Dental pulp 2 l Oral histology and biology MCQs for dental students

Dental pulp anatomy and microscopic features l Oral histology and biology MCQs for dental students 

 

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Pulp anatomy and biology

Definition:

• Loose, delicate and specialized connective tissue which occupy the cavity lying in the center of the dentin (tooth).

Origin :

• Dental papilla (Ectomesenchymal origin).

Morphology:

Coronal pulp :

• Pulp chamber (In crown).

Radicular pulp :

• It is that part of the pulp extending from the cervical region of the crown to the root apex (Root canal and Apical foramen).

Apical foramen:

• The pulp organs are continuous with the periapical tissue through the apical foramen.
• The average size of the apical foramen : 0.3 mm in mandibular teeth & 0.4 mm in maxillary teeth.

1. The root may has 1 root canal opens in 1 apical foramen.
2. The root may has 1 root canal opens in 2 apical foramens.
3. The root may has 2 root canals open in 1 apical foramen.
4. The root may has 2 root canals open in 2 apical foramens.

Accessory canals :

• They are commonly seen to extend from the radicular pulp laterally through the root dentin to the periodontal ligament.
• They are numerous in the apical third of the root.

-Functions of the pulp:

1. Inductive : Dental papilla induces the enamel organ formation and also determines the morphology of the tooth (Reciprocal induction).
2. Formative: Pulp organ produces dentin. Odontoblasts develop the organic matrix and function in its calcification.
3. Nutritive: Pulp nourishes the dentin through the odontoblasts and their processes.
4. Protective : The sensory nerves in the tooth respond with pain to all stimuli. Pain sensation is a useful alarm system of the pulp.
5. Defensive or Reparative :

• If the pulp is exposed to irritation, it will respond to irritation by producing reparative (tertiary) dentin and mineralizing any affected dentinal tubules.
• Theses reparative reactions are an attempt to wall off the pulp from the source of irritation.
• The presence of macrophages (histocytes) and lymphocytes as leukocytes aids in the process of repair of the pulp.

 

Zones of the pulp: Odontogenic zone — Central zone (Pulp core) :

1- Odontogenic zone :

a) Odontoblastic zone :

• Formation : Odontoblasts attached to each other.
• Location: Adjacent to the predentin with the cell bodies in the pulp and cell processes in the dentinal tubules. (It provides bordering to the pulp).

b) Cell free zone :

• Formation: Fibers and ground substance.
• Location : Beneath the odontoblastic layer.
• Function : Permits mobilization (Motion) and replacement of the odontoblasts.

 c) Cell rich zone:

• Rich with fibroblasts, undifferentiated mesenchymal cells and other cells.

2- Central zone (Pulp core) :

• Contains the blood vessels and nerves of the pulp.

Histological structures of the pulp :

• Cells , Fibers , Intercellular substances , Blood vessels and Nerves.

Cells of the pulp:

1. Synthetic (Formative) cells : Odontoblasts - Fibroblasts.
2. Defensive (Inflammatory) cells : Macrophages — Lymphocytes — Eosinophiles - Mast cells - Plasma cells.
3. Progenitor cells : Undifferentiated mesenchymal cells — Stem cells.

Odontoblasts :

• In the early stages of development : They consist of a single layer of columnar cells.
• In the late stages of development : They appear ”Pyriform" where the broadest part of the cell contains the nucleus.
• Attached to each other with desmosomal junction.
• Columnar at Pulp chamber.
• Cuboidal and Flattened in root canal.

Fibroblasts :

• They are the numerous type of cells in the pulp.

Function:

1. Fibroblasts have a dual function : Synthesis and degradation of fibers and ground substances in the same cell.
2. The main function of fibroblasts is ”Formation of collagen fibers of the pulp".
3. In active state of fibroblasts (In young pulp) :

Electron microscope

1. Fibroblasts : Large, dark in staining and stellate in shape and have numerous well developed Rough Endoplasmic Reticulum , Golgi apparatus and Mitochondria.
2. Nucleus : Open faced, oval and centrally placed.
3. Collagen fibers : Fine and small.
4. Processes of fibroblasts : Multiple, elongated and large.
5. In inactive state of fibroblasts (In periods of less activity and aging = With agel:
6. Fibrob|asts : Small, rounded and spindle in shape with few organelles, they are called "Fibrocytes".
7. Nucleus : Closed faced.
8. Collagen fibers : Bundles, thick and large.

