片側性変形性顎関節症患者における食いしばり時の顎筋の筋電図パワースペクトル

Electromyographic power spectrum of jaw muscles during clenching in unilateral temporomandibular joint osteoarthritis patients.

抄録

変形性顎関節症と咀嚼筋障害との関係はあまり理解されていない。また、筋電図（EMG）のパワースペクトル解析は行われていない。本研究の目的は、片側性変形性顎関節症患者と健常対照者において、持続的食いしばり時の筋電図パワースペクトル、および食いしばり前後の圧痛閾値（PPT）の違いを比較することである。咀嚼筋痛を伴わない片側変形性顎関節症患者19名と健常対照者20名を対象とした。側頭筋と咬筋の最大随意収縮時のEMG振幅、70％持続食いしばり時のEMGパワースペクトルからの中央周波数、食いしばり前後のPPTを測定した。持続的食いしばり時のPPT低下には、筋間、群間に有意差はなかった。変形性顎関節症患者の患側と非患側の最大随意収縮筋電図活動比、咬筋と側頭筋の患側と非患側の最大随意収縮筋電図活動比に有意差はなかった。頻度の中央値は、持続的な食いしばりの開始から終了まで減少し、群と食いしばりの間の交互作用は有意であった：頻度の中央値の減少は変形性顎関節症群で大きかった。この結果から、片側性変形性顎関節症患者の咀嚼筋は、健常者よりも持続的食いしばり時に疲労しやすいことが示唆された。

The relationship between temporomandibular joints (TMJ) osteoarthritis and masticatory muscle disorders is poorly understood. The data are sparse, the results are conflicting, and electromyographic (EMG) power spectrum analysis has not been used. The aims of this study were to compare the differences in EMG power spectrum during, and pressure pain thresholds (PPTs) before and after, sustained clenching in patients with unilateral TMJ osteoarthritis and healthy control subjects. Nineteen patients with unilateral TMJ osteoarthritis without masticatory muscle pain and 20 control subjects were evaluated. We measured EMG amplitudes at maximum voluntary contraction, median frequency from the EMG power spectrum during sustained clenching at 70% and PPTs before and after the clenching in both temporalis and masseter muscles. There were no significant differences in PPT decrease between muscles or between groups during sustained clenching. There were no significant differences in maximum voluntary contraction EMG activity ratios of affected to unaffected sides between groups, or of masseter to temporalis muscles between affected and unaffected side of patients with TMJ osteoarthritis. Median frequencies decreased from the beginning to the end of the sustained clench, and the interaction between group and clench was significant: the median frequency decrease was larger in the osteoarthritis group. Our results suggested that masticatory muscles of patients with unilateral TMJ osteoarthritis are more easily fatigued during sustained clenching than normal subjects.