The purpose of this study was to clarify the usefulness of the integral value of masseteric electromyographic waveforms as a parameter for evaluating sleep bruxism (SB).

The subjects were 76 patients with suspected SB and obstructed sleep apnea syndrome (OSAS) who visited a respiratory medical clinic and underwent an overnight sleep examination. Polysomnography with audio and video recording was used for the examination. From the masseteric EMG that was obtained, phasic bursts and tonic bursts were extracted, and episodes that were aggregated formations of SB waveforms were also extracted. The numbers of waveforms and integral values were calculated for all 76 subjects, 38 subjects of who were positive for both SB and OSAS based on the results of the sleep test [SB (+) OSAS (+) group] and 20 subjects of who were positive for SB only [SB (+) OSAS (−) group].

In each classification, a significant correlation was found between the number of bursts or episodes and the standardized integral value, but the distribution varied considerably and the correlation was not necessarily strong. The integral value per waveform for the tonic bursts was significantly larger than that for the phasic bursts. In terms of values per unit time, the number of phasic bursts was significantly larger than the number of tonic bursts. Regarding the integral value, the value for the tonic bursts was either significantly larger than that for the phasic bursts or there was no significant difference between them. That is, the tendency for the phasic bursts to be dominant in the number of waveforms was not demonstrated in terms of the integral value.

The ratio of phasic bursts and tonic bursts obtained by the evaluation using the integral value showed a different tendency from that using the number of waveforms. This suggested the importance of using not only the number of waveforms but also the integral value as a parameter for evaluating SB.

The purpose of this study was to clarify the relationship between the periodontal tactile sensation and the activity of the prefrontal cortex. Eleven young, healthy Japanese participants (mean age 28.0±3.7 years) volunteered to participate in this study. We tested either the left side central incisors or the first molars. The periodontal tactile sensation of each tooth was evaluated using calibrated monofilaments (von Frey hairs). A magnitude estimation method was used as a psychophysical method, and the periodontal ligament tactile and periodontal tactile sensation values were determined by Stevens’ power law. Prefrontal cortex activation was evaluated using a wearable functional near-infrared spectroscopy device that measured cerebral blood flow, and the experimental task involved maintaining occlusal force within an instructed range. The logarithmic values of the physical and sensory quantities of periodontal tactile sensation showed a linear relationship, and had a significantly high correlation coefficient. Regarding the periodontal tactile sensation values, no significant difference was found between the central incisors and first molars. In the molar teeth, negative correlations were found between the periodontal tactile sensation values and the cerebral blood flow in all measurement fields. Moreover, the mean occlusal force value of molars was below the instructed range, and showed significantly lower values compared to those of anterior teeth. Based on the above results, it was shown that Stevens’ power law can be applied to periodontal tactile sensation, and the periodontal tactile sensation value in molars calculated from Stevens’ power law is related to the cerebral blood flow in the prefrontal cortex and inhibition of occlusal force. The site-specific importance of the periodontal tactile sensation value was suggested during the task of maintaining occlusal force.

The purpose of this study was to clarify the effect of difference in chewing side on the sway of the center of gravity of the body. The sway of the center of gravity of 25 healthy dentate subjects （10 males and 15 females） was measured using a foot pressure distribution measurement system （Footview Clinic^®, Nitta Corporation）, and the total trajectory length of body sway was used as a quantitative parameter. The masticatory movements were recorded using chewing gum as a test food under four conditions: free chewing before and after softening and unilateral chewing （right side and left side）. The total trajectory length of body sway was compared between the free chewing before softening and free chewing after softening, between the right-sided chewing and left-sided chewing, and between the habitual chewing and non-habitual chewing. The total trajectory length was significantly shorter in free chewing after softening than in free chewing before softening, and the body sway was more stable in free chewing after softening. Comparisons between the right-sided chewing and left-sided chewing did not show any significant differences, indicating that there was no relationship between the dominant hand side and the body sway. Comparisons between the habitual chewing and non-habitual chewing showed that the total trajectory length of body sway was significantly shorter for the habitual chewing, and that the body sway was more stable with the habitual chewing than the non-habitual chewing. From these results it was suggested that the body sway was unrelated to the dominant hand side, and was most stable while chewing on the habitual chewing where the movement was most stable.