ORIGINAL ARTICLE

Evaluation of pharyngeal airway space changes after bimaxillary orthognathic surgery with a 3-dimensional simulation and modeling program Sila Mermut Gokce,a Serkan Gorgulu,a Hasan Suat Gokce,b Ali Osman Bengi,c Umit Karacayli,a and Fatih Orsd Etlik, Ankara, Turkey

Introduction: The aims of this study were to use 3-dimensional simulation and modeling programs to evaluate the effects of bimaxillary orthognathic surgical correction of Class III malocclusions on pharyngeal airway space volume, and to compare them with the changes in obstructive sleep apnea measurements from polysomnography. Methods: Twenty-five male patients (mean age, 21.6 years) with mandibular prognathism were treated with bilateral sagittal split osteotomy and LeFort I advancement. Polysomnography and computed tomography were performed before surgery and 1.4 6 0.2 years after surgery. All computed tomography data were transferred to a computer, and the pharyngeal airway space was segmented using SimPlant OMS (Materialise Medical, Leuven, Belgium) programs. The pretreatment and posttreatment pharyngeal airway space determinants in volumetric, linear distance, and cross-sectional measurements, and polysomnography changes were compared with the paired samples t test. Pearson correlation was used to analyze the association between the computed tomography and polysomnography measurements. Results: The results indicated that setback procedures produce anteroposterior narrowing of the pharyngeal airway space at the oropharyngeal and hypopharyngeal levels and the middle and inferior pharyngeal volumes (P \0.05). In contrast, advancement of the maxilla causes widening of the airway in the nasopharyngeal and retropalatal dimensions and increases the superior pharyngeal volume (P \0.05). Distinctively, bimaxillary orthognathic surgery induces significant increases in the total airway volume and the transverse dimensions of all airway areas (P \0.05). Significant correlations were found between the measurements on the computed tomography scans and crucial polysomnography parameters. Conclusions: Bimaxillary orthognathic surgery for correction of Class III malocclusion caused an increase of the total airway volume and improvement of polysomnography parameters. A proposed treatment plan can be modified according to the risk of potential airway compromise or even to improve it with 3-dimensional imaging techniques and polysomnography. (Am J Orthod Dentofacial Orthop 2014;146:477-92)

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rthognathic surgery has gained wide popularity in maxillofacial surgery over the last 30 to 40 years.1 Recently, mandibular setback surgery has decreased in frequency and is used in less than 10% of mandibular prognathism patients; 2-jaw surgery was preferred in about 40% of patients; maxillary advancement alone is performed in the remaining

From Gulhane Military Medical Academy, Etlik, Ankara, Turkey. a Associate professor, Department of Orthodontics, Dental Sciences Center. b Associate professor, Medical Design and Manufacturing Center. c Professor and chairman of Dental Sciences Center, Department of Orthodontics. d Associate professor, Department of Radiology. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Sila Mermut Gokce, Department of Orthodontics, Dental Sciences Center, Gulhane Military Medical Academy, Etlik, Ankara, Turkey 06018; e-mail, [email protected]. Submitted, June 2013; revised and accepted, June 2014. 0889-5406/$36.00 Copyright Ó 2014 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2014.06.017

patients.2,3 One aspect of these surgeries, which has gained prominence over the last 2 decades, is the effect of the skeletal movements on the pharyngeal airway space (PAS). Many investigations support the idea that after surgical movement of the jaws, changes in the positions of the tongue and hyoid bone also occur, resulting in narrowing of the PAS.2,4-9 Research in this area shows an association between the PAS and obstructive sleep apnea (OSA).1,4,10-12 Thus, it can be concluded that any alteration of the facial skeleton that replicates these features can provoke some airway disorder.1 Bimaxillary orthognathic surgery for Class III correction could be an alternative to mandibular setback surgery if there is less risk for restriction of the upper airways because a smaller mandibular setback would be needed, and hence more space would be available for the tongue.13,14 However, most studies have reported a significant reduction of the upper airway.4,5,7,15,16 These 477

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studies compared the radiographic changes that patients experienced postoperatively without investigating the possibility of the development of OSA on the basis of polysomnography (PSG). The specificity and accuracy of PSG has made it the standard diagnostic test for OSA.13,17 Two-dimensional (2D) lateral cephalograms have traditionally served as the radiographic standard for airway assessment. Although cephalometric measurements are useful for analyzing airway size in the sagittal plane, they do not accurately depict the 3-dimensional (3D) airway anatomy. Finally, although the most physiologically relevant information is obtained from axial images, perpendicular to the direction of airflow, the axial plane cannot be visualized on lateral cephalograms.4,18 In contrast, an accurate 3D image of the airway can be obtained using computed tomographic (CT) data in the coronal, axial, and sagittal planes.18 Although in many studies changes were demonstrated among patients with bimaxillary orthognathic surgery, the correlation between severity and prevalence of sleep apnea and airway parameters has not been examined.4,5,7,13,14,16 The purposes of this study were to investigate the morphologic changes in PAS after bimaxillary orthognathic surgery in patients with Angle Class III malocclusion using a 3D modeling program and PSG, and to investigate possible correlations among the studied PSG variables and the 3D airway morphology in these patients. MATERIAL AND METHODS

