Actual state of the diurnal masseteric electromyogram: Differences between awareness and non-awareness of awake bruxism.

PURPOSE: This study aimed to elucidate the relationship between diurnal masseter muscle activity and awareness of diurnal awake bruxism (d-AB) by conducting a comparative analysis of electromyographic (EMG) data from individuals with and without awareness of diurnal awake bruxism (d-AB), utilizing EMG data gathered from multiple subjects. METHODS: Unilateral masseter electromyography (EMG) recordings were performed during the daytime using an ultraminiature wearable EMG device. A total of 119 participants (59 with awareness of diurnal tooth clenching [d-TC] and 60 without awareness of d-TC) were included. Waveforms longer than 0.25 s with the two amplitude conditions, exceeding twice the baseline and >5% of maximum voluntary clenching, were extracted. In addition, the number of bursts and episodes (groups of bursts), burst duration, and burst peak amplitude were calculated for each participant. RESULTS: There were no significant differences in the EMG parameters between the groups with and without awareness of d-TC. Additionally, the frequency distribution of the number of EMG waveforms exhibited wide ranges and substantial overlap between the two groups. CONCLUSIONS: The variability in the number of bursts and episodes, burst peak amplitude, and burst duration among subjects suggests the need for an objective classification of d-AB severity based on EMG values. The absence of significant differences and large overlap in frequency distributions between the groups with and without awareness of d-TC indicate difficulty in predicting muscle activity solely based on awareness of d-AB.

Examination of the relationship between masseter muscle activity during sleep and wakefulness measured by using a wearable electromyographic device.

Purpose This study aimed to measure masseter muscle activity throughout the day in outpatients suspected of having awake bruxism (AB) and/or sleep bruxism (SB) and examine the relationship between AB and SB by comparing muscle activity during daytime wakefulness and nighttime sleep.Methods Fifty outpatients with suspected SB and/or AB participated in this study. A single-channel wearable electromyogram (EMG) device was used for EMG recording. The selected EMG bursts were divided into bursts during sleep (S-bursts) and bursts during awake state (A-bursts). The number of bursts per hour, average burst duration, and ratio of burst peak value to maximum voluntary contraction were calculated for both the S- and A-bursts. These values of the S- and A-bursts were then compared, and the correlations between them were analyzed. Additionally, the ratios of phasic and tonic bursts in the S- and A-bursts were compared.Results The number of bursts per hour was significantly higher for A-bursts than for S-bursts. No significant correlation was found between the numbers of S- and A-bursts. The ratio of phasic bursts was large and that of tonic bursts was small in both the S- and A-bursts. A comparison of the S- and A-bursts showed that the S-bursts had a significantly lower ratio of phasic bursts and higher ratio of tonic bursts than the A-bursts.Conclusions The number of masseteric EMG bursts during wakefulness did not show any association with that during sleep. It became clear that sustained muscle activity was not dominant in AB.

Frequency distribution of the number and amplitude of electromyographic waveforms of the masseter muscle during sleep in patients with a clinical diagnosis of sleep bruxism.

OBJECTIVE: This study aimed to clarify frequency distribution of number and peak amplitude of electromyographic (EMG) waveforms of sleep bruxism (SB) in outpatients with clinical diagnosis of SB (probable bruxer: P-bruxer). METHODS: Subjects were 40 P-bruxers. Masseteric EMG during sleep was measured at home using a wearable EMG system. EMG waveforms with amplitude of more than two times the baseline and with duration of 0.25 s were extracted as SB bursts. Clusters of bursts, i.e. SB episodes, were also scored. RESULTS: There were large variations among the subjects in numbers of SB bursts and episodes and in burst peak amplitude. As for burst peak amplitude within a subject, a wide right-tailed frequency distribution was shown with the highest frequency at the class of 5-10% maximum voluntary contraction. CONCLUSION: The number and amplitude of SB waveforms for P-bruxers were distributed over a wide range, indicating the existence of large individual differences.

Portable and wearable electromyographic devices for the assessment of sleep bruxism and awake bruxism: A literature review.

