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Local actions of acetylcholine on vasomotor regulation in rat incisor pulp were investigated in anaesthetized animals. Pulpal blood flow was measured with laser Doppler flowmetry. lontophoresis (40 or 60 muA for 20 s) with acetylcholine or carbachol on an exposed dentin surface caused a biphasic response: an initial vasoconstriction was followed by an atropinesensitive vasodilation. The vasoconstrictor response was enhanced by 171% in the presence of atropine, whereas in control experiments, using isotonic saline as a medium for the direct current, similar vasoconstriction was unaffected by atropine. Carbachol-induced vasodilation was significantly reduced by 30% after intravenous injection of the nitric oxide synthesis blocker N omega-nitro-L-arginine methyl ester (10 mg kg-1), and the remaining vasodilation was abolished by atropine. The present results support the concept of a cholinergic modulation of sympathetic vasoconstrictor function and of a partial contribution of nitric oxide in carbachol-induced vasodilation in rat incisor pulp.

The use of iontophoresis for facilitated diffusion of vasoactive agents into the dental pulp was investigated in lower incisor teeth of anaesthetized rats. Acetylcholine, carbachol and noradrenaline were iontophoresed with anodal and sodium nitroprusside with cathodal direct current through a superficial dentin exposure. Pulpal blood flow was measured with laser Doppler flowmetry. Current intensities below 100 microA of both polarities, using sodium chloride as a medium, caused no or minor afferent nerve-induced vasodilation, but excited sympathetic fibres of the pulp in a current-dependent manner. The current threshold for facilitated diffusion of acetylcholine was about 20 microA. The vascular responses to the cholinergic and noradrenergic drugs appeared within a minute after the onset of current and they were abolished by systemic administration of atropine and phenoxy benzamine, respectively. Iontophoresis of acetylcholine (40-100 microA for 20-120 s) caused a 3-fold increase of pulpal blood flow which was not dose-dependent; carbachol provoked a high-magnitude, long-lasting vasodilation and so did sodium nitroprusside. Noradrenaline caused a long-lasting vasoconstriction. In denervated rats iontophoresis of carbachol had effects similar to those seen in intact animals. None of the drugs used locally had any effect on systemic blood pressure. The results of this study indicate that iontophoresis can be used for delivery of vasoactive agents from an exposed dentin surface into the pulp in sufficient quantity to elicit drug-specific local vascular responses without causing systemic vascular effects.

The possible involvement of the neuropeptides substance P and calcitonin gene-related peptide (CGRP) in the development of neurogenic plasma extravasation in the lower lip, gingiva and incisor pulp was examined in anaesthetized rats by means of the Evans blue method and by using newly developed blockers of substance P (CP-96,345) and CGRP (CGRP8-37). Electrical stimulation of the inferior alveolar nerve (15 V, 2 ms, 10 Hz) for 5 min significantly increased the Evans blue content of the ipsilateral lip, gingiva and pulp by 60 (p < 0.01), 62 (p < 0.01) and 92% (p < 0.05), respectively (n = 8). Pretreatment with CP-96,345 (total dose: 1.5 mg/kg, intravenously) counteracted the dye leakage in the lip and pulp but not in the gingiva (n = 6). The inactive enantiomer (CP-96,344, 1.5 mg/kg, n = 8) or the nitric oxide synthesis inhibitor (N omega-nitro-L-arginine methyl ester hydrochloride, 10 mg/kg, n = 7) did not reduce the stimulation-induced dye extravasation in any of the tissues. Pretreatment with CGRP8-37 (0.3 mg/kg, n = 7) did not significantly influence the development of neurogenic extravasation in the lip and incisor pulp, but it slightly attenuated extravasation in the gingiva. The results indicate that the afferent nerve-induced dye extravasation in the lip and pulp, but not in the gingiva, is to a large extent mediated by substance P acting via neurokinin-1 receptors. There was no evidence for an involvement of nitric oxide or CGRP in neurogenic extravasation in rat incisor and lip.

The role of nitric oxide in the mediation of (a) antidromic and (b) substance P-induced vasodilation in the pulp, lip, oral mucosa and submandibular gland was investigated in anaesthetized rats by means of laser Doppler flowmetry. Bolus or continuous infusion of Nω-nitro-L-arginine methyl ester (L-NAME) increased mean arterial blood pressure and reduced basal blood flow in the pulp but not in the lip. Electrical stimulation of the inferior alveolar nerve, in the presence of phenoxybenzamine, resulted in a long lasting vasodilation in lower lip and incisor pulp. Infusion of L-NAME enhanced the antidromic vasodilation in both lip and pulp. Pretreatment with L-arginine prevented these effects. Administration of the enantiomer (D-NAME) did not exert any effect on basal blood flow and on antidromic vasodilation. Infusion of substance P resulted in a transient vasodilation in all of the oral tissues studies. L-NAME reduced this vasodilation in the submandibular gland (only the lower doses) but it potentiated the responses in the pulp and oral mucosa. Pretreatment with L-arginine prevented the potentiated responses in the pulp and those induced by the lower doses of substance P in the oral mucosa. Thus, nitric oxide appears to differentially regulate the basal blood flow and the antidromic or substance P-induced vasodilation in the microvasculature of the lip and dental pulp.

