The conductive properties of the whole nerve and muscle allow measurement of electrical activity with extra-cellular (surface) electrodes. Typical monitoring sites for masticatory muscles include the masseter, anterior temporalis, posterior temporalis, and digastric suprahyoid muscles. These electrodes to not penetrate the cell membrane, but detect potential differences external to the muscle fiber and distant from the potential source. In the whole muscle or nerve, local current flow is not limited to the membrane surface but will spread throughout the surrounding tissue. A field of current spreads through the extracellular space from the depolarizing membrane.

There is no external current flow and therefore no potential difference is recorded between the two poles of the bipolar electrode until a cellular action potential is initiated. As depolarization initiated by a neural action potential proceeds along the muscle fiber, the outward flow of current through adjacent regions to the membrane makes the recording electrode more positive with respect to the reference electrode.

Action potentials propagating down the nerve are the means by which the central nervous system potentiates contraction of muscle fibers. When the neural action potential crosses the motor end plate the subsequent potentiation of muscle cell electrical discharge creates a current that has a higher potential relative to the reference electrode. As the action potential moves further along the muscle fiber, the recording EMG electrode ceases to be affected by the current flow and the action potential returns to the original baseline.

SURFACE ELECTROMYOGRAPHY

Surface electromyography has long been the "gold standard" for monitoring muscle activity of masticatory muscle at REST and in FUNCTION. The value of surface EMG is best expressed by C.J. DeLuca, Professor of Biomedical Engineering and Research and Professor of Neurology at Boston University, "Surface EMG utilizes sensing electrodes placed on the skin, which allows the clinician to directly and accurately monitor muscle activity. This is far more accurate procedure than conventional manual palpation or touch which can provide only gross assessments of muscle activity." 1988. W.D. McCall also states "...there is general agreement among both clinicians and investigators that masticatory muscle activity is increased in symptomatic patients as compared with normal subjects. Electromyography is the principal tool used to investigate such differences." (The Musculature. A Textbook of Occlusion, Quintessence, 1988).

Many investigators have confirmed the safety, efficacy and value of surface electromyography for assessing RESTING and FUNCTIONAL status of muscle. There is a broad body of literature that supports the physiologic basis for using surface EMG as an aid in assessment of muscle function/dysfunction. (Moyers, 1949; Lippold, 1952; Perry, 1954; Bigland and Lippold, 1954; Jarabak, 1956; Perry, 1957; Porritt, 1960; Grossman, 1961; Moss and Greenfield, 1965; Moller, 1976; Mitani et al., 1972; Moss and Chalmers, 1974; Moller, 1975; Yemm, 1976; Milner-Brown and Stein, 1975; Pruim et al., 1978; Bakke et al., 1980; Riise et al., 1982; Sheikholeslam et al., 1982; Sheikholeslam et al., 1983, Riise et al., 1984; Algren et al., 1985; Myslinski et al., 1985; Sherman, 1985; Goldensohn, 1986; Hermans et al., 1986; Kydd et al., 1986; Sheikholeslam et al., 1986; Balciunas et al., 1987, Burdette and Gale, 1987; Wood, 1987; Crain and Klemons, 1988; Chong-Shan and Hui-yun, 1989; Christensen, 1989; Koole et al.; Neill et al., 1989; Van Eijen et al., 1990; Jankelson, 1992; Lynn et al, 1992)

There is substantial evidence based upon controlled studies that confirm that surface electromyography is reliable and reproducible (Bigland and Lippold, 1954; Goldensohn, 1966; Lloyd, 1971; Mitani and Yamashita, 1972; Molin, 1972; Moss, 1974; Ahlgren, 1975; Milner-Brown and Stein, 1975; Moller, 1975; Mitani and Yamashita, 1978; Hermens et al., 1986; Kydd et al., 1986; Burdette and Gale, 1987; Christensen, 1989; Neill, 1989; Van Eijden, et al., 1990; Dean et al., 1992)

ELECTROMYOGRAPHY TO MONITOR MUSCLE POSTURAL (REST) ACTIVITY

There is a large body of literature documenting the validity and efficacy of surface electromyography to study resting and hypertonic states of masticatory muscles. ( Jarabak, 1956; Shpuntoff and Shpuntoff, 1956; Lous, et al., 1970; Moller et al., 1971; Yemm, 1976; Clark et al., 1979; Clark et al., 1981; Riise et al., 1982; Sheikholeslam et al., 1982; Panteleo et al., 1983; Keefe and Dolan, 1984; Riise et al., 1984; Mann et al, 1985; Myslinski et al., 1985; Sherman, 1985; Sheikholeslam et al., 1986; Crain and Klemons, 1988; Erlandson and Poppen, 1988; Konchak et al., 1988; Chong-Shan and Hui-yun, 1989; Gervais et al., 1989; Carlson et al., 1991; Lynn, 1990; Mann et al., 1990; Lynn and Mazzocco, 1991; Burdette and Gale, 1988; Burdette and Gale, 1992)

Many of the above studies have suggested that the postural activity of temporalis and masseter muscles are significantly higher in subjects with functional disorders of the masticatory system than controls without signs and symptoms of dysfunction.

ELECTROMYOGRAPHY TO MONITOR MUSCLE FUNCTION

The use of EMG to study muscle function is well documented. There are many studies confirming a strong linear relationship between muscle motor unit recruitment, muscle force and EMG. There are many studies showing that maximal bite force and the electrical activity of masticatory muscle during maximal bite in the intercuspal position is significantly weaker in patients with functional disorders of the masticatory system than controls without disorders. ( Lippold, 1952; Bigland and Lippold, 1954; Goldensohn, 1966; Lloyd, 1971; Molin, 1972; Helkimo et al., 1975; Milner-Brown and Stein, 1975; Moller, 1975; Pruim et al., 1978; Bakke and Moller, 1980; Sheikholeslam et al., 1980; Panteleo et al., 1983; Sheikholeslam and Riise, 1983; Cooper and Rabuzzi, 1984; McDonald and Hannam, 1984; Riise et al., 1984; Riise and Sheikholeslam, 1984; Ahlgren, 1985; Kydd et al., 1986; Balciunas et al., 1987; Wood, 1987; Michler et al., 1988; Chong-Shan, 1989; Chong-Shan and Hui-yun, 1989; Humsi et al., 1989; Christensen, 1989; Mongini et al., 1989; Neill et al., 1989; Jankelson, 1990; Van Eijden et al., 1990; Bakke and Michler, 1991; Koole et al., 1991; Lynn and Mazzocco, 1991; Naeije and Hansson, 1991; Choi, 1992; Dean et al., 1992; Kroon and Naeije, 1992; Visser, et al., 1992; Hickman et al., 1993)

1. Ahlgren J, Sonesson B and Blitz M. An electromyographic analysis of the temporalis function of normal occlusion. Am. J. of Orthod. Vol. 87, No. 3, March 1985
   
   Electromyographic (EMG) activity was recorded from the anterior, middle and posterior regions of the temporalis muscles using bipolar intramuscular electrodes in ten subjects with normal occlusion of the teeth and with the mandible at rest and during clenching. The study showed that the EMG recordings could be well controlled and reproducible and that the error of the method was small in comparison with the individual variations. The study confirmed earlier reports of a close correlation between EMG activity and tension during isometric contraction.
   
   Note: This is one of the early studies to suggest a linear correlation between EMG/motor unit recruitment and bite force.
2. Bakke M and Moller E. Distortion of maximal elevator activity by unilateral premature tooth contact. Scand. J. Dent. Res. 80:67-75, 1980
   
   In four subjects the electrical activity in the anterior and posterior temporal and masseter muscles during maximal bite was recorded bilaterally with and without premature unilateral contact. Unilateral premature contact caused a significant asymmetry of motor recruitment in all muscles under study. The mean EMG voltage decreased proportionate to thickness of the overlay introduced as a prematurity. The authors conclude the significant findings were 1, asymmetry of muscle activity with strongest activity on the side of premature contact and, with this asymmetry maintained, 2) a reduction of mean voltage on both sides with increasing height of the overlay.
   
