Abstract
The purpose of the present study was to evaluate the maturation of the neuromuscular system of masticatory muscles in children. For this purpose, the examination of the stretch reflex of masseter muscles known as one type of masticatory muscle reflex, and the subsequently occuring silent period were made. In addition, the effects of muscle activities on the duration of the silent period were also discussed.
A total of 25 subjects: 1) 10 children (mean age,6y 2m), all with sound dentitions and functionally normal occlusions (designated as the CN group); 2) 10 adults (mean age,21.1y), with functionally normal occlusion and without any stomatognathic system disorder as well (designated as the AN group); and 3) 5 adults (mean age,27.2y), whose bite forces are very poor (designated as the AS group).
Stretch reflex was induced by applying chin taps with constant strength at the following positions; 1) the rest position representing voluntary isometric contraction of the muscles,2) the clenching (the maximum clenching ad libitum that the subject could maintain 10% and 50% levels respectively),3) the biting of occlusal force meter (5 kg,10 kg and Max. B., the maximum bite ad libitum respectively). The recording of muscle activities were obtained using surface electrodes applied on the bilateral masseter muscles.
The results obtained in the present study were outlined as follows:
1) The latency of the stretch reflex was shown to be longer in the rest position than at any level of clenching and biting in all groups when comparing the three groups, the latency of the CN group was shown to be longer than other two groups.
2) With the increase of muscle activities, the duration of the silent period significantly descreased. This was noted both in the CN and AN groups as well, whereas no significant change was recognized in the AS group.
3) As far as the duration of the silent period is concerned, it was the shortest in AN group, and followed by the CN, and the AS group at maximum biting.
The results obtained in the present study suggest that the growth and development of the masticatory muscles could affect the duration of silent period, in other words, the silent period was possitively influenced by the activities of masticatory muscle.
