Suppression of sleep bruxism: effect of electrical stimulation of the masseter muscle triggered by heart rate elevation.

PURPOSE: To examine whether electrical stimulation of the masseter muscle triggered by heart rate elevation preceding sleep bruxism (SB) can actively suppress SB. MATERIALS AND METHODS: Ten volunteers who were aware of their SB habits participated in the study. Baseline electromyogram (EMG) activity of the unilateral masseter muscle and electrocardiogram (ECG) signal were recorded on the first night. The individual mean sensation and pain thresholds to electrical stimulation of the unilateral masseter muscle were determined in awake subjects before the experiment. On the second night, electrical stimulations at either of the two threshold intensities were automatically generated and delivered to the masseter muscle on the opposite side from where electrodes were placed immediately after the heart rate exceeded 110%. On the third night, electrical stimulations at the other threshold intensity were delivered. RESULTS: The numbers of SB events per night and per hour, the number of EMG bursts per SB event, and the duration of SB events decreased significantly on the nights when stimulation was applied compared with the baseline data. There were no significant differences between cases where the sensation threshold was used as the stimulation intensity and those in which the pain threshold was used as the stimulation intensity. CONCLUSION: The results suggest that electrical stimulation of the masseter muscle triggered by heart rate elevation can significantly suppress SB.

Identification of sleep bruxism with an ambulatory wireless recording system.

PURPOSE: To examine whether an ambulatory bruxism recording system, including a biologic monitor, that measures sleep variables and sympatho-vagal balance can specifically identify sleep bruxism (SB) at home. MATERIALS AND METHODS: Twenty-six volunteers, including 16 SB subjects, were recruited. Each participant recorded his or her electromyogram (EMG), sympatho-vagal balance, and sound level for 3 consecutive nights using an audio-video recorder to identify SB. Data of sleep variables were compared among the 3 experimental nights. The episodes were classified into SB episodes with and without grinding and non-SB episodes. EMG patterns, amplitude, sympatho-vagal balance, and sound level of all episodes were analyzed so as to determine the appropriate thresholds to detect SB episodes and grinding sound. Then, all episodes without video-recording data were classified into SB and non-SB episodes by using the appropriate thresholds, and the sensitivity and specificity to detect SB episodes were calculated. RESULTS: With regard to sleep variables, there were no significant differences except for sleep latency between the first and second nights. The appropriate EMG pattern and thresholds of amplitude, sympatho-vagal balance, and sound level were phasic or mixed EMG pattern, 20% of maximum voluntary contraction, mean + 1 SD, and mean + 2 SDs, respectively. The sensitivity and specificity to detect SB episodes were 88.4% and 74.2%, respectively. CONCLUSION: The results suggest that this system enables the detection of SB episodes at home with considerably high accuracy and little interference with sleep.

Prediction of sleep bruxism events by increased heart rate.

PURPOSE: To investigate the hypothesis that sleep bruxism (SB) events could be predicted by an increase in heart rate. MATERIALS AND METHODS: Fourteen sleep bruxers were recruited. Each participant recorded his or her own electromyography (EMG) and electrocardiography (ECG) at home for 2 consecutive nights using a portable telemetry system. Ten heartbeats before (B10 to B1) and three heartbeats after (A1 to A3) the onset of SB events were analyzed, and the threshold for the prediction of an SB event was determined. The validity of the threshold was tested by EMG and ECG recorded in the same manner for an additional night. The prediction accuracy of SB events was evaluated for sensitivity and specificity. RESULTS: A gradual increase in heart rate was observed before an SB event, and B1, A1, A2, and A3 were significantly higher than B10 (P < .01). The threshold value was set at 110% when the mean of all heart rates of the second night of recording was set at 100%. A total of 324 SB events were observed and 299 were preceded by increased heart rate that exceeded the threshold (sensitivity, 92.3%). The total number of increased heart rate events was 1,239, and the total number of threshold applications was estimated to be 120,000. The specificity was 99.2%. CONCLUSION: Over 90% of SB events could be predicted by an increasing heart rate of 110%. Since the sensitivity and specificity were extremely high, the hypothesis that SB events could be predicted by increased heart rate was positively verified.

No effect of conscious clenching on simple arithmetic task in healthy participants.

PURPOSE: This study aimed to investigate whether clenching aids performance in a task requiring mental concentration in healthy participants. MATERIALS AND METHODS: Twenty healthy participants (an average of 26.8 ± 2.0 years, nine females and 11 males) were recruited from our department. Participants performed four sets of hundred-square calculations as a mental arithmetic task. Among these sets, the third and the fourth sets were randomly divided into two conditions: one condition where participants made an effort to not allow their teeth to touch ('no tooth-contact' condition), and another where they made a conscious effort to rhythmically clench their teeth ('clenching' condition) during the task. Surface EMG was recorded from the left masseter muscle. Arithmetic performance was compared between the tooth-contact and clenching conditions using paired t-tests. In addition, we computed Pearson product-moment coefficients of the correlations between the difference in EMG activity and arithmetic performance in the two conditions. RESULTS: No significant change in arithmetic score was found between the no tooth-contact (68.8 ± 12.2) and clenching conditions (66.5 ± 12.7; P=0.27). No significant correlation was found between the difference in EMG activity and changes in arithmetic performance (r=0.32, P=0.17). CONCLUSION: In healthy participants, conscious clenching was not associated with any benefit in arithmetic performance. Although our study was limited by only measuring the short-term effects of clenching on a simple arithmetic task, the results indicate that it may not be harmful for clinicians to encourage their patients to refrain from clenching their teeth.

Ambulatory bruxism recording system with sleep-stage analyzing function.

PURPOSE: The aim of this study was to develop an ambulatory bruxism recording system capable of sleep-stage analysis. METHODS: A portable EMG system was used to record masseter muscle activity. An EMG sensor was attached onto the masseter muscle belly at either side. EMG data were stored on a notebook type personal computer. A sound level meter was used to assess the sound level of bruxism. Sound level (dB) readings were taken every second and recorded on the same computer. A prototype of sleep sensor, a wristwatch-style biological signal sensor-recorder device, recorded and stored pulse wave, acceleration and temperature on a memory card. All stored data were transferred to a personal computer and analyzed. RESULTS: The whole system was transportable within a protective case and weighed approximately 5kg. Raw EMG signals were processed to derive integrated EMG data. TOSHIBA Sleep Analysis Program classified sleep-stages as awake, shallow sleep, deep sleep and REM based on the activity of the autonomic nervous system that was estimated from the fluctuations of pulse intervals. An EMG, sound level and sleep-stage analysis program was developed to analyze all data simultaneously. Using this program, the masseter muscle activity, sound level and sleep-stage could be quantified and correlated. CONCLUSION: We developed an ambulatory bruxism recording system that analyzes sleep-stage. We expect that this system will enable us to measure sleep bruxism activity in each sleep-stage on an electromyographical and auditory basis at the subject's home.