   Note: This is supportive of EMG as a functional indicator of proprioceptive influence of occlusal contact on muscle motor unit recruitment.
3. Bakke M and Michler L. Temporalis and masseter muscle activity in patients with anterior open bite and craniomandibular disorders. Scand. J. Dent. Res. 99:219-228, 1991
   
   Facial morphology of 22 patients with anterior open bite and craniomandibular dysfunction were studied . Electromyographic activity was recorded by surface EMG after primary treatment with a reflex release stabilizing occlusal appliance. Maximal voluntary contraction was reduced compared to reference values particularly in patients with muscle dysfunction. Muscle activity increased significantly during maximal bite using the stabilizing appliance. Maximal voluntary contraction was positively correlated to molar contact and negatively to anterior face height, mandibular inclination, vertical jaw relation and gonial angle. The authors concluded that subjects with little occlusal stability and muscle activity would benefit from an increase of tooth contact to utilize their full elevator muscle capacity and increase strength, thereby reducing the risk of muscular strain and overload.
   
   Note: These findings support the EMG function protocol to assess occlusal stability and muscle response to a specific occlusal position and contact.
4. Balciunas BA, Staling LM and Parente FJ. Quantitative electromyographic response to therapy for myo-oral facial pain: A pilot study. J. of Prosth. Dent. Vol. 58 No.3, Sept. 1987
   
   Five subjects with common symptoms of TMD were studied using integrated EMG of the anterior temporalis and masseter muscles. The authors conclude that "Our results agree with those of other investigators who demonstrate a positive contribution by masticatory EMG data to confirm and quantify objectively the subjective symptoms."
   
   Note: The authors note in conclusion that "the occlusal position of clenching was the jaw position that provided the most definitive information." This is supportive of the maximal clench clinical protocol.
5. Bigland B and Lippold OCJ. The relation between force, velocity and integrated electrical activity in human muscles. J. of Physiol. 123:214-224, 1954
   
   The authors compared needle and surface electrodes under isometric conditions. Good correlation was obtained. The authors conclude that tension, velocity and electrical activity are interdependent and the integration of EMG signals provides a composite measure of the number of active fibers and their frequency of excitation.
   
   Note: This early study supports the validity of the EMG signal as a reliable indicator of muscle motor unit function.
6. Burdette BH and Gale EN. Reliability of surface electromyography of the masseteric and anterior temporal areas. Arch Oral Biol. Vol. 35 9:747-751, 1990
   
   Bipolar surface EMG electrodes were used to record tonic resting EMG activity of the anterior temporalis and masseter muscles for 2 consecutive sessions in thirty seven patients suffering from MPD. The authors suggest that the reliability of tonic postural EMG data recorded from the masseteric area is satisfactory when recording conditions are standardized. Smaller coefficient correlation of anterior temporal postural activity was noted and possibly attributable to the dynamic role the this muscle in maintaining postural rest position of the mandible.
7. Burdette BH and Gale EN. Intersession Reliability of surface electromyography. J. of Dent. Res., Abstr. No. 1370, Volume 66, 1987
   
   The purpose of this experiment was to compare EMG data from trials both within the same session without moving the electrodes and between sessions two weeks apart. Using the standardization techniques described, repeatability of surface EMG data between recording sessions was considered satisfactory for the masseter muscles.
8. Burdette BH and Gale EN. The effects of treatment on masticatory muscle activity and mandibular posture in myofascial pain-dysfunction patients. J. Dent. Res. 67(8):1206.682.8200, August 1988
   
   Forty one TMD patients were evaluated with surface EMG to measure anterior temporalis and masseter postural EMG activity. Twenty three asymptomatic subjects were tested as controls. The pre-treatment EMG values of both the masseteric and anterior temporalis muscles were significantly higher for the pain group than the control group. These result suggest that tonic masticatory muscle activity may be elevated in MPD patients. They also suggest that a decrease in EMG activity in the masseter and anterior temporalis muscles and an opening of the postural rest position of the mandible may accompany completion of psychophysiologic therapy, but these changes do not correspond directly with the outcome of that therapy.
   
   Note: This study confirms many others that suggest elevated postural EMG activity is a consistent finding in patients suffering from TMD.
9. Carlson CR, Okeson JP, Falace DA, Nitz AJ and Anderson D. Stretch based relaxation and the reduction of EMG activity among masticatory muscle pain patients. J. Craniomandib. Disord Facial Oral Pain 5:205-212, 1991
   
   This study of 34 patients with myogenous pain with no arthrogenous pain used bipolar EMG surface electrodes to study response to relaxation procedures. The authors conclude that the study of EMG activity after relaxation is a useful research tool to understand mechanisms of muscle pain disorders.
10. Chaconas SJ and Fragiskos FD. Vertical dysplasias and myofascial pain dysfunction syndrome. Compend Contin Educ Dent. Vol. XI, No. 7, 1990
    
    The authors present a clinical case study of a patient who had sought relief from MPD symptoms from multiple practitioners. Electromyography was used to identify masticatory muscle spasm and to assist establishing a therapeutic occlusal position. The patient's symptoms completely resolved after placement of an appliance in a neuromuscularly coordinated position.
11. Choi J. A study on the effects of maximal voluntary clenching on the tooth contact points and masticatory muscle activties in patients with temporomandibular disorders. J. Craniomand Disord Facial Oral Pain 6:41-46, 1992
    
    This study was conducted to evaluate the occlusal contact stability at the moment of dynamic occlusal tooth contacts and to investigate the correlations between the occlusal contact stability and masticatory muscle activity during maximal voluntary clenching in twenty TMD patients. The authors concluded the muscular disharmony of the anterior temporal muscles of the patient group was significantly greater than that of the control group. Masseter muscle disharmony was not significantly greater than the control group. TMD patients demonstrated less symmetrical and simultaneous tooth contact resulting in asymmetrical anterior temporalis activity during maximal clench. There was a significant improvement in muscle synergy after one week of occlusal splint use in the patient group.
    
    Note: Correlation of occlusal stability and Muscle EMG symmetry supports EMG maximal clench protocol.
12. Chong-Shan, S. Proportionality of mean voltage of masseter muscle maximum bite force applied to diagnosing tempormandibular joint disturbance syndrome. J. Prosthet Dent 62:682-684, 1989
    
    Maximum bite force in the molar area and the corresponding mean EMG value of the corresponding masseter in 29 patients and 27 controls were recorded. In contrast to the controls, the maximum bite force of the patients was smaller, the mean voltage was nearly equal and the proportionality of the mean voltage to the maximum bite force of the patients was greater. These result indicate that the masticatory muscles of patients with temporomandibular joint dysfunction are in a state of hyperactivity and tension.
13. Chong-Shan S and Hui-yun W. Postural and maximum activity in elevators during mandible pre- and post-occlusal split treatment of temporomandibular joint disturbance syndrome. J. Oral Rehabil. Vol. 16:155-161, 1989
    
    "Electromyograms of the temporal and masseter muscles in sixty patients with temporomandibular joint disturbance syndrome and thirty controls were recorded and integrated on-line in the postural position and during maximum clenching, before and after splint therapy. Contrasting with the controls, the myoelectric activity of the patients was higher in the postural position and lower during maximal clenching, whilst the former in percentage terms increased when compared to the later...The results show that the mandibular elevators in the patients with TMJDS were hyperactive and tense, and that the occlusal splint was useful for treating such dysfunction."
    
    Note: This well controlled study supports the clinical protocol for both posture and function EMG studies of TMD patients.
14. Chong-Shan S and Hui-yun. Value of EMG analysis of mandibular elevators in open-close-clench cycle to diagnosing TMJ disturbance syndrome. J. Oral Rehabil. Vol. 16:101-107, 1989
    
    The EMG's of the temporal and masseter muscles in 60 TMD patients and 30 controls were recorded during rhythmical open-close-clench movement before and after occlusal splint therapy. The author concluded that the duration of muscle contraction before initial tooth contact was significantly different in subjects and controls, and it is a useful modality in diagnosis of muscular dysfunction.
15. Clark GT, Beemsterboer PL, Solberg WK, Rugh JD. Nocturnal electromyographic evaluation of myofascial pain dysfunction in patients undergoing occlusal splint therapy. J. Am. Dent. Assoc. Vol. 99:607-611, 1979
    
    The level of nocturnal masseter muscle activity in 25 MPD patients was monitored with surface EMG before, during and after therapy with occlusal splints. Correlations were made between the severity of symptoms before treatment and the effectiveness of the splint in reducing nocturnal activity of muscle.
16. Clark GT, Beemsterboer PL and Rugh JD. Noctural masseter muscle activity and the symptoms of masticatory dysfunction. J Oral Rehabil. 8:279-286, 1981
    
    "The results presented in this study support the hypothesis that prolonged jaw closing muscle hyperactivity is correlated with the symptoms of jaw dysfunction. More specifically, the greater the level of nocturnal EMG a subject had the more likely he was to have signs and symptoms of jaw dysfunction.
    
