Pain, 23 (1985) 223-229

Elsevier

223

PA1 00813

Extrasegmental Transcutaneous Electrical Nerve Stimulation and Mechanical Vibratory Stimulation

as Compared to Placebo for the Relief of Acute Oro-Facial Pain

Anders Ekblom and Per Hansson Department of Ph.ysioiogy II, Karolinska Insiiruret, Box 60 400, 104 01 Stockholm (Sweden)

(Received 2 April 1985, accepted 13 June 1985)

Summary

The present paper describes the pain reducing effect of high and low frequency transcutaneous electrical nerve stimulation (TENS) and 100 Hz mechanical vibra-

tory stimulation as compared to placebo stimulation of the HoKu point in 50

patients suffering acute oro-facial pain. Ten of the 30 patients receiving actual stimulation reported pain reduction during treatment. In the placebo group of 20

patients, 4 of the subjects experienced pain relief during the trial. The findings in the present study showed that extrasegmental superficial stimulation of the HoKu point

alters pain intensity in the patients studied to only a minor degree. The number of patients reporting pain alleviation and the magnitude of pain reduction in the groups receiving actual stimulation was comparable to that observed in earlier studies using intrasegmental placebo stimulation.

Introduction

Much effort has been devoted to investigate the effect of different modes of afferent stimulation for pain treatment. The gate control theory, postulated by Melzack and Wall [lo] and later modified [19], gave rise to a renewed interest in

Correspondence to: Anders Ekblom, Department of Physiology II, Karolinska Institutet, Box 60 400, S-104 01 Stockholm, Sweden.

03~3959/85/$03.?0 0 1985 Elsevier Science Publishers B.V. (Biomedical Division)

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clinical pain treatment using peripheral electrical and mechanical stimulation. Pres-

ently, it is generally agreed that transcutaneous electrical nerve stimulation (TENS)

and vibratory stimulation are potent pain relieving measures in experimental and

clinical pain when administered in or near the segment related to the origin of the

pain [20]. However. equivocal results have been published concerning the pain alleviating efficiency of extrasegmental stimulation such as acupuncture [l-3.8,11,16,17], ice massage [9], and TENS [2,18]. Data on extrasegmental stimula- tion in acute oro-facial pain using vibration are lacking.

In the present paper we report on studies of the pain relieving effect in patients

suffering acute oro-facial pain, of vibration, TENS and placebo stimulation applied superficially to the HoKu locus (a traditional acupuncture point used for dental

pain) of the dorsum of the hand ipsilateral to the side of the pain. From the results, we conclude that electrical and mechanical stimulation altered pain intensity in our

subjects to a minor degree. Furthermore the magnitude of pain relief of vibration

and TENS appears to be comparable to that of intrasegmental placebo stimulation.

as has been reported earlier [e.g., 5,181.

Methods

Fifty patients (23 males, 27 females) ages 20-63 years participated voluntarily in the study. All were from an emergency clinic for dental and oral surgery and had

suffered pain for l-8 days prior to testing. None of them had used any analgesic medication within 10 h before applying for treatment. The causes for their pain were

either pulpal inflammation, apical periodontitis, postoperative pain or pericoronitis. Before receiving afferent stimulation the patients were examined clinically and

radiographically, told their diagnosis and treatment procedure, and asked if they were willing to participate in the experiments. All subjects were informed that they might or might not experience alleviation or pain aggravation during stimulation. Care was taken to avoid suggestion.

The TENS electrodes (measuring 3 cm X 3 cm made of conducting rubber) and the disc shaped probe (3 cm in diameter) of the vibrator were placed on the skin over

the dorsum of the hand at the HoKu point unilateral to the painful side for 30 min

of stimulation. The 50 patients were randomly assigned to one of the 5 following groups: (A) 10

patients received 2 Hz TENS (consisting of trains of monopolar square wave pulses

0.2 msec duration, each train with an internal frequency of 71 Hz and a total duration of 84 msec, originally described by Eriksson and Sjijlund [4]). The intensity used gave rise to non-painful contractions of surrounding muscles; (B) 10 patients were given 100 Hz TENS consisting of monopolar square wave pulses (duration 0.2 msec) with an intensity experienced as tingling but not painful; (C) 10 patients received placebo TENS using a TENS apparatus lacking batteries; (D) 10 patients received 100 Hz mechanical vibratory stimulation (Bruel and Kjaer vibrator) with an amplitude of 500-850 pm with a pressure giving contact with the metacarpal bones I and II; (E) 10 patients were given placebo vibration with a non-vibrating probe

