Dental pulp 1 l Oral histology and biology MCQs for dental students

Dental pulp structure  l Oral histology and biology MCQs for dental students 

 

Dental pulp in biology

• Is the soft connective tissue located in the central portion of each tooth.

• All pulps have similar morphologic characteristic, such as a soft, gelatinous consistency in a chamber surrounded by dentin. The pulps of molars teeth are approximately four times larger than those of the incisors. Each pulp has a crown (coronal part) & a root (radicular part)

1- Coronal pulp

1. Occupies the crown of the tooth.
2. In general the coronal pulp follows the contour of the outer surface of the crown, it has six surfaces; mesial, distal, buccal, lingual, occlusal, & the floor.
3. The protrusions of pulp that extend into the cusps of the teeth known as pulp horns.
4. The number of the horns depends on the number of cusps.
5.  At the cervical region the coronal pulp joins the root pulp
6. The coronal pulp decrease in size with age because of continued dentin formation

2- Radicular pulp

1. Pulpal root extend from the cervical region to the apex of the root.
2. In the anterior teeth is singular, whereas the posterior teeth have multiple root pulps.
3. The shape of the radicular pulp is conical or tapered
4. Like coronal pulp, become smaller with age because of continuous dentinogenesis.

 

Apical foramen & accessory canals

• The apical foramen is the opening of root pulp into the periodontium.
• This opening varies from 0.3-0.6 mm in diameter.
• It generally located in the center of newly formed root apex but with age it become more eccentric

Structures of the pulp:

• Centrally the pulp is composed of large nerve trunks & blood vessels.
• Peripherally, the pulp is circumscribed by the specialized odontogenic region which composed of:

1. Dentin forming cells (odontoblasts)
2. Cell-free zone (Weil’s zone): is a space in which the odontoblast may move pulpward during tooth development.
3. Cell-rich zone: is composed principally of fibroblast & undifferentiated mesenchymal cells

• However, pulp organ contain the following structures

A- Intercellular substance

• Is dense & gel like in nature, varies in appearance from finely granular to fibrillar. It is composed of both acid mucopolysaccharides & protein polysaccharide compounds, but within age the pulp contains less of all of these substances.

• The ground substance tends support to the cells of the pulp & serves as a means for transport of nutrients from the blood vessels to the cells, as well as for transport of metabolites from cells to blood vessels.

B- Cells

 1-Fibroblasts

• Are the most numerous cells type in the pulp. They function in collagen fiber & ground substance formation throughout the pulp during the life of the tooth.

• Fibroblasts have a typical stellate shape & extensive processes that contact & are joined by intercellular junctions to the processes of other fibroblasts.

• With the age the fibroblast become less active & appear rounded or spindle shaped with short processes & they are termed fibrocytes. 

2- Undifferentiated mesenchymal cells

• Are the primary cells in the very young pulp, but a few are seen in the pulps after root completion. They appear larger than fibroblasts & are polyhedral in shape with peripheral processes & large oval nuclei.

• They are found long pulp vessels, in the cell-rich zone & scattered throughout the central pulp. These cells function as a cell pool & are called into action when new odontoblasts or fibroblasts are needed.     

3- Odontoblasts

• The second most prominent cell in the pulp. Reside adjacent to the predentin with cell bodies in the pulp & cell processes in the dentinal tubules.

• The form & arrangement of the bodies of the odontoblasts are not uniform throughout the pulp.

•  They are more cylindrical & longer (tall columnar) in the crown & more cuboid in the middle of the root, while in the apex of an adult tooth the odontoblasts are ovoid & spindle shaped.

• The function of odontoblasts is the formation of dentin.

