Stress-, Anxiety-, and Gender-Related Modulation of Masseter Muscle Activity During Wakefulness.

Background: Psychological stress and anxiety are known to influence muscle activity, particularly in the masticatory system. However, the interactive effects of stress, trait anxiety, and gender on objective masseter muscle activity remain poorly understood.

Objectives: This study investigates the association between psychological factors, stress and trait anxiety, as well as gender, and masseter muscle activity during various tasks designed to induce stress or relaxation.

Methods: Thirty-four healthy participants (16 males, 18 females; mean age 28.1 ± 3.1 years) were recruited. Trait anxiety was assessed using the State-Trait Anxiety Inventory (STAI-Y2), and stress levels were measured using a Visual Analog Scale (VAS). Participants completed four randomised tasks (reading, video-watching, math-solving, bead-grabbing) over two experimental days while wearing a wireless EMG logger to record masseter muscle activity. Main outcomes included burst frequency (per hour), wave peak value (%MVC), and integral activity (%MVC·s). Linear mixed models assessed the effects of stress, trait anxiety, and gender. Self-reported oral behaviours (partial Oral Behaviour Checklist; POBC) were also evaluated.

Results: Stress significantly reduced burst frequency (-3.5% per unit; p = 0.016) and wave peak value (-1.9% per unit; p < 0.001) in males but not females. Low-anxiety individuals exhibited increased integral muscle activity with rising stress (+4.8% per unit; p = 0.002), while other groups showed no such trend. Trait anxiety positively correlated with POBC scores (r_s = 0.409, p = 0.016).

Conclusions: Masseter muscle activity is differentially modulated by stress, anxiety, and gender. These findings highlight the psychophysiological complexity underlying stress-related oral parafunctional behaviours and support individualised assessment approaches.