225

applied against the HoKu point. The 20 patients receiving placebo TENS and

placebo vibration were told that some people may not experience the stimulation. Before the start of stimulation all patients rated their pain intensity on a 5-graded

verbal scale - light, light to moderate, moderate, moderate to severe or severe pain (Fig. 1). Their subjective pain intensity was also scored before and after stimulation

using a visual analogue scale (a horizontal line on a card with the words ‘no pain’

and ‘worst pain ever’ placed at the left and right hand extremes of the line respectively) and a graphic rating scale (a horizontal line on a card with 0, meaning no pain, and 10, meaning worst pain ever, at left and right extremes of the line

respectively). During stimulation the patients continuously rated their pain intensity using a graphic rating scale, consisting of a lever attached to a potentiometer. The

potentiometer controlled the position of a pen on an ink-writer out of sight of the

patient. The patients were instructed to move the lever from zero position (indicating

pain intensity before starting stimulation) to one side when pain was reduced

(endpoint = 0, meaning no pain) and in the opposite direction if pain increased in

intensity (endpoint = 10, meaning worst pain ever). All patients were also interviewed whether any special sensations were experi-

enced from the oro-facial region during stimulation such as anaesthesia or

paraesthesia.

Statistical analysis was performed with the chi-square test.

Results

The results of the present study are summarized in Table I and Fig. 1. A total of 9 patients in the groups receiving TENS or vibratory stimulation reported pain relief

to some extent, including 3 patients, one in each group, reporting more than 50% pain relief. No tendency was seen towards more pronounced pain reduction in patients with low pain intensity, as seen in Fig. 1. It is also notable that 100 Hz

vibration showed a slight tendency towards giving pain alleviation in a larger number of patients than did high and low frequency TENS respectively. Interest-

ingly, no patient reported pain reduction during placebo vibration, but 4 of 10 receiving placebo TENS experienced pain relief. The trend towards a greater number

TABLE I

NUMBER OF PATIENTS IN THE DIFFERENT GROUPS EXPERIENCING: (a) INCREASE IN

PAIN INTENSITY; (b) NO CHANGE IN PAIN INTENSITY; (c) PAIN REDUCTION; (d) PAIN

REDUCTION LESS THAN 50%; (e) PAIN REDUCTION EXCEEDING 50%

2 Hz TENS (n = 10)

100 Hz TENS (n = 10)

100 Hz vibration (n = 10)

Placebo vibration (n = 10)

Placebo TENS (n = 10)

a b c d e

2 5 3 2 1

3 5 2 1 1

3 3 4 3 1

4 6 0 0 0

2 4 4 3 1

L L-M M M-S s

Fig. 1. Number of patients with different degrees of pain (L = light pain. M = moderate pain, S = severe

pain) which were treated with: 2 Hz TENS (2), 100 Hz TENS (100) or placebo TENS (PT), 100 Hz

vibration (100 V) or placebo vibratory stimulation (PV). Patients who experienced pain reduction

exceeding 50% are represented by hatched areas.

of patients reporting pain reduction receiving actual stimulation (9/30; 30%) com- pared with those receiving placebo (4/20; 20%) was not significant.

None of the 50 patients experienced anaesthesia or paraesthesia from the oro-fa- cial region during the stimulation period, however, several patients (receiving actual

stimulation) spontaneously reported paraesthesia and/or anaesthesia from the stimulated hand area. In the patients receiving actual stimulation and reporting pain alleviation the induction time to the first sign of pain relief was less than 10 min in 8 of the 9 patients.

In 8 patients maximal pain alleviation was obtained after 25-30 min of stimula- tion. In the patients reporting pain reduction during stimulation the obtained pain

suppression persisted after the stimulator was turned off. Due to ethical considera-

tions for the patients postconditioning effects could not be studied for more than

15-30 min.

Discussion

Results from previous studies of extrasegmental stimulation for the relief of pain have been inconsistent. Andersson and Holmgren [l] and Andersson et al. [2] reported a large increase of the electrical tooth pain threshold when giving acupunc- ture and TENS to the infraorbital region. Stimulation of the HoKu point, however, did not alter the pain threshold but postconditioning pain threshold increase following simultaneous stimulation of both sites was prolonged if the extrasegmental stimulation was continued after the ter~nation of stimulation in the infraorbital region. Mumford and Bowsher [II] reported only minor tooth pain threshold

