PULP DENTIN COMPLEX

Presented By,

Seminar Outline:-

1) Introduction

2) Dentin - Composition

- Development - Histology

Dentinal Tubules Peritubular Dentin Intertubular Dentin Interglobular Dentin Incremental Growth Lines Granular Layer of Tomes

- Types of Dentin

Primary Dentin Secondary Dentin Tertiary Dentin

- Dentin Permeability

3) Pulp - Cells of Pulp

Odontoblasts Fibroblasts Macrophages Undifferentiated Ectomesenchymal

Cells Dentritic Cell Lymphocytes Mast Cell Matrix and Ground substance

- Morphological Zones of Pulp

Odontoblast Layer Cell Poor Zone Cell Rich Zone Pulp Proper

- Metabolism - Vasculature – Regulation of pulp blood flow - Lymphatics - Innervation - Dentin Sensitivity

PULP DENTIN COMPLEX

Dentin is hard mineralized connective tissue. Pulp is a soft tissue of

mesenchymal origin with specialized cells (odontoblasts) arranged peripherally in

direct contact with dentin matrix.

Although dentin and pulp have different structures and compositions once formed

they react to stimuli as a functional unit. Exposure of dentin through attrition,

trauma or caries, procedures profound pulpal reaction that tends to reduce dentin

permeability and stimulate formation of additional dentin. These reactions are

brought about by changes in fibroblasts, nerves, blood vessels, odontoblasts,

leukocytes and the immune system. This close anatomical and functional

relationship between pulp and dentin is referred to as Pulp Dentin complex.

There is great deal of evidence that dentin and pulp are functionally coupled and

hence integrated as a tissue.

DENTIN

Dentin is the hard, elastic, yellowish white, avascular mineralized connective

tissue portion of the pulp dentin complex which surrounds and encloses pulp. It

forms the bulk and general form of the tooth. It supports the enamel and

compensates for its brittleness. Dentin is bone like matrix characterized by the

multiple closely packed dentinal tubules that transverse its entire thickness and

contain the cytoplasmic extensions of odontoblasts that once formed dentin and

then maintain it. The cell bodies of the odontoblasts are aligned along the

peripheral boundary of dental pulp, against the Predentin.

Dentin is light yellowish in colour and darkens with age. It is viscoelastic and is

harder than bone but softer than enamel. It is harder in the central part than near

the pulp.

Composition of Dentin:-

Predentin -

- It is the first dentin deposited.

- It is a layer of unmineralised organic matrix, about 10-15 micro meter

thick.

- It lines the inner most (pulp) portion the dentin; situated between the

odontoblast layer and the mineralized dentin.

- It consists of collagen and non collagenous components. It gradually

mineralizes into dentin as various non-collagenous matrix proteins

get incorporated.

- Its thickness remains constant by addition of new mineralized matrix

- It is thickest during dentinogenesis and diminishes with age.

Mature Dentin:-

Inorganic Material - 70% by weight or 45% by volume

Organic Material - 20% by weight or 33% by volume

Water - 10% by weight or 22% by volume

minerals and interstices

between crystals.

-Inorganic component consists of substituted hydroxyapatite in form of plates.

Each hydroxyapatite crystal is composed of several thousands of unit cells with a

formula

3Ca3 (PO) 4. Ca (OH) 2

The inorganic component also consists of fluorine, magnesium, zinc,

metalphosphates and sulphates.

-Organic substitute consists of 30% collagenous fibrils (mainly Type I with small

amounts of Type II and III) and a ground substance of mucopolysaccharides

(proteoglycans and glycosaminoglycans).

-Small amounts of phosphates, carbonates and sulfates are also present.

-Miscellaneous components- acidic protein, growth related factors, lipids, serum

derived proteins.

-Organic and inorganic substances can be separated by either decalcification or

incineration.

DEVELOPMENT: -

Dentin is formed by cells called odontoblasts, which differentiate from

ectomesenchymal cells of dental papilla. Thus the dental papilla is the formative

organ of dentin and eventually becomes the pulp of the tooth. Dentinogenesis is

a 2 stage or phase sequence in which the collagen matrix is formed first and then

calcified. Von Korff’s fibers have been described that the initial deposition begins

at the cusp tips after odontoblast differentiation.

As odontoblasts differentiate, they change from an ovoid to a columnar shape

and their nuclei become basally oriented at early stage of development. One or

several processes arise from the apical end of cells in contact with basal lamina.

Length of the odontoblast then increases to 40 m and remains constant.

Proline appears in rough surface endoplasmic reticulum and golgi apparatus.

This proline migrates into cell process in dense granules and is emptied into the

extracellular collagenous matrix of predentin.

As cell recedes, it leaves behind a single extension and several initial processes

join into one, which becomes enclosed in a tubule.

As matrix formation continues, the odontoblast process lengthens, as does

dentinal tubules. The odontoblasts secrete both the collagen and other

components of the extracellular matrix.

Initially daily increments of approximately 4 micro meter of dentin are formed.

As each increment of predentin is formed along the pulp border, it remains a day

before it is calcified and the next increment of predentin forms. All the predentin

is formed in the apical end of the cell and along the forming tubule wall. This

continues until crown is formed and teeth erupt and move into occlusion. After

this time dentin production slows to about 1 micro met /day.

After root development is complete, dentin formation may increase further.

Mineralization:

The earliest crystal deposition is in the form of very fine plates of hydroxyapatite

on the surface of the collagen fibrils and in the ground substance.

Subsequently, crystals are laid down within the fibrils themselves.

