Quantitative electromyographic diagnosis of myofascial pain-dysfunction syndrome

Quantitative electromyographic diagnosis of myofascial pain-dysfunction syndrome Hiroo Kotani, D. D.S. ,* Yasuyuki Kawazoe, D.D.S.,** Sanae Yamada, D.D.S., D.M.Sc.**** Hiroshima

University,

School of Dentistry,

Hiroshima,

yofascial pain-dysfunction (MPD) syndrome is a problem of special interest to dentists. However, its pathophysiologic characteristics are still unclear, making it difficult to establish a precise diagnostic criterion. Laskin’ has reported that masticatory muscle spasm is the primary factor responsible for the symptoms of pain-dysfunction syndrome. The most common cause is thought to be muscle fatigue produced by chronic oral habits that are often an involuntary tension-relieving mechanism.’ Therefore, to differentiate MPD syndrome from other facial pains without muscle fatigue such as referred pain from abscessed teeth, split teeth, dying pulp, tic douloureux, temporal arteritis, and galvanic shock, there is a great need for a more reasonable clinical electromyographic examination of fatigue in masticatory muscles. A study? was made previously standardizing the method for recording and processing the relationship between integrated electromyographic activity and biting force. This was established to electromyographically observe fatigue in masticatory muscles and to determine the ranges of the slopes of the voltage/tension (V/T) curves in healthy masticatory muscles. The purpose of the present study was to determine the ranges of the slopes of the V/T curves in patients with MPD syndrome, to compare the results obtained with those in healthy subjects, and to establish a more quantitative electromyographic criterion for the diagnosis of MPD syndrome.

*Advanced Student, Department of Prosthetic Dentistry. **Lecturer, Department of Prosthetic Dentistry. ***Associate Professor, Department of Prosthetic Dentistry. ****Professor and Chairman, Department of Prosthetic Dentistry.

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VOLUME 43

NUMBER 4

D. D.Sc.,***

and

Japan

M

450

Taizo Hamada, D.D.S.,

MATERIALS

AND METHODS

Recordings. Subjects were seated in a dental chair with their heads positioned so that the Frankfort plane would be parallel to the floor. The skin surface was cleaned vigorously. Miniature surface electrodes* were affixed to double-sided adhesive tapes placed 20 mm apart on the skin surface. The center between the electrodes was placed on the center of the superficial part of the masseter muscle at the same height as the occlusal plane. For the temporal muscle, the center between the electrodes was placed 40 mm anteriorly from the anterior border of the meatus of the external ear and 40 mm above the Frankfort plane. The resistance between the surface electrodes was less than 20 k0, and an ear-clip electrode served as ground. The electrodes were first connected to an amplifier-f having an input impedance of 5 rnti and then to an integrator.$ Direct electromyograms (EMGs) and integrated EMGs were recorded by an electromagnetic oscillograph§ having a paper speed of 10 cm/set. The unit of measurement of the integrated electromyographic activity was expressed in PV X sec. The bite force was obtained from a strain-gauge force transducer11 and was recorded by an electromagnetic oscillograph simultaneously with EMG recordings. Surface EMGs from the muscles of mastication contain frequencies of at most 600 cycles/set and the frequency distribution has its peak at 100 to 200 *Beckman Instruments, Inc., Fullerton, Calif. tRB-5 Biophysical Amplifier, Nihon Koden Kogyo Co., Ltd., Tokyo, Japan. SRFJ-5 Integrator, Nihon Koden Kogyo Co., Ltd., Tokyo, Japan. $Type 2924 Photocorder, Yokogawa Electric Works, Ltd., Tokyo, Japan. (/MPM-2401 Jaw Force Meter, Nihon Koden Kogyo Co., Ltd., Tokyo, Japan.

OOZZ-3913/80/040450

+ 07$00.70/O 0 1980 The C. V. Mosby Co.

