Recent advances in wearable devices have enabled the evaluation of awake bruxism [14][15][16]; electromyographic recordings can be used to diagnose awake bruxism during wakefulness [10]. Although previous studies have evaluated the association between sleep bruxism and tooth wear using a portable electromyographic measurement system, the relationship between them remains unclear [8]. Additionally, no study has been conducted on the association between awake bruxism and tooth wear. This study aimed to assess masseter electromyographic activity during wakefulness and sleep in individuals with moderate or severe tooth wear compared to an age-and sex-matched control group with no or mild tooth wear. We hypothesized that there was no significant difference in masseter electromyographic activity during wakefulness and sleep between the two groups.

Background: Masticatory movement occurs complicatedly and bilaterally. Although the tongue plays an important role in mastication, bilateral tongue function during mastication has not been clarified yet. Objective: To investigate the effect of food properties on posterior tongue activity and coordination of muscles bilaterally by electromyography (EMG). Methods: Twenty healthy adults (10 males and 10 females; mean age 28 years; range: 22-33 years) participated in this study. Three test foods, gummy jelly (hard food), sponge cake (soft food requiring crushing), and mashed potatoes (soft food not requiring crushing), were used. Bilateral masseter N-EMG (surface electromyography for measuring the muscle activity of posterior tongue) and submental EMG were carried out while the participants chewed three test foods. The participants were instructed to masticate three test foods only on the right side and only on the left side unilaterally. Results: In the case of gummy jelly, N-EMG activity on the mastication side was significantly larger than that on the non-mastication side (P < .01). Regarding temporal relationship between the masseter and N-EMG activity, in the case of gummy jelly, the percentage of cases where the N-EMG peak was observed during masseter muscle EMG bursts was significantly higher than those for sponge cake and mashed potatoes (P < .01). Conclusion: N-EMG activity on the mastication side was significantly larger than that on the non-mastication side in the mastication of hard foods. Tongue showed activity pattern changes and coordinated with the masseter muscle depending on food texture.

Background: Fatigue is an important factor for muscle strengthening in rehabilitation medicine. Frequency analysis has been regarded as the gold standard for muscle fatigue assessment in surface electromyography (EMG). However, there are no experiments quantifying fatigue with grouped discharge (GD), which is one of the historical phenomena observed in patients having fatigue, by using high sampling rate recording of EMG.Objective: To investigate the effect of fatigue, which is induced by repeated posterior tongue lift movement (TLM), on the occurrence of GD peaks, thus, to provide possible basis as a parameter for future fatigue evaluation.Methods: Nineteen healthy adults (9 men and 10 women) participated in this study.The muscle fatigue protocol consisted of repetitive posterior TLM and maximum voluntary contractions (MVC). Bilateral N-EMG (Neck surface EMG for measuring the muscle activity of the posterior tongue) was recorded. Results:Subjective tongue fatigue at the end of the protocol was significantly higher than at beginning throughout the muscle fatigue protocol (p < .01). The frequency of occurrence of GD peaks was 0.9 ± 1.2 (per second) at the baseline in 33 of 38 subject sides, and significantly increased depending on fatigue progression (p < .01). Conclusion:It was shown that fatigue due to repetitive posterior tongue lifting resulted in significant increase in the frequency of occurrence of GD peaks. Especially, the nature of GD, showing very few occurrences at non-fatigue condition, might work as an advantageous property for its use in future absolute evaluation of fatigue phenomena.

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