The first aim of this study was clarify whether principal component analysis (PCA), one of the multivariate analysis, can reduce the number of degrees of freedom of perioral skin movement (i.e., time-series data with 45 degrees of freedom) . The second was to evident whether the analysis of the movement of perioral soft tissue during mastication by the application of PCA is useful to evaluate masticatory movement and stomatognathic functions.
The subjects were 15 persons with natural dentition and 4 complete denture wearers. The chosen experimental food for this study was sufficiently softened chewing gum.
The results of analysis showed that over 97% of the perioral soft tissue movement (time-series data with 45 degrees of freedom) during mastication with natural dentition could be expressed by a search up to the 3rd principal component. Therefore, the perioral soft tissue movement during mastication with natural dentition could be expressed as movement with a 3-dimensional variable. Similarly, perioral soft tissue movement during mastication in complete denture wearers could be expressed as movement with a 4-dimensional variable. Moreover, the time analysis of the movement of perioral soft tissue during mastication was possible by the application of the principal component score graph.
The results of this study showed that the spatiostructural and time analysis of the movement of perioral soft tissue during mastication was possible by the application of the PCA, one of the multivariate analysis, and that elucidation of this movement by this analysis would be useful to evaluate masticatory movement and stomatognathic functions.

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The purpose of this study was to investigate the electromyographic features of masseter muscle activities before and after a clenching task in the mandibular rest position in patients with temporomandibular disorders (TMD) by a multi-channel analyzing system. The subjects included eight patients with TMD (TMD group) and eight normal subjects (Normal group) .
The following results were obtained.
1) Masseter muscle activities in the mandibular rest position (MMA) increased after the clenching task in four of the Normal group, and such increase in the activity was observed in nine of the 18 masseter muscle sites examined. In the TMD group before treatment for TMD, MMA increased after clenching task in seven patients, and this increase in the activity was observed in all of the 18 sites. In the TMD group after treatment for TMD, MMA increased after clenching task in four patients, and the increase in the activity was observed in seven of the 18 sites. The two groups showed no differences as far as the areas of masseter muscles were concerned.
2) MMA in the Normal group had been significantly lower from the 2nd frame after clenching task on the preferred chewing side (PCS) and from the 3rd frame after clenching task on the non-preferred chewing side (NPCS) than in the 5th frame before clenching task (p<0.05) . MMA in the TMD group before treatment were significantly higher on both sides in the 1st frame after clenching task than in the 5th frame before clenching task (p<0.05) . MMA in the TMD group before treatment had decreased from the 1st frame after clenching task, but even MMA in the 5th frame after clenching task did not get to MMA level in the 5th frame before clenching task. MMA in the TMD group after treatment were similar to those in the Control group.
3) Before the clenching task, there were no significant differences between average masseter muscle activities (AMMA) in the Normal group and in the TMD group before treatment. However, after clenching task, AMMA in the TMD group before treatment were significantly higher than those in the Normal group. There were no significant differences between AMMA in the Normal group and in the TMD group after treatment both before and after clenching task.
4) AMMA on the NPCS before clenching task and those on both sides after clenching task were significantly lower in the TMD group after treatment than in the TMD group before treatment.
5) There were no relationships between the masseter muscle activities in the rest position and the seventy of clinical symptoms.
The results showed that in TMD patients who have not been treated, a clenching task causes an increase in masseter muscle activities in the mandibular rest position.

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In order to clearify the main occludinng area during mastication, we asked three patients who showed food impaction to clench on a temporary stopping. It was found that the main occluding area shifted from the area of the occlusal contact on the inner inclines of the functional cusp of the maxillary and mandibular first molars to the interproximal area in the intercuspal position, thus causing food impaction.
Occlusal reconstruction of the maxillary first molar was carried out and the main occluding area was shifted back to the above-mentioned cusps; In doing so, any further food impaction was prevented.
From the above findings, it became obious that food impaction was caused not only by the reasons discussed by other authors, but also by an inappropriate occlusal relation. Moreover, from the properties of the impacted food, it became clear that the main occluding area during mastication played an important role in chewing fibrous food in addition to hard food.

