The role of bioelectronic instrumentation in the documentation and management of temporomandibular disorders
Temporomandibular disorders (TMDs) can affect the form and function of the temporomandibular joint, masticatory muscles and dental apparatus. Electronic measurement of mandibular movement and masticatory muscle function provides objective data that are defined by commonly accepted parameters in patients with TMDs; these data then can be used to design and monitor therapy and enhance treatment efficacy.
In this study, data on 3681 patients with TMD are presented; including electronic test data on 1182 treated patients with TMDs. Electronic jaw tracking was used to record mandibular movement and to compare the presenting and therapeutic dental occlusal positions. Electromyography was used to analyze the resting status of masticatory muscles and occlusal function at presentation and after therapeutic intervention. Transcutaneous electrical nerve stimulation therapy relaxed masticatory muscles and aided in the determination of a therapeutic occlusal position. The data show a positive correlation between the clinical symptoms of TMD and the presenting occlusion, accompanied by specific unhealthy muscle activity. A strong positive correlation also appears to exist between a therapeutic change in the dental occlusion to a neuromuscularly healthy position with use of a precision orthotic appliance and the significant relief of symptoms within 1 month and at 3 months. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1997; 83:91-100)
Temporomandibular disorders (TMDs) can effect the structure and function of the temporomandibular joints (TMJs), the dentition and its supporting structures, and the neuromuscular system.1 It has been hypothesized that TMDs arise from an imbalance in the relationship of the mandible and skull with the muscles that posture and move the mandible into dental occlusion.
The initial diagnosis of TMD and decision to institute treatment is based on a comprehensive history, clinical examination and the clinical judgment of the dentist. Recognition of the symptoms and clinical presentation of TMDs is valuable as it alerts dentists and medical practitioners to the presence of a physical, rather than a psychosocial illness.
Once a decision to institute treatment is made, the therapeutic plan should be based in part on an evaluation of the physical parameters of each patient's illness. This process may be significantly enhanced by the use of techniques that objectively measure mandibular and masticatory function, reducing reliance on subjective assessment of clinical observations, which is the historical norm. Rational treatment is based upon an understanding of the pathogenesis of the disease being treated, but it should also be based upon an accurate diagnosis. It has been shown repeatedly that clinical examination per se can lead to gross error in diagnosis.[2, 3]
Because TMDs most often manifest with a muscular abnormality, surface electromyography has been proposed for its analysis. Electromyography has demonstrated muscular hyperactivity with the mandible at rest and weak or asymmetric functional activity in patients with occlusal disharmony and a TMD.4-7 Maximum bite force and peak electrical activity during maximal bite are directly correlated,8-11 and both are statistically weaker in patients with neuromuscular disorders.12-14 The electrical activity of the resting temporalis and masseter muscles have been demonstrated to be greater in patients with these disorders than in subjects with no symptoms. Electromyographic testing has also demonstrated decreases in resting electrical activity in masticatory muscles following the use of transcutaneous electrical neural stimulation (TENS).
Electronic jaw tracking accurately records mandibular movements during opening and closing and can compare rest position of the mandible before and after TENS-induced muscle relaxation. Electronic jaw tracking also Identifies, in three dimensions, the present position of dental occlusion and a therapeutic occlusal position selected following muscular relaxation. Recordings at later stages of therapy are used to test the accuracy of the therapeutic occlusion. The creation of a neuromuscularly balanced therapeutic occlusion has been shown to result in a stable occlusal position with reduced resting activity of postural muscles and improved masticatory function.
This article retrospectively reviewed a series of 1182 treated patients (out of 3681 presenting patients) with TMDs who underwent surface electromyography and electronic jaw tracking prior to and following therapeutic intervention. Our purposes for collecting this case series were as follows:
- To assess the value of TENS in lowering electrical activity in hyperactive, weakened muscles at presentation and to assess changes in electrical activity during maximum voluntary clench;
- To determine the stability of functional improvement and occlusion after therapy to establish a neuromuscularly based occlusal position;
- To demonstrate the utility of electromyography, TENS and electronic jaw tracking in evaluating and treating patients with TMDs; and
- To evaluate the etiologic role of occlusion in TMDs and the effect of establishing a neuromuscular occlusion on the patients' symptoms.