    Note: This study supports the universal axiom that TMD patients have elevated EMG activity and that a shift to lower activity is a therapeutic objective.
17. Christensen LV. Reliability of maximum static work efforts by the human masseter muscle. Am J Orthod Dentofac Orthop 95:42-45, 1989
    
    Six healthy subjects clenching in centric occlusion were studied for reliability of nonfatiguing maximum voluntary static work effort. Maximum voluntary teeth clenching was performed for 10 seconds on 2 different days, each with two trials, and maximum static work efforts quantified by integrated surface EMG. Reliability was determined by factorial analysis of variance and intraclass correlations. Date reduction showed that maximal voluntary static work efforts were reproduced reliably during the four different trials.
    
    Note: This study supports the reliability of the EMG maximal clench protocol. The author also adds that the most ideal method would be to take EMG records before and after treatment protocols within a day. This is consistent with the intra-patient data clinical protocol routinely used.
18. Cooper BC and Rabuzzi DD. Myofascial pain dysfunction syndrome: a clinical study of asymptomatic subjects. Laryngoscope, Vol. 94, No.1, p 68-75, Jan 1984
    
    A study of 26 asymptomatic subjects using EMG to evaluate occlusal and muscle function revealed the presence of subclinical muscle asymmetry and dysfunction in a significant number of patients. The author concludes that measuring mandibular movement and muscle function with EMG is a valuable adjunct to subjective history records.
19. Cooper BC, Cooper DD and Lucente FE. Electromyography of masticatory muscles in craniomandibular disorders. Laryngoscope, Vol. 101:150-157, Feb 1991
    
    Electromyographic recording using surface electrodes were made bilaterally on the masseter, anterior temporalis and digastric muscles in 641 craniomandibular dysfunction patients, before and after transcutaneous electrical neural stimulation, at their initial presentation and following insertion of a mandibular appliance. The TENS therapy significantly decreased muscle hyperactivity. The use of a neuromuscularly balanced appliance resulted in significant reduction of symptoms, reduction of resting EMG activity, Increase in muscle activity in maximum effort and improved coordination of muscle groups during mandibular movement. The authors conclude "Electromyography of certain masticatory muscles is a clinically useful method of quantifying musculoskeletal dysfunction in patients with clinically diagnosed craniomandibular disorders...The use of electromyography is paramount in documenting increased and more symmetrical clenching force following creation of a neuromuscularly based occlusal or biting position."
20. Crain JR and Klemons IM. EMG: Comparisons in craniofacial muscles following therapy for head and neck pain. Med. Electr. pp 106-110, Dec. 1988
    
    The anterior and posterior temporalis, masseter, and digastric muscles of thirty consecutive patients diagnosed as having headaches due to MPD were monitored with surface EMG pre- and post- treatment. All patients reported improvement in head pain. There was a statistically significant correlation between reduction of symptoms and reduction of EMG activity in 25 of the 29 patients. The authors conclude "It appears that the bioelectric activity measured by the computerized EMG may be an effective indicator of the efficacy of treatment amongst patients experiencing head pain of musculoskeletal origin.
21. Cram JR and Engstrom D. Patterns of neuromuscular activity in pain and nonpain patients. Clin Biofeed and Health Vol. 9, No. 2, p 106-115, 1986
    
    This study compared the patterns of surface EMG activity in normal subjects and in patients with history of chronic pain. Surface EMG activity was sampled from the right and left homologous sites of ten muscle groups in sitting and standing posture. Statistical comparisons between the normal subjects (N=104) and chronic pain patients (N=200) were conducted on each of 40 samples of surface EMG. The results of the study indicate that chronic pain patients exhibit a higher level of surface EMG activity. These findings support previous research indicating abnormal neuromuscular activity and posture in chronic pain patients.
22. Dean JS, Throckmorton GS, Ellis E and Sinn DP. A preliminary study of maximum voluntary bite force and jaw muscle efficiency in pre-orthognathic surgery patients. J. Oral Maxillofac Surg. 50:1206.682.8200, 1992
    
    This study compared the ability to generate occlusal force for 84 patients requiring orthognathic surgery for facial deformities and 57 controls. Maximal and submaximal bite forces were measured at the incisor and first molar bit positions. Electromyographic activity was recorded bilaterally from the anterior temporalis, posterior temporalis, and masseter muscles during each bite. An efficiency ratio was calculated for the jaw muscles by dividing the level of EMG by the occlusal force. There was a reduced ability to generate occlusal forces in the patients before surgery. The reduction in maximal occlusal force was correlated with reduced efficiency of the jaw muscles.
23. Erlandson PM and Poppen R. Electromyographic biofeedback and rest position training of masticatory muscles in myofascial pain-dysfunction patients. J. Prosthet Dent. 62:335-338, 1998
    
    Twenty-four women patients with myofascial pain dysfunction were divided into three groups of eight. All received bilateral masseter EMG biofeedback training. One group received biofeedback only; one group received additional instructions to place their jaw in rest position using EMG; and one group was treated with a prosthetic appliance. The instruction and prosthesis groups obtained significantly greater electromyographic reductions in masseter activity and increases in ROM compared to the biofeedback only group. Subjects with pain obtained a significant reduction in pain. The authors conclude "Two procedures that directly placed the jaw in a relaxed or rest posture resulted in decreased masticatory muscle activity in MPD patients. This decreased activity supports previously reported findings."
24. Gervais RO, Fitzsimmons GW and Thomas NR. Masseter and temporalis electromyographic activity in asymptomatic, subclinical, and temporomandibular joint dysfunction patients. J. Craniomand Pract. Vol. 7, No. 1, p 52-57, Jan. 1989
    
    Resting EMG levels for each masseter and temporalis were obtained from three groups of subjects: asymptomatic (N=24); subclinical (N=31) and symptomatic patient (N=61). The patient group demonstrated significantly higher EMG activity than the asymptomatic or subclinical groups for all variables except the right masseter. The temporalis was found to be the site of greatest EMG activity more frequently than the masseter. These findings strengthen diagnostic and assessment procedures and criteria, as well as suggest alternate treatment and research protocols.
    
    Note: This is one of many recent studies statistically confirming a significant difference in resting activity in symptomatic and asymptomatic patients.
25. Goldensohn ES. Electromyography from Disorders of the Temporomandibular Joint. Schwartz L, ed. W.B.Saunders, Philadelphia, Jan 1966
    
    The author emphasizes that surface electrodes are the electrodes of choice for temporomandibular dysfunction studies. The EMG studies showed a significant difference in EMG activity at rest, during function and during clenching between patients complaining of facial pain and dysfunction versus asymptomatic patients.
26. Helkimo E, Carlsson GE and Carmeli Y. Bite force in patients with functional disturbances of the masticatory system. J. Oral Rehab. Vol. 2:397-406, 1975
    
    In thirty patients treated because of dysfunction and thirty six control subjects bite force was registered before, during and after treatment. Repeated tests of bite force in the control group gave identical results. Bite force in the patient group was lower than the control group but increased with palliation of the symptoms during treatment.
    
    Note: The finding of significant difference between bite force in patient and control groups is supplemental to the rationale for the EMG function test since integrated EMG and bite force are linear.
27. Hermens HJ, Boon KL and Zilvold G. The clinical use of surface EMG. Medica Physica. 9:119-130, 1986
    
    The use pf surface EMG as a tool for quantification is described. The specific advantages of surface EMG for evaluating functions of the neuromuscular system are discussed. The authors conclude " that surface EMG can certainly lead to a reproducible method of quantification."
    
