INTRODUCTION

To compensate for the airway constriction caused by the mandibular setback in patients with skeletal Class III, two-jaw surgery (maxillary advancement in conjunction with mandibular setback) can be performed.^1,2 Because maxillary advancement can pull the velopharyngeal aponeurosis attachments (palatoglossus, palatopharyngeus, uvulae, levator veli palatine, tensor veli palatine, and soft tissue with fat pads) forward, the airway volume of the nasopharynx and hypopharynx can be increased.³

In skeletal Class III cases with labioversed maxillary incisors, protrusive upper lip, and acute nasolabial angle, extraction of the upper premolars and space closure using orthodontic treatment or anterior segmental osteotomy (ASO) of the maxilla has been used with the mandibular setback surgery.^4–6 However, the orthodontic treatment to close the maxillary premolar extraction space takes place long before mandibular setback (SB) surgery, and the ASO procedure alone cannot produce enough vertical and transverse correction of the maxilla.^5,6 If the ASO procedure is combined with Le Fort I osteotomy for placement of the maxillary segments into the proper positions, surgical complexity and morbidity can be a problem to clinicians and patients.⁶ To avoid these problems, two-jaw surgery (posterior impaction [PI] of the maxilla only and setback of the mandible or PI and SB (PI/SB) of the maxilla and SB of the mandible) can be performed.⁵ These approaches are recommended to correct the labially inclined maxillary incisors, protrusive upper lip, paranasal depression, and flat occlusal plane in patients with skeletal Class III.^5,6 Because of the nonextraction approach, these approaches permit easy occlusal settling during postoperative orthodontic treatment.⁶

However, there has been no published study on the changes in the retropalatal airway and velopharyngeal dimensions after two-jaw surgery with PI only or PI/SB of the maxilla in patients with skeletal Class III. Thus, the purpose of this study was to evaluate the changes in retropalatal airway and velopharyngeal dimensions after PI only or PI/SB of the maxilla in patients with skeletal Class III treated with two-jaw surgery using three-dimensional computed tomography (3D-CT). The null hypothesis was that there was no significant difference in the amount of change in the retropalatal airway and the velopharyngeal dimensions between PI of the maxilla and PI/SB of the maxilla.

MATERIALS AND METHODS

The subjects consisted of 60 patients with skeletal Class III (26 men and 34 women; mean age, 23 years; age range, 18–32 years). Patients underwent two-jaw surgery (one-piece LeFort I osteotomy and bilateral sagittal split ramus osteotomy) between January 2010 and October 2012 by one surgeon at the Department of Oral and Maxillofacial Surgery, Seoul National University Dental Hospital. This retrospective study was reviewed and approved by the institutional review board of Seoul National University School of Dentistry. (S-D20130030)

Subjects were divided into two groups: group 1 (n  =  30; 12 men and 18 women; PI of the maxilla only, mean, 2.6 mm and range, 2.0–3.5 mm) and group 2 (n = 30; 14 men and 16 women; PI of the maxilla, mean, 2.8 mm and range, 2.0–4.0 mm; SB of the maxilla, mean, 1.8 mm and range, 1.0–3.0 mm) (Table 1).

Table 1. Demographic Data for the Subjects

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A 3D-CT (Somatom Sensation 10, Siemens, Forchheim, Germany) scan was taken for all subjects 1 month before surgery (T0) and at least 6 months after surgery (T1) at 120 kVp and 80 mAs with a slice thickness of 0.75 mm. InVivo dental software (version 5.1; Anatomage, San Jose, Calif) was used to reconstruct the CT data into 3D images. When patients were awake and in a supine position with their neck in a neutral position, 3D-CT scanning was performed during quiet tidal breathing.

The variables used in this study were as follows: retropalatal airway volume, minimum cross-sectional area within the retropalatal airway, anteroposterior (AP) dimension of the minimum cross-sectional area, lateral dimension of the minimum cross-sectional area, soft palate length, soft palate angle, and pharyngeal depth. The definitions of the reference lines and variables are enumerated in Figures 1 and 2. The retropalatal airway was defined as the space between the superior reference plane (a plane that passes the anterior nasal spine [ANS] to the posterior nasal spine [PNS] of the maxilla) and the inferior reference plane (a plane that intersects the most inferior point of uvula and runs parallel to the ANS-PNS plane). A 3D-CT image showing the most inferior point of uvula was chosen as the midsagittal view, which was used to measure the soft palate length, soft palate angle, and pharyngeal depth; a 3D-CT image with the smallest cross-sectional area was used to measure the AP dimension and lateral dimension of the minimum cross-sectional area.

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The values of the variables obtained at T0 and T1 stages were statistically analyzed with a paired t-test and independent t-test. A P value <.05 was considered statistically significant.

RESULTS

There was no significant difference in the amount of PI of the maxilla between groups 1 and 2 (2.6 mm vs 2.8 mm; Table 1). However, group 2 showed 1.8 mm SB of the maxilla (Table 1). In addition, there was no significant difference in the amounts of mandibular SB between groups 1 and 2 (Table 1). Therefore, difference in the amount of change in the variables between groups 1 and 2 could be more affected by the SB of the maxilla than by the PI of the maxilla and SB of the mandible.

In group 1 (PI of the maxilla only), the retropalatal volume and minimum cross-sectional area were significantly increased (P < .01 and P < .05, respectively; Table 2). However, the lateral and AP dimensions of the minimum cross-sectional areas were not significantly changed (Table 2). Soft palate length and pharyngeal depth significantly increased (all P < .01; Table 2), although the soft palate angle did not change (Table 2).

