Histology of Dental Pulp

Histology of Pulp

• The pulp is the vital, central part of a tooth.
• Without the pulp, a tooth cannot survive except with extensive and costly treatments.
• The pulp's structure is consistent with the tooth type.
• The pulp occupies a cavity surrounded by mineralized tissues.
• The coronal pulp is within the pulp chamber.
• The root pulp is located within the root canal(s).
• The pulp is composed of 75-80% water and 20-25% organic material.

Pulp Composition

• Cells:

  • Odontoblasts: These are the most distinctive cells, lining the outer edge of the pulp in the odontogenic zone, extending into dentin. They create dentin and have sensory functions.
  • Fibroblasts: Abundant in the cell-rich zone, these cells create and manage the extracellular matrix, which includes collagen and ground substance. Their activity is high in young pulps and diminishes with age.
  • Undifferentiated Cells: These cells are located in the cell-rich zone and pulp core. They have the potential to develop into odontoblasts or fibroblasts. Mesenchymal stem cells (MSCs) are a kind of undifferentiated cell that displays potential for regeneration.
  • Defence Cells: The pulp core possesses various cells like macrophages and lymphocytes (including T and B lymphocytes). The number of some leukocytes (white blood cells) increases during infection. Dendritic cells, found close to the odontoblast zone, play an immunosurveillance function, increasing in carious teeth (cavities).

• Extracellular Matrix:

  • Fibers: Primarily type I and III collagen fibers, whose abundance increases with age. The apical pulp area has the highest concentration of these fibers.
  • Ground Substance: The ground substance is a connective tissue-like material surrounding the pulp's cells, made of glycosaminoglycans, glycoproteins, and water.

Pulp Structure

• Zones: The microscopic pulp structure has four zones:
  • Odontoblast zone (lines the periphery of the pulp).
  • Cell-free zone (a space between zones with sparse fibers).
  • Cell-rich zone (contains most pulp cells, except odontoblasts).
  • Pulp core (contains blood vessels, nerves, and some cells).

Pulp Anatomy and Vascular/Nerve Supply

• Anatomy: The location and shape of the pulp cavity's components—such as the pulp chamber, pulp horns, and root canals—are adapted to the type of tooth.
• Vascular Supply: Blood vessels (arterioles and venules) enter and exit the pulp through the apical foramen and some accessory foramina, creating an extensive capillary network, especially in the coronal portion.
• Nerve Supply:
  • The pulp has a rich nerve supply entering through the apical foramen along with the vascular and lymph system.
  • The sensory afferent nerve fibers of the trigeminal nerve are the predominate component enabling pain perception
  • Sympathetic nerve branches help regulate smooth muscle and blood flow in the vascular vessels. The nerve bundles are myelinated and unmyelinated.

Pulp Functions

• Formative: The pulp forms dentin.
• Circulatory: The pulp's vascular network delivers nutrients and removes waste.
• Protective: The pulp's cells and structure defend against injury and infection.

Pulp Over Time

• As a tooth ages, secondary dentin formation gradually decreases the pulp size and the diameter of the apical foramen.
• This aging process leads to reduced circulation, innervation, the reduction of odontoblasts, and an increase in fibers and collagen.
• These changes reduce the pulp's ability to respond and repair.

Clinical Significance of the Pulp

• The pulp's capacity for repair in response to injury or stimuli is limited by the size of the apical foramen.
• Excessive or prolonged stimulation can cause irreversible pulp inflammation and tissue damage, often with consequent pain.
• Pulp necrosis can occur in severe cases, and it may be necessary to remove the injured pulp for the survival of the tooth.

Structural Anomalies

• Pulp Stones: Small calcified tissue spots, similar to dentin. They can interfere with endodontic treatments due to them reducing the cell content of the pulp.
• Accessory Canals: Disruptions in root development can lead to extra root canals, posing problems for bacteria ingress and both endodontic and periodontal procedures.

Clinical Application and Links to Other Sessions

• Pulp health or disease relates to a variety of dental procedures. The knowledge of pulp provides the basis to determine health, symptoms (pain history), differential diagnoses (differentiating between conditions), assessment of dental abscesses, and identification and treatment of periodontitis.