Archs oral Bid. Vol. 35, NC. 9,
pp. 747-751,
1990 Copyright
Printedin Great Britain.All rightsreserved
0
0003-9969/90 $3.00 + 0.00 1990 Pcrgamon Press plc
RELIABILITY OF SURFACE ELECTROMYOGRAPHY OF THE MASSETERIC AND ANTERIOR TEMPORAL AREAS B. H. BURDETTE’ and E. N. GALE* ‘Department of Oral Diagnosis and Patient Services, Medical College of Georgia, School of Dentistry, 15th and Laney Walker Blvd, Augusta, GA 30912-1241and 2Department of Behavioral Sciences, State University of New York, School of Dental Medicine, 360 Squire Hall, 3435 Main St, Buffalo, NY 14214, U.S.A. (Received 26 March 1990)
Abstract-This was studied in 37 patients suffering from myofascial paindysfunction. Bipolar surface electrodes were used to record tonic, resting EMG activity for 2 consecutive trials. This protocol was repeated at a svxond recording session 2 weeks later. A custom-made, plastic template was constructed for each subject during the first visit in order to relocate the electrodes accurately at the second recording session. Correlation coefficients were calculated for each muscle area. Within-session (same day) r values ranged from 0.‘7620to 0.8884 for the masseteric area and from 0.8686 to 0.9109 for the anterior temporal area. Across-session (different day) r values ranged from 0.5645 to 0.6503 for the masseteric area and 0.3309 to 0.4844 for the anterior temporal area. The lower correlation between different day recordings could reflect a methodological shortcoming in relocating the electrodes, particularly on the anterior temporal area. The greater variability recorded from the anterior temporal area could also reflect the dynamic role of the temporalis muscle in maintaining the postural rest position of the mandible. Key words: electromyography,
reliability, masseteric, anterior temporal.
INTRODUCl.ION Great variability may be found when EMG values recorded from the surface of masticatory muscles on different days are compared (Barbenel, 1969). Despite the difficulties of obtaining reliable measurements (Angelone, Clayton and Brandhorst, 1960), some report good results when recording conditions are carefully controlled (Frame, Rothwell and Duxbury, 1973; Nouri, Rothwell and Duxbury, 1976; Pancherz and Winnberg, 1981; Garrett and Kapur, 1986). These conditions include changes in head and body posture, skin resistance, temperature and humidity, as well as muscle tfatigue, emotional factors, the continuous activity of the eye muscles, topographical location of the electrodes over the muscle areas, and the factor of removing and replacing the electrodes (Mailer, 1966; Yemm, 1969; Lund, Nishiyama and Mnrller, 1970; Frame et al., 1973; Garnick, 1975; Pancherz and Winnberg, 1981; Basmajian and Deluca, 1985; Garrett and Kapur, 1986). Various methods of standardization have been suggested to control recording variables. Because the primary reason for across-session variability is inaccurate repositioning of the electrodes, various templates and/or tattoos on the skin over the muscle areas have been used in order to accurately relocate the electrodes (Frame et al., 1973; Garnick, 1975; Nouri et al., 1976; Pancherz and Winnberg, 1981; Garrett and Kapu.r, 1986). Other methods of standardization include the use of the same surface electrodes for each subject at the return session
Abbreviation: EMG, electromyograph. AOB 35/9-D
(Frame et al., 1973; Nouri et al., 1976) and the maintenance of a constant bite force by the subject as the EMG activity is recorded (Greenfield and Wyke, 1956; Angelone et al., 1960; Garrett, Angelone and Allen, 1964; Frame et al., 1973; Nouri et al., 1976; Hosman and Naeije, 1979; Pancherz and Winnberg, 1981; Garrett and Kapur, 1986). All of the studies cited above have been of asymptomatic subjects only. The EMG has also been used extensively to study patients with painful and/or dysfunctional masticatory muscles (Mercuri, Olson and Laskin, 1979; Moody et al., 1981; Majewski and Gale, 1984), but its reliability across repeated measures has not been demonstrated with symptomatic subjects. Significant reductions in tonic, postural EMG values have been reported in patients with temporomandibular disorders after biofeedback therapy (Burdette and Gale, 1988), yet good reliability must be demonstrated before EMG changes are meaningful and pre- and post-treatment EMG values can be satisfactorily compared. Surface EMG recordings of areas of symptomatic masticatory muscle may have diagnostic value if their reliability can be demonstrated. Sherman (1985) recorded the resting EMG activity from the masseteric areas of patients who had the primary complaint of pain emanating from the region of the temporomandibular joint and of controls with no evidence of such problems. All his subjects were evaluated for history or signs of bruxism and classified as bruxist or non-bruxist. He reported significantly higher EMG values in the bruxists than in the non-bruxists regardless of whether the bruxists were patients with pain in the mandibular joint or controls. The EMG values of the non-bruxists with
B. H. BURDETTE and E. N. GALE
748
joint problems were not different from those of the non-bruxist controls. Burdette and Gale (1988) recorded tonic, postural EMG values from the masseteric and anterior temporal areas of patients with temporomandibular disorders using bipolar surface electrodes. The patients then completed an intensive treatment regimen, which included splinting and psychophysiological therapies. Retrospective analyses revealed that the small group who failed to respond satisfactorily to therapy (n = 7) had presented for treatment with a significantly higher level of tonic, postural EMG activity in the anterior temporal area than had the satisfactorily treated patients. These findings suggest that elevated surface EMG values may help identify those patients with temporomandibular disorders for whom bruxism is an important contributing factor. They also suggest that bruxist patients may prove more resistant to treatment than non-bruxist. We have now sought to determine the reliability of tonic, postural EMG data recorded from the masseteric and anterior temporal areas of patients reporting pain and dysfunction of masticatory muscles (Laskin, 1969), while using a very simple template to relocate the surface electrodes at the return session.
