Reliability of surface electromyography of the masseteric and anterior temporal areas

Can the subject reliably reproduce maximum voluntary contraction of temporalis and masseter muscles in surface EMG?

OBJECTIVE

To evaluate the repeatability of the surface EMG variables of myoelectric signals from the masseter and temporalis muscles according to three methods to induce maximum voluntary contraction (MVC) in healthy adults.

METHODS

Thirty healthy young subjects performed the following three MVC tasks three times each in three sessions on the same day without replacing surface electrodes: clenching the teeth (MVCIC) and biting down on two cotton rolls bilaterally with the posterior teeth (MVCBP) or first molars (MVCB6).

RESULTS

The intra-class correlation coefficient (ICC) of the amplitudes during the three MVC tasks ranged from 65 to 79%. The ICCs of the spectral variables ranged from 78 to 86%. The ICCs of the asymmetry index of the masseter ranged from 77 to 86%, and those of the activity index ranged from 68 to 90%.

CONCLUSION

The surface EMG measurements according to the three MVC methods exhibited good to excellent reproducibility.

Effect of transcutaneous electrical nerve stimulation (TENS) on the electromyographic activity of human masticatory muscles in young people with normal occlusion

STATEMENT OF PROBLEM

Transcutaneous electrical nerve stimulation (TENS) has been used in several clinical areas. However, the effect of TENS on the masticatory muscles of young individuals with normal occlusion remains unclear.

PURPOSE

The purpose of the study was to assess the effect of TENS on the surface electromyographic (sEMG) activity of masticatory muscles in a young population with normal occlusion.

MATERIAL AND METHODS

Twenty residents (5 men and 15 women, mean 24.27 ±2.59 years) of Dalian Stomatological Hospital were enrolled as the study participants. A trained operator collected the required information from the participants. The experiment was divided into 3 stages: pre-TENS acquisition, TENS application, and post-TENS acquisition. The pre-TENS stage was performed using surface electromyography (sEMG) (Myotronics Inc) to acquire the potential values of masticatory muscles in the following 3 states 5 times each: resting, intercuspal occlusion (ICO), and maximum voluntary clench (clenching). The potential values of the anterior of temporalis (TA), the masseter (MM), the sternocleidomastoid (SCM), and the anterior digastric (DA) muscles were collected in the resting state, and TA and MM were collected in the ICO and clenching states. During the TENS application phase, a TENS Unit device (J5 Myomonitor) (J5) was used on each participant for 45 minutes. The post-TENS acquisition phase involved the same procedure as the pre-TENS phase. The experimental data were recorded, and the normality of each group was analyzed using the Shapiro-Wilk test in a statistical software program (IBM SPSS Statistics, v26.0). The paired-sample t test was used to compare the differences in the mean values of sEMG and the asymmetry index (As); the independent-sample t test was used to compare the activity index (Ac) and torque index (To) (α=.05).

RESULTS

Significant differences were observed in the mean potential values of TA, MM, LSCM, and RDA before and after TENS in the resting state and RTA, LMM, and RMM before and after TENS in the clenching state (P<.05). Moreover, although AsDA values showed a significant difference (P=.027) before and after TENS in the resting state, the differences in As values for the other muscles in the resting state were statistically similar. Furthermore, in each state, the mean values of Ac and To after TENS showed no significant differences before and after TENS (P>.05).

CONCLUSIONS

The resting EMG values of the TA and MM differed significantly before and after TENS. After TENS, the resting EMG activity decreased, whereas the functional EMG activity tended to increase.

Uses of electromyography in dentistry: An overview with meta-analysis

OBJECTIVE

The purpose of this study was to review the uses of electromyography (EMG) in dentistry in the last few years in related research. EMG is an advanced technique to record and evaluate muscle activity. In the previous days, EMG was only used for medical sciences, but now EMG playing a tremendous role in medical as well as dental sector.

MATERIALS AND METHODS

Several electronic databases such as Google Scholar, PubMed, Science Direct, and Web of Science were systematically searched for studies published until July 2015.

RESULTS

EMG can be used in both diagnosis and treatment purpose to record neuromuscular activity. In dentistry, we can utilize EMG to evaluate muscular activity in function such as chewing and biting or parafunctional activities such as clenching and bruxism. In case of TMJ and myofascial pain disorders, EMG widely is used in the last few years.

