0099-2399/90/1602-0048/$02.00/0 JOURNAL OF ENDODONTICS Copyright 9 1990 by The American AssOCiation of Endodontists
Printed in U.S.A.
VOL 16. NO. 2. FEBRUARY1990
SCIENTIFIC ARTICLES Neurovascular Interactions in the Dental Pulp in Health and Inflammation Syngcuk Kim, DDS, PhD
and there is a lack of information on the neurovascular relationship in the inflamed pulp. In this article the interrelationship between microcirculation and sensory nerve activities in health and disease will be examined using current basic research information. The inflammatory processes in the pulp does not differ significantly from that in other tissues in most respects, with a notable exception, however, which is the physical environment of the pulp. the low compliance environment, created by dentin and enamel. Figure l represents a schematic illustration of events involving inflammation in general, in which noxious stimuli have profound effects on the tissue cells. Mechanical stimuli, such as drilling or cutting tooth structure generate noxious vibration or frictional heat; chemical components of various dental materials and cavity washing agents and bacterial byproducts as a result of caries are considered chemical and bacterial stimuli, respectively. When reaching the noxious range, the stimuli degranulate mast cells, disrupt important nutrient flow, damage cells, and in the process lower the excitability threshold of sensory nerves. The attendant release of various inflammatory mediators, e.g. histamine, 5-hydroxytryptamine, kinins, prostaglandins, substance P, and other neurokinins causes pain directly by lowering the sensory, nerve excitability threshold. These substances also cause pain indirectly by vasodilating arterioles and by promoting vascular leakage in venules, resulting in edema and subsequent elevation in tissue pressure, which is of critical importance in pulpal inflammation. Finally, the mediators cause chemotaxis via leukocytes. Pulpal inflammation, if unattended, eventually leads to pulpal necrosis, which in turn causes periapical pathosis. An example of such a case is shown in Fig. 2. a radiograph of fully crowned mandibular anterior teeth of a healthy female patient. There was no pulpal or periapical pathosis prior to the prosthodontic procedures, but as shown in the radiograph, periapical radiolucencies are present on all of the treated anterior teeth. Since these teeth had no history, of decay or trauma prior to the restoration, the probable cause of the periapical pathosis was the restorative procedure. The questions are "Why does tooth preparation result in periapical pathosisT' and "What are the mechanisms of this process?" This fundamental problem in clinical dentistry can be partially explained by the dynamic relationship between blood vessels and sensory nerves in the pulp.
The two key components in pulpal inflammation are microcirculation and sensory nerve activity. With advancement of techniques they can be measured simultaneously in the same tooth. Excitation of Adelta fibers seems to have an insignificant effect on puIpal blood flow (PBF), whereas C fiber activation causes an increase in PBF. This C fiber-induced PBF increase is caused by neurokinins, especially substance P, which is released from the C fiber nerve terminals. Manipulation of PBF has varying effects on sensory nerve activity. An increase in PBF causes excitation of both A-delta and C fibers via an increase in tissue pressure, whereas flow reduction has an inhibitory effect on A-delta fibers, but no discernible effect on C fiber activity. Understanding of this complex neurovascular relationship in the pulp, especially given the fact that the pulp is in a low compliance system, is prerequisite to more comprehensive characterization of pulpal inflammation.
Pulpal inflammation is a subject of interest not only to endodontists, but to all dental disciplines. We understand pulpal inflammation clinically as a toothache and histologi cally as an accumulation of polymorpholeukocytes around the site of insult in a pulp section. In addition to this evidence, however, are many complicated dynamic mechanisms, some of which are known and more which are as yet unknown. It is, however, generally well-accepted knowledge that the two key components in pulpal inflammation are microcirculation and sensory nerve activity. Sensory nerve activity and microcirculation in the pulp have been studied as separate entities by many investigators (1-7) and special emphasis has been given to the characterization of pulpal nerve activity, since pain is the more acute clinical problem in an inflamed tooth. With advancements in circulatory techniques and methods, microcirculatory contributions to pulpal inflammation have also been studied (8, 9). There is, however, a relative paucity of information generated from simultaneous measurements of microcirculatory and neural parameters in the same tooth, 48
Neurovascular Reactions in Pulp
Vol. 16, No. 2, February 1990
Injurious Agents
Before discussing this interrelationship, let us first look at circulation and sensory nerve fimction independently of each other.
(McclumJeal / Chemac.tl / Bactenad)
~lll $t C~ll
Dis;~ptJon
Stimulation
l~grl~uhttlon
Blood Vef~,,cls
~nsor 7 Nerves
L__
i ___
/
/--
,/
!
\
,
.... ~
~
Kinlns
etc.
\ ,~rterlol. ~.
_~ --
~
.... --
v.oo.a.o
......... ~_.
....
-
~
I
Pain
Leakage Chemotaxis
PULPAL MICROCIRCULATION
J
[ Nerves
--_ t..eui,.
I Histamine
49
J/~
~ /
~
,
--/
;
..... .... ~-. -
.-., - -"
FIG 1. Schematic illustration of events involving inflammation in gen-
eral.
Studies of pulpal microcirculation have greatly advanced in the last 15 yr due to the development of sophisticated techniques employing radioisotope tracers (1, 4, 6, 10), radioisotope-labeled microspheres (7, 9), plethysmography (11), and laser Doppler flowmetry (12). Many of these techniques are noninvasive of the pulp (7, 9-12) and have facilitated a quantitative and qualitative analysis of pulpal blood flow (PBF) under various experimental conditions in animal and human teeth. Basically three types of PBF responses to stimuli have been established. In Type I PBF decreases markedly with the intraarterial (i.a.) administration of norepinephrine (13) or 5-hydroxytryptamine (9), with electrical stimulation of the cervical sympathetic nerve and reflex excitation of the sympathetic nervous system by hemorrhage and extreme hematocrit variations (13, 14). This type of flow response is due to activation of a-receptors located in pulpal resistance vessels and the activation of sympathetic adrenergic vasoconstrictor fibers (8, 13). In the Type II response, PBF decreases gradually, as after the i.a. infusion of histamine. This gradual flow reduction is most probably due to an increase in capillary permeability and resultant increased tissue pressure in the low compliance system of the dental pulp. Finally, the Type Ill PBF respon.~ is biphasic; an initial increase is followed by a rapid decrease. This unusual response is caused by the known vasodilators substance P (SP), isoproterenol, prostaglandin E2, and bradykinin (8, 15). The initial vasodilation in response to isoproterenol indicates the presence of ~-adrenergic receptors in the resistance vessels (13, 15). This biphasic flow response to the vasodilators is a result of the low compliance environment of the pulp, in which passive compression of venules may result from active dilation of arterioles with an attendant rise in pulpal tissue pressure, i.e. an inflammatory process (13, 16). It seems clear, that the low compliance environment of the tooth plays an important role in the unusual reduction of PBF during inflammation, since mediators released in the pulp during inflammation, e.g. SP, prostaglandin E2, and bradykinin, etc., are powerful vasodilators. P U L P A L SENSORY NERVE ACTIVITY
FiG 2. A radiograph of mandibular anterior teeth of a patient with fullmouth reconstruction. Extensive periapieal radiolucencies occurred following preparation of the teeth.
