The relationship between sleep bruxism and sleep-related respiratory events under oral appliance therapy in patients with obstructive sleep apnea

Introduction Sleep bruxism (SB), which is associated with obstructive sleep apnea (OSA), has been receiving increased attention. Oral appliance (OA) therapy is likely to indirectly improve SB by reducing the number of respiratory events and arousals that induce SB. Objectives This study aimed to clarify how OA therapy influences SB, which is likely to induce arousal, by analyzing the relationship between muscle activity during SB and sleep-related respiratory events before and after OA therapy in patients with OSA. Material and methods Patients diagnosed with OSA based on polysomnography (PSG) at Fukuoka University Hospital between October 2020 and May 2025 were referred for OA therapy. Twenty-one participants (10 males, 11 females; mean age, 57.8 ± 16.0) were enrolled in this study. The masseter muscle activity was simultaneously measured using an identical single-channel wearable electromyography device. They underwent a second PSG and EMG evaluation after OA therapy, and a comparison of the data between baseline and reevaluation was conducted. Results The results of baseline and reevaluation PSG evaluations showed a significant improvement in AHI from 17.3 ± 7.3 to 12.3 ± 10.7 (p = 0.008). The total number of SB episodes and SB/h significantly decreased (p = 0.002 and p = 0.001, respectively), and the spontaneous arousal index during the rapid eye movement stage significantly increased (p = 0.007). Significant reductions in total SB episodes and SB/h were observed not in the effective group, including 10 participants with apnea/hypopnea index (AHI) reduction ≥50% or AHI in reevaluation <5, but in the ineffective group, including 11 participants with AHI reduction <50% and AHI in reevaluation ≥5 (p = 0.013 and p = 0.013, respectively). The effective group experienced a significant decrease in the respiratory arousal index during total sleep time (p = 0.002) and a significant increase in the spontaneous arousal index (p = 0.011). Conclusions The mechanism underlying the generation of SB appears to be derived not only from the presence of OSA but also from a multifactorial etiology, and OAs may not only be simple respiratory assist devices but also effective for helping to manage SB.