Dr. Ashok AyerAssistant ProfessorDepartment of Conservative Dentistry & EndodonticsB.P.Koirala Institute of Health Sciences, Dharan, Nepal

Contents:

Introduction Coronal and radicular pulp Apical foramen Accessory canal Functions of dental pulp Components of dental pulp Functions of pulpal extracellular matrixOrganization of cells in the pulp The principle cells of the pulp The pathways of collagen synthesisMatrix and ground substances Vasculature and lymphatic supply Innervation of Dentin- pulp complex Disorders of the dental pulp Advances in pulp vitality testing Conclusion

Dental Pulp

Occupies the center of each tooth.

Soft connective tissue that supports the dentin.

Total 52 pulp organs; 32: Permanent, 20: Primary

Total Volume of all permanent teeth pulp organs is 0.38 cc.

Mean volume of a single adult human pulp is 0.02 cc.

Maxillary (Cubic Centimeter)

Mandibular (Cubic Centimeter)

Central Incisor 0.012 0.006

Lateral Incisor 0.011 0.007

Canine 0.015 0.014

First Premolar 0.018 0.015

Second Premolar 0.017 0.015

First Molar 0.068 0.053

Second Molar 0.044 0.032

Third Molar 0.023 0.031

Orban’s Oral histology & embryology: Pulp; Department of Oral Surgery, Newcastle - Tyne, England

Coronal Pulp:

Six surfaces

Pulp horns, dependson the cuspalnumber.

Radicular Pulp:

The radicular portion of the pulp organs arecontinuous with the periapical connective tissuethrough the apical foramen or foramina.

As growth proceeds, more dentin is formed, so thatwhen the root of teeth are matured the radicular pulpis narrower.

The apical pulp canal becomes smaller also because ofapical cementum deposition.

Apical foramen:

Average size of apical foramen of the maxillary teethin the adult is 0.4 mm

Mandibular teeth 0.3 mm

Sometimes it is found on the lateral side of the apexalthough the root itself is not curved.

Frequently there are two or more foramina separatedby a portion of dentin and cementum or by cementumonly.

Accessory canal:

Leading from the radicular pulp laterally through theroot dentin to the periodontal tissue.

May be seen anywhere along the root but are mostnumerous in the apical third of the root.

Clinically significant in spread of infection, eitherfrom the pulp to the periodontal ligament or viceversa.

Occur in areas where there is premature loss of rootsheath cells; these cells induce the formation ofodontoblasts which form dentin.

May also occur where the developing root encountersa blood vessel.

Functions of dental pulp

Inductive: Interact with the oral epithelial cells

Differentiation of the dental lamina and enamel organ formation.

Cells of pulp + blood vessels & nervesprovides the tooth vitality

Formative:

Produces dentin that surrounds and protects the pulp.

Pulpal odontoblasts develop the organic matrix andfunction in its calcification.

Nutritive:

Blood vascular system of the pulp; nourishes dentin through the odontoblasts and their processes.

Protective:

Sensory nerve respond to pain

Nerves initiate reflexes that control circulation in the pulp.

Defensive or reparative:

First line of defense to injuries and infection of dentine

Tertiary dentine

Immuno-competent

Clearance of toxic substances

Components of dental pulp

Cells + (extracellular) Matrix

Fiber Ground substance

• Collagen

• Elastin

Structural Adhesive

• Fibronectin

• Laminin

• HS

• DS

• CS

GAG Proteoglycan

• Decorin

• Versican

Components of dental pulp

CELLS (odontoblast, fibroblast,

undifferentiated cell, macrophage,

dendritic cell)

FIBERS AND GLYCOPROTEIN (collagen

type I, III, no elastic fiber, fibronectin)

GROUND SUBSTANCES

(glycosaminoglycans, chondroitin sulfate

proteoglycan)

BLOOD VESSELS, NERVES, LYMPH

VESSELS

Maintain tissue’s physical properties and integrity

Control of growth and development and repairs

Control of cell migration

Control of diffusion of macromolecules

Functions of pulpal extracellular matrix

Collagen in dental pulp

Concentration varies from species to species, 32% in human pulp.

Higher content in the middle and apical pulp.

Total collagen decreases with age.

Interestingly high level of collagen type III. (43%) : vascular content, tissue extensibility (cf. Elastin)

Absence of elastin (except in b.v.).

Adhesive glycoproteins in dental pulp

Fibronectin found inpredentine NOT maturedentine.

Fibronectin present inpulp and dental papilla.

Fibroblasts synthesizepulpal fibronectin.