The physiological characterization of the pulpal sensory fibers was made using two techniques: multiunit intradental recording, in which electrodes measure nerve activity from dentinal cavities in canine teeth (4, 17) and single fiber unit recording, in which nerve activity is measured from the dissected inferior alveolar nerve in dogs and cats (3, 18). In these studies two types of nerve fibers were found in the pulp: fast-conducting, low-threshold, myelinated A-delta fibers (mean conduction velocity 13.4 m per s and 8.4 to 13.4 mA mean threshold with 20-ms pulse) and slow-conducting, highthreshold, unmyelinated C fibers (mean conduction velocity 1.0 m per s and 37.4 to 40.4/zA mean threshold with 10-ms pulse) (19). Fast-conducting A-beta fibers have also been identified, but their role in the pulp is still unclear. In addition
50
Journal of Endodontics
Kim
to conduction and threshold differences, there are other functional differences between the A and C fibers. C fibers are activated by noxious heat or application of bradykinin and histamine (20, 21). A-della fiber activity, on the other hand, is evoked by stimulation of the exposed superficial dentin by mild thermal, mechanical, and osmotic means (saturated CaCI2); this is most plausibly explained by the hydrodynamic theory (22). However, some hyperosmotic agents (e.g. 3 M NaCI) did not elicit intradental neural activity when applied in shallow cavities, but did cause excitation of A-delta fibers when applied in deep dentinal cavities; the most probable mechanism being direct ionic diffusion (23, 24). Thus, contrary to current thinking, recent experimental evidence supports two mechanisms for pulpal pain, the hydrodynamic and direct ionic diffusion theories. In addition to the differences between A and C libers, there are significant differences in the character of tooth pain associated with A or C fibers. For instance, in response to heat stimulation, immediate, sharp pain can be attributed to A-delta fibers, while a delayed, dull pain is indicative of C fiber activity. The theory, that the initial phase of pulpal inflammation, often accompanied by sharp pain, involves A-delta fibers and that the latter phase, more often characterized by dull pain, involves C fibers, has been advanced (21, 25).
BloodFlowMeasurement 3~
1. 133Xenon washout method 2. Radioisotope labeled microsphere method 3. Laser Doppler flowmetry
2L~ --.-
~
SensoryNerveRecording 4. Intradental 5. Single fiber unit
FiG 3. Schematic representation of a simultaneous recording of blood flow and sensory nerve activity in the pulp. The simultaneous recording of blood flow and sensory nerve activities can be made using any combination of methods shown in the diagram. The most widely used combination is laser Doppler flowmetry for PBF and intradental recording technique for sensory nerve activity measurement.
Saline I 3M NaCI
5 secs
S I M U L T A N E O U S RECORDING OF P U L P A L B L O O D FI,OW AND S E N S O R Y NERVE ACI'IVITIES When studying inflammation in the pulp, the simultaneous recording of blood flow and sensory nerve activity from the same tooth has provided most useful insights into the mechanisms. A schematic representation of the way in which the two parameters can be recorded simultaneously is presented in Fig. 3. The first attempt at this was made in 1970 by a group in Sweden (1). They used the radioactive iodine desaturation technique for measuring pulpal blood flow and the intradental recording technique for measuring the sensory nerve activities in feline teeth. More recently, a modified intradental recording technique and laser Doppler flowmetry have facilitated the in-depth examination of the neurovascular interactions (26). Shown in Fig. 4 are simultaneous recordings of PBF and intradental sensory nerve activity (INA) in response to osmotic stimulation with 3 M NaCI applied to a deep dentin cavity. NaCI applied in dentinal cavities caused increases in both PBF and 1NA, with PBF increases preceding the INA increases. This sequence suggests that PBF changes have an effect on INA. ROLE OF PULPAI. TISSUE P R E S S U R E IN PULPAL INFLAMMATION Pulpal tissue pressure measurements, like PBF and sensory nerve recordings, have benefited from technological advancements in research equipment and increased sophistication in research methods and can now be measured very precisely. Using a micropipettc with a 2- to 4-~,m tip diameter, controlled by a servo-nulling counter-pressure system, precise pulpal tissue and intravascular pressures were recorded (27). The normal resting tissue pressure has been recorded at 6 to 10 mm Hg, but when the pulp is locally inflamed, the local
It
FIG 4. A polygraph tracing of simultaneous recordings of PBF and INA in response to application of 3 M NaCI into a dentinal cavity in a cat canine tooth. The top racing represents PBF measured with laser Doppler flowmetry and the bottom tracing represents INA recorded with the intradental recording technique.
tissue pressure rises to about 16 mm Hg (28). This tissue pressure increase would be insignificant in other tissues, but in the low compliance environment of the pulp, even a small rise can a have significant impact on local circulation as well as sensory nerve activities. Nfirhi (18), recording from the single nerve fiber, has found that an increase in the tissue pressure increases sensory nerve activity. EFFECTS OF C I I A N G E S IN PUI,PAL B L O O D F L O W ON P U L P A L SENSORY NERVE ACrlVITIES A number of separate studies on microcirculation and sensory nerve activity in the dental pulp have shown that an interrelationship exists and several investigators state that local microcirculatory changes may have profound effects on sensory nerve functions in the pulp (1, 4, 30, 31). A severe reduction in PBF in feline teeth, caused by the apical injection of adrenaline or electrical stimulation of the sympathetic
Neurovescular Reactions in Pulp
Vol. 16, No. 2, February 1990
nerve, resulted in concomitant decreases in INA (1, 32); the excitability of intradental sensory, units seems thus modulated by sympathetic vasoconstrictor fibers. This linear relationship between the reduction of pulpal blood flow and ofintradental nerve activity has not been duplicated in our laboratory. Careful examinations reveal that pulpal blood flow must be reduced significantly (approximately 90%) for a substantial duration of more than 10 min, in order to have an effect on intradental nerve activities. It has been hypothesized that the fast-conducting A fibers lose their function rapidly as a result of ischemia, to which the slow-conducting C fibers are less sensitive (28). [his suggests that C fibers may maintain their functional capacity longer than A-delta fibers during inflammation, in which PBF and therefore O2 content are reduced as a result of the low compliance system of the pulp (30, 33). A systematic study of the possible modulating effect of ischemia on nerve fiber activity should provide important insights into dentinal pain mechanisms, especially during inflammation. Changes in pulpal blood flow may not have a direct effect on pulpal C fiber activities; however, increases in pulpal tissue pressure by flow elevation cause excitation of the sensory nerves. Increased tissue pressure is a function of an increase in blood flow accompanied by an increase in vascular permeability. Thus, we could conclude that changes in blood flow have a direct effect on pulpal A fiber activities but minimum effect on C fibers. However, tissue pressure elevation excites all sensory nerves (Fig. 5).