The crystals associated with the collagen fibrils are arranged in an orderly

fashion, with their long axis paralleling the fibrils long axes and in rows

conforming to the 64 mm striation pattern.

Within the globular islands of mineralization, crystal deposition appears to take

place radially from common centers in a so called spherulite form. These are

seen as the first sites of calcification of dentin.

General calcification process is gradual, but the peritubular region becomes

highly mineralized at a very early stage.

Although there is some crystal growth as dentin matures, the ultimate crystal size

remains very small, about 3 nm in thickness and 100 nm in length.

The apatite crystals resemble those found in bone and cementum but they are

300 times smaller than those found in enamel.

Calcospherite mineralization is seen occasionally along the pulp predentin

forming front.

HISTOLOGY OF DENTIN:-When viewed microscopically following structural features can be identified

- Dentinal Tubules

- Peritubular Dentin

- Intertubular Dentin

- Interglobular Dentin

- Incremental growth lines

- Granular layer of Tomes

DENTINAL MATRIX:

The dentinal matrix of collagen fibers are arranged in a random network. As

dentin calcifies, the hydroxyapatite crystals mask the individual collagen fibers.

Collagen fibers are visible only under electron microscope and have a diameter

of 50nm.

DENTINAL TUBULES:

A characteristic of human dentin is the presence of tubules that occupy from 20

to 30 % of the volume of intact dentin. These tubules house the major cell

processes of odontoblasts. Tubules extend through the entire width of the Dentin

from Dentinoenamel junction or Cemento dentinal junction to pulp and form a

network for diffusion of nutrients throughout dentin. Their configuration indicates

the course taken by the Odontoblasts during dentinogenesis. They have a gentle

S shape curve in the coronal dentin, as they extend from Dentinoenamel junction

to Pulp. This S – shaped curvature least pronounced beneath the incisal edges

and cusps, where they may run almost straight course. This curvature is

presumed as result of crowding of odontoblasts as they migrate towards the

center of the pulp. As they approach the pulp, tubules converge because the

surface of the pulp chamber has a much smaller area than surface of dentin

along Dentinoenamel junction. These tubules end perpendicular to

Dentinoenamel junction and

Cementodentinal junction. Along the entire lengths, they exhibit minute

secondary curvatures that are sinusoidal in shape. Tubules are longer than the

entire thickness (3 to 10 mm) of dentin due to their curve through dentin. The

ratio between outer and inner dentin is about 5:1. Accordingly Tubules are further

apart in peripheral layers and are more closely packed near pulp. They are larger

in diameter near the pulpal cavity (3 to 4 micro meters) and smaller at the outer

ends (1 micro meter). The ratio between the number of tubules per unit area on

pulpal and outer surface of dentin is about 4:1. There is more number of tubules

per unit area in the crown than in root.

The dentinal tubules have lateral braches throughout dentin, which are called

Canaliculi / microtubules, which are 1 um or less in diameter. They originate

more or less at right angles to the main tubule every 1-2 um along its length.

Some may enter adjacent or distant tubules while others end in intertubular

dentin. Thus form anastomosing canalicular system. They contain branches of

main odontoblastic process. Researchers have demonstrated they form

pathways for movement of materials between main processes and the more

distant matrix.

Major branches occur frequently in root dentin than in coronal dentin. This tubular

nature of dentin bestows an unusual degree of permeability on this hard tissue

that can enhance a carious process and accentuate the response of the pulp to

dental restorative procedures. Few dentinal tubules extend through

dentinoenamel junction into enamel for several mm and are termed enamel

spindles.

PERITUBULAR DENTIN:-

Dentin lining the dentinal tubules is termed peritubular dentin, which is a highly

calcified matrix and forms the walls of tubules in all but dentin near pulp.

It is presumed to be the precursors of dentin matrix that is deposited around each

odontoblast processes are synthesized by the odontoblast transported in

secretory vesicles out into the process, and released by reverse pinocytosis.

With the formation of peritubular dentin, there is a reduction in diameter of the

process near dentinoenamel junction.

It is more mineralized than intertubular dentin. Therefore, harder. Hence this

hardness provides added structural support for intertubular dentin thus

strengthening the tooth. It is twice as thick in outer dentin than inner dentin.

It contains few collagen fibrils and higher proportion of sulphated proteoglycans.

Due to its decreased collage content, dissolves more quickly in acid than

intertubular dentin.

By removal of peritubular dentin, acid etching agents used during dental

restorative procedures enlarge the openings of the dental tubules, thus making

the dentin more permeable.

It is rich in proteins like dentinsialoprotein.

After decalcification the odontoblastic processes appear to be surrounded by

empty space.

The calcified tubule wall has an inner organic lining termed as Lamina limitans,

which is a thin organic membrane high in glycosaminoglycans (GAG) and similar

to the lining of lacunae in cartilage and bone.

INTERTUBULAR DENTIN:-

This is located between the rings of peritubular dentin and constitutes bulk of

dentin. Its organic matrix consists mainly of interwoven network of collagen fibrils

having diameter of 50-200 um. Fibrils are arranged randomly at right angles to

dentinal tubules.

Ground substance consists of noncollagenous proteins proper to calcified tissues

and some plasma proteins. Although highly mineralized, it is retained after

decalcification. Hydroxy appetite crystals are formed along the fibers with their

long axis oriented parallel to collagen fibers.

INTERGLOBULAR DENTIN (Or Spaces):-

The term describes areas of unmineralised/ hypomineralised dentin where

globular zones / areas of mineralization (calcospherites) have failed to fuse into a

homogenous mass within mature dentin. (mineralization of dentin begins in small

globular areas which fail to fuse- zones of hypomineralization between globules.