Fibronectin is expressedduring reparativedentinogenesis.

Immunoreactive fibronectin molecules detected

along the border of predentine and between odontoblast (Yoshiba et al., 1994)

Glycosaminoglycans in dental pulp

Chondroitin sulfate, dermatan sulfate, hyaluronicacid present

Amount of uronic acid decreases with age

Total GAG decreases with reduced dentinogenicactivity

Decorin may involve in mineral nucleation at themineralization front

Organization of cells in the pulp

tight junction

nerve terminals

Four distinct zones:

1. The odontoblastic zone at the pulp periphery

2. A cell free zone of Weil beneath the odontoblast;prominent in the coronal pulp

3. A cell rich zone; high cell density

4. The pulp core; major vessels and nerves

The principle cells of the pulp:

Odontoblasts

Fibroblast

Undifferentiated mesenchymal cells

Macrophages

Immunocompetent cells

Odontoblasts:

The most distinctive cells of the dental pulp

Form a layer lining the periphery of the pulp and havea process extending into the dentin

Arranged in palisade pattern of three to five cells deep

59,000 to 76,000 per square milimeter in coronaldentin, with a lesser number in root dentin.

Active cells:

Elongated, basal nucleus, much basophilic cytoplasm, promonent golgi zone.

Resting cell:

Stubby, little cytoplasm, more hematoxophilic nucleus.

Odontoblast process begins at the neck of the cellsjust above the apical junctional complex where the cellgradually begins to narrow as it enters predentin.

The process is devoid of major organelles but doesdisplay an abundance of microtubules and filamentsarranged in a linear pattern along its length.

The pathways of collagen synthesis:

The spherical distensions contain free polypeptidesthat assemble as a triple helix in the cylindricaldistensions to form the procollagen molecule.

The cylindrical distension bud off as secretorygranules.

Secretory granules that are transported toward theodontoblast process, where their content is released.

Synthesis of collagen and its assembly into fibrils and fiber

Some types (of 15) of known collagen

Type Molecular Tissue distribution

Fibril-forming I [a1(I)]2 a2(I) bone, skin, tendon, ligaments

(90%) of body collagen

II [a1(II)]3 cartilage, intervertebral disc,

notochord, vitreous humor of eye

III [a1(III)]3 skin, blood vessels, internal organs

V [a1(V]2 a2(V) as type I

XI [a1(XI] a2(XI) a3(XI) as type II

Fibril-associated IX [a1(IX] a2(IX) a3(IX) cartilage (with type II)

XII [a1(XII)]3 tendon, ligaments (with some type I)

Network-forming IV [a1(IV)]2 a2(IV) basal laminae

VII [a1(VII)]3 anchoring fibrils beneath stratified

squmous epithelia

RGD = cell-binding domain

The structure of a fibronectin dimer.

Structure of a GAG

Structure of proteoglycans

Aggrecan mechanical support

(cartilage)

Betaglycan binds TGF-beta

(cell surface*, matrix)

Decorin binds type I and (CNT)

TGF-beta

Perlecan basal laminae

(basal laminae)

Syndecan-1 binds FGF

(cell surface*)* = Integral membrane proteoglycan

Some known proteoglycans:

Junctions occur between adjacent odontoblastsinvolving

Gap junctions

Occluding zones (Tight junctions)

Desmosomes

The actin filaments inserting into the adherent junction are prominent and form a terminal cell web.

This junctional complex does not form a zonula,completely encircling the cell, as occurs in epithelia;

(it is focal, and there is some debate whether it canrestrict the passage of molecules and ions from thepulp into the dentin layer)

Serum proteins seem to pass freely betweenodontoblasts and are found in dentin

Fibroblasts:

Greatest number in the pulp

Numerous in coronal pulp where they form the cell-rich zone.

The function is to form and maintain pulp matrix.

Undifferentiated Ectomesenchymal Cells:

Represents the pool from which the connective tissuesof the pulp are derived.

Depending upon the stimulus these cells may give riseto odontoblasts and fibroblasts.

In older pulp they diminish, thereby reducing theregenerative potential of the pulp.

Macrophages

Located throughout the pulp center.

Involved in the elimination of dead cells, the presenceof which indicates that turnover of dental pulpfibroblast occurs.

Lymphocytes

In normal pulp T lymphocytes are found, but B lymphocytes are scare.

Dendritic Cells

Bone marrow derived, antigen presenting dendriticcells.

Beneath the odontoblast layer.

They capture and present foreign antigen to the T cells.

