Background: Studies have shown co-contraction of jaw and neck muscles in healthy
subjects during (sub) maximum voluntary jaw clenching, indicating functional interrelation
between these muscles during awake bruxism. So far, coherence of jaw and
neck muscles has not been evaluated during either awake or sleep bruxism.
Objective: The objective of this study was to evaluate the coherence between jaw
and neck muscle activity during sleep bruxism.
Methods: In a cross-sectional observational design, the electromyographic activity
of jaw (masseter, temporalis) and neck (sternocleidomastoid, trapezius) muscles in
individuals with “definite” sleep bruxism was measured using ambulatory polysomnography
(PSG). Coherence for masseter-temporalis, masseter-sternocleidomastoid
and masseter-trapezius was measured during phasic and mixed rhythmic masticatory
muscle activity episodes using coherence-analysing software. Outcome measures
were as follows: presence or absence of significant coherence per episode (in percentages),
frequency of peak coherence (FPC) per episode and sleep stage.
Results: A total of 632 episodes within 16 PSGs of eight individuals were analysed.
Significant coherence was found between the jaw and neck muscles in 84.9% of the
episodes. FPCs of masseter-temporalis were significantly positively correlated with
those of masseter-sternocleidomastoid or masseter-trapezius (P < .001). Sleep stages
did not significantly influence coherence of these muscular couples.
Conclusion: During sleep bruxism, jaw and neck muscle activation is significantly coherent.
Coherence occurs independently of sleep stage. These results support the
hypothesis of bruxism being a centrally regulated phenomenon.