histology of pulp

Histology Of Pulp

Aurelian Jovita Alexander

MDS I Year

Dept Of. Oral and Maxillofacial Pathology

Content

• Definition

• Zones of Pulp

• Principal Cells of Pulp

• Collagen Synthesis

• Pulp Calcifications

• Age Changes in Pulp

• The dental pulp is the soft connective tissue of the tooth that supports the dentin.

Definition

Zones Of Pulp

• The odontoblastic zone at the pulp periphery

• A Cell- Free Zone of Weil beneath the odontoblasts

• A Cell- Rich Zone

• Pulp Core

Dentin

Predentin

Odontoblasts Layer

Cell rich Zone

Cell free Zone

Pulp Proper

Odontoblasts• The outermost(pulp)

• located immediately subjacent to the predentin;

• Pass through the predentin into the dentin

Cell Free Zone

• Immediately subjacent to the odontoblast layer in the coronal pulp.

• width 40 μm

• Free of cells

• It is traversed by blood capillaries, unmyelinated nerve fibers, and fibroblasts.

Function

• In this space, the odontoblast may move pulpward during tooth development and later to limited extent in funtioning teeth.

Cell Rich Zone- Include number of macrophages, dendritic cells

and undifferentiated mesenchymal or stem cells.

Pulp Proper

• The pulp proper is the central mass of the pulp.

• The connective tissue cells consist of fibroblasts or pulpal cells

Principal Cells of the Pulp

• Odontoblasts

• Fibroblasts

• Undifferentiated Ectomesenchymal cells

• Macrophages

• Other Immunocompetent Cells

Odontoblasts

• Most distinctive cells of the dental pulp.

• No. Of Odontoblasts corresponds to No. of dentinal tubules.

• 59000- 76000 per square millimeter in coronal dentin. Less in root dentin.

• In fully developed teeth,

Region Shape and size

Crown Of the Pulp Columnar , 50µm in height

Midportion Of the Pulp Cuboidal

Apical Portion Of the Pulp Flattened

Columnar

Flattened

Cuboidal

ElongatedBasal NucleusBasophilic cytoplasmProminent Golgi Zone

• 3 Stages

- Secretory Stage

- Transitional Stage

- Resting Stage

Secretory Phase

• The organelles of an active odontoblasts are prominent consisting

- Numerous Vesicles

- Much Endoplasmic Reticulum

- Well developed Golgi Complex located on dentinal side of nucleus

- Numerous Mitochondria

- Nucleus- periphally dispersed chromatin & several nucleoli

Electron micrograph showing the Golgi region of a secretoryodontoblast in which well-developed synthesis organelles such as cisternae of rough endoplasmic reticulum (RER), Golgi stacks (G), and secretory granules (g) are abundant. M, mitochondria (32,500×).

Transitional Phase

• Narrower cell

• Nucleus displaced from the basal extremity

• Condensed Chromatin

• Reduced ER

• Autophagic Vacuoles are present and ass. with reorganisation of cytoplasm.

Resting Or Aged Phase

• Nucleus situatated more apically, creating a prominent infranuclear region

• Fewer cytoplasmic organelles clustered

• Supranuclear region devoid of organelles

• Large lipid filled vacuoles containing tubular and filamentous structures.

Couve E , and Schmachtenberg O J

DENT RES 2011;90:523-528

Cont.

• Synthesizes :

• Mainly Type I Collagen • Small amounts of - Type V proteoglycans

-Sialoprotein-Phosphophoryn- Alkaline Phosphatase

Odontoblast Process• The odontoblast process occupies most of the

space within the tubule and coordinates the formation of peritubular dentin.

• The process is limited to the inner third of dentin.

( Garberoglio R, Brännström M: 1976)

• Extending further into the tubule, often as far as the DEJ.

(Kelley et al,1981) (Grossman et al,1983)

• Extends throughout the entire thickness of dentin

(Sigal et al,1984)

Electron micrograph showing the mineralized dentine/predentine/odontoblast layer interface.

An odontoblasts processes (P) that arises from the odontoblast cell body (O) crosses the entire predentine and penetrates into a tubule of the mineralized dentine. Some branches (double arrowheads) of the odontoblast processes are clearly observed in other odontoblast process (5400×).

