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SCIENTIFIC STUDIES SUPPORTING THE EFFICACY OF SURFACE ELECTROMYOGRAPHY IN CLINICAL DENTISTRY
- Hyperactive/strained muscles vs. Calm/ rested muscles
- Resting muscle activity are measured in microvolts. Normal resting muscle activity levels range from 1.5-2.8 mV.
Surface electromyography (sEMG) is a series of tests to more specifically delineate and define hypertonic musculature in the compromised TMJ patient. These series of tests are necessary to differentially diagnose between intra-capsular interference (mensical or otherwise) and extra-capsular interference (influence of the surrounding hypertonic muscular matrix) so as to determine the predominant dysfunctions. Surface electrodes are placed over the muscles which in turn send impulses to the recording instrument. Defining the etiology of the TMJ patient’s predominate neuromuscular dysfunctions will preclude misdirected palliative treatment regimens.
Surface EMG is not a measure of pain.
Surface electromyography (EMG) utilizes eight channels monitoring the right and left anterior temporalis muscles, right and left masseters, and right and left anterior digastric muscles and right and left cervical group of muscles. A clinical hands-on muscle palpation examination is not able to quantify and objectively record muscle hypertonicity without subjective intervention.
Muscles of the face and jaw can be recorded to determine hyperactive muscle activity and/ or resting muscle activity. A strained jaw position can effect muscle activity. The objective is to determine the optimal resting jaw position at physiologic rest that harmonizes with resting EMG levels.
Surface EMG – A Gold Standard for Monitoring Muscle Activity
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).
- 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. (38 + studies support this ending with Lynn et al, 1992).
- There is substantial evidence based upon controlled studies that confirm that surface EMG is reliable and reproducible. (18 studies ending with Dean et al., 1992).
- 87 studies verifying the use, safety, and efficacy of EMG to monitor masticatory muscle function/ dysfunction.
“In summary, based on well controlled empirical and clinical studies that have been conducted in several universities over the past three decades throughout the world, there is unequivocal evidence to strongly support the use of EMG for the evaluation and diagnosis of temporomandibular disorders.” – Robert Jenkelson, D.D.S.
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. (Moyer, 1949; Lippold, 1952; Perry, 1954; Bigland and Lippold, 1954; Jarabak, 1956; Perry, 1957; Porrit, 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; Kyslinski 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 Clemons, 1988; Chong-Shan and Hui-yun, 1989; Christensen, 1989; Koole et al.; Neil etal., 1989; Van Eijen et al., 1990; Jankelson, 1992; Lynn et al, 1992).
The following list below is a partial list of the large body of supportive evidence documenting the use and efficacy of electromyography as applied in clinical dentistry.
Physiologic Basis for Using Quantitative EMG
There are numerous studies that support the physiologic basis for using quantitative electromyography in the diagnosis of temporomandibular and occlusal disorders (Moyers, 1949; Perry, 1954; Jarabak, 1956; Perry, 1957; Porritt, 1960; Grossman, 1961; Moller, 1966; Yemm, 1976; Bakke et al., 1980; Riise et al,, 1982; Sheikholeslam et al., 1983; Riise et al., 1984; Kydd et al., 1986).
Surface EMG is Reliable and Reproducible
There is evidence, based on controlled studies that used extensive statistical tests, that surface electromyography is reliable and reporducible (Goldensohn, 1966; Lloyd, 1971; Mitani and Yamashita, 1978; Riise, 1983; Hermens et al., 1986; Burdette adn Gale, 1987).
Relationship Between EMG and Muscular Force
Controlled studies that used extensive statistical tests show that there is a strong relationship between EMG and muscular force (Lippold, 1952; Bigland et al., 1954; Molin, 1972; Milner-Brown, 1975; Pruim, 1978).
EMG Studies of Postural Rest and Maximal Bite Position
Several studies have quantitatively investigated the EMG during postural activity of the mandible and during maximal bite in the intercuspal position. The EMG values for the temporal and masseteric muscles have been quantitatively investigated in these studdies for control subjects without functional disorders and for patients with functional disorders. (Lous et al., 1970; Moller et., 1971; Sheikholeslam et al., 1980; Sheikholeslam et al., 1982; Moller et al., 1982; Cram and Engstrom, 1986). Thsese studies replicated the results that quantified statistically significant differences between the normal population and the patient population. The slight variability among these studies was due to the type of EMG instrumentation used in each study (i.e. range of filter frequency).
EMG Studies of Bite Force in Patients with Functional Disorders
There is evidence based on controlled studies that used extensive statistical test that maximal bite force and the electrical muscle activity during maximal bite in the intercuspal position are significantly weaker in patients with functional disorders of the masticatory system than controls without such disorders (Molin, 1972; Helkimo et al., 1975; Randow et al., 1976; Sheikholeslam et al., 1980; Moller et al., 1982; Sheikholeslam et al., 1982; Kydd et al., 1986.)
EMG Postural Studies of Temporalis and Masseter Muscle Activity
Controlled studies that used extenisve statistical tests conclude that postural activity of temporalis and masseter muscles are significantly higher in patients with functional disorders of the masticatory system thncontrols without such disorders (Moller, 1966; Lous et al., 1970; Moller et al., 1971; Sheikholeslam et al., 1982; Pantaleo et al., 1983; Geraris et al., 1989.)
EMG is Effective in the Diagnosis of Myofacial Pain
Clinical studies investigating Electromyography of temporal and masseteric muscles concluded that EMG was effective in the diagnosis of Myofacial Pain Disorders (Sheikholeslam et al., 1986; Pantaleo et al., 1983; Cooper et al., 1986; Moller, 1969; Hlekimo et al., 1975; Mylinski et al., 1985; Riise et al., 1982; Sheikholeslam et al., 1983; Riise et al., 1984.) These studies further validate the basis for the use of EMG in clinical dentistry. The patients examined in the above studies exhibited high levels of EMG postural activity and weak EMG activity during maximal bite in the intercuspal position. Occlusal therapy resulted insignificant improvement in symptoms and pain , and the successfully treated patients had significantly lower postural activity and significantly improved and symmetrical maximal bite activity.
Validity of Surface Electromyography (sEMG) in Orthodontics
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In summary, based on well controlled empirical and clincal studies that have been conducted in several universities over the past three decades thoughout the world, there is unequivocal evidence to strongly support the use of EMG for the evaluation and diagnosis of temporomandibular joint and occlusal disorders.
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