The purpose of this study was to evaluate the Shaping of the Mandibular Path during the Occlusal Phase of Mastication. We have previously developed a new computer simulation method for calculating the shearing strain energy in a model of food as an index for detection the energy of occlusion, and this method allowed us to suggest that the occlusal condition could be evaluated using this index. The aim of this report was to verify the hypothesis that the path of the masticatory stroke is shaped to enhance the efficiency of food breakdown. The below-mentioned method was done as follows;
1. Twelve spatial (bucco-lingual and vertical) relationships between maxillary first molar and second premolar, and mandibular first molar were set up for the occlusal phase of mastication. At each relationship, models of teeth and food were made by CAD, and FEM was applied to each model in order to calculate the shearing strain energy in the model of food. For loading, the direction of the masticatory muscle's action was decomposed into its horizontal and the vertical components related to the occlusal plane, and the force for 0.01mm displacement was given to each direction.
2. The ratio of the shearing strain energy in the model of food (P) was calculated by dividing the horizontal load by the vertical load.
Results:
1. During the path of closure, P became higher in all bucco-lingual relationships.
2. As the mandibular first molar moved from the working side into the intercuspal position, the change rate of P increased accordingly.
In conclusion, these results imply that the horizontal component of the path of mastication increases during the occlusal phase in order to enhance the efficiency of food breakdown.

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The applicability of accelerometer to the observation of body motion during mandibular movement was examined. Two healthy participants adopted a upright sitting posture with their head, neck and trunk unsupported, and were made to perform repetitive jaw tapping movement.
The acceleration signals of 1) the head and the mandible in the up-and-down direction, 2) the head, mandible, neck and trunk in the antero-posterior direction were measured. Piezoelectric accelerometers were attached to the body surfaces at the forehead, the mentum and over the spinous processes of the sixth cervical (C6), twelfth thoracic (T12) and third lumbar (L3) vertebrae, respectively. These signals of acceleration were recorded simultaneously with the path of mandibular movement by means of a Mandibular Kinesiograph (MKG) .
The results were as follows:
1. On the signals measured at the mentum, there were superposition of the low frequency component, the wave form of which did not correspond to each stroke of jaw tapping, and the high frequency component appeared synchronously with the occurrence of tooth contact. We might assume that the former consisted of the body fluctuation and the latter of the tooth vibrations. To clarify the acceleration signals accompanied by jaw move-ment, it was suitable for them being cut off with high-pass filter at 2Hz and low-pass filter at 100Hz.
2. The acceleration time traces measured at the mentum, filtered in this manner, obviously reflected the phases of mandibular movement. And around onset of jaw opening and closing, the direction of the acceleration signals agreed with the one in which the mandible displaced.
3. The acceleration signals measured on the head, neck and trunk were observed. The mobility tended to occur in the particular direction depending on the location of the accelerometer.
4. These results confirm us that the body motion, particularly its direction, can be detected with accelerometer.

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It has been reported that during mandibular tapping movements the head moves in functional coordination with the mandible in subjects with a normal occlusion and free of TMD symptoms. However, whether this finding can be applied to TMD patients remains unclear.
The purpose of this study was to confirm the coordination of head and mandibular movements during tapping in TMD patients. Using the Trimet system, we measured tridimensionally both the movement of the head and the mandible by tracking upper and lower incisal points respectively during tapping movements, then analyzed chronometrically the vertical component of these movements.
We found that the incidence of coordinated head and mandibular movements in TMD patients was lower than in normal subjects.
Our findings confirmed the existence of coordination between the head and mandibular movements during tapping, and conclude that it is different for normal subjects and TMD patients. Our results raise the question on whether there is a relation between the presence and intensity of the TMD symptoms and the decrease in the incidence of the coordinated head and the mandible movements during tapping in TMD patients.

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Distribution of occluding forces on a dental arch at various clenching strength and occluding forces of each subject were measured and analyzed by Dental Prescale to determine the relation between the clenching strength and the occluding force measured by Dental Prescale.
1. The amount of muscular activities and the occluding forces increased in direct proportion with the increase of clenching strength.
2. The distribution of the occluding forces was greatest at the second molar followed by the first molar, second premolar, first premolar, canine, lateral incisor and central incisor.
3. At each session of 20%, 40%, 60%, 80%, and 100%MVC the coefficient of variation of the standardized occluding forces were 17.4%, 9.7%, 8.3%, 8.2%, and 11.8% respectively. The 20%MVC had the largest value followed by, in the decreasing order, 100%MVC, 40%MVC, 60%MVC, and 80%MVC.
4. From the above results it was clear that the distribution of occluding forces on a dental arch had its own pattern and that the clenching strength had no effect on that pattern and that the occluding forces as displayed by Dental Prescale had the smallest individual variations at the medium clenching strength of 40%MVC to 80%MVC.