Previous studies have shown that sympathetic nerve stimulation reduces afferent nerve-induced vasodilation by mechanisms unrelated to vasoconstriction in the rat incisor pulp. The present investigation concerned whether similar modulatory mechanisms might also influence neurogenic plasma extravasation in dental pulp. Rat mandibular incisors were electrically stimulated and blood flow reactions in the pulp were recorded by laser Doppler flowmetry. Plasma extravasation in the incisor pulp, gingiva and lip were indirectly assessed by the Evans-blue method. Stimulation of teeth with 50 microA (5 min) did not cause increased dye accumulation in the stimulated pulps whereas stimulation with 100 microA significantly increased the dye content in ipsilateral pulps by 32% as compared to controls; 100 microA stimulation was without effect in unilaterally denervated animals. Tooth stimulation with 50 microA (5 min), in the presence of either the alpha-adrenergic blocker phenoxybenzamine (3 mg/kg), or the alpha 1-adrenergic antagonist prazosin (50 micrograms/kg), as well as in chronically sympathectomized animals, significantly increased the Evans-blue content in the stimulated pulps by 47, 83 and 86%, respectively. Application of short trains of impulses (same number of impulses as for the continuous stimulation but producing minimal vasoconstriction) resulted in some dye accumulation, which was enhanced in the ipsilateral pulps in the presence of prazosin (100 micrograms/kg) or after acute resection of the superior cervical sympathetic ganglion by 70 and 64%, respectively. The Evans-blue content in the lip and gingiva was uninfluenced by the tooth stimulation. The results indicate that activation of sympathetic nerves inhibits the afferent nerve-induced plasma extravasation in rat incisor pulp and this effect is mediated by alpha-adrenoceptors not associated with vasoconstriction.

Previous studies of the sympathetic nerve supply of the rat mandibular incisor pulp have shown conflicting results. Here, the neurovascular control of the rat lower incisor pulp was investigated by stimulating the tooth crown and the cervical sympathetic trunk electrically and monitoring blood-flow changes in the pulp by laser Doppler flowmetry. In addition the presence of noradrenaline (NA) in the pulp and gingiva was examined biochemically in untreated and sympathectomized animals by high-performance liquid chromatography. The tissue concentrations of NA in the pulp were 11-fold greater than those of gingiva. Surgical sympathectomy significantly reduced the NA content in the pulp by 76%. Monopolar electrical stimulation of teeth (25-50 microA) for 1 min resulted in a frequency-dependent reduction followed by an increase in pulpal blood flow. At 16 Hz the reduction in blood flow was 65% and the subsequent increase was 9%. After intravenous administration of the alpha-adrenoceptor antagonist phentolamine, the stimulation-induced reduction in pulpal blood flow was diminished by 94% while the increase was significantly enhanced (from 9 to 40%). Infusion of the beta-adrenoceptor antagonists propranolol and timolol significantly reduced this increase in blood flow by 53 and 55%, respectively. Preganglionic sympathetic nerve stimulation also induced a frequency-dependent reduction followed by a slight increase in pulpal blood flow. This reduction in blood flow was almost abolished after alpha-adrenergic blockade and there was no subsequent increase. These findings suggest that there are sympathetic nerve fibres in rat incisor pulp and that they are activated upon monopolar electrical stimulation of teeth resulting in alpha- and beta-adrenoceptor mediated blood-flow responses.

In 15 subjects, laser-Doppler flowmetry (LDF) was used to investigate whether the nervous control of pulpal blood flow (PBF) is affected by three tests known to excite the sympathetic nervous system. For comparison, skin blood flow was similarly recorded. Dynamic exercise (bicycle ergometer, 5 min, 90–100 W) in eight subjects was accompanied by a rise in PBF. PBF was increased by the cold pressor test (2 min) in eight subjects, while in five the flow decreased or remained unaffected. The isometric hand grip (2 min, 30% MVC) and the subsequent muscle ischaemia (2 min) led to a rise in PBF in two subjects and a fall in four. Following unilateral anaesthesia of the mandibular nerve, PBF in five subjects became unresponsive to dynamic exercise or the cold pressor test, indicating pressure autoregulation. All three tests triggered increases in mean arterial pressure (MAP) and heart rate (HR). Skin blood flow usually increased in response to the tests, but could also decrease, and often changed in a direction opposite to that of PBF. It is concluded that the circulation of blood in the human tooth is affected by evoked changes in autonomic nerve activity, involving activation of both vasodilator and vasoconstrictor nerves to vessels serving the tooth.

