Experimental toothclenching in common migraine.

The effect of 30 min voluntary toothclenching was studied in 48 patients with common migraine, randomized in two groups. Group 1 performed low-level tension at 5% and group 2, high-level tension at 30% of the individual maximum, as judged by surface EMG from the temporal muscle. Pericranial muscle tenderness was evaluated by manual palpation and a four-point verbal scale. Headache, nausea, and soreness of the chewing muscles were scored on visual analogue scales. Although surface EMG, soreness, blood pressure, heart rate and difficulty in completing the toothclenching session all showed that group 2 patients were subjected to significantly higher levels of muscle tension than group 1 patients, headache developed equally often in both groups (63%). Headache was even more pronounced in group 1 (n.s.). Five patients in group 1 and none in group 2 developed an attack of migraine during the following 24 h. Pericranial muscle tenderness was unaffected by the experimental procedure. There was no significant correlation between headache intensity and pericranial muscle tenderness. Muscle ischemia, muscle "fatigue", and strain on muscle insertions are thus unlikely to cause attacks of common migraine.