Excitability of the central masticatory pathways in patients with sleep bruxism

Since sleep bruxism (SB) is defined as a stereotyped movement and mainly associated with rhythmic masticatory muscle activity, the aim of this study was to get a better understanding on the subcortical and cortical networks related to the excitability of the central masticatory pathways in SB patients. Of 26 SB patients (12 females and 14 males; mean age: 24.9±4.0 years) and 30 normal subjects (18 females and 12 males; mean age: 24.1±3.1 years) selected, the motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) in masseter muscles, and the masseter inhibitory reflex (MIR) elicited by magnetic stimulation with single and double-shock techniques were studied. The MEPs elicited by TMS were similar in both SB patients and normal subjects. As for the MIR elicited by single magnetic stimulation, the latency and duration of the early silent periods (SP1) between the two groups were similar; but in 5 patients the late silent periods (SP2) was absent, and this difference in the frequency of absence of the SP2 between SB patients and normal subjects was significant; with double-shock technique, the recovery of SP2 was significantly lower in SB patients compared to normal subjects. These results suggested an abnormal excitability of the central masticatory in SB patients; and it is also indicated that SB may be mainly under the influence of brainstem networks rather than that of cortical networks.