The effect of angiotensin II (Ang II) was studied on blood flow in the submandibular gland and tongue in male rats. Blood flow changes were determined with laser Doppler flowmetry and Ang II was infused into the common carotid artery before and after i.v. doses (18 nmol kg-1) of the angiotensin II antagonist saralasin. Angiotensin II (10-60 pmol min-1) dose-dependently increased blood pressure and tongue blood flow, whereas glandular blood flow decreased at all of the doses used. After saralasin administration the angiotensin II effects on blood pressure, tongue and glandular blood flow were significantly diminished (glandular blood flow reduction was diminished from 29%-3%, P less than 0.005, n = 9). However, the responsiveness of these 3 parameters to local infusions with noradrenaline (0.75-3.0 pmol min-1) was unaffected by saralasin. The dose of saralasin used in the present study did not affect any of the parameters on it's own. Our results show that vascular receptors sensitive to angiotensin II operate in the submandibular gland but not in the tongue.

The blocking effect of lidocaine on nerve-induced vascular reactions was investigated in lower incisor teeth of anaesthetized rats. Pulpal blood flow was measured with laser Doppler flowmetry. Monopolar electrical stimulation of the rat incisor evoked a biphasic vascular response: an initial vasoconstriction was followed by a long-lasting vasodilation. Iontophoresis of lidocaine on a superficially exposed dentin surface with 60 microA of anodal direct current for 20 min blocked almost completely the stimulus-induced blood flow increase for about 25 min without any systemic effects. Iontophoresis of lidocaine with 40 microA for 20 min was almost without effect. Topical application of a mixture of lidocaine and prilocaine (25 + 25 mg/ml) in deep dentinal cavities was also without effect on the neurogenic reactions. Intravenous administration of lidocaine at 5 and 10 mg/kg in rats pretreated with phenoxybenzamine reduced the stimulus-induced increase in blood flow by an average of 29% and 54%, respectively, whereas the remaining alpha-adrenoceptor resistant vasoconstriction was not influenced. The present results show that iontophoresis of lidocaine on exposed dentin blocks nerve-induced vascular responses without causing systemic effects.

A strong neurotensin-like immunoreactivity (NT-like IR) was detected in the odontoblast cells of the rat teeth. 4 h after a partial pulpotomy performed in two maxillary molar teeth a decreased NT-like IR was observed in the odontoblast layer located at the vicinity of the lesion together with edema and nuclear pyknosis. NT-like IR became further decreased after 24 h. After 7 days NT-like IR had almost fully disappeared with signs of necrosis of the dental pulp and infiltration of polymorphonuclear lymphocytes. It seems possible that NT like peptides in the odontoblast cell layer may play a role, e.g., in dentinogenesis and/or nociception.

This investigation was designed to study the formation of secondary dentin in permanent teeth of young cats after denervation. In eight animals, cervical dentin was exposed bilaterally in the mandibular canines, 7-10 d after unilateral resection of the inferior alveolar nerve. The observation intervals were 30 d, 90 d and 180 d, after which histological examination of dentin was performed. In order to verify the loss and regeneration of pulpal innervation and an intact blood supply, blood flow responses to electrical stimulation of the tooth and to i.v. injections of substance P (SP) were recorded by laser Doppler flowmetry before and at 7-10 d after denervation, at the end of the experiments, and at predetermined intermediate intervals. SP-induced vasodilation was significantly enhanced at 1 wk and 30 d postoperatively and was normalized to control values at 90 and 180 d. Vasodilation in response to electrical tooth stimulation, which was absent after denervation, reappeared after 90 d in two of four cats. There was no irregular dentin formation under the exposed dentin at any time in denervated or control teeth. Formation of regular secondary dentin appeared to be enhanced on the denervated side at 30 d and 90 d postoperatively, whereas at 180 d there was no difference between sides. The results indicate that intradental nerves influence secondary dentin formation in feline permanent teeth.

In this study the newly developed blockers of substance P (CP-96,345) and calcitonin gene-related peptide (CGRP8-37) were used to examine whether substance P and CGRP are involved in the afferent nerve induced vasodilation in the rat lower incisor pulp and lip. Electrical stimulation of the inferior alveolar nerve (10 V, 2 ms, 10 Hz, 30 s) in the presence of phenoxybenzamine (3 mg kg-1) induced an immediate vasodilation in the pulp and lip (52 and 186% increase in blood flow respectively, n = 12) with a long duration. Infusion of 2 mg kg-1 CP-96,345, a dose that inhibited the vasodilator effects of substance P (5-25 ng kg-1) in oral tissues, did not have any effect on antidromic vasodilation in either tissue. After infusion of CGRP8-37 (0.3 mg kg-1) the duration of the antidromic vasodilation in the pulp and lip was significantly reduced by 72 and 67% respectively (P < 0.05, n = 4), whereas the maximal increase of the response was unaffected. The blocking effect of the drug was short-lasting. When combined infusions of CP-96,345 and CGRP8-37 were given, a similar reduction in the duration of antidromic vasodilation in the pulp and lip occurred but in this case the amplitude of vasodilation in the pulp was reduced (from 35 +/- 9 to 12 +/- 3%, P < 0.05, n = 4). However, in the lip, the amplitude of vasodilation was not significantly reduced. The present findings indicate an involvement of CGRP in the mediation of the late phase of antidromic vasodilation in rat oral tissues and a role of substance P in the initiation of antidromic vasodilation in the incisor pulp.