CONCLUSIONS

EMG is one of biometric tests that occur in the modern evidence-based dentistry practice.

An assessment of the usefulness of Kinesiograph as an aid in the diagnosis of TMD: a review of Manfredini et al.'s studies

AIM

Performing a literature review of publications by Dr. Manfredini et al. related to their temporomandibular joint (TMJ) injection therapy outcome with conclusions on the clinical utility of computerized measurement devices used in the management of temporomandibular disorders (TMDs). In addition, reviewing their published opinion on an occlusion: TMD versus a biopsychosocial paradigm for TMD. Manfredini et al. authored an article published in the Journal of the American Dental Association (JADA) 2013, "An Assessment of the usefulness of jaw kinesiography in monitoring temporomandibular disorders," the most recent of 12 articles. In all studies, subjects received TMJ injections with an objective measurement outcome criterion; increased maximum mouth opening (MMO) and subjective symptom improvement of pain and chewing function. In the 2013 JADA article, the Mandibular Kinesiograph, referred to as KG, measured MMO before and after therapy. In 11 prior articles, all subject groups with limited mouth opening exhibited very significant increased MMO post-treatment, documenting treatment success using the same 2013 protocol. The 2013 study showed a 1·1 mm improved MMO, described as insignificant. The authors did not critique or explain the aberrant, skewed 2013 outcome data contrasted with their prior studies, which showed overwhelmingly significant increased MMO. Instead, they concluded that the MMO recording device was clinically useless. This motivated a literature review of the authors' TMD publications.

CONCLUSION

The publications by Manfredini et al. recognized proponents of the psychosocial model of TMD, including the 2013 article, appear to be part of a campaign denying an occlusion: TMD relationship and disparaging the specific computerized measurement devices and the dentists using them in the management of their TMD patients using neuromuscular occlusion dental treatment.

Parameters of an Optimal Physiological State of the Masticatory System: The Results of a Survey of Practitioners Using Computerized Measurement Devices

While bioelectronic instruments have been available for nearly 30 years to assist dentists in day-to-day evaluations of patients' masticatory systems, little guidance has been published to support physiological norms or ideals. An electronic questionnaire was developed and administered to an international group of dentists familiar with the use of bioelectronic instrumentation. Respondents were asked to provide feedback on the norms or ideal parameters of jaw movement, masticatory muscle function with electromyography, and joint sounds through electrosonography that they use in guiding evaluation and treatment of patients with temporomandibular disorders, neuromuscular occlusion, and orthodontics. Surveys were collated to determine areas of consensus. Out of 150 surveys, 55 responses were received from dentists representing nine different countries. Sixty percent of the respondents reported treating more than 150 cases in the past five years using bioelectronic testing. While experience ranged from 2-30 years with different types of devices, average experience was longer with mandibular/jaw tracking (mean 15.3 years) and electromyography (mean 14.1 years) than with electrosonography (mean 7.0 years). Parameters proposed as norms or ideals for electromyographic rest and clench values, and mandibular tracking (velocity, freeway space, and trajectory to closure) were very consistent. Although a smaller number of respondents reported utilization of electrosonography, their criteria for data significance and tissue-type genesis of joint sounds were consistent. While the intra-patient variability may limit the diagnostic use of bioelectronic instruments, the current study demonstrates that through decades of experience, dentists have independently arrived at very consistent definitions of an ideal physiology that can be used to guide treatment.

Coordination of the non-paretic leg during hemiparetic gait: expected and novel compensatory patterns

BACKGROUND

Post-stroke hemiparesis is usually considered a unilateral motor control deficit of the paretic leg, while the non-paretic leg is assumed to compensate for paretic leg impairments and have minimal to no deficits. While the non-paretic leg electromyography (EMG) patterns are clearly altered, how the non-paretic leg acts to compensate remains to be established.

METHODS

Kinesiological data were recorded from sixty individuals with chronic hemiparesis (age: 60.9, SD=12.6 years, 21 females, 28 right hemiparetic, time since stroke: 4.5 years, SD 3.9 years), divided into three speed-based groups, and twenty similarly aged healthy individuals (age: 65.1, SD=10.4 years, 15 females). All walked on an instrumented split-belt treadmill at their self-selected speed and control subjects also walked at slower speeds matching those of the persons with hemiparesis. We determined the differences in magnitude and timing of non-paretic EMG activity relative to healthy control subjects in four pre-defined regions of stance phase of the gait cycle.

