Relationship between autoregressive model coefficients of EMG and its potentials of jaw closing muscles at rest position and clenching

At rest position and varied clenching levels at intercuspal position, autoregressive (AR) models of myoelectrical activities of both masseter and anterior temporal muscles of 11 healthy subjects with intact natural dentitions were established. The relationship between the AR model coefficients of surface EMGs and their potentials was analyzed by multiple linear regression. It was found that the fourth order coefficient of AR had the greatest effect on the EMG potential levels and their relationship was positive in all recorded muscles. The results indicate the AR coefficients may become a characteristic parameter to describe myoelectrical activity of jaw closing muscles.     

Electromyographic activity of the human masticatory muscles during submaximal clenching in the inter-cuspal position

The activity patterns of the masseter and the anterior temporal muscles were studied in twenty-one healthy male subjects while clenching at 10, 20, 30, 40 and 50% of the maximum clenching level. At low clenching levels the temporal muscle activity tended to dominate, at high levels the masseter muscle activity was stronger (P less than 0.001). The asymmetry in muscle activity also depended upon the clenching level (P less than 0.001), while at each level the masseter muscle asymmetry was greater than the temporal muscle asymmetry (P less than 0.05-P less than 0.025). By comparing the electromyographic activities of the left and right side within each subject it was found that the masseter muscle with the higher electromyographic activity tended to have the larger cross-sectional area (P less than 0.01) and at the 50% clenching level it tended to be on the side with the greater number of post-canine tooth contacts (P less than 0.001).     

Power spectral analysis of electromyographic signal of masticatory muscles at rest position and habitual clench

Thirteen normal subjects were selected for this investigation. At the vertical dimension of rest position and habitual clench, their myoelectric activities of the masseter, anterior and posterior temporal, and digastric muscles on the left and right sides were simultaneously sampled and processed by computer, and the mean power frequency (MPF) and the mean amplitude (MA) of the myoelectric signal were calculated. At rest position, the temporal muscles were major muscles and the MPF differences of various masticatory muscles were not significant. At habitual clench, with the increase in MA, the MPF of various muscles increased. The results show that MPF may have application in describing a central tendency of myoelectrical signal frequency distribution and in evaluating recruitment of motor units. MPF and MA are the quantitative indices reflecting masticatory muscle function.     

Electromyographic biofeedback and rest position training of masticatory muscles in myofascial pain-dysfunction patients

Twenty-four women outpatients with myofascial pain-dysfunction were divided into three groups of eight. All received bilateral masseter electromyographic biofeedback training. One group received biofeedback only; one group received additional instructions and modeling to place their jaw in the "rest" position; and one group was given a prosthetic guide that spaced the incisors 6.8 mm apart. Two 15-minute training sessions were conducted at a 1-week interval, with posttreatment assessment 2 weeks later. The instruction and prosthesis groups obtained significantly greater electromyographic reductions in masseter activity and increases in mandibular range of motion compared with the biofeedback-only group. Subjects with pain obtained a significant reduction in therapist and self-report pain ratings. The results suggest that short-term biofeedback treatment may be meaningfully augmented by procedures that place the mandible in the rest position.     

Correlation between autoregressive moving-average model parameters of electromyogram of human jaw closing muscles and maximum clenching time at intercuspal position

During maximum clenching in the intercuspal position, surface electromyograms of left masseter and anterior temporal muscles were sampled in 16 healthy subjects with natural dentitions to establish a four-order, autoregressive (AR) moving-average (MA) model of the myoelectrical signals. The correlation coefficients and the linear regresssion between the model parameters and the clenching time were calculated. The model parameters had the positive or the negative correlation, and AR model parameters had the higher correlation than MA model parameters. The model parameters relate to muscular fatigue and the slope of the regressive equation relates to the endurance time of the isometric contraction.     