Whether increased extravasation of plasma protein may occur in the rat incisor pulp as a result of antidromic stimulation of afferent nerves was investigated, and this preinflammatory reaction compared with that in adjacent soft tissues. In anaesthetized rats, the inferior alveolar nerve was exposed and stimulated electrically (10-15 V, 2 ms, 10 Hz for 30 s or 5 min). Blood flow changes in the lower lip and incisor pulp were recorded by laser Doppler flowmetry. Increased vascular permeability in the lip, gingiva and pulp was indirectly determined by means of the Evans blue dye method and spectrophotometric analysis. Stimulation of the inferior alveolar nerve for 30 s, in the presence of the alpha-adrenergic blocker phenoxybenzamine (3 mg/kg), increased blood flow in the lip by 172 +/- 16% and in the pulp by 38 +/- 5% as compared to basal blood flow. Intravenous (i.v.) administration of atropine (1 mg/kg), chlorisondamine (3 mg/kg), timolol (150 micrograms/kg), cimetidine plus mepyramine (3 mg/kg of each), methysergide (1 mg/kg) and diclofenac sodium (3 mg/kg) was without effect on this response. Acute pretreatment with capsaicin (1-3 mg/kg, i.v.), however, abolished the vasodilation in the pulp and reduced that in the lip by 58% (p0.05). In untreated animals, stimulation of the inferior alveolar nerve for 5 min increased the Evans blue content in the ipsilateral lip by 164% (p0.001), gingiva by 55% (p0.01) and pulp by 67% (p0.01). Pretreatment (i.v.) with a combination of cimetidine and mepyramine counteracted the dye extravasation only in the gingiva.(ABSTRACT TRUNCATED AT 250 WORDS)

In order to elucidate a possible influence of the sympathetic nervous system on afferent nerve function, rat mandibular incisors were electrically stimulated and blood flow changes monitored in the incisor pulp of untreated and sympathectomized animals by a laser Doppler flowmeter. Monopolar electrical stimulation of the tooth (200 microA, 5 ms, 40 Hz, 1 s) in normal animals resulted in a transient reduction in pulpal blood flow (PBF) (16% reduction, n = 10) followed by a small but long-lasting increase (11% increase). After administration of phenoxybenzamine or phentolamine (3 mg kg-1, i.v.) the initial dip in PBF was reduced by 59% (P < 0.001) while the subsequent increase was enhanced by 185% (P < 0.001). Similarly, infusion of prazosin (50 micrograms kg-1, i.v.) and idazoxan (0.5 mg kg-1, i.v.) significantly enhanced the increase in PBF by 118 and by 79%, respectively. In chronically sympathectomized animals the increase in PBF was 250% larger than that seen in untreated animals (P < 0.001). This increase in PBF was not further enhanced after alpha-adrenergic blockade. Acute resection of the superior cervical sympathetic ganglion, also resulted in some enhancement (by 56%) of the stimulation-induced increase in PBF (P < 0.01, n = 6). The increase in PBF was unaffected by infusion of timolol (150 micrograms kg-1) and atropine (1 mg kg-1) but was totally abolished by intravenous pre-treatment with capsaicin (1-3 mg kg-1). The present results suggest that activation of sympathetic nerves exerts inhibitory effects on the afferent nerve-induced vasodilation in the rat incisor pulp unrelated to sympathetic vasoconstriction.

A unilateral resection of the mandibular nerve ( n = 20) was made 10–14 days before investigation of the contribution of afferent nerves in vasodilator reactions in the dental pulp. Lower canine teeth were subjected to various stimuli and pulp blood-flow responses monitored by laser Doppler flowmetry. An absence of response to bipolar electrical (5 impulses, 50 μA, 5 ms, 2 Hz) stimulation on the tooth surface was used to demonstrate a successful chronic nerve lesion. Local application of capsaicin (10 −4 M) in a deep dentinal cavity induced a long-lasting increase in pulpal blood flow in control teeth only. Bradykinin (10 −3 M) induced significantly larger responses in control than in denervated teeth (58.3 ± 9.8% and 24.5 ± 4.9%, respectively, p n = 8); in addition, the onset was slower and the duration of the response significantly (60%) shorter than in control teeth. Intermittent grinding of surface dentine instantly increased flow in control teeth by 53.0 ± 12.5% ( n = 12) whereas in denervated teeth the response was delayed and significantly (70%) smaller. Deeper preparation produced responses of similar magnitude in control and denervated teeth (69 and 50%, respectively) but the onset was delayed in denervated teeth. Low-intensity ultrasonic stimulation caused vasodilation in intact teeth (38% increase) but had no effect in denervated teeth. This effect was abolished after local anaesthetic (mepivacaine) injection. Sympathectomy ( n = 3) did not influence stimulation-induced blood-flow responses in the dental pulp. The results show that afferent nerves make an important contribution to haemodynamic reactions in the pulp in response to experimental and clinical procedures directed at the tooth.