FINDINGS

Integrated EMG activity and EMG timing in the non-paretic leg were different in many muscles. Multiple compensatory patterns identified included: increased EMG output when the muscle was typically active in controls and novel compensatory EMG patterns that appeared to provide greater propulsion or support with little evidence of impaired motor performance.

INTERPRETATION

Most novel compensations were made possible by altered kinematics of the paretic and non-paretic leg (i.e., early stance plantarflexor activity provided propulsion due to the decreased advancement of the non-paretic foot) while others (late single limb stance knee extensor and late stance hamstring activity) appeared to be available mechanisms for increasing propulsion.

Influence of different upper cervical positions on electromyography activity of the masticatory muscles

OBJECTIVE

The aim of this study was to determine the activity of the masseter and anterior temporalis muscles in relation to different positions of the upper cervical spine during maximal voluntary isometric clenching by surface electromyography (EMG).

METHODS

This was a cross-sectional study with a repeated-measures design performed using 25 asymptomatic subjects (13 female and 12 male; mean age, 31 years; SD, 8.51). The EMG activity of the masseter and anterior temporalis muscles was recorded bilaterally during maximal clenching at neutral position and during extension, flexion, ipsilateral lateral flexion, contralateral lateral flexion, and ipsilateral and contralateral rotations in maximal flexion. In addition, the upper cervical range of motion and mandibular excursions were assessed. The EMG activity data were analyzed using a 3-way analysis of variance in which the factors considered were upper cervical position, sex (male and female), and side (right and left), and the hypothesis of importance was the interaction side x position.

RESULTS

The 3-way analysis of variance detected statistically significant differences between the several upper cervical positions (F = 13.724; P < .001) but found no significant differences for sex (F = 0.202; P = .658) or side (F = 0.86; P = .53) regarding EMG activity of the masseter muscle. Significant differences were likewise observed for interaction side x position for the masseter muscle (F = 12.726; P < .001). The analysis of the EMG activity of anterior temporalis muscle did not produce statistically significant differences (P > .05).

CONCLUSION

This preliminary study suggests that the upper cervical movements influence the surface EMG activity of the masseter muscle. These findings support a model in which there are interaction between the craniocervical and the craniomandibular system.

Temporomandibular disorders: A position paper of the International College of Cranio-Mandibular Orthopedics (ICCMO)

PURPOSE

Two principal schools of thought regarding the etiology and optimal treatment of temporomandibular disorders exist; one physical/functional, the other biopsychosocial. This position paper establishes the scientific basis for the physical/functional. THE ICCMO POSITION: Temporomandibular disorders (TMD) comprise a group of musculoskeletal disorders, affecting alterations in the structure and/or function of the temporomandibular joints (TMJ), masticatory muscles, dentition and supporting structures. The initial TMD diagnosis is based on history, clinical examination and imaging, if indicated. Diagnosis is greatly enhanced with physiologic measurement devices, providing objective measurements of the functional status of the masticatory system: TMJs, muscles and dental occlusion. The American Alliance of TMD organizations represent thousands of clinicians involved in the treatment of TMD. The ten basic principles of the Alliance include the following statement: Dental occlusion may have a significant role in TMD; as a cause, precipitant and/or perpetuating factor. Therefore, it can be stated that the overwhelming majority of dentists treating TMD believe dental occlusion plays a major role in predisposition, precipitation and perpetuation. While our membership believes that occlusal treatments most frequently resolve TMD, it is recognized that TMD can be multi faceted and may exist with co-morbid physical or emotional factors that may require therapy by appropriate providers. The International College of Cranio-Mandibular Orthopedics (ICCMO), composed of academic and clinical dentists, believes that TMD has a primary physical/functional basis. Initial conservative and reversible TMD treatment employing a therapeutic neuromuscular orthosis that incorporates relaxed, healthy masticatory muscle function and a stable occlusion is most often successful. This is accomplished using objective measurement technologies and ultra low frequency transcutaneous electrical neural stimulation (TENS).

CONCLUSION

Extensive literature substantiates the scientific validity of the physical/functional basis of TMD, efficacy of measurement devices and TENS and their use as aids in diagnosis and in establishing a therapeutic neuromuscular dental occlusion.

CLINICAL IMPLICATIONS

A scientifically valid basis for TMD diagnosis and treatment is presented aiding in therapy.

