Dental Pulp Chapter 6
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Why is the dental pulp termed a microcirculatory system?
It lacks true arteries and veins
What is the primary function of the dental bloody supply?
To regulate the interstitial environment of dental pulp via transport of nutrients, hormones, and gases
To remove metabolic waste
How are arterioles and venules arranged in the pulp?
Axially in the pulp with capillary loops extending outward toward the dentin
Diameter of arterioles?
The transitional structure between arterioles and capillaries:
terminal arteriole (fewer smooth muscle cells)
How are the smooth muscle cells arranged around the arterioles?
Low resistance path connecting many smooth muscles cells of the endothelium is termed?
Intercellular electrical coupling
Names the arterioles from largest to smallest?
Arterioles > Terminal Arterioles > Precapillaries (Metaarterioles)
Every cell in the body is within ___ to ____ of capillaries.
Branch points of terminal arterioles and capillaries are characterized by the presence of
clumps of smooth muscle (precapillary sphincter)
At any given moment, only about __% of the blood supply circulates in capillaries
Capillaries consist of (histology)
single layer of endothelium, surround by a basement membrane, loose reticular and collagenous fibers
Capillaries often form extensive ____ in the _______________ region
Thickness of wall of capillary
.5um (therefore semipermeable membrane), big proteins stay in (albumin) higher collodial pressure as it gets to venules
Fenestrated capillary: fenestrations in capillary walls, open or occluded by thin diaphgram
Also found in GI, sulcular gingiva, renal glomerulus
Continuous (non fenestrated) capillary:
gap junctions intercellulary 5-10nm openings, found in pulp (heart lungs skin muscle).
Found near odontoblasts in tooth development (here they are fenestrated and afterward switch back and retreat to subodontoblastic layer)
discontinuous endothelium, wide intercellular spaces 5-10nm, BM is d/c
Found in spleen, liver, bone marrow, not in pulp
Tight junction capillary
: found in CNS and retina
not in pulp
Three major layers of the microcirculation of the subodontoblastic region?
- 1. Terminal capillary network: odontoblastic layer
- 2. Capillary network: pre and post capillary vessels adjacent to OD layer
- 3. Venular network: last layer
How many layers to capillary organization in aging?
one; associated with reduced electrical conductance of odontoblasts, less metabolic support
What are AVA and how do they aid in tissue injury?
Arteriovenous anastomosis: shunts and vascular loops permit shunting of blood from arterioles to venules following injury
Permeability of lymphatic system?
absorb solutes of high molecular weight reducing colloidal osmotic pressure (regulate edema)
Lymphatic vessels coalesce to form larger vessels that resemble?
Veins, they also have valves to prevent back flow
Lymph of pulp drains where (glands nodes?)
submaxillary, submental glands and eventually into superficial and deep cervical glands
Main difference between capillary and lymphatic vessels?
Lymphatics do not have fenestrations and BM
Lymph capillaries originate as ______ _______ near the ____ of _____ and _____________ layer.
- blind openings
What are the enzyme differences with lympg and blood vessles that allow to identify them?
5'-Nase in lymphatics
ALPase (alkaline phosphatase) blood vessels
Pulp lymph vessels are found where?
Cell free zone, just beneath the odontoblastic layer or some found close
The first determinant of exchange of stuff between interstitial compartment and capillaries is:
control of micro circulation by terminal arterioles and precapillary sphincters
directs capillary blood flow to places of metabolic need
affects Pc (capillary hydrostatic pressure)
capillary perfusion ranges from 10% (vasconstriction) to 100%
Major sites of blood volume control and postcapillary resistance are
Rt is total resistance (affected by epi and norepi)
others define hydrostatic pressure
The second determinant of exchange of stuff between interstitial compartment and capillaries is:
First morphology (fenestrations)
1. Diffusion: down respective gradient (glucose, O2, CO2, H2O)
2. Osmosis: selective movement through semipermeable membrane
Second factor (compostion and concentration)
1. smaller or more lipophilic substances cross cell membrane easily
Third Factor: Pinocytosis
Osmotic driven exchange of fluid and solutes is termed
capillary filtration; major mechanism for exchange of solutes
Rate of capillary filtration defined by
Pc-Pi (hydrostatic pressure) favors and outward flow (filtration) at arteriolar end
COPc-COPi (colloidal osmotic pressure) favors movement into venules
Altered during inflammation (increased interstitial pressure)
What methods can be used to measure pulpal interstitial pressure Pi?
