[Human mastication and its observation].

Human mastication is a very complicated three dimensional jaw movement. The movement is driven primarily by the chewing center or the rhythm generator located in the brain stem below the level of the mesencephalus. Recent studies have revealed that the first opening action is voluntary and food determined, while the later opening and closing movements are solely of central regulation. Variability of speed, direction, and range of vertical, horizontal, and anteroposterior deflection ect, in the chewing strokes is reflexly modulated through peripheral and central feedback. The effects of pain in teeth, oral mucosa, muscles and temporomandibular joints on the masticatory movements can be instantaneous and transient. However the altered pattern, if it lasts long, can become one's new pattern and needs time to be eliminated even when the cause is removed. Observation of the jaw movement during mastication requires a system with minimum interference and careful interpretation. Photoelectric, magnetoelectric and radio isotopes have been used although none of them is completely undistorted. The jaw movement during different types of food chewing in different situations have long been studied in detail. The results have suggested a high intraindividual and even higher interindividual difference, which made the categorization of chewing movement impractical. Conclusions drawn from the comparison of normal and abnormal patterns of chewing movement should be based on very carefully defined parameters.