Study limitations
The present study has several limitations. First, the CBCT scans were performed in awake state. Therefore, the upper airway morphology may not be the same as that in sleep state. However, acquiring a radiologic image of the upper airway during sleep is clinically challenging. Besides, as the baseline and follow-up CBCT images in our study were both taken in the supine position, the comparisons of the changes of upper airway between responders and non-responders were not biased. Second, two types of MAD were used in this study. However, our previous study has suggested that there was no significant difference between these two types of MAD in affecting PSG parameters and upper airway dimensions [