51
changes depend on the degree of neural stimulation. For instance, weak orthodromic stimulation of the tooth surface, which excites only A-delta fibers, causes no changes in PBF, suggesting that excitation of the A-delta fibers has no significant effect on PBF (Fig. 6). However, strong orthodromic stimulation of the tooth surface causes erratic changes in PBF, most likely by C fiber excitation (Fig. 6). Antidromic stimulation of the inferior alveolar nerve in cats, pretreated with an a-adrenergic blocker, caused an increase in PBF and biphasic neural activity; an increase followed by a prolonged depression (31). This neurogenic vasodilation is mediated by the neurokinin SP, which is released from unmyelinated C fiber endings when antidromic stimulation is applied (35, 36). Recent evidence suggests that this neurogenic vasodilation is mediated not only by SP, but also by neurokinin A, B, and especially by calcitonin gene-related peptides. The biphasic neural response following the antidromic stimulation may be related to the biphasic PBF response after i.a. infusion of SP (16), since SP effects are both vascular and neural. Another explanation for the biphasic neural response is that SP triggers the release of histamine, which causes an elevation of pulpal tissue pressure via an increase in vascular permeability (31). Thus, an increase in PBF by vasoactive substances, released either from the sensory nerve endings or from other cellular components, may have profound effects on both circulatory and neural behavior. '9
EFFECI" OF C H A N G E S IN PULPAL S E N S O R Y NERVE ACI'IVITIES ON P U L P A L B L O O D F L O W Evidence that excitation of pulpal sensory fibers has a profound effect on pulpal microcirculation has been provided by a number of researchers (26, 34). However, the flow
PBF
AS|
l
(low flow)
|
NEUROPEPTIDES SP, CGRP etc.
C C|
= tPBF
FIG 5. Relationship of pulpal tissue pressure and A-delta and C fiber nerve activities. + represents excitation or an increase in nerve activity. An increase in pulpal tissue pressure as a consequence of an increase in PBF has an excitatory effect on both A-delta (A-d) and C fibers. An excitation of C fibers in turn causes pulpal flow increase via neurokinins released from the C fiber nerve endings.
TISSUE
)
PBF PRESSURE
FiG 6. Relationship of pulpal blood flow and A-delta (A-d) and C fiber nerve activities. Excitation of A-~, has little effect on PBF. while a decrease in flow has an inhibitory effect on A-~ fiber excitability. Excitation of C fibers increases PBF via neuropeptides, namely, SP and calcitonin gene-related peptide (CGRP). An increase in PBF per se has little effect on C fiber activity, but an increase in tissue pressure excites the nerve.
52
Kim
Journal of Endodontics
The important question "What are the roles of these peptides in pulpal inflammation and under what circumstances are these peptides released?" remains. It is known that a simple tooth preparation can cause the release of a significant amount of SP-like or bradykinin-like substances (37). Also, noxious stimuli of mechanical, thermal, and chemical characters, which excite C fibers, can trigger the release of neuropeptides. These, in turn, have an effect on pulpal blood flow and subsequently on pulpal tissue pressure. Shown in Fig. 7 are the key mediators involved in pulpal inflammation. Inflammatory mediators prostaglandins and bradykinin are released from the tissue components, and various kinins and SP are released in response to sensory nerve excitation. The neurokinins have a direct effect on the vasculature causing vasodilation and leakage, while the simultaneous release of 5-hydroxytryptamine and kinins from vascular components cause mast cells to release histamine which in turn causes further vascular leakage. To return to the initial question about the periapical pathosis shown in the radiograph in Fig. 2, a hypothetical mechanism of pulpal necrosis can be constructed (Fig. 8). As a result of noxious stimulation, i.e. the mechanical, thermal. and chemical stimulation caused by tooth preparation, inflammatory mediators and neuropeptides are released. These mediators alter normal neural and vascular functions, which results in an increase in tissue pressure. Tissue pressure elevation in the low compliance environment of the pulp quickly leads to a decrease in pulpal blood flow instead of an increase as in other tissues. Increased blood flow facilitates the removal of the inflammatory mediators and thereby helps heal the tissue, but in the pulp the decreased flow results in an accumulation of mediators, which in turn causes varying degrees of vessel damage. This vicious cycle, once begun, leads to successive areas of inflammation and eventual pulp necrosis. The discovery of the neuropeptide involvement in pulpal inflammation revolutionized our thinking. It is now clear that neuropeptides play an important role in the progression of pulpal inflammation by linking the actions of the sensory nerves and blood vessels. The term neurogenic inflammation describes a pathological change in the neurovascular relationship, resulting in inflammation. Since pulpal inflammation is
InSUltS
---
roll
~'~I>"
J ~
'
PGs-
/
Hyp . . . . c i t a t i o n
SP i
I
r
!
-
~
(noxious
Release
(BK.
stimulation)
of M e d l a t c r s PG,)
Release
5.HT, Histamine,
of N e u r o p e p t i d e s {SP. CGRP}
9 Hyperexcltatlon I=, 9 V a s o d l l a t l o n , 9 Vascular leakage
14
J
[ ....
I
Pulpal Tissue P r e s s u r e I
I Pulpal Blood Flow (low c o m p l i a n c e system)
A c c u m u l a t i o n of Mediators Vessel Damage I
Pulpal I n f l a m m a t i o n
Pulpal Death F=~ 8. Hypothetical mechanism of pulpal necrosis as a consequence of tooth preparation for a full crown placement. See text for explanation.
primarily neurogenic in nature, our understanding of the neurovascular interrelationship in the pulp in health and disease is of paramount importance. This work was supported by NIH/NIDR Grants DEO-05605 and DEO-O121. The author wo~Jld like to acknowledge his co-workers, Drs. M. Liu, K. Markowdz, J Bilotto, and Ms. J. Dorscher-Kim, for their contributions to this article. Or Kim is chairman, Department of Endodontics, and director, Laboratory of Oral Physiology, Columl~a University, School of Dental and Oral Surgery, New York, NY.
