Masseter Muscle Fatigue Research Articles

Effect of Gum Chewing Training on Masseter Muscle Oxygen Dynamics.

This study aimed to clarify the effect of 1month of gum chewing (GCh) training on masseter muscle oxygen dynamics and determine its effectiveness in improving muscle endurance and fatigue. A total of 16 healthy adult subjects were included in this study. The subjects were randomly assigned to two groups: control and training groups (eight subjects each). GCh training using prototype gum of moderate hardness was performed for 10 min (5 min for each side) three times a day before each meal for 30days. Clenching effects were evaluated before and after interventions. Masseter muscle oxygen dynamics were measured using spatially resolved near-infrared spectroscopy. Furthermore, masseter muscle fatigue was assessed using the Visual Analog Scale (VAS). After training, a significant increase was observed in total haemoglobin and oxygenated haemoglobin during clenching, and the 1/2 recovery time was significantly shortened. The changes in the VAS score showed a decreasing trend after training. In conclusion, 1month of GCh training changed masseter oxygen dynamics during clenching and recovery and improved muscle aerobic capacity.

Bruksizmde Digastrik Kas Hassasiyetinin Önemi

Objective. It was aimed to assess the differences in the sensitivities of masticatory and digastric muscles during examination because of continuous and excessive forces in case of bruxism. Material and Method. From the masticatory muscles of 162 individuals with bruxism and 162 control individuals, masseter, temporalis, medial / lateral pterygoideus muscles and digastric muscles were examined. Perceived sense of discomfort-pain during muscle examinations was scored according to a numerical rating scale and recorded as right and left. Results. In individuals with bruxism, the pain scores of the patients for each examined muscle were higher than the control group (p<0.05). In the ROC analysis performed in bruxism, cut-off values for digastric muscle, lateral pterygoideus muscle and other muscles were 2.5, 1.5 and 0.5, respectively. The sensitivity and specificity of the digastric muscles were found to be higher than other muscles (sensitivity: right=72.8%, left=72.8%, specificity: right=18.5%, left=17.9%). Conclusion. Bruxism affects digastric muscles more than masticatory muscles. Digastric muscles and other masticatory muscles should be evaluated in addition to masseter muscle pain, hypertrophy and fatigue in the clinical diagnosis of bruxism.

Jaw-Clenching Intensity Effects on Masseter Oxygen Dynamics and Fatigue: A NIRS Oximetry Study.

The purpose of this study was to clarify the effects of jaw-clenching intensity on masseter muscle oxygen dynamics during clenching and recovery and masseter muscle fatigue using the spatially resolved method of near-infrared spectroscopy. Pulse rate, mean power frequency from electromyography in the masseter and visual analogue scale for masseter fatigue were also examined as related items. The 25% and 50% maximum voluntary contractions were determined using electromyography before the experiment and used as visual feedback on the screen. Twenty-three healthy adult male subjects volunteered for this study. Clenching decreased oxygen and oxygenated haemoglobin, and increased deoxygenated haemoglobin in the masseter muscle. The higher the intensity of clenching, the more prominent the effect. The oxygen dynamics tended to return to normal after clenching, but the change was slower with higher clenching intensity. Pulse rate increased with clenching, and the increment was more prominent with higher clenching intensity. Clenching caused a shift of mean power frequency to a lower range, an increase in subjective fatigue, an early appearance of a breakpoint appearance time and a prolongation of a 1/2 recovery time. All of these effects were more evident with increasing clenching intensity. In conclusion, clenching intensity influenced the oxygen dynamics of the masseter muscle and fatigue state during clenching and recovery. The higher the intensity, the greater the impact.