In order to test the hypothesis that ACh mediates the transmission of pain stimuli from dentin to sensory intradental nerve endings the following experiments were performed. Intradental nerve impulses were recorded by means of low impedance electrodes inserted in dentinal cavities in the tooth of the cat. An air blast proved to be an efficient physical stimulus to excite the intradental nerves. Local application of acetylcholine caused a similar response. This response to acetylcholine was followed by a transient blockage to repeated application. The response to acetylcholine could be blocked by d-tubocurarine, atropine, succinylcholine and hexamethonium administered locally. In contrast, the response to physical stimuli (air blasts) could not be blocked by these drugs. Moreover, during the period of depression following acetylcholine the preparation responded to physical stimuli. These findings suggest that acetylcholine is not a mediator in the intradental pain transmission provoked by physical stimuli.

Blood flow changes in the dental pulp of lower canine teeth of mature cats and incisors of mature rats were investigated with simultaneous laser Doppler flowmetry and local 125I-clearance (wash-out) during electrical sympathetic stimulation, efferent stimulation of n. alveolaris inferior (IAN) (cats) and i.a. infusions of substance P (SP) (cats). Stimulation (1-4 Hz, 4 V., 1.5 ms) of the cervical sympathetic trunk produced frequency-dependent decreases in both laser Doppler output and disappearance rate of iodine tracer from the dental pulp. For the effects of sympathetic stimulation, the correlation (r2) between the results obtained by the two methods was 0.89 (12 observations, six animals). Blood flow measurements by both methods were increased following i.a. infusions of SP (r2 = 0.64, six observations, three animals). However, upon stimulation of IAN (10 Hz 10 V, 5 ms) the laser Doppler flow values showed an increase while the local 125I clearance rate was unaffected or even decreased. The discrepancy between the results obtained following IAN stimulation indicates that the two methods reflect blood flow changes in different parts of the pulpal vascular bed and that the flow is unevenly distributed to these parts during antidromic IAN stimulation. The laser Doppler flowmetry seems to reflect the total blood flow in the coronal pulp and therefore this non-invasive method may be useful for monitoring blood flow changes in the tooth.

Ammonia and organic acids constitute a major part of the bacterial metabolites formed in carious decay. The aim of the present study was to investigate their effect on the intradental sensory nerves. Nerve impulse activity was recorded from canine teeth in cats after application of the test solutions in deep dentinal cavities. Ammonia (17-134 mM) consistently generated nerve impulses, whereas organic acids (0.001-1 M) failed to induce any impulse activity. In contrast, acid application resulted in an inhibition of the ongoing nerve activity induced by various stimuli (hypertonic NaCl solution, mechanical pulp exposure, and compound 48/80). However, acid treatment of the cavities resulted in an enhanced neural response to ammonia stimulation. Thus, the present results demonstrate that these bacterial metabolites can influence intradental sensory nerve activity. It is suggested that they may also modulate the symptoms from decayed teeth.

It can be concluded that the sympathetic vasoconstrictor regulation is dominant among the remote control mechanisms of pulpal blood flow. The local systems, neurogenic and humoral, probably act by modulating t h e sympathetic vasoconstrictor tone. The basal vascular tone, of fundamental importance in other vascular beds, has not been analyzed in the dental pulp.

In this study three different models of the relation between intradental nerve impulse activity (INA) and pain report, expressed by finger-span (FS), in man were investigated. The techniques were (i) a previously described mathematical model, (ii) the relation between the Areas of INA and FS and (iii) the relation between the Peaks of INA and FS. Their usefulness in 533 clinical experiments on 15 subjects were evaluated by means of a statistical analysis of the variability and accuracy of the models. It was shown that the mathematical model was the most accurate and stable method of the three different methods investigated. This was indicated by, among other things, a significantly smaller variability for the mathematical model within experimental sessions than between sessions. The two other methods were found to be of less scientific value since they had an undesired high variability within sessions, and also showed contradicting results during control conditions.

The effects of tooth surface stimulation on intradental nerve activity (INA) and subsequent pain perception were studied in human lower incisors later to be extracted for periodontal reasons. The INA elicited by hot gutta-percha briefly applied to the tooth surface was monitored by means of labial electrodes deeply implanted in the dentin and perceived pain was continuously rated using a finger-span technique. After each stimulation the subject was also requested to select a sensory descriptor that was appropriate to describe the maximal pain intensity. The very first application of heat induced a typical pattern of nerve activity consisting of three phases. An initial burst of 3-5 s duration, phase I, was followed by a depression relative to the baseline lasting for 20-30 s, phase II, that gradually turned into phase III constituting a slowly increasing firing rate. The spontaneously emerging activity (phase III) in the absence of a physical stimulus passed unnoticed by all the subjects despite an average increase in firing rate of 67% relative to the prestimulus noise level. Repeated heat applications at short intervals led to a decrease and finally to abolishment of the whole nerve response. The lack of pain during phase III may be explained in two ways: the rate of increase in firing frequency may be too slow to trigger those perceptual pathways involved in processing of pain; the slow development of the increased sensory nerve activity may lead to central habituation.(ABSTRACT TRUNCATED AT 250 WORDS)

