Electrical Tooth Stimulation Research Articles

Effect of Intermittent Long-Lasting Electrical Tooth Stimulation on Pulpal Blood Flow and Immunocompetent Cells: A Hemodynamic and Immunohistochemical Study in Young Rat Molars

Release of sensory neuropeptides after stimulation of afferent nerve fibers has previously been shown to induce vasodilation and increased vascular permeability in the dental pulp, a condition recognized as neurogenic inflammation. In the present study a possible role for the sensory neuropeptides in transendothelial migration of immunocompetent cells was investigated. The dental pulp is an isolated tissue densely innervated with sensory fibers containing neuropeptides, and following electrical stimulation of the crown, the effect on pulpal blood flow and immunocompetent cells can be studied in a noninvasive model. A laser Doppler flowmeter was used to measure relative changes in pulpal blood flow during long-lasting intermittent stimulation of innervated and denervated rat first molars. In the innervated teeth, stimulation promptly increased pulpal blood flow by on average 45% at the start of the experiment, whereas almost no blood flow increase was recorded after 4 to 5 h stimulation. Surgical sectioning of the inferior alveolar nerve abolished blood flow increase upon stimulation. After stimulation, a quantitative analysis of CD43+, CD4+, CD11+, and I-A antigen-expressing cells was performed, and the effect of stimulation on calcitonin gene-related peptide (CGRP)-immunoreactive and substance P (SP)-immunoreactive (IR) nerve fibers was studied. Immunohistochemistry was performed by the avidin–biotin peroxidase method. Stimulation resulted in an almost complete depletion of CGRP- and SP-IR nerve fibers in the first molar pulp, whereas nerve fibers in the gingiva and neighboring teeth were unaffected. A significant increase in the number of CD43+cells was found in the innervated tooth after stimulation compared to the stimulated denervated (P<0.01) and unstimulated control (P<0.05) first molars. For I-A antigen-expressing cells a significant increase (P<0.05) was found between the innervated stimulated and unstimulated control, but not between the innervated and denervated stimulated first molars. Hence, from the present experiment it is concluded that the pulpal nerves participate in and facilitate transendothelial migration of CD43+cells during acute neurogenic inflammation.

Trigeminal-parabrachial connections: possible pathway for nociception-induced cardiovascular reflex responses

Noxious stimulation of dental nerves elicits marked changes in cardiovascular function. In order to investigate central pathways mediating reflex changes in cardiovascular activity, immunohistochemical localization of cells expressing the immediate-early gene, c- fos, was used to identify central neurons responding to noxious electrical stimulation of mandibular, incisor tooth dentin or chemical (capsaicin) stimulation of tooth pulp in the anesthetized rat. Injections of Fluoro-Gold were made in the lateral parabrachial region to identify efferent projections from the spinal trigeminal nucleus. Electrical and chemical stimulation produced similar patterns of Fos-positive neurons in the spinal trigeminal nucleus: subnuclei caudalis, interpolaris and oralis. Fos-positive neurons were most dense in laminae I and II of the dorsomedial subnucleus caudalis with fewer Fos-positive neurons located in the interpolaris and oralis subnuclei. Sham stimulation of tooth dentin and control vehicle injections into the tooth pulp resulted in either a few weakly stained or no Fos-positive neurons in the spinal trigeminal nucleus. Cell bodies double labeled with Fluoro-Gold following injections into the parabrachial region and Fos-protein subsequent to electrical stimulation of incisor tooth were present in all three subnuclei of the spinal trigeminal nucleus. The largest number of Fos-positive neurons with efferent projections to the lateral parabrachial region were located in subnucleus caudalis (32.2 .3 S.E.M.) and fewer were located in the interpolaris (0.4 .4 S.E.M.) and oralis (19.8 .5 S.E.M.) subnuclei. The results demonstrate that nociceptive dental input received by the three subnuclei of the spinal trigeminal nucleus, particularly the subnucleus caudalis, is relayed to the lateral parabrachial nucleus.