OBJECTIVE: The current state of portable/wearable electromyographic (EMG) devices for assessment of bruxism was reviewed. METHODS: A search of full-text articles relevant to portable/wearable EMG devices capable of being used at home was performed. The data source used was MEDLINE via PubMed from January 1970 to July 2019. RESULTS: There were nine kinds of wearable EMG devices capable of being used under unrestrained conditions. Ultra-miniaturized wearable EMG devices with a level of performance equivalent to that of conventional stationary EMG devices have been developed and are being used during sleep and in the daytime. The devices have a high level of diagnostic accuracy for sleep bruxism. A definite cut-off value for awake bruxism has not been established. DISCUSSION: Assessment of sleep bruxism with a high level of accuracy can be performed using a portable/wearable EMG device. However, a definite cut-off value is required for assessment of awake bruxism.

Can malocclusion provide clinicians with information for differential diagnosis of temporomandibular joint diseases?: A review.

The aim of this literature review was to summarize the clinical characteristics and symptoms of temporomandibular joint diseases, and to discuss the associations between temporomandibular joint diseases and categorization of malocclusion. Electronic literature searches were performed using the PubMed database. The authors established a differential diagnostic method for temporomandibular joint diseases related to malocclusion. A literature search using PubMed yielded 213 texts, of which based on exclusion criteria, 28 were included in this study. Malocclusions were categorized into 5 types. The authors suggested a diagnostic tree of temporomandibular joint diseases based on the types of malocclusion and 4 variables in clinical characteristics and symptoms. Clinicians treating malocclusions must attempt to clarify the cause of the occlusal condition. If caused by temporomandibular joint disease, it is important to make a proper differential diagnosis at first, and not to overlook the causative disease. Further clinical knowledge of associations between temporomandibular joint diseases and malocclusions should be accumulated, and the diagnostic tree should be improved based on new information.

Validity of clinical diagnostic criteria for sleep bruxism by comparison with a reference standard using masseteric electromyogram obtained with an ultraminiature electromyographic device.

Evaluation of sleep bruxism (SB) in clinical practice is currently conducted based on clinical findings, i.e., clinical diagnostic criteria consisting of medical interview, findings of tooth wear, and symptoms of temporomandibular joint (TMJ) and muscles. However, there are many unclear points about validity of the criteria. In this study, validity tests were conducted to clarify the accuracy of the clinical diagnostic criteria for SB by comparison with a reference standard using a single-channel masseteric electromyogram (EMG) obtained with ultraminiature electromyographic devices. The subjects included 30 'probable' bruxers (P-bruxers) who were clinically diagnosed as having SB and 30 non-bruxers. EMG was recorded during sleep under unrestrained and accustomed condition at each subject's home using ultraminiature cordless EMG devices. Bursts with amplitudes of more than 5%, 10%, 20% of the maximum voluntary contraction (MVC) value (EMG-burst-5%, EMG-burst-10%, and EMG-burst-20%) and episodes of sleep bruxism (EMG-episode) were selected for analyses. In all conditions for burst selection, the P-bruxer group showed a significantly larger number of bursts and episodes than those in the non-bruxer group. Accuracy of the clinical diagnosis criteria was 66.7% with the reference standard using EMG-burst-5%/h and 58.3% with that using EMG-episodes/h. By applying single-channel EMG as the reference standard, we were able to conduct validity tests of clinical diagnostic criteria with a larger sample. It was clarified that the level of accuracy of clinical diagnostic criteria for SB were not high despite using the combination of an interview and clinical findings.

A newly developed ultraminiature wearable electromyogram system useful for analyses of masseteric activity during the whole day.

PURPOSE: We describe the characteristics of a new data-logger-type ultraminiature electromyogram (EMG) system (FLA-500-SD) and methods used for recording and we show its potential in clinical applications by presenting an example of a clinical case. METHOD: FLA contains electrodes, an amplifier, 12-bit analog-to-digital (A/D) converter at a sampling frequency of 1kHz, 16-bit CPU, a 3.7-V coin-shaped lithium battery, and a micro SD card. The size of FLA is 37.0×23.5×8.6mm, and its weight is 6g (9g with a battery inserted). The device is wearable and patients can attach the device and operate it by themselves in daily life. Data recorded in the micro SD card are transferred to a personal computer and analyzed. Although the device is ultraminiature and wearable, it has the capacity for recording a precise and clear masseteric surface electromyogram that is not inferior to that recorded by conventional stationary-type EMG recording systems. CONCLUSIONS: To our knowledge, the device is the smallest and lightest device with capacity for the longest consecutive measuring time as a data-logger-type electromyograph with built-in electrodes and memory. The device is useful for analyses of masseteric activity during the whole day. In the future, it is expected that applications of the device will expanded to observation, evaluation and diagnosis of normal or abnormal gnathic functions, e.g., assessment of sleep and awake bruxism and observation of the chewing state in daily life.

