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Objectives Investigate the activity of rhythmic masseter muscles activity (RMMA) during sleep in patients with dentofacial deformities. Materials and methods Fifty patients with dentofacial deformities (16 male, 34 female) who required orthognathic surgery. An electrode was attached to the masseter muscle bilaterally, and preoperative polysomnography was performed. The frequency of RMMA onset per hour was measured on the left and the right sides. Values were classified as phasic (grinding: P-RMMA) and tonic (clenching: T-RMMA) to examine the onset of RMMA. Correlation between the RMMA index and various morphological and physical factors were determined including sleep or awake, rapid eye movement (REM), non-rapid eye movement (NREM) phases (NR1-NR4) in the sleep stage, phasic and tonic, gender, and mandibular asymmetry. Results The RMMA index values at the time of sleep were significantly small than during awake. The values were significantly higher during the NREM sleep than during the REM sleep and were the highest in the NR1 phase. P-RMMA index was significantly higher than the T-RMMA index. The P-RMMA index was also significantly higher than the T-RMMA index for men. In patients with greater asymmetry in the RMMA index values between the left and the right side (more than 30% difference), deviation between the midpoint of the maxillary and the mandibular incisal edges (U1-L1 deviation) was significantly higher. Conclusion RMMA in patients with dentofacial deformity was statistically higher in awake than sleep, higher in NREM sleep than REM sleep, higher in male than female on grinding, and higher in upper and lower incisor high deviation.

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Objective Prevalence of silent obstructive sleep apnea (OSA) in patients with dentofacial deformities is unknown, although OSA is severe risk of airway obstruction in perioperative orthognathic surgery or complication after surgery. The aim of this study was to investigate prevalence and risk factors of silent OSA in patients with dentofacial deformities. Methods We analyzed 72 patients (24 male, 48 female) with dentofacial deformities without previous OSA symptoms. Polysomnography was performed before orthognathic surgery. Prevalence and risk factors of silent OSA were statistically analyzed as related to Apnea hypopnea index (AHI). Results Mean AHI was 1.6 (range: 0-12.1) /h. Three patients of 72 patients (4.1%) were diagnosed silent OSA. AHI during REM sleep phase 3.7 (0-32.3) was higher than AHI during NREM sleep phase 1.0 (0-9.7). AHI of male patients was higher than that of female. AHI was increased according to high BMI. AHI was higher in deep bite than open bite, edge to edge bite and nomal bite. AHI of mandibular asymmetry cases were higher than that of symmetry cases. Conclusions The prevalence of silent OSA was 4.1%. Obesity, male, deep bite, mandibular asymmetry and REM sleep phase were risk factors of silent OSA.