This is prevalent in people who had ( vit D deficiency resistant rickets or

exposure to high levels of fluorides at time of dentin formation,

Hypophosphatasia)

It is seen in circumpulpal dentin just below mantle dentin, where pattern of

mineralization is largely globular. It follows incremental pattern.

INCREMENTAL GROWTH LINES (Von Ebner / Imbrication Lines):-

These are fine lines? Striations in dentin.

They run at right angles to dentinal tubules and mark normal daily rhythmic linear

pattern of dentin deposition in an inward and rootward direction.

Organic matrix of dentin is deposited incrementally at a daily rate of 4 um and

mineralized in 12 hr cycle.

5 day increment can be seen as Incremental lines of Von Ebner.

Contour Lines Of Owen: Incremental lines are accentuated because of

deficiencies in mineralization process. They can be demonstrated by longitudinal

ground sections- Soft x-ray shows hypocalcified bands.

Neonatal Line:- Is the zone of hypocalcification found in enamel and dentin of

deciduous teeth and permanent molar. They separate post and pre natal dentin.

Reflects abrupt change in environment /physiological trauma of birth.

GRANULAR LAYER OF TOMES:-

This is an optical phenomenon seen when root dentin is dry ground and viewed /

visualized in transmitted light, a granular-appearing zoneis seen below the dentin

surface, where root is covered by cementum. This is known as granular layer.

This zone increases slightly in amount from the cementoenamel junction to root

apex.

Number of interpretations proposed about these structures were:-

- They were thought to be associated with minute hypomineralised

areas of interglobular dentin.

- Thought to be true spaces.

- Finally spaces representing sections made through looped terminal

portions of dentinal tubules found only in root dentin and seen only

because of light refraction in thick ground sections.

- Recently interpretation relates this layer to a special arrangement of

collagen and non-collagenous matrix at the interface between

dentin and cementum.

- The cause of development was a result of odontoblasts turning on

themselves during early development of teeth.

DENTINAL FLUID:-

This is the free fluid which occupies about 22% of total volume of dentin. It is an

ultrafiltration of blood in pulpal capillaries, and its composition resembles plasma

in many respects. This fluid flows outwards between odontoblasts into the

dentinal tubules and eventually escape through small pores in enamel.

Tissue pressure of pulp is 14 cmH2O ( 10.3mmHg)

Pressure gradient between pulp and oral cavity results in the outward flow of

fluid.

Exposure of tubules by tooth fracture or during cavity preparation often results in

the outward movement of fluid to the exposed dentin surface in the form of tiny

droplets. Dehydrating surface of dentin with compressed air, dry heat or

application of absorbent paper can accelerate this outward movement of fluid.

Rapid flow of fluid through tubules is thought to be the cause of dentin sensitivity.

Dental caries, restorative procedures or growth of bacteria beneath restorations

result in bacterial products or other contaminants to be found in dentinal fluid.

Dentinal fluid serves as a sump from which injurious agents can percolate into

pulp producing an inflammatory response.

TYPES OF DENTIN:-

1) PRIMARY DENTIN (Developmental Dentin) Development Dentin is one which forms during tooth development

Mantle dentin is the 1st formed Dentin in the crown underlying DEJ

Sub adjacent to Enamel / Cementum

Not present in root dentin

Outer most peripheral part of dentin about 20 Micro meter

thick

Bounded by DEJ & zones of interglobular Dentin

Consists of thick fan shaped collagen fibers, deposited

immediately subjacent to basal lamina during initial stages of

dentinogenesis

fibers run perpendicular to DEJ

It is less mineralized than the rest of the primary dentin with

organic matrix derived from dental papilla.

Circumpulpal Dentin forms remaining primary Dentin or bulk of tooth

Represents all Dentin formed before root completion after layer of Mantle

Dentin is deposited and

Organize matrix is composed of collagen fibers which are smaller in

diameter and are oriented right angle to long axis to ditubules and are

closely packed together & form an interwoven network

May contain more mineral then mantle dentin.

2) SECODARY DENTIN

It is a narrow band of Dentin bordering the pulp & representing that Dentin

formed after root completion

Has a tubular structure which is continuous with the primary dentin is most

parts

Contains fewer incremental and tubular than Primary Dentin

Not deposited evenly around the periphery of the pulp chamber (molar

teeth) and greater amounts of deposition on roof & floor of coronal pulp

chamber leads to asymmetric reduction in its size & shape. These

changes in pulp space are clinically referred to as pulpal recession.

Important in determining form of cavity preparation for dental restorations.

E.g.:

Young Patients – risk of involving dental pulp by mechanically exposing pulp

horn

Tubules of Secondary Dentin scleroses more rapidly than those of the Primary

Dentin. Thus reduce overall permeability of dentin thereby protecting the pulp.

3) TERTIARY DENTIN : - ( Reactive / Reparative Dentin)

This localized formation of Dentin on pulp dentin border , formed in

reaction to trauma such as caries or restorative procedures ( chemical ,

thermal , microbial stimuli ) attrition.

Forms along entire pulp dentin border by cells directly affected by the

stimuli

Quantity depends on the intensity, duration of stimuli

Cells forming it line its surface or become included into Dentin latter case

called osteodentin.

It can be sub classified into :

Refractory Dentin- deposited by pre-existing odontoblasts in response to

mild dentinal stimuli

Reparative Dentin- deposited by newly differentiated ( secondary)

odontoblast like cells in response to more intense

stimuli

Extensive abrasion, erosion, caries or operative procedures may lead death of

the odontoblast processes or deposition of reparative dentin, if they survive.

