a specialized connective tissue located within the pulp chamber and root canals which forms dentin on the walls of pulp by odontoblasts.
• At the apical constriction of the root canal, the dental pulp transitions into the periodontal ligament.
• The periphery of the dental pulp contains a layer of columnar, polarized odontoblasts between the pulp and dentine.
• The periphery contains nerve terminals of trigeminal afferents and specialized dendritic antigen-presenting cells which detect external stimuli and initiate a response.
• The loose connective tissue supports the other components of the dental pulp.

Root Anatomy

• The apical foramen, located at the root's end, allows nerves and vessels to enter the tooth as a neurovascular bundle.
• Accessory canals branch from the main canal, especially in the apical third of the root and are most commonly seen in posterior teeth.
• Furcation foramina are small vascular canals that enter the pulp chamber from the bone between the roots in multirooted teeth.

Dental Pulp Composition

• The dental pulp consists of 75% water and 25% organic materials, including cells and ECM.
• Loose connective tissue contains cells embedded in an extracellular matrix of fibers in a semifluid gel.

Extracellular Matrix (ECM)

• The ECM contains versatile polysaccharides and proteins secreted by cells to form a framework or scaffold for tissue function and structure.
• The matrix actively controls cell activity, including development, migration, division, shape, and function.
• Collagen makes up 25–32% of the dry weight.
• The ECM has fiber and non-fiber components.

ECM Fiber Components

• Primarily collagen type I (60%) and type III (40%) create fibrils of 50 nm diameter, thinly and irregularly scattered, forming 3-5% of pulp's wet weight.
• Fibers arrange in parallel along the forming predentine surface at the periphery.
• Small amounts of collagen types V and VI form a meshwork of fine microfibrils, with type IV being nonfibrous and present in blood vessel basement membranes.
• Fibronectin, a glycoprotein in various forms, anchors cells and influences their shape.
• Noncollagenous beaded microfibrils of 10–14 nm diameter, formed from fibrillin, are associated with elastic fibers.

ECM Non-fiber Components

• Macromolecules comprise the nonfibrous component of the extracellular matrix, including proteoglycans, glycoproteins, and unbound glycosaminoglycans.

Glycosaminoglycans (GAGs)

• GAGs consist of unbranched polysaccharide chains of repeating disaccharide units.
• include chondroitin sulfate, dermatan sulfate, heparan sulfate, and hyaluronic acid.
• Hyaluronic acid (60% in mature pulp) is the major GAG, and is the only GAG unbound to protein in the greatest quantity.
• GAGs covalently bind to a protein core, forming proteoglycans that make gels.
• In developing pulp, chondroitin sulfate is the major GAG.

Proteoglycans

• Proteoglycans are diverse molecules where some contribute to the matrix bulk and may bind to fibers or other nonfibrous components.
• Syndecan contributes to the basement membranes of epithelially derived cells like Schwann and endothelial cells.

Glycoproteins

• Glycoproteins, fibronectin and tenascin, are in the pulp and concentrated near the odontoblast layer.
• Four groups of cell adhesion molecules are recognized: immunoglobulin superfamily, selectins, cadherins, and integrins.

Cells

• The organic matrix contains odontoblasts, fibroblasts, immune cells, and some stem cells.

Odontoblasts

• Odontoblasts are columnar, polarized, fully differentiated cells
• Postmiotic cells can't divide, having a long process inside the tubule.
• Insulted or injured odontoblasts result in the death of odontoblasts.

Polarization

• Asymmetrical polarization indicates the plasma membrane contains different invaginations which divide the cell into compartments with different functions.
• There are small processes link adjacent odontoblasts and other pulp cells such gap junctions, desmosomes and tight junctions.
• The cell body is 50µm long and 5-10µm wide, with the nucleus sitting in the basal (pulpal) half and organelles like the rough endoplasmic reticulum, Golgi complex, and mitochondria above it.
• Histological sections of odontoblasts look like multilayered columnar cells defined as pseudostratified columnar cells because cutting an oblique results in multiple layers.
• Cervical root sections appear cuboidal, and apical root sections appear spindle shaped.

Odontoblast Functions

• Odontoblasts secrete dentine.
• They create a barrier to reduce toxins reaching the pulp by numerous cell-to-cell junctions that limit its permeability.
• They allow tissue fluid from the pulp to enter the dentinal tubules (outward washing pressure) controlling fluid composition.
• Odontoblasts produce proinflammatory mediators in response to bacterial toxins.
• They produce cytokines such as interleukin (IL)-8, which recruits neutrophils in case of injury.

Cell-to-Cell Junctions

• Cell-to-cell junctions maintain the integrity and limited permeability.
• Desmosomes (macula adherens junctions) have a clear intercellular component, intracellular anchoring fibrils, and are largely responsible for mechanical union.
• Gap junctions allow small molecules to move directly between cells and are important in cell-to-cell communication, synchronizing odontoblast activity.
• Tight junctions appear as a near fusion of cell membranes, limiting cell layer permeability.