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The aim of this study was to develop a method to measure the range of the mandible during the occlusal phase of mastication. The mandibular movement of one healthy male subject (age 25 yrs), with normal occlusion, was measured with an opto-electronic motion analysis system (TRIMET, Tokyo shizaisha, Tokyo, Japan) . This system is able to measure mandibular motion with six degrees of freedom, and has a sampling frequency of 100 Hz. The subject was initially instructed to perform mandibular excursive movements, with tooth contact, on 4 occasions each lasting 30 seconds. Thus 12, 000 positions of the mandible were obtained. From this a three-dimensional curved mesh diagram of mandibular excursion was constructed for the mandibular incisal point which extended 15 mm anteriorly, 13 mm posteriorly (x axis), and 14 mm to the left and to the right (y axis), with intercuspal position at the origin with the resolution of 0.1 mm. To determine the supero-inferior position (z axis) of this mesh, the 12, 000 mandibular positions were. searched and, if two or more z values corresponded to a single x-y coordinate, the z value closest to the horizontal plane was chosen. In addition, this curvilinear mesh diagram could be constructed for any mandibular landmark. A masticatory cycle (for chewing gum) from the subject was compared to this mesh diagram. Coincidence between this cycle and the mesh indicated occlusal contact during mastication, and for this subject contact was observed for a distance of 3.8 mm (opening phase: 3.4 mm; closing phase: 0.4 mm) .
The curved mesh diagram of mandibular excursion enabled visualization of excursive movements of any point on the mandible, and is useful in examining and understanding the mandibular function.

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The aim of this study was to elucidate the fatigue characteristics of the masticatory muscles. In five healthy, fully dentate male subjects, maximal voluntary isometric bite force and elbow flexion and knee extension isometric strength were registered with the Dental Prescale System and a load cell with weight indicator respectively. Simultaneous to the tasks, the electromyographic (EMG) activity from the masseter, temporal, biceps brachial, and rectus femoral muscles was recorded with the Multi Telemeter System. A protocol involving three 5-second and three 30-second long isometric contractions with 10-second rest periods in between was designed to induce fatigue in the muscles studied. The 5-second tasks were made five times during the fatigue recovery period at different rest intervals. The 5-second isometric contractions were compared to a control 5-second one that was recorded at the beginning of the protocol. The EMG signals of each muscle during the tasks were integrated and their peak frequency of power spectrum was calculated. As a parameter of muscle fatigue, the ratio of muscle force and integrated EMG was used to observe the efficiency with which the muscle action potentials were transformed into mechanical work.
The results are as follows:
1. The maximum voluntary isometric bite force, elbow flexion and knee extension strength decreased gradually with repeated trials, and increased gradually in the fatigue recovery stage.
2. The onset of muscle fatigue and of recovery of the masseter and temporal muscles occurred earlier than those of the biceps brachial and rectus femoral muscles.
3. In all the muscles, a shift in the peak frequency of the EMG power spectrum was observed according to the state of the muscle; lower values in the fatigue phase, and higher values in the recovery stage.
4. In the masticatory muscles the integrated EMG decreased with muscle fatigue.
5. The muscle force/integrated EMG ratio of the masseter and temporal muscles showed higher values than the biceps brachial and rectus femoral muscles.
From these results, we suggest, that the masticatory muscles have fatigue resistant characteristics that differ form those of the limbs.

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The purpose of this study was to examine equilibrium function in the subjects with temporomandibular joint dysfunction syndrome, and anterior open bite using a stabilometer.
1. The body sway was significantly larger (p<0.05) and the locus length per unit area was significantly smaller (p<0.01) in the TMJ pain group than in the normal subject group. However, these scores were in the normal range of Tokita's data.
2. The body sway was significantly smaller (p<0.01) in the TMJ sound group than in the normal subject group. However these scores were in the normal range of Tokita's data.
3. No significant difference was found between the normal subject group and the anterior open bite group, but the body sway tended to be larger and the locus length per unit area tended to be smaller than those in the normal subject group.
These findings suggested that temporomandibular joint dysfunction syndrome and anterior open bite had any influence upon equilibrium function.

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The purpose of this study was to investigate the relationship between the occlusal condition and the patterns of masticatory movement during the final stage of occlusion by means of evaluating the efficiency in food breakdown.
The methods and the results were as follows:
1. Two subjects with Angle's Class II and one subject with normal occlusion were selected. On the basis of the occlusal condition and the relationship of the maxillary and mandibular teeth, the mastication, and the occlusal force of the subjects, the efficiency in food breakdown was evaluated by finite element non-linear dynamic analysis. The results showed that there was only little characteristic difference in the timing of the masticatory efficiency among the subjects.
2. In each subject, according to the subjects' records of mastication, the movement direction of their mandibular first molars during the final stage of occlusion was observed. The results showed that the amount of the movement of mandibular first molars in the subjects with Angle's Class II, compared with that in the subject with normal occlusion, was large in antero-posterior direction.
3. During the final stage of occlusion, the movement direction of mandibular first molars in the subjects with Angle's Class II was replaced by that of the subject with normal occlusion, and the efficiency in food breakdown was evaluated. The results showed the conspicuous declination in the timing of the masticatory efficiency.
The obtained results imply that the masticatory movement direction compensates for the difference in the position and the occlusal surface morphology of the maxillary and mandibular teeth; consequently, the efficiency in food breakdown is made to be higher.

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