When the odontoblast processes die, they are replaced by migration of cells in

cell rich zone, undifferentiated perivascular cells arising in deeper regions of the

pulp to dentin interface.

Both remaining and newly differentiated odontoblasts begin to deposit reparative

dentin, which seals off the zone of injury as healing is initiated by pulp, resulting

in resolution of inflammation.

DENTIN PERMEABILITY:Permeability of dentin has been well characterized.

Dentin tubules are the major channels for fluid diffusion across dentin.

Fluid permeation is proportional to the diameter and number of tubules.

Dentin permeability increases as the tubules converge on pulp.

Total tubular surface near dentinoenamel junction is 1% of total surface of dentin

while close to pulp chamber tubular surface is 45 %

Therefore, dentin below deep cavity preparation is more permeable than dentin

underlying a shallow cavity when the formation of sclerotic or reparative dentin is

negligible.

Study has shown that permeability of radicular dentin lower than coronal dentin

because decrease in density of dentin tubules.

Factors modifying dentin permeability is the presence of odontoblast processes

in the tubules and the sheath like lamina limitans that lines the tubules.

In dental caries, inflammatory reaction develops in pulp long before pulp actually

gets infected. This indicates that bacterial products reach pulp in advance of

bacteria.

Dentinal sclerosis below carious lesion reduces permeation by obstructing the

tubules thus decreasing the concentration of irritants into pulp.

Cutting of dentin during cavity preparation produces microcrystalline grinding

debris that coats the dentin and clogs orifices of dentin tubules. This layer of

debris is called smear layer (small particle size, therefore is capable of

preventing bacteria from penetrating dentin).

Removal of grinding debris by acid etching greatly increases permeability of

dentin by using surface resistance and widening orifices of the tubules.

Consequently, incidence of pulpal inflammation may be increased significantly if

cavities are treated with an acid cleanser, unless a cavity liner, base or dentin

bonding agent is used.

PULP

Cells of the Pulp:-1) Odontoblasts

2) Fibroblasts

3) Undifferentiated ectomesenchymal cells

4) Macrophages

5) Dentritic cells

6) Lymphocytes

ODONTOBLASTS:-

Odontoblast is the most distinctive and easily recognized cells of dental pulp.

Because it is responsible for dentinogenesis, both during tooth development and

in mature tooth, they are the characteristic cell of pulp dentin complex.

They form a layer lining the periphery of the pulp and during dentinogenesis the

odontoblasts form the dentinal tubules and their presence in dentin makes dentin

a living tissue.

Odontoblasts, osteoblasts and cementoblats have the general characteristics of

protein secreting cells. The most significant difference between odontoblasts,

osteoblasts and cementoblasts are their morphologic characteristics and the

anatomic relationship between the cells and the structures they produce.

Odontoblasts in the crown of fully developed tooth are columnar and measure

approximately 50 um in height in midpoint of pulp they are cuboid and apical part

more flattened.

Ultrastructural features of odontoblasts:-

The cell body of the active odontoblast has a large nucleus that may contain up

to four nucleoli and the nucleus is situated at basal end of cell and is within a

nuclear envelope. Golgi apparatus is located centrally in the supranuclear

cytoplasm and it consists of an assembly of smooth walled vesicles and

cisternae

Numerous mitochondria are evenly distributed.

Rough endoplasmic reticulum is prominent, consisting of closely stacked

cisternae (dispersed diffusely within the cytoplasm)

Ribosomes mark the site of protein synthesis.

The odontoblast synthesis mainly Type I, collagen (small amounts of type V

collagen have been seen)

They secrete proteoglycans and collagen. They also secrete dentin sialoprotein

and phosphophoryn, a highly phosphorylated phosphoprotein. (This is unique to

dentin)

The odontoblast also secretes alkaline phosphotase.

They resting or inactive odontoblast, has decreased number of organelles and

may become progressively shorter.

Odontoblast Process:-

A dentinal tubule forms around each of major process of odontoblast. The

odontoblast process occupies most of the space within the tubule.

Microtubule and microfilaments are principal ultrastructural components of the

process.

Microtubules extend from the cell body out into the process. These straight

structures are parallel to the long axis of the cell and input the impression of

rigidity.

The plasma membrane of the odontoblast process closely approximates the wall

of dentinal tubules. Localised constrictions in the process occasionally produce

relatively large spaces between tubule wall and process. These spaces may

contain collagen fibrils and ground substance.

The extent to which the process extends outwards in the dentin has been a

matter of considerable controversy. But this knowledge is important in restoring a

tooth, cavity or crown preparation. It has long been thought that the process is

present throughout the full thickness of dentin. However, ultrastructural studies

using electron microscopy, describe the process being limited to inner third of

dentin. This could possibly be the result of shrinkage during fixation and

dehydration during histologic processing.

In an attempt to resolve this issue, monoclonal antibodies were directed against

microtubules to demonstrate tubulin in microtubules of process. Immunoreactivity

was seen throughout the tubule suggesting the process extends throughout the

entire thickness of dentin.

The life span of odontoblasts generally is believed to equal that of viable tooth

because the odontoblasts are end cells, which means, once differentiated, they

cannot undergo further division.

When pulp tissue gets exposed, repair can take place by the formation of new

dentin. This means that new odontoblasts must have differentiated and migrated

to the exposure site from pulp tissue, most likely from the cell rich subodontoblast

zone.

PULP FIBROBLAST:-

The cells occurring in greatest numbers in the pulp are fibroblasts. They are

particularly in the coronal portion of the pulp, where they form cell rich zone.

