Abstract
We reported that, in children with normal occlusion, the difference was found as to how masticatory muscles are used for mastication in deciduous dentition and in the permanent dentition. In a word, the temporal muscle works mainly in the deciduous dentition, while on the other hand, the masseter muscle works mainly in the permanent dentition. In cases of crowding, however, the functional development of muscles related to mastication which is one of the functions of the stomatognatic system not explained. This investigation was carried out for the purpose of estimating the masticatory function of muscles in cases of crowding.
The subjects consisted of 50 children with cases of crowding. They were divided into groups from IIA to IIIC according to Hellman's dental stage. The control consisted of 50 children with normal occlusion.
The muscles examined bilaterally were the anterior temporal muscles (TA), the posterior temporal muscles (TP) and the superficial portion of masseter muscle (M) utilizing four established movements such as gum free chewing, peanuts free chewing, marshmallow free chewing and maximum bite. After the actions of the above muscles were recorded using electromyography (EMG), the data was integrated. The TA%, TP% and M%, which are the percentage of the total action potential of TA, TP and M, were calculated to determine the quantity of the action between each muscle.
Concerning the results, we found, in comparison with the control, the decrease of the TA percentage and the increase of the M percentage were small with the advance of the dental stage in cases of crowding. Both in the deciduous dentition and in the permanent dentition, the anterior temporal muscle worked mainly in cases of crowding.