The 1182 study participants who elected to be treated came from a much larger group of 3681 patients evaluated in both the Myofacial Pain/ Temporomandibular Joint Clinic of the New York Eye and Ear Infirmary (1156) and in private consultation (2525) between 1979 and 1996. The total examined population consisted of 804 male patients (mean age, 40 years) and 2879 female patients (mean age, 41 years), ranging in age from 5-95. The private patients who received comprehensive treatment included 277 male patients (mean age, 39 years) and 905 female patients (mean age, 38 years). The age group distribution of subjects in the treated population were similar to the total population examined.
During the period of data collection, the electronic instruments and testing procedures underwent developmental changes. Jaw tracking was used on all patients, but electromyography was added several years later. Data for some subjects were not available for calculation in this study either because of the nature of the data obtained with early electromyography or the absence of complete data.
The diagnosis of TMD was based on a patient symptom questionnaire, patient interviews by a dentist, intraoral and extraoral muscle examination, palpation and auscultation of TMJs, intraoral dental examination, and observation of mandibular movements for signs of dysfunction. All patients were examined and screened by the same investigator and were then evaluated by a bioelectronic testing protocol that involved electronic mandibular tracking, electromyographic measurements of muscle resting activity and functional ability, and TENS to achieve muscle relaxation. All testing was performed by the same technician and the same clinician. The procedures performed initially before treatment and at subsequent appointments are summarized in the table below.
The decline in the number of subjects evaluated at 3 months and at the institution of long-term resulted from natural attrition of the treated patient population in the private practice. A sub-group of patients who elected to undergo long-term therapy, such as restoration of posterior teeth or the use of a long-term removable orthosis, were also tested at the initiation of long term treatment (N=313).
Subjective symptom occurrence
The frequency of occurrence of major symptoms, including headaches, limited opening of the mouth, TMJ complaints related to joint pain and sounds, ear symptoms, facial pain, dental pain, and cervical and back pain was similar in the total examined patient population and the treated group.
Clinical examination findings
Clinical examination findings were comparable in both groups evaluated for extraoral and intraoral muscle tenderness to palpation, TMJ pain and joint sounds, the quality and fluidity of mandibular movement, and selected dental findings including worn incisal edges, deep overbite, depressed posterior teeth, missing posterior bite, midline discrepancy and severe overjet .
Electronic mandibular tracking
Mandibular movements during function, the rest position of the mandible, and movement of the jaw from rest to occlusion were evaluated with electronic mandibular tracking instruments. Three successive models of jaw tracking instruments were used during the period of this study (the Mandibular Kinesiograph [model K5-R] was used initially, K6 Diagnostic Instrument subsequently and the Computerized Mandibular Scan [model K6-I], Myotronics, Inc. Tukwila, Wash.). All of these instruments record mandibular position and movement by tracking the magnetic field created by a 0.1 oz magnet temporarily affixed to the gingiva below the mandibular incisors. The instruments recorded three-dimensional movements of the jaw with measurement accuracy of 0.1 mm near occlusion.19
Electromyographic recordings of the anterior temporalis, middle masseter, and anterior digastric muscles were made bilaterally using a bipolar surface electrodes. Measurements were made at muscle rest and during maximum functional clenching. From 1984 -1990 an EM-2 instrument was used to evaluate patients, and from 1991-1996 patients were evaluated on a K6-I instrument, which combines computerized mandibular scanning and electromyography.
Electromyography permits evaluation of resting muscle activity at presentation, after TENS-induced relaxation, and following a treatment intervention. Representative antagonistic muscle groups (mandibular elevators and depressors) were simultaneously monitored with jaw tracking, and this aided in the selection of both a mandibular resting position and a therapeutic mandibular treatment mandibular position. In addition, activity was analyzed to evaluate the effectiveness and symmetry of function of various recorded occlusal relationships, including the presenting habitual occlusion and a therapeutically corrected occlusion.18 Periodic objective testing during therapy enabled the dentist to make ongoing changes in treatment.