The early differentiating fibroblasts are polygonal and well separated and evenly

distributed within ground substance.

Cell to cell contacts are established between the multiple processes that exceeds

out from cells and these contacts take the form of gap junctions, which provide

for electronic coupling of one cell to another.

As the cells mature, the cells become stellate in form and golgi complex

enlarges, RER proliferates, secretory vesicles appear and fibroblasts take

appearance of protein-secreting cells.

With an increase in the number of blood vessels, nerves and fibers, there is a

relative decrease in the number of fibroblasts in pulp.

These cells synthesize type I and III collagen, as well as proteoglycans and

GAGS. Thus they produce and maintain matrix proteins of the extracellular

matrix. Fibroblasts are also responsible for collagen turnover in the pulp.

MACROPHAGES:-

Macrophages are the monocytes that have left the blood stream, entered the

tissues and differentiated into subpopulations.

Macrophages appear as large oval or spindle shaped cells that under light

microscope exhibit a dark stained nucleus.

A major subportion of macrophages is quite active in endocytosis and

phagocytes. Because of these activities and mobility, they are able to act as

scavengers, remaining dead cells, dead RBCs, foreign bodies from tissues.

Another subset participates in immune reaction by processing antigen and

presenting it to memory T cells. These help in T cell dependent immunity.

UNDIFFERENTIATED ECTOMESENCHYMAL CELLS:-

These cells represent the pool from which connective tissue cells of pulp are

derived. Depending on the stimulus, these cells may give rise to odontoblasts

and fibroblasts.

They are found throughout the cell rich area and pulp core and often are related

to blood vessels.

They appear as large polyhedral cells possessing a large, lightly stained,

centrally placed nucleus.

In older pulps the number of differentiated mesenchymal cells diminishes, along

with number of other cells in pulp core. This reduction reduces the regenerative

potential of the pulp.

DENTRITIC CELLS:-

Dentritic cells are accessory cells of the immune system. These cells are termed

as “antigen-presenting cells” and are characterized by dentritic cytoplasmic

process and the presence of cell surface class II antigens. Their function is

similar to langerhan’s cells.

They are known to play a central role in the induction of T cell-dependent

immunity.

Like antigen-presenting macrophages, they engulf protein antigens and present

an assembly of peptide fragments of antigens and class I molecules. The

assembly binds to T-cell receptor and T cell activation occurs.

LYMPHOCYTES:-

In normal pulps T-lymphocytes are found but B-lymphocytes are scarce.

The presence of macrophages, dentritic cells and T-lymphocytes indicate that ulp

is well equipped with cells required for the initiation of immune response.

MAST CELLS:-

Mast cells are seldom found in the normal pulp tissue, although they are

routinely found in chronically inflamed pulp. The granules of mast cells contain

heparin, an anticoagulant and histamine, an important inflammatory mediator.

MATRIX AND GROUND SUBSTANCE:-

Connective tissue is a system consisting of cells and fibers, both embedded in

the pervading ground substance or extra cellular matrix.

Fibers and cells have recognizable shapes; extra cellular matrix is described as

being amorphous. It is considered as gel rather sol and therefore considered to

differ from tissue fluids.

Because of its content of polyelectric polysaccharides, extra cellular matrix is

responsible for water holding properties.

The matrix consists of collagen fibers and ground substance.

The fibers are principally type I and II collagen. The ratio of these two remains

stable whereas the overall collagen content of pulp increases with age. The

increased amount organizes into fiber bundle. The greatest concentration occurs

in most apical portion. This is of practical significance when a pulpectomy is

preformed. Engaging the pulp with a barbed broach in the region of the apex

affords a better opportunity to remove the tissue intact than does engaging the

broach more coronally, where the pulp is more gelatinous and liable to tear.

The ground substance resembles any other connective tissue. It is principally

composed of GAG, glycoprotein and water.

GAG acts as adhesive molecules that can bond to cell surfaces and other matrix

molecules.

Fibronectin is a major surface glycoprotein. In pulp the principal proteoglycans

include hyaluronic acid, heparin sulphate and chondroitin sulphate. The

proteoglycan content of pulp tissue decreases approximately 50% with tooth

eruption.

The long GAG chains of proteoglycan molecules from relatively rigid coils

constituting a network that holds water, this forming gel.

Ground substance also acts as a molecular sieve in that it excludes large

proteins and urea cell metabolites, nutrients and waste pass through the ground

substance between cells and blood vessels.

Degradation of ground substance can occur in certain inflammatory lesions in

which there is a high concentration of lysosomal enzymes.

Connective Tissue Fibers of the pulp:-Two types of structural proteins seen are:-

a) collagen

b) elastin

Elastins are confined to the walls of arterioles and unlike collagen are not seen in

extra cellular matrix.

Type I and III collagen are seen in the pulp.

Collagen Fibers in the pulp exhibit typical cross striations at 64 nm (640 A ) and

range in length from 10-100nm or more. Bundles of these fibers appear

throughout the pulp. In very young pulp fine fibers ranging in diameter from 10-

12nm (100-120 A ) have been observed. Their significance is unknown. Pulp

collagen fibers do not contribute to dentin matrix production, which is the function

of the odontoblast. After root completion the pulp matures and bundles of

collagen fibers increase in number. They may appear scattered throughout the

coronal or radicular pulp, or they may appear in bundles. These are termed

diffuse or bundle collagen depending on their appearance, and their presence

may relate to environmental trauma. Fiber bundles are most prevalent in the root

canals, especially near the apical region.

