Pulpal Pathophysiology and Inflammation

1. Heat causes inward fluid movement in tubules

2. Cold causes outward fluid movement in tubules

3. Concurrent distortion of odontoblastic process stimulates primary neurons at the pulpo-dentinal junction

4. Distortion leads to impulse conduction

Functions: Induction, Formation, Nutrition, Defense, Sensation

Development: Ectomesynchymal cells proliferate to form Dental papilla which gives rise to odontoblasts/dentin and pulpal tissues

A-delta fibers:

• Mechanoreceptors
• Respond to hydrodynamic stimuli (cold, heat, air, hyper-osmotic sol; plexus of rashkow; dentinal pain

C fibers:

• Polymodal nociceptors
• Respond to tissue injury, Capsaicin, prolonged heat, inflammatory mediators, acids; pulp proper; pulpal pain

• A. >2000 neural axons innervate human premolar.
• B. 80% pulpal neurons are unmyelinated C fibers.
• C. Myelinated A fibers are late to innervate pulp, may take up to 5 years (EPT unreliable in young teeth – see Fuss/Trowbridge, Fulling/Andreasen).
• D. Threshold stimulus level decreases significantly with apical closure.

90%

Matthews 1994

Edwall 1985 / Trowbridge 1986

1. Sympathetic efferent fibers originating from the superior cervical ganglion.

2. Innervate smooth muscle cells of arterioles and precapillary sphincters.

3. Vasoconstriction and reduction of blood flow to the pulp.

There is an absence of parasympathetic vasodilation in the pulp.

• Density:
• DEJ – 18,000 tubules/mm2
• Pulp – 45,000 tubules/mm2

• Diameter:
• DEJ – 0.8 μm
• Pulp – 2.5 μm

• Occupied Space:
• DEJ – 1% surface area
• Pulp – 22% surface area

Intratubular A fibers extend into dentinal tubules as far as 100 μm.

A fibers are most numerous in the pulp horns (40% tubules).

A fibers are least numerous in root dentin (1% tubules).

Sigel – Odontoblastic process extends to DEJ

Holland – Odontoblastic process extends ½ way through the tubule.

Aubin – Odontoblastic process extends to DEJ

Type I Anaphylactic - IgE mediated (Mast cells/Basophils → Histamine, C4 leukotrienes – ↑ vasodilation/vascular permeability and bronchial smooth muscle contstriction), IMMEDIATE  ie: drugs, foods, asthma, bites, allergic rhinitis

Type II Cytotoxic - IgG, IgM mediated (complement or phagocytosis)- Transfusion rxn, autoimmune hemolytic anemia, idiopathic thrombocytopenia

Type III Immune complex (Ag-Ab) rxn – IgG form complexes w/ complement, 6-8 hrs, ie: serum sickness, arthus, immune vasiculitis, lupus, viral hepatitis

Type IV Delayed Hypersensitivity rxn - Cell mediated (no Ab): T cell (Killer T cells, Memory T cells), Macrophages; antigen sensitized T cells/Macrophages. More important than anaphylaxis rxn. 24-48 hours DELAYED

ie: 48 hours contact dermatitis, poison ivy, tissue graft rejection, TB, autoimmune diseases; Granulomatous Inflammation (i.e.: Periapical granuloma)

Type I Anaphylactic - IgE mediated (Mast cells/Basophils → Histamine, C4 leukotrienes – ↑ vasodilation/vascular permeability and bronchial smooth muscle contstriction), IMMEDIATE  ie: drugs, foods, asthma, bites, allergic rhinitis

Type II Cytotoxic - IgG, IgM mediated (complement or phagocytosis)- Transfusion rxn, autoimmune hemolytic anemia, idiopathic thrombocytopenia

Type III Immune complex (Ag-Ab) rxn – IgG form complexes w/ complement, 6-8 hrs, ie: serum sickness, arthus, immune vasiculitis, lupus, viral hepatitis

