Lack of Efficacy of Low-Dose Cyclobenzaprine on Electromyographic Activity Related to Sleep Bruxism: A Randomized Crossover Double-Blind Placebo-Controlled Clinical Trial.

Sleep bruxism (SB) is a motor activity characterized by repetitive masticatory muscle contractions during sleep, commonly associated with tooth damage and jaw pain or headache. Pharmacological management strategies targeting its central nervous system-related mechanisms remain limited. This study aimed to evaluate whether a low dose of a central muscle relaxant, cyclobenzaprine, reduces SB-related muscle activity, maximum voluntary bite force and self-reported bruxism awareness. A randomized, double-blind, placebo-controlled, crossover clinical trial was conducted. Twenty participants underwent baseline SB motor activity recordings followed by two intervention phases consisting of 5 mg of cyclobenzaprine or placebo for three consecutive nights. Masticatory muscle activity during sleep was quantified using portable surface electromyography. Maximum voluntary bite force was measured using a bite force-recording device. Self-reported outcomes related to SB and secondary effects (e.g., dry mouth) were collected each morning. Comparison of cyclobenzaprine to placebo and baseline nights failed to show a difference in mean frequency of masticatory muscle activity during sleep and maximum voluntary bite force. No self-reported differences were observed for SB awareness. Few secondary effects were identified between cyclobenzaprine use and placebo; a significant increase in perception of tolerable dry mouth upon awakening (p = 0.034) and a marginally statistically significant reduction in the perceived leg movements during sleep (p = 0.046). In conclusion, low-dose cyclobenzaprine was not effective in modifying SB-related muscle activity or masticatory muscle force, suggesting limited clinical utility for SB. Future studies using higher doses of cyclobenzaprine are warranted before ruling out its clinical utility, within a safety profile.