Impact of Sleep Bruxism on Training-induced Cortical Plasticity

Objectives: To investigate the effect of sleep bruxism on training-induced cortical plasticity using transcranial magnetic stimulation (TMS).

Methods: Thirty-eight participants were recruited in this study that consisted of 2 sessions; a screening session and a lab session. Prior to the lab session, all participants used a portable EMG device to measure temporal muscle activity during sleep for 7 consecutive nights. According to the number of EMG events, participants were divided into a bruxer group (N=19) and a non-bruxer group (N=19). In the lab session, the participants performed a tooth-clenching training task (TCT) at right first molar teeth for 58 minutes at 3 force levels (10%, 20% and 40% of maximum voluntary contraction) in a randomized order. EMG activity in masseter muscles were recorded during TCT. Single pulse TMS was applied to elicit motor evoked potentials (MEPs) from right masseter and right first dorsal interosseous muscle (as an internal control) immediately before TCT (pre-TCT session) and immediately after TCT (post-TCT session). The motor threshold (MT) of MEPs was defined as the minimum stimulus intensity that produced 5 out of 10 discrete MEPs clearly discernible from the background EMG activity. Stimulus-response curves were constructed by 90%, 100%, 120%, and 160%MT.

Results: The masseter MEPs in the non-bruxer group at 120% and 160%MT were significantly higher than in the bruxer group in the pre-TCT session (P<0.05). The masseter MEPs in the non-bruxer group in the post-TCT session were significantly higher than the pre-TCT session (P < 0.05), however, there were no differences in the bruxer group between pre- and post-TCT.

Conclusions: Our results suggest that sleep bruxism may be associated with significant changes in the excitability of corticomotor pathways and features of training-induced cortical neuroplasticity. Overall, these findings support the notion that sleep bruxism may primarily be related to central nervous system function.