1992 年 46 巻 1 号 p. 355-372
Myofunctional therapy has been in use as an auxiliary means of orthodontic treatment. A number of case presentations have been made on myofunctional therapy. Not many fundamental studies however have been made to date. Six adult subjects with good occlusion without any abnormality in the oral soft tissue therefore were selected and given lip exercise for three months to make chronological examinations of the effect of muscle training. Lip exercise was done 20 times at a time by the button pull method. The exercise was done twice a day, every day, and changes in myofunctions before, during and for two months after the training were examined. For this study, lip strength against instantaneous and sustained pulling of a strung button, integrated EMG activity under the load of weights each attached to the upper and lower lips, labial and lingual pressures on the maxillary and mandibular incisors at rest were examined about every half a month. The results were as follows : 1. Lip strength against pulling of the strung button increased significantly (p<0.05). For two months after the training, no significant changes were seen. 2. EMG activity of the upper lip against loading with weights tended to decrease and showed no significant changes for two months after the training. EMG activity of the lower lip showed various changes depending on the loads but on the whole showed decrease from 0.5 to 1.5 months after the start of the training, and tended to increase gradually for two months after the training. 3. Labial pressure at rest on the mandibular incisor increased significantly (p<0.05) by the training and decreased significantly (p<0.05) for two months after the training. Labial pressure on the maxillary incisor showed great individual differences and no significant changes were seen. Lingual pressure at rest, on the other hand, decreased significantly (p<0.05) for both the maxillary and mandibular incisors and increased significantly (p<0.05) for two months after the training. On the basis of the foregoing findings, muscle training of the lips appeared to prompt increase in muscle strength and muscle pressure of the lips and adaptation of EMG activity to the load. Lip exercise therefore was considered effective for orthodontic treatment of malocclusion accompanied by abnormality in myofunction and for prevention of relapse after treatment.