References
BK --
t
Tooth Preparation
~
t G ~-~) / %
Vasodi|ation
Leakage
- 7
|
',
L LOW Comphance Environment F,G 7. Relationship between loulpal inflammation and inflammatory
mediators, See text for explanation.
I
1. Edwall L, Scott D Jr. Influence of changes in microoirculation on the excitability of the sensory unit in the tooth of the cat. Acta Physiol Scand 1971 ;82:55-6. 2. Haegefstam G The origin of impulses recorded from dentinal cavdies m the tooth of the cat. Acta Physiol Scand 1976;97:121-8. 3. Matthews B Responses of intradental nerves to electrical and thermal stimulation of teeth in dogs. J Physio11977;264:641-64. 4. Olgart L. Excitation of intradental sensory units by pharmacological agents. Acta Physiol Scand 1974;92:48-55. 5. Narhi MVO, Hirvonen TJ, Hakumaki MOK. Responses of intradental nerve fibers to stimulation of dentine and pulp. Acta Physiol Scand 1982:115:173-8. 6. Tender KH, Naess G. Nervous control of blood flow in the dental pulp in dogs. Acta Phys~ol St.,and 1978;104:13-23. 7. Kim S. Edwall U Trowbndge H, C h i n S. Effects of local anesthetics on pulpal blood flow in dogs. J Dent Res 1984;63:650-2. 8. Kim S Microcirculation of the dental pulp in health and disease. J Endodont 1985;11:465-71. 9. Kim S, Trowbridge H, Dorscher-Kim J. The effects of 5-hydroxytryptamine on pulpal hemodynames in dogs. J Dent Res 1986;65:682-5. 10. Kim S, Schuessler G, Chlen S. Measurement of blood flow in the dental pulp of dogs with the Xe-133 washout method. Arch Oral Bio11983;28:501-5. 11. Shoher I, Mahler Y, Samueloff S. Dental pulp photoplethysmography in
Vol. 16, No. 2, February 1990 human beings. Oral Surg, Oral Meal, Oral Pathol 36:914. 1973. 12. Gazelius B, Olgart L, Edwall B, Edwall L Non-invaswe recording of blood flow in human dental pulp. Endod Dent Traum 2"219-21. 1986. 13. Kim S. Regulation of pulpal blood flow. J Dent Res 64(spaciai issue):590-6. 1985. 14. Kim S. Fan FC, Chen RYZ, Simchon S, Schuessler GB, Chien S. Effects of changes in the systemic hemodynamic parameters ~n pulpal hemodynam~cs. J Endodon 1980;63:394-9. 15. K,m S. Fleguiation of blood flow of the dental pulp: macrocirculat~on and mlcrocirculation studies IPhD Dissertation}. New York, NY: Columbia University, 1981. 16. Kim S, D0rscher-Kim J, Liu M-T, Trowbridge H. Biphasic pulp bloodflow response to substance P in the dog as measured with a rad=olabeled. microsphere injection method. Arch Oral B=o11988;33:305-9. 17. Bilotto G, Markowitz K. Kim S. Experimental procedure to test the efficacy of chemical agents ~n altenng intradental nerve actwity J Endodon 1987;13:459-65. 18. Narhi M Activation of dental pulp nerves of the cat and the dog with hydrostatic pressure. Proc Finn Dent Soc 1978;1-64.74(suppl V): 19. Narhi M, Virtanen A, Huopaniemi T, Hirvonen T. Conduction velocities of single pulp nerve units in the cat. Acta Physiol Scand 1982;116:209-13. 20. N~irhi M. Jyvasjarvi E, Huopaniemi T. Functional differences in intradental A- and C-nerves units in cats. Abstracts of the IVth World Congress on Pain. IASP, Seattle, Washington, 1984. 21. Narhi M. The characteristic of intradentai sensory units and their responses to stimulation. J Dent Res 1985;64(special issue):564-71. 22. Brannstrom M, Astrom A. The hydrodynamics of the dentine; its possil04e relationship to dentinal pain. Int Dent J 1972:22:219-27. 23. Orchardson R The generation of nerve ~mpulses in mammalian axons by changing the concentration of the normal constituents of extracelfular fluid. J Physlo11978;275:177-89. 24. Bilotto G, Markowitz K, Kim S. Effects of ~omc and non-ionic solutions
Neurovascular Reactions in Pulp 53 on intradentaJ nerve activity in the cat. Pain f 988:32:231-8. 25. Mumford JM, Orofacial pain. Aetiokx:jy, diagnosis and treatment. 3rd ed, Edinburgh: Churchill Livingston, 1982. 26. Markowrtz K. Bilotto G, Liu M, et al. Intradental nerves and pulpal blood flow measured by a laser Doppler flowmeter. J Dent Res 1988;67:215. 27. Markowtiz K, Bilotto G, Liu M, Jo~ YT, Kim S. Physiokxjicai studies of neurogenic inflammation in the dental pulp. J Endodon 1989; 15:170. 28. Tender K, Kvinnsland I. Micropuncture measurements of interstitial fluid pressure in normal ancl inflamed dental pulp in cats. J Endodon 1983;9;105-9 29. Tonder K. Blood flow and vascular pressure in the dental pulp [Doctoral dissertation]. Bergen, Norway: University of Bergen, 1980 30. Olgart L. The role of tocat factors in dentin and putp in intradentat pain mechanisms. J Dent Res. 1985;64(special issue):572-8. 31. Gazelius B Studies on the release and effects of putative mediators of pain in the dental pulp [Thesis[. Stockholm, Sweden: Karolinska Institute, 1981. 32. Olgart L, Gazelius B. Effects of adrenaline and felypressm (Octapressin) on Izdood flow and sensory nerve activity =n the tooth Acta Odontol Scand 1977;35:69-75. 33. Jyvasjarvi E, Nat'hi M, Virtanen A, Huopaniem= T. Differential blockade of intradental A-delta fibers by ischemia. J Dent Res 1983;62(spec=al issue):35 34. Dorscher-Kim J, Liu M-T, Trowb{idge H, Kim S InferK)r alveolar nerve stimulation and pulpal blood flow in dogs. J Dent Res. 1986;64(special issue): 146. 35. Gazelius B, Brodin E, Olgart L, Panopoulos P Evidence that substance P is a me~ator of antidromic vasodilation using sornatostatin as a re~ease inhibitor. Acta Physiol Scand 1981 ;113: f 55-9. 36. Brodin E, Bazelius B, Olgart L, Nilsson G Tissue concentration and release of substance P-like immunoreactivity in the dental pulp. Acta Physiol Scand 1981;111:141-9. 37. Kroeger D. Possible role of neurohumoral substances in the pulp. In: Ir~nn SB, ed. Biology of the dental pulp organ: a symposium. Birmingham: University of Alabama Press, 1968;333-46.
