A New Short-Term Assessment Condition for Evaluating Nonfunctional Electromyographic Activity of Masseter Muscle During Wakefulness.

Background: Awake bruxism involves masticatory muscle activity during wakefulness, potentially leading to clinical concerns. Accurate electromyography (EMG) assessment is challenging with brief durations.

Objective: To establish a reliable, short-term measure for nonfunctional masseter muscle activity during wakefulness.

Methods: Thirty-four healthy participants completed the Oral Behavior Checklist (OBC) and were assessed with an EMG logger (FLA-500-SD) across three sessions. On Day 1, participants performed four tasks (reading, bead-grabbing, video watching and math) for 15 min each in random order. On Day 2, scheduled at least 1 week later, tasks were repeated in a different sequence. On Day 3, participants underwent a 7-h continuous EMG recording during daily activities while maintaining activity diaries. Main outcomes included the mean number of EMG bursts per hour, burst duration, burst peak value relative to maximum voluntary contraction (%MVC) and integral value (μV.s, %MVC.s).

Results: Participants (mean age: 28.0 ± 3.1) scored low on AB likelihood per partial OBC results, contrasting with EMG activity levels. Significant differences in EMG parameters were noted across tasks, with consistent values between Days 1 and 2. The reading, video, and math tasks showed strongest correlations with long-term EMG measurements (r = 0.62-0.66, p < 0.001). Reading task demonstrated high test-retest reliability (ICC > 0.9), with the highest specificity (100%) and positive predictive value, though sensitivity was limited compared with long-term AB measures.

Conclusions: EMG measurements during a 15-min reading task may correspond to prolonged monitoring, suggesting the potential for short-task EMG assessments in practice. Integrating such assessments might enhance diagnostic accuracy, although judgement remains essential.