Rhythm and amplitude of rhythmic masticatory muscle activity during sleep in bruxers - comparison with gum chewing.

OBJECTIVES: The aim of this study was to elucidate characteristics of rhythmic masticatory muscle activity (RMMA) during sleep by comparing masseteric EMG (electromyogram) activities of RMMA with gum chewing. METHOD: The parts of five or more consecutive phasic bursts in RMMA of 23 bruxers were analyzed. Wilcoxon signed-rank test for matched pairs and Spearman's correlation coefficient by the rank test were used for statistical analysis. RESULTS: Root mean square value of RMMA phasic burst was smaller than that during gum chewing, but correlates to that of gum chewing. The cycle of RMMA was longer than that of gum chewing due to the longer burst duration of RMMA, and variation in the cycles of RMMA was wider. DISCUSSION: These findings suggest that the longer but smaller EMG burst in comparison with gum chewing is one of the characteristics of RMMA. The relation between size of RMMA phasic bursts and gum chewing is also suggested.

Weak association between sleep bruxism and obstructive sleep apnea. A sleep laboratory study.

PURPOSE: No definitive associations or causal relationships have been determined between obstructive sleep apnea-hypopnea (OSAH) and sleep bruxism (SB). The purpose of this study was to investigate, in a population reporting awareness of both OSAH and SB, the associations between each specific breathing and jaw muscle event. METHODS: Polysomnography and audio-video data of 59 patients reporting concomitant OSAH and SB history were analyzed. Masseteric bursts after sleep onset were scored and classified into three categories: (1) sleep rhythmic masticatory muscle activity with SB (RMMA/SB), (2) sleep oromotor activity other than RMMA/SB (Sleep-OMA), and (3) wake oromotor activity after sleep onset (Wake-OMA). Spearman's rank correlation coefficient analyses were performed. Dependent variables were the number of RMMA/SB episodes, RMMA/SB bursts, Sleep-OMA, and Wake-OMA; independent variables were apnea-hypopnea index (AHI), arousal index(AI), body mass index(BMI), gender, and age. RESULTS: Although all subjects had a history of both SB and OSAH, sleep laboratory results confirmed that these conditions were concomitant in only 50.8 % of subjects. Moderate correlations were found in the following combinations (p < 0.05); RMMA/SB episode with AI, RMMA/SB burst with AI and age, Sleep-OMA burst with AHI, and Wake-OMA burst with BMI. CONCLUSIONS: The results suggest that (1) sleep arousals in patients with concomitant SB and OSAH are not strongly associated with onset of RMMA/SB and (2) apnea-hypopnea events appear to be related to higher occurrence of other types of sleep oromotor activity, and not SB activity. SB genesis and OSAH activity during sleep are probably influenced by different mechanisms.

Temporal association between sleep apnea-hypopnea and sleep bruxism events.

There is some evidence suggesting that obstructive sleep apnea-hypopnea syndrome is concomitant with sleep bruxism. The aim of this study was to investigate the temporal association between sleep apnea-hypopnea events and sleep bruxism events. In an open observational study, data were gathered from 10 male subjects with confirmed obstructive sleep apnea-hypopnea syndrome and concomitant sleep bruxism. Polysomnography and audio-video recordings were performed for 1 night in a sleep laboratory. Breathing, brain, heart and masticatory muscle activity signals were analysed to quantify sleep and sleep stage duration, and number and temporal distribution of apnea-hypopnea events and sleep bruxism events. Apnea-hypopnea events were collected within a 5-min time window before and after sleep bruxism events, with the sleep bruxism events as the pivotal reference point. Two temporal patterns were analysed: (i) the interval between apnea-hypopnea events termination and sleep bruxism events onset, called T1; and (ii) the interval between sleep bruxism events termination and apnea-hypopnea events onset, called T2. Of the intervals between sleep bruxism events and the nearest apnea-hypopnea event, 80.5% were scored within 5 min. Most intervals were distributed within a period of <30 s, with peak at 0-10 s. The T1 interval had a mean length of 33.4 s and was significantly shorter than the T2 interval (64.0 s; P < 0.05). Significantly more sleep bruxism events were scored in association with the T1 than the T2 pattern (P < 0.05). Thus, in patients with concomitant obstructive sleep apnea-hypopnea syndrome and sleep bruxism, most sleep bruxism events occurred after sleep apnea-hypopnea events, suggesting that sleep bruxism events occurring close to sleep apnea-hypopnea events is a secondary form of sleep bruxism.

