14 Pulp Biology

8/2/2019 14 Pulp Biology

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Pulp Biology

Joyce Chia-Yi Chen, DDS

Division of Endodontics, School of Dental and Oral Surgery

Columbia University


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Topics

Embryology of the dentalpulp

Pulpodentin complex

Pulp tissue

Pulp reaction to caries anddental procedures


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Early Development of Pulp

Pulp originates from ectomesenchymal cells ofthe dental papilla.

Differentiation of odontoblasts is accomplished

through an interaction among mesenchymalcells, dental epithelium, basement membrane,and proteins present in extracelluarcompartment.

Cells of inner enamel epithelium are importantand essential participants in this differentiationprocess.


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Formation of dentin by odontoblastsbegins with deposition of unmineralizedmatrix at the cusp tip and progressescervically.

Deposition is rhythmic and regular,averaging about 4.5 m per day, and

follows the crown shape that has beenpredetermined by the proliferative patternof inner enamel epithelium.


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During crown formation, growth andorganization of the pulp vasculature

occur. Unmylinated sensory nerves and

autonomic nerves grow into pulpaltissue.

Myelinated sensory nerve ingrowth isslower to develop and mature.


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Root Formation

In the cervical region of the crown, thejunction between the inner and outerenamel epithelia is known as the cervicalloop.

From this region, root formation begins,initiated as apical proliferation of the twofused epithelial structures (Hertwigsepitelial root sheath).

After the first dentin has formed, theunderlying basement membrane breaks up,and the innermost root sheath cells secretea hyaline-like material over the newlyformed dentin.


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Root Formation

Fragmentation of Hertwigs epithelial rootsheath also allows cells of the investingfollicle to pass through and contact thenewly formed dentin surface.

Here the cells differentiate intocementoblasts and initiate cementumformation.

Portions of the fragmented root sheath

persist in the periodontium in closeproximity to the root after rootdevelopment epithelial cell rests ofMalassez.


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Pulp tissue

light micrograph of mature coronal pulp


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Something about the Pulp

normal mandibular first molar at

50 days of postnatal life. (Reprinted

from DSouza et al with permission)


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A soft tissue of mesenchymal originwith specialized cells, the

odontoblasts, arranged peripherally indirect contact with dentin matrix.

In many ways similar to otherconnective tissues of the body,including nerves, vascular tissue,connective tissue fibers, ground

substance, interstitial fluid, fibroblasts,antigen-presenting cells..etc.


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Unlike most tissue the pulp lacks atrue collateral systemand is

dependent on the relatively fewarteriols entering through the rootforamina.

Within a low-compliance environmentthat limits its ability to increase involume during episodes ofvasodilation and increased tissue

pressure.Careful regulation of blood flow is critically

important to the vitality of the pulp.


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Pulp tissue

Cells in the pulp

Odontoblasts

FibroblastsUndifferentiated mesenchymal cells

Immunocompetent cells


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Odontoblasts

They belong to the unique group ofspecialized cells, like the nerve cells,that normally last the entire life of theteeth.

If destroyed by trauma, inflammation orother means, replacement odontoblasts

may be differentiated fromundifferentiated cells in the dental pulpunder favorable conditions.


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The Odontoblast Porcess

Devoid of the typical organellesassociated with protein synthesis

Its ultrastructure demonstratesmicrotubules, microfilaments,granules and vesicles.

The full length of odontoblast processis in the pulpal 0.1mm to 1mm of thedentin.


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Undifferentiated Cells

Depending on the stimulus they maygive rise to fibroblasts and

odontoblasts. These precursor cells are found in the

cell-rich zone adjacent to theodontoblast layer and in the pulp coreassociated with blood vessels.


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Fibroblasts

The most common cell type in thepulp.

Producing collagen and groundsubstance and eliminate collagenduring the process of remodeling.

Present throughout the pulp but tendto concentrate in the cell-rich zone.


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Immunocompetent Cells

Antigen-presenting dendritic cells arepresent in the odontoblast layer, andmacrophae-like cells are foundcentrally in the pulp.

A small number of recirculating T cellsare identifiable whereas B cells are

extremely rare or undetectable. Plasma cells are absent in the normal

pulp.


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Extracellular matrix

Type I collagen is the predominantcollagen in dentin, whereas both type

I and type III collagen are found inpulp.

The overall collagen content becomesmore apparent with age because it isorganized more as bundles.


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Extracellular matrix

Pulp ground substance is composedprincipally of glycosaminoglycans,glycoproteins, and water.

A sol-gel that supports cells and actsas medium for transport of nutrientsand metabolites.

The interstitial fluid is similar incomposition to plasma except for lessplasma proteins, favoring capillaryabsorption.


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Blood supply in the pulp

Arterioles and venules enter and leave thedental pulp through the apical foramen. Theybranch and end up in a dense capillary network

which is particularly predominant in thesubodontoblastic region.