Printed in U.S.A.
VOL 16. NO. 2. FEBRUARY1990
SCIENTIFIC ARTICLES Neurovascular Interactions in the Dental Pulp in Health and Inflammation Syngcuk Kim, DDS, PhD
and there is a lack of information on the neurovascular relationship in the inflamed pulp. In this article the interrelationship between microcirculation and sensory nerve activities in health and disease will be examined using current basic research information. The inflammatory processes in the pulp does not differ significantly from that in other tissues in most respects, with a notable exception, however, which is the physical environment of the pulp. the low compliance environment, created by dentin and enamel. Figure l represents a schematic illustration of events involving inflammation in general, in which noxious stimuli have profound effects on the tissue cells. Mechanical stimuli, such as drilling or cutting tooth structure generate noxious vibration or frictional heat; chemical components of various dental materials and cavity washing agents and bacterial byproducts as a result of caries are considered chemical and bacterial stimuli, respectively. When reaching the noxious range, the stimuli degranulate mast cells, disrupt important nutrient flow, damage cells, and in the process lower the excitability threshold of sensory nerves. The attendant release of various inflammatory mediators, e.g. histamine, 5-hydroxytryptamine, kinins, prostaglandins, substance P, and other neurokinins causes pain directly by lowering the sensory, nerve excitability threshold. These substances also cause pain indirectly by vasodilating arterioles and by promoting vascular leakage in venules, resulting in edema and subsequent elevation in tissue pressure, which is of critical importance in pulpal inflammation. Finally, the mediators cause chemotaxis via leukocytes. Pulpal inflammation, if unattended, eventually leads to pulpal necrosis, which in turn causes periapical pathosis. An example of such a case is shown in Fig. 2. a radiograph of fully crowned mandibular anterior teeth of a healthy female patient. There was no pulpal or periapical pathosis prior to the prosthodontic procedures, but as shown in the radiograph, periapical radiolucencies are present on all of the treated anterior teeth. Since these teeth had no history, of decay or trauma prior to the restoration, the probable cause of the periapical pathosis was the restorative procedure. The questions are "Why does tooth preparation result in periapical pathosisT' and "What are the mechanisms of this process?" This fundamental problem in clinical dentistry can be partially explained by the dynamic relationship between blood vessels and sensory nerves in the pulp.
The two key components in pulpal inflammation are microcirculation and sensory nerve activity. With advancement of techniques they can be measured simultaneously in the same tooth. Excitation of Adelta fibers seems to have an insignificant effect on puIpal blood flow (PBF), whereas C fiber activation causes an increase in PBF. This C fiber-induced PBF increase is caused by neurokinins, especially substance P, which is released from the C fiber nerve terminals. Manipulation of PBF has varying effects on sensory nerve activity. An increase in PBF causes excitation of both A-delta and C fibers via an increase in tissue pressure, whereas flow reduction has an inhibitory effect on A-delta fibers, but no discernible effect on C fiber activity. Understanding of this complex neurovascular relationship in the pulp, especially given the fact that the pulp is in a low compliance system, is prerequisite to more comprehensive characterization of pulpal inflammation.
Pulpal inflammation is a subject of interest not only to endodontists, but to all dental disciplines. We understand pulpal inflammation clinically as a toothache and histologi cally as an accumulation of polymorpholeukocytes around the site of insult in a pulp section. In addition to this evidence, however, are many complicated dynamic mechanisms, some of which are known and more which are as yet unknown. It is, however, generally well-accepted knowledge that the two key components in pulpal inflammation are microcirculation and sensory nerve activity. Sensory nerve activity and microcirculation in the pulp have been studied as separate entities by many investigators (1-7) and special emphasis has been given to the characterization of pulpal nerve activity, since pain is the more acute clinical problem in an inflamed tooth. With advancements in circulatory techniques and methods, microcirculatory contributions to pulpal inflammation have also been studied (8, 9). There is, however, a relative paucity of information generated from simultaneous measurements of microcirculatory and neural parameters in the same tooth, 48
Neurovascular Reactions in Pulp
Vol. 16, No. 2, February 1990
Injurious Agents
Before discussing this interrelationship, let us first look at circulation and sensory nerve fimction independently of each other.
(McclumJeal / Chemac.tl / Bactenad)
~lll $t C~ll
Dis;~ptJon
Stimulation
l~grl~uhttlon
Blood Vef~,,cls
~nsor 7 Nerves
L__
i ___
/
/--
,/
!
\
,
.... ~
~
Kinlns
etc.
\ ,~rterlol. ~.
_~ --
~
.... --
v.oo.a.o
......... ~_.
....
-
~
I
Pain
Leakage Chemotaxis
PULPAL MICROCIRCULATION
J
[ Nerves
--_ t..eui,.
I Histamine
49
J/~
~ /
~
,
--/
;
..... .... ~-. -
.-., - -"
FIG 1. Schematic illustration of events involving inflammation in gen-
eral.
Studies of pulpal microcirculation have greatly advanced in the last 15 yr due to the development of sophisticated techniques employing radioisotope tracers (1, 4, 6, 10), radioisotope-labeled microspheres (7, 9), plethysmography (11), and laser Doppler flowmetry (12). Many of these techniques are noninvasive of the pulp (7, 9-12) and have facilitated a quantitative and qualitative analysis of pulpal blood flow (PBF) under various experimental conditions in animal and human teeth. Basically three types of PBF responses to stimuli have been established. In Type I PBF decreases markedly with the intraarterial (i.a.) administration of norepinephrine (13) or 5-hydroxytryptamine (9), with electrical stimulation of the cervical sympathetic nerve and reflex excitation of the sympathetic nervous system by hemorrhage and extreme hematocrit variations (13, 14). This type of flow response is due to activation of a-receptors located in pulpal resistance vessels and the activation of sympathetic adrenergic vasoconstrictor fibers (8, 13). In the Type II response, PBF decreases gradually, as after the i.a. infusion of histamine. This gradual flow reduction is most probably due to an increase in capillary permeability and resultant increased tissue pressure in the low compliance system of the dental pulp. Finally, the Type Ill PBF respon.~ is biphasic; an initial increase is followed by a rapid decrease. This unusual response is caused by the known vasodilators substance P (SP), isoproterenol, prostaglandin E2, and bradykinin (8, 15). The initial vasodilation in response to isoproterenol indicates the presence of ~-adrenergic receptors in the resistance vessels (13, 15). This biphasic flow response to the vasodilators is a result of the low compliance environment of the pulp, in which passive compression of venules may result from active dilation of arterioles with an attendant rise in pulpal tissue pressure, i.e. an inflammatory process (13, 16). It seems clear, that the low compliance environment of the tooth plays an important role in the unusual reduction of PBF during inflammation, since mediators released in the pulp during inflammation, e.g. SP, prostaglandin E2, and bradykinin, etc., are powerful vasodilators. P U L P A L SENSORY NERVE ACTIVITY
FiG 2. A radiograph of mandibular anterior teeth of a patient with fullmouth reconstruction. Extensive periapieal radiolucencies occurred following preparation of the teeth.