MORPHOLOGIC ZONES OF THE PULP:-

1) Odontoblast layer

2) Cell poor zone

3) Cell rich zone

4) Pulp proper

Odontoblast Layer:-

The outer most stratum of cells of the healthy pulp is the odontoblast layer.

This layer is located immediately subjacent to the predentin; the odontoblast

processes, however pass on through the predentin into the dentin.

The tight packing together of these tall, slender cells produces the appearance of

a palssade. The odontoblasts vary in sheight and often produce the appearance

of a layer 3-5 cells in thickness. Between odontoblasts there are small

intercellular spaces ( app. 300-400 A in width)

Between adjacent odontoblasts there are seriesof specialized cells to cell

junctions (i.e. junctional complexes) including desmosomes (i.e. zonula

adherens), gap junctions (i.e. nexuses) and tight junctions(i.e. zonula occludens)

Gap junctions provide low resistance pathways through which electrical

excitation can pass between cells.

Cell Poor Zone (Weil’s zone):- Immediately subjacent to the odontoblast layer, in the coronal pulp, there

is often a narrow zone approximately 40 mm in width. This is relatively free of

cells.

It is traversed by blood capillaries, unmyelinated nerve fibers, and the

cytoplasmis process of fibroblasts.

The zones presence is dependent on functional status of pulp. It may be

apparent in young pulp, where dentin forms rapidly, or in older pulps, where

reparative dentin is being produced.

Cell rich Zone: - This is a stratum containing a relatively high proportion of fibroblasts,

compared with the more central region of pulp.

It is more prominent in coronal pulp than in radicular pulp.

Besides fibroblasts, the cell rich zone includes number of macrophages, dentritic

cells and lymphocytes.

On the basis of few evidence, it has been suggested that cell rich zone is formed

as a result of peripheral migration of cells in the central region of pulp at the time

of tooth eruption.

Although cell division is rare within this zone, death of odontoblasts causes a

great increase in rate of mitosis.

PULP PROPER:-The pulp proper is the central mass of pulp. It contains the larger blood vessels

and nerves. The connective tissue cells in this zone are fibroblasts or pulpal

cells.

METABOLISM:- The metabolic activity of pulp has been studied by measuring rate oxygen

consumption and the production of carbon dioxide or lactic acid by pulp tissue in

vitro.

Because of relatively sparse cellular composition of pulp, the rate of oxygen

consumption is low compared to other tissue.

During active dentinogenesis, metabolic activity is much higher than after crown

completion. The greatest metabolic activity is found in the region of odontoblast

layer.

The pulp has the ability to produce energy through a phosphogluconase shunt

type of carbohydrate metabolism (in addition to usual glycolytic pathway),

suggesting that the pulp may be able to function under varying degrees of

ischemia. (This explains pulp functioning during vasoconstriction as in local

anaesthesia)

Several commonly used dental materials ( e.g. eugenol, calcium hydroxide, zinc

oxide and eugenol, silver amalgam have shown to inhibit oxygen consumption by

pulp tissue, indicating the capability of depressing metabolic activity of pulp cells.

Even orthodontic forces interfere the metabolic activity.

VASCULAR SUPPLY:-The blood vessels enter and exit the dental pulp by the way of the apical and

accessory foramina.

One or sometimes two vessels of arteriolar size (about 150 um) enter the apical

foramen along with nerve bundles.

Smaller vessels without any nerve bundles, enter the pulp through minor

foramina.

Vessels leaving the dental pulp are associated closely with arterioles and nerve

bundles entering the apical foramen.

The arterioles occupy a central portion within the pulp and as they pass through

radicular portion of pulp, give off smaller lateral branching that extend and branch

into subodontoblastic area.

The number of branches given off in this manner increases coronally, so as to

form an extensive vascular capillary network.

Occasionally U-looping of pulpal arterioles is seen, and tought to be related to

the regulation of blood flow.

The capillaries in the subodontoblastic area range from 4-8 um in diameter, and

the main portion of capillary bed is located just below the odontoblasts.

During dentinogenesis they extend to about predentin. On the periphery of

capillaries at random intervals, pericytes are present. These cells are thought to

be contractile capable of reducing the size of vessel lumen.

Arteriovenous anastomoses (AVAS) may be present in both the coronal and

radicular portions of pulp, such vessels provide direct communication between

arterioles and venules, thus bypassing the capillary bed.

REGULATION OF BLOOD SUPPLY:-Several systems are involved in regulation of pulpal blood flow:-

- Sympathetic adrenergic vasoconstriction

- B-adrenergic vasodilation

- Lymphatic cholinergic vasoactive system

- Antidromic vasodilation system involving sensory nerves,

including axon reflex vasodilatation.

The walls of arterioles and venules are associated with smooth muscle that is

innervated by unmyelinated sympathetic fibers. When stimulated, these fibers

transmit impulse causing muscle fibers to contract, thereby decreasing the

diameter of vessel.

Activation of adrenergic receptor by administration of epinephrine containing

local anesthetic solution results in a marked decrease in pulpal blood flow.

A unique feature of pulp is that it is rigidly encased within the dentin. This

process it in a low compliance environment, much like brain, bone marrow, nail

bed. Thus pulp has limited ability to expand. So, vasodilation and increased

vascular permeability (as inflammation) result in increase pulpal hydrostatic

pressure.

Theoretically, if tissue pressure increases to the point equal to into intravascular

pressure, the venules would be compressed, thereby increasing vascular

resistance and reducing pulpal blood flow. This explains why injection of

vasodilators into an artery leading to pulp results in a reduction rather than

increased blood flow.