MATERIALSAND
METHODS
Subjects
The selected subjects were 37 patients accepted for treatment of temporomandibular disorders at the State University of New York at Buffalo. Their chief complaint was pain in the masticatory musculature, dysfunction with accompanying mandibular attributable to the pain. Patients with primary disease of the joint and those whose general ill-health might compromise their participation were excluded from the study. T~rty-two females and 5 males participated; their ages ranged from 21 to 68 yr, with a mean age of 42.3 yr. All subjects gave informed consent. Equipment
Two Autogen 1500~ units (Autogenic Systems, Inc., Berkeley, CA, U.S.A.) were used to measure the resting surface EMG from the masseteric and anterior temporal areas. Electrode impedance was measured upon application (Grass Medical Instruments, model EZM 5A Impedance Meter) and controlled at less than 5 kR to minimize artefacts due to movement-induced variations in electrode potentia1 and the recording of environmental electromagnetic radiation. The Autogen 15OOc responds only to frequencies well above the electrical power frequency (60 Hz) and in a narrow band (100-200 Hz) to minimize the effects of amplifier noise (ASI, 1977). The high-frequency bandpass also ensures that low frequency signals due to electrode movement, and cardiac and encephalic electrical activity are rejected. Rugh and Schwitzgebel (1977) measured the minimum detectable signal that could be used for biofeedback with this equipment at 0. I5 pV peak-to-peak, a level of sensitivity sufficient for monitoring the low levels of tonic EMG activity
present in surface measurements of relaxed muscle tissue. The output of the Autogen EMG monitors was connected to two Autogen model 5000 digital integrators with electrically isolated inputs to minimize electrical interference. These integrate EMG activity over a programmable time interval @V-s) and compute and display the mean activity (,uV) for that interval. Procedures
Each subject was seen for 2 data-gathering sessions, separated by an interval of approx. 2 weeks. Subjects were given only minimal info~ation about the purpose of the sessions, and were given no treatment during the 2-week interval. Each subject was seated comfortably upright in a dental chair. Bipolar surface electrodes were used to record the tonic EMG activity on the side that was most painful. With the technique described by Lippold (1967), 2 points of electrode placement were located and marked on the skin over the palpated belly of the masseter muscle as the subject clenched. Two more points were marked on the same side over the palpated belly of the anterior temporahs. A flexible plastic template was constructed (Gale, 1979) for each subject in order to ensure accurate relocation of the electrodes at the second session. This template is more quickly and easily constructed at the chairside than some described earlier (Nouri et al., 1976; Garrett and Kapur, 1986). The skin was thoroughly cleansed with ethyl alcohol, and double-stick electrode collars were placed around each point to help stabilize the electrodes. Electrode paste (Teca Corp., Pleasantville, NY, U.S.A.) was the contact medium. Four goldplated electrodes were taped into place inside the collars and a ground electrode clipped to each earlobe. To allow natural muscular activity, the subject’s head was not restrained nor leaned back against the headrest. To ensure that the head remained in a stable and reproducible position in order to reduce variability due to postural changes, a spot was marked at eye level on a blackboard 6 ft in front of the subject and served as a point on which to focus during the trials. To record EMG values, an Autogen 5600 DAC was programmed to run a series of 5 consecutive sub-trials. The subject was asked to sip a small amount of water and swallow, then to sit comfortably and still without swallowing again for 30 s. The EMG measurement was started as soon as the subject appeared completely relaxed after the swallow. This procedure was intended to produce a simple mandibular rest position and resulted in very consistent levels of tonic muscle activity in the masseteric and anterior temporal areas, as determined by electronic jaw-tracking and EMG recordings (Burdette and Gale, 1988). Each sub-trial lasted 4 s and was followed by a 2-s delay, for a total recorded trial of 20 s of tonic activity. The electrodes were not disturbed between trials. Three trials were recorded and the last two were saved each day, as the first trial was simply to acclimatize the subject to the equipment and to the experimental protocol. The DAC computer printed a
Reliability of masticatory EMG digital readout of the mean and standard deviation values (expressed in ~‘(3 of the EMG activity during each 4-s sub-trial, as well as the same values for the entire 20-s trial. The ebstrodes were removed and the subject released. This protocol was repeated with each subject at the second recording session scheduled 2 weeks later. RESULTS