The physiological characterization of the pulpal sensory fibers was made using two techniques: multiunit intradental recording, in which electrodes measure nerve activity from dentinal cavities in canine teeth (4, 17) and single fiber unit recording, in which nerve activity is measured from the dissected inferior alveolar nerve in dogs and cats (3, 18). In these studies two types of nerve fibers were found in the pulp: fast-conducting, low-threshold, myelinated A-delta fibers (mean conduction velocity 13.4 m per s and 8.4 to 13.4 mA mean threshold with 20-ms pulse) and slow-conducting, highthreshold, unmyelinated C fibers (mean conduction velocity 1.0 m per s and 37.4 to 40.4/zA mean threshold with 10-ms pulse) (19). Fast-conducting A-beta fibers have also been identified, but their role in the pulp is still unclear. In addition
50
Journal of Endodontics
Kim
to conduction and threshold differences, there are other functional differences between the A and C fibers. C fibers are activated by noxious heat or application of bradykinin and histamine (20, 21). A-della fiber activity, on the other hand, is evoked by stimulation of the exposed superficial dentin by mild thermal, mechanical, and osmotic means (saturated CaCI2); this is most plausibly explained by the hydrodynamic theory (22). However, some hyperosmotic agents (e.g. 3 M NaCI) did not elicit intradental neural activity when applied in shallow cavities, but did cause excitation of A-delta fibers when applied in deep dentinal cavities; the most probable mechanism being direct ionic diffusion (23, 24). Thus, contrary to current thinking, recent experimental evidence supports two mechanisms for pulpal pain, the hydrodynamic and direct ionic diffusion theories. In addition to the differences between A and C libers, there are significant differences in the character of tooth pain associated with A or C fibers. For instance, in response to heat stimulation, immediate, sharp pain can be attributed to A-delta fibers, while a delayed, dull pain is indicative of C fiber activity. The theory, that the initial phase of pulpal inflammation, often accompanied by sharp pain, involves A-delta fibers and that the latter phase, more often characterized by dull pain, involves C fibers, has been advanced (21, 25).
BloodFlowMeasurement 3~
1. 133Xenon washout method 2. Radioisotope labeled microsphere method 3. Laser Doppler flowmetry
2L~ --.-
~
SensoryNerveRecording 4. Intradental 5. Single fiber unit
FiG 3. Schematic representation of a simultaneous recording of blood flow and sensory nerve activity in the pulp. The simultaneous recording of blood flow and sensory nerve activities can be made using any combination of methods shown in the diagram. The most widely used combination is laser Doppler flowmetry for PBF and intradental recording technique for sensory nerve activity measurement.
Saline I 3M NaCI
5 secs
S I M U L T A N E O U S RECORDING OF P U L P A L B L O O D FI,OW AND S E N S O R Y NERVE ACI'IVITIES When studying inflammation in the pulp, the simultaneous recording of blood flow and sensory nerve activity from the same tooth has provided most useful insights into the mechanisms. A schematic representation of the way in which the two parameters can be recorded simultaneously is presented in Fig. 3. The first attempt at this was made in 1970 by a group in Sweden (1). They used the radioactive iodine desaturation technique for measuring pulpal blood flow and the intradental recording technique for measuring the sensory nerve activities in feline teeth. More recently, a modified intradental recording technique and laser Doppler flowmetry have facilitated the in-depth examination of the neurovascular interactions (26). Shown in Fig. 4 are simultaneous recordings of PBF and intradental sensory nerve activity (INA) in response to osmotic stimulation with 3 M NaCI applied to a deep dentin cavity. NaCI applied in dentinal cavities caused increases in both PBF and 1NA, with PBF increases preceding the INA increases. This sequence suggests that PBF changes have an effect on INA. ROLE OF PULPAI. TISSUE P R E S S U R E IN PULPAL INFLAMMATION Pulpal tissue pressure measurements, like PBF and sensory nerve recordings, have benefited from technological advancements in research equipment and increased sophistication in research methods and can now be measured very precisely. Using a micropipettc with a 2- to 4-~,m tip diameter, controlled by a servo-nulling counter-pressure system, precise pulpal tissue and intravascular pressures were recorded (27). The normal resting tissue pressure has been recorded at 6 to 10 mm Hg, but when the pulp is locally inflamed, the local
It
FIG 4. A polygraph tracing of simultaneous recordings of PBF and INA in response to application of 3 M NaCI into a dentinal cavity in a cat canine tooth. The top racing represents PBF measured with laser Doppler flowmetry and the bottom tracing represents INA recorded with the intradental recording technique.
tissue pressure rises to about 16 mm Hg (28). This tissue pressure increase would be insignificant in other tissues, but in the low compliance environment of the pulp, even a small rise can a have significant impact on local circulation as well as sensory nerve activities. Nfirhi (18), recording from the single nerve fiber, has found that an increase in the tissue pressure increases sensory nerve activity. EFFECTS OF C I I A N G E S IN PUI,PAL B L O O D F L O W ON P U L P A L SENSORY NERVE ACrlVITIES A number of separate studies on microcirculation and sensory nerve activity in the dental pulp have shown that an interrelationship exists and several investigators state that local microcirculatory changes may have profound effects on sensory nerve functions in the pulp (1, 4, 30, 31). A severe reduction in PBF in feline teeth, caused by the apical injection of adrenaline or electrical stimulation of the sympathetic
Neurovescular Reactions in Pulp
Vol. 16, No. 2, February 1990
nerve, resulted in concomitant decreases in INA (1, 32); the excitability of intradental sensory, units seems thus modulated by sympathetic vasoconstrictor fibers. This linear relationship between the reduction of pulpal blood flow and ofintradental nerve activity has not been duplicated in our laboratory. Careful examinations reveal that pulpal blood flow must be reduced significantly (approximately 90%) for a substantial duration of more than 10 min, in order to have an effect on intradental nerve activities. It has been hypothesized that the fast-conducting A fibers lose their function rapidly as a result of ischemia, to which the slow-conducting C fibers are less sensitive (28). [his suggests that C fibers may maintain their functional capacity longer than A-delta fibers during inflammation, in which PBF and therefore O2 content are reduced as a result of the low compliance system of the pulp (30, 33). A systematic study of the possible modulating effect of ischemia on nerve fiber activity should provide important insights into dentinal pain mechanisms, especially during inflammation. Changes in pulpal blood flow may not have a direct effect on pulpal C fiber activities; however, increases in pulpal tissue pressure by flow elevation cause excitation of the sensory nerves. Increased tissue pressure is a function of an increase in blood flow accompanied by an increase in vascular permeability. Thus, we could conclude that changes in blood flow have a direct effect on pulpal A fiber activities but minimum effect on C fibers. However, tissue pressure elevation excites all sensory nerves (Fig. 5).
