The purpose of this study was to compare the lateral contact pattern within the intercuspal range with that of an edge-to-edge position. Occlusal contacts of 52 young adults were examined using metal strips in regulated lateral positions; 0.5, 1, 2 and 3mm from the intercuspal position, where the 0.5mm position was defined as a position within the intercuspal range and 3mm position in an edge-to-edge position. The pattern of occlusal contact in the 0.5mm position had distinct characteristics from those of the 3mm position, showing marked prevalence of working and non-working side posterior tooth contacts. Even a slight variance in the examining position resulted in a great difference in the non-working side contact pattern. It is necessary to distinguish contact patterns between an edge-to-edge position and within the intercuspal range, i.e. between parafunctional and functional ranges. The examining position needs to be regulated when describing and checking the pattern of occlusal contact in eccentric positions, otherwise factors regarding occlusal contact will not be relevant, and the theory of occlusion will remain unclear.

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³¹P-Magnetic Resonance Spectroscopy (MRS) is a non-invasive method for analyzing the intracellular metabolism of high energy phosphate compounds. In this study, ³¹P-MRS was used to clarify whether the energy source was consumed in masseter muscles of TMD patients. The subjects were seven TMD patients suffering from pain and contracture of masseter muscles, and seven healthy volunteer controls.³¹P-MRS and electromyography (EMG) were performed in one side of the masseter muscles of each subject. From the obtained spectra of³¹P-MRS, phosphocreatine (PCr) /β-ATP ratios and inorganic phosphate (Pi) /β-ATP ratios were calculated. PCr acts as the energy source to reproduce ATP.
The following results were obtained:
1. The PCr/β-ATP ratios in TMD patients during rest (mean ratio: 1.8±0.6) were significantly lower (P<0.01) than those in the controls (mean ratio: 3.6±0.3) . This suggests that a decrease in the energy source of muscle-cells may be one of the causes of fatigue in the masseter muscles of TMD patients.
2. The Pi/β-ATP ratios in the controls during clenching increased, while the ratios in the TMD patients during rest did not increase.
3. There was no increase in EMG activity in the masseter muscles of the TMD patients during rest.
The last two results suggest that the decrease in PCr of the TMD patients during rest was not the change that occurred during or just after acute consumption of energy such as energy consumption by clenching.

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The characteristics of temporomandibular joint (TMJ) sounds such as clicking and crepitation have been assessed by many studies, however reports concerning sounds of asymptomatic joint are still scarce. Also, recording TMJ sounds with contact microphones is a difficult matter because several factors cause variation of the recordings.
The purpose of this study was to clarify the characteristics of TMJ sounds in normal subjects and to determine the location of an optimum recording site. TMJ sounds and mandibular movements in nine fully dentate, healthy subjects who had no history of TMJ pathology were respectively recorded with contact microphone and a jaw tracking device.
Three velocity parameters of jaw opening were studied in four recording sites. The results were as follows:
1. Sound of TMJ movement in normal subjects was distributed below 30 Hz with peak frequency of 2-4 Hz.
2. TMJ sounds picked up by the contact microphone were considered to be those associated with condylar movement within the joint.
3. Frequency of TMJ sound changed in relation to the recording site; and the magnitude of sound was also affected by the velocity of mandibular opening.
4. TMJ sounds generated by TMJ movement were best recorded when the contact microphone was located 20 mm anterior to the average condylar point.

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The purpose of this study was to determine the stability of the terminal point of chewing movement in children. The subjects were divided in three groups: the primary dentition group which consisted of six subjects (5 boys, l girl) ; the early mixed dentition group which consisted of seven subjects (4 boys, 3 girls), and the permanent dentition group consisting of nine women. Chewing gum was chosen as the experimental foodstuff, and 10 chewing cycles were recorded from each subject. The lower incisal point and the working and non-working condyle were selected as reference movement points and tracked tridimensionally in six degrees of freedom with the TRIMET system. The most superior measuring point of each cycle was recognized as the terminal position of the masticator cycle. The standard deviation (SD) of 10 cycles from each subject, regarded as an index of stability, was calculated and compared between groups.
Results:
The SD was highest in the primary dentition group, and smallest in the permanent dentition group. In all groups, the SD of right and left directions was largest in three directions at the lower incisal points, and the anteroposterior direction was largest in both condyles. The lower incisal point's SD of the early mixed dentition group was similar to that of the primary dentition group, and the condyles' similar to the permanent dentition group.