Table 1 shows the means and standard deviations of EMGs for each muscle area as measured during the different sessions. IPearson correlation coefficients were calculated for each muscle area between consecutive EMG means (within-session) and also between EMG means obtained on different days (acrosssession). Within-session r values ranged from 0.7620 to 0.8884 for the masa,eteric area and from 0.8686 to 0.9109 for the anterior temporal area. Across-session r values ranged from 0.5645 to 0.6503 for the masseteric area and from 0.3309 to 0.4844 for the anterior temporal area. All masseteric correlation coefficients were significant at p x 0.001. All anterior temporal correlation coefficients were significant at p < 0.01 except 0.3309, which was significant at p < 0.05. DISCUSSION
Within-session correlation coefficients were highly significant for both muscle areas, but were smaller than those found in some earlier studies of EMG reliability (Frame et al., 1973; Garrett and Kapur, 1986) in which the subjects maintained a constant bite force during the recordings. Although static function ensures optimal reliability, the resulting muscular contractions increase the EMG amplitude and obliterate the tiny fluctuations in EMG activity that are discernible at the postural rest position (Rugh and Schwitzgebel, 1977). Thus, recording while each subject was at the rest position was considered necessary to achieve our purposes. The subject swallowed and was then asked to simply “sit comfortably and relaxed”. No head support or restraint was used. No mention was made of the subject’s jaw until both recording sessions were completed so that the subject’s attention would not be drawn to his/her jaw posture. This protocol enabled EMG measurements of the masticatory muscle areas while the subject’s tonic, postural activity was present. EMG activity in these areas can be Table 1. EMG means and standard deviations of s,ample (n = 37) Session
Trial
Mean (V)
SD 0’)
Anterior Temporal Area 1
1
1 2 2
2 1 2
1 1 2 2
1 2
1.6166 1.5483 1.5314 1S706 Mmseteric
1 2
1.4147 1.3191 1.2435 1.2185
Area
1.4956 1.5068 I .3992 1.4429
0.8619 0.8221 0.7203 0.9198
149
significantly reduced by increasing the subject’s in&al opening beyond the postural rest position (Rugh and Drago, 1981; Burdette and Gale, 1989). However, this requires conscious action directed by the experimenter and thus may provide a less accurate measure of the level of tonic activity present in these muscle areas. Our across-session r values of the masseteric area were lower than the correlation coefficients of 0.92-0.99 found by Garrett and Kapur (1986). However, we consider our measurements sufficient to support the validity of the surface EMG data across repeated measures. Across-session correlation coefficients averaged 0.6176 for the masseteric area compared to 0.4273 for the anterior temporal area. Several factors may contribute to this difference in the reliability of data between the 2 muscle areas. The masseteric area has been studied extensively and its surface EMG activity is found to be very constant from day to day, similar to that of limb muscles (Frame et al., 1973). Our findings suggest that of the 2 muscle areas, the resting activity of the anterior temporal may be more variable, as this area consistently had greater EMG variability during every trial than that of the masseteric area (see Table 1). This variability supports the proposal by some investigators (Carls66, 1952; Latif, 1957; Ahlgren, Ingervall and Thilander, 1973) that the temporalis functions as the principal postural muscle of the mandible, because the tonic activity recorded from the anterior temporal area seems to reflect more closely the normal daily variations in the postural rest position (Rugh and Johnson, 1984). The smaller correlation coefficients of the anterior temporal measurements could also reflect a methodological shortcoming in not accurately relocating the electrode at the second recording session. Electrode placement is a significant factor influencing the amplitude of the recording on the anterior temporal area (Liebman and Cosenza, 1960), and the recording sites may be harder to relocate accurately because the hairline interferes in many subjects. Also, the flexibility and design of our template may have made electrode repositioning more accurate on the larger, smoother masseteric surface than on the smaller, more variable, anterior temporal surface. The anterior temporal recording area includes several muscles whose constant and variable activity may influence the surface EMG signal. The anterior segment of the temporalis muscle, epicranius and periorbital muscles are active in this area. The main part of the epicranius muscle consists of the occipital and frontal bellies of the occipitofrontalis, united by the epicranial aponeurosis. The temporoparietalis, which is also classified as part of the epicranius, is the name given to muscle fibres (if present) at the side of the scalp between the frontal belly of occipitofrontalis and the auricular muscles (McMinn, Hutchings and Logan, 1981, p. 113). The contributing periorbital muscles include the orbital and palpebral parts of the orbicularis oris, the depressor supercilii and the levator palpebrae superioris (McMinn et al., 1981, p. 119). These may be especially influential when a subject blinks, as eye potentials may account for a significant portion of the surface EMG activity recorded from the anterior temporal area during an
