We have been focusing on research of the function of human prefrontal cortex, in order to develop methods that can maintain and/or improve cognitive functions as well as quality of life. The prefrontal cortex is known to have an important cognitive function named executive function which plays important roles in making a future plan, decision making, control for behaviors, etc. In general, people feel decline of their cognitive functions by themselves after middle age. However, in fact, the functions of the prefrontal cortex decline linearly from age 20. The recent investigations of cognitive neuroscience show beneficial effects by cognitive trainings to prevent such age related decline of cognitive functions. Particularly, the working memory training is the one can improve non-trained prefrontal functions and induce plasticity for brain structures of the prefrontal cortex. Previously, we measured brain activity during movements of mouth, tongue, or rip by functional MRI. We found only the sensori-motor area of the bilateral cortices was activated, and no activation in the prefrontal cortex. Our results combined with the fact that mastication does not require working memory function lead a conclusion that one cannot improve cognitive functions only by mastication.

View full abstract

Purpose: The number of patients complaining of uncomfortable occlusion has recently increased. However, methods for differentiating dysesthesia from disorder of aesthesia causing uncomfortable occlusion have not been established. The purposes of this study were to set the normal range of periodontal mechanosensitive threshold in adult dentulous persons and to utilize clinically.
 Methods: 32 adult dentulous subjects (20 males and 12 females, mean age: 26.1 ± 3.7 years) with normal dentition evaluated by add picture regulated bite force were selected. The subject teeth were 28 teeth between the bilateral second molar on maxillary and mandibular. Measurement was performed with their eyes closed, sitting on a chair. In measuring periodontal mechanosensitive threshold, von Frey's hair came into contact with the subject teeth from the labio-buccal surface side, and stimulation was applied in the lingual direction. Measurement was performed by a dentist with sufficient knowledge and training, and thresholds were determined applying the up-down method of the method of limits of psycho-physical measurement methods. The interquartile range of periodontal mechanosensitive threshold of the normal subjects was calculated.
 Periodontal mechanosensitive threshold of the man complained uncomfortable occlusion after orthodontic treatment were measured from one month after the removal of the device every the 14^th.
 Results: There were no abnormal occlusal contact both normal subjects and clinical case. It was shown that periodontal mechanosensitive threshold gradually increased from the anterior tooth to molar area. The interquartile range of periodontal mechanosensitive threshold was 0.5-1.7g in the maxillary anterior tooth area, 1.5-3.0g in the canine teeth, 1.5-4.0g in the premolar area, and 3.7-8.8g in the molar area. The interquartile range of periodontal mechanosensitive threshold was 0.3-1.0g in the mandibular anterior tooth area, 0.7-3.0g in the canine teeth, 0.8-5.0g in the premolar area, and 3.0-11.6g in the molar area.
 Periodontal mechanosensitive threshold when one month passed was 190.0g or less in molar teeth and was 7.0g or less in anterior teeth. Afterwards, the value of periodontal mechanosensitive threshold was decreased. The value of periodontal mechanosensitive threshold when three months passed after removal device was decreased until the interquartile range, and uncomfortable occlusion was disappeared. The change was not shown in periodontal mechanosensitive threshold and uncomfortable occlusion when seven months passed after removal device.
 Conclusion: These results revealed that periodontal mechanosensitive threshold become objective index of sensitive of teeth.

View full abstract

Purpose:
Various types of artificial teeth have been developed to improve chewing ability of complete denture wearers. Bladed artificial teeth are one of typical artificial teeth. However, there are a few reports about the effect of the bladed artificial teeth on chewing ability of complete denture wearers. This study aimed to investigate the characteristics of chewing ability of complete denture with bladed artificial teeth.
Methods:
Nine edentulous patients wearing complete denture in a dental clinic were subjected. Four patients wore the dentures with bladed artificial teeth (bladed teeth denture), and other 5 patients wore the dentures using anatomical formed artificial teeth (normal teeth denture).
Measurement of maximum bite force at the first molar region and assessment of diet and satisfaction for the dentures through use of questionnaire were made and compared between two groups.
Result and Discussion:
Maximum bite force and chewing scores calculated from the questionnaire did not show significant difference between bladed teeth denture group and normal teeth denture group. When the subjects masticated the foods which need shearing force for chewing, chewing ability was significantly different between two groups. Bladed teeth denture is useful for improving the chewing ability for the foods needed shearing force. significant correlation between chewing ability and maximum bite force was not observed in the blade teeth denture group, although significant correlation was seen in the normal denture group. These results suggested the possibility that bladed teeth denture may improve chewing ability of patients with small maximum bite force.

View full abstract

It may be expected that experience of the different kind food during postnatal development, such as milk (liquid) at preweaning stage, weaning food (semi-liquid) at weaning stage and pellet (solid) at postweaning stage, should be crucial for development of ability to adapt mandibular movement and masticatory muscle activities to physically different food. Two groups of rabbits were raised on pellet and powder diet from 6-weeks old (just after weaning) to 33-weeks old during postnatal development, respectively. Around 31-32 weeks old, short term recordings of jaw movements and EMGs of the masseter muscle were made not only during mastication of the primary diet, but also during mastication of the diet which was used in the other group. The data obtained from the two groups during mastication of the same diet were compared to examine effects of the long term raising on soft food on functional developments of mastication. It was found that the rabbits of the powder-raised group were able to masticate pellet with no difficulty and no hesitance, even though this was the first time for the rabbits to masticate pellet at all. Mandibular movement pattern of the powder-raised group during pellet mastication was found to be of grind type, which was similar to those observed in the pellet-raised group during the same diet, pellet mastication. There was no significant difference in a number of chewing cycles consisting of a chewing sequence and in duration of jaw-closing phase between the two groups during mastication of 1-g pellet. These findings suggest that long term powder raising would not necessarily lead to impairment of the masticatory function to adapt masticatory apparatus to physically different diet, especially to hard diet. However, not fundamental but notable functional differences between the two groups were found; 1) duration of the jaw-opening phase was shorter in the powder-raised group compared with the pellet-raised group and 2) the masseter muscle activities appeared in the jaw-opening phase in the powder-raised group and the corresponding difference in the trajectories of the jaw movement was found between the two groups.

View full abstract