Dental Pulp: Morphology and Function

Dental Pulp

• Soft connective tissue occupies the central portion of the tooth, also known as the pulp space.
• Dentin surrounds it on all sides, other than at the apical foramen & accessory pulp canals, communicating with periodontal soft tissue.

Deciduous Pulp Organs

• These function for 8 years and 3 months.
• The duration is divided into three periods.
• Growth period: From root formation's start to its completion.
• Maturation period: From root completion until root resorption begins.
• Regression period: From the beginning of root resorption until tooth exfoliation.
• Permanent pulp organs require a longer development time compared to deciduous ones.

Morphology of pulp

• The pulp is comprised of two parts.
• Pulp chamber: Pulp cavity portion in the crown/coronal part.
• Coronal pulp within the pulp chamber.
• Radicular canal/Root canal/Root canal system: Pulp portion within the root.
• Radicular pulp found along the roots.

Pulp Horns

• These are extensions of the pulp chamber located under the cusps of teeth, specifically the buccal and mesiobuccal cusps.
• Pulp horns are important in restorative dental procedures.

Apical Foramen

• The opening of a root canal can vary in shape, size, and location, depending on functional changes.
• Average size: 0.3 – 0.4 mm.

Extra Root Canals

• This is also known as Accessory, lateral, secondary canals or apical ramifications.
• Canals develop in any part of the root, mainly in furcations (in multirooted teeth) or the apical third.
• The canals can spread infection between the pulp and periodontal ligament in both directions.
• Numerous small canals along the apical thirds, typically called apical ramification.

Dental Papilla

• The dental papilla develops into the pulp organ.
• Development begins around the 8th week of embryonic life.
• Young dental papilla are highly vascularized with a well-organized network of vessels during early dentin formation.
• Includes undifferentiated mesenchymal cells & stellate-shaped fibroblasts.

Distinct Zones of the Pulp

• The pulp contains four distinct zones:
• Odontoblastic zone/dentin-forming zone: Located at the pulp periphery, adjacent to the dentin.
• Cell-free zone/zone or basal layer of Weil: Lies beneath the odontoblastic layer.
• This area involves mobilization and replacement of odontoblasts.
• Cell-rich zone: High cell density.
• The Cell-rich zone is seen in coronal pulp between the cell-free zone and pulp core.
• The Cell-rich zone comprises mainly fibroblasts & undifferentiated mesenchymal cells.
• Pulp core/Pulp proper: Contains major vessels and nerves of the pulp.

Cellular Elements

• Odontoblasts: Tall, columnar cells in the peripheral pulp area with oval nuclei at the pulpal end.
• Tomes fibers extend into the dentinal tubules.
• Fibroblasts: Most numerous cell type, responsible for collagen fiber formation.
• They have a typical stellate shape with extensive processes.
• Defense cells: Play a role in inflammation.
• Histiocytes/Macrophages: Adventitial cells, possess dark oval nuclei with granulated cytoplasm.
• Pulp macrophages function in inflammation.
• Undifferentiated mesenchymal cells: Pluri-potential cells that can develop into any type of connective tissue under stimulus.
• Ameboid wandering cells: Possess dark nuclei.
• They migrate to inflammation sites from the bloodstream.

Pericytes

• Rouget’s cells feature round or oval nuclei outside the endothelial wall, which is where endothelial cells are located.
• Pericytes function as contractile cells, reducing the size of the vessel lumen.

Intercellular Substance

• Fibers:
• Precollagenous fibers, Argyro phil, Reticular, or Korff’s fibers, which are minute rope-like.
• Corkscrew-shaped structures lie among the odontoblasts.
• These structures are essential for dentin matrix formation, acting as the initial dentin deposition along the cusp tips.
• Collagenous.
• Gelatinous ground substance: The jelly-like material suspends the cellular & fibrous pulp elements.

Blood Vessels

• Abundant blood vessels within, including arteries & veins.
• Vessels originate from the superior and inferior alveolar arteries and veins.
• Vessels enter through the tooth's apical foramen.

Nerves

• Nerves enter through the apical foramen, following the course of blood vessels, which travel along the central pulp core.
• Parietal layer of nerve or nerve plexus of Raschkow.
• It consists of nerve fibers from superior and inferior alveolar nerves, which innervate the odontoblastic layer.

Lymphatic Vessels

• Vessels collect waste, impurities & possess valves.

Functions of the Pulp

• Inductive: Induces enamel organ formation.
• Formative: Functions in the production of Dentin.
• Nutritive: Nourishes the dentin through the Odontoblasts.
• Protective/Sensory: Elicits pain. Sensory nerves respond to stimuli, preventing tooth damage.
• Reparative/Defensive: Achieved by the cellular pulp elements to form:
• Morphotic response produces tertiary dentin & sclerotic dentin.
• It provides a protective barrier to stimuli outside the tooth.
• Inflammatory response through defense cells (histiocytes, ameboid wandering, & undifferentiated mesenchymal cells).
• The cells are activated when an inflammatory process occurs.

Changes in the Pulp in Relation to Senility

• Secondary dentin formation and recession of pulpal horns occurs with age.
• Decreases size of the pulp cavity
• Pulp horns become less visible.
• Pulp stones (pulp nodules or denticles) are calcific deposits.

Denticles Classification by Histological Structure

• True denticle: Structure of true dentin, with irregularly arranged dentinal tubules.
• False denticles: Consist of concentric lamellae of calcified tissues (calcium salts).
• Mixed type: True and false denticle combination.

Denticles Classification by Location

• Free denticle: Completely surrounded by the pulp.
• Attached denticle: Partially fused to the dentin wall.
• Embedded denticle: Entirely surrounded by the dentin.

Denticles Classification by Form

• Nodular has a rounded mass of irregular shape.
• Amorphous has indefinite form.
• Fibrillar (Diffused) is elongated calcification, following the course of blood vessels & nerve.

Possible Causes of Pulpstones

• Degenerated cells, sometimes surrounded by calcium salts.
• Remnants of HERS stimulating true dentin formation.
• Atrophy of the pulp causes decreased pulp size because of decreased structural contents.
• The pulp sometimes has a reticular atrophy appearance.
• Fibrosis of the pulp increases fibrous elements but decreases cellular elements.

Clinical Considerations

• Form and size of pulp cavity must be considered in operative procedures and root canal therapy.
• Young individuals have wider pulp cavities with prominent pulp horns, making deep cavity preparation a risk.
• Older individuals need root canal treatment due to smaller pulp canals.
• Older individuals are less sensitive because of degenerative changes in the pulp tissue.
• Proximity of Pulp stones to blood vessels may cause pain due to impingement.
• Pulp stones can interfere with root canal therapy by obstructing the root canals.
• Free pulp stones are removed by Pulp extirpation.
• Accessory root canals (if infected/neglected) could cause infection in periodontal tissues.
• Periodontal infections may infect the pulp through accessory canals.
• Operative procedures with heat production may injure the odontoblast & pulp.
• Chemicals from filling materials may harm the pulp.
• Pulp capping or pulp amputation may treat exposed pulp, especially in young patients.