A new method of recording somatosensory evoked potentials by randomized electrical tooth stimulation with 6 levels of intensity

Dental somatosensory evoked potentials (SEPs) corresponding to the stimulus intensity levels were recorded at 6 different levels of intensity presented in a randomized order. The relationships between the amplitude of the late SEP component with latency between 150 and 300 msec and each stimulus intensity level were also compared in conditions of randomized intensity and constant intensity. The amplitude of the late component increased significantly with the increased stimulus intensity both in the randomized and constant intensity stimulation. The amplitude of the late component in the randomized stimulation with a 1-sec interstimulus interval (ISI) increased in the same manner as that in the constant intensity condition with a 1-sec ISI. The randomized stimulation with the prolonged ISI increased the amplitude of the late component. The latency of the late positive component significantly increased with the randomized stimulation with a 3-sec ISI. This phenomenon might be attributable to the psychological contamination. SEP recording in the randomized dental stimulation with a 1-sec ISI may have applications in neuropharmacological research or physiological research on pain and evaluation of the effects of analgesics, anesthetics, acupuncture and transcutaneous electrical nerve stimulation (TENS).

Enhanced formation of secondary dentin in the absence of nerve supply to feline teeth.

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.

Effect of Electrical Tooth Stimulation on Blood Flow, Interstitial Fluid Pressure and Substance P and CGRP-Immunoreactive Nerve Fibers in the Low Compliant Cat Dental Pulp

The effect of vasodilation on simultaneously measured interstitial fluid pressure (IFP, micropuncture) and blood flow (laser-Doppler) in the low compliant pulpal connective tissue was investigated in 10 cats. Vasodilation was induced by electrical stimulation of the tooth after pretreatment with the sympathetic blocker guanethidine. Visualization of the sensory neuropeptides calcitonin gene-related peptid (CGRP) and substance P (SP) was performed using immunocytochemistry. The study was designed to answer the following questions. (1) Does vasodilation promptly increase IFP in low compliant tissues? (2) Does an increase in IFP counteract the blood flow increase? (3) Does repeated electrical stimulation cause reduced staining of CGRP- and SP-immunoreactive nerve fibers in the dental pulp? Electrical stimulation resulted consistently in a nearly synchronous increase in both blood flow and IFP. IFP was nearly doubled, from 6.3 ± 0.18 mm Hg in control to 11.7 ± 0.44 mm Hg, whereas blood flow increased by 28%. However, despite continued vasodilation the IFP fell to control level, or even lower, within 1-5 min. The results indicate that the increased IFP will promote fluid absorption into the blood, counteracting a further IFP increase in low compliant tissues during vasodilation. Accordingly, transmural pressure is only transitorily reduced and compression of vessels does not take place. There was considerably less CGRP- and SP-immunoreactive fibers in the stimulated teeth than in the contralateral controls, suggesting that the vasodilation was caused by liberation of these sensory neuropeptides.

Activation of sympathetic fibres in the pulp by electrical stimulation of rat incisor teeth

Previous 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 μA) 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 α-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 β-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 α-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 α-and β-adrenoceptor mediated blood-flow responses.

Response characteristics of tooth pulp-driven postsynaptic neurons in the spinal trigeminal subnucleus oralis of the cat.

Neuronal activity in the spinal trigeminal subnucleus oralis in response to electrical tooth stimulation was recorded in the anaesthetized cat in order to compare the electrophysiological characteristics of the oralis neurons with those of subnucleus caudalis and interpolaris neurons recorded in previous studies. The most sensitive oralis neurons had lower thresholds and shorter latencies than the most sensitive caudalis and interpolaris neurons. The thresholds of the oralis neurons were lower and their strength-duration curves flatter than those depicting liminal dental pain in man but similar to those depicting liminal jaw reflexes in the cat. Noxious conditioning stimulus elevated the threshold of only 1 of 10 neurons tested. The converging input from the skin and oral mucosa was from low-threshold mechanoreceptors. The results indicate that the response properties of the subnucleus oralis neurons differ significantly from those of other spinal subnuclei. Human pain thresholds cannot be explained by the liminal response properties of oralis neurons. These neurons might be important in the mediation of liminal reflex events evoked by dental stimuli.