- pressure transducer systems,
- tonometric measurements, and
- micropuncture techniques (2-4um pipettes)
What has Pi been recorded in studies with micropuncture?
Bishop's cat pulp study showed Pi 16mmHg at site of inflammation and only 1-2mm away it was 7mmHg, significance?
Pi response to pulp inf. is restricted to site of injury.
This goes against the Strangulation theory. (Tonder and Kvinnsland refuted)
What factors restrict Pi increase to prevent strangulation?
1. Local Pi increase reduces difference Pc-Pi therefore reducing the pressure gradient, less fluid coming out of vessel
2. increase of Pi at site of inf. ↥ absorption in capillaries nearby in uninf tissue
3. ↥ lymph outflow
Collective regulation of Pi is simplified into a formula, it is:
Pi = ΔV/Ci
change in pulp tissue volume(reg by capillary filtration rate)/compliance of pulp (which is low due to hard mineral)
List the factors that lead to increased interstitial fluid volume (6):
- 1. Arteriolar dilation
- 2. dec colloidal osmotic pressure in capillaries
- 3. inc colloidal osmotic pressure in interstitial compartment
- 4. increased capillary permeability
- 5. reduced lymphatic outflow
Measuring Pulpal blood flow utilizes tracers, which ones are best
K, Pb, Xe tracer
yield values 40-50 ml/min per 100g of pulp tissue
Blood flow in the pulp is the ________ among oral tissues and is similar to levels found in the _______
Highest capillary density occurs:
__% of the volume of the dental pulp consists of blood vessels
Where does the AVA shunting primarily occur?
Apical half of pulp
U-turn loops aid in shunting in addition to AVA
What is PBF equation?
RT is the arteriolar resistance and is the major determinant during homeostasis.
What are the three factors that regulate arteriolar vasoconstriction?
Paracrine, Autocrine, Endocrine Factors
Studies have suggested which metabolic agents affect vasodilation in pulp arterioles?
- low interstitial p02 levels,
- low pH,
- or elevated pCO2 levels
Metabolic hyperoxia can be prevented how?
Shunted away by the AVA shunts into the venules, hyperoxia induced toxicity is reduced
Three major neuronal systems are implicated in the regulation of pulpal blood flow:
Sympathetic fibers (Norepinephrine used)
Afferent (sensory) fibers
Which fibers innervate the arterioles as free nerve endings in the periphery and center of pulp?
Sympathetic postganglionic fibers
Describe the distribution of sympathetic fibers in the pulp?
Highest in the blood vessel in the pulp horns near OD region
Lowest in the apical region of mouse molars
What is released when sympathetic fibers (sensory C fibers too) are depolarized? Effect?
do not respond to drying, heat, cold, osmotic or hydrostatic, only electrical
Stimulation of pulpal sympathetic fibers reduces pulpal blood flow by
more than 80%
block by phenoxybenzamine
What happens when sympathetic fibers are excited with nitroprusside (hypotension) or decrease in oxygen transport?
Which receptors are responsible for contraction of vascular musculature?
alpha-adrenergic (noreponephrine works here too)
alpha 1 is more effective than alpha 2
What do beta-adrenergic receptors due in response to PBF?
What major neurotransmitters are found to activate the parasympathetics in the pulp?
acetylcholine (acetylcholinesterase found in pulp) activated by muscarinic receptors
vasoactive intestinal polypeptide
Dental pulp is innervated by sensory neurons originating from
the trigeminal ganglion
What neuropeptides are released giving the sensory neurons an efferent function?
Substance P (neurokinin 1 receptor OD and subOD layer)
Where are the neuropeptides of the pulp pooled (finite) and released?