Cells participate in immunosurvillance and increase in number in carious teeth.

Infiltrate odontoblast and project their processes into the tubules.

8% of total cell population.

Matrix and Ground Substance

Principally Type I and Type III collagen.

Composed of glycosaminoglycans, glycoproteins, and water.

Overall collagen content increases with age.

The greatest concentration of collagen generallyoccurs in the most apical portion of the pulp.

Significance:

During pulpectomy; Engaging the pulp with a barbedbroach in the region of apex affords a betteropportunity to remove the tissue intact.

Vasculature and Lymphatic Supply

Circulation establishes the tissue fluid pressure.

One or sometimes two vessels of arteriolar size(about 150µm) enter the apical foramen with thesensory and sympathetic nerve bundles.

Smaller vessels, without any accompanying nervebundle, enter the pulp through the minor foramina.

Pulp vasculature

The arterioles occupy a central position within thepulp and, as they pass through the radicular portion ofpulp, give off smaller lateral branches.

Occasionally U- looping of pulpal arterioles is seen,and this anatomic configuration is thought to berelated to the regulation of blood flow.

Pulp tissue is highly vascularized.

40-50 ml/min/100g

(Kim, 1985)

Some terminal capillary loops extend upward betweenthe odontoblasts to abut the predentin ifdentinogenesis is occurring.

Located on the periphery of the capillaries at randomintervals are pericytes.

Pericytes are contractile cells capable of reducingthe size of the vessel lumen.

Anastomosis are point of direct communicationbetween the arterial and venous sides of thecirculation.

Lymphatic vessels also occur in the pulp tissue, theyexit via one or two large vessels through the apicalforamen.

Sympathetic adrenergic nerves terminate in relationto the smooth muscle cells of the arteriolar walls.

Afferent free nerve endings terminate in relation toarterioles, capillaries and veins and serve as effectorsby releasing various neuropeptides that exert aneffect on the vascular system.

Dental pulp interstitial fluid (ISF) and exchange of substances between plasma and ISF. (* values from Tonder and Kvinnsland, 1983; Ciucchi et al., 1995)

(5.5-10.3 mm Hg*)

(43 mm Hg)

(20 mm Hg)

(35 mm Hg)

Hydrostatic pressure in dental pulp

Innervation of Dentin- Pulp Complex

Nerve enter the pulp throughapical foramen, along theafferent blood veessels, andtogether from theneurovascular bundle.

Each nerve fiber has beenestimated to provide at leasteight terminal branches.

These branches ultimately contribute to anextensive plexus of nerves in the cell freezone just below the cell bodies of theodontoblasts in the crown portion of thetooth.

Approx. 1800 non myelinated +400 myelinated

Intradentinal nerves are mostly found in pulpalhorns.

This plexus of nerves, which is called thesubodontoblastic plexus of Raschkow, occupies thecell- free zone of Weil and can be demonstrated insilver nitrate stained sections under the lightmicroscope or by immunocytochemical techniques.

The nerve bundles that enter the tooth pulp consist principally of :

Sensory afferent nerves of the trigeminal nerve

and

Sympathetic branches from the superior cervical ganglion.

As the nerve bundle ascends coronally;

The myelinated axons gradually loose their mylein coating,

So that a proportional increase in the numberof unmyelinated axons occurs in the morecoronal aspect of the tooth.

A-delta fibers Conduction velocity 2-30 m/s

Lower threshold

Involved in fast, sharp pain

Stimulated by hydrodynamic stimuli

Sensitive to ischemia

Sharp pain

C fibers Conduction velocity 0-2 m/s

Higher threshold

Involved in slow, dull pain

Stimulated by direct pulp damage

Sensitive to anesthetics

Dull pain

Types and properties of pulpal sensory nerve fibers

A-beta fibers Conduction velocity 30-70 m/s

Very low threshold, non-noxious sensation

50% of myelinated fibers in pulp

Functions not fully known

Non-myelinated sympathetic fibers

Conduction velocity 0-2 m/s

Post-ganglionic fibers of superior cervical ganglion

Vasoconstriction

A small number of axons pass between theodontoblast cell bodies to enter the dentinal tubulesin proximity to the odontoblast process.

Possible mechanisms of dentine sensitivity

Hydrodynamic mechanism(Gysi, 1900; Brannstrom, 1963)

Pulp venules

STIMULATION

Increased pulp interstitial fluid

Increased pulp pressure

Increased tubular fluid flow

Release of inflammatory

agents?