Periaqueductal gray matter and nucleus raphe magnus involvement in anterior pretectal nucleus-induced inhibition of jaw-opening reflex in rats

In previous studies we have shown that electrical stimulation of the cortex or anterior pretectal nucleus (APT) inhibits the jaw-opening reflex (JOR). In the present study we investigated whether these effects are mediated by a relay in the periaqueductal gray matter (PAG) or rostroventromedial medulla (RVM). Experiments were performed on chloralose-urethane anesthetized rats. The JOR which was elicited by electrical stimulation of the mandibular incisor tooth was monitored by recording the evoked digastric muscle activity. Conditioning stimulation (20 ms-train of 0.2 pulses at 400 Hz) was delivered to the facial area of the sensorimotor cortex, APT, PAG or nucleus raphe magnus (NRM) 50 ms prior to the test stimulus to the tooth that evoked the JOR. In addition, the effects of microinjections of glutamate into APT, PAG and NRM on the tooth-evoked JOR were also evaluated. The inhibition of the JOR by electrical and glutamate conditioning stimulation was found to be most potent for activation of the NRM and least potent for the APT. Local anesthetic (2% Iidocaine, 0.3–0.6 μl) block of the PAG could partially, significantly (P < 0.05) and reversibly reduce both the APT and cortical-induced depression of the JOR. Lidocaine block of the ventromedial pons reversible reduced the PAG, APT and cortical-induced inhibition of the JOR (P < 0.05). Lidocaine block of the lateral RVM had powerfully (P < 0.01) and reversibly reduced the PAG-induced inhibition, but had onaly a small effect (P < 0.05) on the APT-induced inhibition and no significant effect on the cortical-induced inhibition. Lidocaine block of NRM produced a small reversible reduction in the PAG- and APT-induced inhibition but had no significant effect on cortical-induced inhibition of the JOR. These findings suggest that the inhibitory effects of APT and cortical stimulation on the JOR are mediated in part by a relay in the PAG and that in addition the APT-induced inhibition may also be partly mediated by a relay in the RVM.

歯科口腔外科施術時における情動反応の電気生理学的研究

Discussions were made on whether muscular activities of the limbs would be an index to the objective evaluation of anxiety and fear at the time of dental and oral surgery. Furthermore, electrophysiological and psychosomatic investigations were made as to differences in anxiety and fear between normal adults and patients with odontophobia. As stress stimuli, stimulus by presentation of a video showing tooth extraction, electrical stimulation of teeth and stimulus by local anesthesia were used.1. EMGs were measured in the masseter muscle, orbicularis oculi muscle, trapezius muscle extensor digitorum muscle and peroneus longus muscle at times of stimulations as mentioned above. The integral value of the EMG of these muscles showed an increase during the stress stimulus period as compared to the vest period.2. The rate of increase in the EMG integral value was higher in patients with odontophobia (early treatment group) than in normal adults, the former showing strong muscle tension under stress.3. Among patients with odontophobia, those for whom the behavior therapy centered treatment had progressed showed changes in EMG integral value at times of stimulation only in the same degree as normal adults, suggesting the effectiveness of behavior therapy.4. DAS, as a criterion for evaluating anxiety at the actual scene of dental treatment scored 9.05±3.06 in normal adults, whereas it scored high, 15.57±3.10, in patients with odontophobia (those at the early stage of being treated). DAS was lower, 8.33±3.78, in those patients at the advanced stage of being treated.5. With regard to MAS, the proportion of those with great anxiety was estimated as 0% in normal adults, whereas it was estimated as 50% or more in patients with odontophobia. Thus, individuals predisposed to chronic anxiety were presumed to be more prone to odontophobia.These results suggested that that muscular activity could be an index to the objective valuation of the degree of anxiety and fear at the time of dental and oral surgery.