Effect of tooth loss on masticatory muscle pain of patients with bruxism

Aim: It was aimed to compare the patients’ masticatory muscle pain according to the gender, side of the face with pain, muscle tenderness, and tooth loss.Material and Methods: The patients were selected randomly and the data were collected from 109 patients aged 18-50 years. Patients were examined by a maxillofacial surgeon and a prosthodontist blindly. During intraoral examination grinding, clenching confirmed by sleep partners or roommates, hyperkeratosis of cheek mucosa (linea alba), indented tongue, the unilateral masseter muscle hypertrophy, tooth wear, hypersensitivity, pain and fatigue in the chewing muscles in the daytime or in the morning were recorded. To classify tooth loss the Eichner index was used. It was asked to participants to score the masticatory muscle pain. Each participant scored the masticatory muscle pain on a visual analog scale (VAS/0-10). Data were analyzed with a non-parametric Mann-Whitney U test to compare the VAS results because the data were distributed non-normally. Chi-square test was used to compare categorical variables and Spearsman correlation test was performed to test the possible correlation between the masticatory muscle pain and age. Results: The percentage of bruxism in female (52.3%) was higher than in male (47.7%). A total of 15 patients (13.7%) had tooth loss (premolar or molar). Pain score was higher in patients with tooth loss than without tooth loss (p=0.49).Conclusion: The tooth loss may be increased the masticatory muscle pain. It should be considered both muscle pain and tooth loss together in clinical examination and perform the preventive treatment.

Oxygen saturation and electromyographic changes in masseter muscle during experimental chewing of gum with harder texture

Objective. The purpose of this study was to clarify the relationship between changes in masseter muscle oxygenation measured by near-infrared spectroscopy (NIRS) and changes in the electromyographic (EMG) power spectrum during experimental chewing of gum with harder texture, to improve the understanding of the use of NIRS in assessing masseter muscle fatigue. Material and methods. Ten female volunteers with normal occlusion were examined. Mean age (standard deviation) was 28.4 (3.8) years. Mean fracture stress of gum was 12.5 × 104 N/m2. Subjects were instructed to chew gum for 60 s (75 strokes) on the voluntary chewing side at a pace of 1.25 strokes/s. Simultaneous recordings of NIRS and EMG signals from masseter muscle were performed during gum chewing. Results. Oxygen saturation levels decreased from the start of chewing, then stabilized with a break point between the two phases. The normalized EMG amplitude increased and the mean frequency of the EMG power spectrum decreased during gum chewing. The timing of break point appearance was related to the timing of a significant decrease in median frequency, but no clear relationships were found between break point appearance and increased EMG amplitude. Conclusions. These results suggest that the break point of the oxygen saturation curve, as obtained from NIRS measurements, could be used as an indicator of masseter muscle fatigue as assessed by a shift in the EMG power spectrum to lower frequencies.

Mechanomyogram and electromyogram analyses for investigating human masseter muscle fatigue

The purpose of this study was to examine the validation of mechanomyogram (MMG) for assessing the masseter muscle fatigue. Data were obtained from 16 healthy Japanese males (aged 25.6 ± 2.3 years). The measuring device for the MMG consisted of an amorphous sensor and a small magnet. The bite-force, the MMG, and the electromyogram (EMG) signals were recorded simultaneously. The subjects were instructed to perform 0%, 5%, 10%, and 20% maximal voluntary contraction (MVC) for 20 s as the pre-fatigue trials. A recovery period of 5 min was allowed after each pre-fatigue trial. As the fatigue task, the subjects were instructed to sustain 40% level of MVC until they feel intolerable discomfort. The subjects were asked to perform 0%, 5%, 10%, and 20% MVC for 20 s as the post-fatigue trials. No recovery period was allowed after each post-fatigue trial. The mean values of the average rectified value for EMG of the post-fatigue trials were significantly higher than those of the pre-fatigue trials at 10% ( p < 0.05) and 20% MVC ( p < 0.05). The mean values of the electromechanical efficiencies of the post-fatigue trials were significantly lower than those of the pre-fatigue trials at 10% ( p < 0.01) and 20% MVC ( p < 0.05). These findings suggest that the MMG analysis combined with the EMG may be a more useful method for evaluating the masseter muscle status.

