Biting force during functional movements applies stress to the teeth, periodontal ligament, mandible and maxilla and produces distortion in all of them. Schöhl (1960), Behrend (1974, 1978), Siebert (1980), Kato (1981, 1982), Miura (1985), and several other researchers have described the significance of the physiological tooth displacement during function and have measured it, which is a very complicated task. To assess such task, the three dimensional tooth displacement transducer type M-3 was developed. It consists of a transducer with three Magnesensors (three pick-up heads and three magnets, a universal joint, a measuring probe and a set-up plate. Its total weight is 48.7grs. The displacement transducer type M-3 is screwed into a paraocclusal splint, which is made up of a 2mm thick aluminium plate and autopolimerizing acrylic resin. This splint is fixed at the labial surface of the anterior teeth with a momentary adhesive. All parts of the transducer -except for the measuring probe- are extraoral, hence the normal masticatory movement, is not altered by its presence and also, the intraoral temperature and humidity do not affect the transducer.
The free end of the 0.3mm diameter measuring probe is attached to the buccal middle surface of the tooth to be tested. Its movement in three directions is accuratory transmitted to the magnets by the universal joint. The displacement transducer type M-3 is contacting type, therefore some measuring pressure is essential, but since this measuring pressure must alternate with the physiological tooth displacement it should be kept as light as possible. As a result of using pivots in the universal joint, the measuring pressure was kept at less than 0.4grs. The linearity error of each transducer was less than 2% within a range of ±200μm. There was a minimum interference among the three transducers.
It became possible to measure the three dimensional physiological tooth displacement during function.

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The study was undertaken to quantitatively evaluate the nature of TMJ sound of CMD patients. Four groups of subjects were clinically classified as follows: Group A, patients with audible TMJ sound; Group B, patients who were aware of TMJ sound and it was also perceptible to the clinician; Group C, patients who were not aware of TMJ sound but it was perceptible to the clinician; Group D, which consisted of subjects free of CMD symptoms. TMJ sound during opening and closing movements of all subjects were recorded with a contact microphone, frequency analysis was made and results were compared among the four groups.
1. For CMD patients, peaks in the area above 100Hz were found for groups A and B, whereas most of the peaks were below 100Hz for group C. Compared to group A, group B had fewer high frequency components and group C fewer than group B. On the other hand, the power spectra for group D had a pattern limited to a frequency below 100Hz and most of the subjects showed no peaks of frequency component.
2 . Group A had the highest cumulative 100% value and cumulative 80% frequency value, followed by group B, C and D. Siginficant differences were found between each and every respective group except between groups A and B, and between groups C and D for the cumulative 100% value, and between each and evey respective group for the cumulative 80% frequency value.
3 . From this results it was concluded that the differences in the nature of TMJ sound of CMD patients caused the differences in the pattern of power spectra, and the cumulative 100% value and particularly the cumulative 80% frequency value could be used as an effective index for quantitatively evaluating the nature of TMJ sound of CMD patients.

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The purpose of this study was to observe and investigate the coordination among tongue and jaw movement, perioral muscle activity and sucking pressure during bottle feeding in infants.
Twenty-five healthy infants, born normally at full term and with a mean age was 13.0±4.5 weeks after birth, were selected as subjects for this study. A feeding bottle equipped with a CCD videocamera and pressure sensor was devised to show the tongue movement in infant and record the sucking pressure. Muscle activity was examined by unilateral surface electromyography from the temporalis (TM), masseter (MM), orbicularis oris (OM) and suprahyoid muscles (SM) .
The results are as follows:
1) The tongue movement was peristaltic. When the infant began to suck, the apex of the tongue rose, then the medial part of the tongue became a bell shaped bulge which moved backwards to the root of the tongue. At the final stage the tongue receded quickly and reversed forwards; i.e. the suckling cycle.
2) High correlation was recognized among tongue movement, suckling pressure and jaw movement. While the mandible pulled up until the bell shape appeared in the tongue and the nipple diameter was reduced, and sucking pressure was positive. After mouth closure the bell shape on the tongue moved backwards, and the pressure became negative, then the jaw also moved backwards and the mouth opened.
3) The TM and MM were most active when the sucking pressure became positive and the mandible was closing. The OM and SM were active in both positive and negative sucking phases, with the OM activity being most intense in the positive pressure phase and the SM showing its highest activity in the negative pressure phase.
It was concluded that tongue movement, perioral muscle activity and sucking pressure are highly coordinated during suckling in infants.