Type IV Delayed Hypersensitivity rxn - Cell mediated (no Ab): T cell (Killer T cells, Memory T cells), Macrophages; antigen sensitized T cells/Macrophages. More important than anaphylaxis rxn. 24-48 hours DELAYED


ie: 48 hours contact dermatitis, poison ivy, tissue graft rejection, TB, autoimmune diseases; granulomatous Inflammation (i.e.: Periapical granuloma)

1. T-lymphoctyes (CD4+ and CD8+): B cell/Macrophage activation, mem.

2. Macrophages: Phagocytosis, APC

3. Dendritic Cells: APC, phagocytosis; Perivascular/Periodontoblastic

4. Lack of B-lymphocytes, Mast cells from healthy pulps (see Suda)

Fibroblasts are most numerous cell in pulp and produce nerve growth factor (NGF) and proinflammatory cytokines during inflammation

True.  Mast Cells are NOT present in the healthy dental pulp.

Suda

Baum

Found correlation between depth of penetration of bacteria within dentin and severity of inflammation

Brannstrom / Lind

Pulpal changes occur early in caries, even in incipient lesions. Impairment of odontoblast layer, accumulation of lymphocytes.

Reeves and Stanley

Irreversible pulpitis detected when bacteria were 0.5mm from the pulp.

Minimal pathosis seen if >1.2 mm from pulp.

If bacteria invade reparative dentin = irreversible pulpitis.

Stanley

Rate of reparative dentin formation = 1.49 micrometers/day.

Tertiary dentin begins 19 days after operative procedures.

Jontell / Bergenholtz



Macrophages/Dendritic cells (APCs) initiate pulpal response to caries. 

T lymphocytes present. B lymphocytes/mast cells later arrivals. 

Multiple immune responses: Antigen-Ab IgG (III), Delayed type Hypersensitivity w/T cell/Macrophages (IV), Vascular and Neurogenic interactions.

1st defense: Sclerotic dentin (crystals) deposition, ↓dentin permeability

2nd defense: Tertiary dentin formation, Mild stimuli – Reactionary dentin, Aggressive stimuli (death of odontoblast) – Reparative dentin

3rd defense: Immune response

• Chronic inflammatory response –Initially Odontoblasts, later dendritic cells as most peripheral cells contain PRRs to respond to PAMPs with innate/adaptive immune response
• Release of Cytokines, Chemokines – phagocytosis, chemotaxis, recruitment of lymphocytes, macrophages, and plasma cells
• Neurogenic inflammation – SP, CGRP, NKA released from pulpal nociceptors (PRRs – TLRs on nociceptors)

Acute excerbation of chronic inflammatory response – Influx of PMNs

Localized inflammation, Focal Microabscesses, Progressive necrosis

0-24 hrs:

• PAMPs bind PRRs (TLRs, CD14) on resident immune cells (dendritic cells, macrophages), odontoblasts, and peripheral nociceptors (TRPV1 C fibers)
• Pro-inflammatory cytokines (i.e.: IL-1β, IL-6, IL-8, TNF-α) and neuropeptides (CGRP, SP, NKA) are released to activate/recruit immune cells as well as sensitize/activate nociceptors, ↑ nerve sprouting, and effect vasodilatory responses
• Complement activation via cytokines and neuropeptides → releasing C3a, C5a → vascular endothelium for chemotaxis, opsonization and killing of foreign antigens

>24hrs

• Cytokines (i.e.: IL-1, TNF-α) & C3a/C5a effect endothelial cells for chemotaxis and migration of PMNs, Bradykinin, other pro-inflammatory cells
• C3a/C5a & neuropeptides (SP, CGRP) activate mast cells to produce Histamine, Leukotrienes, Platelet Activating Factor (Vasodilation, ↑ Vascular Permeability)
• Sensitization/Activation of Nociceptors → Hyperalgesia, Allodynia, Spont. pain
• Vasodilation, Vascular Permeability → Edema, Inc. Tissue pressure
• Non-specific phagocytosis – PMNs (0-48hrs), Macrophages (48 hrs +)
• Cytokines effect Osteoclasts to promote RANK/RANKL binding and bone resorption