Macrophages :

• Shape : Irregular in shape with short blunt processes.
• Nucleus : Small, more rounded and darker in staining than fibroblasts and centrally palced.
• Site : They are distributed around the odontoblasts and small blood vessels and capillaries.
• Function : Engulfment of foreign bodies (Play a role in inhibition of foreign bodies).

Plasma cells:

• Size : Large.
• Nucleus : Small, eccentric, negative staining and the chromatin in it is arranged in a cart wheel shape, this give the plasma cell the cart wheel appearance.
• Function : Production of antibodies in case of inflammation.

Lymphocytes :

• Small lymphocytes : Have rounded nucleus.
• Large lymphocytes : Have eccentric kidney shaped nucleus.
• Function : Engulfment of foreign bodies (Play a role in inhibition of foreign bodies).

Eosinophils :

• Cytoplasm : Filled with granules and take eosinophilic stain.
• Nucleus : Bilobed.
• Function : Play a role in inhibition of foreign bodies.

Mast cells :

• Shape : Rounded and have many vesicles.
• Nucleus : Rounded (Oval).
• Function : Production of histamine and heparin in case of inflammation that cause vasodilation.

Undifferentiated mesenchymal cells :

• Shape : Stellate with multiple processes.
• Function : Differentiate into fibroblasts or odontoblasts.

Stem cells :

• Function : Differentiate into undifferentiated mesenchymal cells (Differentiate into any other epithelial or connective tissue cells).

Ground substance :

• Formation : Glucoseaminoglycans — Glycoprotein — Mucopolysaccharide.
• Function : Provide a medium for transport of nutrition and support the cells (The environment that promotes life of the cells).

Innervation of the pulp :

• Pulp has an abundant nerve supply which follows the distribution of the blood vessels.
• Nerve supply is provided through the subodontoblastic plexus of Rashkow (Aggregation of nerves below odontoblasts).
• Nerves pass through the apical foramen.
• Sensory response in the pulp cannot differentiate between heat, touch, pressure or chemicals because the pulp organs lack those types of receptors.
• Its sensation (response) is pain only.

Clinical considerations :

• Problem that happen : Pulp exposure.
• "Nerve Broach" is used to remove the pulp.
• Removal of the pulp in the old age is easier (better) than in infants.

Age changes :

• With age, the size of the pulp and the apical foramen decreases because of continuous secondary dentin formation.
• With age, the cellular elements (number of cells), vascularity (number of blood vessels) and vitality decrease.
• So reticular atrophy of the pulp occurs.
• Pulp calcification : Localized calcification (Pulp stones/Denticles)

Key Points

• The pulp is a soft connective tissue surrounded by dentin.
• The shape of the pulp is similar to that of the tooth.
• Extensions of the pulp into the cusps are pulp horns.
• Each root has one or more root canals which contain the radicular pulp.
• The apical end of the root canal is the apical foramen.
• Accessory canals are the lateral branches of the root canal.
• Histologic zones of the pulp are as follows:

1. Odontoblastic zone
2. Cell-free zone of Weil
3. Cell-rich zone
4. Pulp core

• Odontoblasts are highly differentiated cells that may be in active, transitional or resting phase.
• Each odontoblastic process extends into the dentinal tubule.
• The space between the odontoblastic process and the dentinal tubule contains dentinal fluid.
• The cell-free zone of Weil may show a few fibres. This zone permits the movement of odontoblasts towards the pulp.
• Fibroblasts are the highest population of cells in the pulp.
• Interstitial fluid pressure of normal pulp is 6 mmHg and of inflamed pulp is 20 mmHg.
• Arteriovenous anastomosis and U looping of blood vessels help in regulation of blood flow.
• The cell-rich zone shows the undifferentiated mesenchymal cells in the pulp.
• The plexus of nerves formed by extensive branching of the nerve fibres at the cell-free zone is known as the plexus of Raschkow.
• The functions of the pulp are as follows:

1. Inductive: Epithelial–mesenchymal interaction
2. Formative: Organic matrix of dentin
3. Nutritive: Through vascular supply
4. Protective: Through the sensory nerves
5. Reparative: Through the undifferentiated mesenchymal cells

• Pulp stones are calcified structures seen more commonly in the coronal pulp. They may be true or false pulp stones depending on the presence of dentinal tubules. On the basis of the dentin relations, pulp stones may be free, attached or embedded.
• Changes due to age are as follows:

1. Cellularity decreases
2. Fibrosis
3. Degeneration of nerves
4. Dystrophic calcification