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The influence of defective anterior guidance on occlusal function has been broadly studied; however, the effect of the lack of the anterior component of anterior guidance in some patient populations is unclear. The objective of this study was to investigate the state of oral function in open bite patients (OBPs) in order to determine the physiological importance of anterior guidance. Thirteen female open bite patients (age range 15-27) were selected for this study from the Orthodontics Clinic of this University prior to treatment. The following parameters of oral function were evaluated: 1) occlusal contacts in the intercuspal position (IP) and lateral eccentric position, 2) analysis of skeletal patterns with lateral cephalometry, 3) distribution of signs and symptoms of temporomandibular disorder (TMD), 4) bite force, as measured with the Dental Prescale, 5) analysis of tridimensional jaw and condylar movements with a 6-degree-of-freedom measuring device (JKN-1) .
OBPs with occlusal contact points only in the molar teeth in IP were classified as M Type (7 OBPs), and those with molar and premolar contact points as MP Type (6 OBPs) . Five M Type OBPs showed Class II skeletal patterns, but the skeletal patterns of the MP Type OBPs varied between Class I and Class III; this implies that the skeletal pattern may affect the number of contacting teeth. Five M Type OBPs, who had Class II skeletal patterns, were diagnosed as TMD patients.
Mandibular stability was determined from the convergence and the paths of the incisal and condylar points in the sagittal and frontal planes during tapping and clenching; although it was reduced in both groups, the jaw movements in the M Type, particularly the Class II OBPs, were considered much more unstable than in the MP group. It was assumed that this was due to the finding that the M Type showed significantly shorter moment arms between the condyles and the guiding teeth. The latter suggests that, aside from the neurophysiological properties of the teeth, the longer the moment arm between the condyles and the guiding teeth becomes, as in canine guidance or group function, the finer the control of lateral jaw movements might be. It was concluded that such occlusal schemes of anterior guidance are essential for mandibular stability and smooth functional jaw movements, and therefore it should be restored in all patient populations.

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In order to investigate the possibility of improving the distinctive technical characteristics of the MKG, first the output data (a set of primary data) of MKG were corrected by the compensation equation of the MKG Analyzer to obtain a set of secondary data. Then to each positional coordinate of the secondary data, six additional positions that were 2.5mm away, up and down, right and left, and front and back from that position were corrected each to obtain a set of tertiary data. The percentage of error was calculated for each set of data and the results were compared.
1. Each positional coordinate of the primary data was close to the actual positional coordinate at the vicinity of its original position and showed relatively satisfactory linearity. However as the coordinate moved away from the original position it deviated from the actual position and became non-linear.
2. For each positional coordinate of the secondary data, the non-linearity was somewhat improved, but as it moved away from the original position it deviated from its actual position and became non-linear.
3. For each positional coordinate of the tertiary data, the non-linearity had improved greatly compared to the secondary data, and showed linearity.
4. The percentage of error for each positional coordinate of the primary, secondary and tertiary data were 29.5%, 8.7% and 1.6% respectively. The primary data had the largest percentage of error by far, followed by secondary data and tertiary data. Significant differences were found between each two sets of data.
5. From these results, it was concluded that with proper compensation measures the linearity of a MKG that showed non-linearity can be improved to the level similar to or surpassing that of other mandibular movement recording apparatus sold on the market.

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It has been recognized that clarifying the masticatory function of the elderly is important because of their remarkable increase in population and QOL. The purpose of this study was to investigate the usefulness of the normalized EMG linear envelope analysis to compare masticatory muscle activity patterns of the elderly with young. We applied EMG linear envelope analysis to the elderly who were different in oral conditions with the young. Four elderly complete denture wearers (one male and three females; mean age, 71.0 years; range, 68-75 years) and eight young dentate volunteers (four males and four females; mean age, 25.3 years; range, 23-28 years) participated in this experiment. EMG signals were recorded from the bilateral masseter and anterior temporal muscles during gum chewing on the preferred chewing side for 90 seconds. The Rower incisal point movement was tracked by the Mandibular Kinesioguraph (MKG) simultaneously. Root mean square values were calculated from the raw EMG signals. Each rectified EMG signal was smoothed by weighted moving average method to produce a linear envelope. These data were divided into individual chewing strokes and each stroke was divided into 3 phases using the data for vertical displacement of the MKG: closing, compressive, and opening phases. The time base average for each phase was then normalized to 100 points representation, 300 points in total, for each stroke period. 10 stable strokes were selected and each stroke was normalized by setting the mean ensemble value over a single stroke to 100%. Ten normalized EMG amplitudes were averaged. It was possible to compare each volunteer's masticatory muscle activity patterns because the activity patterns were reduced inter- and intra- volunteer variability.
The results were obtained as follows;
1. Normalized EMG linear envelopes of the elderly complete denture wearers showed plane curves on both sides. Their peaks of the activities were not clear and their amplitudes were low.
2. Normalized EMG linear envelopes of the young dentate volunteers showed sharp curves on the working side and smooth on the non-working side. Their peaks of the activities were near the 100 points of the stroke.
3. Masticatory muscle activity patterns of the elderly complete denture wearers and young dentate volunteers were different.
The normalized EMG linear envelope analysis was useful to compare masticatory muscle activity patterns of the elderly population with the young.

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