Two Components of Adaptive Immune Response (48 hrs +):

Humoral Immune Response – Antibody mediated response

Cellular Immune Response – T cell mediated response – CD4+ T cells

1. Antigen presenting cells (APCs), i.e.: Macrophages, Dendritic cells, B cells, present to immature TH0 cells within lymph nodes via MHC II receptor, activating TH0 cells

2. TH0 cells differentiate into TH1or TH2 cells via cytokine regulation: TH1 via IFN-δ, TH2 via IL-4, IL-10 (suppresses IFN-δ and TH1 production)

3. Cellular Immune Response: TH1 → Maximizes killing by Macrophages, CD8+ cells (NKT cells, Cytotoxic T cells), Memory T cell production

4. Humoral Immune Response: TH2 → B cell activation → Plasma Cells → Antibody production (allows binding to antigen for complement killing or phagocytosis), Memory B cell production

1. Vasodilation and Increase Vascular Permeability

2. Recruit/Activate Inflammatory cells (PMN, Mast cells, Macrophages, Lymphocytes, Bradykinin) & Complement system (C3a, C5a)

3. Sensitize/Activate Nociceptors

Histamine – Mast cells (stimulated by C3a, SP, CGRP), Platelets

Prostaglandins (Prostacyclin) – All leukocytes, Mast cells (COX pathwy)

CGRP – Pulpal nociceptors

1. Bradykinin – Plasma activated through kinin system cascade

2. Leukotrienes – All leukocytes, Mast cells (LIPOX)

3. C3a, C5a – Plasma complement system cascade

4. Substance P – Pulpal nociceptors

C3b, C5b – Plasma complement system cascade

TNF (cytokine) – Macrophages

IL-1 (cytokine) – Macrophages

Chemokines – Macrophages, PMNs, Endothelial cells, Fibroblasts

1. C3a, C5a – Plasma complement system cascade

2. Leukotrienes – All leukocytes, Mast cells

3. Chemokines – Macrophages, PMNs, Endothelial cells, Fibroblasts

4. TNF – Macrophages

Lysosomal enzymes – PMNs, Macrophages - phagocytosis

Free oxygen radicals – Activated leukocytes

Nitric oxide – Macrophages

1. Vasodilation (via CGRP & mast cells → histamine)

2. Increased Vascular Permeability (via SP & mast cells → Leukotrienes)

3. Nerve sprouting/Pain (via SP/CGRP → Fibroblasts → NGF) - Byers

4. Activate Macrophages/T lymphocytes → cytokines: IL-1, TNF-α, IL-6

5. Bone resorption and Immune regulation in AP development - Byers

Substance P

Calcitonin Gene Related Peptide

Neurokinin A

Neuropeptide Y

Vasoactive Intestinal Peptide

Trigeminal primary cell bodies (mainly C-fibers) – Trigeminal ganglion

Interact with Mast cells: ↑ Release of histamine & leukotrienes

Activates Macrophages/Lymphocytes: ↑ Release of inflammatory mediators (ie: Cytokines, PGs, Thromboxanes)

Stimulate Pulpal cells (ie: Fibroblasts, Odontoblast like cells): ↑NGF

Trigeminal primary cell bodies – Trigeminal ganglion

Interact with Mast cells: ↑ Release of histamine & leukotrienes

Stimulate Pulpal cells (ie: Fibroblasts, Odontoblast like cells): ↑NGF

Trigeminal primary cell bodies – Trigeminal ganglion

Activates Macrophages/Lymphocytes: ↑ Release of inflammatory mediators (ie: cytokines, PGs, Thromboxanes

Sympathetic efferent derived (co-localized with Norepinephrine) – Superior Cervical ganglion

Sympathetic vasoregulation - ↓ Vasodilation (↓ Pulpal Blood Flow)

Parasympathetic efferent derived (co-localized with Acetylcholine)

