| Angle class II division 1 malocclusion is a kind of malocclusion that often occurs in mixed and the early permanent dentition. Muscular activator is one of the functional appliances widely used and have good effects on the treatment the of Angle class II division 1 malocclusion, Angle's class II division 1 malocclusion. In this study, twenty cases of retrognathic Angle class II subdivision 1 malocclusion occurring in dental transitional and the early permanent tooth period were clinically corrected with Modified Activator, ten patients with the same deformity who did not receive any treatment were as controls. Curative effects of the activator were analyzed through cepbalometric radiography, temporomandibular joint tomography and electromyography (EMG) of masticatory muscle. Results from the present study produce powerful evidence that, in the period of growth development, muscular activator can reduce the patients sagittal maxillomandibular inconsistency and promote the growth of mandible. Conclusions are as follows:1. After 7 to 14 of correction with the activator, on average, ANB angle was reduced 2.9 degrees, SNA angle was reduced 1.1 degrees, SNB angle was increased 1.8 degrees, the length of mandible was increased 2.2 millimeters, lower incisors moved backwards for 1 .7millimeters. Compared with controls, all the above changes were statistically significant. 2. Treatment with the Activator results in obvious morphological changes of soft tissue. On average, FH-Ng'- was increased for 1.9 degrees.. Pg'-N'-S 2.4 for degrees.. Si-N'-S for 2.0 degrees. 3. After treatment, myoelectric value of the anterior brounch of temporal muscle was significant increased. 4. Results from temporomandibular joint tomography show that there was no significant change in the area ofjoint space. 5. Muscular activator can promote the development of mandible, It is possible for the effective correction of the etrognathic Angle class II subdivision 1 malocclusion through the growth potential of the jaws.
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