Taihiko Yamaguchi

Comparison of ambulatory and polysomnographic recording of jaw muscle activity during sleep in normal subjects

Clinicians and investigators need a simple and reliable recording device to diagnose or monitor sleep bruxism (SB). The aim of this study was to compare recordings made with an ambulatory electromyographic telemetry recorder (TEL-EMG) with those made with standard sleep laboratory polysomnography with synchronised audio-visual recording (PSG-AV). Eight volunteer subjects without current history of tooth grinding spent one night in a sleep laboratory. Simultaneous bilateral masseter EMG recordings were made with a TEL-EMG and standard PSG. All types of oromotor activity and rhythmic masseter muscle activity (RMMA), typical of SB, were independently scored by two individuals. Correlation and intra-class coefficient (ICC) were estimated for scores on each system. The TEL-EMG was highly sensitive to detect RMMA (0·988), but with low positive predictive value (0·231) because of a high rate of oromotor activity detection (e.g. swallowing and scratching). Almost 72% of false-positive oromotor activity scored with the TEL-EMG occurred during the transient wake period of sleep. A non-significant correlation between recording systems was found (r = 0·49). Because of the high frequency of wake periods during sleep, ICC was low (0·47), and the removal of the influence of wake periods improved the detection reliability of the TEL-EMG (ICC = 0·88). The TEL-EMG is sensitive to detect RMMA in normal subjects. However, it obtained a high rate of false-positive detections because of the presence of frequent oromotor activities and transient wake periods of sleep. New algorithms are needed to improve the validity of TEL-EMG recordings.

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.

Sclerostin Enhances Adipocyte Differentiation in 3T3-L1 Cells.

Sclerostin, a secreted protein encoded by the Sost gene, is produced by osteocytes and is inhibited by osteoblast differentiation and bone formation. Recently, a functional association between bone and fat tissue has been suggested, and a correlation between circulating sclerostin levels and lipid metabolism has been reported in humans. However, the effects of sclerostin on adipogenesis remain unexplored. In the present study, we examined the role of sclerostin in regulating adipocyte differentiation using 3T3‐L1 preadipocytes. In these cells, sclerostin enhanced adipocyte‐specific gene expression and the accumulation of lipid deposits. Sclerostin also upregulated CCAAT/enhancer binding protein β expression but not cell proliferation and caspase‐3/7 activities. Sclerostin also attenuated canonical Wnt3a‐inhibited adipocyte differentiation. Recently, the transcriptional modulator TAZ has been involved in the canonical Wnt signaling pathway. Sclerostin reduced TAZ‐responsive transcriptional activity and TAZ‐responsive gene expression. Transfection of 3T3‐L1 cells with TAZ siRNA increased the lipid deposits and adipogenic gene expression. These results show that sclerostin upregulates adipocyte differentiation in 3T3‐L1 cells, suggesting a possible role for the osteocyte‐derived sclerostin as a regulator of fat metabolism and as a reciprocal regulator of bone and adipose tissues metabolism. J. Cell. Biochem. 117: 1419–1428, 2016.

Analyses of muscular activity, energy metabolism, and muscle fiber type composition in a patient with bilateral masseteric hypertrophy.

ABSTRACT Hyperwork of the masseter muscles due to habitual parafunction is thought to induce masseteric hypertrophy (so called work hypertrophy). However, the causes underlying this disease are not yet fully understood. Recently, we had a patient with bilateral masseteric hypertrophy, and we performed a partial excision of the masseter muscles. In this patients case, we examined muscular activity, energy metabolism, and fiber type composition of the masseter muscles using electromyograms (EMG), 31P-magnetic resonance spectroscopy (MRS), and enzyme-histochemistry. The EMG showed no hyperactivity, and the 31P-MRS showed normal energy spectral patterns and PCr contents of the masseter muscles. The fiber type composition, however, in the muscles in this case was very different from that in muscles with “work hypertrophy” and also that in normal masseter muscles: 1. Loss of type MB fibers; 2. Increases in type IIA and in type IM & IIC fibers; and 3. Decrease in type I fibers. The findings suggest that this is not a case of work hypertrophy but a case of compensatory hypertrophy possibly due to a lack of high-tetanus-tension type IIB fibers.

Symptoms and physiological responses to prolonged, repeated, low-level tooth clenching in humans.

The traditional view contends bruxism, such as tooth grinding/clenching, is part of the etiology of temporomandibular disorders (TMD) including some subtypes of headaches. The purpose of this study is to investigate if a low‐level but long‐lasting tooth‐clenching task initiates TMD symptoms/signs.

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.

Regional Differences of Metabolism in Human Masseter Muscle by Two-dimensional 31P-Chemical Shift Imaging:

Many reports have demonstrated significant region-dependent differences in the fiber-type composition of the human masseter muscle. Therefore, it is considered that there is intramuscular heterogeneity of metabolic activity in the muscle. The present study was carried out, with two-dimensional Chemical Shift Imaging, to detect differences between the deep and superficial parts of the human masseter muscle at rest. Masseter muscle from 11 volunteers, from 20 to 27 years old, was examined, and characteristic spectra of the inorganic phosphate (Pi), phosphocreatine (PCr), and a-, β-, and γ-adenosine triphosphate (ATP) from each part of the muscles were obtained. In this study, the deep and superficial parts of the masseter muscle were distinguished by the existence of aponeurosis. The Pi/PCr, PCr/β-ATP, and Pi/β-ATP ratios as well as the pH in the deep and superficial parts were calculated from the peak spectra. Compared with the deep part, the Pi/PCr of the superficial part was lower (p < 0.05) and the PCr/β-ATP was higher (p < 0.01). The Pi/β-ATP and pH showed no significant differences between the two parts. The results indicate that the superficial part of the masseter muscle contains more PCr than the deep part, and this may be related to functional differences between these two parts. In future examinations of the metabolic activity of the human masseter muscle, the deep and superficial parts must be measured separately.

Electromyographic activity of the jaw-closing muscles during jaw opening in patients with masseter muscle contracture.

ABSTRACT Contracture of the jaw-closing muscles is one of the causes of limitation of jaw opening. This study examined whether there is any difference between the EMG activities of jaw-closing muscles during jaw opening in healthy people and in patients with masseter muscle contracture (MMC), who do not have a history of trauma or infection. The patient group consisted of eleven females, 18 to 62 years old with no history of trauma or infections, with limited mouth opening due to MMC. The control group included eleven healthy females, 23 to 50 years old. The EMG activity was recorded bilaterally in the central portion of masseter muscles (Mm), the anterior portion of temporal muscles (Tm), and the anterior belly of digastric muscles (Dm). Nine out of the patient group showed obvious EMG activity in Mm during jaw opening which was different from typical EMG patterns during jaw opening of up to 40 mm in the control group. Among the nine patients, eight showed antagonistic contraction in Tm as well as Mm. The mean integral value of Mm and Tm during jaw opening in the patient group was significantly higher than in the control group (P<0.01). These results suggest that EMG activity during jaw opening in MMC patients with no history of trauma or infections is different from that in healthy people.

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.

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

Abstract 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 ß-ATP, the PCr/ß-ATP ratio, was analyzed. Results showed that PCr/ß-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.