Pressure sensitive paper (Prescale) developed color by biting and masticated peanut fragments left on a shieve (10 mesh) were analized by means of image processor with a program “ASPECT”. Using the above mentioned method, biting force of each tooth, occlusal contact area and points and masticatory performance were measured . The correlation coefficient between masticatory performance (Manly' method) and total areas of peanut fragments on the shieve was highest (-0.974). Instead of Manly' method, the image processor analysis could be available for index of masticatory performance.

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To elucidate the role of cheeks during mastication in humans, the electromyographic activity (EMG) was recorded from the buccinator muscle and the masseter muscle with bipolar surface electrodes in five adult subjects with normal dentition during the mastication of gumi and chewing gum. Gumi was made of gelatine . Summary findings are: (1) The buccinator muscle activity during mastication on the chewing side was larger than that on the balancing side.(2) The buccinator muscle activity during the mastication of gumi was gradually decreased according to the progress of mastication, but it was not changed during the mastication of chewing gum. The relation between these buccinator muscle activities and the role of cheeks during mastication was discussed.

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The magnitude of masticatory muscle activites and its harmonious activities were examined in two patients who visited here having a trouble in their everyday life because of an uneasiness sense of occlusal contacts after receiving the orthodontic treatments for the adult's patient. Nevertheless the satisfactory forms of occlusion had been obtained orthodontically in both cases, the two patients claimed the sense of uneasiness strongly. Therefore, the mental cause as a factor was guessed. As the results of examination; in one case, the muscle activities of posterior and anterior temporal muscle and masseter muscle of one-side were higly unstable at the rest position, and showed remarkably unbalanced magnitude of muscle activities in one side at the time of chewing and mastication. In the another case, the tranquilizer was being taken, the almost same magnitude of muscle activities on the working side and balancing side at the time of mastication were observed. In both cases, the harmonious activities of masticatory muscles were ruined, despite of getting well-balanced form of occlusion by orthodontic treatment. The author has already found that the patient who has malocclusion discloses a harmonious pattem of muscle activities peculiar to the type of malocclusion. Therefore, it was imagined that a habitual harmonious pattern of masticatory muscle activities before application of orthodontic treatment was retained in the adult patients of these two clinical cases. This harmonious pattern could not accommodate to the occlusal contacts obtained from the orthodontic treatment, thus, adding to the mental factor, it was guessed that a heigh sense of uneasiness of occlusal contacts was caused.

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Ten normal volunteers (ages 28-85) underwent measurement of regional cerebral blood flow using intravenous blous injection of oxygen-15 lebeld water and positron emission tomography under three different conditions: resting, chewing gums, and tasting candy. An increase in blood flow was observed in the lower part of the bilateral pre-and postcentral gyri, extending to the operculum and the insula, both in “gum” and “candy” compared to “rest” in all subjects, which suggested that the operculum-insula as well as the lower Rolandic area is responsible for the oromasticatory sensori-motor function. The blood flow increase was smaller in old subjects than in young subjects, whitch was considered to reflect a reduced muscle work and/or decreased neuronal or cerebrovascular responce.

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To measure energy consumption during the process of chewing gum, and to investigate the effects of gum-chewing on levels of sugar and lipids in blood and pituitary - adrenal hormones concentrations in plasma, a study was designed in which nine healthy male volunteers chewed two pieces of marketed gum (6.18g;E-gum) for ten minutes with a chewing rhythm of about 80 times per minute while oxygen intake (VO2) and heart rate (HR) were measured continuously for 30 minutes before (rest period), during the 10 minutes (chewing period) and for 30 minutes after chewing (recovery period). Blood samples were drawn before, immediately after, 10 minutes and 30 minutes after gum-chewing via a catheter introduced into the brachial vein for measurements of blood sugar (BS), FFA, TG plasma ACTH, plasma adrenaline (pAd), noradrenaline (pNorad), and insulin (IRI) concentrations. Two pieces of the control gum (1.30 g; C-gum), a gum base containing no additional elements and harder than E-gum, were also chewed in the same manner as the E-gum. Both E- and C-experiments were carried out continuously in the sitting position and fasting state in no particular order, separately, during a different period between 10 a.m. and 2 p.m.

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To make clear the present situation of the dental disease among Nigerian children and adults, a longitudinal dental survey was jointly conducted from 1980-1991 by Obafemi Awolowo University, School of Dentistry, Ile-Ife, Nigeria, and a team of Japanese researchers. The survey was funded and supported by the Overseas Survey Grant in Aid for Scientific Research of the Ministry of Education, Science and Culture of Japan.
During the final survey in 1991. dental arch width and length and mesiodistal crown diameters of 68 Yoruba children [41 males and 27 females, Age: 3-6] and 64 Yoruba young adults [33 males and 31 females, Age: 11-23] were measured and compared with those of Japanese. The following results were obtained.
1. Nigerian deciduous dentition were larger than Japanese in size of all items of arches, showing a statistically significant difference in the arch length and mandibular dental arch width in both sexes.
2. Nigerian deciduous teeth were larger than those of Japanese except upper deciduous second molar.
3. The statistically significant differences were observed in the maxillary and mandibular arch width and length in all cases of both sexes, especially remarkable in dental arch length.
4. Nigerian permanent teeth were larger in mesiodistal diameter those that of Japanese in all teeth. Statistically significant differences were found for male's upper central incisor and canine, lower teeth except central incisor and female's all teeth.

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This paper describes a control method for the mastication robot in order to reduce the temporomandibular joint force (TMJF). We have developed the WJ (Waseda Jaw) mastication robot series from 1986 using seven Direct-Current (DC) motors, wires, a dental study model and a duralumin madibular, and carried out research theoretically and experimentally by using actual foods. From engineering point of view, we can regard the mandibular and masticatory muscle as a redundant system because the human mandibular has four degrees of freedom and the number of masticatory muscle is more than four. Generally speaking we can not decide the position and orientation of the redundant object. Therefore we must find some kind of control criterion for the mastication robot. So we are convinced that to formulate mandibular's equation of motion and to calculate the set of wire tensions by using linear programming whose objective function is minimizing the TMJF give one quantitative solution for the temporomandibular joint (TMJ) arthrosis. As results of computer simulation we clarified the tension set of wires and experimentally confirmed the reduction of TMJF with our mastication robot.

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