Transcutaneous electrical neural stimulation
The TENS used in this study (Myomonitor, Myotronics Inc., Tukwila, Wash.) delivered low frequency, low voltage stimulation to provide neuromuscular stimulation to effect muscle relaxation.20 The mandibular division of the trigeminal nerve located deep to the mandible was stimulated through the notch between the coronoid and condylar processes of the mandible. Stimulation was also delivered to the superficial fibers of the facial nerve that traverse the area. The instrument, which was powered by a 9 volt battery, used 2 active bilateral electrodes and a third grounding electrode placed on the rear of the neck.21 A repetitive stimulus of approximately 8-12 mA for 500 microseconds was delivered at 1.5 second intervals for a period of 60-90 minutes to produce rhythmic contractions of the muscles innervated by the mandibular division of the trigeminal nerve, and facial muscles innervated by the fibers of the facial nerve.
Baseline data collection consisted of electromyographic recordings of the anterior temporalis; middle masseter and anterior digastric muscles as the patient assumed a resting jaw position with the teeth not touching. Three sets of data were obtained and averaged. Data representing artifact such as tooth contact during swallowing were discarded. Maximum muscle activity during function was recorded by asking patients to maximally "clench" their teeth in their natural occlusion for three separate recordings, which were averaged.
The electronic mandibular tracking instrument recorded the postural position of the mandible at rest relative to the position at maximum intercuspation. The distance the mandible traversed from rest to occlusion and the trajectory of movement in three dimensions were also recorded.
TENS therapy was applied for 60-90 minutes. The threshold intensity of the stimulus was established for each patient as the minimal amplitude necessary to activate elevator muscles, causing a palpable motion of the patient's chin. The intensity of TENS was adjusted during use due to avoid overstimulation.
Following the period of TENS, another set of electromyographic readings at the mandibular rest position was made to determine if muscle relaxation had been achieved. Three sets of measurements were obtained and averaged. Clenching activity testing was deferred until after the bite registration was obtained.
Electronic mandibular tracking was then used to locate the rest position of the mandible relative to the natural intercuspal position; this served as a reference position for the selection of a treatment position. With slight increase in the intensity of the TENS, the mandible was moved on a neuromuscular trajectory and recorded on the tracking instrument. The point 1 mm from the TENS-induced and electromyographic- monitored rest position on that trajectory was identified as the neuromuscular occlusion position (the treatment position). An intraoral registration of this position was made with a soft low-resistance acrylic material (Bosworth Sapphire, H.J. Bosworth Co., Skokie, Ill). The bite registration was removed from the mouth in a rubbery semi-cured state and transferred to study casts for full curing. The hardened registration was returned to the patient's mouth for electromyographic verification of function; it was used for the fabrication of a mandibular appliance with a precise anatomic occlusal surface. The therapeutic appliance was designed to create an occlusal position close to the TENS-induced rest position of the mandible on a neuromuscularly stimulated trajectory of mandibular movement.
After the patient wore the appliance 24 hours a day for no fewer than three months, a second complete electronic testing study was performed in which the baseline data collection protocol was followed. Data were obtained on muscle resting activity, as well as maximum muscle electrical activity associated with clenching when the appliance was in place and with the cured acrylic bite registration was in place. The accuracy and coincidence of the therapeutic occlusal position provided by the orthotic appliance and by the bite registration were also tested.
Electromyographic activity during rest before and after TENS was compared, as was electromyographic maximum clench activity in various occlusal positions: the presenting occlusion and the treatment occlusal position with the bite registration inserted, and with the appliance in place. A statistical comparison of electromyographic resting muscular activity (masseter, temporalis and digastric) and maximal clench activity (masseter and temporalis) was performed using the Student t test. The data are presented with a level of confidence of p<0.001.
