The wave analysis of swallowing sounds has been receiving attention because the recording process is easy and non-invasive. However, up until now, an expert has been needed to visually examine the entire recorded wave to distinguish swallowing from other sounds. The purpose of this study was to establish a methodology to automatically distinguish the sound of swallowing from sound data recorded during a meal in the presence of everyday ambient sound. Seven healthy participants (mean age: 26·7 ± 1·3 years) participated in this study. A laryngeal microphone and a condenser microphone attached to the nostril were used for simultaneous recording. Recoding took place while participants were taking a meal and talking with a conversational partner. Participants were instructed to step on a foot pedal trigger switch when they swallowed, representing self-enumeration of swallowing, and also to achieve six additional noise-making tasks during the meal in a randomised manner. The automated analysis system correctly detected 342 out of the 352 self-enumerated swallowing events (sensitivity: 97·2%) and 479 out of the 503 semblable wave periods of swallowing (specificity: 95·2%). In this study, the automated detection system for swallowing sounds using a nostril microphone was able to detect the swallowing event with high sensitivity and specificity even under the conditions of daily life, thus showing potential utility in the diagnosis or screening of dysphagic patients in future studies.

AimThe role of parafunctional masticatory muscle activity in tooth loss has not been fully clarified. This study aimed to reveal the characteristic activity of masseter muscles in bite collapse patients while awake and asleep.Materials and MethodsSix progressive bite collapse patients (PBC group), six age- and gender-matched control subjects (MC group), and six young control subjects (YC group) were enrolled. Electromyograms (EMG) of the masseter muscles were continuously recorded with an ambulatory EMG recorder while patients were awake and asleep. Diurnal and nocturnal parafunctional EMG activity was classified as phasic, tonic, or mixed using an EMG threshold of 20% maximal voluntary clenching.ResultsHighly extended diurnal phasic activity was observed only in the PBC group. The three groups had significantly different mean diurnal phasic episodes per hour, with 13.29±7.18 per hour in the PBC group, 0.95±0.97 per hour in the MC group, and 0.87±0.98 per hour in the YC group (p<0.01). ROC curve analysis suggested that the number of diurnal phasic episodes might be used to predict bite collapsing tooth loss.ConclusionExtensive bite loss might be related to diurnal masticatory muscle parafunction but not to parafunction during sleep.Clinical Relevance: Scientific rationale for studyAlthough mandibular parafunction has been implicated in stomatognathic system breakdown, a causal relationship has not been established because scientific modalities to evaluate parafunctional activity have been lacking.Principal findingsThis study used a newly developed EMG recording system that evaluates masseter muscle activity throughout the day. Our results challenge the stereotypical idea of nocturnal bruxism as a strong destructive force. We found that diurnal phasic masticatory muscle activity was most characteristic in patients with progressive bite collapse.Practical implicationsThe incidence of diurnal phasic contractions could be used for the prognostic evaluation of stomatognathic system stability.

Summary Background Retraction of the posterior tongue facilitates bolus formation, food transfer and Stage II transport in chewing and swallowing. Surface electromyography of the neck region (N‐EMG) enabled the evaluation of muscle function at the posterior tongue. Although previous studies showed that food hardness increased masticatory muscles EMG activity and volitional chewing altered swallowing, the effect of food properties and chewing condition on N‐EMG activity has not yet been elucidated. Objective To investigate the effect of food properties and chewing conditions on N‐EMG. Methods Twelve healthy adults (six men and six women, mean age 28.1 ± 2.7) participated in this study. Three test foods were used: a cookie (solid food), crushed cookies adjusted using agar and water (semisolid food) and crushed cookies adjusted using thickening agent and water (soft food). Masseter and submental muscle EMG and N‐EMG activity were recorded while chewing the three test foods. Participants were instructed to masticate the three test foods in three chewing conditions: (a) chewing freely, (b) chewing test foods with the same number of chewing cycles as when chewing solid food and (c) chewing with a maximum effort. Results Total N‐EMG activity when chewing solid food was higher than that in the other two test foods regardless of the chewing condition. In soft food and semisolid food, the total N‐EMG activity was increased by increasing the number of chewing cycles. Conclusion The total N‐EMG activity was increased while chewing hard food, which indicates the positive effect of chewing hard food on rehabilitation at the posterior tongue.

Elevation of the posterior part of the tongue is important for normal deglutition and speech. The purpose of this study was to develop a new surface electromyography (EMG) method to non-invasively and objectively evaluate activity in the muscles that control lifting movement in the posterior tongue. Neck surface EMG (N-EMG) was recorded using differential surface electrodes placed on the neck, 1 cm posterior to the posterior border of the mylohyoid muscle on a line orthogonal to the lower border of the mandible. Experiment 1: Three healthy volunteers (three men, mean age 37·7 years) participated in an evaluation of detection method of the posterior tongue lifting up movement. EMG recordings from the masseter, temporalis and submental muscles and N-EMG revealed that i) N-EMG was not affected by masseter muscle EMG and ii) N-EMG activity was not observed during simple jaw opening and tongue protrusion, revealing the functional difference between submental surface EMG and N-EMG. Experiment 2: Seven healthy volunteers (six men and one woman, mean age 27·9 years) participated in a quantitative evaluation of muscle activity. Tongue-lifting tasks were perfor-med, exerting a prescribed force of 20, 50, 100 and 150 gf with visual feedback. For all subjects, a significant linear relationship was observed bet-ween the tongue-lifting force and N-EMG activity (P < 0·01). These findings indicate that N-EMG can be used to quantify the force of posterior tongue lifting and could be useful to evaluate the effect of tongue rehabilitation in future studies.

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.