Abstract
It has been reported (Moyers) and generally recognized that the sucking reflex in a new born baby would develop into chewing in accordance with the eruption of the incisors. The perception acquired at the periodontal membrane of the deciduous teeth may be assumed to play a role in the transition from the sucking reflex into chewing. The purpose of the present study was to clarify the possible role of the perception of the periodontal membrane on the development of chewing in new born puppies with the aid of electromyograms.
Fifty puppies were used and divided into four experimental groups as follows;
1) Control
2) Enucleation of all tooth-germ before eruption of the deciduous teeth (Enucleation group)
3) Nerve block before eruption of the deciduous teeth (Block group)
4) Extraction of all teeth after eruption of the deciduous teeth (Extraction group)
The electromyograms of temporalis and masseter muscles were recorded with needle electrodes (RBL-85, Nihon-Koden Co., Tokyo, japan). The transitional time from the sucking reflex into chewing was assessed either by the sensation of the index finger inserted into the mouth of a new born puppy, or by electromyogram activities of the masticatory muscles.
The results obtained in the present study were as follows:
1) Normally, as observed in the control group, the time of the transition from the sucking reflex into chewing and the formation of chewing cycle occured simultaneously when the puppies were 20.1 days old. The time was precisely related to the eruption of the deciduous incisors (22.3 days of age).
2) In the enucleation group, the time of the transition was evidently delayed about 7 days, and chewing cycle did not developed till 60 days of age.
3) In the block group, chewing was delayed 4 days, although the chewing cycle was not noticed just after the beginning of chewing, it emerged afterward at the 49.0th day of age.
4) In regard to the chewing cycle as was examined in the extraction group, about 6 days were required after the extraction to catch up to a similar chewing cycle observed before the extraction.
From the results obtained in the present study, it was concluded that the eruption and presence of deciduous teeth has an important role in the development from the sucking reflex into chewing, and on establishing the chewing cycle. Also it may be assumed that the impulses given to the periodontal nerves of deciduous teeth may play the possible role of a trigger to a neural switch mechanism from sucking reflex into chewing, and also give stimulation to develop the central chewing rhythm generator.