QUANTITATIVE

Table

ELECTROMYOGRAPHIC

I. Slopes of the V/T

DIAGNOSIS

OF MPD SYNDROME

curves in patients

with MPD

syndrome

Masseter muscle

Temporal

muscle

Patients

PCS

r

NPCS

r

PCS

r

NPCS

r

A B C D E F G H I

0.093* 0.075* 0.070* 0.061* 0.057 0.054* 0.047* 0.044 0.044* 0.037* 0.058

0.98921 0.98839 0.98894 0.99187 0.98523 0.99679 0.99124 0.98733 0.98997 0.98873

0.092* 0.078* 0.038 0.054* 0.057 0.051* 0.046 0.056* 0.034 0.036* 0.054

0.98751 0.98699 0.97585 0.99238 0.98557 0.99075 0.99059 0.98696 0.99089 0.98504

0.030 0.020 0.045* 0.024 0.032* 0.024 0.035 0.034 0.033 0.035 0.031

0.97750 0.98643 0.98828 0.99081 0.99106 0.98570 0.99248 0.98417 0.99382 0.99201

0.037 0.026 0.039 0.024 0.025 0.024 0.032 0.019 0.029 0.036 0.029

0.98845 0.98132 0.98946 0.99186 0.97840 0.98380 0.98935 0.96915 0.98931 0.98512

J Mean

Note: PCS = preferred chewing muscle pain or tenderness.

Table

II. Analysis

side; NPCS

of variance

Source

= nonpreferred

chewing

for the slopes of the V/T df

Subjects (A) Healthy MPD Muscles (B) Masseter muscle Temporal muscle Chewing sides (C) PCS NPCS Ax& AxC BxC Error Total

AVote:PCS = preferred squares; F = variance

ss

OF PROSTHETIC

* = muscle

with

symptoms

such as

curves MS

F

P

301.3513

301.3513

29.1125

< .Ol

1

901.0013

901.0013

87.0427

< .Ol

1

3.2513

3.2513

0.3141

-

I

46.5613 37.4113 3.5113 0.7763 1293.8641

46.5613 37.4113 3.5113 0.0069

4.4981 3.6142 0.3392

.05 -

side; NPCS

= nonpreferred

chewing

cycles/set:’ Therefore, to reduce artifacts arising from movements of electrodes and cables, the lower limiting frequency was increased to about 50 cycles/ sec. The high-cut frequency was set at 1,000 cycles/ sec. A metronome was used to control and standardize the speed of clenching which was made against the force transducer as hard and as quickly as possible at the rate of 1 cycle/Z sec. Three measurements were made for each masseter and temporal muscle on both sides. The average of the three slopes obtained from each measurement was evaluated. Processing the relation between integrated electromyographic activity and biting force. The portion in which the biting force increased linearly and as quickly as possible was selected on the recording

THE IOURNAL

coefficient;

1

1 1 112 118 chewing ratio.

side; r = correlation

DENTISTRY

side; df = degrees of freedom;

SS = sum of squares;

MS = mean

paper. Ten values of the integrated potentials were plotted against 10 values of the computed biting force (moment) within the portion, and the curve thus obtained showed a linear relationship. Therefore, a regression equation (Y = a + bX) was calculated foreach curve by the least-square method and the slope b was expressed as a regression coefficient. V/T curves in patients with MPD syndrome. Six men and four women with MPD syndrome, 22 to 40 years of age, were selected as patients for the study. The recordings were made five times a month for each patient, and the mean slopes of the curves on 5 separate days were compared with those of healthy subjects previously reported.’ Effect of electrical muscle stimulation on the V/T

451

KOTANI

P .050

c

NPC

s

0 \*A.. *030-

S

? ‘0

&

-

&.p&--&fj a-’

.OlO-

1 0

1

1 30

1

1 60

I

I

I

--I

t

I

9Omin

Fig. 1. A, Changes in the slopes of the V/T curves before and during electrical muscle stimulation in patients with MPD syndrome. Ordinate, the slope of the V/T curve; abscissa, duration of the electrical muscle stimulation; PCS, preferred chewing side; NPCS, nonpreferred chewing side; l , slope of V/T curve in the masseter muscle; o, slope of V/T curve in the temporal muscle.