Age Changes

• Throughout life, odontoblasts deposit secondary dentine, decreasing the size of the pulp chamber and root canals.
• The odontoblast layer becomes flatter, transitioning from columnar to cuboidal and spindle-shaped, declining in number by apoptosis with age.
• Half of the odontoblasts in a premolar die within 4 years after root formation.

Fibroblasts

• Fibroblasts are abundant cells that form a loose network with adherens-type junctions and gap junctions.
• Their morphology is highly variable, stellate shape, with arms linking fibroblasts to fibroblasts or odontoblasts.
• Fibroblasts functions slowly produces fibers and ground substances, degrade extracellular matrix, matrix turnover, and produce growth factors and cytokines.

Immune Cells

• Immune cells include T-cells, macrophages, and dendritic cells.
• T-Lymphocytes are small numbers in normal pulp and numbers increase when the pulp is injured.
• Macrophages have different morphologies and are widely distributed in big numbers, denser around blood vessels and odontoblasts.
• Dendritic Antigen Presenting Cells have three or more branching processes, some extend in tubules and are in close relationship with odontoblasts.

Stem Cells

• Stem cells reside in different locations and the subodontoblastic layer contains odontoblast progenitors.
• These progenitors can differentiate into only one kind of cell and can be isolated and directed to differentiate into different cell types for regenerative purposes.

Blood Vessels

• Blood supply (arterioles and venules) is related with the nerve and becoming neuro vascular bundle.
• Enters the tooth from the apical foramen and lateral canals, branches in the peripheries and in the crown until they reach the coronal part branch profusely making up plexus.
• Larger vessels are 150 um in diameter.
• Arterio-venous and venous-venous anastomoses allow rapid changes in blood perfusion.
• Terminals of sympathetic nerves are in association with arteriole's smooth muscles to control the arteriole Vasoconstriction.
• High pulpal blood flow of 20-60ml/minute per 100g of tissue creates high fluid pressure, defending pushing pathogens out through dentinal tubules.

Capillary Plexus

• Profuse branching happens within the coronal pulp chamber, ending with Subodontoblastic capillary plexus
• Capillaries are 6-8μm in diameter.
• Within and beneath the odontoblastic layer and between the odontoblasts and predentine
• 4-5% are fenestrated, with rapid movement of materials out of the capillary.

Visualizing Blood Vessels

• Blood vessels under the microscope appear as circles and if it is arteriole will have a thick wall because of the muscles around it, and venule has a thin wall.

Lymphatics

• Lymphatics are like any another tissue but are hard to observe.
• Can know from the lumen, the arterioles and venules maybe have RBCs, lymphatics don't.

Nerves

• Nerves enter as part of the neuro-vascular bundle, and are heavily innervated, branching in the coronal part of the pulp to form the Plexus of Raschkow, ending around the odontoblastic layer.
• The plexus is evident after tooth eruption.
• Branches then enter the dentinal tubules.
• Many axons in the tubules lack Schwann cells (unmyelinated) at the peripheries of dentine and among odontoblastic bodies, which facilitates response to stimuli.

Nerve Fibers

• There are two types of inner nerve fibers:
• 25% myelinated afferents, where cell bodies lie in the trigeminal ganglion. About 90% of these are Aδ fibers (1-6µm) and they sense sharp pain. The remaining myelinated nerves are Aβ fibers (6-12µm) in diameter. -75% Unmyelinated C fibers are the majority trigemenal afferents for dull pain and scarce sympathetic efferents to control arterioles for contraction of smooth muscles.

Dental Pulp Regions

• Pulp contains 5 regions: Supraodontoblastic region, Odontoblastic layer, Subodontoblastic region, Cell free zone of Weil and the Bulk of the pulp.

Supraodontoblastic Region

• Located between odontoblastic cell bodies and predentine but appear shrunken in prepared sections.
• Contains unsheathed axons (predentinal plexus of Bradlaw).
• Predominantly in crown, not a true plexus, but an area for axon congregation and entry into tubules.
• Dendritic antigen-presenting cells or their processes are also present.

Cell Free Zone

• It contains cell processes of fibroblasts and antigen-presenting cells, axons, and capillaries.
• Described as an anuclear zone.
• Absent from the radicular pulp and usually appears in the coronal pulp of erupted teeth

Cell Rich Zone

• The cell-rich zone implies is full of cells.
• Either because shrinkage pulls cells or because Subodontoblastic capillary plexus/Subodontoblasticneural plexus, as we see Schwann cells and endothelial cells. There are many other cells.

Bulk of The Pulp

• Pulp is formed by the ECM with fibroblasts and we can find capillaries, lymphatics, and nerve supply.
• The central area of the pulp is generally loose CT.

Aging of the Pulp

• Pulpal size decreases (in crown and root) with age as secondary dentin forms, characterized by decreased vascularity, more fibrous tissue, reduced innervation, and calcification (pulp stones or small specs of snow storm calcification).

Pulp Stones

• Can be single or in groups and can be be detected on radiographs.
• They can be true (resemble dentine (tubular)) or false (resemble bone (trapped cells) or lamellated (layers)) denticles.