Association of masticatory function with morphology and function of the central nervous system

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In recent years, an important role of the tooth and the relevant functions such as biting, chewing and mastication has been addressed. Under such background, the present study was designed to investigate the influences of stomatognathic functions on the development of the other tissues and organs, the central nervous system in particular, by use of rats and mice as experimental animals and human subjects.In an experiment with osteopetrotic (op/op) mice involved with defects in osteoclastic activity and tooth eruption, the reduced masticatory function produced a decrease in the number of neurons in the central nervous system. Such phenomena were similarly observed in normal mice and rats subjected to artificial reduction in mechanical stimuli from mastication and physical exercise. These findings were eliminated to some extent, approaching the normal controls, by an artificial injection of osteoclast induction agents, which generate tooth eruption and recover in masticatory function. Furthermore, . mechanical stimuli to the teeth in rats induced a specific C-fos protein in the central nervous system. Meanwhile, such association in humans has been studied by use of a portable electromyogram recorder, demonstrating the nature of masticatory function in subjects with occiusal discrepancy. In conclusion, it is emphasized that external mechanical stimuli from stomatognathic functions substantially affect the development of the central nervous system, indicating an important role of the dentition and the related masticatory function.