    "It is possible to indicate a range of normal values to discern pathology. It is also possible to measure changes in parameters during a follow-up investigation."
28. Hickman DM, Cramer R and Stauber WT. The effect of four jaw relations on electromyographic activity in human masticatory muscles. Archives of Oral Biol. Vol. 38, No. 3, pp 261-264, 1993
    
    This study of 20 asymptomatic subjects used surface EMG of the anterior temporalis and masseter muscles to evaluate masticatory muscle function at postions determined by the leaf gauge (LG), manually manipulated (CR) and neuromuscular (NM) bite during maximal static clench.The leaf gauge position consistently demonstrated the lowest EMG activity, while the neuromuscular position displayed the highest degree of muscle activity. Similarly, the ratio of the masseter/temporalis EMG activity during maximal clench was lower for the leaf gauge and centric relation positions and highest for the neuromuscular position. These data indicate that the neuromuscular position produced the greatest total muscle recruitment, with more masseter involvement during clenching, and enabled the subjects to generate greater biting forces in the neuromuscular position compared to the leaf gauge and centric relation position.
29. Humsi ANK, Naeije M, Hippe JA and Hansson TL. The immediate effects of a stabilization splint on the muscular symmetry in the masseter and anterior temporal muscles of patients with craniomandibular disorder. J Prosthet Dent. 62:339-343, 1989
    
    "In 36 myogenous craniomandibular disorder patients, the immediate effects of a stabilization splint on the symmetry in the activities of the masseter and anterior temporal muscles during submaximal clench were investigated electromyographically. The immediate changes in masseter muscle activity suggest that muscular symmetry is an objective tool in the evaluation of the treatment provided."
30. Ingervall B and Carlsson GE. Masticatory muscle activity before and after elimination of balancing side occlusal interference. J. Oral Rehabil. Vol. 9:183-192, 1982
    
    The activity of the masseter and anterior and posterior temporal muscles was studied by electromyography (EMG) in thirteen subjects with unilateral balancing side interferences and in twelve control subjects without such interferences. In both groups the EMG recordings were made during postural activity and various functions of the masticatory system and in the interference group they were repeated twice after occlusal adjustment. The findings of this study were inconclusive regarding the influence of balancing interferences in a young adult population but the authors conclude "It is obvious from the present results that there is a relationship between occlusal factors and muscle activity in mandibular posture and during functions such as chewing and swallowing."
31. Jankelson RR. Analysis of maximal electromyographic activity of the masseter and anterior temporalis muscles in myocentric and habitual centric in temporomandibular joint and musculoskeletal dysfunction. Pathophysiology of Head and Neck Musculoskeletal disorders. Bergamini M (ed), Front Oral Physiol. Basel, Karger, 7:83-98, 1990
    
    Analysis of 46 TMD patients showed masseter EMG activity significantly lower than anterior temporalis EMG activity during maximal bite to habitual occlusion. This study supports previous studies showing reduced EMG activity during maximal bite in TMD patients. The was a positive correlation between reduced patient symptoms and increased maximal EMG activity. The author concludes that integrated EMG of maximal clench appears to be a reliable quantitative modality to identify functional disorders of the masticatory system. The use of maximal effort EMG is a reliable quantitative indicator of pre- and post- treatment masticatory function.
32. Jankelson, RR. Validity of surface electromyography as the "gold standard" for measuring muscle postural tonicity in TMD patients. Anthology of Craniomandibular Orthopedics Vol. II, ed. Coy,R pp. 103-125, 1992
    
    The author presents a comprehensive scientific literature review examining the validity of surface EMG to study postural activity of craniomandibular muscles. After examination and critique of biologic electro-chemical models the author concludes that manual palpation is not a reliable indicator of histochemical/electrical status of muscle and that EMG is well established in the literature as the "gold standard" for measure postural muscle tonicity. Lowering of postural activity of hypertonic muscle is a universal therapeutic objective and surface EMG is a reliable indicator of muscle in the resting state.
33. Jarabak JR. An electromyographic analysis of muscular and temporomandibular joint disturbances due to imbalances in occlusion. Angle Orthodont. (26)3:170-190, 1956
    
    In a study of twenty two patients EMG records of neuromuscular activity from the temporal muscles was analyzed during biting, rest after biting and rest after speaking. The author concluded: " 1. The behavior of skeletal muscle is a faithful index of the state of the motor nerve center (lower motor neuron). 2. Temporal muscle spasms occur simultaneously with functional disturbances in the temporomandibular joint. 3. Functional disturbances in the temporomandibular joint may have their etiology in occlusal interferences of the teeth. 4. Muscle spasms disappear in the temporal muscles when occlusal interferences were removed. Upon removal of the splint, muscle spasms re-occurred."
34. Keefe FJ and Dolan EA. Correlation of pain behavior and muscle activity in patients with myofascial pain-dysfunction syndrome. J Craniomandib Disord Facial Oral Pain 2:181-184, 1984
    
    The authors studied 31 patients diagnosed as having MPD in order to examine the degree to which overt pain behavior relates to muscle tension in MPD patients. Monitoring masseter muscle activity with surface EMG the authors concluded; "This study found a significant relationship between overt pain behavior and muscle tension in MPD patients."
35. Konchak PA, Thomas NR, Lanigan DT and Devon RM. Freeway space measurement using mandibular kinesiograph and EMG before and after TENS. Angle Orthodont. p 343-350, Oct 1988
    
    This study expands on a previous pilot study of the efficacy of TENS to assist in determination of the resting position of the mandible. Surface EMG of the masseter and anterior temporalis to quantify muscle activity before and after application of TENS.
36. Koole P, deJongh HJ and Boering G. A comparative study of electromyograms of the masseter, temporalis, and anterior digastric muscles obtained by surface and intramuscular electrodes:Raw EMG. J Craniomand Pract Vol. 9, No. 3:228-240 July 1991
    
    Electromyographic activity was synchronously recorded by surface and intramuscular needle electrodes in the same muscle. The activity of the masseter, temporalis and anterior digastric was studied. The authors concluded "The use of surface and intramuscular electrodes in cyclic jaw movements gives comparable results with respect to the onset and offset of activity of the muscles of mastication."
37. Kroon GW and Naeije M. Electromyographic evidence of local muscle fatigue in a subgroup of patients with myogenous craniomandibular disorders. Arch Oral Biol. Vol. 37, 3:215-218, 1992
    
    Ten patients with myogenous craniomandibular disorders and ten controls were studied using surface EMG monitoring of the masseter and anterior temporalis muscles. The authors concluded: "The results for the maximum voluntary bite force and for the 50% isometric endurance time were indicative of masticatory muscle weakness in the patients with craniomandibular disorder. The maximum voluntary bite force was significantly lower in patients than controls. The endurance times were the same for the two groups despite the lower bite forces sustained by the patients. These results were confirmed by the characteristics of the electromyograms."
38. Kydd WL, Choy E and Daly C. Progressive jaw muscle fatigue and electromyogram activity produced by isometric unilateral biting. J. Craniomand Pract. Vol. 4, 1:18-21
    
    The purpose of this study using 30 subjects was to quantify the duration of force required during unilateral biting to produce the onset of subjective fatigue and pain in the masseter and anterior temporalis muscles of healthy adult females. "In the subjects with contralateral pain discomfort, EMG evaluation demonstrated that integrated EMG activity on the nonstressed contralateral side was twice that of the ipsilateral side where the force was applied." This study confirms many others that correlate pain, bite force and EMG activity.
39. Lippold OCJ. The relation between integrated action potentials in a human muscle and its isometric tension. J. Physiol. 117:492-499, 1952
    
    EMG action potentials were recorded from calf muscles of thirty subjects at ten different strengths of contraction.
    
    The study found that in all thirty patients the relation between the isometric tension of a voluntarily contracting human muscle and its integrated electromyogram is always directly linear.
    