Electrical activity of muscles at rest At the pre-treatment baseline testing, electromyographic resting activity was elevated in all muscles at presentation compared with the after TENS and the activity recorded subsequently (3 months) after treatment activity for the same group of muscles. At baseline testing, temporalis activity was higher than masseter activity. The averaged combined bilateral activity (in microvolts) of temporalis, masseter and digastric was 2.70 ± 0.2. Following 60-90 minutes of TENS, activity in all muscles was significantly reduced to 1.7 ± 0.1, a 36.7% decrease from the presenting resting activity.
Electromyography performed after at least 3 months of full-time orthosis usage demonstrated that presenting combined bilateral resting activity was lower (2.3 ± 0.1) than presenting activity recorded at baseline testing. After 60-90 minutes of TENS, averaged combined activity was further reduced to 1.9 ± 0.3 (p<0.001). Despite inter-patient variability, the data demonstrate a significant difference in the average values for the test group at baseline and at after treatment. The amount of TENS-induced reduction in activity during the baseline test was of greater magnitude than that achieved in the second test following treatment.
Electrical activity of muscles in function (clench)
Bilateral electromyographic recordings of the anterior temporalis and middle masseter muscles recorded the electrical output associated with maximum voluntary clenching into either the patient's presenting occlusion or the occlusal position established with an acrylic bite registration and an orthotic appliance. Muscle electrical activity during maximum voluntary clench at baseline testing for the natural occlusal position was compared for the natural presenting occlusal position (before TENS) was compared to activity after TENS with the bite registration in place. At the in-treatment test, the comparison was made between the maximum clench on the orthotic (before TENS) and the activity measured after TENS with the original acrylic bite registration in place.
At the baseline test, bilateral recordings during maximum clench into the natural dentition averaged 75.2 ± 2.8 microvolts for the combined temporalis and masseter muscles (Table V). After 60-90 minutes of TENS, a bite registration in the neuromuscular occlusion position was obtained and tested. Electromyographic maximum muscle clench activity on the registration was significantly elevated for all muscles (averaged combined temporalis and masseter, 128.7 ± 3.5). The therapeutic alteration in occlusion by the bite registration showed a statistically significant increase in clench function of 53.6% for the temporalis and 89.8% for the masseter muscle.
At the in-treatment test, after at least 3 months of full time appliance usage, presenting maximum clench activity on the orthosis recorded for the combined temporalis and masseter was 91.6 ±4.5 and notably stronger for all muscles than the function recorded at baseline testing on the natural dentition. After TENS, maximum clench activity in the bite registration was further elevated for all muscles with averaged recordings for the combined temporalis and masseter muscles (131.9 ±5.6).
The change in temporalis activity between the clench into the orthosis (pre-TENS) and the bite registration (post-TENS) represents an increase of 37.7% in temporalis muscle and 50.0% in the masseter muscle, with a perpetuation of masseter dominance demonstrated at baseline test in the bite registration. Both occlusal positions at the second (in-treatment) test, orthosis and bite registration, represent therapeutic interventions. The natural dentition was not tested. Although the appliance lost some anatomic precision due to attrition with full-time usage over the 3 months, the bite registration had been preserved after its use in the fabrication of the appliance and remained unchanged since the baseline test.
Electronic mandibular tracking
Recordings of mandibular position and movement from rest to occlusion (in millimeters) at the incisal point were displayed as separate vertical, anterior/posterior and lateral components (vectors), together with sagittal and frontal recordings of trajectories of movement from rest to occlusion.
Freeway space analysis
Recordings were made at similar treatment times as electromyographic recordings. Initial Test was performed before and after TENS to compare differences between resting mandibular position and natural occlusion. After TENS, average freeway space increased by: +1.68 (vertical), +0. 48 (anterior/posterior) and +0.16 (lateral).
The same protocol was used at the in-treatment test before and after TENS. A smaller change in freeway space was shown after TENS compared with the baseline testing, because the corrective orthosis was in place.
A third test was performed for patients undergoing long term treatment.
Sagittal and frontal recordings permitted an analysis of the trajectory of mandibular movement from the rest position to occlusion under various occlusal conditions. At the baseline test trajectory from the rest position (after TENS) was recorded during voluntary closure into the natural presenting occlusion. This was compared with a TENS stimulated movement from the same rest position to the therapeutically selected neuromuscular occlusion position. A total of 19.8% of patients had natural occlusion on the neuromuscular trajectory, 77.2% had overclosure (excess vertical freeway space >2.0 mm), 65.4% had posterior displacement, and 25.3% had lateral displacement.