The effect of temporal parameters on subjective sensations evoked by electrical tooth stimulation

The effect of stimulus duration and frequency on subjective sensations evoked by electrical tooth stimulation was studied in 12 subjects. The sensory responses were classified using 5 equi-sensation categories (perception threshold, prepain, pain threshold, moderate pain, intense pain). Both continuously increasing and randomised stimuli were applied. A comparison was made with the activation thresholds of intradental A- and C-fibres in the cat. The mean threshold of intradental A-fibres was lower than the perception threshold at all pulse durations. Perception threshold decreased with increasing stimulus frequency. Current intensities which evoked prepain at a stimulus frequency of 1 Hz were rated as pain at 20 Hz. At supraliminal pain levels the effects of summation were more marked. High-frequency stimulation produced intense pain sensations at intensities well below the activation thresholds of pulpal C-fibres in the cat. We conclude that both perception and pain thresholds and supraliminal pain are modified by temporal summation, and that activation of different pulpal fibre populations is not responsible for production of prepain and pain sensations.

Evidence against a central stimulus for collateral reinnervation of oro-facial tissues in the cat

Experiments in adult cats have shown that when the inferior alveolar nerve is sectioned and regeneration prevented, there is collateral reinnervation from neighbouring ipsilateral and contralateral nerves. Trigeminal rhizotomy prevents nerve impulses from entering the central nervous system and causes central degeneration but leaves the trigeminal ganglion and peripheral nerve intact. This investigation was designed to determine whether these central changes provide the stimulus for collateral reinnervation. In 5 adult cats, under general anaesthesia, a unilateral trigeminal rhizotomy was carried out via a temporal craniotomy. Evidence for the development of collateral innervation was sought by testing, at 3-week intervals, for the return of the jaw opening reflex evoked by electrical stimulation of the lower teeth, skin, mucous membrane and tongue, on the side of the rhizotomy. In addition, 12 or 15 weeks after the rhizotomy, recordings were made from ipsilateral and contralateral branches of the trigeminal nerve to determine whether collateral fibres were present. There was little evidence for the return of reflex responses to stimulation of tissues on the side of the rhizotomy and at the terminal experiment recordings revealed only a few collateral fibres. These results show that trigeminal rhizotomy does not stimulate collateral innervation and so suggest that the stimulus for sensory nerve sprouting is peripheral rather than central.

The excitability of dog pulp nerves in relation to the condition of dentine surface

Sixteen intradental A-fiber units (cv 24.5±4.8 (SD)m/s) were identified with monopolar electrical stimulation of the dog's canine tooth. All of the units were activated by drilling and probing of dentine, 15 units by air blasts. Scanning electron microscopy of epoxy resin replicas and specimens of dentine showed that after acid etching of dentine, the apertures of dentinal tubules were open. Accordingly, nerve responses to probing and air blasts could be easily evoked. After drilling and resin or potassium oxalate impregnation, the apertures were partly or completely blocked and nerve responses were weak or totally absent. The results indicate that intradental A-fibers are responsible for dentine sensitivity. The responsiveness of these fibers can be affected by obstructing and opening the dentinal tubules.

Nociceptive evoked potentials revisited in the frequency domain.

Human somatosensory evoked potentials (SEP), especially those evoked by electrical stimulation of toothpulp and teeth or by laser thermal stimulation of skin, have attracted biomedical attention since 1975 as possible indicators of the quantity of acute pain being perceived by the subject. The dental variety has been claimed as an "objective correlate of acute laboratory pain." But investigators of SEP for mechanical, electrical, and thermal stimulation of skin and mucocutaneous junctions have provided data which seriously question the meaning of that claim. Most recently dental SEP workers have rediscovered some well-known ambiguities in their own data, all of which refer only to time-domain or transient characteristics of event related brain potentials (ERBP). Perhaps we should reconsider an older approach to understanding ERBP, using concurrent analysis of their transient temporal and steady-state frequency characteristics.