The purpose of the present investigation was to find neurophysiological correlates of pain perception. The magnitude and time course of perceived pain was successfully related to the neural discharge evoked by rapid cooling of the tooth surface in 6 dental patients whose lower incisors were to be extracted for prosthodontic reasons. Two cavities were prepared on the facial surface of human lower incisors. The cavities were deepened using hand driven instruments until the pulp was visible through a thin layer of dentin. A metal tube was placed in contact with amalgam on each cavity bottom and fixed in place by composite filling material. The tubes were connected to standard equipment for electrophysiological recordings by a flexible circuit. The magnitude of perceived pain was assessed by a cross-modality matching to finger span in combination with sensory verbal pain descriptors and magnitude estimation. The striking agreement between the integrated nerve activity, probably of the Aδ type and pain perception, is of great importance from the methodological point of view since it strongly argues in favor of the appropriateness of the techniques applied here to elucidate the neural substrate of some types of nociception and also to evaluate various means of relieving such pain.

The aim of the study was to investigate in commonly used experimental animals the pulpal wall and the dentin with special reference to the number and diameter of the dentinal tubules. The coronal dentin of a total of 26 permanent, intact teeth from rat, cat, dog and monkey was fractured experimentally. The calculations were based on the study of about 150 scanning electron microscope (SEM) photographs of fractured surfaces and of the pulp chamber wall. The number of dentinal tubules per unit area was calculated and the tubule diameter was measured at various distances from the pulp. The tubules were found to be widest at the pulpal wall, where the mean diameter ranged form 1.7 to 2.8 mum, the highest value being found in monkey and the lowest in the incisors of rat. In the middle part of the dentin the mean diameter varied from 1.0 to 1.3 mum and at the periphery it was 0.6 to 0.9 mum. The largest number of tubules per unit area was found immediately incisal of the pulp horn and the smallest number cervically, near the enamel. At the pulpal wall the mean number of the tubules ranged from 50,000 to 90,000/mm2, in the middle of the dentin it was between 37,000 and 50,000/mm2 and at the periphery it was between 10,000 and 25,000/mm2. In all species examined the dentinal tubules showed a straight course, except in incisors of rat, where local irregularities were seen. A comparison was also made between the species studied and homo with respect to the number and width of the dentinal tubules.

Using a modification of the flying spot method for estimation of flow velocity in micro vessels, comparative observations were made on arterioles, venules and capillaries in the pulp of the rat incisor by vital microscopy. It was found that stimulation of the sympathetic nerves to the tooth, either at its apex or in the cervical sympathetic trunk, produced marked reduction of flow which was followed by a return to normal velocities at the cessation of stimulation. Direct stimulation of the sympathetic trunk produced very rapid reduction of flow velocity. Changes were also observed in response to administration of anesthetics and other procedures.

The objective of the study was to determine the response in the pulpal blood flow to vasodilator substances at different levels of vasomotor tone.Simultaneous determinations of iodide disappearance rate (k-value) from dentinal cavities and, as control, from the adjacent alveolar submucosa were performed on anesthetized cats. Changes in k-value reflected changes in blood flow. Close i.a. infusion of acetylcholine, histamine and bradykinin did not influence pulpal microcirculation when the sympathetic nervous tone was low. At a higher level of nervous vascular tone, obtained by direct electrical stimulation of the cut sympathetic cervical trunk, the substances were shown to increase the pulpal blood flow. Papaverine and warming had a more pronounced vasodilator influence on pulpal blood flow, suggesting the presence of a local myogenic vascular tone regulating the exchange function, which was unaffected by acetylcholine, histamine and bradykinin. These substances were thus shown to act as inhibitors of symp...

In order to investigate the origin of intradentinal nerve-like structures, unilateral transection of the sensory (inferior alveolar nerve) and/or the autonomic (cranial cervical sympathetic ganglion) supply was performed in 6 cats. After 2—4 weeks, when degenerative change was expected in the cut nerves, electrophysiological recordings from the dentin showed total absence of impulse activity in teeth subjected to sensory denervation regardless of whether or not the autonomic innervation was intact. Control teeth, on the other hand, responded to different local pain stimuli. Electron microscopic study of predentin and inner dentin in control teeth showed intratubular nerve-like structures similar to «associate cells» earlier described in human teeth. In teeth subjected to sensory nerve resection, however, the intradentinal «associate cells» showed advanced degenerative change or were absent. Resection of the sympathetic nerve supply did not influence the appearance of these intratubular structures.The pres...

Simultaneous determinations of radioactive iodide disappearance rate (k-value) and sensory nerve impulse frequency from dentinal cavities were performed on canine teeth of anesthetized cats. Changes in k-value reflecting changes in pulpal microcirculation were obtained by direct sympathetic nerve stimulation or by thermal stimulation. Sympathetic nerve stimulation re duced the k-value and induced an initial increase in nerve impulse frequency. During maximal sympathetic nerve stimulation this initial increase was followed by a marked depression in impulse frequency. Application of heat increased k-value as well as impulse frequency, while cold reduced k-value and induced an initial increase in nerve impulse frequency followed by a decrease. Thermal stimulation superimposed during maximal sympathetic stimulation, when k-value was depressed, was inadequate to evoke an appreciable increase in sensory nerve in pulse frequency. It is suggested that the excitability of sensory units in the tooth is strongly modulated by changes in pulpal microcirculation induced by, for example, stimulation of sympathetic vasoconstrictor fibres.