curves in patients with MPD syndrome. It is known that electrical muscle stimulation in low-frequency current increases the blood supply to injured tissue and stimulates the rate of repair by rapidly promoting absorption of waste products.’ The Myomonitar,* a commercial device for electrical muscle stimulation, is used in dental clinics to provide muscle relaxation and relief of pain in patients with paindysfunction syndrome of the stomatognathic system.j If electrical muscle stimulation has such an effect on the fatigued masticatory muscles in patients with MPD, the slopes of the V/T curves (which are regarded as a measure of the efficiency of individual fibers composing a muscle2) should be influenced by this stimulation. The effect of electrical muscle stimulation on the V/T curves of masticatory muscles was examined in four patients with MPD (22 to 56 years of age) and two healthy subjects (23 years of age). An electronic stimulatort was used for electrical muscle stimulation by rectangular pulse having 1 msec duration and 1.5 set interval at the clinical threshold. Electrical stimulation was established as the first palpable contraction of the muscle and the first visible rise of the mandible that could be identified.6 Cathode electrodes were placed on the skin surface covering the right and left mandibular notch, and an anode electrode was also placed on the posterior midline of the neck at the hairline. The recordings were made every 15 minutes for each subject, while the stimulus was applied to each subject for 90 minutes. Effect of occlusal splint on the V/T curves in patients with MPD syndrome. The occlusal splint is *Myo-tronics Research, Inc., Seattle, Wash. JFSEN-3101 Electronic Stimulator, Nihon Koden Tokyo, Japan.

452

Kogyo

Co., Ltd.,

ET AL

one of the most universally accepted treatments for the pain-dysfunction syndrome of the stomatognathit system. 7-s The purpose of using the splint is to ‘provide muscular relaxation which may result from reduction of muscular activity when the patient is not chewing or swallowing.1o When the masticatory muscle activity is reduced by the splint, as described by Solberg and associates,“’ the slope of the V/T curve in MPD should be affected by the splint therapy because muscle fatigue should be improved by a decrease in muscle activity. Therefore, the effect of occlusal splints on the V/T curves of masticatory muscles were examined in four patients with MPD (23 to 56 years of age) and in two healthy subjects (21 and 24 years of age). A full-arch maxillary stabilization splint was used which was made from heat-cured acrylic resin. The splint was inserted and adjusted to provide a stable flat plane occlusion with posterior centric stops and with uniform anterior and canine guidance.7 The patients were instructed to insert the splint before sleeping, and the recordings were made prior to and during splint therapy. RESULTS V/T curves in patients with MPD syndrome. The slopes of the V/T curves in the masseter muscles ranged from 0.037 to 0.093 with a mean of 0.058 on the preferred chewing side and from 0.034 to 0.092 with a mean of 0.054 on the nonpreferred chewing side. In the temporal muscles, they ranged from 0.020 to 0.045 with a mean of 0.031 on the preferred chewing side and from 0.019 to 0.039 with a mean of 0.029 on the nonpreferred chewing side (Table I). The slopes of the curves were significantly steeper in patients with MPD than those of healthy subjects reported previously.’ This tendency was more remarkable in the masseter muscles because the temporal muscles had fewer symptoms (Table II). Effect of electrical muscle stimulation on the V/T curves in patients with MPD syndrome. The results obtained are shown in Figs. 1 and 2. In the patients with MPD, the slopes of the curves were markedly influenced by the electrical muscle stimulation. The changes in slopes during stimulation were divided into two groups. The first group showed a decrease in the slopes with an increase in the duration of stimulation (Fig. 1, A). The second group also showed a decrease in the slopes with an increase in the duration of stimulation, but the slopes reached the minimum values within 90 minutes of stimulation and then increased as the duration of stimula-

APRIL 1980

VOLUME

43

NUMBER

4

QUANTITATIVE

ELECTROMYOGRAPHIC

DIAGNOSIS

OF MPD SYNDROME

P

c

s

NPCS 9

.OQO-

w P

c

s

0

30

60

QOmin

NPCS

.220: .200

::

-

/ I :

.1804 .160

\ \ \ \ : .,

t I

f

I

\ \ \ \ \

I .140

.l 20

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: l’

S

0

.130

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N

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QOmin

Fig. 1. B-D, For legend, see facing page.

tion was increased beyond each value (Figs. 1, B to D). The cause of this phenomenon is thought to be muscle fatigue produced by overstimulation because the muscles in MPD are easily fatigued.” In healthy subjects, few changes in slopes were observed during stimulation (Fig. 2). Effect of occlusal splint on the V/T curves in patients with MPD syndrome. The slopes of the V/T curves in MPD reduced gradually after insertion of the splint and reached the ranges of the slopes in healthy subjects reported previously’ (Fig. 3). When the changes in slopes reached equilibrium, the patients became almost asymptomatic. In healthy subjects with normal occlusion and without symptoms, few changes were observed during splint therapy (Fig. 4).

