Masataka Hisano

Functional relationships between the masseter and sternocleidomastoid muscle activities during gum chewing

The purpose of this study was to investigate the functional relationship between masseter muscle (MM) and sternocleidomastoid muscle (SCM) activities and between mandibular and head movements during mastication, under experimental muscle fatigue. The sample consisted of 12 adults with individually normal occlusion. The subjects were asked to chew gum at three different times: before maximum clenching, immediately after maximum clenching, and 3 minutes after maximum clenching. At these times, we examined the activity of the MM and SCM as well as the movement of the mandible and head. The activity and movement were simultaneously measured using both electromyography and the motion capture system. The MM activity time after clenching was significantly shorter than that before clenching, whereas the SCM activity time was significantly longer after clenching. There was no significant difference in the changes of three-dimensional distance of the mandibular movement between the respective times. On the other hand, the changes in the three-dimensional distance of head movement after clenching increased when compared with before clenching. Furthermore, the difference in the time of MM and SCM activity onset and of mandibular and head movement onset after clenching was shorter than that before clenching. A functional relationship exists between the MM and SCM activities and between mandibular and head movements during mastication.

Vertical Control by Combining a Monoblock Appliance in Adult Class III Overclosure Treatment

Monoblock appliances were used in combination with intermaxillary elastics for treatment of adult skeletal Class III patients. The patients showed predisposing upper incisors problems, significant mobility in patient 1 and root resorption in patient 2, which contraindicated direct intrusion of the incisors. Using the monoblock with selective extrusion of the molars, a clockwise rotation was induced to reduce overbite and to achieve a better profile. It was also possible to reduce the excessive force to the upper incisors during and after treatment, which improved incisor mobility to a physiologic extent (patient 1) and prevented further progression of root resorption (patient 2). Stability was high after the 2-year follow-up, which suggests a stable vertical control approach by using the monoblock appliance in combination with a fixed appliance in adults.