    Note: This classic study confirms the basis for an integrated EMG/motor unit recruitment correlation that is the basis of the maximal clench isometric function test.
40. Lloyd A. Surface electromyography during sustained isometric contractions. J. Appl. Physiol. 30 5:713-719, 1971
    
    Ten subjects were asked to maintain isometric contractions of the elbow flexor muscles as long as possible at 50% and 70% of maximum voluntary strength and to report when they experienced five successive levels of pain resulting from the contraction. Surface EMG recordings were made on the biceps muscle and three peripheral muscles. EMG frequency analysis demonstrated that during sustained contraction amplitude resulted from an increase in the activity within a narrow frequency band. The authors conclude: "The results of the present experiment suggested that with an increase in the duration of a constant force, synchronization and recruitment produced a increase in the amplitude of the surface EMG. Surface EMG recordings during strenuous work endurance seemed to provide considerable information about muscle activity."
41. Lous I, Sheikholeslam A and Moller E. Postural activity in subjects with functional disorders of the chewing apparatus. Scand. J. Dent. Res. 78:404-410, 1970
    
    In 39 patients with functional disorders of the temporomandibular joint and the muscles of mastication and in 45 controls, the activity in the temporal and masseter muscles was recorded with the subjects seated upright and the mandible at rest. The purpose was to investigate the concept of hyperactivity or muscle spasms and to relate the electromyographic and clinical findings. The authors concluded: " In the present study muscle activity in patients with functional disorders of the chewing apparatus was for the first time compared statistically with the activity in a group without symptoms or signs of such disorders. It emerged that the average level of postural activity in the temporal and masseter was raised significantly in the patients as compared to the controls."
    
    Note: This is one of the early classic studies with a large control group confirming the hypertonicity characteristic of myogenous TMD.
42. Lynn JM. Craniofacial neuromuscular dysfunction vs. function:A comparison study of the condylar position and intro-articular space. Pathophysiology of Head and Neck Musculoskeletal Disorders. Bergamini M (ed) Front Oral Physiol. Basel, Karger Vol. 7, p 136-143, 1990
    
    This study of 100 patients (200 joints) with signs and symptoms of TMD were monitored and measured for condylar position change comparing habitual position with a TENS/EMG/CMS generated position. The author concludes that there is no standard normal joint space in neuromuscular dysfunction patients. However, the use of EMG to generate a rest position of the mandible resulted improvements in resting and functional EMG activity that correlated with the reduction in symptoms.
43. Lynn JM and Mazzocco M. Intraoral splint therapy: muscles objectively. Funct Orthodont. p 11-27 Nov/Dec 1991
    
    This study of 203 consecutive TMD patients used EMG data from four paired muscle groups to help establish a therapeutic position for an occlusal appliance. EMG values were recorded at rest and during function before and after appliance therapy. All resting measures showed a significant decrease in EMG activity while function increased significantly 12 weeks after treatment. The study found significant correlation between reduction of pain and lowered EMG resting levels and increased maximal function activity.
    
    
    Note: This study with a large patient sample statistically establishes significant longitudinal intra-patient EMG parameters and subjective pain history.
44. Lynn JM, Mazzocco MW, Miloser SJ and Zullo T. Diagnosis and treatment of craniocervical pain and headache based on neuromuscular parameters. Am J Pain Management. Vol. 2, No.3 July 1992
    
    This study attempted to identify the relationship of EMG-measure neuromuscular dysfunction to reported craniocervical pain and the effectiveness of EMG-based orthoses on reversing myospastic conditions. Results of the study indicate a significant decrease in muscle spasm at rest and a significant increase in muscular activity during function following treatment with EMG based appliances. Craniocervical pain reduction correlated to the decrease in resting EMG and increase in function EMG activity. The authors conclude that utilization of electromyography is a valuable tool during the assessment and treatment of chronic facial pain patients.
45. MacDonald JWC and Hannam AG. Relationship between occlusal contacts and jaw-closing muscle activity during tooth clenching: Part I. J. Prosth. Dent. Vol. 52, No. 5:718-729 Nov 1984
    
    In 10 subjects surface EMG was recorded from the masseter and temporalis muscles during vertical clenching and eccentric clenching. The authors conclude "The findings on this electromyographic study on changes of the contact points, size of contact point, and the direction of effort applied on a contact point confirm their specific association with the activity of muscle groups."
46. Mann A, Zuazola RV, Sirhan R, Quiroz M and Rocabado M. Relationship between the tonic elevator mandibular activity and the vertical dimension during the states of vigilance and hypnosis. J Craniomand Pract Vol. 8, No. 2:163-170 April 1990
    
    The variation of the masseter and anterior temporalis postural EMG activity during vigilance and after hypnosis was studied and referenced to vertical dimension. Under hypnosis a significant reduction of postural EMG activity was observed together with an significant increase of interocclusal space. The authors conclude that hypnosis is a good technique to produce effective neuromuscular relaxation of mandibular muscles and may be effective in reducing spasm of TMD patients.
47. Manns A, Miralles R and Cumsille F. Influence of vertical dimension on masseter muscle electromyographic activity in patients with mandibular dysfunction. J Prosth Dent Vol. 53, No. 2:243-247, Feb. 1985
    
    This study of 61 TMD patients analyzed the EMG response to occlusal splints adjusted to different vertical dimensions. The authors conclude: "This study suggests that an increase in vertical dimension of occlusion to or near the vertical dimension of least EMG activity by means of occlusal splints can be an effective way to obtain a reduction in masseteric muscle activity."
48. Michler L, Bakke M, Andreassen S and Hennington E. On-line analysis of natural activity in muscles of mastication. J. Craniomand Disord:Facial and Oral Pain 2:65-82, 1988
    
    The authors present an EMG on-line analysis to record muscle activity during mastication. They conclude that the computerizing of the EMG protocol is a significant addition to quantitative methods of whole-muscle EMG routinely used clinically and experimentally the past 20 years. The function EMG protocol provides "Instant presentation of results during treatment represents a valuable check of procedures to improve occlusal stability as judged by the patient's nervous system in keeping with correlations between muscle activity and stability."
49. Milner-Brown HS and Stein RB. The relation between the surface electromyogram and muscular force. J. Physiol. 246:549-569, 1975
    
    A linear relation between electrical activity and tension during constant or zero velocity change in muscle length was demonstrated using both needle and surface EMG. This study validates the rational for clinical EMG protocol using isometric maximal bite. The EMG function test quantifies motor unit recruitment at a given mandibular position. This study demonstrated that as the electrical activity increases, the proportion of overlap between potentials arising in different parts of the muscle remains constant. The excitation is related to the number and discharge frequency of active units.
50. Miralles R, Zuniga C, Santander H and Manns A. Influence of mucosal mechanoreceptors on anterior temporalis EMG activity in patients with craniomandibular dysfunction: a preliminary study. J. Craniomand. Pract. Vol. 10 No.1:21-27, Jan 1992
    
    Bilateral surface EMG electrodes placed on the anterior temporalis muscles were used in this study to evaluate postural (tonic) EMG activity in 15 patients with craniomandibular dysfunction. There was not significant differences in EMG activity before and after the use of a palatal base appliance.
51. Miralles R, Mendoza C, Santander H and Zuniga C. Influence of stabilization occlusal splints on sternocleidomastoid and masseter electromyographic activity. J. Craniomand. Pract. Vol. 10 No.4:297-304, Oct 1992
    
    Bipolar surface EMG recordings of the masseter and sternocleidomastoid muscles on 14 symptomatic subjects were monitored to analyze the effect of a occlusal appliance on muscle activity. Postural (tonic) EMG activity, as well as during swallowing and maximal voluntary clenching, was recorded with and without a stabilization occlusal appliance. These parameters were monitored with and without the occlusal appliance. During swallowing the activity of both muscles was significantly lower with the appliance, suggesting possible efficacy of the appliance to reduce muscle tenderness.
52. Mitani H and Yamashita Y et al. On the Power spectra of the surface electromyograms of masticatory muscles. J Osaka Dent Univ. Vol. 6, No. 1, 1972
    
    The surface EMG of the bilateral middle masseter and anterior and posterior temporalis of three subjects with normal occlusion was recorded, analyzed and a power spectrum obtained. This study of the power spectra of surface electromyograms of masticatory muscles helped define the technical and physical parameters for the present clinical EMG.
53. Molin, C. Vertical isometric muscle forces of the mandible: A comparative study of subjects with and without manifest mandibular pain dysfunction syndrome. Acta Odont Scand. 30:485-499, 1972
    
    This study of 31 female subjects with TMD and 30 healthy control subjects compared isometric bite forces at maximal and submaximal levels. The conclusion was that the symptomatic subjects could produce only one-half to two- thirds the bite forces produced by the control group. The linearity between bite force and integrated EMG support diminished maximal bite EMG activity in the symptomatic patient.
54. Moller, E. Clinical electromyography in dentistry. Acta Odont Scand. Vol. 19, 2:250-266, 1975
    
