Is temporomandibular dysfunction a cranial dystonia? An electrophysiological study

In 26 patients suffering from temporomandibular dysfunction (TMD) the silent period (ES), which consists of an early (ES1) and a late (ES2) inhibition which interrupts the voluntary electromyographic activity after an electrical stimulus, was recorded from the masseter muscles. Several different patterns were identified: in 8 patients (group I) the ES was normal; in 1 patient (group II) the ES was entirely absent; in 11 patients (group III) only the ES2 was absent and in 6 patients (group IV) ES1 and ES2 were combined. Such results can be explained by hypothesizing several functional states: normal excitability in group I, absolute (group II) or relative (group III) inexcitability and hyperexcitability in group IV. A central origin of TMD can be related either to a "dysregulation" of circuits located in the brainstem which give rise to the ES or to the centers, probably located in the basal ganglia, which control the circuits of the brainstem.