Abstract
The present study investigated the effects of muscle stiffness of the masseter muscle (Mm) and anterior portion of the temporal muscle (Ta) in various maxillomandibular relations. The results obtained were as follows:
1. Both Mm and Ta exhibited less difference in the stiffness at the rest condition and maximum voluntary contraction when they fatigued. Additionally Mm has a greater difference in the stiffness than Ta before and after fatigue.
2. No change in stiffness was observed from Mm and Ta at rest condition in various position of mandible.
3. When a maximum voluntary contraction was done in dentulous and edentulous subjects, Mm and Ta stiffness increased slightly together with increase of vertical dimension.
4. When a maximum voluntary contraction was done in edentulous subjects, Mm stiffness decreased markedly together with decrease of vertical dimension.
5. As to horizontal movement of mandible both dentulous and edentulous subjects showed the highest muscle stiffness in habitual closing position at the maximum voluntary contraction.
6. In Mm, the stiffness on ipsilateral side and contralateral side at maximum voluntary contraction showed unclear difference, but showed clearly higher muscle stiffness onthe ipsilateral side than on the contralateral side in Ta.
7. Measurement of the masticatory muscle stiffness suggested enable to examine muscle activity.