↑ Vasodilation (↑Pulpal Blood Flow)

Microcirculation – increased PBF by C fiber stimulation (neurokinin A, substance P, CGRP released from C fiber nerve terminals)

Sensory nerve activity – excitatory effect from increased pulpal blood flow via increased tissue pressure (effect on A delta fibers)

Van Hassel – 1st to discuss Localized Inflammation – vascular collapse spreads incrementally from the site of injury, not by strangulation at the apex

Heyeraas (Tonder) – Pulpal lymphatics – drainage of interstitial fluid/proteins to ↓ Interstitial tissue pressure

Kim/Takahashi – Pulpal Collateral Circulation circumvents blood flow around the area of injury/inflammation (AV, VV shunts, U-shaped arteriole)

VanHassel – 1st to discuss localized inflammation in pulp – vascular collape spreads incrementally from site of injury (pressure differences)

Heyeraas (Tonder) – localized increased tissue pressure may persist in the inflamed area w/out a circumferential spread to the rest of the pulp.  Negative feedback system prevents pulpal strangulation (lymphatic drainage)

Kim & Takahashi

• Discovered presence of arteriovenous anastomosis and venous-venous anastomosis and u shaped arterioles (unique feature of pulpal vascular network) = collateral circulation – circumvents blood flow around the area of inflammation (localized)
• Also found sympathetic adrenergic vasoconstritor fibers (NPY) = ↓ Vasodilation (↓ Pulpal Blood Flow)

No Pulp Strangulation Theory

Farnoush - Found in inflamed and non-inflamed pulpal tissue

Suda – Mast Cells are NOT present in normal pulps

Bernick – demonstrated lymphatics in the pulp

Heyeraas (Tonder) - Pulp may have a beneficial blood flow increase during inflammation in spite of simultaneously increased tissue pressure.  This supports the concept of lymphatic drainage. Localized increased tissue pressure without circumferential spread! Lymphatic drainage of interstitial fluid/proteins prevents spread of tissue pressure

Langeland

• Yes.
• Antigens in the root canal system can initiate an immune response with antibodies.

Hahn

• Yes.
• IgG, major class of immunoglobulins in normal and irreversible groups

Pulver

• No.
• Normal pulps do NOT have immunoglobulins-containing cells.
• In inflamed pulps, IgG most common, IgA, IgE, IgM containing cells are also seen.

Jontell / Bergenholtz

• No.
• B lymphocytes, mast cells, and Abs are NOT present in normal pulp.

Activated by pro-inflammatory cytokines, neuropeptides, bacterial antigens.

Mediate vascular responses: C3a, C5a → Mast Cells → Histamine (vasodilation), Leukotrienes (↑ Vascular Permeability)

Leukocyte chemotaxis: C3a, C5a → PMNs, T/B cells, Bradykinin

Opsonizination of targets for phagocytic cells (C3b, C5b)

Directly damage of target cells (C5-9, MAC)

Most important step is cleavage of C3

Classical pathway:  activated by Ab coated targets or Ag-Ab complexes (IgM, IgG – Type III foreign body rxn)

Alternate pathway:  activated by LPS, aggregated IgM or IgG, Ag-IgG complexes, plasmin

40-60%

Holland / Michaelson

Narhi – Endogenous opioids and somatostatin released by inflammatory cells are capable of inhibiting firing of sensory nerve fibers.

Mudie/Holland 2006 – Endorphins are located within lymphocytes in inflammed pulps.

Sessle – Neuropeptides mediate release of inflammatory mediators from immune cells (i.e.: macrophages, mast cells, platelets) resulting in inflammatory cascade 

Byers – injury leads to “sprouting” of sensory nociceptors: Neuropeptides (SP/CGRP) → fibroblasts → NGF → Nerve sprouting = ↑ Nociceptor receptive field + response

Wakisaka 1990 – neuropeptides may help regulate pulpal blood flow + pain transmission as well as promote inflammatory response

Hargreaves – sympathetic transmission may modulate pain (capsaicin study)