Day-To-Day Variation in Masseteric Electromyographic Waveforms During the Diurnal Awake State.

Background: To establish diagnostic/assessment criteria for awake bruxism (AB) using electromyography of the masseter muscle during the diurnal awake state (d-EMG), it is necessary to refer to the actual state of variation of d-EMG waveforms between different days (d-variation).

Objective: This study aimed to clarify the actual state of d-variation in various indices of d-EMG waveforms.

Methods: The participants included 91 volunteers with or without awareness of diurnal tooth clenching. Measurements were conducted on three days within a two-week period using a wearable EMG device set at the unilateral masseteric region. A waveform with an amplitude more than twice the baseline and a duration of more than 0.25 s was defined as a burst. The number of bursts/h, number of episodes/h, number of bursts ≥ 20% maximum voluntary clenching (MVC)/h, burst integral value/h, and standardised burst integral value/h were calculated. The coefficient of variation (CV) of the three measurement days was calculated for each index.

Results: The five indices showed no significant differences among the three days. The median CV for the number of episodes/h, number of bursts/h, number of bursts ≥ 20% MVC/h, burst integral value/h, and standardised burst integral value/h were 0.233, 0.276, 0.507, 0.417, and 0.482, respectively. Of the indices, bursts/h and episodes/h had the smallest day-to-day variation. The CV for the number of waveforms tended to be smaller the larger the number of waveforms.

Conclusion: These findings are considered useful as reference data for establishing diagnostic/assessment criteria for AB using masseter EMG in the future.