Junction between Odontoblasts

• Gap Junctions

• Tight Junctions

• Desmosomes

Fibroblasts

• Occuring in greatest numbers.

• Numerous in coronal portion of the pulp.

• They appear to be tissue-specific cells that are capable of giving rise to cells that are committed to differentiation

• (e.g., odontoblast-like cells) if given the proper signal.

• Synthesize types I and III collagen and proteoglycan

Function

Form and maintain Pulp matrix that consists Collagen and

Ground substance

• They produce and maintain the matrix proteins .

• Mitotic activity preceding the differentiation of replacement odontoblasts appears to occur primarily among perivascular fibroblasts. (Especially in dentinal bridge formation after pulpotomy or exposure)

(Fitzgerald et al,1990)

Images captured by a confocal microscope(representative bars: 20 µm).

Macrophages

• Monocytes that have left the bloodstream, enters the tissues, and differentiate into various subpopulations.

• It plays in phagocytic activity.

• Macrophages participate in immune reactions by processing antigen and presenting it to memory T cells.

• In inflammatory stimuli, it produces a large variety of factors, including interleukin-1, tumor necrosis factor, growth factors, and other cytokines

Dendritic Cells

• Accessory cells of the immune system

• Bone marrow derived

• characterized by:

-dendritic cytoplasmic processes

-presence of cell surface class II antigens

Functions• Are termed

antigen-presenting cells

• They act as antigen-presenting cells that are essential for the induction of helper T cell dependent immunity.

It engulf protein antigens and then present an assembly of peptide

fragments of the antigens and class II molecules

Undifferentiated Mesenchymal Cells

• Polyhedral in shape.

• Have peripheral processes and large oval staining nuclei.

• Totipotent cells

• May become formation of odontoblasts, fibroblasts and macrophages.

Lymphocyte

• (Hahn et al,1989) found T lymphocytes in normal pulps from human teeth.

• Lymphocytes have also been observed in the pulps of impacted teeth.

(Langeland et al,1965)

Mast Cells

The granules contain heparin, an anticoagulant, histamine, other chemical factors which release and causeInflam. & attack to harmful substance.

Metabolism

• (Yu CY et al,2002) reported that:* odontoblasts consumed O2 at the rate of 3.2 ±

0.2ml/min/100 g of pulp tissue..• It is higher during dentinogenesis than after crown

development • Dental materials ?inhibit oxygen consumption by

pulp tissue as they depress the metabolic activity of pulpal cells.

(Fisher et al,1957 (Jones et al,1979)

• Orthodontic force? causes changes in respiratory activity of the pulp.

(Hamersky et al,1980)

Ground Substance

• An amorphous , gel like, polyanionicpolysaccharides matrix with water holding properties where C.T cells and fibers are embeded

• Nearly all proteins of are glycoproteins.

Role of GROUND SUBSTANCE:

Forms a cushion capable of protecting cells and vascular components. (especialy in young pt,the water pulp is

hight)

It acts as a sieve passage of nutrients , between cells and blood.

Regulate osmotic pressure by excluding osmotically active molecules.

Connective Tissue Fibres Of Pulp

Two types of structural proteins:

A- ELASTIN: fibers are confined to the walls of arterioles.

B- COLLAGEN

tropocollagen

Found In..

I skin, tendon, bone, dentin, and pulp

II cartilage.

III unmineralized connective tissues

IV component of basement membranes

V a constituent of interstitial tissues

VI widely distributed in low concentrations in

soft tissues at interfibrillar filaments.

VII component of basement membranes

Collagen Synthesis

• Type I collagen is synthesized by odontoblastsand osteoblasts

• Fibroblasts synthesize types I, III, V, and VII collagen.

mRna

Specific AA into Polypeptide Chains on Ribosomes ass. With RER in Cytoplasm

Amino Acid In Nuclues

Lumen of the RER

Hydroxylation of Proline and Lysine Residues- permits hydrogen bonding

ProlylhydroxylaseLysylhydroxylase

Glycosylation of some hydroxylysine residues,Addition of galactose

galactosyltransferase

3 polypeptide chains assembled in triple helix

Disulfide bonding at C- terminal extension, catalysed by protien disulfide isomerase

Proper allignment of the chain

Transported to Golgi Complex , Glycosylation completes

Secretory granules containing the procollagenmolecules are formed at the trans face of Golgi Complex

Addition of glusoce to O- linked galactose residues

Exocytosisat cell surface

The formation of typical banded collgen fibrils ocurs extracellularly

C and N proteinases

The C-terminal and part of N- terminal extensions are removed in the secretory granules

Secreted into extra cellular matrix

Oxidation of lysin and hydroxylysin=Final collagen- short end diameter

Lysyloxidase

Short Collagen Fibrils-parrallel,and into the gaps hydroxyapatite crystals get lodged

Blood Vessels

• Arise from inferior or superior alveolar artery.