    The author concludes that surface electrodes are applicable to study the action of the temporalis, masseter and other facial muscles. Other conclusions state "Electromyography of the activity during full effort is an important supplement to the clinical examination of the muscles of mastication.... Electromyography provides an objective means of deciding the degree of predominance of one side during natural chewing...As a supplement to the clinical and radiological investigation, electromyography can contribute to a more precise diagnosis of functional disorders of the chewing apparatus and of the importance of function in malocclusion."
55. Moller, E. The chewing apparatus: An electromyographic study of the action of the muscles of mastication and its correlation to facial morphology. Acta Physiol Scand Vol. 69, Supp 280 2:73-75, 1975
    
    A controlled study of 36 healthy subjects monitoring anterior temporalis, posterior temporalis and masseter muscle activity investigating maximal EMG activity when the subjects clenched in the intercuspal position. Values for electromyographic data and facial morphology using logarithmic transformation was established.
56. Moller E, Sheikholeslam A and Lous I. Response of elevator activity during mastication to treatment of functional disorders. Scand J Dent Res 92:64-83, 1984
    
    The pattern of elevator muscle activity using bipolar surface EMG of the temporalis and masseter muscles during mastication in 37 patients with pain and dysfunction and 43 control subjects was studied before and after treatment. Compared to controls, patients before treatment chewed with greater percent of maximal elevator activity, with longer relative contraction times and stronger intermediary activity between chewing strokes. These EMG parameters established quantitative profiles of muscle hyperactivity.
    
    The significant difference between patients and controls suggest that there is an increased load put on muscle during mastication due to unstable functional occlusion caused by muscle control beyond the guidance necessary for chewing. The authors further conclude, "Hyperactivity in terms of relatively increased postural activity has also been shown and included all muscles under study, but the most substantial differences concerned the temporal muscles. Hence, the temporal muscles tend to be susceptible to static overload while the masseter muscles are most likely to acquire the symptoms and signs of overload during the strong, dynamic contractions of mastication."
57. Moller E, Sheikholeslam A and Lous I. Deliberate relaxation of the temporal and masseter muscles in subjects with functional disorders of the chewing apparatus. Scand J Dent Res 79:478-482, 1971
    
    This controlled study replicated the results of Lous (1970) using bilateral surface EMG to study the activity of the anterior temporalis and masseter muscles comparing response of 24 patients with functional disorders of the muscles of mastication and the TMJ with 45 patients without such disorders. The use of Electromyography permits direct observation of muscle relaxation. The authors conclude, "Our findings suggest that hyperactivity in the temporal muscles reflects abnormal posture of the mandible and that the supine position is suitable for inducing relaxation during clinical examination and treatment."
58. Mongini F, Tepia-Valenta G and Conserva E. Habitual mastication in dysfunction: a computer-based analysis. J. Prosthet. Dent. 1:484-494, 1989
    
    The different parameters of habitual mastication in stomatognathic dysfunction, mandibular movements and electromyographic activity of elevator muscles were recorded during three chewing sequences in 86 dysfunctional subjects. Bipolar surface EMG electrodes were used in the study. The author concluded, "The EMG data also showed marked alterations with increase of masseter activity during opening in some patients and an irregular and more random distribution during closing. In particular the distinction between a prevalently isotonic and a prevalently isometric muscle contraction pattern observed in the normals during closing was less evident. An index of isometric contraction was calculated for each subject and showed a tendency to reduce or suppress the isometric phase of contraction. This tendency was more marked in the TMJ-impaired patients as opposed to the muscle patients. Indeed, between normal and TMJ-impaired patients the discriminative capability of the index was good with few instances of false positive or false negatives."
59. Moss JP and Greenfield BE. An electromyographic investigation of class III cases. Tr. Br. Study Orthod. p 147-156, 1965
    
    A clinical EMG protocol for assessing muscle activity is described. Thirty two patients with Class III malocclusion and forty patients with normal occlusion were compared for differences in electromyographic patterns. Significant difference in these patterns was found. "The electromyographic patterns of 40 Class I cases and 32 Class III cases have been investigated and the activity of the anterior masseter muscle and the posterior temporal muscle have been shown to be important in determining the anteroposterior relationship of the jaws.
    
    A longitudinal study during treatment has shown that following treatment, when the incisors are in a Class I relationship, the jaw may be in a posterior relationship, and further treatment is necessary to eliminate this displacement and possible loosening of the incisors." The authors conclude that this EMG protocol a valid clinical method of assessing the relationship of the jaw before and after treatment.
60. Moss JP and Chalmers CP. An electromyographic investigation of patients with a normal jaw relationship and a class III jaw relationship. Am J Orthod. Vol. 66 5:538-556, Nov 1974
    
    Surface EMG electrodes were determined to be the most suitable to monitor anterior masseter and posterior temporalis muscle activity in four groups of patients; normal adults, normal children, postural Class III and skeletal Class III subjects. The authors concluded, "that recordings of a group of patients with a similar occlusal relationship would look like recordings of the same individual made on separate occasions. Their pattern would be distinct, and the correlation and variance covariance structure would be fixed and quite unlike that due to errors in the method itself. The authors conclude that the ratio of masseter to temporal activity is a suitable discriminator.
61. Munro RR. Electromyography of the masseter and anterior temporalis muscles in patients with atypical facial pain. Australian Dent J. p 131-139, April 1972
    
    This study of 26 patients with atypical facial pain used surface electrodes on the masseter and anterior temporalis to study duration of muscle contraction before initial tooth contact and latency and duration of inhibition. When compared to a large control group the duration of muscle contraction and latency in the open-close-clench cycle was significantly longer.
62. Myslinski NR, Buxbaum JD and Parente FJ. The use of electromyography to quantify muscle pain. Meth and Find Exptl Clin Pharmacol Vol. 7 10:551-556, 1985
    
    This study was designed to determine the validity of using electromyography to quantify muscle pain in patients with chronic MPD. Ten patients with mild to severe pain and no psychologic overlay were studied. Measurement of subjective pain and EMG activity were recorded before and after standard analgesic therapy. Surface EMG recordings were obtained from the masseter and anterior temporalis muscles during rest, swallow, clench and chewing modes of activity. The authors conclude, " In the present study, there was a parallel relationship between objective EMG and perceived pain. It showed that the test for the multiple R was statistically reliable. As the pain attenuated after treatment and then returned, the EMG signals followed accordingly in a graded manner."
63. Naeije M, and Hansson TL. Short-term effect of the stabilization appliance on masticatory muscle activity in myogenous craniomandibular disorders patients. J Craniomnanib Disord Facial Oral Pain. 5:245-250, 1991
    
    The short-term effect (4 to 6 weeks) of a stabilization appliance on masticatory muscle activity was investigated in 26 myogenous craniomandibular dysfunction patients. Surface EMG recordings of the anterior temporalis and masseter muscles were made before and immediately after appliance delivery. The average EMG activity of the masseter muscles remained the same during the period of appliance use, whereas the anterior temporalis muscles showed an immediate and long lasting reduction in activity. The appliance also resulted in an improvement in the balance of left and right masseter activity. There was minor improvement in temporal muscle symmetry at the 50% clench level and after 4 weeks of appliance use. The authors conclude, "The main short term effects of the stabilization appliance on the masticatory muscle activity during submaximal clenching efforts are a reduction in temporal muscle activity and an improvement in masseter muscle asymmetry."
64. Nakamura T, Inoue T, Ishigaki S, Morimoto T and Maruyama T. Differences in mandibular movements and muscle activities between natural and guided chewing cycles. Int J Prosthodont 2:249-253, 1989
    
    Twenty subjects with no symptoms of TMD were monitored with the Mandibular Kinesiograph and surface EMG of the masseter and digastric muscles. With different types of food both masseter and digastric burst of activity were shortened as the chewing rate increased, with the masseter activity more closely related to the chewing rate than was the digastric activity. When the chewing rate was altered voluntarily, the duration of the digastric burst varied more than the masseteric burst.
65. Nielsen I and Miller AJ. Response patterns of craniomandibular muscles with and without alterations in sensory feedback. J. Prosth. Dent. Vol. 59 3:352-362, March 1988
    