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Masticatory movement in children and adults has been studied from several perspective. The movement around the terminal position of mastication in children is a matter that is still not well understood. The purpose of this study was to clarify the concordance between the intercuspal position and the terminal position of chewing movement in children. We divided the subjects into three groups according to dental age: primary dentition group (5 boys, 1 girl) ; early mixed dentition group (4 boys, 3 girls) ; and permanent dentition group (9 women) . The lower incisal point and the working and non-working condyles were used as reference points for tridimensional tracking. The concordance of these reference points was evaluated by calculating the distance between the intercuspal and terminal positions of mastication. Chewing gum was used as food sample for this study.
At the lower incisal point, the distance between the intercuspal and terminal positions decreased with dental age. Moreover, the primary dentition group had the largest distance in the anterior-posterior direction in three directions.
At the condyles as well, the distance between the intercuspal and terminal positions decreased with dental age. Furthermore, for the early mixed dentition group, the movement resembled that of the permanent dentition group. The underlying reason for these findings may be physiological growth, maturation, and adaptation of the occlusal function.

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Masticatory movements are a result of the complex coordination of the neuromuscular system. The purpose of the this study was to determine whether measuring and observation of these movements with linear envelope analysis is a viable approach. Three normal volunteers (average age of 25.3) participated in this experiment. All had complete natural dentition that included the second molar, and none showed any signs or symptoms of problems in the stomatognathic system. Bipolar surface EMG of the anterior temporal and masseter muscles, tongue and mandibular movements were simultaneously recorded during gum chewing, which they were instructed to chew ad lib for 90 seconds. Tongue movement was observed through ultrasonography at the median saggital plane of a line bisecting the right and left mandibular first molars, and a mandibular kinesiograph was used for tracking incisal point movement during chewing. It was possible to trace normalized linear envelopes for tongue movements, mandibular movements and EMG activity of jaw elevator muscles for each stroke during chewing.
Results:
1. The lowest point of tongue movement was occlusal phase of mandibular movement each stroke. Tongue and mandibular movements were functionally cooperated.
2. Peak activity for anterior temporal and masseter muscles was at between closing stroke and occlusal phase.
3. EMG profiles showed stable pattern after 60-75 seconds after initiation of chewing.

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This study analyzed the movements of tongue and the mandible related to progress of mastication. Six subjects (average age: 26.7, range 23-29yrs) with no evidence of neurological disorders were given rice cracker, boiled fish paste and pickled radish as foodstuffs and asked to chew freely and swallow. Tongue movement was observed through ultrasonography and mandibular movement with the MKG-K6 device. The oral stage of mastication was divided into three phases: sorting out (SO-phase), development (DE-phase) and bolus formation (BF-phase) . Results:
1. Mandibular movement: As mastication progressed the duration of closing phase became shorter and the duration of occlusal phase longer. There were no specific change in the duration of opening phase.
2. Tongue movement: As mastication progressed no change occurred in the time lag between beginning points of closing stroke and lowest points of tongue stroke. Time lag between beginning points of occlusal phase and lowest points of tongue stroke shortened. Time lag between beginning points of opening phase and lowest points of tongue stroke did not change.
3. The SO-phase was significantly different among foodstuffs as mastication progressed; however, the BF-phase was not.

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The trajectory of the incisal point has been used as a parameter by many studies concerning jaw movements during mastication. Little information, however, is available regarding the movements of molars, in which area masticatory movement is actually performed. Our previous studies reported that sagittally-viewed masticatory patterns are different among incisal and molar points, while frontally-viewed patterns are same within the individual. However, these findings were based on the analysis of only masticatory envelopes. The purpose of this study was to clarify the movements of molars as related to those of incisor, especially close to the intercuspal range.
Using chewing gum as foodstuff, masticatory movements were measured on 50 normal young adults (22 males & 28 females, 19-35 yrs, mean 22.3 yrs) using the 3-D mandibular movement analyzing system. The analyzing points were medial edge of the left lower incisor and distobuccal cusp of the working-side and non-working-side lower 1st molar. Their 3-D position at every 0.1mm level was calculated for each stroke at each analyzing points from ICP to 3.0mm opening level. After averaging the data from 10 strokes on each subject, the individual averaged anteroposterior and lateral positions of incisal, working-side and non-working-side molar points were obtained. Difference in the antero-posterior and lateral locations of the opening and closing paths were tested statistically among 3 analyzing points. Statistical significance was set at 5% and determined by Post-Hoc test and Fisherman's PLSD test. The results were as follows:
1. Frontally-viewed opening and closing path was consistent in location among 3 analyzing points.
2 . Sagittally-viewed opening path was also consistent among 3 analyzing points, while closing path were different among each point, i.e, the closing path of working-side molar points located posteriorly and non-working-side molar points located aoteriorly, compared to that of incisal point.
It was concluded that the masticatory closing path of the molar points were different in location from incisal point close to the intercuspal range.