750
B. H. BURDETTE and E. N. GALE
eye blink (J. D. Rugh, unpublished). The epicranius muscle is also active during blinking. The superior, inferior, lateral and medial recti muscles exhibit fairly strong, persistent activity to maintain the position of the eye during waking hours (Basmajian and Deluca, 1985). The masseteric EMG is also influenced by the large number of muscles that lie within the potential recording area of the surface electrodes. The primary muscle is the masseter, made up of superficial, middle and deep layers. Other possible contributors include the platysma, zygomaticus major and minor, risorius, orbicularis oris, depressor anguli oris, depressor labii inferioris, levator anguli oris, medial pterygoid, buccinator and possibly even the lateral pterygoid muscles (McMinn et al., 1981, pp. 93-l 19). Like the anterior temporal area, the masseteric area may also be influenced by potentials from the eye blink (E. N. Gale, unpublished). Another factor that may have contributed to the difference in reliability of measurements between the 2 muscle areas was the difference in interelectrode distance. This distance between the centres of the bipolar recording electrodes was approx. 2 cm greater on the larger masseteric area than on the smaller anterior temporal area. Pancherz and Winnberg (1981) found that the amplitude of EMG measurements of the masseteric area recorded during chewing and maximal biting increased significantly when the interelectrode distance was increased by 1 cm. Their findings, made with bipolar hook electrodes, illustrate the potential for variability in EMG amplitude as the interelectrode distance varies. Our results suggest that the reliability of tonic, postural EMG data recorded from the masseteric area with surface electrodes is satisfactory when recording conditions are standardized in a very simple and practical way. Further research is needed to determine if the reliability of recordings from the surface of the anterior temporal area is limited by the inherently variable muscle activity within the recording zone of the surface electrodes, or if our results could be improved by use of a more stringent technique for relocating the electrodes. authors gratefully appreciate the help of Tom Fronczak, Kevin Gorey, Pat Jankowiak, Carol Acknowledgements-The
Nottingham and Marilyn Sulzbach for their help in conducting the investigation and preparing this manuscript. This research was supported by USPHS Research Grants DE07089 and DE04358 from the National Institute of Dental Research, National Institute of Health, Bethesda, MD 20205, U.S.A.
REFERENCES
Ahlgren J., Ingervall B. and Thilander B. (1973) Muscle activity in normal and post normal occlusion. Am. J. Orrhod. 64, 445-456.
Angelone L., Clayton J. A. and Brandhorst W. S. (1960) An approach to quantitative electromyography of the masseter muscle. J. denr. Res. 39, 17-23. Autogenic Systems Incorporated (1977) Instruction Manual for the Autogen 15m, o. 38. Berkeley, CA. Barbenel J. C-(1969) Analysis of forces at the temporomandibular joint during function. Denr. Practit. 19, 305-310.
Basmajian J. V. and Deluca C. J. (1985) Muscles Alive, 5th edn, Chap. 21, p. 471. Williams & Wilkins, Baltimore, MD. Burdette B. H. and Gale E. N. (1988) The effects of treatment on masticatory muscle activity and mandibular posture in myofascial pain-dysfunction patients. J. dent. Res. 67, 11261130. Burdette B. H. and Gale E. N. (1989) Electromyographic activity of masticatory muscles of MPD patients during opening. J. dent. Res. 68, 391. Carl&i S. (1952) Nervous coordination and mechanical function of the mandibular elevators. Acfa odont. stand. 10 (Suppl. 11), I-126. Frame J. W., Rothwell P. S. and Duxbury A. J. (1973) The standardization of electromyography of the masseter muscle in man. Archs oral Biol. 18, 14191423. Gale E. N. (1979) Biofeedback for TMJ pain. In: Clinical Research in Behavioral Dentistry (Edited by Ingersoll B. D. and McCutcheon W. R.) p. 87. West Virginia School of Dentistry, Morgantown, WV. Garnick J. J. (1975) Reproducibility of the electromyogram. J. dent. Res. 54, 867871.
Garrett F. A., Angelone L. and Allen W. I. (1964) The effect of bite opening, bite pressure, and malocclusion on the electrical response of the masseter muscles. Am. J. Orrhod. 50, 435444.
Garrett N. R. and Kapur K. K. (1986) Replicability of electromyographic recordings of the masseter muscle during mastication. J. prosthet. Dent. 55, 352-356. Greenfield B. E. and Wyke B. D. (1956) Electromyographic studies of some of the muscles of mastication. Br. dent. J. 100, 129-143. Hosman H. and Naeije M. (1979) Reproducibility of the normalized electromyographic recordings of the masseter muscle by using the EMG recording during maximal clenching as a standard. J. oral Rehab. 6, 49-54. Laskin D. M. (1969) Etiology of the pain-dysfunction syndrome. J. Am. dent. Ass. 79, 147-153. Latif A. (1957) An electromyographic study of the temporalis muscle in normal persons during selected positions and movements of the mandible. Am. J. Orrhod. 43, 577-591.