    Surface EMG recordings were made from paired anterior temporal, masseter and suprahyoid complex muscles while tracking mandibular movement with a Mandibular Kinesiograph. Twenty normal subjects were monitored for 16 different patterns of response during clenching and mandibular movement. The authors conclusions included, "These data support the concept that movement of the mandible from the intercuspal or rest position develop a coactivation pattern that will excite or inhibit a given muscle regardless of whether clenching with occlusal contacts or no occlusal contacts is involved. The data also demonstrate that the maxillary splint can alter the use of the jaw elevator muscles, predominantly in mastication."
66. Neill DJ, Kydd WL, Nairn RI and Wilson J. Functional loading of the dentition during mastication. J. Prosthet Dent. 62:218-228, 1989
    
    The use of electromyography of the masseter and anterior temporalis muscle to establish an index of chewing force is described. By using the Mandibular Kinesiograph it was possible to determine the interrelationship of the phase of chewing cycle and to measure the duration of each phase. Ten dentate subjects and two completely edentulous denture patients were studied to analyze forces and loading. The authors state,"...the EMG signal is likely to give us a reasonable indication of the magnitude of the applied load and a valuable method of comparing the force used by a given subject in chewing different food."
67. Pruim GJ, Ten-Bosch JJ, and deJongh HJ. Jaw muscle EMG-activity and static loading of the mandible. J Biomech. Vol. 11 p 389-395, 1978
    
    The study was designed to relate jaw muscle EMG-activity to static (isometric) bite forces. Bipolar surface electrodes were applied to masseter, anterior temporalis and posterior temporalis in combination with small bite transducers. The EMG activity was then correlated with bite force. The authors verified previous investigators findings that their is a linear relationship between integrated EMG-activity and the force exerted by individual muscle during isometric contraction. The role of depressor muscles as elevator antagonists in muscle force analysis was also discussed.
68. Perry HT. Muscular changes associated with temporomandibular joint dysfunction. J Am Dent Assoc. Vol. 54 p 644-653, 1957
    
    This retrospective study of 126 TMD patients concluded that in every instance where electromyographic evidence of spasm at rest was noted before treatment, the final EMG after treatment indicated a normal or near normal picture of EMG activity. Of the 126 subjects, 118 experienced relief with either occlusal equilibration or occlusal splinting. The EMG was a reliable indicator of the change in resting EMG. The author adds, "In all of the patients studied electromyographically, the pattern of muscle spasm closely followed the topographic distribution of subjectively recognized pain." The author confirms the value of EMG for functional evaluation, "The electromyogram has supplied another useful adjunct in studying functional problems."
69. Perry HT and Harris SC. Role of the neuromuscular system in functional activity of the mandible. J. Am Dent Assoc. Vol. 48 p 665-673, June 1954
    
    This study of ten patients with normal occlusion studied the activity of the masseter and temporal muscles during gum chewing. The author concluded that as the temporal and masseter muscles reached maximal activity both sides were synchronized, the temporal muscles displayed electrical activity before the masseter muscles, there was greater harmony and smoothness of action-potential discharge on the side preferred for mastication. The author found these patterns different in Class II Division 1 malocclusion patients and of clinical significance.
70. Pantaleo T, Prayer-Galletti F, Pini-Prato G, and Prayer-Galletti S. An electromyographic study in patients with myofacial pain-dysfunction syndrome. Bull Gr Int Rech sc Stomat et Odont. Vol. 26, p 167-179, 1983
    
    This study of 11 MPD patients and 5 normal control subjects monitored temporalis and masseter activity with bipolar surface EMG electrodes. EMG activity was studies both at rest and during maximal biting in the intercuspal position. The control subjects had significantly less EMG activity at rest than the patient group. All MPD patients had elevated EMG resting activity which was reduced by TENS application and by an occlusal splint. The authors concluded that TENS/occlusal splint therapy effectively reduced both pain and resting EMG activity indicating reduced muscle spasm. All MPD patients displayed abnormal EMG patterns during the maximal bite in intercuspal position. After correction of the occlusal malrelation with splints, EMG patterns improved and appeared more similar to those of control subjects. The authors conclude, "The correction of occlusal position by acrylic splints was able to induce a persistent reduction or a suppression of the abnormal EMG activity at rest and a good relief of pain; moreover, after the correction, higher levels of EMG activity were found during maximal biting in the intercuspal position."
71. Riise C and Sheikholeslam A. The influence of experimental interfering occlusal contacts on the postural activity of the anterior temporal and masseter muscles in young adults. J. Oral Rehab. Vol. 9 p 419-425, 1982
    
    This study of 11 asymptomatic subjects with full dentitions using surface EMG electrodes examined the effect of intercuspal occlusal interferences on the pattern of anterior temporalis and masseter postural activity. The pattern of postural activity is influenced by the introduction of an experimental occlusal interference. "One week after the insertion of the interference there was still a significant increase of postural activity in either the right or left temporal muscle while there was no significant change in the masseter muscles. Immediately after removal of the remaining interference there was no significant response in the pattern of postural activity. One week later the postural activity had returned almost to its original pattern in all subjects."
72. Riise C and Sheikholeslam A. Influence of experimental interfering occlusal contacts on the activity of the anterior temporal and masseter muscles during mastication. J. Oral Rehab. Vol. 11 p 325-333, 1984
    
    Quantitative electromyography (EMG) was used to study, in eleven subjects with complete natural dentitions, the effects of an experimental intercuspal occlusal interference on the pattern of activity of the anterior temporal and masseter muscles during mastication. The results show that a small occlusal interference (about 0.5) in the intercuspal position can change the co-ordination pattern of muscle activity during mastication. There was a prolonged contraction time and reduction in temporalis and masseter function in all subjects, especially on the side of the interference. After removal of the interference the pattern of co-ordination of muscular activity returned almost to the pre-experimental pattern within two weeks."
73. Sheikholeslam A and Riise C. Influence of experimental interfering occlusal contacts on the activity of the anterior temporalis and masseter muscles during submaximal and maximal bite in the intercuspal position. J. Oral Rehab. Vol. 10 p 207-214, 1983
    
    The effects of an experimental intercuspal occlusal interference on the pattern of anterior temporal and masseter activity during submaximal and maximal bite were studied on 11 subjects. Using bipolar surface EMG electrodes the results show that during maximal and submaximal bite an occlusal interference is able to disturb the almost symmetric pattern of activity in the anterior temporal and masseter muscles. The level of muscle motor unit recruitment during maximal bite decreased significantly in all muscles studied. After eliminating the interference, the muscular co-ordination pattern improved and the level of motor unit recruitment increased significantly.
74. Sheikholeslam A, Moller E and Lous I. Pain, tenderness and strength of human mandibular elevators. Scand J Dent Res 88:60-66, 1980
    
    This study compared the mean EMG amplitude of the temporalis and masseter muscles during maximal bite in the intercuspal position in 39 patients with functional disorders of the chewing apparatus and 45 control subjects. Maximal EMG activity was significantly stronger in the controls than in the patient group. The authors conclude, "We suggest that the weaker elevator muscles of the patients was a predisposing factor making these muscles less fit to endure hyperactivity induced psychologically or as a reflex response to occlusal interferences and functional disorders of the temporomandibular joints or other elements of the oral neuromuscular system. The sample of controls had much stronger elevators, less susceptible to hyperactivity."
75. Sheikholeslam A, Holmgren K and Riise C. A clinical and electromyographic study of the long-term effects of an occlusal splint on the temporal and masseter muscles in patients with functional disorders and nocturnal bruxism. J Oral Rehab. Vol. 13 p 137-145, 1986
    
    "The postural activity of the temporal and masseter muscles in thirty-one patients with signs and symptoms of functional disorders were studied: before, during and after 3-6 months of occlusal splint therapy. The fluctuating signs and symptoms, as well as the postural activity of the temporal and masseter muscles were significantly reduced after treatment. Further, the coefficients of correlation within pairs of postural activity of the right and left muscles increased significantly. After cessation of the splint therapy the signs and symptoms recurred to the pre-treatment level within 1-4 weeks in about 80% of the patients. The results indicate that an occlusal splint can eliminate or diminish signs and symptoms of functional disorders and re-establish symmetric and reduced postural activity in the temporal and masseter muscles, which can facilitate procedures, such as functional analysis and occlusal adjustment."
76. Sheikholeslam A, Moller E and Lous I. Postural and maximal activity in elevators of mandible before and after treatment of function disorders. Scand J Dent Res. 90:37-46, 1982
    