Electrical activity of the anterior temporal and masseter muscles in mouth and nasal breathing children

Mouth breathing has been associated with severe impact on the development of the stomatognathic system.

Aim

This paper aims to analyze the electromyographical findings and patterns of electrical activity of the anterior temporal and masseter muscles in mouth and nasal breathing children.

Materials And Method

The patients were divided into two groups: mouth breathers (n=17) and nasal breathers (n=12). The children underwent bilateral electromyographic examination of the anterior temporal and masseter muscles at maximal intercuspal position and during usual mastication. A Myosystem Br-1 electromyograph with 12 acquisition channels, amplification with total gain of 5938, rate of acquisition of 4000 Hz, and band-pass filter of 20-1000Hz, was used in the examination. The signal was processed in Root Mean Square(RMS), measured in µV, analyzed and expressed as a normalized percentage. The data set was statistically treated with the T-test (Student).

Results

The observed level of electrical activity in the mouth breathing (MB) group was lower in all analyzed muscles, with statistical significance found only in the left temporal muscle; during mastication, mouth breathers also presented increased electrical activity on the right side and on the temporal muscle.

Conclusion

Mouth breathing impacts the electrical activity of the muscles studied at maximal intercuspal position and during usual mastication.

Atividade eletromiográfica dos músculos temporal anterior e masseter em crianças respiradoras bucais e em respiradoras nasais

A respiração bucal tem sido estudada por causar sérios efeitos no desenvolvimento do sistema estomatognático. OBJETIVO: Estudar, através da análise eletromiográfica, o padrão de atividade elétrica dos músculos temporal anterior e masseter em crianças com respiração bucal, comparando-os com o de crianças com respiração nasal. MATERIAL E MÉTODO: Foram estudados dois grupos de crianças: 17 respiradoras bucais (RB) e 12 respiradoras nasais (RN). As crianças foram submetidas à avaliação eletromiográfica bilateral dos músculos supracitados nas situações de máxima intercuspidação e mastigação habitual. Utilizou-se o eletromiógrafo Myosystem Br-1, com 12 canais de aquisição, amplificação com ganho total de 5938, taxa de aquisição de 4000Hz e filtro passa-faixa de 20-1000Hz. O sinal foi processado em RMS, mensurado em µV e analisado e expresso em %, normalizado. Os dados foram tratados estatisticamente através do Teste t (Student). RESULTADOS: Observou-se que o nível de atividade elétrica do grupo RB foi inferior para todos os músculos e estatisticamente significante somente para o temporal esquerdo; os respiradores bucais apresentaram predomínio de atividade elétrica no lado direito e no músculo temporal durante a mastigação habitual. CONCLUSÃO: A respiração bucal interferiu na atividade elétrica dos músculos estudados nas situações funcionais de máxima intercuspidação e mastigação habitual.

Surface electromyography in the assessment of jaw elevator muscles

Surface electromyography (EMG) allows the non-invasive investigation of the bioelectrical phenomena of muscular contraction. The clinical application of surface EMG recordings has been long debated. This paper reviews the main limitations and the current applications of the surface EMG in the investigation of jaw elevator muscles. Methodological factors associated with the recording of the surface EMG may reduce the reliability and sensitivity of this technique and may have been the cause of controversial results reported in different studies. Despite these problems, several clinical applications of surface EMG in jaw muscles are promising. Moreover, technological advances in signal detection and processing have improved the quality of the information extracted from the surface EMG and furthered our understanding of the anatomy and physiology of the stomatognathic apparatus.

Establishment of a temporomandibular physiological state with neuromuscular orthosis treatment affects reduction of TMD symptoms in 313 patients

