Abstract
Class I open bite during mixed dentition has been treated by means of improvement of oral function in many cases. However, Class I open bite has abnormalities in the dental arch forms. Therefore, We tried to treat Class I open bite during mixed dentition using the Maxillary removable expansion plate. Analysis was made by face and intra-oral photograms, mounting casts, cephalograms and The EMG of the jaw closing muscles with The mandibular in the rest position during pre-treatment (6years and 8 months) of age, post-treatment (8 years and 6 months) of age and progress observation (10 years and 6 months) of age. The results were as follows:
1. The Upper and Lower dental arch lengths decreased slightly. The Upper and Lower molar width expanded, and the anterior incisors were aliened.
2. The vertical balance of the facial profile was shortened at the upper lip. and the upper lip retreated and the lower lip protruted.
3. The mandibular position moved to the lower-posterior position from the pre-treatment to the posttreatment observations, and did not move from the post-treatment to the progress observations. The EMG activities of the masseter muscle at the mandibular rest position decreased from the pretreatment to the post-treatment observations, whereas they decreased from the post-treatment to the progress observations slightly. The EMG activities of the temporal muscle in the mandibular rest position decreased from the pre-treatment to the progress observations.