4- Defense cells

• These are cells important in the defense of the pulp. Defense cells include:

1. Histocytes or Macrophages
2. Mast cells & Plasma cells
3. Neutrophils, Eosinophils, Basophils, Lymphocytes, & Monocytes (these cells migrate from the pulpal blood vessels & develop mainly in response to inflammation)

• The Histocyte, or Macrophage, is an irregularly shaped cell with short blunt processes, in the case of a pulp inflammation these cells exhibit granules & vacuoles in their cytoplasm & their nuclei increase in size & exhibit a prominent nucleolus, but when the Macrophage is inactive & not in the process of ingestion foreign materials, it has difficulty distinguishing them from fibroblast.

• Both Lymphocytes & Eosinophils are found extravascularly in the normal pulp, but during inflammation they increase in number.

• Mast cells are seen along vessels in the inflamed pulp, & also increase in number during inflammation. The Plasma cell during inflammation function in the production of antibodies

 

C- Fibers:

•   Appear scattered throughout the coronal & radicular pulp (diffuse collagen) or appear in bundles (bundle collagen depending on their appearance.

• The collagen fibers in the pulp exhibit typical cross striation at 64 μm& range in length from 10-100 μm.

D- Blood vessels:

• The pulp is highly vascularized, & it is arise from the inferior or superior alveolar artery & also drain by the same veins in both the mandibular & maxillary regions.

• Small arteries & arterioles enter the apical canal & run in a direct route to the coronal pulp. 

• Along their course they give off numerous branches in the radicular pulp that pass peripherally to form a plexus in the odontogenic region.

• Pulpal blood flow is more rapid than in most areas of the body

E- Lymph vessels

• Lymph vessels draining the pulp & periodontal ligament, those draining the anterior teeth pass to the submental lymph nodes, those of the posterior teeth pass to the submandibular & deep cervical lymph nodes.

F- Nerves

• The majority of the nerves that enter the pulp are nonmyelinated, & many of these gain a myelin sheath later in life. The large myelinated fibers mediate the sensation of pain that may be caused by external stimuli.

• Adjacent to the cell-rich zone the peripheral axons form a network of nerves known as the plexus of Rashkow. 

• The nerve axons then pass through the cell-rich zone & cell-free zone & either terminate among or pass between the odontoblasts to terminate adjacent to the odontoblast processes in the dentinal tubules.

• Sensory response in the pulp can’t differentiate between heat, touch, pressure, or chemicals. This is because the pulp organs lack those types of receptors that specifically distinguish these stimuli

 

Functions of the pulp

1-Induction:

• The primary role of the pulp is to interact with the oral epithelial cells, which leads to differentiation of the dental lamina & enamel organ formation. 
• The pulp also interacts with the developing enamel organ as it determines a particular type of tooth.

2- Formation:

• The pulp cells produce the dentin through the odontoblasts cells.

3- Nutrition:

• The pulp nourishes the dentin through the odontoblasts & their processes & by means of blood vascular system of the pulp.

4- Protection:

• The sensory nerves in the tooth respond with pain to all stimuli, the nerves also initiate reflexes that control circulation in the pulp.

5- Defensive & reparative function:

• Pulp responds to irritation, whether mechanical, thermal, chemical, or bacterial, by producing reparative dentin & sclerotic dentin to wall off pulp from this source of irritation.

• Pulp may inflame due to bacterial infection or by cutting action. In this case the macrophage, lymphocytes, neutrophils, monocytes, & plasma with mast cells aid in the process of repair of the pulp

Aging changes

• Within age the pulp become less cellular & more fibrous in both the inter-cellular & in the wall of blood vessels.

Pulp stone (denticles):

• are nodular, calcified masses appearing in either or both coronal & root portions of the pulp. They usually are asymptomatic unless they impinge on nerves or blood vessels.

Generally classified according to their structure into:

1. True denticles: are similar in structure to dentin in that they have dentinal tubules, this type is rare & usually located close to the apical foramen.
2. False denticles: do not exhibit dentinal tubules but appear as concentric layers of calcified tissue around necrotic cells.

Both false & true stones may be classified as:

1. Free: in which the stone entirely surrounded by pulp tissue.
2. Attached: are partly fused with the dentin
3. Embedded: are entirely surrounded by dentin.