THE JOURNAL

OF PROSTHETIC

DENTISTRY

DISCUSSION It is known that masticator-y muscle spasm is the primary factor responsible for signs and symptoms of the pain-dysfunction syndrome of the stomatognathic system. The most common cause of muscle spasm is thought to be muscle fatigue produced by chronic oral habits such as clenching or grinding of the teeth. ’ It has been reported previously that the slope of the V/T curve showed the degree of fatigue in masticatory muscles.‘! In the present study, the slopes in MPD were significantly steeper than those in healthy subjects. Therefore, it is considered that the most simple diagnostic procedure is to compare the slopes in MPD with those of healthy subjects. However, as some of the slopes in MPD were within

453

KOTANI

P

c

ET AL

NPCS

s

.040

c

NPCS

PCS .040

I - @

b

’

i0

’

sb

$kOrnin ’

’

’

’

’

Fig. 2. A and B, Changes in the slopes of the V/T curves before and during electrical muscle stimulation in healthy subjects. Ordinate, the slope of the V/T curve; abscissa, duration of the electrical muscle stimulation; PCS, preferred chewing side; NPCS, nonpreferred chewing side; l , slope of V/T curve in the masseter muscle; o, slope of V/T curve in the temporal muscle.

P

c

N

s

P c

s

.OQO

0

P

N

C

s

P

C

S

\

.070

.050 .030

.OlOL @

“-9”“--27 -7

1

10 17 29 36 43 50 64day

Fig. 3. A-D, Changes in the slopes of the V/T curves before and during splint therapy in patients with MPD syndrome. Ordinate, the slope of the V/T curve; abscissa, time course before and during splint therapy; -, before splint therapy; +, during splint therapy; PCS, preferred chewing side; NPCS, nonpreferred chewing side; l , slope of V/T curve in the masseter muscle; o, slope of V/T curve in the temporal muscle; +, splint insertion.

a!54

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VOLUME

43

NUMBER

4

QUANTITATIVE

ELECTROMYOGRAPHIC

DIAGNOSIS

OF MPD SYNDROME

0

P c s

.130

N

P

C

S

0

.llO

.OQO

.070

.050

.030

.OlO

(+‘l~~i~‘~~“’ -31-26-2048

-9

-1

1

7

14

21 28 35 42

51

62

71day NPCS

.140

.120 I .lOO

I

.080 I .060

.040 I .020

t

1 m-22

-11I

-1I

4I

11 , 18I

25I 42II

63 70I 82I 94I, ll4day

Fig. 3. C-D, For legend, see facing page. normal limits, it was difficult to differentiate the fatigued muscles in MPD from the nonfatigued muscles by simply comparing the slopes. It is also known that electrical muscle stimulation with low-frequency current is effective against muscle spasm and pain produced by sustained contraction of skeletal muscles.5 The slopes were not influenced by the electrical stimulation in healthy muscles without fatigue, but in the muscles of MPD patients they were considerably reduced by stimulation of moderate duration. This was true even in muscles with their slopes within normal limits. This finding indicates that the masticatory muscles of MPD patients with muscle fatigue can be cleariy differentiated from healthy muscles by observing the changes in the slopes before and during electrical muscle stimulation.

