Pulp dentin complex[1]/Dental implant courses by Indian dental academy

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.

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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 Water

- 20% by weight or 33% by volume - 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

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Peritubular Dentin

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Intertubular Dentin

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Interglobular Dentin

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Incremental growth lines

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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.

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Thought to be true spaces.

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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.

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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 1012nm (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)

1.

Ao

Motor, proprioception

12-20

Conduction Velocity (m/sec) 70-120

2.

3.

AB Ar

Pressure, Touch Motor, to muscle

5-12

30-70

3-6

15-30

4.

Ad

spindles Pain, temperature,

6-30

B

Touch Preganglionic

1-5

5.

C dorsal root sympathetic

autonomic Pain Postganglionic

<3 0.4-1

3-15 0.5-2

sympathetic

0.3-1.3

0.7-2.3

6.

7.

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 â&#x20AC;&#x201C; 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 doesnâ&#x20AC;&#x2122;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 donâ&#x20AC;&#x2122;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 â&#x20AC;&#x201C; 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 are1) 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.