Purpose: A mono-block type oral appliance （OA） that restrains jaw-opening and a two-piece type OA with structure allowing jaw-opening are used for the treatment of obstructive sleep apnea syndrome. The aim of this study was to elucidate the difference between feeling and mental stress when wearing mono-block OA and those when wearing two-piece OA.
Materials and Methods: The subjects were twelve healthy volunteers. For each subject, a mono-block OA and a two-piece OA were made at the same mandibular position with a 5-mm bite raising from centric occlusion. Measurements under three conditions （without OA, with mono-block OA and with two-piece OA） were performed for two courses consisted of three nights with interval of two weeks. Salivaα-amylase activity, electrocardiograph （ECG） R-R interval, psychological test, self-assessment score of sleep state and awareness score for preference of use were examined.
Results: As for salivaα-amylase activity, ECG R-R interval and psychological test, most subjects with OA didn't show deviated data from the standard range, and there were no significant differences between the data with mono-block OA and those with two-piece OA. Regarding self-assessment score of sleep state and awareness score for preference of use, two-piece OA showed significantly higher values than those of mono-block OA.
Conclusion: It was suggested that two-piece OA with structure allowing jaw-opening was superior to mono-block OA in the assessment items （self-assessment score of sleep state and awareness score for preference of use） that were dominantly based on subjective feeling.

Recently, the decline in mastication, swallowing, and respiratory function has become an important issue due to developmental delay and inadequate acquisition of oral function in children. The failure to develop oral function is related to body type, nutrition and respiration as “other functions” besides eating and speaking functions. In this study, we investigated the relationship between body posture and oral function during adolescence, just before the completion of the final permanent dentition.
The subjects were 96 pediatric patients after the beginning of second molar eruption （45 males and 51 females, mean age 16.6±2.7 years） who had been under regular management at one dental clinic. Body posture was classified into two types: normal and slouching posture according to subjective judgments by the individual and dentist. As oral functions, maximum bite force, occlusal contact area, lip pressure, tongue pressure, and masticatory ability were measured.
Of the 96 subjects, 34 and 62 subjects were assessed to have normal and slouching posture, respectively. The mean values of lip pressure, tongue pressure, and masticatory ability in the subjects with slouching posture were lower than those with normal posture. The mean values of maximum occlusal force and occlusal contact area in the subjects with slouching posture were almost the same or slightly higher than those with normal posture. The results of logistic regression analysis showed that four factors affecting body posture were substituted, with masticatory ability being a significant coefficient. These results suggest that body posture is significantly related to masticatory ability.

This study aimed to clarify the masticatory movement rhythm before and after the perception of bitterness in food. Twenty-two healthy adults were asked to chew bitter and non-bitter gummy jellies, and the movement of the incisal point was recorded. Recordings were first performed during mastication of non-bitter gummy jelly （mastication A） followed by mastication of bitter gummy jelly （mastication B）, with a 5-minute interval between recordings. Subjects were asked to press a switch when they perceived bitterness, and 10 cycles starting from the 11th cycle before pressing the switch were defined as pre-bitterness, and 10 cycles starting from the 2nd cycle after pressing the switch were defined as post-bitterness. Next, for these ten cycles, the opening, closing, occluding, and cycle times were calculated. Further, the coefficient of variation （CV） was obtained from the mean time of the ten cycles and its standard deviation. The mean value was considered a parameter of movement rhythm and the CV as a parameter of stability of the movement rhythm. The values of parameters representing movement rhythm and its stability were compared between mastication A and B. The movement rhythm and its stability in mastication A and B were similar before bitterness recognition, with no significant differences. After bitterness recognition, the values of both parameters representing movement rhythm and its stability were larger in mastication B than in mastication A, with significant differences for all parameters, except the CV of the closing time. These findings suggested that food taste, especially bitterness, affects the movement rhythm during chewing.

Outline of the case: We reported a case of severe awake bruxism （AB） with frequency of muscle activity during an awake state being far from normal but with amount of muscle activity during sleep being within the normal range. The patient was a female in her 80s who visited our hospital with chief complaint of shifting of mandible to the right and awareness of clenching teeth. After clinical examinations, conventional electromyography （EMG） was performed at the hospital, but involuntary muscle activity at rest were not distinctly observed. A conventional upper jaw oral appliance was set to stabilize mandibular position. Then, the upper and lower removable partial dentures and other necessary dental treatments were conducted, and the mandibular position became stable without feeling of shift of mandible to the right. However, the patient was still aware of clenching and complained pain of mucosa under the dentures when wearing for a long time. Therefore, using a wearable EMG device, EMG were examined during awakening and sleep in daily life.
Results: The number of EMG episodes was extremely high during daytime awakening, while those during sleep was within normal range. Therefore, on the upper and lower jaws, we manufactured oral appliances with denture structure in missing teeth area so that the load on the ridge of missing teeth area at the time of clenching could be controlled during awakening. As a result, the pain of the jaw ridge disappeared, and the awareness of clenching was reduced.
Conclusions: By using the wearable EMG device, the abnormal activities of the masticatory muscles during the daytime which was not found in the hospital was able to be detected. Based on the EMG findings, effective countermeasures were conducted. The present case demonstrated that severe AB can occur even in a patient who is not a sleep bruxer.