Liebman F. M. and Cosenza F. (1960) An evaluation of electromyography in the study of the etiology of malocclusion. J. prosthet. Dent. 10, 10651077. Lippold 0. C. J. (1967) Electromyography. In: A Manual of Psychophysiological Methoa!s (Edited by Venables P. H. and Martin I.) p. 285. Wiley, New York. Lund P., Nishiyama T. and Moller E. (1970) Postural activity in the muscles of mastication with the subject upright, inclined, and supine. Stand. J. dent Res. 78, 417424.
Majewski R. F. and Gale E. N. (1984) Electromyographic activity of anterior temporal area pain patients and non-pain subjects. J. dent. Res. 63, 1228-1231. McMinn R. M. H., Hutchings R. T. and Logan B. M. (1981) Color Atlas of Head and Neck Anatomy. Year Book Medical, Chicago, IL. Mercuri L. G., Olson R. E. and Laskin D. M. (1979) The specificity of response to experimental stress in patients with myofascial pain-dysfunction syndrome. J. dent. Res. 58, 18661871. Moller E. (1966) The chewing apparatus. An electromyographic study of the action of the muscles of mastication and its correlation to facial morphology. Acta physiol. stand. Suppl. 280 69. Moody P. M., Calhoun M. A., Okeson J. P. and Kemper J. T. (1981) Stress-pain relationship in MPD syndrome patients and non-MPD syndrome patients. J. prosthet. Dent. 45, 8488. Nourl A., Rothwell P. S. and Duxbury A. J. (1976) The
reproducibility of electromyographic recordings of the masseter muscle in humans. J. oral Rehab. 3, 189-200.
Reliability of masticatory EMG Pancherz H. and Winnberg A. (1981) Reliability of EMG registrations. Electromyog. Clin. Neurophysiol. 21, 67-81. Rugh J. D. and Drago C. J. (1981) Vertical dimension: a study of clinical rest position and jaw muscle activity. J. prosthet. Dent. 45, 67&675. Rugh, J. D. and Johnson R. W. (1984) Vertical dimension discrepancies and masticatory pain/dysfunction. In Abnormal Jaw Mechanics: Diaanosis and Treatment (Edited by Solberg W. K. and Clark G. T.) Chap. 6, p. 124. Quintessence, Chicago, IL.
751
Rugh J. D. and Schwitzgebel R. L. (1977) Variability in commercial electromyographic biofeedback devices. Behav. Res. Meth. Instrum. 9, 281-285. Sherman R. A. (1985) Relationships between jaw pain and jaw muscle contraction level: underlying factors and treatment effectiveness. J. prosthet. Dent. 54, 114-118. Yemm R. (1969) Variations in the electrical activitv of the human masseter muscle occurring in association with emotional stress. Archs oral Biol. 14, 873-878.
pp. 747-751,
1990 Copyright
Printedin Great Britain.All rightsreserved
0
0003-9969/90 $3.00 + 0.00 1990 Pcrgamon Press plc
RELIABILITY OF SURFACE ELECTROMYOGRAPHY OF THE MASSETERIC AND ANTERIOR TEMPORAL AREAS B. H. BURDETTE’ and E. N. GALE* ‘Department of Oral Diagnosis and Patient Services, Medical College of Georgia, School of Dentistry, 15th and Laney Walker Blvd, Augusta, GA 30912-1241and 2Department of Behavioral Sciences, State University of New York, School of Dental Medicine, 360 Squire Hall, 3435 Main St, Buffalo, NY 14214, U.S.A. (Received 26 March 1990)
Abstract-This was studied in 37 patients suffering from myofascial paindysfunction. Bipolar surface electrodes were used to record tonic, resting EMG activity for 2 consecutive trials. This protocol was repeated at a svxond recording session 2 weeks later. A custom-made, plastic template was constructed for each subject during the first visit in order to relocate the electrodes accurately at the second recording session. Correlation coefficients were calculated for each muscle area. Within-session (same day) r values ranged from 0.‘7620to 0.8884 for the masseteric area and from 0.8686 to 0.9109 for the anterior temporal area. Across-session (different day) r values ranged from 0.5645 to 0.6503 for the masseteric area and 0.3309 to 0.4844 for the anterior temporal area. The lower correlation between different day recordings could reflect a methodological shortcoming in relocating the electrodes, particularly on the anterior temporal area. The greater variability recorded from the anterior temporal area could also reflect the dynamic role of the temporalis muscle in maintaining the postural rest position of the mandible. Key words: electromyography,
reliability, masseteric, anterior temporal.
