Tension-type headache patients, without signs or symptoms of temporomandibular disorders,
were evaluated for temporalis contraction intensity over a three day period.
Tension-type headache patients clench their jaws, on average,
14x more intensely during sleep than asymptomatic controls.

The surface emg electrodes were placed on the temporalis and maxium outputs was recorded
over the preceding 30 minutes.  The graph below shows how the clenching intenstiy increases as
the headache patients are sleeping.  The habitual nightly intense contractions make the temporalis
"over contract" during regular function (the spiking during lunch time recordings).

A possible goal of treatment and prevention of TMD's and tension-type headaches might
be to specifically reduce the intensity of  temporalis activity.