LYMPHATICS:-

The presence of lymph vessels in the dental pulp is questioned. Support for this

system stems from the investigators who use injection of fine particulate

substances into dentin or peripheral pulp, which are subsequently reported

present in some of the thin walled vessels that exit apical foramen.

Lymph capillaries are described as endothelium lined tubes that join thin walled

lymph venules or veins in central pulp. The larger vessels have an irregular

shaped lumen composed of endothelial cells surrounded by an incomplete layer

of pericytes, also there is absence of RBC and presence of lymphocytes.

Lymph vessels draining pulp and periodontal ligament have a common outlet.

Those draining anterior teeth pass to submental lymph nodes, those draining

posterior teeth pass to submandibular and deep cervical lymph nodes.

INNERVATION:-

The dental pulp is innervated richly. Nerves enter the pulp through the apical

foramin, along with afferent blood vessels and together form neurovascular

bundle.

Regardless of the native of sensory stimulus, whether it is thermal change,

mechanical deformation, injury to tissues, are afferent impulses from the pulp

result in sensation of pain.

The innervation of the pulp includes both afferent neurons, which conduct

sensory impulses, and autonomic fibers, which provide neurogenic modulation of

microcirculation and perhaps regulate dentinogenesis.

Nerve fibers are usually classified according to their diameter, conduction

velocity and function.

Sl.No. Type of Fiber

Function Diameter (um)

Conduction Velocity (m/sec)

1. A o Motor, proprioception 12-20 70-120

2. AB Pressure, Touch 5-12 30-70

3. A r Motor, to muscle

spindles 3-6 15-30

4. A d Pain, temperature,

Touch 1-5 6-30

5. B Preganglionic

autonomic <3 3-15

6. C dorsal root Pain 0.4-1 0.5-2

7. sympathetic Postganglionic

sympathetic 0.3-1.3 0.7-2.3

In pulp there are two types of sensory nerve fibers:-

1) Myelinated ( A fibers)

2) Unmyelinated ( C fibers)

The might be overlapping between pulpal A and C fibers.

The A fibers include both – A beta and A delta.

The A beta fibers may be slightly more sensitive to stimulation than A delta

fibers.

The sensory nerves of the pulp arise from trigeminal nerve and pass into

radicular pulp in bundles via the foramen. Each of the nerves entering the pulp is

invested within Schwann cells.

Most of the unmyelinated C fibers entering the pulp are located within these

fibers bundles, the remainder are situated towards the periphery of the pulp.

It is noticed that single pulpal nerve fibers have been reported to innervated

multiple tooth pulp.

The A fibers gradually increase after the eruption of teeth. This relatively late

appearance of A fibers in the pulp may help to explain why electric pulp test

tends to be unreliable in young teeth.

The nerve bundles pass upward through radicular pulp together with blood

vessels. Once they reach coronal pulp, they act beneath cell rich zone, branch

into smaller bundles and ramify into a plexus of single nerve axons- Plexus of

Raschkow. Full development of this plexus doesn’t occur until the final stages of

root formation.

It is in the plexus that A fibers emerge from their myelin sheath, and while still in

schwann cells, branch repeatedly to form subodontoblastic plexus.

Finally terminal axons exit from Schwann cells and pass between odontoblasts

as free nerve endings.

With the exception of intracellular fibers, dentin is devoid of sensory nerve fibers.

So pain producing agents don’t elicit pain when applied to exposed dentin.

On basis of their location and pattern of branching several types of nerve endings

have been described and it has been found that some simple fibers run from

subodontoblastic nerve plexus toward the odontoblast layer. But these fibers

donot reach predentin, they terminate in extracellular spaces in cell rich zone,

cell poor zone or odontoblast layer.

Some fibers enter the dentinal tubule. Most of the intracellular fibers extend into

the dentinal tubules only for a few mm, but few may penetrate as far as 100

micron.

The nerve fibers lie in a groove or gutter along the surface of odontoblast

process, and toward their terminal ends they twist around the process like

corkscrew. The cell membranes of odontoblast process and nerve fiber are

closely approximately and run parallel but are not synaptically linked.

If odontoblasts were acting as a receptor cell, it would synapse with adjacent

nerve fiber. But researches have been unable to find synaptic junctions.

Another study showed that a reduction in pulpal blood flow induced by

stimulation of sympathetic fibers leading to pulp, results in depressed excitability

of pulpal a fibers.

Of considerable clinical interest is the evidence that nerve fibers of the pulp are

relatively resistant to necrosis. This is because nerve bundles, in general, are

more resistant to autolysis than other tissue elements

PULP TESTING:-

The electric pulp tester delivers a current sufficient to overcome the resistance of

enamel and dentin and stimulate sensory A fibers at pulp dentin border zone.

Bendel et al found that in anterior teeth the optional placement site of electrode is

incisal edge of anterior teeth, as the response threshold is lowest here and

increases as electrode is moved towards the cervical region or tooth.

Cold tests using carbon dioxide snow or liquid refrigerants and heat tests

employing heated gutta percha or hot water activated hydrodynamic forces within

the dentinal tubules, which in turn excite the intradental A fibers.

It has been shown that cold tests do not injure the pulp. Heat tests have a greater

potential to produce injury.

DENTIN SENSITIVITY:-

One of the most unusual features of the pulp dentin complex is its sensitivity. The

extreme sensitivity of this complex is difficult to explain.

Converging evidence indicates that movement of fluid in the dentinal tubules is

the basic event in arousal of pain.

It now appears that pain producing stimuli, such as heat, cold, airblasts and

probing with the tip of an explorer, have in common the ability to displace fluid in

the tubules. This is referred to as hydrodynamic mechanism of dentin sensitivity.