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The relationship between bite force and craniofacial morphology has been studied with various methods in subjects free of temporomadibular disorder (TMD) signs and symptoms; however, whether these variables have any relation in TMD patients remains unclear. The aim of this study was to determine the relation between lateral facial morphology and bite force in TMD symptomatic and asymptomatic orthodontic patients. Experimental data were obtained from 42 orthodontic female patients (TMD free group: 23 patients; TMD group: 19 patients) using the Occlusal Prescale system. The following results were obtained:
The mean total bite force was 768.8±525.8N in the TMD free group and 438.1±380.1N in the TMD group. The mean occlusal contact area was 12.9±11.9mm² in the TMD free group and 6.4±2.8mm² in the TMD group. The mean average occlusal pressure was 59.8±13.4kg/mm² in the TMD free group, and 69.9±9.0kg/mm² in the TMD group. The distribution of bite force, occlusal contact area and average occlusal pressure increased anteroposteriorly. Bite force, occlusal contact area and average occlusal pressure in the molar area of the TMD group were significantly lower than that of the TMD free group. Bite force, occlusal contact area and average occlusal pressure were significantly different between the TMD free and the TMD groups.
Total bite force and contact area of the TMD free group showed a negative correlation to mandibular plane angle, gonial angle and a positive correlation to L1 to mandibular plane angle. Molar bite force and contact area in the TMD free group showed a negative correlation to mandibular plane angle, gonial angle, occlusal plane to FH and positive correlation to Ll to mandibular plane angle and UL-SN. Premolar bite force and contact area in the TMD free group also correlated negatively to mandibular plane angle and gonial angle. However, there was no correlation between lateral cephalometric and occlusal parameters and in TMD group. These results suggest that bite force relates to lateral craniofacial morphology in orthodontic patients with TMD free patient but not with TMD populations.

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Having the mandibular movement in mild, this research attempted to search for the best method in quantitatively recording the movement of a point that was clearly three dimensionally away from the points of measurement. 3 LEDs were placed in the incisal area of the articulator. Positions A was the point on the plane of the incisal path. Positions B (B 1 to B 10) were the points on the sagittal plane of the incisal plane of the incisal path as the upper member of the articular was raised vertically. The positional coordinates of these points were recorded with the three dimensional recording system equipped with 2 CCD cameras. Then the movement of position C, the central point of the mandibular condyle, was calculated by using method I which used the vectors, method II which used the rotating angles of x, y, z axes, and method III which set the lines between all points of a body constant. For method I and II the rotating angle between respective points B and A, and for method III the distance between respective points B and LED and between B and C were measured.
1. The X-axis rotating angle between each point B and point A was smallest for B1 and increased gradually from B2 to B10. The rotating angle of y-axis was less than I and small at all points. All these angles were similar for methods I and II. On the other hand the rotating angles of z-axis were less than 2 for method II, but for method III was extremely large, being about 40 to 60.
2. The distances between each LED and point C were similar to the distances between each position B and position A, and the differences were less than 0.02mm.
3. The amount of movement at point C was largest for method I, smaller for method II and the smallest for method
III. Statistically significant differences were found between each method.
4. From these results it was concluded that in recording quantitatively the movement of a point clearly three dimensionally away from the triangle of the three LEDs, the method which set the distances between each point on a body constant was superior than the methods using vectors or x, y, z axes rotating angles.

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The purpose of this study was to determine the optimum morphology of occlusal facets of molars from the standpoint of harmony with jaw movements. First, we defined a simplified occlusal reference surface (ORS) on both the working and nonworking sides in the following manner: A working-side ORS was defined by using the trajectories of retrusive and lateral sliding movements obtained with a 6-degree-of-freedom measuring device, while a nonworking-side ORS was defined by using the trajectories of protrusive and lateral sliding movements. Then, three different occlusal facets were introduced, one equivalent to the ORS (harmonious occlusal facet) and two comparative ones whose orientations were intentionally deviated from that of the ORS (inharmonious occlusal facet) . Occlusal contacts on these facets formed in antagonistic second molars of two subjects were evaluated during lateral excursions and chewing movement through computer simulation. Results were as follows: 1) the harmonious working-side and nonworking-side occlusal facets induced no considerable interference with jaw movement during the fourth and fifth phases of the chewing cycle, respectively; and 2) the inharmonious facets with a steeper inclination (15 degrees) tended to interfere with jaw movements at lateral excursive positions, while those with a gentler inclination (-15 degrees) tended to cause disocclusion at lateral excursive positions.