51
changes depend on the degree of neural stimulation. For instance, weak orthodromic stimulation of the tooth surface, which excites only A-delta fibers, causes no changes in PBF, suggesting that excitation of the A-delta fibers has no significant effect on PBF (Fig. 6). However, strong orthodromic stimulation of the tooth surface causes erratic changes in PBF, most likely by C fiber excitation (Fig. 6). Antidromic stimulation of the inferior alveolar nerve in cats, pretreated with an a-adrenergic blocker, caused an increase in PBF and biphasic neural activity; an increase followed by a prolonged depression (31). This neurogenic vasodilation is mediated by the neurokinin SP, which is released from unmyelinated C fiber endings when antidromic stimulation is applied (35, 36). Recent evidence suggests that this neurogenic vasodilation is mediated not only by SP, but also by neurokinin A, B, and especially by calcitonin gene-related peptides. The biphasic neural response following the antidromic stimulation may be related to the biphasic PBF response after i.a. infusion of SP (16), since SP effects are both vascular and neural. Another explanation for the biphasic neural response is that SP triggers the release of histamine, which causes an elevation of pulpal tissue pressure via an increase in vascular permeability (31). Thus, an increase in PBF by vasoactive substances, released either from the sensory nerve endings or from other cellular components, may have profound effects on both circulatory and neural behavior. '9
EFFECI" OF C H A N G E S IN PULPAL S E N S O R Y NERVE ACI'IVITIES ON P U L P A L B L O O D F L O W Evidence that excitation of pulpal sensory fibers has a profound effect on pulpal microcirculation has been provided by a number of researchers (26, 34). However, the flow
PBF
AS|
l
(low flow)
|
NEUROPEPTIDES SP, CGRP etc.
C C|
= tPBF
FIG 5. Relationship of pulpal tissue pressure and A-delta and C fiber nerve activities. + represents excitation or an increase in nerve activity. An increase in pulpal tissue pressure as a consequence of an increase in PBF has an excitatory effect on both A-delta (A-d) and C fibers. An excitation of C fibers in turn causes pulpal flow increase via neurokinins released from the C fiber nerve endings.
TISSUE
)
PBF PRESSURE
FiG 6. Relationship of pulpal blood flow and A-delta (A-d) and C fiber nerve activities. Excitation of A-~, has little effect on PBF. while a decrease in flow has an inhibitory effect on A-~ fiber excitability. Excitation of C fibers increases PBF via neuropeptides, namely, SP and calcitonin gene-related peptide (CGRP). An increase in PBF per se has little effect on C fiber activity, but an increase in tissue pressure excites the nerve.
52
Kim
Journal of Endodontics
The important question "What are the roles of these peptides in pulpal inflammation and under what circumstances are these peptides released?" remains. It is known that a simple tooth preparation can cause the release of a significant amount of SP-like or bradykinin-like substances (37). Also, noxious stimuli of mechanical, thermal, and chemical characters, which excite C fibers, can trigger the release of neuropeptides. These, in turn, have an effect on pulpal blood flow and subsequently on pulpal tissue pressure. Shown in Fig. 7 are the key mediators involved in pulpal inflammation. Inflammatory mediators prostaglandins and bradykinin are released from the tissue components, and various kinins and SP are released in response to sensory nerve excitation. The neurokinins have a direct effect on the vasculature causing vasodilation and leakage, while the simultaneous release of 5-hydroxytryptamine and kinins from vascular components cause mast cells to release histamine which in turn causes further vascular leakage. To return to the initial question about the periapical pathosis shown in the radiograph in Fig. 2, a hypothetical mechanism of pulpal necrosis can be constructed (Fig. 8). As a result of noxious stimulation, i.e. the mechanical, thermal. and chemical stimulation caused by tooth preparation, inflammatory mediators and neuropeptides are released. These mediators alter normal neural and vascular functions, which results in an increase in tissue pressure. Tissue pressure elevation in the low compliance environment of the pulp quickly leads to a decrease in pulpal blood flow instead of an increase as in other tissues. Increased blood flow facilitates the removal of the inflammatory mediators and thereby helps heal the tissue, but in the pulp the decreased flow results in an accumulation of mediators, which in turn causes varying degrees of vessel damage. This vicious cycle, once begun, leads to successive areas of inflammation and eventual pulp necrosis. The discovery of the neuropeptide involvement in pulpal inflammation revolutionized our thinking. It is now clear that neuropeptides play an important role in the progression of pulpal inflammation by linking the actions of the sensory nerves and blood vessels. The term neurogenic inflammation describes a pathological change in the neurovascular relationship, resulting in inflammation. Since pulpal inflammation is
InSUltS
---
roll
~'~I>"
J ~
'
PGs-
/
Hyp . . . . c i t a t i o n
SP i
I
r
!
-
~
(noxious
Release
(BK.
stimulation)
of M e d l a t c r s PG,)
Release
5.HT, Histamine,
of N e u r o p e p t i d e s {SP. CGRP}
9 Hyperexcltatlon I=, 9 V a s o d l l a t l o n , 9 Vascular leakage
14
J
[ ....
I
Pulpal Tissue P r e s s u r e I
I Pulpal Blood Flow (low c o m p l i a n c e system)
A c c u m u l a t i o n of Mediators Vessel Damage I
Pulpal I n f l a m m a t i o n
Pulpal Death F=~ 8. Hypothetical mechanism of pulpal necrosis as a consequence of tooth preparation for a full crown placement. See text for explanation.
primarily neurogenic in nature, our understanding of the neurovascular interrelationship in the pulp in health and disease is of paramount importance. This work was supported by NIH/NIDR Grants DEO-05605 and DEO-O121. The author wo~Jld like to acknowledge his co-workers, Drs. M. Liu, K. Markowdz, J Bilotto, and Ms. J. Dorscher-Kim, for their contributions to this article. Or Kim is chairman, Department of Endodontics, and director, Laboratory of Oral Physiology, Columl~a University, School of Dental and Oral Surgery, New York, NY.
References
BK --
t
Tooth Preparation
~
t G ~-~) / %
Vasodi|ation
Leakage
- 7
|
',
L LOW Comphance Environment F,G 7. Relationship between loulpal inflammation and inflammatory
mediators, See text for explanation.