Masseter Muscle Fatigue Induced by Experimental Sustained Light Clenching

Purpose: The aim of this study was to clarify the characteristics of masseter muscle fatigue induced by experimental sustained light clenching with rest intervals between clenching events.Materials and Methods: The subjects consisted of 18 healthy young adults. For each recorded task, the subjects were asked to perform experimental tooth clenching 3 times, with a duration of 60s for each event and an interval (30s or 60s) between successive clenching events. The experimental clenching forces selected were 10% and 20% of maximum voluntary clenching (MVC). The electromyographic activity during the experimental procedure was measured. The mean power frequency (MPF) of muscle activity was used as an indicator of muscle fatigue. Changes to lower frequencies of the MPF were then analyzed.Results: Despite the light clenching forces used (10% and 20% of MVC), masseter muscle fatigue occurred. When the subjects performed experimental clenching at 10% of MVC with intervals of 60s between clenching events, the MPF changes were gradually larger depending on the events. The regression line had the best fit to data when the subjects were asked to perform experimental clenching under the conditions mentioned above.Conclusion: It was possible to obtain a regression line that represented the relationship between clenching events and masseter muscle fatigue.

Inhibition of muscle spindle afferent activity during masseter muscle fatigue in the rat.

The influence of muscle fatigue on the jaw-closing muscle spindle activity has been investigated by analyzing: (1) the field potentials evoked in the trigeminal motor nucleus (Vmot) by trigeminal mesencephalic nucleus (Vmes) stimulation, (2) the orthodromic and antidromic responses evoked in the Vmes by stimulation of the peripheral and central axons of the muscle proprioceptive afferents, and (3) the extracellular unitary discharge of masseter muscle spindles recorded in the Vmes. The masseter muscle was fatigued by prolonged tetanic masseter nerve electrical stimulation. Pre- and postsynaptic components of the potentials evoked in the Vmot showed a significant reduction in amplitude following muscle fatigue. Orthodromic and antidromic potentials recorded in the Vmes also showed a similar amplitude decrease. Furthermore, muscle fatigue caused a decrease of the discharge frequency of masseter muscle spindle afferents in most of the examined units. The inhibition of the potential amplitude and discharge frequency was strictly correlated with the extent of muscle fatigue and was mediated by the group III and IV afferent muscle fibers activated by fatigue. In fact, the inhibitory effect was abolished by capsaicin injection in the masseter muscle that provokes selective degeneration of small afferent muscle fibers containing neurokinins. We concluded that fatigue signals originating from the muscle and traveling through capsaicin-sensitive fibers are able to diminish the proprioceptive input by a central presynaptic influence. In the second part of the study, we examined the central projection of the masseter small afferents sensitive to capsaicin at the electron-microscopic level. Fiber degeneration was induced by injecting capsaicin into the masseter muscle. Degenerating terminals were found on the soma and stem process in Vmes and on the dendritic tree of neurons in Vmot. This suggests that small muscle afferents may influence the muscle spindle activity through direct synapses on somata in Vmes and on dendrites of neurons in Vmot.

Relaxation rate in the assessment of masseter muscle fatigue

The aim of this study was to assess a simple method of measuring relaxation rate in the jaw-closing system for the purpose of quantifying jaw muscle fatigue. A summary of the various different methods of measuring relaxation rate is also provided. The rates of twitch contraction and relaxation were measured in 30 symptom-free subjects following bilateral direct electrical stimulation of the masseter muscles. The resulting twitch force was recorded via a force transducer placed between the anterior teeth. The transducer was held between the teeth with as little force as possible while four single stimuli were delivered at 5-s intervals. The stimulating electrodes were then removed and replaced and the experiment was repeated. The force records of the resulting twitches were averaged and the half-contraction time, twitch amplitude and half-relaxation time were measured. There was a significant difference in half-relaxation time between males and females, being faster in females (P=0.0045, independent t-test). No significant difference was found in twitch amplitude and half-contraction time between males and females. Half-relaxation time and half-contraction time were independent of twitch amplitude. This method of measuring the relaxation rate of the masseter muscles was found to be practical and the results were reproducible between sessions.