INTRODUCl.ION Great variability may be found when EMG values recorded from the surface of masticatory muscles on different days are compared (Barbenel, 1969). Despite the difficulties of obtaining reliable measurements (Angelone, Clayton and Brandhorst, 1960), some report good results when recording conditions are carefully controlled (Frame, Rothwell and Duxbury, 1973; Nouri, Rothwell and Duxbury, 1976; Pancherz and Winnberg, 1981; Garrett and Kapur, 1986). These conditions include changes in head and body posture, skin resistance, temperature and humidity, as well as muscle tfatigue, emotional factors, the continuous activity of the eye muscles, topographical location of the electrodes over the muscle areas, and the factor of removing and replacing the electrodes (Mailer, 1966; Yemm, 1969; Lund, Nishiyama and Mnrller, 1970; Frame et al., 1973; Garnick, 1975; Pancherz and Winnberg, 1981; Basmajian and Deluca, 1985; Garrett and Kapur, 1986). Various methods of standardization have been suggested to control recording variables. Because the primary reason for across-session variability is inaccurate repositioning of the electrodes, various templates and/or tattoos on the skin over the muscle areas have been used in order to accurately relocate the electrodes (Frame et al., 1973; Garnick, 1975; Nouri et al., 1976; Pancherz and Winnberg, 1981; Garrett and Kapu.r, 1986). Other methods of standardization include the use of the same surface electrodes for each subject at the return session
Abbreviation: EMG, electromyograph. AOB 35/9-D
(Frame et al., 1973; Nouri et al., 1976) and the maintenance of a constant bite force by the subject as the EMG activity is recorded (Greenfield and Wyke, 1956; Angelone et al., 1960; Garrett, Angelone and Allen, 1964; Frame et al., 1973; Nouri et al., 1976; Hosman and Naeije, 1979; Pancherz and Winnberg, 1981; Garrett and Kapur, 1986). All of the studies cited above have been of asymptomatic subjects only. The EMG has also been used extensively to study patients with painful and/or dysfunctional masticatory muscles (Mercuri, Olson and Laskin, 1979; Moody et al., 1981; Majewski and Gale, 1984), but its reliability across repeated measures has not been demonstrated with symptomatic subjects. Significant reductions in tonic, postural EMG values have been reported in patients with temporomandibular disorders after biofeedback therapy (Burdette and Gale, 1988), yet good reliability must be demonstrated before EMG changes are meaningful and pre- and post-treatment EMG values can be satisfactorily compared. Surface EMG recordings of areas of symptomatic masticatory muscle may have diagnostic value if their reliability can be demonstrated. Sherman (1985) recorded the resting EMG activity from the masseteric areas of patients who had the primary complaint of pain emanating from the region of the temporomandibular joint and of controls with no evidence of such problems. All his subjects were evaluated for history or signs of bruxism and classified as bruxist or non-bruxist. He reported significantly higher EMG values in the bruxists than in the non-bruxists regardless of whether the bruxists were patients with pain in the mandibular joint or controls. The EMG values of the non-bruxists with
B. H. BURDETTE and E. N. GALE
748
joint problems were not different from those of the non-bruxist controls. Burdette and Gale (1988) recorded tonic, postural EMG values from the masseteric and anterior temporal areas of patients with temporomandibular disorders using bipolar surface electrodes. The patients then completed an intensive treatment regimen, which included splinting and psychophysiological therapies. Retrospective analyses revealed that the small group who failed to respond satisfactorily to therapy (n = 7) had presented for treatment with a significantly higher level of tonic, postural EMG activity in the anterior temporal area than had the satisfactorily treated patients. These findings suggest that elevated surface EMG values may help identify those patients with temporomandibular disorders for whom bruxism is an important contributing factor. They also suggest that bruxist patients may prove more resistant to treatment than non-bruxist. We have now sought to determine the reliability of tonic, postural EMG data recorded from the masseteric and anterior temporal areas of patients reporting pain and dysfunction of masticatory muscles (Laskin, 1969), while using a very simple template to relocate the surface electrodes at the return session.
