Original article
Three-dimensional upper-airway changes associated with various amounts of mandibular advancement in awake apnea patients

https://doi.org/10.1016/j.ajodo.2006.06.024Get rights and content

Introduction: Mandibular advancement appliances have been used for years in the treatment of obstructive sleep apnea (OSA). However, it has not been completely clarified how the upper airway changes after mandibular advancement. The purpose of this study was to examine the effects of mandibular advancement on anatomic structures of the upper airway in patients with OSA by magnetic resonance imaging. Methods: Eleven OSA patients (aged 48.0 ± 5.86 years) with apnea and hypopnoea index values of 46.8 ± 21.47 participated in this study. A series of magnetic resonance images was taken for each subject with a custom-made device in the mouth that could advance the mandible by 0, 2, 4, 6, and 8 mm. In addition, an image with the mandible in centric occlusion was taken. Changes in cross-sectional area, sagittal diameter, transverse diameter, and cross-sectional shape in the whole upper airway and the different regions were compared between the various amounts of mandibular advancement. Results: The minimum and mean cross-sectional area of the velopharynx and the mean transverse diameter of the velopharynx increased significantly (P = 0.0001 and P = 0.0016, respectively) during mandibular advancement. However, no statistically significant changes (P >0.05) in sagittal diameter were found between the various mandibular advancements. In cross-sectional shape, a significant increase (P = 0.0066) was found when the mandible was advanced to 8 mm from 0 mm or centric occlusion position. Conclusions: Mandibular advancement significantly increases the cross-sectional area of the velopharynx in awake OSA patients. This contributes to the increase in its transverse dimension rather than the sagittal, thus resulting in the change of its shape.

Section snippets

Material and methods

Eleven adults from the Hospital of Stomatology, Tongji University, Shanghai, China, participated in this investigation (Table I). The inclusion criteria were OSA as determined by an apnea/hypopnea index (AHI) score greater than 10 per hour with whole night polysomnography (Medcare Monet, TMS International, Enschede, Netherlands) and no previous CPAP therapy or upper-airway surgery. In addition, no patients had crowns, bridges, dental implants, or ferromagnetic fillings. Their average age was

Results

High resolution images of MRI were observed and measured in all 11 patients for each mandibular position. Typical changes in the velopharynx with the various amounts of mandibular advancement are shown in Figure 3. The CSA and the transverse diameter of the velopharynx appeared to increase with mandibular protrusion.

Table II gives the changes in minimum and mean CSA for the whole upper airway and the different regions during mandibular advancement. The minimum and mean CSA of the velopharynx

Discussion

The results of this study showed that the amount of mandibular advancement increased the velopharynx caliber in awake OSA patients. The enlargement of CSA in the velopharynx is mostly attributed to the increase in the transverse diameter. Since no significant changes in the sagittal diameter of the velopharynx occurred, it may be that the cross-sectional shape of the velopharynx became an ellipse with an increasing transverse long axis after mandibular advancement. A previous study indicated

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    Supported by the National Natural Science Foundation of China (30471913, 2004).

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