• Drain by the same veins.

• Infection spread through the communication.

Arteries

• Small arteries give off numerous branches in radicular pulp

• Largest arteries- 50-100µm in diameter.

• Pulpal blood flow rapid & pulpal blood pressure

Blood flow in arteries: 0.3 -1 mm/sec

Blood flow in veins : 0.15 mm/ sec

Blood flow in capillaries: 0.08mm/sec

• These vessels contain 3 layers

Tunica Intima Tunica media Tunica Adventitia

• Tunica intima

– squamous or cuboid endothelial cells surrounded by closely associated basal lamina.

• Tunica media

– 5µm thick. Consists 1-3 layers of smooth muscle cells.

A basal lamina surrounds and passes between these muscle cells and seperates them from intima.

Occasionally endothelial cell wall is in contact with muscle cells- MYOENDOTHELIAL JUNCTION.

Tunica adventitia

– made up of few collagen fibres forming a loose network around the large arteries.

Arterioles

• 20-30µm in diameter

• 1-2 layers of smooth muscle cells common throughout the dental pulp.

• Tunica adventitia blends with the fibres of surrounding intercellular tissue.

Terminal Arterioles

• 10-15µm in diameter, peripherally in the pulp.

• Endothelial cells contain numerous micropinocytotic vesicles- which function in transendothelial fluid movement.

• Single layer of smooth muscle cells found.Occasionally a fibroblast or pericyte lies on the surface of the vessels.

Precapillaries

• Smaller diameter arterioles.

• Slightly larger than the terminal capillaries.

• Exhibit a complete or incomplete single layer of muscle cells surrounding endothelial lining. 8-12µm in diameter.

Veins and Venules

-Larger than arteries.

-Appear in central region of the root pulp.

-100-150µm in diameter.

-Walls- less regular than those of arteries because of bends and irregularities along their course,

and thinner in relation to the size of lumen.

Endothelial cells- more flattened and cytoplasm does not project into the lumen. Fewer intracytoplasmic filaments.

-Tunica media:

1-2 layers of thin smooth muscle cells that wrap around endothelial cells, and appear discontinuous or absent in smaller venules.

-Basement membrane: thin and less distinct.

-Tunica Adventitia:

lacking or appears as fibroblasts and fibrescontinuous with surrounding pulp tissue.

Capillaries

• Appear as endothelium lined tubes, 8-10µm in diameter.

• Nuclei: lobulated and have cytoplasmic projections into the luminal surface.

• Few peripheral capillaries found among the odontoblasts have fenestrations in endothelial cells – involved in rapid transport of metabolites during time of dentinal matrix formation and calcification by the active odontoblasts.

• Both fenestrated and continuous terminal capillaries are found in the odontogenic region.

• During active odontogenesis, capillaries appear among the odontoblasts adjacent to the predentin.

Lymph Vessels

• Endothelium lined tubes• Join the thin walled lymph venules or veins in

the central pulp• Thin walls• Larger vessels have an irregular-shaped lumen

composed of endothelial cells surrounded by an incomplete layer of pericytes or smooth muscle cells or both.

• Cells contain multivesicular structures, WeibelPalade bodies and paracrystalline inclusions.

• Absence of RBC and presence of lymphocytes.

• Basement membrane shows discontinuity.

• Lymph vessels draining the pulp and PL have common outlet.

• Anterior teeth: drained to submental lymph nodes.

• Posterior teeth: drained to submandibular and deep cervical lymph nodes.

Nerves

• Majority- Non Myelinated and many of these gain myelin sheath later in life.

• Found in close association with blood vessels, many being sympathetic in nature.

• They have terminals on the muscle cells of the larger vessels and function in vasoconstriction.

• Thick nerve bundles enter the apical foramen-pass along the radicular pulp to the coronal pulp where the fibres separate and radiate peripherally to the parietal layer of nerves.