Table 2. Comparsion of the Variables Between Preoperative (T0) and Postoperative (T1) Stages in Each group and the Amount of Change During T0–T1 Between the Two Groups

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In group 2 (PI/SB of the maxilla), the retropalatal volume, minimum cross-sectional area, and lateral and AP dimensions of the minimum cross-sectional area were significantly decreased (all P < .01; Table 2). Although the soft palate angle and pharyngeal depth did not show significant change, the soft palate length increased significantly (P < .001; Table 2).

Groups 1 and 2 were significantly different in the retropalatal volume, minimum cross-sectional area, and AP dimension of the minimum cross-sectional area (P < .05, P < .001, and P < .05, respectively; Table 2 and Figure 3).

DISCUSSION

The effects of the mandibular SB surgery on airway constriction are still controversial.^7–10 These inconsistent results might be attributed to different physiologic adaptations among patients ⁸ or to different investigation methods of the airway (eg, lateral cephalometric radiographs^3,9 and CT images^10,11). In the present study, 3D-CT scanning was performed during quiet tidal breathing while patients were awake and in a supine position with their neck in a neutral position. However, because the dimension of the upper airway changes during normal breathing cycle,¹² there is also a need to investigate the dynamic aspect of the airway in future studies.

Because the narrowest and the most collapsible part within the oropharynx is located at the retropalatal airway (behind the soft palate) and the constriction of this space can precipitate sleep-related breathing disorder,^13,14 the retropalatal airway space was evaluated in this study.

The results from this study showed that group 1 showed significant increase in retropalatal airway volume and minimum cross-sectional area (P < .01 and P < .05, respectively; Table 2). When PI of the maxilla is performed, it is logical to imagine that the PNS is moved superoanteriorly, pulling the velopharyngeal aponeurosis and soft palate superoanteriorly, subsequently enlarging the retropalatal airway.

Degerliyurt et al.¹⁰ reported that mandibular SB surgery can decrease both AP and lateral dimensions and the cross-sectional area at the soft palate and uvula.¹⁰ In this study the amounts of mandibular SB were not statistically different between groups 1 and 2 (Table 1), and group 1 showed a significant increase in the retropalatal airway volume and minimum cross-sectional area (P < .01 and P < .05, respectively; Table 2) despite the mandibular SB surgery. These findings imply either that the amounts of increase in the retropalatal airway volume and the minimum cross-sectional area by PI of the maxilla only were large enough to compensate for the constriction effect of the mandibular SB surgery or that the mandibular SB surgery did not have a significant effect on the retropalatal airway volume or dimensions. Moreover, although the effects of the mandibular SB surgery on the retropalatal airway cannot be ignored, it is logical to assume that the surgical movement of the maxilla had greater effects on the retropalatal airway than that of the mandible.

The finding that group 2 showed a significant decrease in the retropalatal airway volume, minimum cross-sectional area, and lateral and AP dimensions of the minimum cross-sectional area (P < .01, P < .01, P < .05, and P < .01, respectively; Table 2) implies that SB of the maxilla can push the soft palate and uvula posteriorly. In addition, there were significant differences in retropalatal airway volume, minimum cross-sectional area, and AP dimension of the minimum cross-sectional area between groups 1 and 2 (P < .05, P < .001, and P < .01, respectively; Table 2), which implies that constriction of the retropalatal airway can worsen the signs and symptoms of sleep-related breathing disorders.

In groups 1 and 2, the soft palate length was significantly increased (P < .01 and P< .001, respectively; Table 2). This is a significant finding because patients with obstructive sleep apnea syndrome are known to have a longer soft palate than the normal.¹⁵ An increase in the soft palate length may reduce muscle tone within the velopharyngeal aponeurosis and subsequently increase the collapsibility of the soft palate. Therefore, patients with a long soft palate before orthognathic surgery who are treated by PI of the maxilla (clockwise rotation of the maxillomandibular complex) may still have a longer soft palate at the postoperative stage compared to the preoperative stage.

When the maxilla is advanced, the angle between the hard palate and soft palate can be increased.¹⁶ However, there was no significant change when PI only or PI/SB of the maxilla was performed (Table 2). This implies that the amounts of PI or SB of the maxilla were not large enough to affect the soft palate angle. The reason why the pharyngeal depth increased only in group 1 (P < .01; Table 2) seems to be that with PI of the maxilla, the PNS rotated superoanteriorly and the distance between the PNS and the posterior pharyngeal wall was increased. On the other hand, in patients who underwent PI/SB of the maxilla, the retropalatal airway dimensions decreased and the soft palate length increased. These findings show that SB of the maxilla reduced the retropalatal airway dimensions and lengthened the soft palate.

Care should be taken when performing SB of the maxilla. If the maxilla undergoes excessive SB, it will result in an aged look with an overly retruded upper lip and decreased orbicularis oris muscle tonus.¹⁷ According to Bell and Dann,¹⁸ soft tissue will change with a factor of 0.85 in relation to the amount of maxillary SB. Also, the nasolabial angle will increase by 9° with 1 mm SB movement of maxilla.¹⁹ These values were used by the authors as the reference for surgical planning. In this study, subjects in group 2 received maxillary SB surgery by a mean amount of 1.83 mm with a range from 1.0 mm to 3.0 mm. This would retract the soft tissue upper lip by a mean of 1.5 mm and a range from 0.85 mm to 2.55 mm. The amount of maxillary SB was determined cautiously to avoid an aged look.

Although the present study might give guidelines for changes in the retropalatal airway and velopharyngeal dimension in patients undergoing PI and/or SB of the maxilla, it is necessary to perform further studies with longer follow-up periods and pre- and postoperative polysomnography results.

CONCLUSION

• Because the direction of surgical movement of the maxilla can determine the changes in the retropalatal airway and velopharyngeal dimensions, it is recommended that clinicians investigate whether patients suffer from sleep-related breathing disorders before performing PI/SB of the maxilla.

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