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All capillaries in the subodontoblasticlayer are normally not functional at the

same time. They may be filled quickly and an

almost instant local or generalhyperemia may be established duringpulp irritation.


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The presence of lymphatics in thedental pulp was once a debate.

However, studies have confirmed theirexistence.

The lymphatic vessels are composedof an endothelium with opening in thewalls, which permit passage ofinterstitial tissue fluid and removeinflammatory exudates.


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Pulp tissue pressure

Compared to most other tissues, thepulpal tissue pressure seems high, 5-

20 mmHg. The significance of a relatively high

tissue pressure in a low complianceenvironment may be linked to aneurogenic defense mechanism thathelps to protect the pulp against entryof harmful agents via exposed

dentinal tubules


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Innervations of the pulp

V2 and V3 of the trigeminal nerveprovide the principal sensoryinnervation to the pulp of maxillaryand mandibular teeth.

Pulp also receives sympatheticinnervation from T1 and T2 via the

superior cervical ganglion. Theycauses pulpal vasoconstrictionthrough activating alpha receptors.


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Myelinated A- and non-myelinated C-fibers are somatic afferent nerves

which carry sensory pain impulses. Stimulation of A- fibers results in fast,

sharp, and relatively localized pain.Stimulation of C fibers produces painthat is slower in onset and duller andmore diffuse.


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The sensory nerve fibers, which areresponsible for tooth sensation, also

have a profound impact on pulpalcirculation through releasingneropeptides.

Release of neuropeptides from pulpalnerve endings may in fact be theearliest reaction to pulp inflammation.


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Pulp-dentin organ


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Developmentally, Pulp and dentin developfrom the dental papilla during the bell stageof the enamel organ.

Structurally, pulpal elements such asodontoblast processes and neuronalterminals extend into the dentin


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In functional aspect,

1) pulp is capable of elaborating

dentin both physiologically and inresponse to external stimuli

2) pulp carries nerves that give dentin

its sensitivity3) encapsulation in dentin creates alow-compliance environment thatinfluences the defense potential of the

pulp


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Although the dentin and pulp arebasically different, they remain

anatomically and functionally closelyintegrated throughout the life of thetooth. Thus, the two tissues are oftenreferred to as the pulpodentincomplex.

All procedures performed in dentinare in essence treatment of bothdentin and pulp.


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cavity preparationon the cervical root of a rat molar


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Dentin Hypersensitivity

Pain elicited by scraping or cutting ofdentin or by application of cold or

hypertonic solutions.


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Theories of DentinHypersensitivity

Direct Innervation of dentin

- the nerves are present only in the

inner third of the dentin- nerves are absent in root dentin

- application of pain-producing and

pain-relieving substances to dentinfails to elicit a nervous response.


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Odontoblasts as Receptors

the odontoblast process extended

only partway through dentinthe odontoblast membrane potential istoo low to permit transduction


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Hydrodynamic theory

Brannstrom and Astrom, 1972

rapid movement of fluid in the dentinaltubules results in distortion of nerveendings in the plexus of Raschkow.


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Agents that block exposed dentinaltubules

Pashley discovered that oxalate saltsare effective agents to block dentinaltubules.

Potassium oxalate solution forms amicrocrystal consisting of calciumoxalate.


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Agents that reduce intradental nerveexcitability

Sodium, lithium, and aluminumcompunds have little effects onreducing sensory nerve activity

Potassium compounds were mosteffective ingredients for sensory nerveactivity reduction.


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Dental Caries

Affected dentin & Infected dentin

Diagrammatic illustration of Newbruns six zones


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Pulpal reaction to Cariesand Dental Procedures


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Pulpal Reaction to DentalCaries

A decrease in the dentin permeability

dentin sclerosis

dentinal tubules become partially orcompletely filled with apatite andwhitlockite crystals


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The formation of tertiary dentin

Reactionary dentin is defined as a tertiarydentin matrix secreted by survivingpostmitotic odontoblast cells

Reparative dentin is defined as a tertiarydentin matrix secreted by a new generationof odontoblst-like cells in response to anappropiate stimulus after the death of theoriginal odontoblasts.


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Effects of local anestheticson the pulp

Both infiltration and mandibular blockinjections cause a significant

decrease in pulpal blood flow. With the ligamental injection, pulpal

blood flow ceases completely forabout 30 minutes when 2% lidocaine

with 1: 100,000 epi. is used.


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Effects of local anestheticson the pulp

Irreversible pulpal injury is particularlyapt to occur when dental procedures

such as full crown preparations areperformed immediately following aligamental injection.

the release and accumulation of

vasoactive agents, such as substanceP, during tooth preparation


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Cavity and Crown preparation

It was found in a retrospective studythat 11% of over 1000 restored teeth

followed for a long period of timeshowed pulp necrosis

During the preparation of a tooth andthe placement of a restoration there

are many steps during which pulpaldamage can occur.


