The purpose of this study was to examine the relationship between the habitual chewing side, symptomatic side of temporomandibular disorders (TMD) and occlusal factors.
One hundred patients, from whom informed consents were obtained, participated in this study. They were questioned about their habitual chewing sides and TMD symptomatic sides. Occlusal contact was examined with Dental Prescale 50H, type R; the patients were instructed to bite as hardly as possible for 3 seconds in the intercuspal position. The occlusal force and the occlusal contact area were analyzed with the Occluzer. The statistical test for the proportion and the chi-square test for independence were carried out.
54 patients had their habitual chewing side in the right side and 46 in the left. The greater occlusal force was recorded in the habitual chewing side in 72 patients and in the opposite in 27 (p<0.01) . The larger occlusal contact area was recorded in the habitual chewing side in 65 patients and in the opposite in 30 (p<0.01) . With regard to TMD, among 36 unilateral symptomatic patients, the habitual chewing side coincided with the symptomatic side in 26 but not in 10 (p<0.05) .
It is inferred that the occlusal factors such as occlusal force and occlusal contact area in the intercuspal position could contribute to the development of an habitual chewing side, and the TMD symptomatic side also might be close relationship with the habitual chewing side.

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The purpose of this study was to develop a new method for effective visualization of the three-dimensional joint space using a reconstruction of the temporomandibular joints' (TMJs) osseous components based on computed tomography (CT) .
Axial CT scans, with a 2 mm-thickness and a slice space of 1mm, were made from the right and left TMJs of one subject. In order to relate the digitally reconstructed TMJ images to the upper dentition, he wore a reference face bow unit that had three markers attached onto it through alminum tubes.
The three-dimensional data points from the serial CT scans were measured to reconstruct digitally the TMJs. The TMJ images composed of approximately 12000 points and the fossa of approximately 24000 points were reconstructed using graphic software. A triangle indicating the occlusal plane was described simultareously on the display.
The distance distribution map was composed of the reconstructed condylar surface shaded with pseudo-colors according to the calculated joint space distance of 0-5mm at 1mm intervals between each fossa and condyle measurement point. The distance distribution map with pseudo-colors could be observed on the screen at any direction.
The results were as follows:
1. The axial CT scanning required only one examination to reconstruct the right and left TMJs in the same coordinate system.
2 . By the three-dimensional reconstruction of the TMJs with the occlusal plane indicated by the triangle, it was possible to estimate the positional relationship of the TMJs to the upper dentition by means of the reference face bow unit.
3. The distance distribution map made it possible to visualize effectively the morphologic characteristics of the condyle and the relationship between the condyle and the fossa.

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It is important to reconstruct occlusion with appropriate anterior guidance through prosthetic treatment. The present study examined the influence of altered anterior guidance on the activity of the masseter and the posterior temporal muscles. Three adult subjects without any symptoms of mandibular dysfunction and with unilateral balancing molar contact caused by edge-to-edge or anterior open-bite occlusions were used. EMG and mandibular movement recordings were performed for each subject without (G0) and with metal artificial copings which were adjusted to the angles of the incisal paths of the same (G1), plus 10 degrees (G2) and plus 20 degrees (G3) ; the copings were attached to both sides of the maxillary canines. G2 and G3 copings eliminated the unilateral balancing molar contact.
During lateral sliding movement, G1 copings caused various changes on EMG activity. Compared with G0 and G1, 02 copings tended to cause a reduction of EMG activity from the intercuspal position to the lateral side and to cause an increase of EMG activity when returning to the intercuspal position. Compared with G2, G3 copings tended to cause a reduction of EMG activity. Altered anterior guidance was more effective on EMG activity during lateral sliding movement than that during mastication of gum chewing. Masticatory rhythm did not show significant change. Unilateral balancing molar contact on the contralateral side may affect the stability of masticatory rhythm and chewing stroke.

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The purpose of the present study was to investigate the influence of endurance tasks on masticatory muscles. Twenty healthy volunteers without masticatory muscle pain were instructed to perform several endurance tasks. Each task consisted of clenching at a 50% maximum voluntary contraction (MVC) as long as possible with 1-minute intervals.
The degree of masticatory muscle pain, pressure pain threshold (PPT), and bite force were measured before and after the endurance task. The degree of masticatory muscle pain at rest was measured with a 100 mm visual analog scale (VAS) . PPTs were measured at six masticatory muscle sites (superficial and deep masseter; anterior, middle and posterior temporalis; and sternocleidomastoid), and temporomandibular joint (lateral and posterior capsule) . Bite force was measured by Dental Prescale (FUJI FILM Co, Tokyo, Japan) . Each item was measured before, and 1-, 2-, 3-, and 7-days after the endurance task.
The degree of masticatory muscle pain was significantly higher at 1-day after the endurance task in all subjects. Though it was highest at 1-day after the endurance task in both male and female subjects, only female subjects showed a significant difference (p<0.05) .
In female subjects PPT of deep masseter at 1-day after the endurance task was significantly lower than that before and at 7-days after the endurance task (p<0.05) . In male subjects, on the other hand, there was no significant difference in each site. Hence it was suggested that the patterns of response of the stomatognathic system to the endurance task could differ according to with gender.