The rate of disappearance of radioactive iodide from a deep dentinal cavity has been used as a means to measure the influence of various cavity washing agents on pulpal microcirculation. Hydrogen peroxide in concentrations of 2–4% exerted a pronounced influence when it was allowed to act in deep dentinal cavities where the red colour of the pulp was barely visible through the dentin. Repetitive treatments of 3 % hydrogen peroxide of 40 sec duration caused a potentiated depression of the microcirculation. This was true when the dentinal wall between the cavity and the pulp was intact. In cases of pulp exposure the influence seemed to be much less. All other agents tested failed to influence the pulpal microcirculation as reflected by the present method.

Because of discrepancies between results from animal and human experiments on nervous activity of teeth, experiments were done on human teeth to find clinical relevance. When a dentist manipulates a tooth with a probe, an air blast, or a bur, the patient suffers from hydrodynamic excitation of the A-delta nerves. Dull pain is more likely to be the result of C-fiber stimulation and is associated with tissue damage and inflammation of the pulp.

The present investigation was undertaken to ascertain whether local insults can affect the sympathetic vasoconstrictor regulation of pulpal blood flow. The rate of disapperance (k-value) of iodide from dentinal cavities was measured in anaesthetized cats. Changes in k-value reflected changes in blood flow. It has previously been shown that stimulation of sympathetic vasoconstrictor nerve fibres generally causes a clearcut decrease in the k-value. Deep cavity preparation was found to inhibit the vasoconstrictor response in a few cases in experiments on mature cats. Heating or cooling the tooth during cavity preparation induced a more frequent inhibition, which proved to be reversible within a few hours. Compound 48/80 applied locally to the cavity was also found to induce inhibition of the vasoconstrictor effect, but in this case no sign of reversibility was observed. Chronic insults were produced by exposing the cavity to oral microorganisms during 1-4 weeks before the experimental procedure. In this case, the sympathetic vasoconstrictor response was not inhibited. A histological study was performed to examine the pulp tissue after cavity preparation and the application of insults. It was found that cavity preparation and acute insults caused little or no disturbance, while chronic insults resulted in severe damage to the pulpal tissue.

The ability of a mathematical model to evaluate the effects of two different pain modulating procedures (partial nerve block and vibration) on acute experimental pulpal pain was studied. The results were also compared with placebo procedures and it was shown that the model could accurately quantify the parameters that determine the pain response following cold-induced intradental nerve impulse activity (INA). The most effective pain relieving method was found to be partial nerve block which induced significant parameter alterations reflecting decreased pain sensation and increased reaction time. Thus, it was shown that the present mathematical model is a useful tool enabling detailed analysis of differences in pain relieving procedures on human pulpal pain mediated by nerves of the A type.

Intermediate bases are placed between restorative materials and dentin to protect the vital pulp. For cases in which the pulp has been subjected to injury, bases may be used for therapeutic purposes. Two pulp medicaments commonly used as bases are zinc oxide-eugenol (ZOE) and calcium hydroxide. ZOE preparations are widely used for their sedative effect on pulpal pain, but the mechanism by which ZOE reduces sensitivity has not been elucidated. Although McDonald 1 has stated that ZOE is capable of reducing inflammation, this has not been verified experimentally. Eugenol is generally considered an anodyne and the ingredient in ZOE that is responsible for sedation. It has been shown that eugenol is capable of blocking action potentials in nerve fibers, 24 and this suggests that it has a direct effect on nerve cell membranes. Calcium hydroxide is routinely used for pulp protection in deep excavations or for healing of traumatic pulp exposures.' Because of its alkalinity, calcium hydroxide is frequently placed beneath phosphoric acid cements. Calcium ions raise the threshold for initiation of nerve impulses, and Olgart ~ has reported that application of calcium chloride to freshly cut dentin is capable of eliminating impulse activity of intradental nerves. Although calcium hydroxide is only slightly soluble in water, some calcium ions are released, and this raises the possibility that the diffusion of free calcium ions into the pulp may reduce the excitability of intradental sensory nerves. The purpose of this investigation was to determine whether ZOE and calcium hydroxide are capable of modulating intradental nerve activity when they are placed as bases in dentinal cavities.

Intradental sensory nerve impulse activity was measured from dentinal cavities in canine teeth of anesthetized cats. No spontaneous activity was usually recorded in cavities filled with isotonic saline. Heat stimulation of 15–20oC failed to give any impulse activity, while other stimuli, such as air blasts produced bursts of impulses. Lowering extracellular calcium ion concentration. by local application of sodium citrate, sodium oxalate or EDTA, induced impulse activity. Under these conditions, heat produced a rapid increase in discharge activity. which lasted as long as the stimulus was applied. Increased extracellular calcium concentration abolished this response to heat. The present findings show that a change in the extracellular calcium ion concentration modulates the excitability of intradental sensory units, and may thus also modulate the resulting experience of pain.