Masseter muscle fatigue before and after rehabilitation with implant-supported prostheses

To establish whether different implant-supported prosthetic reconstructions influence jaw muscle resistance to clenching efforts, sustained submaximal (50%) clenching was performed in two groups of patients who were edentulous in one or both jaws. One group consisted of patients who were rehabilitated by means of an overdenture on two to four implants connected by a bar; the other group consisted of patients who were rehabilitated with an implant-supported fixed prosthesis on four to seven implants in either the maxilla or the mandible. Results indicated that after rehabilitation with implant-supported fixed reconstructions, the myoelectric output level increased over time, which was parallel to a higher bite force level. For the other group, such a time-dependent change in electromyographic amplitude did not occur. On the other hand, power spectrum analysis revealed a significant downward shift of the mean power frequency during sustained clenching after rehabilitation with implant-supported overdentures but not with implant-supported fixed prostheses. The absence of a spectral shift in the latter group probably expressed a fear of biting too hard and fracturing the prosthesis.

Masseter muscle fatigue during sustained clenching in subjects with complete dentures, implant-supported prostheses, and natural teeth

A sustained submaximal (50%) clenching effort was performed in four patient groups to establish whether implant-supported prosthetic reconstructions influence myoelectrical signal parameters. The first group consisted of patients with natural teeth in both jaws. The other three groups consisted of patients who were edentulous in both jaws: one group had complete dentures; one had an overdenture in the mandible on two implants connected by a bar; and the third had an implant-supported fixed prosthesis in either the maxilla or the mandible. Surface electromyography indicated an increased myoelectrical output level that paralleled a higher bite force level for implant-supported reconstructions compared with complete dentures. Power spectrum analysis revealed a downward shift of the mean power frequency during sustained clenching in all groups except the implantsupported fixed prosthesis. The absence of a spectral shift in the latter group probably reflected a fear of biting too hard and fracturing the prosthesis.

こう筋の筋疲労回復過程における筋電位伝導速度

The purpose of this research was to study muscle fiber conduction velocity (MFCV) of the masseter muscle during recovery from fatigue.The subjects were 7 healthy male volunteers, aged 24-30 years. Masseter muscle fatigue was induced in subjects by asking them to perform protracted clenching at 75% of maximum voluntary contractions (75%MVC) while the mean power frequency (MPF) of surface electromyogram in the muscle was being measured. As soon as 75%MVC clenching finished, the subjects were asked to perform intermittent weak contractions (10 seconds of contraction and 10 seconds of rest) for 8 minutes and MFCV of the masseter muscle was measured.In all subjects, an average of 32% of MPF reduction was observed at the end of 75%MVC clenching. Although there were some variations in MFCV during recovery due to unequal fatigability of units, from 22 units measured, MFCV increased in 17 units (p<0.05) with an average of 41% increase from the initial velocity value.Therefore, the findings in this study indicate that MFCV of the masseter muscle decreases during fatigue and decrease of MFCV may be a contributor to the power spectrum in order to lower frequencies during fatigue in the masseter muscle.

Masseter muscle fatigue in man objectively quantified by analysis of myoelectric signals

Localized muscle fatigue in the masseter muscle was studied with a method based on power spectrum analysis of myoelectric signals. Under the influence of fatiguing contractions, a gradual shift of the spectral curve occurred; the rate of change was taken as a measure of the development of fatigue. The fatigue was dependent on the bite force. The existence of a threshold value of force, below which significant myoelectric fatigue changes do not develop, was shown.