The objective of this investigation was to test the hypothesis that alteration of the occlusions of patients suffering from temporomandibular disorders (TMD) to one that is neuromuscularly, rather than anatomically based, would result in reduction or resolution of symptoms that characterize the TMD condition. This hypothesis was proven correct in the present study, where 313 patients with TMD symptoms were examined for neuromuscular dysfunction, using several electronic instruments before and after treatment intervention. Such instrumentation enabled electromyographic (EMG) measurement of the activities of the masticatory muscles during rest and in function, tracking and assessment of various movements of the mandible, and listening for noises made by the TMJ during movement of the mandible. Ultra low frequency and low amplitude, transcutaneous electrical neural stimulation (TENS) of the mandibular division of the trigeminal nerve (V) was used to relax the masticatory muscles and to facilitate location of a physiological rest position for the mandible. TENS also made it possible to select positions of the mandible that were most relaxed above and anterior to the rest position when the mandible was moved in an arc that began at rest position. Once identified, the neuromuscular occlusal position was recorded in the form of a bite registration, which was subsequently used to fabricate a removable mandibular orthotic appliance that could be worn continuously by the patient. Such a device facilitated retention and stabilization of the mandible in its new-found physiological position, which was confirmed by follow up testing. Three months of full-time appliance usage showed that the new therapeutic positions achieved remained intact and were associated with improved resting and functioning activities of the masticatory muscles. Patients reported overwhelming symptom relief, including reduction of headaches and other pain symptoms. Experts consider relief of symptoms as the gold standard for assessment of effectiveness of TMD treatment. It is evident that this outcome has been achieved in this study and that taking patients from a less to a more physiological state is an effective means for reducing or eliminating TMD symptoms, especially those related to pain, most notably, headaches.

The clinical usefulness of surface electromyography in the diagnosis and treatment of temporomandibular disorders

BACKGROUND

This article presents a comprehensive review of the recent literature regarding the scientific support for the use of surface electromyography (SEMG) in diagnosing and treating temporomandibular disorders (TMDs).

TYPES OF STUDIES REVIEWED

The authors conducted a Medline search involving human studies using the key words "surface electromyography or electromyography" and "masticatory muscles or temporomandibular disorders or craniomandibular disorders." They also reviewed relevant articles regarding the clinical usefulness of SEMG based on reliability, validity, sensitivity and specificity, as well as additional references included in some of the articles.

RESULTS

The clinical use of SEMG in the diagnosis and treatment of TMD is of limited value when one considers reliability, validity, sensitivity and specificity as measurement standards. SEMG does not appear to contribute any additional information beyond what can be obtained from the patient history, clinical examination and, if needed, appropriate imaging.

CONCLUSIONS

Clinically, the determination of the presence or absence of TMD does not appear to be enhanced by the use of SEMG. However, the modality may be useful in a meticulously controlled research setting.

CLINICAL IMPLICATIONS

SEMG has limited value in the detection or management of TMD and in some instances may lead to unnecessary dental therapy as a solution for those disorders.

An electromyographic evaluation of the bilateral symmetry and nature of masticatory muscle activity in jaw deformity patients during normal daily activities

This study was designed to investigate the nature of masticatory muscle activity and the balance in the bilateral symmetry of the masticatory muscle activity in jaw deformity patients. Fifteen patients (19.9 +/- 5.3 years) with lateral shift of the mandible caused by transverse craniofacial deformity and 15 controls (28.6 +/- 1.9 years) were used as the subjects in this study. Surface electromyographic (EMG) activities were recorded from the bilateral masseter and anterior temporal muscles during daytime (142 min, including mealtime) and sleep (142 min). The averaged rectified EMG values were normalized with reference to the EMG amplitude induced by a 98-N bite force. Bilateral symmetry of masseter and anterior temporal muscle activities was examined using an asymmetry index (AI) for both the controls and the patients. The normalized activities of the masseter and anterior temporal muscles during normal daily activities were lower in patients than in the controls. Asymmetry indices in patients were significantly greater during usual daytime activities and sleep for the anterior temporal muscle and significantly smaller during sleep for the masseter muscle as compared with the controls. The results show that masticatory muscle activity is lower in these jaw deformity patients in association with more prominent asymmetry of anterior temporal muscle activity than in the controls. It is suggested that these findings are highly relevant to occlusal interference and instability because of malocclusion and lateral mandibular deviation.

Masticatory muscle activity assessment and reliability of a portable electromyographic instrument

STATEMENT OF PROBLEM

Masticatory muscle hyperactivity is thought to produce muscle pain and tension headaches and can cause excessive wear or breakage of restorative dental materials used in the treatment of prosthodontic patients. The quantification and identification of this type of activity is an important consideration in the preoperative diagnosis and treatment planning phase of prosthodontic care.

PURPOSE

This study investigated the quantification process in complete denture/overdenture patients with natural mandibular tooth abutments and explored the reliability of instrumentation used to assess this parafunctional activity.

MATERIAL AND METHODS

The nocturnal EMG activity in asymptomatic complete denture/overdenture subjects was assessed with and without prostheses worn during sleep. Because of the large variance within and between subjects, the investigators evaluated the reliability of the 3 instruments used to test nocturnal EMG activity in the sample.