Increased blood viscosity and rbc

congestion in capillary bed

Increased A-V shunt blood flow

Outward dentinal fluid flow and aspiration of odontoblasts

CNS, Pain, Reflexes

Vasodilation, Increased permeability

Pulpal axonal reflex due to dentine stimulation

Without infection, Vascular changes couldbe resolved.

Axon reflex

SP, CGRP

Dentine

Disorders of the Dental Pulp

Pulp Stones

Pulp stones, or denticles, frequently are found in pulptissue.

Discrete calcified masses that have calcium phosphorusratios comparable to that of dentin.

More frequently at the orifice of the pulp chamber orwithin the root canal.

Concentric layers of mineralized tissue formed bysurface accretion around blood thrombi, dying ordead cells, or collagen fibers.

Occasionally a pulp stone may contain tubules andbe surrounded by cells resembling odontoblasts.

Such stones are rare and, if seen, occur close to theapex of the tooth. Such stones are referred to as ‘true’pulp stones as opposed to ‘false’ stones having no cellsassociated with them.

If during the formation of a pulp stone, union occursbetween it and the dentin wall, or if secondary dentindeposition surrounds the stone, the pulp stone iscalled an attached stone.

The presence of pulp stones is significant in that

They reduce the overall number of cells within the pulp

and

Act as an impediment to debridement and enlargement of the root canal system during

endodontic treatment.

Age Changes

Decrease in the volume of pulp chamber and rootcanal brought about by continued dentin deposition.

On occasion can appear to be obliterated almostcompletely.

From about the age of 20 years, cells graduallydecrease in number until age 70, when the cell densityhas decreased by about half.

Fibrosis is due to aging & Injury.

Increase in collagen fibers’bundles which becomes moreevident with the decrease in pulpsize

Lose and a degeneration of myelinated andunmyelinated axons that correlate with an age-related reduction in sensitivity.

Irregular areas of dystrophic calcification,especially in central pulp.

Gradual reduction of tubule diameter.

The continued deposition often leads to complete closure of the tubule;

as can be seen readily in a ground section of dentin, because the dentin becomes translucent (or sclerotic).

Sclerotic dentin is found frequently near the root apex in teeth from middle aged individuals.

Pulpitis

Acute or chronic.

Partial or total.

Open or closed.

Exudative or suppurative.

Reversible or irreversible.

Pulpitis is a dynamic process and presents acontinuous spectrum of changes reflectinginterplay between cause and hostdefenses.

Poor correlation between microscopicchanges & clinical symptoms.

Pulpitis: Clinical Features

Presents as pain which patient may have difficultyin localizing to a particular tooth.

Pain may radiate to adjacent jaw, face, ear, or neck.

May be continuous for several days or may occurintermittently over a longer period.

Pulpitis is often described as acute or chronicbased on duration and severity of symptoms.

Acute pulpitis

Severe throbbing, lancinating pain on thermalstimulation or lying down, keeps patient awake.

Generally lasts 10-15 minutes but may be more orless continuous (reversible pulpitis).

With progression, may become spontaneous &continuous (irreversible pulpitis).

Chronic pulpitis

Bouts of dull aching which can last for an hour or more.

Pain on thermal stimulation or spontaneously.

Pulpitis may be asymptomatic.

Most important decision clinically is whetherpulpitis is reversible or irreversible.

Decision is made based on many factorsincluding:

1. Severity of symptoms.2. Duration of symptoms.3. Size of carious lesion.4. Pulp tests.5. Direct observation during operative procedure.6. Age of patient.

Pulpitis: Etiology

Microbial:

Dental caries.

Traumatic exposure.

Marginal leakage.

Cracked tooth

Coronal fracture.

Attrition.

Abrasion.

Traumatic restorative procedure.

Invaginated odontome.

Advanced periodontitis (periodontal-endodonticlesion).

Pulpitis starts before leading organisms incarious dentin reach pulp.

Pulpitis is not usually seen histologicallyuntil organisms are within 1 mm of thepulp in permanent teeth, or 2 mm indeciduous teeth.

Chemical and thermal injury

During restorative procedures: frictional heat, irritant substances.

May respond by reactionary dentin formation.

Barotrauma (aerodontalgia)

Flying at high altitude in unpressurized aircraft,or rapid decompression in divers.

Attributed to formation of nitrogen bubbles inpulp tissue or vessels.

Thought not to be a direct cause, but rather anexacerbating cause in presence of caries.

Pulpitis: Histopathology

Poor correlation between microscopic changes &clinical symptoms.

