The purpose of this study was to verify the hypothesis that the increased activity of the ipsilateral SHLP described above serves to antagonise the occlusal force acting on the condyle. In total, 9 healthy volunteers were requested to perform left unilateral clenching at the first molar or first premolar region for 1 minute at 20% or 40% maximum voluntary clenching force. Changes in the mean proton transverse relaxation time (∆T2) were examined from the magnetic resonance images obtained before and after each clenching act as an index of the activity in all masticatory muscles. Correlation analyses of the mean ΔT2 for each volume of interest were performed with the first molar or premolar clenches to analyse the correlation between the activities in each muscle. A statistically significant correlation was exhibited between the ipsilateral temporal and ipsilateral SHLP (r = .651, P = .003) during first premolar clenching. However, no significant correlations were observed in the ipsilateral SHLP during first molar clenching. The results of this study suggest that the ipsilateral SHLP may contribute to the pulling of the mandibular condyle forward against the occlusal force generated by the ipsilateral temporal muscle.(仮説を検証する目的で、9名の被験者の片側嚙みしめ時における筋活動の様相を筋機能的MRIにより計測・分析した。小臼歯での嚙みしめ後の外側翼突筋上頭のT2値の変化は、同側側頭筋との相関が高く、本研究の結果から、外側翼突筋上頭は側頭筋がもたらす咬合力に抗して下顎頭を前方に引く役割を果たしていると推察された。）
45(1):9-16
Yamaguchi Satoshi, Okada Chika, Watanabe Yoshihiko, Watanabe Makoto, Hattori Yoshinori