In the second in-treatment test, the trajectory of movement (after TENS) from rest to the appliance occlusal position was analyzed relative to the neuromuscular occlusal position. There was significant improvement in coincidence of occlusion on the neuromuscular trajectory (67%), less negative findings of over-closure (17.9%), posterior displacement (24.1%) and lateral displacement (9.4%). Oral appliances in full-time use undergo attrition losing some occlusal accuracy; because of this, in addition to simultaneous remodeling of muscle, joint and vascular supply during the treatment period, some subtle inaccuracy in the appliance can result. At the test of the long-term occlusal position, 93.4% of patients were on the neuromuscular trajectory, 1.6% had overclosure, and 1.31% and 0.2% had posterior and lateral displacement, respectively.
Subjective symptom improvement
Patients were asked to complete an in-office symptom evaluation questionnaire that listed their pre-treatment symptoms, by indicating Unchanged, Improved or Cured for each symptom at 1 and 3 months after the initiation of treatment. At 1 month, headaches were reported to be improved or cured in 67.9% of patients. Improvement or cure was also reported for temporomandibular joint symptoms (58.8%); ear symptoms (61.5%); facial pain (38.4%); cervicalgia (38.0%); and back pain (25. %). At 3 months, improvement or cure of headaches was noted by 78.4% of patients. At this time, improvement or cure was also noted for TMJ symptoms (68%); ear symptoms (69.5%); facial pain (42.6%); cervicalgia (43.6%); and back pain (29.2%).
Patients with TMDs have elevated electrical resting activity in the masticatory muscles as demonstrated by surface electromyography.15,22 Muscles in spasm accumulate lactic acid and adenosine diphosphate (ADP). Under normal circumstances, these metabolic waste products are cleared through the vascular channels by the intermittent contraction of the muscles. A muscle in 25% maximal contraction with no spasm has reduced blood supply, which results in accumulated metabolites.23 Low-voltage, low-frequency TENS stimulation, used as a neuromuscular stimulator, produces rhythmic contractions of the muscles in spasm, which may facilitate clearance of the waste products. This may be analogous to reducing muscle spasms by massaging (kneading) fatigued or cramped muscles.
Previous studies by Thomas24 reveal that after forced muscle fatigue, peak frequency spectra of masticatory muscles shift from 125 to 75 Hz. After a 20-minute resting interval, muscles of healthy patients return to peak frequency of 125 Hz. However, fatigued muscles of patients with TMDs return to resting peak frequencies only after TENS neuromuscular stimulation25, which suggests the utility of TENS for TMDs.
The electromyographic data in our case series suggests that TENS stimulation decreases muscle resting activity in the temporalis, masseter and digastric muscles. Before treatment, the temporalis had a higher average resting activity than the masseter muscle, presumably because of its primary role in mandibular posturing, whereas masseter muscles are primarily involved in generating compressive chewing force. The exception is in patients who brux, in whom masseter resting activity is elevated.26 TENS resulted in lower EMG activity after 60-90 minutes in the population tested.
Similar patterns of reduction of muscle resting activity with the same TENS instrument were observed in 172 subjects tested on an earlier EMG instrument, whose TMD treatment is reported in this article.18
Mandibular posturing and rest position
The mandible is held in a postural position by coordinated activity in antagonistic groups of muscles grouped as: elevators (temporalis, masseter and internal pterygoids) and depressors (external pterygoid, anterior digastric and anterior cervical). Because their resting activity is represented as minimal tonic electrical activity, absolute limits for assessing resting electromyographic activity cannot be set. In addition, increased resting activity may result from blood flow/muscle spindle feedback effects and not solely result from a primary muscle hypertonicity. The pterygoid muscles cannot be analyzed with surface electromyography used here.
