Abstract
The purpose of the present study was to investigate the characteristics of mastication in infants by evaluating the electromyographic coordination pattern of the masticatory muscles and VTR and to discuss the development of the mastication in infants from sucking or weaning to adulthood with maturated chewing. A total of eighty-nine subjects were divided into the following seven groups, the sucking group (G 0: as a control,23 subjects), G 1 (6 to 7 months in age,14 subjects), G 2 (8 to 9months,14 subjects), G 3 (10 to 12 months,8 subjects), G 4 (1 to 2 years,7 subjects), G 5 (3 years,13 subjects) and G 6 (adults,10 subjects). The transition of the coordination pattern of masticatory muscles (TM: temporal, MM: masseter and SM: suprahyoid muscles) while ingesting cooked rice as a test food were analyzed.
When compared to the G 0, both the chewing cycle time and the burst duration measured in the TM became significantly longer throughout G 1 to G 3, and then the values gradually declined in G 4to G 6. The coefficient of the variation in the chewing cycle time was higher in G 1 to G 3 than that of G 4 to G 6. The masticatory pattern for the weaning period infants were characterized by the coincidental activation of the TM and SM. The mastication pattern of infants, therefore, can be classified into three types, such as the continuous tongue compression (Type I), the cyclic tongue compression (Type II) and the maturation type (Type III). The fequency of Type III significantly increased from G 1 (1%) to G 6 (74%), while the Type I significantly decreased, especially after G 4.
As the coincident of the bursts of the TM and the SM was recognized during each chewing cycle in the earlier period of weaning, food was considered to be ingested by the active movement of the tongue around this period. The development of chewing in terms of the EMG coordination pattern for the masticatory muscles, therefore, disclosed that the function of the jaw closing muscles and of the SM differentiated gradually as the time proceeded from the initiation of weaning. The turning point for the phenomena is considered to exist between G 3 and G 4.