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The purpose of this study was to evaluate the characteristics of mandibular jaw movement as a unit in children.
Twenty-one subjects with normal occlusion were divided in three age groups: primary dentition group (1 boy, 3 girls), early mixed dentition group (2 boys, 5 girls), and permanent dentition group (2 men, 8 women) . Jaw movement was measured with a 6 degrees of freedom jaw tracking device.
Jaw movement of the whole mandible was simulated on a graphic terminal. The elements of translation and rotation of the mandible during lateral excursion were determined by the intermaxillary axis model.
The results obtained were as follows:
1.The kinematic condylar point could be detected in 5 children.
2.The distance of working condylar path during lateral excursion was significantly larger in children than in adults.
3.During lateral excursion the working condyle was not the center point of rotation in many children.
4.The results of the intermaxillary axis model analysis indicated that translation of the mandible in children was larger than in adults, and that rotation of the mandible in children was consistent with that of adults. The results suggested that lateral excursion in children has a large element of translation.

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The purpose of this study was to develop a three-dimensional occlusal examination system and to observe the parameters of occlusal contact and mandibular displacement.
Two normal subjects and two patients with TMD whose chief complaints were noise in the joint participated in this study. Two silicone occlusal registrations were taken for each subject with different occlusal forces, under 5%MVC (Maximum Voluntary Clenching) and 30%MVC. The silicone occlusal registration was digitized by noncontact three-dimensional form measuring device (SURFLACER VMS-2508, UNISN Inc., Osaka, Japan) and the occlusal contact area of intraocclusal distance under 60μ m was calculated. The 3D-data were analyzed by CAD software (SURFACER, Imageware Inc., Michigan, USA) with a personal computer (Digital PC 5510 6300, DEC, Japan) . The inclination and size of occlusal contact area were computed and displayed as tooth vector and dentition vector. The cranio-facial bones were reconstructed from CT data and the frame of reference on the cranio-facial system was established. The maker-registration of 3D-data, the silicone occlusal registration and cranio-facial bones, were made using teflon balls. The markerless-registration of upper and lower dentition was made and the mandibular displacement during intercuspation was estimated from displacement of lower dentition.
The reproducibility was high and precision was under ±20μm of non-contact three-dimensional form measuring.
The mandibular displacement was small and the occlusal contact was equilibrated in normal subjects. The mandibular displacement was large and the occlusal contact was disequilibrated in patients with TMD.
The three-dimensional occlusal examination system was developed and occlusal contact and mandibular displacement were evaluated quantitatively and visually.

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We developed a portable electromyographic (EMG) recording/analyzing system, which consists of a portable EMG recording unit and a cassette data recorder, and a software for data analysis. This system allows longterm nocturnal masticatory muscle self-EMG recordings at home under natural conditions. With this system, bruxism activity in detail, e.g., the number of bruxism events, duration, and activity, can be analyzed using nocturnal masseter muscle EMG recordings. In addition, data containing artifacts can be removed as much as possible by checking the raw EMG data, procedure that improves the quality of the data.
We measured the nocturnal masseter muscle activity in 2 bruxers and 2 normal control subjects for 7 consecutive nights using this system. A bruxism event was defined as the activity of the masseter muscle that exceeded the 10% of the maximum voluntary contraction (MVC) . Then the number of bruxism events, duration and activity were calculated. We also evaluated the day to day variation of the bruxist activity within each subject.
The nocturnal masseter muscle activity that represents the same activity as the bruxism-like voluntary grinding and clenching movement was confirmed in bruxers. The EMG activity for the bruxers was significantly larger than that for the controls (p <0.05, ANOVA) . The 2 bruxers in this study showed many bruxism events, whose EMG activity was between 50 and 70%MVC level, compared with control subjects. The distribution of EMG activity was different among subjects, and varied in the recording period even in the same subject. We also confirmed the day to day variation of the bruxism activity within each subject. The coefficient of variance of the bruxism activity showed 20-30% for each subject.
These results suggested that the newly developed portable EMG recording/analyzing system is useful for the evaluation of nocturnal bruxism.

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The purpose of the study was to investigate the characteristics of mastication in infants by evaluating the electromyographic chewing rhythm of the masticatory muscles and VTR, and to discuss the development of masticatory function in infants at the stage of the weaning period. Sixty subjects were divided into the following five groups, GO (the sucking group as a control), G1 (up to 8 wks after the initiation of weaning), G2 (up to 16 wks), G3 (up to 24 wks) and G4 ( more than 25 wks) .
When compared to the control both the chewing cycle time and the burst duration in the temporal muscle became significantly longer in 01 and 02, and then declined gradually in G3 and G4. The mastication pattern of infants can be classified into three types, such as continuous tongue compression, cyclic tongue compression and the maturation type. The frequency of the maturation type was significantly increased from 01 (2.6%) to 04 (49.5%) as the time proceeded from the initiation of weaning.
The coincidence of the bursts of the temporal muscle and the suprahyoid muscles was recognized during each chewing cycle in the earlier period of weaning, while the burst timing of the both muscles were, thereafter, differentiated gradually. Therefore, the development of masticatory function in the weaning period infants disclosed that the function of the jaw closing muscle and of the jaw opening muscles is differentiated gradually.

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