In an everyday life, we experienced and know that gum-chewing raises arousal, but this effect has not been proved experimentally. In the present experiment, it was examined using Japanese UMACL test. UMACL test (UWIST Mood-Adjective Checklist) is a self-reported questionnair, which was originally composed in English by Matthews, Jones and Chamberlain (1990). It consists of 3 dimensional-scales; Energetic Arousal (active-tired), Tense Arousal (nervous-calm) and Hedonic Tone (pleasure-displeasure). Fifty four undergraduate students were tested in class of psychology (December 8, 1992, 6: 00p.m.-7: 30p.m.). The UMACL test was performed twice; when the subjects were chewing gum, and they were not (for control). Gum chewing affected all the three UMACL scales significantly, in comparison to the control data. It raised Energetic Arousal. In Contrast, it Lowered Tense Arousal. It also raised Hedonic Tone. This pattern of results suggests that arousal effect from gum chewing is excellent and expedient.

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To investigate, record and compare the dental health of Nigerians with those of the Japanese, a longitudinal dental survey, funded by a Grand-in-Aid for Overseas Scientific Research of Ministry of Education, Science and Culture of Japan, was jointly conducted by Japanese investigators and Nigerian team in lle-lfe, Nigeria from 1980 to 1991. The interesting results were as follows: Both caries prevalence rate and the average DMFT were very low (1). The average number of missing teeth was 4 between the ages of 60 to 70 years (2). Amongst the follow-up subjects between 1986 and 1991 surveys, 7 first and 4 second molars previously charted as C₁ caries lesion were intact at the later survey. Two first molars changed from C₂ category to intact (3). The Nigerian dental arch was larger than that of the Japanese (4). In spite of the marked deposition of caluculus there were fewer incidences of severe periodontal disease than those of the Japanese (5). The average maximum alveoral bone loss was 28% over the age of 60 years (6). Severe attrition of the teeth had gradually trans-formed the shape of the condylar head from round to ultra-flat (7). These changes could be attributable to the physical consistence of the diet.

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The effect of hyposalivation on the chewing time of foods and the water content of food bolus at the time of swallowing were examined in 6 young adults. The foods selected were steamed rice, cookie and sausage, and hyposalivation was induced by taking 0.5 mg atoropine sulfate. The volume of saliva was determined by subtracting the initial weight of food from that of the food bolus after subjects had chewed it normally and then spat it into a weighed container, without swallowing . The chewing times per one mouthful of food were longer statistically when the salivary flow rate was decreased rather than the normal flow rate. But there were no significant differences in the water content of food bolus after chewing. It is concluded that the effect of the salivary flow rate is important in the masticatory efficiency.

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This paper includes two topics, a newly designed mastication robot mechanism using a human skull model and reduction of the temporomandibular joint force (TMJF) focused on the fan shape of the M.temporalis. Although the authors designed former mechanisms of the mastication robots based on simple geometrical planes because these robots consist of the dental model and the duralumin mandible, actual human mandible has complicated 3D shape. Therefore the authors developed a human-like mastication robot by using a human skull model. Furthermore the authors placed the actuators correspond to anterior and posterior part of M.temporalis with refer to the fan shape of the M.temporalis. The reduction of TMJF was confirmed in simulations with variable force vectors of M.temporalis. Experimentally the authors confirmed the 28% reduction of TMJF by using this robot. As conclusions, the authors proved the effectiveness of proposed theory in this study both simulations and experiments.

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The ability of tongue to find out an object in the mouth (threshold of object perception ; PT) and the ability of tongue to carry it to the masticatory surface (chewing threshold ; CT) were studied in healthy twelve adult subjects. Fine spherical materials (the lens of fish) of a size varying 0.3mm to 1.9mm in diameter were used. Both the PT and the CT values were determined by giving the spherical materials of successively increasing diameter. To estimate the tongue movement in the mouth, electromyographic activity (EMG) was recorded from the mylohyoid muscle with bipolar surface electrodes. In every subject, the PT value was smaller than the CT value. The mean value of PT in twelve subjects was 0.48±0.12mm, while the mean value of CT was 0.61±0.16mm.

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There have heretofore been a variety of dental treatment methods in use, including mechanical treatment methods, those depending entirely upon the stabilized location of the mandible and others. However, not only have we not settled upon one specific method of treatment, in spite of a process of trial and error extending over a period of many years, we have even been witnessing lately a tendency toward an increase in the occurrence of temporomandibular arthrosis and other disorders. We carried out occlusion and mastication treatment in three cases of temporomandibular arthrosis and mastication dysfunction based on recent research and elucidation of the mastication system, involving improvements in occlusion restructuring and mastication patterns that take into consideration induction of the mandible into the physiologic location, making occlusion possible at that location, the elimination of hypertonia in mastication-related muscles and the control of temporomandibular joint inflammation and immune response. As a result of this treatment, there was an alleviation of the various constitutional dysphoria attendant upon the collagen disease, psychosomatic disorders, etc., that were manifested throughout the system. It became clear from this that the mastication system and the constitution are closely related and that there is a need for new developments from the standpoint of the dental treatment of the mastication system.

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