Objectives: To improve understanding of the physical characteristics of patients with obstructive sleep apnea （OSA） by measuring muscle stiffness in the submental region in both patients with OSA and healthy participants as a normal control.
Methods: In total, 16 participants with OSA （8 men and 8 women, 51.8 years） and 14 healthy participants （7 men and 7 women, 50.1 years） were recruited. Submental muscle stiffness was measured at the habitual occlusal position （HOP）, maximum mandibular protrusive position （MPP）, and tongue protrusive position （TPP） during breathing cessation. A muscle hardness meter was used for the measurements.
Results: The HOP was significantly lower than the MPP and TPP in both groups （p＜0.05）. While similar tendencies were observed in women across the groups, in males, the HOP was significantly lower than the MPP in the control group and lower than the TPP in the OSA group. Interestingly, there was a tendency for muscle stiffness in each jaw position to be higher in women than men between the two groups. A significant negative correlation between TPP/HOP and apnea hypopnea index （AHI） was observed.
Conclusion: There was no significant difference for the muscle stiffness in each jaw position between the OSA group and the control group, and there was also no significant difference for the muscle stiffness in each jaw position between women and men. Furthermore, there was a significant negative correlation between TPP/HOP and AHI. These findings suggest that the muscle stiffness test may be useful in the examination of OSA.

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Objectives: Social jet lag （SJL） is a recurrent state of jet lag caused by the discrepancy in a person’s sleep pattern between workdays and holidays due to work and social schedules. It has been reported that a larger SJL is significantly correlated with lower academic performance. The present study included fifth-year dental students who attended a remote lecture course for two months prior to starting clinical practice. We deduced that it was difficult for them to maintain their daily rhythm during the two months of remote learning. We focused on the chronotype and SJL of those students who had to make a switch to a morning-oriented daily rhythm and investigated the association with academic performance.
Methods: The Japanese version of the Morningness-Eveningness Questionnaire （MEQ）, which has 19 items, was distributed to the students and collected on the spot after they completed it—they were asked to indicate their sleep start and end times on the days with lectures and practical work, and on holidays. Based on their MEQ score, they were classified into three chronotypes: morning type, intermediate type, and night type. The median time of sleep （midpoint of sleep on workdays ［MSW］ and midpoint of sleep on free days ［MSF］） was calculated by adding the sleep start and end times and dividing by two. SJL was calculated by subtracting MSW from MSF. Grade Point Average （GPA） was analyzed using the total score of the achievement test, which was held every three weeks and 12 times throughout the year.
Results: In GPA, there was no significant difference between genders, but there was a significant difference （p＜0.05） between the students who had repeated grades and the students who had not. Among the students who had repeated grades, there was a significant negative correlation （rs＝−0.462, p＜0.05） between GPA and SJL.
Conclusions: We found that there was a significant negative correlation between SJL and academic performance among dental students who had been retained. This indicates that irregular circadian rhythms may affect dental students’ academic performance.

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Introduction: Continuous positive airway pressure and oral appliances （OA） are typical treatments for obstructive sleep apnea （OSA）. There are many reports confirming the effect of OA by polysomnography （PSG） for improvement of OSA. However, many reports included only objective evaluations; few reports also evaluated subjective changes in sleep. Therefore, we investigated and compared the results of objective sleep tests before and after OA treatment with a subjective sleep questionnaire.
Method: We enrolled 99 consecutive patients with OSA who were diagnosed by PSG and answered the Pittsburgh Sleep Questionnaire （PSQI） from January 2016 to December 2017 at the Ota Memorial Sleep Center. As for the method, cases in which the apnea-hypopnea index （AHI） decreased to less than 5/h or more than 50% after wearing an OA were classified into the improved group, and the others were classified into the non-improved group. We compared each parameter before and after wearing the OA by statistical analysis. The parameters were PSQI, AHI, Non-REM AHI, REM AHI, total sleep time, sleep latency REM latency, sleep efficiency, sleep stage （Stage 1-3 + 4, REM） ratio, arousal time, total arousal index and respiratory-related arousal index.
Results: There were 60 cases in the improved group and 39 cases in the non-improved group. In the improved group, significant improvements of PSQI total score, sleep quality and sleepiness were observed after OA treatment. In the non-improved group, there was a significant subjective improvement of sleep onset time, difficulty sleeping and sleepiness after OA treatment. PSG results showed a significant decrease in AHI, Non-REM AHI, REM AHI, Stage 1, increase in Stage 2, and a decrease in respiratory-related arousal index in both groups. In the improved group, a significant increase in Stage REM, and a decrease in total arousal index and arousal time were observed.
Conclusion: Subjective sleep improved before and after OA treatment for OSA, regardless of improvement in AHI.

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