Three-dimensional changes in the postural rest position of the mandible recorded on mandibular tracking after TENS were associated with electromyographic recorded reductions in postural muscle resting activity.27 Ideally, the rest position should have the lowest and most balanced resting activity level. Simultaneous electromyographic measurement of mandibular elevators and depressors is valuable in locating the mandibular rest position. Small changes in rest position and occlusion are therapeutically significant because the goal of treatment is to make the smallest modification in occlusal position necessary to effect a beneficial change in function and comfort. Data presented in the freeway space analysis section represent therapeutically significant measurements.
Neuromuscular occlusion position represents an occlusal position established by electrical neural stimulation of masticatory muscles, which caused movement of the mandible from a rest position on a stimulated trajectory. Identification of the mandibular rest position is used as a reference point for the selection of a neuromuscularly based occlusal position. 1,7,17-21 Physiologic ergonomic principles dictate that muscles function best at resting length.28 It has therefore been postulated that a physiologic occlusal position should exist near the electromyographically determined rest position. In this case series, the mandibular position associated with minimal resting activity in antagonistic muscles (anterior temporalis/ masseter and anterior digastric) is designated as the rest position of the mandible. The rest position, achieved by TENS, is determined by simultaneous electromyographically monitored resting activity and mandibular position on tracking. From the rest position, the TENS stimulation is increased slightly, causing the mandible to rise on a trajectory visualized on the jaw tracking computer. A therapeutic occlusal position is selected approximately 1 millimeter above rest on the neuromuscularly stimulated trajectory.29
If the proposed postulation is correct, muscle compressive strength should be improved when the patient functions in this neuromuscular occlusal position. One measure of this is the electrical activity generated during maximum clenching, a direct correlate of force produced.30
With neuromuscular occlusion, resting electromyographic activity remained reduced in comparison to the pretreatment (baseline) status, and the rest position of the mandible remained relatively stable even after additional TENS at the during- treatment tests and at long-term tests. The new occlusion was stable over time as demonstrated in the 3 month and long-term tests, which showed significant concurrence of the therapeutic occlusion with the originally selected position on the neuromuscular trajectory without overclosure or posterior or lateral displacement. The creation of a neuromuscular occlusion is demonstrated to be associated with significant reduction in subjective symptoms in the overwhelming majority of patients who were treated
It is acknowledged that in this retrospective clinical study there was no parallel control group because the study was conducted on patients who were treated in a private practice. The data obtained before treatment, however, serves as a control against treatment outcome.
Electromyography of masticatory muscles together with electronic jaw tracking are clinically useful and objective methods of quantifying physical components of TMDs in patients being screened for treatment.31,32 Recent electronic evaluations include electrosonography of the jaw joints, over the range of 0 to 600 Hz, which recognize the contribution of joint mechanics to the TMD condition and also quantitatively assesses pre- and posttreatment.
Electronic measurements create objective milestones in planning treatment and evaluating outcome.33 Improved relaxation and function obtained through occlusal alteration may reduce the predisposition to future TMDs by reducing accommodative requirements of muscle and mandibular function. The goals of treatment are the elimination of pain and dysfunction and the establishment of healthy functioning relationships among the teeth, TMJ and neuromusculature. The creation of a neuromuscularly based occlusion was shown to accomplish these goals.
The specific therapeutic philosophy of intervention and the decision to institute treatment remain the decision of the dentist, but they can now be based on history, clinical examination and objective test measurements. The ability to measure transcends treatment philosophies and has become a common language that can be used by clinicians to evaluate and compare different management strategies, outcomes, and the need to continue, modify or discontinue treatment. Successful treatment incorporates physiological improvement and patient subjective symptom improvement.
The data from this clinical study support the hypothesis that occlusion has a role in the cause and management of TMDs. The establishment of a neuromuscular occlusion using electronic instruments was associated with resolved symptoms in a treated population with TMDs.
- Cooper BC. Craniomandibular Disorders, in Management of Facial Head and Neck Pain, BC Cooper and F E Lucente, (Eds.), WB Saunders, Philadelphia, 1989; 153-254.
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- Bakke, M., Moller E.: Distortion of maximal elevator activity by unilateral premature tooth contact, Scand J Dent Res 1980; 80:67-75.