Laser Doppler flowmetry was applied to human teeth to study whether blood How in the pulp can be recorded. In sensitive, intact incisors the level of the output signal Ironi the flowmeter was clearly distinguishable from that obtained in adjacent nonsensitive or pulpeetomized teeth. Heart beat synchronous oscillations, which were present in the recording signal from normal teeth, were absent in nonvital teeth. Local injection of lidocaine (20 mg/ml) with adrenaline (12.5 μg/ml) caused a pronounced and long-lasting reduction of the flowmetric values in healthy teeth. The oscillations were also reduced in amplitude. Repeated recordings showed good reproducibility. Thus, changes in blood (low may be assessed in a tooth by tin's non-invasive method. The instrument is a promising tool in the clinical evaluation of pulp vitality following traumatic injuries.

Changes in intra-alveolar tooth position and local 125I clearance from the periodontal ligament (PDL) were monitored simultaneously in cats. Axial tooth movements, reflecting periodontal ligament volume changes, were measured with an ultrasonic transit time technique. Local blood flow changes in the PDL were studied indirectly by measuring the local clearance of 125I-. Stimulation of the cervical sympathetic trunk caused an intrusive movement of the tooth with a concomitant reduction of the 125I- clearance. Infusion of noradrenaline induced a similar response. Stimulation of the inferior alveolar nerve during systemic treatment with phentolamine caused an extrusive movement of the tooth with a concomitant increase in the clearance of the tracer from the PDL. Intra-arterial infusion of the vasodilator substance P mimicked that response. Fixation of the tooth to the jaw bone, thus preventing an intrusive movement, did not change the reductions in clearance seen on sympathetic stimulation, indicating that this blood flow reduction was not dependent on tooth movement. A qualitative relation between PDL blood flow (as measured by local 125I clearance) and PDL volume (as measured by tooth position) is shown. The two variables measured are suggested to reflect two aspects of blood flow in the PDL.

Publisher Summary This chapter discusses the existence of nervous control of blood circulation in the dental pulp and the periodontal tissues. The influence of sympathetic nerve activation on the blood circulation in the dental pulp and the periodontal tissues has been estimated by measuring the change of rate of disappearance or clearance of diffusible tracers from local depots. The chapter presents an experiment in which to study the effect of the sympathetic vasomotor control in the different tissues, the appropriate sympathetic nerves to the jaws of the dog and cat were stimulated and the rate of disappearance of tracer from depots in the pulp, gingival, and periodontal membrane was measured. Such stimulation elicited reduction in tracer disappearance in all the tissues studied, which was related to the frequency of stimulation. The chapter discusses that the activation of the sympathetic nerves to the oral tissues results in a pronounced reduction of blood flow in the pulp and the periodontal tissues.

The disappearance rate of I125 and Xe133 from a depot in the gastrocnemius muscle of the dog was determined during vasodilatation caused by activation of the sympathetic cholinergic vasodilator nerves. During vasodilatation the disappearance rate of I125 and Xe133 increased. No systematic difference in the disappearance rate was observed between the water-soluble (I125) and the fat-soluble (Xe133) tracer. The vasodilatation did not usually last far more than 30 sec, and during this period the increase in disappearance rate often exceeded the increase in blood flow. The disappearance rate of Xe133 was studied from different muscles during stimulation of hypothalamic vasodilator pathways and was found to be enhanced from the splenius, latissimus dorsi and gastrocnemius muscles but not from the maeseter muscle. Vasodilator nerve stimulation and acetylcholine infusion caused comparable increases in disappearance rate during the blood flow increase. When the blood flow was back to resting levcls, a decrease in disappearance rate below control values was seen. The increase in disappearance rate during sympathetic nervous vasodilatation was usually less than during metabolic vasodilatation and after metabolic vasodilatation no decrease was observed in the disappearance rate. The results support the hypothesis that during metabolic vasodilatation precapillary sphincters are opened up leading to an increased capillary surface area while the vasodilator nerves do not directly influence the exchange surface area.

The rate of disappearance of diffusible radioactive tracers (xenon and iodide) and blood flow were measured in the canine gastrocnemius muscle. A transport-flow index (TFI) showing the ratio between disappearance rate and blood flow was calculated. Metabolic vasodilatation resulted in TFI values between 2 and 3. These values were higher than those following intra-arterial infusion of acetylcholine, indicating that metabolic vasodilatation causes a higher net transport of tracer between tissue and blood than i.a. infusion of acetylcholine. Reduction of blood flow by low frequency stimulation of vasoconstrictor nerves or by i.a. infusion of nor-adrenaline resulted in TFI:s approaching 1, indicating an approximately equal effect on tracer transport and blood flow. However, high frequency stimulation of vasoconstrictor nerves re duced tracer transport more than blood flow. During partial occlusion of the arterial inflow, the iodide TFI was greater than 1, suggesting a compensatory increase in tracer transport relative to blood flow. The present results indicate that the disappearance rates of xenon and iodide are not only dependent on total blood flow in the muscle but are also influenced by local factors in the capillary section affecting the exchange function. Thus the calculation of muscle blood flow from xenon disappearance data alone may give misleading results.