Abstract
In the present study, sucking movements of human infants with special interest in the participation and coordination of various masticatory muscles were evaluated.
Two,4 and 5 month old age healthy infants, were the subjects. Muscle activities were examined by surface electromyography from the anterior belly of the temporal muscle, masseter muscle, orbicularis oris muscle, and suprahyoid muscles unilaterally. The sucking pressure (sucking waves) was recorded simultaneously using a feeding bottle specially devised at our department, and the movement of mandibular of the infants during feeding was recorded on video tape.
The following results were obtained:
1) The sucking wave could be divided into the squeezing, aspiration, and deglutition phases, and the deglutition phase appeared after 2-4 simple sucking cycles of positive and negative pressures.
2) During the squeezing phase, the action of the orbicularis oris muscle was followed by those of the masseter muscle and the temporal muscle. In the aspiration phase, the orbicularis oris muscle and suprahyoid muscles were active. During deglutition, primarily the orbicularis oris muscle and suprahyoid muscles acted with coordinated movement also of the masseter muscle.
3) The jaw shifted supra-anteriorly during the squeezing phase and infero-posteriorly during the aspiration phase.
These findings suggest that sucking movements consists of a complex series of the movements of squeezing of milk, aspiration, and deglutition, which are accomplished by coordination of the muscles around the mouth. Also, the orbicularis oris muscle and suprahyoid muscles are considered to play primary roles in sucking.