- Riise C, Sheikloleslam A. The influence of experimental interfering occlusal contacts on the activity of the anterior temporal and masseter muscles during mastication. J Oral Rehabil 1984; 11:325-333.
- Jarabak J R. An electromyographic analysis of muscular and temporomandibular joint disturbances due to imbalances in occlusion, Angle Orthod 1956; 26(3):170-190.
- Jankelson B. Neuromuscular aspects of occlusion: Effects of occlusal position on the physiology and dysfunction of the mandibular musculature. Dent Clin North Am 1979; 23:157-168.
- Milner-Brown HS. The relationship between the surface electromyography and muscular force. J Physiol (Great Britain) 1975; 246:549-569.
- Bigland B. and Lippold OC J. The relation between force, velocity and integrated activity in human muscles, J. Physiol (Great Britain) 1954; 123:214-224.
- Ahlgren J. and Owall AB. Muscle activity and chewing force: A polygraphic study of human mandibular movements, Arch Oral Biol 1970; 15:271-280.
- Kawazoe Y, Kotani H and Hamada T. Relation between integrated electromyographic activity and biting force during voluntary isometric contraction in human masticatory muscles. J. Dent Res 1979; 58:1440.
- Helkimo E, Carlsson G, Carmeli Y. Bite force in patients with functional disturbances of the masticatory system. J. Oral Rehabil 1975; 2:397-406.
- Molin C. Vertical isometric muscle forces of the mandible: A comparative study of subjects with and without manifest mandibular pain dysfunction syndrome. Acta Odontol Scand 1972; 30:485-499.
- Kotani H, Kawazoe Y, Hamada T, et al. Quantitative electromyographic diagnosis of myofascial pain dysfunction syndrome, J Prosthet Dent 1980; 43(4):450-456.
- Gervais R O, Fitzsimmons G W and Thomas NR. Masseter and temporalis electromyographic activity in asymptomatic, subclinical and temporomandibular joint dysfunction patients, J. Craniomand Pract 1989; 7(1):52-57.
- Wessberg GA, Carroll WL, et al. Trancutaneous electrical stimulation as an adjunct in the management of myofascial pain dysfunction syndrome. J. Prosthet Dent 1981; 45(3):307-314.
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- Jankelson B, Sparks S, Crane, P, et al. Neural conduction of the myomonitor stimulus: A quantitative analysis. J Prosthet Dent 1975; 34(3):245-253.
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- Rasmussen OC, Bonde-Petersen F, et al. Blood flow in human mandibular elevators at rest and during controlled biting. Arch Oral Biol 1977; 22:8-9, pp.539-543.
- Thomas NR. The effect of fatigue and TENS on the EMG mean power frequency, Bergamini M, Ed, Pathophysiology of Head and Neck Musculoskeletal Disorders. Front Oral Physiol., Basil, Karger 1990; Vol 7:162-170.
- Kawazoe Y, Kotani H., Mitani T, et al. The slopes of the fatigued muscle voltage tension curves decreased to a greater degree with percutaneous stimulation than with rest alone. Arch Oral Biol 1981; 26:795-801.
- Hamada T, Kotani H, Kawazoe Y, et al, Effect of occlusal splints on the EMG activity in masseter and temporal muscles in bruxism with clinical symptoms, J Oral Rahabil 1982; 9:119-123.
- Konchak P, Thomas N, Lanigan D, Devon R. Freeway space measurement using mandibular kinesiograph and EMG before and after TENS. Angle Orthodont Oct 1988; 343-350.
- Guyton AC. Textbook of Medical Physiology, 6th ed., Philadelphia, W.B.Saunders Co. 1981 p 137.
- Cooper B. The role of bioelectronic Instruments in the management of TMD, New York State Dental Journal, Nov.1995;48-53.
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- Kawazoe Y, Kotani H, Hamada T, et al. Effect of occlusal splints on the electromyographic activities of masseter muscles during maximum clenching in patients with myofascial pain dysfunction syndrome. J Prosthet Dent 1980; 43:578-580.