Dental Pulp- Morphology, Histology, Structure and Function

Contents

What is Dental Pulp?

The Pulp is a soft mesenchymal connective tissue that occupies pulp cavity in the central part of the teeth.

it is surrounded by the hard dentin, enamel and cementum.

Morphology of the Pulp

The shape of the dental pulp is similar to that of the tooth.

It has coronal and radicular parts. The coronal pulp resembles the morphology of the crown.

The extension of the coronal pulp high into the cusps is known as pulp horn.

The radicular portion of the pulp is seen in the innermost part of the roots, where it is called the root canal.

There are lateral branches to these canals called the accessory canals.

At the apical end of the root canal is the opening called the apical foramen.

Through the apical foramen, the pulp communicates with the periapical tissues.

The average size of the apical foramen of maxillary teeth is 0.4 mm and mandibular teeth is 0.3 mm.

The volume of the pulp is very little—on an average, 0.02 cc per tooth. The total pulp 

volume of all the teeth is 0.38 cc.

• Read About

1. Pulp Vitality Tests with Classification and Recent Advances
2. Dentin- Microscopic Structure, Properties, Types and Functions

Histology of the Pulp

The coronal pulp when viewed under the microscope shows the following zones.

A. Odontoblastic zone

B. Cell-free zone of Weil

C. Cell-rich zone

D. Pulp core

A. ODONTOBLASTIC ZONE

Tall columnar odontoblasts are arranged in Palisading pattern forming a single layer in the  Peripheral area of the pulp.

Lines the outer pulpal  wall and consists of  the cell bodies of odontoblast.

B. CELL FREE ZONE OF WEIL

Cell-free zone of Weil appears as a space between the odontoblastic zone and the cell-rich zone.

There are no cells in this zone. However, there are a few fibres which run through this zone.

C. CELL RICH ZONE

Cell-rich zone contains numerous cells, fibroblasts being the highest population.

Undifferentiated mesenchymal cells, mast cells and macrophages are also seen.

D. PULP CORE

 It is central region of the pulp

Contains major blood vessels and nerve of the pulp

Pulpal cells and fibroblasts are also seen

1) Fibroblasts

These cells form the predominant group of cells in the pulp.

The shape of the fibroblasts varies from round to stellate/star shaped.

They secrete Types I, III, V and VI collagen and a wide range of non-collagenous extracellular matrix components, such as proteoglycans and fibronectin.

They synthesize and degrade collagen.

2) Odontoblasts

Second most numerous cells in the pulp.

The fully differentiated is a polarized columnar cell with Diameter- 5-7µm, Length- 25-40µm

Constricts to Diameter 3-4µm near pulp, taper to 1µm into dentin

Shape may vary

3) Undifferentiated Cells

These are totipotent cells which can differentiate into odontoblasts, fibroblasts or macrophages when the need arises.

They are found throughout the cell-rich area and the pulp core and are present in proximity to blood vessels.

4) Defence Cells

They are histiocytes, macrophages, dendritic cells, mast cells and plasma cells.

In addition, neutrophils, eosinophils, basophils, lymphocytes and monocytes are also seen.

they respond to situations that induce inflammation such as dental caries, mechanical and chemical irritation, trauma from occlusion, etc

5) Fibers

Collagen is the major organic component in the dental pulp

They range in length from 10 to 100 nm and exhibit cross striations at 64 nm 

The pulp contains type I and type III collagens, traces of V and VI are also found. 

Type I and III are found in the ratio of 55:45.

Collagen is synthesized and secreted by odontoblasts and fibroblasts

Odontoblasts secrete type I and fibroblasts secrete type III.

Elastic fibres are absent in pulp and is the reason for dental pulp being termed as specialized connective tissue.

TYPE I: Present as thick striated fibrils. Responsible for pulp architecture.

TYPE III : Thinner fibrils, mainly distributed in cell free and cell rich zone. Contributes to the elasticity of the pulp.

TYPE IV : Present along the basement membrane of blood vessels.

TYPE V & VI : Form a dense meshwork in the form of a thin fibril in the entire stroma of the pulp.

Collagen fibres arising from the pulp passing spirally between odontoblasts, enter the predentin

6) Ground Substance

The ground substances consists of acid mucopolysaccharides and neutral glycoprotein.

These substances are the environment that promotes life of the cells

Glycosaminoglycans are bulky molecules and hydrophilic, they form gels that fill most of the extracellular space

They contribute to the high tissue fluid pressure of the pulp

What is the pulp richly supplied with?

Blood Supply

Pulp is a highly vascular tissue

The velocity of blood flow and blood pressure is higher when compared to other tissues

Supplied by the Superior and the Inferior alveolar arteries

Pulp is a micro circulatory system which lacks true arteries and veins

The largest vessels are arterioles & venules which regulate the local interstitial environment

These arterioles undergo extensive branching to form ultimately small capillaries

The flow of blood in   

arterioles  -  0.3 to 1mm/sec

Venules    – 0.15mm/sec

Capilaries – 0.08mm/sec

Nerve Supply

The pulp has an abundant nerve supply.

Two types of nerve fibers are present

Sensory supply

They are involved in perception of pain and transduction

They are derived from the branches of the maxillary and mandibular divisions of the trigeminal nerve

They give out extensive branches near the cell-rich zone, forming the parietal layer of nerves or plexus of Raschkow

The plexus contains both large myelinated A-delta and beta fibres (2–5 μm in diameter) and the smaller unmyelinated C fibres (0.3–1.2 μm)

Autonomic Sympathetic Nerve Fibres

The sympathetic nerve fibres originate from the cervical sympathetic ganglion and join the trigeminal nerve at its ganglion

They are unmyelinated and follow the course of the sensory nerves

Regulate blood flow in the capillary network by innervation of the smooth muscle cells.

What is the function of pulp in the tooth?

FUNCTION OF THE PULP

Inductive - To induce oral epithelial differentiation into dental lamina & enamel organ formation.

Formative - Produce the dentin that surrounds & protects the pulp.

Nutritive - Nourishes the dentin through odontoblasts & by means of blood vascular system.

Protective -Respond with pain to all stimuli.

Defensive or reparative - Produce reparative dentin & mineralize any affected dental tubules.

Pulp Stones (Denticles)

Pulp stones, or denticles are calcified, shiny nodular masses that occur either single or multiple in numbers within the coronal and radicular pulp.

The pulp stones usually are asymptomatic in nature, but may be symptomatic if the stones impinge on nerves or blood vessels.

Pulp stones according to their histological structures, have been classified into two types– true and false

TRUE DENTICLE

Round or ovoid with smooth surfaces.

The remnants of HERS induce differentiation of odontoblasts which form true denticle.

Contain dentinal tubules and found close to root apex

FALSE DENTICLE

Rough and have no particular shape

Cause may be degenerating cells, thrombi and collagen fibrils

Concentric layers of calcified tissue and usually found in the pulp chamber

Pulp stones, according to their relation with the dentin of the tooth, may be divided into three types

Free

Attached

Embedded

The free pulp stones are completely surrounded by pulp. 

The attached pulp stones are partly surrounded by pulp and partly fused with dentin

The embedded pulp stones are completely surrounded by dentin

Diffuse Calcification

They are irregular areas of calcification in the pulp tissue that can be seen as a large mass or fine spicules of calcified tissue.

Appear as irregular calcific deposits in the pulp.

Pulp organ may be free of any pathology but may exhibit these changes more frequently in the roots unlike denticles