[Development of chewing center at transition period from sucking to chewing].

UNLABELLED: The purpose of this study was to identify and to characterize the peripheral movement evoked by electrical stimulation given to the masticatory area of the cerebral cortex (Control group), and to clarify the development of the chewing center by examining the change in the peripheral movement when the tooth germs have been enucleated (Enucleation group). Puppies were used in the present study which were anesthetized with a 25% solution of Urethane (4 ml/kg, i.p.). Their heads were then, fixed in a stereotaxic apparatus, and the surfaces of the orbital gyrus was surgically exposed. Electrical stimulation (Frequency: 25 c/sec,

DURATION: 2 msec) was given to the masticatory area. All of the tooth germs of the deciduous teeth were enucleated at 12-14 days of age in the enucleation group. After the enucleated wound healed, stimulation was similarly performed in the control. The results obtained were as follows; In the control group, a sucking movement was evoked coinciding with the beginning of the eruption of the deciduous teeth (19-23 days of age), and it changed into a chewing movement as eruption proceeded. However, by 14 days of age, neither sucking nor chewing movements were evoked even when stimulation was applied to the area of the cerebral cortex. In the enucleation group, the time of the onset of the sucking movement was considerably delayed until the age of 22-27 days. Also it was converted into a jaw opening movement which occurred after 28 days of age. The chewing movement was observed for some days after 41 days of age. The transition from sucking to chewing was recognized to undergo a little delay when the deciduous teeth was enucleated. These results suggest the afferent impulses provided with the eruption of deciduous teeth presumably play an important role on the development of the chewing center and consequently on the transition from sucking to chewing.