The influence of eye closure on muscle activity in the anterior temporal region

This study aimed to investigate whether the fatigue induced by sustained motor task in the jaw elevator muscles differed between healthy subjects and patients with temporomandibular disorder (TMD). Fifteen patients with TMD and thirteen age- and sex-matched healthy controls performed a fatigue test consisting of sustained clenching contractions at 30% maximal voluntary clenching intensity until test failure (the criterion for terminating the fatigue test was when the biting force decreased by 10% or more from the target force consecutively for >3 s). The pre- and post-maximal bite forces (MBFs) were measured. Surface electromyographic signals were recorded from the superficial masseter muscles and anterior temporal muscles bilaterally, and the median frequency at the beginning, middle and end of the fatigue test was calculated. The duration of the fatigue test was also quantified. Both pre- and post-MBFs were lower in patients with TMD than in controls (P < 0·01). No significant difference was found in the percentage change in MBF between groups. The duration of the fatigue test in TMD patients was significantly shorter than that of the controls (P < 0·05). Our results suggest that, compared to healthy subjects, patients with TMD become more easily fatigued, but the electromyographic activation process during the fatigue test is similar between healthy subjects and patients with TMD. However, the mechanisms involved in this process remain unclear, and further research is warranted.

Section: Discussionmentioning

confidence: 94%

Influence of sustained submaximal clenching fatigue test on electromyographic activity and maximum voluntary bite forces in healthy subjects and patients with temporomandibular disorders

Fan

Cai

et al. 2017

“…The mandibular elevator (closing) muscles accessible to surface electromyography (EMG) are the temporalis and masseter muscles, and as compared with the masseter muscles the anterior portions of the temporalis (AT) muscles are more sensitive to minor changes of the rather low EMG activities associated with the mandibular postural position of rest and occurring during profound changes of body position, such as a change from the upright to the supine position (Lund, Nishiyama & Moller, 1970;Holmgren, Sheikholeslam & Riise, 1985;Miralles et al, 1987). Accordingly, bilateral surface EMG of the AT muscles was used in this study, and to eliminate the influence of visual stimuli and the blink reflex (temporoparietal muscle) on AT EMG recordings the subjects kept their eyes closed throughout the baseline and experimental studies (Widmalm & Ericsson, 1983;Holmgren et al, 1985). Because the highest level of isometric AT EMG activity is obtained during maximum voluntary teeth clenching (MVC) in centric occlusion, the relative AT EMG activities (% MVC) were referenced to this activity (Moller, 1966;Christensen & Donegan, 1990;Van Eijden et al, 1990).…”

Section: Discussionmentioning

confidence: 99%

Electrognathographic and electromyographic observations on jaw depression during neck extension

McKay¹,

Christensen²

1999

Albeit never substantiated through experimental and clinical evidence, the theoretical linchpin of the mechanics of a so-called whiplash injury of the temporomandibular joint (TMJ) is the postulate that a pre-existing depressor force (continual anchoring force), generated by the anterior suprahyoid (SH) muscles, will always act on the mandible and cause traumatic mouth opening (anterior acceleration of the TMJ condyles) when the neck is extended (posterior acceleration of the head). To test aspects of this postulate, six subjects assumed the positions of neutral (0 degrees ), medium (32 degrees ) and maximum (58 degrees ) neck extension while the mandible was in its postural positions of rest and light centric occlusion. By means of surface electromyography, it was shown that the relative contractile activities of the anterior SH muscles never exceeded 7.3% of the contractile activity required to anchor the mandible in a position of maximum depression. By means of electrognathography, it was shown that the maxillary and mandibular incisors were never separated by more than 2.6 mm during neutral, medium, and maximum extension of the neck. In other words, during neck extensions there was no evidence of a continual or induced voluntary or involuntary depressor force that would and could anchor the mandible in a position of traumatic mouth opening. Accordingly, and in agreement with other biophysical and biomedical evidence, it was concluded that there is no foundation for the pseudoscientific speculations and unsubstantiated opinions offered in support of a concept and diagnosis of a so-called TMJ whiplash injury. Additionally, this study found co-activation of cervical flexor muscles and mandibular elevator as well as depressor muscles.

“…The reaction of the nervous system to stimuli is a muscular contraction. A skeletal muscle can be completely at rest without detectable neuromuscular EMG activity and without losing its tone or tonus , 3 which explains why no jaw muscle EMG has been recorded with needle electrodes during MR 4‐6 …”

Section: Introductionmentioning

confidence: 99%

Is SEMG recorded “hyperactivity” during mandibular rest a sign of dysfunctional jaw muscle activity and temporomandibular disorders (TMD)?

Yan

Widmalm

et al. 2020

Background Some authors state that above‐normal surface electromyography (SEMG) levels during mandibular rest (MR) are a general sign of temporomandibular disorders (TMD). Objective The aim was to compare SEMG levels in the masseter and anterior temporalis areas during MR between patients with disc displacement (DD) and subjects identified as healthy. The hypothesis was that average SEMG levels would be higher in the patients during MR before and after repeated clenches with maximal effort. Methods Thirty‐six healthy subjects, and 42 patients with DD, were included. SEMG levels were recorded bilaterally in the temporalis and masseter areas during MR before clenching and after repeated clenches with maximal effort. Multivariate analysis of variance (MANOVA) was used to compare the means of the log‐transformed SEMG‐values for the subject groups. Results The mean MR levels in the four areas before clenching ranged from −0.19 log (µV) to 1.20 log(µV) in healthy subjects and from −0.22 log(µV) to 0.96 log(µV) in patients. The mean MR levels in the four areas after repeated clenches ranged from −0.19 log (µV) to 1.04 log(µV) in healthy subjects and from −0.27 log(µV) to 0.93 log(µV) in patients. The MANOVA test showed no significant differences in the means for MR for the four areas between the groups at the 5% significance level. Conclusion The hypothesis that jaw muscle SEMG levels during MR are on average generally higher in TMD patients is not supported. A possible explanation for the previous findings is that activity in other muscles was mislabelled as jaw muscle activity.