EXCITABILITY OF THE CENTRAL MASTICATORY PATHWAYS IN PATIENTS WITH PAINFUL TEMPOROMANDIBULAR DISORDERS

Much is unclear about the pathophysiological mechanisms underlying pai nful temporomandibular disorders. In addition to various other theorie s, masticatory muscle dysfunction and pain have also been attributed t o primary central nervous system hyperactivity. We assessed this possi bility in a study using recent neurophysiological techniques. From amo ng outpatients whose diagnosis of temporomandibular disorders had been obtained in stomatognathic facilities, we studied 10 patients with bi lateral pain and 15 patients with unilateral pain, in whom electromyog raphic examination of the trigeminal reflexes disclosed normal finding s except for absence or amplitude asymmetry of the jaw jerk. Transcran ial magnetic stimulation yielded masseter motor evoked potentials of n ormal latency and amplitude, but five patients had to exert a near-max imum contraction to obtain their responses. The masseter silent period s elicited by the double-shock technique recovered normally. Because t hese tests measure the excitability of the masticatory system (includi ng motor cortex, corticobulbar and corticoreticular connections, retic ular interneurones and lower motoneurones), the lack of facilitation i n these patients' responses excluded central hyperactivity as the prim ary cause of their masticatory dysfunction and pain. (C) 1997 Internat ional Association for the Study of Pain. Published by Elsevier Science B.V.