THE JOURNAL

OF PROSTHETIC

DENTISTRY

If the existence of muscle fatigue in MPD patients has been verified, the question of whether the muscle fatigue in MPD was caused by occlusal problems should be raised. Therefore, the changes in the slopes were observed during splint therapy in patients with MPD. It is still unclear how splints work and why they are effective for treating patients with pain-dysfunction syndrome of the stomatognathic system. However, there is general agreement that occlusal splints eliminate occlusal interferences with minimal amount of opening of the vertical dimension of occlusion.’ This causes a change in the degree of tactile afferent impulses from the periodontal mechanoreceptors,” thus producing muscle relaxation. The slopes of the V/T curves in patients with MPD reduced gradually during splint therapy, but

455

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c-0 ‘CT ,,,,,,,,,,

t-t @-

I

21 - 13 - 7

-1 P

1 c

4

7

a’D-0

ET AL

-%3-0~

11 14 lQday

s

I

N

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C

S

Fig. 4. A and B, Changes in the slopes of the V/T curves before and during splint therapy in healthy subjects. Ordinate, the slope of the V/T curve; abscissa, time course before and during splint therapy; -, before splint therapy; +, during splint therapy; PCS, preferred chewing side; NPCS, nonpreferred chewing side; l , slope of V/T curve in the masseter muscle; o, slope of V/T curve in the temporal muscle; -+, splint insertion. in healthy subjects, few changes in the slopes were observed during therapy. This finding suggests that improvements in symptoms can be quantified by the slope of the V/T curve and that it can be determined by observing the changes in the slopes during splint therapy whether or not the symptoms have been produced by occlusal problems. Patients having changes as shown in this study should receive occlusal therapy such as occlusal adjustment or fixed prosthodontic therapy following the splint therapy.

SUMMARY The slopes of the V/T curves of masticatory muscles were determined in patients with MPD syndrome, and the changes in the slopes were observed prior to and during electrical muscle stimulation and splint therapy. The slopes of the V/T curves in patients with MPD syndrome were significantly steeper than those of the healthy subjects. In patients with MPD the slopes were decreased by electrical muscle stimulation of moderate duration and by insertion of the splint. These findings suggest that the most simple procedure for the diagnosis of MPD syndrome is to compare the slopes in MPD patients with those of healthy subjects. The observation of the changes in slopes during electrical muscle stimulation and splint therapy permits a more quantitative diagnosis of MPD syndrome. It also permits a quantitative measurement of improvement of symptoms in patients with MPD syndrome.

456

REFERENCES 1. Laskin, D. M.: Etiology of the pain-dysfunction syndrome. J Am Dent Assoc 79:147, 1969. 2. Kawazoe, Y., Kotani. H., and Hamada, T.: Relation between integrated electromyographic activity and biting force during voluntary isometric contraction in human masticatory muscles. J Dent Res 58: 1440, 1979. 3. Stacy, R. W., Hickey, J. C., Woelfel, J. B., and Rinear, L. L.: Electromyography in dental research. II. Frequency response requirements. J PROSTHETDENT 8: 1049, 1958. 4. Kovacs, R.: Electrotherapy and Light Therapy, ed. 4. Philadelphia, 1942, Lea and Febiger. 5. De Boever, J., and McCall, W. D.: Physiological aspects of masticatory muscle stimulation: The Myomonitor. Quintessence Int 3:57, May 1972. 6. Jankelson, B., and Swain, C. W.: Physiological aspects of masticatory muscle stimulation: The Myomonitor. Quintessence Int 3:57, Dee 1972. 7. Ramfjord, S. P., and Ash, M. M.: Occlusion, ed. 2. Philadelphia, 1971, W. B. Saunders Co. a. Krogh-Paulsen, W. G., and Olsson, A.: Management of the occlusion of the teeth. In Schwartz, L., and Chayes, C. (editors): Facial Pain and Mandibular Dysfunction. Philadelphia, 1968, W. B. Saunders Co., pp 236-280. 9. Greene, C. S., and Laskin, D. M.: Splint therapy for the myofascial pain-dysfunction (MPD) syndrome: A comparative study. J Am Dent Assoc 84:624, 1972. 10. Solberg, W. K., Clark, G. T., and Rugh, J. D.: Nocturnal electromyographic evaluation of bruxism patients undergoing short-term splint therapy. J Oral Rehabil 2:215, 1975. 11. Kawazoe, Y., Kotani, H., and Hamada, T.: Unpublished data. Reprint requeststo: DR. HIROO KOTANI HIROSHIMA UNIVERSITY SCHOOL OF DENTISTRY KASUMI l-2-3 HIROSHIMA, JAPAN

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NUMBER 4