I
1. Edwall L, Scott D Jr. Influence of changes in microoirculation on the excitability of the sensory unit in the tooth of the cat. Acta Physiol Scand 1971 ;82:55-6. 2. Haegefstam G The origin of impulses recorded from dentinal cavdies m the tooth of the cat. Acta Physiol Scand 1976;97:121-8. 3. Matthews B Responses of intradental nerves to electrical and thermal stimulation of teeth in dogs. J Physio11977;264:641-64. 4. Olgart L. Excitation of intradental sensory units by pharmacological agents. Acta Physiol Scand 1974;92:48-55. 5. Narhi MVO, Hirvonen TJ, Hakumaki MOK. Responses of intradental nerve fibers to stimulation of dentine and pulp. Acta Physiol Scand 1982:115:173-8. 6. Tender KH, Naess G. Nervous control of blood flow in the dental pulp in dogs. Acta Phys~ol St.,and 1978;104:13-23. 7. Kim S. Edwall U Trowbndge H, C h i n S. Effects of local anesthetics on pulpal blood flow in dogs. J Dent Res 1984;63:650-2. 8. Kim S Microcirculation of the dental pulp in health and disease. J Endodont 1985;11:465-71. 9. Kim S, Trowbridge H, Dorscher-Kim J. The effects of 5-hydroxytryptamine on pulpal hemodynames in dogs. J Dent Res 1986;65:682-5. 10. Kim S, Schuessler G, Chlen S. Measurement of blood flow in the dental pulp of dogs with the Xe-133 washout method. Arch Oral Bio11983;28:501-5. 11. Shoher I, Mahler Y, Samueloff S. Dental pulp photoplethysmography in
Vol. 16, No. 2, February 1990 human beings. Oral Surg, Oral Meal, Oral Pathol 36:914. 1973. 12. Gazelius B, Olgart L, Edwall B, Edwall L Non-invaswe recording of blood flow in human dental pulp. Endod Dent Traum 2"219-21. 1986. 13. Kim S. Regulation of pulpal blood flow. J Dent Res 64(spaciai issue):590-6. 1985. 14. Kim S. Fan FC, Chen RYZ, Simchon S, Schuessler GB, Chien S. Effects of changes in the systemic hemodynamic parameters ~n pulpal hemodynam~cs. J Endodon 1980;63:394-9. 15. K,m S. Fleguiation of blood flow of the dental pulp: macrocirculat~on and mlcrocirculation studies IPhD Dissertation}. New York, NY: Columbia University, 1981. 16. Kim S, D0rscher-Kim J, Liu M-T, Trowbridge H. Biphasic pulp bloodflow response to substance P in the dog as measured with a rad=olabeled. microsphere injection method. Arch Oral B=o11988;33:305-9. 17. Bilotto G, Markowitz K. Kim S. Experimental procedure to test the efficacy of chemical agents ~n altenng intradental nerve actwity J Endodon 1987;13:459-65. 18. Narhi M Activation of dental pulp nerves of the cat and the dog with hydrostatic pressure. Proc Finn Dent Soc 1978;1-64.74(suppl V): 19. Narhi M, Virtanen A, Huopaniemi T, Hirvonen T. Conduction velocities of single pulp nerve units in the cat. Acta Physiol Scand 1982;116:209-13. 20. N~irhi M. Jyvasjarvi E, Huopaniemi T. Functional differences in intradental A- and C-nerves units in cats. Abstracts of the IVth World Congress on Pain. IASP, Seattle, Washington, 1984. 21. Narhi M. The characteristic of intradentai sensory units and their responses to stimulation. J Dent Res 1985;64(special issue):564-71. 22. Brannstrom M, Astrom A. The hydrodynamics of the dentine; its possil04e relationship to dentinal pain. Int Dent J 1972:22:219-27. 23. Orchardson R The generation of nerve ~mpulses in mammalian axons by changing the concentration of the normal constituents of extracelfular fluid. J Physlo11978;275:177-89. 24. Bilotto G, Markowitz K, Kim S. Effects of ~omc and non-ionic solutions
Neurovascular Reactions in Pulp 53 on intradentaJ nerve activity in the cat. Pain f 988:32:231-8. 25. Mumford JM, Orofacial pain. Aetiokx:jy, diagnosis and treatment. 3rd ed, Edinburgh: Churchill Livingston, 1982. 26. Markowrtz K. Bilotto G, Liu M, et al. Intradental nerves and pulpal blood flow measured by a laser Doppler flowmeter. J Dent Res 1988;67:215. 27. Markowtiz K, Bilotto G, Liu M, Jo~ YT, Kim S. Physiokxjicai studies of neurogenic inflammation in the dental pulp. J Endodon 1989; 15:170. 28. Tender K, Kvinnsland I. Micropuncture measurements of interstitial fluid pressure in normal ancl inflamed dental pulp in cats. J Endodon 1983;9;105-9 29. Tonder K. Blood flow and vascular pressure in the dental pulp [Doctoral dissertation]. Bergen, Norway: University of Bergen, 1980 30. Olgart L. The role of tocat factors in dentin and putp in intradentat pain mechanisms. J Dent Res. 1985;64(special issue):572-8. 31. Gazelius B Studies on the release and effects of putative mediators of pain in the dental pulp [Thesis[. Stockholm, Sweden: Karolinska Institute, 1981. 32. Olgart L, Gazelius B. Effects of adrenaline and felypressm (Octapressin) on Izdood flow and sensory nerve activity =n the tooth Acta Odontol Scand 1977;35:69-75. 33. Jyvasjarvi E, Nat'hi M, Virtanen A, Huopaniem= T. Differential blockade of intradental A-delta fibers by ischemia. J Dent Res 1983;62(spec=al issue):35 34. Dorscher-Kim J, Liu M-T, Trowb{idge H, Kim S InferK)r alveolar nerve stimulation and pulpal blood flow in dogs. J Dent Res. 1986;64(special issue): 146. 35. Gazelius B, Brodin E, Olgart L, Panopoulos P Evidence that substance P is a me~ator of antidromic vasodilation using sornatostatin as a re~ease inhibitor. Acta Physiol Scand 1981 ;113: f 55-9. 36. Brodin E, Bazelius B, Olgart L, Nilsson G Tissue concentration and release of substance P-like immunoreactivity in the dental pulp. Acta Physiol Scand 1981;111:141-9. 37. Kroeger D. Possible role of neurohumoral substances in the pulp. In: Ir~nn SB, ed. Biology of the dental pulp organ: a symposium. Birmingham: University of Alabama Press, 1968;333-46.
