Understanding the intraoral food transport during mastication is important to analyze the formation of a swallowable food bolus, which is the purpose of mastication. Six subjects with normal occlusion or posterior crossbite chewed a silicone rubber impression material, putty type, as a test food to simulate mastication. After chewing, the shape of the silicon was analyzed and the following conclusions regarding intraoral flow were drawn according to the shape of the chewed test food in each occlusal arrangement.
1. During mastication, the test food flowed in the direction of the inner inclines of overlapping cusps of the upper and lower premolars and molars.
2. There are two ways in which the coordinated function of the cheek and tongue carry food onto the occlusal surfaces: sectional mastication, in which sections of food are carried adequately from the lingual side; and whole mastication, in which food is carried in one lump.
3. In normal occlusal contacts, sectional mastication occurs in a smooth way.
4. In posterior cross-bite cases, whole mastication occurs but not smoothly.

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In order to evaluate the validity of Class II occlusal condition of the first molars after orthodontic treatment utilizing single-arch extraction of the upper first bicuspids, computer simulated biomechamcal analysis was carried out. Four sets of setup models were produced. The setup models represented two occlusal conditions (Simple Class II : The Class II occlusal condition with the upper first molar displaced parallel in the mesial direction from a Class I occlusal condition and Modified Class II : The Class II occlusal condition in which mesial rotation and distal angulation were applied to the upper first molar), and two types of upper first molars which differed in terms of the developments of the distal cusps (Type l: well developed and Type 3: poorly developed) . Next, the surface shapes of the setup models were recorded, and the models of the teeth and the bolus (a small mass of food) were produced for the computer simulation. A finite element analysis was applied to the models and the von Mises' stress that arose inside the bolus model was calculated as an index of destruction efficiency of the bolus.
The results were as follows:
1. For the Type 1 upper first molars no remarkable change in the von Mises' stress was recognized between Simple Class II occlusal condition and Modified Class II occlusal condition.
2 . For the Type 3 upper first molars there was a significant change in the von Mises' stress between Simple Class II occlusal condition and Modified Class II occlusal condition.

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The purpose of the present study was to investigate the coordination between the muscle activities of the masticatory, facial and suprahyoid muscles, and the action of the oral, pharyngeal and laryngeal organs in healthy subjects during chewing and swallowing barium bread. Videofluorography (VF) and electromyography (EMG) were recorded while subjects took in, masticated and swallowed the barium bread.
The following results were obtained: in the pharyngeal stage of swallowing, a monophasic wave was observed during laryngeal movement. The reproducibility was confirmed in the relationship between the laryngeal movement wave and bolus position when swallowing. The duration of muscle activity in the masticatory muscles, orbicular oris muscle and suprahyoid muscle during swallowing was significantly longer than in chewing. In the temporal relationship between laryngeal movement and muscle activities, the temporal and masseter muscles began the activities before the onset of the monophasic laryngeal movement, whereas the digastric and mylohyoid muscles were activat-ed almost simultaneously or slightly after onset.

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