Day-to-day variations in salivary cortisol measurements.

PURPOSE: The purpose of this study was to clarify the day-to-day variations of salivary cortisol to discuss the appropriate timing for collecting saliva in a day for stress evaluation. MATERIALS AND METHODS: Saliva samples from twelve healthy adults were collected by means of Salivette(®) (SARSTEDT Co.) three times per day, immediately after awakening (Time1), 6:00 PM (Time2) and 30 min before going to bed (Time3), on 5 nonconsecutive days. Cortisol concentration was measured using a radioimmunoassay. RESULTS: Salivary cortisol concentration showed the larger value at Time1 than that at Time2. The mean value of %CV for day-to-day variation showed the smallest value at Time1 (mean: 43.1%) and the largest value at Time3 (mean: 100.3%). There were significant differences in %CV value between Time1 and Time3, Time2 (mean: 64.1%) and Time3. CONCLUSIONS: There are considerable day-to-day variations in salivary cortisol concentration measurements. From the viewpoint of day-to-day variation, collecting saliva immediately after awakening in the morning is thought to be more advantageous for evaluating cortisol concentration.

Influence of motion and posture of the head on data obtained using the newly developed ultraminiature cordless bruxism measurement system.

PURPOSE: To elucidate the influence of motion and posture of head on the newly developed ultraminiature cordless bruxism measurement system (BMS), we examined masseteric electromyographic (EMG) data of BMS during turning-over movements in bed in comparison with those of a conventional polygraph system (PG). METHODS: Twelve healthy subjects lay on their back and then turned to the right (right turn, 90 degrees) and then to the left (left turn, 180 degrees). Maximum amplitudes and root mean square (RMS) values of EMG data were calculated during the phase of turning movements. The data were high-pass filtered at 10 Hz, 30 Hz, 50 Hz, and 100 Hz. RESULTS: Artifact signals were visibly observed in PG measurement for all subjects and in BMS measurement for three subjects. Maximum amplitudes during right turn measured by BMS were significantly smaller than those measured by PG, while there was no significant difference during left turn. During right turn, RMS values high-pass filtered at 10 Hz obtained by BMS were significantly smaller than those obtained by PG, while there was no significant difference between the data obtained by the two devices at the other cut-off frequencies. During left turn, there was no significant difference between RMS values obtained by the two devices. CONCLUSIONS: Although BMS data were slightly affected by motion and posture of head during simulated sleep-turning, it was suggested that motion artifact of signals during BMS measurements is equivalent to or less than that during PG measurements, and BMS is thought to be suitable to measure sleep bruxism.

Condylar movements of temporomandibular disorder patients with intermittent lock: a pilot study.

The purpose of this study was to clarify which direction of the condylar path is advantageous for releasing TMJ intermittent lock. The subjects were ten patients with temporomandibular disorders (TMD) and intermittent lock caused by anterior displacement of disks without obvious medial or lateral displacement. The patients could not open their mouths fully in habitual opening but could open fully in an intentional winding opening with reduction of the anteriorly displaced disks (winding opening). The two kinds of movement at the kinematic condylar point were measured in each subject and compared. The length of the condylar path in winding opening was significantly larger than that in habitual opening. The affected side condyle of winding opening traced medio-inferior paths in the early part of the condylar translation in comparison with habitual opening. From the viewpoint of the condylar path, the medio-inferior direction of condylar translation is thought to be advantageous for releasing intermittent lock.

The influence of tissue blood flow volume on energy metabolism in masseter muscles.

This study investigated the energy metabolism of masseter muscles by 31P-Magnetic Resonance Spectroscopy (MRS) during increased blood flow induced by hot pack application to clarify the influence of changes in blood flow on muscle fatigue. Twelve healthy subjects with no history of muscle pain in the masticatory system participated in this study. The 31P-MRS measurements were performed before and after hot pack application and the ratio of phosphocreatine (PCr) acting as the energy source to reproduce ATP to beta-ATP, the PCr/beta-ATP ratio, was analyzed. Results showed that PCr/beta-ATP ratios increased significantly by an average of 22.4% after the hot pack application. The results suggest that changes in blood flow volume influence the energy metabolism in masseter muscles and that blood flow increases due to the hot pack cause higher energy levels in masseter muscles and offer an advantageous condition for preventing and relieving muscle fatigue.