Relationship between occlusion and EMG activity of the masseter muscles during clenching at maximal intercuspal position: a comparative study between prognathics and controls

In the prognathic (P) patient group clenching at maximal intercuspal position (MIP), we found that the Ar-Go-Me angle is greater than in the control group (C = 120.9 degrees +/- 7 degrees vs. P = 134.4 degrees +/- 5.2 degrees): the same as the masseter fibers angle (alpha). The average EMG voltage class was similar in both groups (C = 1488.5 +/- 303.4 microvolt vs. P = 1317.6 +/- 293.4 microvolt). The mean total number of contact points in tooth arches was greater in the control group than in the patient group (C = 5.77 +/- 0.43 vs. P = 3.07 +/- 0.29), and there was a greater number of contact points between both premolar and molar areas. Both the control group and the patient group showed balanced occlusion in the premolar and molar areas. Therefore the finding of a similar mean EMG value between the control group and the patients emphasizes the importance of balanced contact points in the posterior areas.     

Activity patterns of the masticatory muscles during feedback-controlled simulated clenching activities

In 10 normal subjects, the electromyographic (EMG) activities of the masseter, anterior and posterior temporalis, medial pterygoid, inferior lateral pterygoid, as well as the anterior digastric, were bilaterally recorded during clenching with various resulting force vectors. The intraoral force transfer was achieved with a three-component force transducer. The direction and magnitude of the force vectors were controlled by visual feedback. The goal of the study was to investigate how various clenching directions at constant magnitude of force influence the EMG activity in the masticatory muscles during gradual increase of the horizontal force component. Depending on the force direction and the individual muscle, an increase or decrease of activity was observed during clenching with increasing horizontal force components at constant magnitude of force. The inferior lateral pterygoid exhibited the highest activation (about 80% of maximal voluntary clenching) of all masticatory muscles. The medial pterygoid showed the greatest range of variation in activation behavior, and it was the most active muscle in relation to all clenching directions. In conclusion, the results show that with growing horizontal force components at constant magnitude of force, all muscles demonstrated an increase or decrease of activity in several clenching directions.     

Correlations between an autoregressive model coefficient of the electromyogram of human jaw-closing muscles and maximum clenching time at the intercuspal position.

During maximum clenching in the intercuspal position, surface electromyograms of both masseters and both anterior temporales in seven healthy subjects with intact natural dentitions were sampled to generate a four-order, autoregressive model of the myoelectrical signal. The correlation coefficients and the linear regression between the model coefficients and the clenching time were calculated. The first-order autoregressive coefficient had the greatest negative correlation on average. In this model the first-order coefficient relates to muscular fatigue and the slope of the regressive equation relates to the length of time the isometric contraction can be maintained.     

Effect of occlusal splint thickness on electrical masticatory muscle activity during rest and clenching

The extent of separation between the maxillary and mandibular teeth in the fabrication of interocclusal splints designed to achieve efficiency and muscle relaxation is controversial and undefined in the literature. Based on this premise, the aim of this study was to evaluate the effect of interocclusal splint thicknesses of 3 and 6 millimeters on the electrical activity of the anterior temporal and masseter muscles during rest and dental clenching. Twenty asymptomatic individuals (10 males and 10 females) were selected using the Research Diagnostic Criteria (RDC). Electromyography (EMG) was performed both with and without the 3- and 6-mm splints using the Bio EMG software package, which recorded values given in microvolts (μV). The results, which were assessed using analysis of variance (ANOVA) to a 5% significance level (p < 0.05), showed increased electrical activity of the masticatory muscles during dental clenching compared with at rest, with greater activity in the masseter muscle. The electrical activity did not differ according to the thickness of the splints or between males and females. We can conclude that both splint thicknesses are effective in treating muscle hyperactivity given their similar clinical behavior for asymptomatic individuals.     

