Abstract
Purpose: Nocturnal bruxism has been recognized as a clinically relevant problem for decades, however, the exact cause of nocturnal bruxism (NB) is not clear. This study investigated the possible association between apnea hypopnea events and masseter contraction (MC) during sleep.
Methods: Twenty-five patients (9 women and 16 men) participated in this study. Patients who had previously received continuous positive airway pressure, surgical treatment or oral appliance for obstructive sleep apnea were excluded. Sleep study was measured using all-night polysomnography. Sleep and its stage were documented by standard electroencephalographic, electrooculographic, and electromyographic (EMG) criteria. EMG activity was recorded from mental, masseter and tibialis anterior muscles. Oxygen saturation was monitored continuously with a pulse oxymeter attached to the index finger. The following classification of MC was used in this study. Phasic MC episode showed three or more EMG bursts with the duration from 0.25 to 2.0 seconds and tonic MC showed EMG bursts lasting more than 3.0 seconds. Spearman's rank correlation test was used to measure the relationship between respiratory disorder index (apnea hypopnea index: AHI, apnea index: Al, arousal index: ArI) and masseter activity index.
Results: MC episodes were elevated especially during sleep stage 1, stage 2 and stage REM. MC episodes did not appear during an apnea episode. A strong correlation was found between the frequency of MC episodes that were associated with the termination of apnea hypopnea episodes per hour of sleep and AHI.
Conclusions: The results indicated that the termination of apnea hypopnea events is often accompanied with MC. It is suggested that MC can be linked to apnea and hypopnea episodes.