RESULTS

Electromyographic activity data of denture/overdenture subjects revealed no differences between prostheses worn versus not worn during sleep but demonstrated a very large variance factor. Further investigation of the instrumentation demonstrated a consistent in vitro as well as in vivo reliability in controlled laboratory studies.

CONCLUSION

The portable EMG instrumentation used in this study revealed a large, uncontrollable variance factor within and between subjects that greatly complicated the diagnosis of parafunctional activity in prosthodontic patients.

Effect of unilateral posterior crossbite on the electromyographic activity of human masticatory muscles

Studies dealing with the electromyographic activity of masticatory muscles in patients with unilateral posterior crossbite are infrequent. The purpose of this study was to assess the electromyographic pattern of masticatory muscles at rest position, during swallowing, and during mastication, in 30 subjects with right posterior crossbite and to compare them to 30 normocclusive subjects. The 2 groups were matched according to age, gender, skeletal Class I, and mesofacial growth pattern. Electromyographic activity of right and left anterior temporalis, posterior temporalis, masseter, and anterior digastric muscles was recorded at rest position, while swallowing water, and while chewing. Disposable bipolar surface electrodes were used in both groups. Data were compared between groups and between right and left sides within each group. The results revealed that the posterior temporalis of the non-crossbite side was more active than that of the same side in subjects with crossbite at rest position and during swallowing. The activity of both anterior digastrics was higher in the crossbite subjects during swallowing. During chewing the right masseter muscle was less active in the crossbite patients than in normocclusive subjects. The results obtained during chewing indicate a bilateral masticatory pattern in both groups.

Effects of spring-loaded posterior bite-block appliance on masticatory muscles

The effects of spring-loaded posterior bite-blocks on masticatory muscles were investigated to evaluate the correlation between masticatory muscles and craniofacial form in long-faced children. The appliance was used in 10 subjects (6 girls and 4 boys) with a chronological mean age of 10.40 +/- 1.12 years for the treatment of skeletal anterior open bite. Electromyographic activity of the anterior and posterior temporal and masseter muscles was recorded before and after treatment during postural position, maximal biting, chewing, swallowing, postural position with the appliance in the mouth, and maximal biting with the appliance in the mouth. After treatment, increases in SNB and overbite (P <.05, P <.001, respectively) and decreases in ANB, SNGoAr, and overjet parameters were found to be statistically significant (P <.05, P <.01). When the measurements related to muscle activity were examined, increases in anterior temporal postural (P <.05), anterior temporal chewing (P <.01), masseter chewing (P <.05), posterior temporal chewing (P <. 05), and masseter swallowing (P <.01) were found to be statistically significant. A positive correlation was found between ANB and anterior temporal postural and a negative correlation between SNGoAr and masseter swallowing. The increase in muscle activities was considered to occur as a result of the appliance used.

Muscle activity with the mandibular lip bumper

This prospective study was designed to measure muscle activity with lip bumper treatment. Surface electromyography was used to measure upper and lower lip activity with and without the appliance in place. Measurements were taken on a sample of 25 adolescent patients (age range, 10 to 17 years) before and after 12 months of lip bumper treatment. Recordings included a closed lip rest position, swallowing of water, and speech of the words "church," "phone," and "pop." Insertion of the lip bumper at the pretreatment recording resulted in significantly increased activity of the upper and lower lips at rest (P <.001) and while swallowing (P <.05), whereas the response for speech was variable. Pretreatment and posttreatment muscle activity measurements of the lower lip were compared to determine whether 12 months of treatment with the appliance resulted in muscle adaptation. The initial increase of muscle activity with insertion of the appliance for the closed lip rest position and for swallowing was not followed by a decrease during the treatment period. There were significant differences in muscle activity when comparing the "new" equilibrium introduced by the lip bumper to the "old" pretreatment equilibrium without the appliance. Although it was shown that the insertion of the appliance had a significant influence on muscle activity of the lips, the results of this study did not indicate adaptation of the lower lip to the appliance over the treatment period.