• Number of fibres in the bundles varies greatly. 150->1200

• Larger fibres: 5-13µm in size.

• Majority are smaller than 4µm.

• The peripheral axons form a network of nerves located adjacent to cell rich zone, called as Parietal layer of nerves / Plexus of Rashkow.

• Axons of Raschkow plexus lose their myelinesheath (but not their Schwann cells) as they penetrate the cell-rich and cell-free zones to make synaptic contact with the odontoblast cell body in the pulp or odontoblastic process within the dentinal tubule.

• Raschkow plexus is responsible for transmitting pain sensation from the pulp of the tooth.

• By virtue of their peptide content they also play important functions in inflammatory events and subsequent tissue repair.

• There are two types of nerve fiber that mediate the sensation of pain:

• A- fibers and C-fibers.

• A-fibers conduct rapid and sharp pain sensations and belong to the myelinated group.

• C-fibers are involved in dull aching pain and are thinner and unmyelinated.

• The A-fibers, mainly of the A-delta type, are preferentially located in the periphery of the pulp, where they are in close association with the odontoblasts and extend fibers to many but not all dentinal tubules.

• The C-fibers typically terminate in the pulp tissue proper, either as free nerve endings or as branches around blood vessels.

Nerve Endings

• Nerve axons pass between odontoblasts to terminate adjacent to the odontoblast processes at the pulp-predentin border or in the dentinal tubules.

• Nerve terminals consist of round or oval enlargements of terminal filaments that contain microvesicles, small, dark, granular bodies and mitochondria.

• Close to odontoblast plasma membrane, seperated only by a 20µm cleft.

• Believed to be sensory receptors.

• Function whether relative to capillaries or odontoblasts in dentinogenesis, is not known.

• More nerve endings found in pulp horns than in other peripheral areas of coronal pulp.

Pulpal Stem Cells

- Stem cells are the body’s "master" cells that regenerate the body’s many cells, tissues, and organs.

• The most commonly known source of adult stemcells is bone marrow, which contains both hematopoietic stem cells (also found in cord blood) and mesenchymal stem cells (also found in teeth).

Types of dental stem cells:

At least five different types of postnatal mesenchymal stem cells have been reported to differentiate to odontoblast-like cells.

• 1.Dental pulp stem cells(DPSC)

• 2.Dental pulp of human exfolliated deciduous teeth(SHED)

• 3.Stem cells of apical papilla(SCAP)

• 4.Dental follicle progenitor cells(DFPC)

• 5.Bone marrow-derived mesenchymalstemcells(BMMCS)

• Stem cell are also present in pulp.

• They migrate to the site of injured odontoblastsand produce dentin.

• Transforming growth factor (TGF beta1) and bone morphogenic proteins (BMP-2) -proliferation and differentiation, and endothelial cell injury, in the migration of these stem cells in response to an injury.

• They were shown to develop adipocytes and neural cells.

• Derived from Pulp tissues of exfoliated deciduous teeth, Primary incisors and Permanent 3rd molars.

• Recent studies show that pulp stem cells synthesise osteoblasts, synthesise 3D woven bone tissue chips in vitro and that are capable to synergically differentiate into osteoblasts and endotheliocytes.

Indications• Dental Tissue Repair

- Repair damaged tooth tissues such as dentin, periodontal ligament, dental pulp.

• Periodontal Regeneration

• Regeneration of Pulp in immature tooth.

• Whole Tooth Regeneration

Pulpal Calcifications

Very common occurrence present in 50% of all teeth.

Pulp calcification is considered: a pathological process related to various forms

of injury.

Pulp calcification may be of microscopic size or may be large enough to be detected radiographically.

• Coronal pulp form →(discrete, concentric pulp stones

• Radicular pulp form →diffuse.(single or attach)

• Variable sizes

• The mineral phase consists of carbonated hydroxyapatite

Pulp stones occupying much of the pulp

chamber

Diffuse calcification near the apical foramen

Age Changes

1. Continued formation of secondary dentin → ↓

size of pulp chambers & canals.

2. ↓ cellularity.

3. ↑ # and thickness of collagen fibers.

4. ↓ # of nerves & blood vessels.5. ↑ Peritubular dentin, dentinal sclerosis & dead

tracts.