MATERIALSAND
METHODS
Subjects
The selected subjects were 37 patients accepted for treatment of temporomandibular disorders at the State University of New York at Buffalo. Their chief complaint was pain in the masticatory musculature, dysfunction with accompanying mandibular attributable to the pain. Patients with primary disease of the joint and those whose general ill-health might compromise their participation were excluded from the study. T~rty-two females and 5 males participated; their ages ranged from 21 to 68 yr, with a mean age of 42.3 yr. All subjects gave informed consent. Equipment
Two Autogen 1500~ units (Autogenic Systems, Inc., Berkeley, CA, U.S.A.) were used to measure the resting surface EMG from the masseteric and anterior temporal areas. Electrode impedance was measured upon application (Grass Medical Instruments, model EZM 5A Impedance Meter) and controlled at less than 5 kR to minimize artefacts due to movement-induced variations in electrode potentia1 and the recording of environmental electromagnetic radiation. The Autogen 15OOc responds only to frequencies well above the electrical power frequency (60 Hz) and in a narrow band (100-200 Hz) to minimize the effects of amplifier noise (ASI, 1977). The high-frequency bandpass also ensures that low frequency signals due to electrode movement, and cardiac and encephalic electrical activity are rejected. Rugh and Schwitzgebel (1977) measured the minimum detectable signal that could be used for biofeedback with this equipment at 0. I5 pV peak-to-peak, a level of sensitivity sufficient for monitoring the low levels of tonic EMG activity
present in surface measurements of relaxed muscle tissue. The output of the Autogen EMG monitors was connected to two Autogen model 5000 digital integrators with electrically isolated inputs to minimize electrical interference. These integrate EMG activity over a programmable time interval @V-s) and compute and display the mean activity (,uV) for that interval. Procedures
Each subject was seen for 2 data-gathering sessions, separated by an interval of approx. 2 weeks. Subjects were given only minimal info~ation about the purpose of the sessions, and were given no treatment during the 2-week interval. Each subject was seated comfortably upright in a dental chair. Bipolar surface electrodes were used to record the tonic EMG activity on the side that was most painful. With the technique described by Lippold (1967), 2 points of electrode placement were located and marked on the skin over the palpated belly of the masseter muscle as the subject clenched. Two more points were marked on the same side over the palpated belly of the anterior temporahs. A flexible plastic template was constructed (Gale, 1979) for each subject in order to ensure accurate relocation of the electrodes at the second session. This template is more quickly and easily constructed at the chairside than some described earlier (Nouri et al., 1976; Garrett and Kapur, 1986). The skin was thoroughly cleansed with ethyl alcohol, and double-stick electrode collars were placed around each point to help stabilize the electrodes. Electrode paste (Teca Corp., Pleasantville, NY, U.S.A.) was the contact medium. Four goldplated electrodes were taped into place inside the collars and a ground electrode clipped to each earlobe. To allow natural muscular activity, the subject’s head was not restrained nor leaned back against the headrest. To ensure that the head remained in a stable and reproducible position in order to reduce variability due to postural changes, a spot was marked at eye level on a blackboard 6 ft in front of the subject and served as a point on which to focus during the trials. To record EMG values, an Autogen 5600 DAC was programmed to run a series of 5 consecutive sub-trials. The subject was asked to sip a small amount of water and swallow, then to sit comfortably and still without swallowing again for 30 s. The EMG measurement was started as soon as the subject appeared completely relaxed after the swallow. This procedure was intended to produce a simple mandibular rest position and resulted in very consistent levels of tonic muscle activity in the masseteric and anterior temporal areas, as determined by electronic jaw-tracking and EMG recordings (Burdette and Gale, 1988). Each sub-trial lasted 4 s and was followed by a 2-s delay, for a total recorded trial of 20 s of tonic activity. The electrodes were not disturbed between trials. Three trials were recorded and the last two were saved each day, as the first trial was simply to acclimatize the subject to the equipment and to the experimental protocol. The DAC computer printed a
Reliability of masticatory EMG digital readout of the mean and standard deviation values (expressed in ~‘(3 of the EMG activity during each 4-s sub-trial, as well as the same values for the entire 20-s trial. The ebstrodes were removed and the subject released. This protocol was repeated with each subject at the second recording session scheduled 2 weeks later. RESULTS
Table 1 shows the means and standard deviations of EMGs for each muscle area as measured during the different sessions. IPearson correlation coefficients were calculated for each muscle area between consecutive EMG means (within-session) and also between EMG means obtained on different days (acrosssession). Within-session r values ranged from 0.7620 to 0.8884 for the masa,eteric area and from 0.8686 to 0.9109 for the anterior temporal area. Across-session r values ranged from 0.5645 to 0.6503 for the masseteric area and from 0.3309 to 0.4844 for the anterior temporal area. All masseteric correlation coefficients were significant at p x 0.001. All anterior temporal correlation coefficients were significant at p < 0.01 except 0.3309, which was significant at p < 0.05. DISCUSSION
Within-session correlation coefficients were highly significant for both muscle areas, but were smaller than those found in some earlier studies of EMG reliability (Frame et al., 1973; Garrett and Kapur, 1986) in which the subjects maintained a constant bite force during the recordings. Although static function ensures optimal reliability, the resulting muscular contractions increase the EMG amplitude and obliterate the tiny fluctuations in EMG activity that are discernible at the postural rest position (Rugh and Schwitzgebel, 1977). Thus, recording while each subject was at the rest position was considered necessary to achieve our purposes. The subject swallowed and was then asked to simply “sit comfortably and relaxed”. No head support or restraint was used. No mention was made of the subject’s jaw until both recording sessions were completed so that the subject’s attention would not be drawn to his/her jaw posture. This protocol enabled EMG measurements of the masticatory muscle areas while the subject’s tonic, postural activity was present. EMG activity in these areas can be Table 1. EMG means and standard deviations of s,ample (n = 37) Session