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The purpose of this study was to investigate the influence of abnormal occlusion on the relationship between the mandibular rotation and the mandibular incisal position during chewing movements.
Measurement of mandibular movements during mastication was made using the Sirognathograph Analyzing System in 25 subjects with normal occlusion, 10 subjects with non-functional side occlusal interference and 10 subjects with posterior crossbite.
At closing phase, interferece subjects showed no correlation between the rotation around the anteroposterior axis and the lateral deviation. The rotation around the vertical axis and the lateral deviation exhibited correlation in the middle of closing (p<0.05), but the regression coefficient is less than normal subjects. Crossbite subjects showed correlation between the both rotation and the lateral deviation (p<0.05), but the regression coefficient is greater than normal subjects.
Consequently, relationship between mandibular rotation and mandibular incisal position varies with occlusion. It is suggested that measuring mandibular rotation is important to comprehend the injury of abnormal occlusion to stomatognathic system.

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During mastication, food is subjected to compressive and crushing forces on the occlusal surfaces in order to form a food bolus; this has led most studies of masticatory efficiency to deal with the mechanical degradation of the food particles only, thus neglecting the matter concerning the flow of the food bolus in the oral cavity. Using a modified sieving method, we have previously reported that the food bolus flows through the occlusal surfaces into the proper cavity of the mouth to proceed to deglutition. This method enabled us to evaluate not only the particle size but the distribution of the food bolus in the oral cavity during mastication. In this study, we applied this method to determine the effect of the unilateral mastication caused by occlusal problems on the masticatory efficiency.
Eight fully dentate subjects sitting upright in a dental chair were asked to chew three grams of dried peanuts in two masticatory schemes:
1) Unilateral chewing. The subject was deliberately forced to chew the test food only in one side and not to alternate sides of mastication.
2) Free-sided chewing. The subject was asked to chew as usual.
In both masticatory schemes, two analyses were done: a) the number of masticatooy strokes required for swallowing was counted by asking the subject to chew the experimental food bolus until swallowing, and b) to determine the distribution of food particles in the vestibule of the mouth and proper oral cavity, the subject made 20 masticatory strokes on the test food, then collected the food particles accumulated in these zones and weighed them after drying them.
Results:
1) A significantly higher number of chewing strokes were required to swallow in the unilateral chewing scheme than in the free-sided chewing one.
2) After completing 20 chewing strokes the proportion of food particles in the proper oral cavity was heavier in free-sided chewing than in the unilateral.
Conclusion:
The food particles flow faster to the proper cavity of the mouth and become readily available for deglutition in free-sided chewing than in an unilateral chewing scheme. From this we infer that unilateral mastication must be inferior in masticatory efficiency.

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The effect of afferent signals from the periodontal ligament and muscle spindles of jaw-closing muscles on adrenal medullary function is not known. We approached this matter through analysis of adrenal sympathetic nerve activity, trajectories of jaw movements, and EMG activity of the masseter muscle recorded simultaneously in anesthetized rats. Rhythmic jaw movements (RJM) were evoked by repetitive electrical stimulation of the cerebral cortex.
There was no significant change in the adrenal nerve activity during RJM. When a 2 mm-thick wooden stick was placed between the opposing incisors during RJM, the activities of the masseter muscle and the adrenal nerve were facilitated. The facilitative response of the adrenal nerve returned to the pre-stimulus level after the wooden stick was withdrawn. After sectioning the bilateral maxillary and inferior alveolar nerves, the facilitative response to the masseteric activity due to application of the wooden stick became greatly reduced but no significant change was seen in the adrenal nerve activity. The masseteric activity increased while the jaw was stretched during RJM to increase the afferent signals from the muscle spindles; however, the adrenal nerve activity did not change significantly. Adrenal nerve activity was facilitated when pressure stimulation was applied manually to the upper incisors. The facilitative effect was much greater during repetitive stimulation to the teeth than that observed during continuous stimulation.
These results indicate that afferent signals from the periodontal ligament are responsible for the facilitation of adrenal nerve activity.

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