Dental Pulp Structure and Function

Dental Pulp

• The dental pulp is a specialized, delicate connective tissue filling the center of each tooth.

Outline

• Introduction
• Definition
• Morphology
• Histological Structure
• Function and age changes

Definition

• The dental pulp is specialized loose connective tissue within the tooth's center.

Morphology

• Coronal Pulp: Located in the pulp chamber, extends towards the tooth's biting surface (incisors/cusps) forming pulp horns.
• Radicular Pulp: Extension of the coronal pulp into the root, tapering to the apical foramen.
• Apical Foramen: Opening at the root tip connecting the pulp to the periapical tissues. The pulp tissue is continuous with periapical tissue through the apical foramen.
• Accessory Canals: Canals extending from the radicular pulp to the periodontal ligament (numerous in the apical third of the root).
• Mechanism of Accessory Canal Formation: Occurs where developing roots encounter large blood vessels; early degeneration of Hertwig's epithelial root sheath; lack of complete union of tongue-like processes.
• Maxillary Teeth: 0.4mm
• Mandibular Teeth: 0.5mm
• Gradual decrease in size of root canal and apical foramen with age due to cementum and dentin deposition.

Histology of the Pulp

• Cells: The dental pulp is made of cells.
• Fibers: The dental pulp also contains fibers.
• Intercellular Substances: The dental pulp contains intercellular substances.
• Blood Vessels and Nerves: The dental pulp involves blood vessels and nerves.
• Pulp zones: Four zones emerge as you move from the dentin-pulp junction toward the pulp cavity center.

Pulp Zones

• Odontogenic Zone:

  • Odontoblastic Zone: Adjacent to pre-dentin containing cell bodies inside the pulp and processes inside dentinal tubules.
  • Cell-free Zone: Area beneath the odontoblastic layer, also referred to as Weil's zone. Contains nerve plexus and capillaries. Area of odontoblast mobilization & replacement. More prominent in coronal (crown) pulp.
  • Cell-rich Zone: Lies below the cell-free zone, composed of fibroblasts and undifferentiated mesenchyme cells.

• Pulp Core: The center of the pulp cavity.

Cells of the Pulp

• Synthetic cells (formative cells): Odontoblasts and Fibroblasts
• Defensive cells: Macrophages, lymphocytes, eosinophils, mast cells, and plasma cells.
• Progenitor cells: Undifferentiated mesenchymal cells (UMC).

Odontoblasts

• Single layer at the pulp periphery, extending processes into dentinal tubules.
• Attached to each other by desmosomes.
• Columnar shape in the crown, cuboidal in the root, and flat at the root apex.

Fibroblasts

• The most numerous pulp cells; spindle-shaped.
• Elongated processes connecting with other fibroblasts (stellate appearance).
• Synthesis and degradation of fibers and ground substances.
• Large in young pulp; appear smaller and round/spindle-shaped with few organelles in aging. Then termed "fibrocytes".

Histiocytes (Macrophages)

• Irregular shape; short, blunt processes.
• Nucleus is smaller and rounder, darker staining than fibroblasts.
• Involved in defense mechanisms; engulf foreign bodies and bacteria.

Plasma Cells

• Seen in inflammation
• Nucleus is small, eccentric in the cytoplasm
• Arrangement of chromatin gives a cart-wheel appearance.
• Produce antibodies.

Lymphocytes

• Show great variation in size and shape.
• T lymphocytes are common; B lymphocytes are few.
• Small ones have a darkly stained, rounded nucleus with little cytoplasm; large cells have eccentric kidney-shaped nuclei.

Eosinophils

• Found in normal pulp and increase during inflammation.

Mast Cells

• Round nucleus; cytoplasm with granules.
• Produce histamine and heparin.

Progenitor Cells (UMC)

• Smaller than fibroblasts; similar appearance.
• Found along blood vessel walls.
• Have the potential to develop into other formative or defensive cells.

Ground Substances of Pulp

• Consist of acid mucopolysaccharides and neutral glycoprotein.
• Provide an environment conducive to cell life.

Nerves of the Pulp

• Pulp is richly innervated.
• Nerves enter via the apical foramen along with blood vessels, forming the neurovascular bundle.
• Two Types of Nerve Supply:
  • Autonomic Sympathetic Nerve Fibers: Regulate blood flow and control blood vessel contraction/dilation.
  • Sensory Nerve Fibers: Involved in pain perception.
  • Involved in sensation of pain and cannot differentiate between other sensations like heat, touch, pressure and chemicals.
• Sub-odontoblastic Plexus (Raschkow): Extensive plexus of nerves in the cell-free zone below odontoblast cell bodies (crown). This is also called the parietal layer of nerves.
  • Consists of large myelinated A-fibers and small unmyelinated C-fibers.

Dental Pain (Pulpitis)

• Inflammation of the dental pulp, usually caused by bacterial infections.
• Two forms: reversible and irreversible pulpitis.

Types of Dental Pain

• Sharp, Stabbing Localized Pain (Reversible Pulpitis): Rapidly conducted by A-delta fibers. Pain is localized, stabbing, and easily detected.

  • Caused by hydrodynamic stimuli (drilling, sweet foods, cold air).

• Slow, Diffuse, and Referred Pain (Irreversible Pulpitis): Conducted by slower C fibers. Pain is not clearly localized and arises from deeper structures in the pulp.

  • Often aching. Increases in intensity after a hot drink.

• Pulp cannot differentiate between heat, touch, pressure or chemicals. This is because the pulp organs lack receptors for those stimuli.

Function of the Pulp

• Inductive: Dental papilla (part of the tooth) induces enamel organ development and determines tooth morphology.
• Formative: Pulp organ produces dentin; odontoblasts create the pulp's organic matrix and participate in its calcification.
• Nutritive: Pulp nourishes dentin. Odontoblasts and their processes are responsible for the transportation of nutrients. The blood vessels carry nutrients and oxygen throughout the pulp.
• Protective: Pulp's sensory nerves provide an alarm system reacting to all stimuli. Pain sensation is a primary way of detecting problems inside the pulp.
• Defensive or reparative: Pulp reacts to irritation by producing reparative dentin, walling off the pulp and engaging cells like macrophages, lymphocytes and leucocytes for repair.

Age Changes of the Pulp

• Size: Continuous secondary dentin deposition leads to a reduction in pulp size, reducing risk of pulp exposure during procedures.
• Cellular Elements: The number, size, and quantity of organelles in pulp cells decrease, especially in UMC causing reduction in pulp's reparative capacity.
• Vascular Changes: Decrease in blood vessel number, increased vessel wall diameter, and calcification around blood vessels occur.
• Neural Changes/Vitality: Loss and degeneration of nerve axons. Nerve axons' degeneration leads to reduced pulp sensitivity.
• Pulp Calcification: Localized calcification is either true or false denticles, while diffuse pulp calcification occurs on top of previously existing hyaline degeneration
• Additional factors include, but not limited to, fibrosis, and secondary dentin production (growth of dentin underneath the pulp)