Trial
Mean (V)
SD 0’)
Anterior Temporal Area 1
1
1 2 2
2 1 2
1 1 2 2
1 2
1.6166 1.5483 1.5314 1S706 Mmseteric
1 2
1.4147 1.3191 1.2435 1.2185
Area
1.4956 1.5068 I .3992 1.4429
0.8619 0.8221 0.7203 0.9198
149
significantly reduced by increasing the subject’s in&al opening beyond the postural rest position (Rugh and Drago, 1981; Burdette and Gale, 1989). However, this requires conscious action directed by the experimenter and thus may provide a less accurate measure of the level of tonic activity present in these muscle areas. Our across-session r values of the masseteric area were lower than the correlation coefficients of 0.92-0.99 found by Garrett and Kapur (1986). However, we consider our measurements sufficient to support the validity of the surface EMG data across repeated measures. Across-session correlation coefficients averaged 0.6176 for the masseteric area compared to 0.4273 for the anterior temporal area. Several factors may contribute to this difference in the reliability of data between the 2 muscle areas. The masseteric area has been studied extensively and its surface EMG activity is found to be very constant from day to day, similar to that of limb muscles (Frame et al., 1973). Our findings suggest that of the 2 muscle areas, the resting activity of the anterior temporal may be more variable, as this area consistently had greater EMG variability during every trial than that of the masseteric area (see Table 1). This variability supports the proposal by some investigators (Carls66, 1952; Latif, 1957; Ahlgren, Ingervall and Thilander, 1973) that the temporalis functions as the principal postural muscle of the mandible, because the tonic activity recorded from the anterior temporal area seems to reflect more closely the normal daily variations in the postural rest position (Rugh and Johnson, 1984). The smaller correlation coefficients of the anterior temporal measurements could also reflect a methodological shortcoming in not accurately relocating the electrode at the second recording session. Electrode placement is a significant factor influencing the amplitude of the recording on the anterior temporal area (Liebman and Cosenza, 1960), and the recording sites may be harder to relocate accurately because the hairline interferes in many subjects. Also, the flexibility and design of our template may have made electrode repositioning more accurate on the larger, smoother masseteric surface than on the smaller, more variable, anterior temporal surface. The anterior temporal recording area includes several muscles whose constant and variable activity may influence the surface EMG signal. The anterior segment of the temporalis muscle, epicranius and periorbital muscles are active in this area. The main part of the epicranius muscle consists of the occipital and frontal bellies of the occipitofrontalis, united by the epicranial aponeurosis. The temporoparietalis, which is also classified as part of the epicranius, is the name given to muscle fibres (if present) at the side of the scalp between the frontal belly of occipitofrontalis and the auricular muscles (McMinn, Hutchings and Logan, 1981, p. 113). The contributing periorbital muscles include the orbital and palpebral parts of the orbicularis oris, the depressor supercilii and the levator palpebrae superioris (McMinn et al., 1981, p. 119). These may be especially influential when a subject blinks, as eye potentials may account for a significant portion of the surface EMG activity recorded from the anterior temporal area during an
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B. H. BURDETTE and E. N. GALE
eye blink (J. D. Rugh, unpublished). The epicranius muscle is also active during blinking. The superior, inferior, lateral and medial recti muscles exhibit fairly strong, persistent activity to maintain the position of the eye during waking hours (Basmajian and Deluca, 1985). The masseteric EMG is also influenced by the large number of muscles that lie within the potential recording area of the surface electrodes. The primary muscle is the masseter, made up of superficial, middle and deep layers. Other possible contributors include the platysma, zygomaticus major and minor, risorius, orbicularis oris, depressor anguli oris, depressor labii inferioris, levator anguli oris, medial pterygoid, buccinator and possibly even the lateral pterygoid muscles (McMinn et al., 1981, pp. 93-l 19). Like the anterior temporal area, the masseteric area may also be influenced by potentials from the eye blink (E. N. Gale, unpublished). Another factor that may have contributed to the difference in reliability of measurements between the 2 muscle areas was the difference in interelectrode distance. This distance between the centres of the bipolar recording electrodes was approx. 2 cm greater on the larger masseteric area than on the smaller anterior temporal area. Pancherz and Winnberg (1981) found that the amplitude of EMG measurements of the masseteric area recorded during chewing and maximal biting increased significantly when the interelectrode distance was increased by 1 cm. Their findings, made with bipolar hook electrodes, illustrate the potential for variability in EMG amplitude as the interelectrode distance varies. Our results suggest that the reliability of tonic, postural EMG data recorded from the masseteric area with surface electrodes is satisfactory when recording conditions are standardized in a very simple and practical way. Further research is needed to determine if the reliability of recordings from the surface of the anterior temporal area is limited by the inherently variable muscle activity within the recording zone of the surface electrodes, or if our results could be improved by use of a more stringent technique for relocating the electrodes. authors gratefully appreciate the help of Tom Fronczak, Kevin Gorey, Pat Jankowiak, Carol Acknowledgements-The
Nottingham and Marilyn Sulzbach for their help in conducting the investigation and preparing this manuscript. This research was supported by USPHS Research Grants DE07089 and DE04358 from the National Institute of Dental Research, National Institute of Health, Bethesda, MD 20205, U.S.A.
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