221

increase during bilateral acupuncture of the HoKu points. In clinical trials, several

studies have revealed adequate analgesia for operative dentistry and root canal

therapy using extrasegmental acupuncture [e.g., 3,16,17] although exceptions have been reported [e.g., 81. However, as pointed out by Taub et al. [17] the analgesic

effect obtained by HoKu point acupuncture seems to be due to psychological and/or placebo effects since placebo stimulation proved to be as effective as actual

acupuncture during operative dentistry. Furthermore, Melzack and Bentley [9] have reported substantial relief of dental pain in patients treated with ice massage at

different sites of the upper extremities. From the result of the present study it seems clear that extrasegmental TENS and vibratory stimulation at the HoKu locus affects subjective pain intensity due to pathological processes in the oro-facial region to a

minor degree only. The number of patients (9/30 = 30%) experiencing pain relief was small, and the magnitude of pain reduction in the different groups (see Table I)

was low, even when compared to placebo stimulation at sites in the same segment as

where the pain originates [5,6,18]. This finding agrees with that of Thorsteinsson et

al. [18] who found that about 35% of chronic pain patients receiving TENS in areas unrelated to the origin of the pain experienced pain relief. The present finding that

only 4 out of 20 (20%) (all in the placebo TENS group) of the patients receiving placebo stimulation experienced pain reduction is also in accordance with earlier

findings by, e.g., Thorsteinsson et al. [18] in chronic pain patients receiving placebo stimulation of areas unrelated to the origin of the pain. They reported about 20% of

the patients experiencing pain relief compared to about 40% when using intraseg- mental placebo stimulation. In an earlier study using TENS in acute oro-facial pain we also found pain reduction in 40% of the patients receiving placebo stimulation in

the painful area [5]. Our results in the present study show a small but non-significant difference in the

number of patients reporting pain reduction following TENS or vibration (30%)

compared to those receiving placebo (20%). To statistically establish with a high power of confidence whether this difference represents a real difference in effective-

ness between TENS/vibration and placebo is not possible with our limited material

since this would necessitate several hundred patients in each group [7]. However, in view of the significantly (much) better results using intrasegmental stimulation with

TENS/vibration [5,6,12,18,20] such an exhaustive study does not seem to be of any

major clinical interest.

The failure to induce substantial analgesia in the present study could be explained

by several factors. First, we have used non-invasive and non-painful stimulation

methods of the HoKu locus, located ipsilateral to the oro-facial pain. Perhaps bilateral stimulation would be more effective in inducing pain relief. Still, anatomical and electrophysiological evidence exists [13] for a projection of afferents from the upper extremities to the trigeminal nuclei. If these afferents have an inhibitory influence this might explain clinical results showing a pain reducing effect of HoKu point stimulation. Whether this effect is executed through direct segmental mecha- nisms or involves inhibitory pathways originating in the brain stem with descending control of trigeminal neurones is presently not fully understood. It is interesting that Sessle et al. [14] have reported results strongly supporting the latter hypothesis.

Secondly, the insertion of a needle into the HoKu point with stimulation of deeply located afferents and accompanied ‘T“Chi’ feeling of soreness, tingling,

heaviness and numbness is perhaps required to induce pain alleviation using extrasegmental stimulation. However, the 2 Hz TENS induced muscle contractions presumably activating muscle afferents, as suggested by Eriksson and Sjiilund [4]. Also, Andersson et ai. ]2] have shown that TENS was superior to needle stimulation

with respect to tooth pain threshold increase when applied intrasegmentally to the teeth being tested. However. the necessity of activating deep afferents is not

supported by the finding by Taub et al. [16] that placebo stimulation was as efficient as real acupuncture in inducing analgesia for operative dentistry. Furthermore we found no beneficial effect from 2 Hz TENS when compared to 100 Hz TENS and

vibratory stimulation. Our results point to the fact that if central opioid-dependent mechanisms are invoived, as suggested using low frequency TENS and acupuncture

14,151, these are not sufficient to alter pain intensity in the group of patients studied

or enough activation is not achieved by the stimulation procedures used.

The present results, together with our own previous findings using intrasegmental

afferent stimulation [5,6,12], support the notion that TENS of high and low

frequency and vibratory stimulation predominantly interact with pain transmission when applied intrasegmentally in patients suffering acute pain due to oro-facial pathology. Thus it seems that the pain relieving potential using TENS and vibratory

stimulation is as follows, in decreasing magnitude: ~ntrasegmental stimulation is significantly best. intrasegmental placebo and extrasegmental stimulation about

equally effective, and least effective extrasegmental placebo.

Acknowledgements

We thank Drs. Jan ~~nnergren and Jim Saunders for constructive criticism of the manuscript, Maud Hoffstedt and Ulla Lindgren for secreterial assistance.

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