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Frictional Heat

Blushing of teeth during or after cavityor crown preparation has beenattributed to frictional heat.

It represents vascular stasis in thesubodontoblastic capillary plexusblood flow.

A dark purplish color indicatesthrombosis, and is associated with apoor prognosis.


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Frictional Heat

The greatest potential for damage waswithin a 1- to 2- mm radius of the dentin

being cut. It is imperative to utilize sufficient water

cooling, well-centered burs and minimalpressure to avoid frictional heat.


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Desication of dentin

When the surface of freshly cut dentinis dried with a jet of air, there is a

rapid outward movement of fluidthrough the dentinal tubules.

Fluid movement results in stimulationof the sensory nerve of the pulp and

drawing odontoblasts up into thetubules.

Do not overdry the cavity preparation


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Remaining dentin thickness

Odontoblast cell numbers were unaffectedby cavity preparation as close as 0.5mm tothe pulp. Deeper cutting (less than 0.3mm

from the pulp) resulted in direct odontoblastinjury and cell death.

It has been shown in vitro that 1mm ofremaining dentin reduces the effect of atoxic material to 10% of the original leveland a 2mm dentin thickness basicallyprevents any pulpal insult by a toxicmaterial.


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Restorative Materials

Properties of materials that producepulp injury

AcidityAbsorption of water during setting

Heat generated during setting

Poor marginal adaptation resulting inbacterial contamination


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Restorative Materials

The pulpal reaction to dental materials ismainly transitory and a manifestinflammation only occurs after bacteria or

their byproducts have been able to reachthe pulp.

Studies have shown that when bacterialcontamination can be prevented, favorablepulpal responses are seen, even tomaterials with established track records ofbeing harmful to the pulp, such as silicatecement and acrylic resin


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Zinc Oxide-Eugenol

Eugenol is known to be toxic, and it iscapable of producing thrombosis ofblood vessels when applied directly to

pulp tissue. It also has anesthetic properties

through blocking the transmission of

action potentials in nerve fibers. Because eugenol injures cells, some

authorities suggest ZOE should notused in very deep cavity preparations

where there is a risk of pulp exposure.


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Zinc Phosphate Cement

When a liner was omitted, severepulpal reactions occurred in teeth

where deep class V cavities wererestored with zinc phosphate cement.

It is likely that irritation to the pulp wasdue primarily to marginal leakage

rather than acidity.

Zi P l b l


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Zinc PolycarboxylateCements

It is well tolerated by the pulp, beingroughly equivalent to ZOE cements.

This may be due to its ability to adaptwell to dentin.


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Composite Resins

The bond strength is less in the deepportion of a cavity compared to

superficial dentin, due to a decreasedarea of intertubular collagen which isnecessary for the formation of ahybrid layer.

It is still advisable today to use a basematerial in the deepest part of a cavity.


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Glass-Ionomer Cement

In vivo tests demonstrated onlyminimal pulp reactions when modifiedglass ionomers was evaluated in non-human usage models.

A in vivo study of direct capping underproper hemorrhage control showed

pulp healing and dentin bridgeformation.


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Dental Amalgam

It is well known that insertion ofamalgam restorations may result inpostoperative thermal sensitivity.

Such sensitivity results fromexpansion or contraction of fluid thatoccupies the gap between theamalgam and the cavity wall.

The use of a cavity varnish or base isrecommended.


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Conclusion

Knowledge of pulpal biology isessential for the development of arational approach to treatment of pulpand associated tissues.


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References

1. Mjor, I. & Heyeraas, K.(1998) Pulp-dentin and PeriodontalAnatomy and Phsiology.In Essential Endodontology, (eds D.Orstavik and T.R. Pitt Ford), pp 9-4 , Blackwell Science, U.K.

2. Hasselgren, G.(1998) Treatment of the exposed dentin-pulpcomplex.In Essential Endodontology, (eds D. Orstavik and T.R.Pitt Ford), pp192-210, Blackwell Science, U.K.

3. Pashely, D.(2002) Pulpodentin Complex.In Seltzer and BendersDental Pulp, (eds D. Hargreaves and Goodis), pp 63-93,Quintessence Publishing, IL

4. Okiji, T.(2002) Pulp as a connective tissue.In Seltzer andBenders Dental Pulp, (eds D. Hargreaves and Goodis), pp 95-150, Quintessence Publishing, IL

5. Torneck,C.& Torabinejad, M.(1996) Biology of the dental pulpand periradicular tissues In Priciples and Practice ofEndodontics, (eds Walton and Torabinejad), pp 6-28, W.B.Saunders Company, Penn.

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14 Pulp Biology

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