14 Pulp Biology
Transcript of 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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Early Development of Pulp
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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Early Development of Pulp
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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Blood supply in the pulp
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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Blood supply in the pulp
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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Innervations of the pulp
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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Innervations of the pulp
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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Theories of DentinHypersensitivity
Odontoblasts as Receptors
the odontoblast process extended
only partway through dentinthe odontoblast membrane potential istoo low to permit transduction
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Theories of DentinHypersensitivity
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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Dentin Hypersensitivity
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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Dentin Hypersensitivity
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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Pulpal Reaction to DentalCaries
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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Pulpal Reaction to DentalCaries
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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.