Event related brain potentials and human pain: A first objective overview

Since 1960 systematic studies of the human scalp-conducted cerebral slow-wave response to painful stimulation have shown only amplitude augmentation of the vertex components of the somatosensory evoked potential (SEP) to be indicators of subjective perception of a noxious or aversive quality in the stimulus. The vertex potential (VP) of the SEP occurs relatively late after onset of either transient or maintained stimuli (100–400 ms depending on stimulus mode and site), is amplitude-focal at vertex on scalp, and may be asymmetrically distributed hemispherically for unilateral stimulation of the hands. Its functional neuroanatomy seems undeterminable by scalp macroelectrodes, and its relationship to analogous vertex potentials in the auditory and visual modalities (AEP and VEP) unknown. Studies of the nociceptive SEP (SEPn) since 1977 concur that VP amplitude is more readily correlatable with subjective pain magnitude estimate than with objective stimulus parameters. They also suggest that the VP is amplitude-sensitive to (a) interstimulus-intervals less than about 350 ms; (b) analgesics and their antagonists; and (c) subjective cognitive status with regard to both the expected aversiveness of the stimulus and the previous experience of chronic pain. These studies have included electrical stimulation of toothpulp and teeth, mechanical and transcutaneous electrical stimulation of palmar and digital glabrous skin, noxious thermal stimulation of hands and forearms, and electrical stimulation of lips, fingers, toes, and anogenital perineum of both sexes. They have been done in the context of both classical and signal-detectability (TSD) methods for concurrent reports of painful versus painless, and in the methodological contexts of conventionally signal-averaged SEP and of single-epoch SEP recovered both raw and processed. Studies designed to analyze differences in the early-intermediate (25–95 ms) and late (500–1000 ms) time-segments of SEP for painful and painless stimulation have provided no convincing evidence of cortical nociceptive signals. Therefore existing data on the SEPn imply that the only cortical slow-wave sign of nociception reflects perceptual-cognitive and endogenous, rather than sensory-discriminative and exogenous, aspects of the conscious pain experience.

Analgesic Effects of Nitrous Oxide with Controlled Painful Stimuli

This study was designed to provide statistical estimates of the effects of N2O on pain and anxiety associated with tooth-pulp shock in a clinical and in a laboratory setting. Amounts of electric stimulation needed to first feel sensation, amounts to feel pain, and pain tolerance were measured. N2O had a significant effect on raising levels of absolute sensation, pain threshold, and pain tolerance in response to increasing electrical stimulation of teeth. These effects were noted when N2O and pulp stimulation were delivered in a clinical dental setting or in a pain-research laboratory. Subjects also decreased their evaluation of the intensity of the same stimulus as N2O was inhaled at various concentrations; their aversion to the same stimulus tended to be influenced by N2O to a greater extent than perceived intensity. Anxiety levels were reduced to a statistically significant degree.

Is a selective stimulation of the rat incisor tooth pulp possible?

The purpose of the present study was to investigate whether electrical stimulation via bipolar intradental or extrapulpal electrodes can selectively activate intrapulpal nerve fibres of the rat lower incisor. The compound action potential was recorded from the mandibular nerve following stimulation. This potential had the same threshold and latency before and after apical pulp extirpation. Transection of the inferior alveolar nerve distal to the connexion between the tooth pulp afferents and this nerve abolished the response. It was also possible to record action potentials of the same shape and amplitude both from the mandibular and the inferior alveolar nerve following the same intrapulpal stimulus. It is concluded that the major part of the compound action potential obtained by stimulating the rat incisor tooth pulp is not produced by pulp afferents but by activity in nerve fibres outside the pulp. The results suggest that electrical stimulation of the rat incisor tooth is not a useful method for physiological studies of nociceptive mechanisms.