Inflammatory process may be modified byseveral factors:

Nature, severity and duration of insult. Efficiency of host defenses. Efficiency of pulpo-dentinal complex defenses. Special anatomy of pulp: surrounded by hard

tissue and cannot tolerate edema.

85

Reactionary dentin may continue to form afteronset of pulpitis if odontoblasts and pulp have notbeen irreversibly damaged, and may protect pulp.

Pulpitis caused by caries starts as a localized area,but extends throughout pulp if caries is nottreated.

86

If inflammation is severe, localmicrocirculation may be compromised,leading to local necrosis and suppurationof pulp (pulp abscess), or diffusesuppuration and necrosis.

Pulpitis: Chronic Hyperplastic Pulpitis(Pulp Polyp)

Open pulpitis or chronic hyperplastic pulpitis (pulp polyp):

Large carious cavities.

Young molar teeth with wide apices and good blood supply.

88

Usually devoid of sensation on gentle probing.

Polyp consists of chronically inflamedhyperplastic granulation tissue protrudingfrom pulp cavity.

May become epithelialized by spontaneousgrafting of desquamated oral epithelial cells fromsaliva.

Pulp Necrosis

May follow pulpitis or trauma to apical blood vessels.

Coagulative necrosis after ischemia.

90

Liquefactive necrosis after pulpitis;

may become gangrenous with foul odor upon infection by putrefactive bacteria from caries.

Pulp necrosis in sickling crisis of sickle cell anemia.

Restorative factors contributing to pulpal injury

Effects of cavity Preparation:

Frictional heat

Desiccation

Exposure of dentinal tubules

Direct damage to odontoblast processes

Chemical treatment to exposed dentinal surface

Cavity preparation: speed, heat, pressure &coolant may all cause pulp irritation.

Aspiration or displacement of odontoblasts intodentinal tubules, with reduction of numbers.

94

Factors associated with the restorative material & its placement

Material toxicity

Insertion pressure

Thermal effects

Induced stresses

Effects subsequent to restoration

Marginal leakage

Cuspal fracture

Effects of cavity preparation & restorative materials mayfurther complicate pulpitis caused by caries or othercauses.

Thickness & nature of remaining dentine may affect pulpresponse to dental material.

Advances in Pulp Vitality testing

Pulse Oximetry

Dental sensor (a modified finger probe) that can besuccessfully applied and adapted to the tooth and wellsuited to detect pulsatile absorbance.

The principle: relates the absorption of light, by asolute to its concentration and optical properties at agiven light wavelength.

It also depends on the absorbancecharacteristics of haemoglobin in the redand infra-red range

In the red region, oxyhaemoglobinabsorbs less light than deoxyhaemoglobinand vice versa in the infrared region.

Hence one wavelength was sensitive tochanges in oxygenation and the second wasinsensitive to compensate for changes intissue thickness, haemoglobin content andlight intensity.

The system consists of a probe containing a diode thatemits light in two wavelengths:

I. Red light of approximately 660 nm

II. Infra-red light of approximately 850 nm

It is also useful in cases of impact injury wherethe blood supply remains intact but the nervesupply is damaged

Dual Wavelength Spectrophotometry

Dual wavelength spectrophotometry (DWLS) is amethod independent of a pulsatile circulation.

The presence of arterioles rather than arteries in thepulp and its rigid encapsulation by surrouding dentineand enamel make it difficult to detect a pulse inthe pulp space.

This method measures oxygenation changes inthe capillary bed rather than in the supply vesselsand hence does not depend on a pulsatileblood flow.

A major advantage is that it uses visible lightthat is filtered and guided to the toothby fibreoptics

The test is noninvasive and yields objective results.

Laser doppler flowmetry

Laser Doppler Flowmetry (LDF) is a noninvasive,electro optical technique,

Which allows the semi-quantitative recording of pulpal blood flow.

The Laser Doppler technique measures bloodflow in the very small blood vessels of themicrovasculature.

The technique depends on the Doppler principle;

whereby light from a laser diode incident on the tissue is scattered by moving RBC's

and

As a consequence, the frequency broadened.

The primary issues in pulp-vitality testing as follows:

A non-vital post-traumatized incisor has a better long-term prognosis;

If root canal therapy is completed before the necrotic pulp gets infected.

The best outcome for the post traumatized immature incisor is for it;

To revascularize and,

Continue normal root development, including increased root wall thickness.

Which is not possible to assess with conventionalelectrical and thermal testing

Conclusion

Thus the Preservation of Healthy Pulp duringoperative procedures and successful managementin cases of disease are two of the most importantchallenges.

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