Relationship between myoelectric activity in masticatory muscles and bite force

Myoelectric activity in the anterior and posterior temporalis and in the masseter muscle was assessed in five subjects biting unilaterally on a bite fork at 50, 100 and 200 N for 60 s. The bite fork was placed between the right first premolars and the first molars. The ipsilateral muscle activity was recorded first, and the contralateral side was evaluated 1 wk later. The relationship between exerted force and EMG-activity was expressed as ratios between EMG-activity and related bite force. EMG-activity increased with increasing force for all muscles tested. Linearity was found for the anterior temporal muscle, but not for the other muscles. Four of the subjects participated in an endurance test, exerting maximum bite force on the right side for as long as possible. The EMG activity of the right masseter muscle was closely related to bite force, in contrast to the other tested muscles. The activity of the left muscles increased at the end of the endurance test.     

Relationship between myoelectric activity in masticatory muscles and bite force

Myoelectric activity in the anterior and posterior temporalis and in the masseter muscle was assessed in five subjects biting unilaterally on a bite fork at 50, 100 and 200 N for 60 s. The bite fork was placed between the right first premolars and the first molars. The ipsilateral muscle activity was recorded first, and the contralateral side was evaluated 1 wk later. The relationship between exerted force and EMG-activity was expressed as ratios between EMG-activity and related bite force. EMG-activity increased with increasing force for all muscles tested. Linearity was found for the anterior temporal muscle, but not for the other muscles. Four of the subjects participated in an endurance test, exerting maximum bite force on the right side for as long as possible. The EMG activity of the right masseter muscle was closely related to bite force, in contrast to the other tested muscles. The activity of the left muscles increased at the end of the endurance test.     

Relationship between depression and masticatory muscles function in a group of adolescents

Objective: The aim of the study is to determine association between depressive symptoms and the electrical activity of muscles in maximum voluntary clench in a group of young adults.

Methods: A total of 186 volunteers (Females = 98, Males = 88), with a mean age of 19 years, were recruited to the study. All participants took a questionnaire survey stating the level of depression (Beck’s scale), clinical examination, and instrumental diagnostics (EMG).

Results: Symptoms of mild or medium depression were found in 35 of the subjects (18.82%). Average electric potentials of the masticatory muscles in maximal voluntary clench were significantly higher among the subjects with depression symptoms in comparison with subjects without those symptoms (85.96 ± 10.25 vs 78.97 ± 15.32, p < . 0.05).

Discussion: An increase in the electrical potentials of masseter muscles in maximal voluntary clench was found in the group with depression symptoms. The study should be continued to confirm this finding.     

The effects of a single intercuspal interference on electromyographic characteristics of human masticatory muscles during maximal voluntary teeth clenching

In 13 healthy subjects (eight men and five women, mean age, 22 years), an aluminum intercuspal interference (height, 0.25 mm) was placed on the maxillary right first premolar to study its effect on the contractile symmetry of the right and left masseter and anterior temporalis muscles when measured through a Percentage Overlapping Coefficient (POC), derived from surface electromyographic recordings of maximum voluntary teeth clenching. Additionally, and to estimate the potential of the experimental intercuspal interference to induce lateral displacement of the mandible, a Torque Coefficient (TC) was derived from surface electromyographic recordings. The conclusion was that the experimental occlusal interference gave rise to asymmetric contractile activity in the studied mandibular elevator muscles as well as a potential to displace the mandible in a lateral direction.     

Volume changes in human masticatory muscles between jaw closing and opening

Most jaw muscles are complex, multipennate with multiple components. The morphologic heterogeneity of masticatory muscles reflects their functions. We hypothesized that the volume of masticatory muscles changes between jaw closing and opening, and that there is a difference in the volume change among the muscles. Magnetic resonance images of the entire head were obtained in ten normal young adult subjects before and after maximum jaw opening. The volume changes of the masseter, medial, and lateral pterygoid muscles were measured. Only slight changes were seen in the masseter and medial pterygoid muscles. The lateral pterygoid muscle, however, significantly decreased its volume during jaw opening. The results provide normative values of muscle volume in living subjects, and suggest that the volume changes differ among jaw muscles.     