In the periphery
Subtance P and CGRP are released from terminals of
Stimulation of a _____ pulpal C fiber is capable of inducing a detectable ________ in PBF
What extract from chilli peppers induce PBF ?
activation of sensory neurons with it cause release of subst P and CGRP
Substance P induces endogenous ___ production by activatin __ synthase in _________ cells
What additional affects are found in Subst P and CGRP?
plasma extravasation, inflammatory movement of immune cells into the tissues
CGRP and subst P exert their effects predominantly on ________ vessels, whereas NO acts on _____________ vessels
What enhances the release of CGRP at the dental terminals?
Bradykinin and prostaglandins
How is bradykinin produced and does what?
Locally produced at a site of inflammation
moves out from plasma as precursor
kininigen + releasing enzyme kallikrein
increases pulpal blood flow
The coadministration of ___________, a cyclooxygenase inhibitor, with bradykinin _____ pulpal blood flow
Administration of _________ __ increases pulpal blood flow by more than __% and causes plasma extravasation.
Histamine cause a great what?
Increase in plasma extravasation but moderate pulpal blood flow
This is released from ischemic and hypoxic tissues and acts in an autocrine or paracrine fashion (extraluminal vasodilation)
This vasoconstrictor peptide can be paracrine or autocrine or systemic, targets smooth muscle
How do anesthetics reduce PBF?
mainly on vascular resistance
Epi exceeding 10-8mol/L
causes pulpal vessels to collapse and total ischemia of pulp
Rat pulp after __ to ___ hours of ischemia is not any different from control pulp.
Both ___________ and _____________ routes of injection of local anesthetic reduce PBF.
infiltration (50% more reduction)
What two routes do dental proced affect PBF?
2. dental tx and restoration
________ of outer dentin produces vasodilation during dental tx
Crown preparation without water spray causes about __% ________ in PBF by 1 hour after preparation.
mediated by trigeminal sensory nerves
Describe the olgart study on the findings that sensory nerve are involved in dec PBF during tooth prep
normally the pulp has vasodilation during drilling, but removing the nerve the peak PBF was reduced by almost 75%, indicating the nerve is responsible for regulation.
Zinc Cement and PBF?
Biphasic, first 33% inc then 33% dec after the cement hardens
Acid etching 36% phos and PBF?
stasis of PBF in over 40% of tested pulps after 60seconds
Zinc phosphate to shallow cavity preps and PBF?
40-50% inc PBF 1 week and 1 month after completion
Fluorescent dye used in cell biology
What minimizes pulpal irriation for indirect restorations?
Orthodontics and PBF?
vasodilation steady and significant increase
inc angiogenic factors
VEGF are embedded in dentin, released during injury
Orthognathic Surgery and PBF?
decreased 82% immediately after surgery, restablishes at later points
Lefort I returns in over 90% of patients but is lower than preoperative
Two major actions of mediators of acute inflammation are
- 1. alterations in PBF
- 2. inc in capillary permeability
leading to plasma extravasation
In acute pulpitis stage following cavity prep w/o water coolant inc permeability is seen in
venular and capillary network
vascular loops, AVA shunts, inc PBF and inc lymphatic outflow may protect against inflammation.
Bacteria (LPS) and PBF?
vasodilation, inc in PBF up to 40% over control
necrosis reduce PBF
In prolonged inflammation, the _________ vessels are closed, resulting in persistently ________ fluid and ________ pressure
Two considerations for use of LDF
1. contraindicated in heavily restored teeth, and those with apical viability (only detect coronal blood flow)
2. pulpal perfusion is significanty higher when they are supine rather than stand or sit.
LDF, how does it work?
principle that reflected light from blood flow will demonstrate a Doppler (freq shifting) effect, depending on relative velocity of blood flow.
Transmitted light photoplethysmography
young permanent teeth testing, 565nm peak intensity, in proportion to pulpal volume.
According to the micropuncture technique in measuring pulpal interstitial pressure what were the results for PA, PC, PV, and PI?
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