Fentanyl Reduces the Intensity of Painful Tooth Pulp Sensations

This study assessed whether experimentally determined narcotic analgesia in human subjects represents a pharmacologic effect or a psychological effect of detecting the administration of an active medication. Forty dental patients used a verbal descriptor procedure to assess both the intensity and unpleasantness of sensations produced by electrical stimulation of intact teeth. Stimuli were rated before and after an intravenous injection og 0.11 mg/kg of diazepam, to produce detectable side effects in all patients, followed by a double-blind intravenous injection of either 0.66 microgram/kg of fentanyl or saline placebo. The results were similar to previous findings in which diazepam was not administered: only intensity responses were reduced after fentanyl administration and only unpleasantness responses were reduced after placebo administration. These results suggest that the reduction in pain intensity following fentanyl administration represents an analgesic effect and not an artifact of detecting the administration of an active medication. They also suggest that diazepam at this dose does not alter pain sensations produced by electrical tooth pulp stimulation.

Masseter inhibitory periods and sensations evoked by electrical tooth pulp stimulation in patients with oral-facial pain and mandibular dysfunction

The masseter inhibitory period (silent period) and sensations evoked by tooth-pulp stimulation were examined in 12 healthy subjects and 12 patients with oral-facial pain and mandibular dysfunction (MPD). Trains of 30 pulses were applied to an upper incisor and the threshold intensities for detecting sensation, for detecting pain sensation and for the masseter inhibitory period were determined. Masseter activity was monitored during tooth stimulation by electromyographic recordings from surface electrodes. Electrical tooth stimulation elicited three different configurations of masseter inhibitory periods in both groups: single, double and merged. MPD patients exhibited a greater proportion of single inhibitory periods. The combined average total durations of the three types of configurations were less in MPD. The findings are consistent with the hypothesis that there is an increase in excitability of the central masseter motorneuron pool in MPD, resulting in a reduction in the effective duration of the masseter inhibitory period. The higher incidence of single inhibitory periods in MPD patients also could result from this increased central excitatory state. There was no difference between masseter inhibitory periods evoked in either painful or non-painful muscles, and no particular configuration associated with pain sensation. The findings do not support the hypothesis that nociceptive input contributes to the increase in duration of the silent period in MPD. Although there were no significant differences between masseter inhibitory period threshold, detection thresholds or pain threshold for both groups, MPD patients had detection thresholds higher than their masseter inhibitory thresholds. These effects may be related to differential central neural influences on sensory-discriminative and reflex pathways in the trigeminal system.

Somatosensory evoked potentials (SEP) through electrical tooth stimulation in man : Y. Isshiki, M. Harazaki, S. Takagi, M. Matsuzaki and N. Tsuyama (Tokyo, Japan)

Somatosensory evoked potentials (SEP) through electrical tooth stimulation in man : Y. Isshiki, M. Harazaki, S. Takagi, M. Matsuzaki and N. Tsuyama (Tokyo, Japan)

Electrical stimulation of teeth with a pulp tester in the cat

Abstract – Responses of 241 pulpal and 219 non‐pulpal nerve fibers to monopolar electrical stimulation were studied in 12 anesthetized cats. Stimulation was carried out with a clinically used pulp tester (Bofors PT‐1®) to the intact crown of mandibular canine tooth and to the surrounding soft tissues not further than 1.5 cm from the tooth. Action potentials from nerve preparations containing either a single or a few functional fibers were recorded. The minimum current strength needed to excite the axon (“threshold current”) was determined. The purpose of the study was to investigate how specifically monopolar electrical stimulation of the tooth crown excites the nerves of the dental pulp and to what extent fibers of surrounding tissue are affected. The mean threshold of excitation of the pulpal nerve fibers was 28.3 μA ± 1.4 s.e.m. Of 219 non‐pulpal fibers sensitive to mechanical stimulation of the tooth and the surrounding area, only 10 fibers of periodontal origin were caused to discharge due to electrical stimulation applied to the tooth crown. Their mean threshold was 96.0 μA± 5.2 s.e.m. When the receptive fields of 50 mechanoreceptor units in soft tissue were stimulated electrically, only nine responded to current values less than 125 μA. It seems that pulp nerve fibers respond to very much lower current intensities than non‐pulpal fibers, when monopolar electrical stimulation is applied to the tooth crown. The risk of activation of non‐pulpal nerves in pulp tests seems to be minimal supposing that reasonable current strength is used.