Objectives: Some obstructive sleep-disordered breathings, such as sleep apnea, are recognized as an independent variable of the cardio-vascular diseases. Oral devices, which can bring and keep the mandible forwards, are claimed to be effective in alleviating the upper airway obstruction for some cases. However, the exact mechanism of such devices is not clear. The true dynamic MRI technique, which has been successfully applied to study TMJ kinematics, was tuned for studying the dynamic aspects of the upper airway. The aim of this preliminary report is thus to present the dynamic images of the upper airway and to explore the influence of mandibular positions on it. Methods: 6 male subjects, 4 of them recognized having snoring during sleep, participated in this study. Bite blocks at different combinations of mandibular protrusion and opening were done with modeling compound. All the dynamic MRIs were obtained by a 1.5 T MR scanner (Siemens Sonata®) with a tfiperf2d protocol at pace of 0.4 sec/frame. During scanning the subjects lay in the supine position with headrest and the bite blocks and kept a natural breathing. Sagittal, coronal and axial scanning planes were used. Results: Sagittal dynamic MRI can display the uvula vibration during expiration of the snorers clearly. With coronal images, rhythmic inwards movements of the lateral pharyngeal walls can also be seen. By changing the mandible positions, the tongue was moved forwards, the uvula vibration were decreased and the frequency of the pharyngeal wall motions were also reduced. However, once the lip seal was disrupted, the effect of bringing tongue forward seems to be disappeared. Conclusions: The dynamic MRIs are able to display the continuous upper airway changes during breathing. The mechanisms of mandibular advancing seem to be alter tongue position and aerodynamic in the upper airway.

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