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Mastication consists of a series of movement that co-activates upper and lower teeth and the soft tissues of the mouth in order to crash food and form swallowable food bolus. To comprehend masticatory function, it is essential to understand food behavior as related to the occlusal surface and its adjacent structures; but there are almost no reports available about it.
The purpose of this study was to observe food behavior following food crushing and consider the association between food behavior and occlusal configuration.
We designed a new method to estimating food behavior. Peanuts which were chewed were gathered separately from buccal side and lingual side after varying numbers of chewing strokes, and then measured the amount and the degree of crushing of each one. As subjects, four young adults with normal occlusion and no experience of dental treatment were selected. The results were as follows:
1. As mastication proceeded, the amount of broken down peanuts on the buccal side decreased significantly, and those on the lingual side increased gradually.
2. The degree of crushing were higher on the lingual side than on the buccal side.
Recently it was stated that the“Squeezing Room”, which exist upper first molar, plays an important role concerning food crushing. It is speculated that one of the factors regulating food behavior is the“Squeezing Room”. To study this speculation, we examined food behavior using two experimental telescopic crowns. One was casted with usual molar anatomy whilst the other one without buccal cusps. Comparing food behavior with these two crowns enable us to imply the functional signification of the“Squeezing Room”on mastication.

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To evaluate muscle tonus, tonic vibration reflex (TVR) was studied in the masseter muscle. The experiment was performed on 16 male adult volunteers, 20-45 years old, without spontaneous pain and tenderness on masticatory muscles. The subjects were seated, the position of their heads was fixed and their mouths were kept open with a bite block. TVR was elicited by vibratory stimulation applied to the mandible (approximately 15 m/s², 160Hz) . EMG was recorded bilaterally from the masseter muscles, and analyzed quantitatively using an arbitrary index (TVR index) . Bite force was measured during clenching. Wide variations in the TVR index were observed among individuals: maximum: 22.7%, minimum: 0.9%, average: 7.7%. The mean index for 5 subjects with a clenching habit was significantly higher than one for 11 without the history of a clenching habit. Tolperizone HCl (100 mg p.o.) was found to reduce the TVR response for 2 hrs. There was a negative correlation (r=-0.504, p<0.05) between bite force and TVR index when their values on the right and left sides were compared. The tonic vibration reflex may be applicable for evaluation of the masseter muscle's condition.

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Recently Muscle Balance Monitor (MBM) has been introduced commercially, This device allows visual detection of occlusal abnormality by means of assymmetry index (AI) . This study was designed to investigate how the muscle tension recorded to AI obtained with MBM.
The 50% AI of the masseter was found significantly correlated positively with the muscle activity at rest, muscle activity during clenching and assymmetry of the tonic neck reflex. The positiveness and negativeness of 50% AI well agreed with the unilateral dominance of these parameters. The left-right difference in the number of teeth in contact (by T-Scan) was also correlated to the 50% AI. However, the positiveness and negativeness of the left-right difference differed in some of the subjects.

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The effect of a metal canine guidance on the activity of the masticatory muscles of a CMD patient with open bite was investigated. A few molar occlusal contacts were present in the habitual occlusion and the lateral gliding movement was guided by both working and balancing molars. Flat and steep metal canine guidances were made in order to exclude molar contacts during the lateral gliding movement. The EMG of the masseter and anterior temporal muscles and the MKG were recorded during the lateral gliding movement, lateral border movement and chewing, with and without the canine guidances.
The activities of the working side muscles reduced and the lateral border movement were stabilized with the canine guidances; but no remarkable differences in the muscles activities were observed among the different inclinations of the canine guidances. More rhythmical and less asymmetrical muscle activities during chewing were observed with the flat guidance than with the steep guidance or without metal guidance.

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We have improved the bite force sensor so that it can be conformed to the occlusal surface of the teeth and measure the occlusal force distribution. The pressure sensitive rubber, which is the core of the sensor, is soft enough to fit the complicated shape of the surface; and in order not to spoil this merit, we therefore introduced newly devised electrode into this sensor. The electrode is particularly processed to be coil shaped, hence the sensor flexibility is not limited.
In the practical use of this sensor we have blended our basic experience and its clinical application. In our prior experiment, we pushed a metal ball onto the sensor, compared its transformation to the surface of the ball, and found that the conformity of the sensor to the metal ball was satisfactory. As a result, we were encouraged to use the sensor clinically and have been able to measure the occlusal force distribution.
These findings suggested that this sensor could be clinically useful as a new bite force sensor.

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