Evaluation of proximal tooth contact tightness at rest and during clenching

The aims of this study were to develop a device for measuring the tightness of proximal tooth contact and to evaluate the proximal contact tightness using this device at rest and during clenching. Twenty young adult volunteers with healthy dentition participated in this experiment. The tightness of proximal tooth contact between the second premolar and the first molar of both the maxilla and the mandible was measured by pulling a stainless steel strip between them at rest, and at 20 and 50% clenching levels of maximum voluntary contraction of masseter muscles at intercuspal position. Proximal contact tightness increased as the clenching levels of both the maxilla and the mandible increased. At rest, proximal contact tightness was less in the maxilla than in the mandible, whereas during clenching it was less in the mandible. These results indicate that during clenching, the teeth are displaced and they contact appropriately with adjacent teeth, making it possible to exert sufficient occlusal force while maintaining the integrity of dental arches.     

Co-activation of jaw and neck muscles during submaximum clenching in the supine position

Objective

The purpose of this study was to test the hypothesis that jaw clenching induces co-contraction and low-level long-lasting tonic activation (LLTA) of neck muscles in the supine position.

Design

Ten healthy subjects developed various feedback-controlled submaximum bite forces in different bite-force directions in supine position. The electromyographic (EMG) activity of the semispinalis capitis, semispinalis cervicis, multifidi, splenius capitis, levator scapulae, trapezius, sternocleidomastoideus, masseter and infra/supra-hyoidal muscles was recorded. For normalization of EMG data, maximum-effort tasks of the neck muscles were performed.

Results

Co-contractions of the posterior neck muscles varied between 2% and 11% of their maximum voluntary contraction. Different bite forces and bite-force directions resulted in significant (p < .05) activity differences between the co-contraction levels of the neck muscles. In addition, LLTA of specific neck muscles, provoked by the jaw clenching tasks, was observed.

Conclusions

This study demonstrated for the first time moderate co-contractions of jaw and neck muscles in the supine position under controlled submaximum jaw clenching forces. LLTA of most neck muscles was observed, outlasting clenching episodes and indicating an additional neuromuscular interaction between the two muscle groups.     

Effect of eccentric clenching on mandibular deviation in the vicinity of mandibular rest position

Although the mechanical compression of the temporomandibular joint (TMJ), which could be caused by bruxism, would probably result in a slight change of the occlusal relationship, the effect of clenching in the eccentric mandibular position on the occlusal contact has not yet been clarified. This study aimed to investigate the effect of eccentric clenching on bilateral condylar position and thus to estimate any change of occlusal contact. Before and after voluntary clenching, with one third of the maximal voluntary clenching force, for 3 min at the canine edge-to-edge position, vertical deviation of the bilateral condyles was measured at the 1 mm open mandibular position. This was regulated by the three-dimensional position of the anterior reference point which stands for the incisor point. The mean vertical displacement of the highly deviated side of the condyle was 141+/-55 microm, and the calculated mean displacement of the mandibular first molar region of the highly deviated side was 65+/-27 microm. From the results of this study, it was revealed that the eccentric clenching gave rise to three-dimensional deviation of the mandible even when the mandible was in the vicinity of the rest position.     

头位左倾和右倾变化对咀嚼肌肌电的影响

目的：研究不同的头位变化对咀嚼肌肌电活动的影响。方法：以30例健康正常[牙合]受试者为研究对象，通过肌电图仪（EMG）测试下颌姿势位和牙尖交错位最大紧咬时，5种头位姿势的颞肌前束（TA）、颞肌后束（TP）、咬肌（MM）、二腹肌前腹（DA）的肌电幅值，并对结果进行统计学分析。结果：下颌姿势位和紧咬位时，与正中头位相比，头左倾和右倾状态时咀嚼肌的肌电值变化无显著性差异（P〉0．05）。结论：咀嚼肌在头位左倾和右倾变化过程中所受影响不大。