Magnetic resonance imaging of human mandibular elevator muscles after repetitive maximal clenching exercise

Exercise can enhance the signal intensity (SI) of skeletal limb muscles on T-2-weighted magnetic resonance imaging (MRI). The purpose here was to eval uate the effects of repetitive maximal clenching exercises involving the ma ndibular elevator muscles with T-2-weighted MRI. Seven normal volunteers we re imaged before and immediately after performing repetitive maximal clench ing and at 3, 6, 9, 12. 15, 20 min after the exercise in a 1.5 T GE magnet with spin-echo sequences. SI in the masseter, medial pterygoid and temporal is increased significantly (p < 0.001) and the cross-sectional area (CSA) o f masseter increased 10.11% on T-2-weighted MRI after exercise. The increas ed SI and CSA declined approximately to the pre-exercise level in about 20 min after exercise. No SI and CSA changes were found in the inactive neck m uscle and no SI changes in the mandibular bone marrow (p > 0.05). The findi ngs suggest that the use of exercise-enhanced MRI might be helpful in the s tudy of the function and dysfunction of muscles in the orofacial region. (C ) 2000 Published by Elsevier Science Ltd. All rights reserved.