Coordinated electromyographic activity of the human masseter and temporalis anterior muscles during mastication

The present report aimed at evaluating the within- and between-subject electromyographic coordination between the masseter (M) and temporalis anterior (T) muscles during the performance of a standardized chewing task. Electromyographic activity of M and T muscles was recorded in 60 young healthy adults (30 men, 30 women) during two 15-s unilateral mastications of gum. Left-right differential potentials (delta M = MR-ML, delta T = TR-TL) were computed and the square root of (delta M2 + delta T2) moduli were calculated. The maximum modulus relative to each masticatory cycle was located, and each modulus and differential potential were expressed as a % of the maximum modulus for each subject and chewing trial. For each subject and chewing side, the masticatory frequency was computed, and statistics of the moduli as %s of the maximum were determined by means of bivariate analysis. Within-subject repeatability of the unilateral chewing patterns was good. Mean population values for the modulus position (bivariate analysis), chewing frequency, and maximum modulus of the differential potentials (univariate statistics) were computed. A significant gender difference was found for the masticatory frequency, with larger values in men than in women. Conversely, no gender or side differences were found for the mean values of the maximum modulus or for the mean position of the percentage moduli. The chewing test applied allowed the evaluation of the neuromuscular coordination during the performance of a standardized physiologic activity. In particular, it quantified the within-subject and chewing side repeatability of the muscular pattern.

Pilot study of the heterogeneous patterns of masticatory muscle coordination in nonpatient population

This pilot study characterized coordination patterns of the muscles of mastication during voluntary chewing in a nonclinical population. Dental students (n = 177) who did not exhibit symptoms of temporomandibular disorder were screened by a comprehensive muscle and temporomandibular joint palpation examination. A group of 44 students was identified on the basis of the presence of four or more tender points indicated during palpation. This group was further subgrouped by the absence (group A-1) and presence (group A-2) of temporomandibular joint clicking. Five volunteers from groups A-1 and A-2 and five volunteers without any palpation tenderness and joint clicking (control group) were examined by simultaneous recordings of electromyography of bilateral masseter and posterior one third of the temporalis muscles and by mandibular kinesiography. The electromyographic coordination pattern for the control group demonstrated predominantly working masseter muscle activity. This "predominant working masseter" pattern was not observed in groups A-1 or A-2. Additional analyses of the recordings indicated that a hypoactive tendency of the working side masseter muscle particularly outlasting the tooth contact was present in group A-1, whereas significant hyperactivity of the posterior one third of the temporalis was present in group A-2. The data suggested that an asymptomatic nonpatient population may be functionally diverse.

Jaw-closing muscles: electromyographic activity of human subjects with reduced periodontal support

The aim of this study was to compare the electromyographic (EMG) activity of jaw-closing muscles of individuals with normal and reduced periodontal bone support. Fourteen adult subjects with more than 24 remaining teeth and low levels of periodontal inflammation, were selected for the study. Subjects of the control group had 90% of the periodontal bone support left, while other subjects presented a reduction of 52% of the original periodontal bone. Chewing experiments were performed using silicone tablets, carrots and white bread. The EMG of masseter and anterior temporal muscles was performed bilaterally, using bipolar surface electrodes, and the EMG amplitude was full wave rectified, integrated and the area extension under the curve was used to access muscle activity. The results of the chewing experiments did not show any statistically significant difference in the EMG activity of the study groups, irrespective of the chewing stuff. The height of periodontal bone support did not seem to influence the electroactivity of jaw-closing muscles, indicating that reduced periodontal support might equally be able to withstand masticatory loads. Hence, individuals with reduced periodontal bone support revealed a similar EMG activity compared to subjects with normal periodontal bone support.

Electromyographic activity of human masticatory muscles in normal young people. Statistical evaluation of reference values for clinical applications

Electromyographic activity of anterior temporal and masseter muscles was measured in 92 young healthy men and women with sound dentitions during rest position, contact in centric occlusion and clench. Male and female mean potentials were similar except in clench, where males had higher electromyographic levels. Mean pooled electromyographic potentials were 1.9 microV (TA) and 1.4 microV (MM) during rest position, 6.5 microV (TA) and 2.8 microV (MM) during contact in centric occlusion. Mean maximum voluntary clench potentials were 181.9 microV (TA) and 216.2 microV (MM) in men, 161.7 microV (TA) and 156.8 microV (MM) in women. Examined muscles were more asymmetric at low electromyographic activity (rest and centric occlusion) with the temporal muscle less asymmetrical than the masseter. In females temporal muscle activity tended to dominate at every contraction level, while in males masseter activity was stronger in clench, and temporal activity in centric occlusion and in rest position.