Thus fluid movement in the dentinal tubules is translated into electrical signals by

sensory receptors located within the tubules or subjacent odontoblast layer.

The evoked pain was of short duration (1-2 sec), on brief application of heat or

cold. The thermal diffusivity of dentin is relatively low, yet the response of the

tooth to tooth stimulation is rapid, often less than a second.

Evidence suggests that –

Thermal stimulation of the tooth results in rapid movement of fluid into dentinal

tubules resulting in activation of sensory nerve terminal in underlying pulp.

Heat expands the fluid within the tubules, causing it to flow towards pulp,

whereas cold cause the fluid to contract, producing outward flow. The rapid

movement of fluid deforms the membrane and activates the receptor.

Some channels are activated by voltage, some by chemicals, and some by

mechanical pressure.

The dentinal tubule is a capillary tube having an exceedingly small diameter.

Therefore the effects of capillary are significant, because the narrower the bore

of capillary tube, the greater the effect of capillarity. Thus if fluid is removed from

the outer end of exposed dentinal tubules by dehydrating the dentinal surface

with an air blast or absorbent paper, or dehydrating solutions, can produce pain if

applied to exposed dentin.

Investigators have shown that it is the A fibers rather than C fibers that are

activated by stimuli applied to exposed dentin. If it is for a longer time, then C

fibers get activated.

It has also been shown that pain producing stimuli are more readily transmitted

from dentin surface when the exposed tubule apertures are wide and the fluid

within the tubules is free to flow outward.

The most difficult phenomenon to explain is pain associated with light probing of

dentin. May be these forces mechanically compress the openings of tubules and

cause displacement of fluid to excite sensory receptors in underlying pulp.

Another example of effect of strong hydraulic forces that are created within the

dentinal tubules is the phenomenon of odontoblast displacement.

The hydrodynamic theory can be applied to an understanding of mechanism

responsible for hypersensitive dentin. Although the dentin may at first be very

sensitive, within a few weeks the sensitivity usually subsides as a result of

gradual occlusion of tubules by mineral deposits.

Currently the treatment of hypersensitive teeth is direct towards reducing the

functional diameter of dentinal tubules to limit fluid movement.

Methods employed are-

1) Formation of a smear layer on sensitive dentin by burnishing the exposed

root surface.

2) Application of agents such as axolane compounds to form insoluble

precipitates within tubules.

3) Impregnation of tubules with plastic resins.

4) Application of dentin bonding agents to seal tubules.

Dentin sensitivity can be modified by laser irradiation.

NEUROPEPTIDES:-

The presence of neuropeptides in sensory nerves is of current interest.

Pulpal nerve fibers contain neuropeptides such as calcitonin gene related peptide

( CGRP), substance P (SP), neuropeptide Y, neurokinin A, and vasoactive

intestinal polypeptide (VIP).

Release of these peptides can be triggered by such things as tissue injury,

complement activation, antigen antibody reactions, or antidromic stimulation of

inferior alveolar nerve. Once released, they produce vascular changes that are

similar to those evoked by histamine and bradykinin (vasodilation). It is reported

that mechanical stimulation of dentin produces vasodilation within pulp.

PLASTICITY OF INNERVATION NERVE FIBERS:-

It is has become apparent that the innervation of tooth is a dynamic complex in

which number, size and cytochemistry of nerve fibers can change because of

dying, tooth injury and dentinal caries. For example, nerve fibers sprout into

inflamed tissue surrounding sites of pulpal injury and the content of CGRP and

SP increases in these sprouting fibers. When inflammation subsides there is a

decrease in the number of sprouts. Regulation of such change appears to be a

function of nerve growth factors (NGF)

NGF receptors are found on intradental sensory fibers and schwann cells.

Maximal sprouting of CGRP and SP containing nerves fibers corresponding to

areas of pulp where there is increases production of NGF.

HYPERALGESIA:-

Three characteristics of hyperalgesia are:-

1) spontaneous pain

2) decreased pain threshold

3) increased response to a painful stimulus.

It is recognized that hyperalgesia can be produced by sustained inflammation as

in case of sunburned skin.

It has been seen that sensitivity of dentin is often increased when pulp becomes

acutely inflamed. We also know that when a pulp chamber of a painful tooth with

an abscessed pulp is opened, drainage of pus soon reduces level of pain. This

suggests that pressure may contribute to hyperalgesia.

In addition certain mediators of inflammation ( eg. Bradykinin, 5-AT,

proteoglandin E2) are capable of producing hyperalgesia.

Leucotriene B4 (LTB4) was shown to have a long lasting sensitizing effect on

intradental nerves, suggesting it may potentiate no receptor activity during pulpal

inflammation.

PAINFUL PULPITIS:-

It is apparent that pain associated with the stimulation of A fibers doesnot

necessarily signify pulp is inflamed or tissue injury has occurred. The clinician

should carefully examine symptomatic teeth to rule out-

- Hypersensitivity

- Cracked or leaking fillings

- Tooth fracture

Pain associated with inflamed or degenerated pulp may be either provoked or

spontaneous.

The hyperalgesic pulp may respond to stimuli that usually do not evoke pain, or

pain may be exaggerated and persist longer. On the other hand, the tooth may

ache spontaneously in the absence of external stimuli. No satisfactory

explanations are there for this pulpal pain.

Narhi has done much to elucidate the role of hydrostatic pressure changes in

activation of pulpal nerve fibers. He theorized that pressure changes produced

local deformities in pulp tissue, resulting in a stretching of sensory nerve fibers.