    This study of 37 patients before and after treatment of functional disorders of the masticatory system and 43 control subjects demonstrated reduction of postural activity and reduction of signs and symptoms in all muscles studied. In both temporalis and masseter muscles reduced activity after treatment was accompanied by less pain and tenderness. The right and left anterior temporal and masseter muscle recruitment became more symmetrical after treatment. Increased postural activity and pain coincide for the muscles of mastication and pain decreases with EMG activity in response to treatment.
77. Shen-gen S, Guan O and Cheng-fan Z. Preliminary study of electromyographic characteristics for distinguishing centric relation and protrusion in edentulous patients. J. of Prosthet Dent. Vol. 69, p 171-175, Feb 1993
78. Sherman RA. Relationships between jaw pain and jaw muscle contraction level: Underlying factors and treatment effectiveness. J of Prosthet Dent. Vol. 54 1:114-118, July 1985
    
    Using surface EMG of the masseter muscle the author evaluated 27 patients and 14 control subjects to determine the differences in postural (tonic) muscle activity between patients who have jaw pain due only to TMJ problems and those with pain of other origin. Patients with TMJ problems plus bruxing/clenching had EMG levels similar to those with bruxing/clenching only. The levels were far higher than those in the groups with little or no TMJ problems and no pain. These findings support many other studies that show patient groups have significantly elevated postural EMG levels compared to asymptomatic control groups.
79. Shpuntoff H and Shpuntoff W. A study of physiologic rest position and centric position by electromyography. J Prosthet Dent. Vol. 6, 5:621-628, 1956
    
    Using surface EMG recordings from the masseter muscles of 215 subjects considered normal using the authors criteria The study concluded that EMG can be used to determine physiologic rest position and centric position. There was a characteristic EMG pattern in all 215 patients in the centric position. The authors conclude that all variety of bite registration techniques should be studied and compared using electromyography.
80. Stohler C, Yamada Y and Ash MM. Antagonistic muscle stiffness and associated behavior in the pain dysfunctional state. Helv Odont Acta 29:2,1985, in Schweiz. Mschr. Zahnmed. 95:719-13, 1985
    
    Surface EMG of the supra-hyoid and masseter muscles combined with Mandibular Kinesiograph jaw tracking was used to establish differences in EMG activity during painful and non-painful voluntary jaw movement. Twenty two patients with TMD were compared to six control subjects with painless clicking and no other symptoms. Electromyography of the masseter and suprahyoid musculature, jaw movement and joint sounds were recorded during 10 open-close-clench cycles. Statistically significant co-contraction was found in the masseter muscles during jaw opening in the pain dysfunction patients. Co-contraction of the suprahyoid muscles during closing was less pronounced. The EMG pattern of co-contraction was significantly different than that observed in non pain subjects.
81. Stohler C and Ash MM. Demonstration of chewing motor disorder by recording peripheral correlates of mastication. J. Oral Rehab. Vol. 12 p 49-57, 1985
    
    Chewing motor performance was examined in 21 patients; 12 with TMJ dysfunction, 8 with occlusal trauma and 1 with CNS impairment. Surface electromyography and three-dimensional jaw tracking with the Mandibular Kinesiograph to record jaw movement were used to analyze changes in mandibular movement and muscle activity resulting from increased pain during chewing. The authors conclude, "In comparison to normals, it might be assumed that a modification of the original behavior pattern for a variable period depended upon the severity of the dysfunctional state."
82. Stohler C and Ash MM. Excitory response of jaw elevators associated with sudden discomfort during chewing. J Oral Rehab. Vol. 13 p 225-233, 1986
    
    Patients with pain in the TMJ area during mandibular movement were electromyographically monitored for EMG response of the anterior temporalis and masseter muscles. The electromyographic pattern of these muscles was quantified by root mean square peak voltage and contraction time. Statistical analysis of group data showed significantly prolonged contraction times and greater EMG amplitudes for chewing cycles with pain as compared to chewing cycles without pain. Individual data showed statistically significant differences between painful and non-painful cycles in some cases.
83. Van Eijden TMGJ, Brugman P, Weijs WA and Ooosting J. Coactivation of jaw muscles: Recruitment order and level as a function of bite force direction and magnitude. J Biomechanics Vol. 23 5:75-485, 1990
    
    Bipolar surface EMG of the masseter, digastric, anterior and posterior temporalis muscles registered muscle activity while the patient produced a bite force of specific direction and magnitude as measured by a three-component force transducer. Vertical, anterior, posterior, lateral and medial force directions were examined; in each direction force levels between 50N and maximal voluntary force were produced. The authors conclude "For all muscles and bite force directions EMG increases linearly with bite force between 50N and maximal voluntary force. As EMG activity can be considered an indicator of the degree of neural input to a muscle, this input also increases linearly. An increase in input results in an increase of muscle force by recruitment of new motor units and an increase in firing rate. In the present study no distinction could be made between these two mechanisms.
84. Vig P. Electromyography in dental science:A review. Australian Dental Journal, p 315-322, Aug 1963
    
    The author states, "...Surface electrodes are therefore suitable for the study of integrated activity of the muscle mass immediately beneath them. By suitable, symmetrical placement of these electrodes over paired muscles, their relative activity may be studies at rest and in various movements." The author concludes, " It should be emphasized that electromyography is not a substitute for thorough clinical evaluation. However, it does provide an additional and unique method of examining the behavior of the neuromuscular system as it pertains to dental science."
85. Visser A, McCarroll RS and Naeije M. Masticatory muscle activity in different jaw relations during submaximal clenching efforts. J Dent Res. 71(2):372-379, Feb. 1992
    
    The EMG activities of the masseter muscles and the anterior and posterior temporalis muscles were investigated in different vertical and sagittal jaw relations using surface electrodes. Relative muscle activities were quantified by means of the Activity Index and the Asymmetric Index. The changing of vertical dimension and repositioning of the mandible with an occlusal splint decreased the activity of the temporalis muscles. The authors conclude that this may explain the therapeutic effect of occlusal stabilization splints in the treatment of craniomandibular disorder patients.
86. Williamson EH, Hall JT and Zwemer JD. Swallowing patterns in human subjects with and without temporomandibular dysfunction. Am J Orthod Dentofac Orthop. 98:507-511, 1990
    
    The swallowing patterns of 25 adult orthodontic patients already known to have TMJ dysfunction and 25 adult control subjects without such dysfunction were examined with the aid of the Mandibular Kinesiograph and electromyographic recordings taken when the patients sipped water. Analysis of the data revealed that 19 patients with TMJ dysfunction used a tongue-thrust open-jaw swallowing pattern, while only nine control subjects used such a swallowing pattern. Six of the patients with TMJ dysfunction had an anterior open bite, while none of the control subjects had an anterior open bite. The authors suggest that patients with aberrant swallowing patterns should be examined for TMJ dysfunction.
87. Wood WW. A review of masticatory muscle function. J Prosthet Dent. Vol. 57, 2:222-232, Feb 1987
    
    The author states that, "Surface electrodes are generally regarded as satisfactory for recording global activity of the muscle, but they pick up some activity from surrounding muscles. Even so, surface electrodes have been shown to be effective for recording from both superficial and deep masseter muscles and superficial parts of both anterior and posterior temporal muscles. "The study of clenching and chewing activity of muscle and how it can be altered to a more favorable situation for each patient concludes that elevator muscles demonstrate maximum activity even when bilateral occlusal contacts occur during clenching in the intercuspal position. The elevator muscles are activated together in the intercuspal zone of tooth contact during chewing when the occlusal contacts are balanced bilaterally in the intercuspal position. Increasing the number of eccentric tooth contacts increases the muscle activity during both chewing and clenching.
88. Yemm,R. Neurophysiologic Studies of temporomandibular joint dysfunction. Oral Sci Rev. 7:31-53, 1976
    
    After extensive review of the literature, and studying the EMG of a group of normal subjects and a group of dysfunctional patients the author concludes, "There is an increasing weight of evidence that hyperactivity of jaw closing muscles may originate in the central nervous system. It is concluded that such centrally induced activity may be sufficient to cause muscle damage, which leads to disturbed function, local pain and tenderness and to pain referred to adjacent structures...The results demonstrate a clear difference between the EMG of the normal group and the patient group."