All patients' written informed consent was obtained. Then, the patients underwent bimaxillary orthognathic surgery at the Dental Sciences Center, Gulhane Military Medical Academy, Turkey. In all patients, based on the cephalometric analysis, anteroposterior maxillary hypoplasia combined with anteroposterior mandibular excess had been diagnosed. The study group consisted of 25 male patients; average age at the time of surgery was 21.6 6 2.7 years (range, 19-25 years), and mean body mass index values before (T0) and 1.4 6 0.2 years after (T1) bimaxillary orthognathic surgery were 22.5 and 21.9 kg/m2, respectively. Patients with breathing problems; craniofacial anomalies; chronic upper airway diseases; previous tonsillectomy, adenoidectomy, genioplasty, or orthognathic surgery; and excessive obesity were excluded from the study. The surgical technique was identical, and only patients with LeFort I advancement osteotomy without impaction combined with bilateral sagittal split osteotomy with the Obwegeser-Dal Pont method were included in the study. The ranges of maxillary advancement and mandibular setback were 3 to 9 mm (mean, 5.1 6 2.9 mm) and 5 to 10 mm (mean, 6.9 6 2.9 mm),

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respectively. Rigid fixation with titanium miniplates was used in all patients. All patients had maxillomandibular fixation for approximately 2 weeks postoperatively. Each patient had presurgical and postsurgical orthodontic treatment for averages of 7.6 and 5.7 months, respectively. Every patient underwent a 1-night sleep study at the Sleep Research Center at Gulhane Military Medical Academy, Turkey, before and more than 1 year after surgery. The evaluations showed that 11 patients had no problem related to airway obstruction or snoring during sleep preoperatively (apnea-hypopnea index [AHI] \5), 9 patients were diagnosed as simple snorers (AHI \5), and 5 were diagnosed with mild OSA (5 # AHI #15). Sleep parameters were recorded on a 32-channel polygraph (Somno Star Alpha Series-4; Sensor Media, Yorba Linda, Calif). The sleep respiratory information, including AHI, sleep efficiency, sleep stages (weakness, first stage, second stage, third stage, and fourth stage), rapid eye movements, and mean lowest arterial oxygen saturation, was used for data analysis.13 This project was approved by the ethics committee of the Institute of Health Sciences of Gulhane Military Medical Academy, Turkey. All CT examinations were performed using a 64-detector CT scanner (Aquilion64; Toshiba Medical Systems, Otawara, Japan), with the patients in the supine position. Scan parameters were 120 kV, 150 mA, and a 400-ms rotation time with a slice thickness less than 0.5 mm and increments of 0.4 mm, using a detector collimation of 64 3 0.5 mm, including the patient's entire head. The CT scans were obtained 1 week before treatment and more than 1 year after the bimaxillary orthognathic surgery while the patients were supine with the head and neck in a neutral position; the Frankfort horizontal plane was perpendicular to the floor. For a standardized position of the oropharyngeal structures, the examinations were obtained at the end of expiration, without swallowing, in natural head posture, and in centric occlusion, because centric occlusion minimizes the variability of mandibular and soft-tissue measurements often associated with rest position.19 A cephalostat was not used during the CT data acquisition to allow for the natural position that was unique for each subject. The patients were instructed to hold their breath at end of expiration, when the scan was done. Axial sections were obtained starting from the top of the cranium to the fourth cervical vertebra. All sections were perpendicular to the airway lumen to allow accurate assessment of the linear and volumetric measurements of the PAS. The data from the CT images were transferred to a network computer workstation on which the 2D

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Table I. Definition of anatomic landmarks used in the study Landmark AWRP UPW NPW RV

Retropalatal anterior pharyngeal wall Upper pharyngeal wall Narrowest pharyngeal wall Retrovelar

U MPW BoT PPW

Uvula Middle pharyngeal wall Base of the tongue Posterior pharyngeal wall

V LPW

Vallecula Lower pharyngeal wall

Definition The point on the retropalatal anterior pharyngeal wall, just behind the posterior nasal spine (PNS) point The intersection point of posterior pharyngeal wall and the line from basion (B) to PNS The intersection of the posterior pharyngeal wall to the narrowest space of the retropalatal region The intersection of the posterior surface of the soft palate to the narrowest space of the retropalatal region The tip of the soft palate, the most postero-inferior point of the uvula The intersection of the perpendicular line from U with the posterior pharyngeal wall The most posterior point on the radix linguae (base of the tongue) to the posterior pharyngeal wall The closest point on the retroglossal posterior pharnygeal wall to the base of the tongue measured perpendicularly to the direction of the airway The intersection of epiglottis and the base of the tongue The intersection of a perpendicular line from V with the posterior pharyngeal wall

Table II. Definition of the 3D pharyngeal airway measurements Landmark Distances AWRP-UPW

RV-NPW

BoT-PPW V-LPW Cross-sectional areas Nasopharyngeal cross-sectional area (NPa) Retropalatal cross-sectional area (RPa) Oropharyngeal cross-sectional area (OPa) Hypopharyngeal cross-sectional area (HPa) Volumes Superior pharyngeal airway volume (SPAV) Middle pharyngeal airway volume (MPAV) Inferior pharyngeal airway volume (IPAV) Total airway volume (TAV)

Definition The narrowest part of the nasopharynx (the distance of the closest point of the retropalatal anterior pharyngeal wall to the posterior pharyngeal wall to the horizontal counterpoint on the posterior pharyngeal wall) The narrowest retropalatal airway space (the narrowest distance between the soft palate (SP) and the posterior pharyngeal wall, measured by a perpendicular line from the posterior pharyngeal wall, representing the minimal airway dimension at the retropalatal region) The narrowest retroglossal airway space (the narrowest distance between BoT and the posterior pharyngeal wall, measured by a perpendicular line from the posterior pharyngeal wall) The narrowest part of the hypopharynx (the distance from vallecula of epiglottis (Epg) to the horizontal counterpoint on the posterior pharyngeal wall) Along a horizontal plane at the narrowest distance between the retropalatal anterior pharyngeal wall to the posterior pharyngeal wall (AWRP-UPW) Along a horizontal plane at the narrowest distance between the SP and posterior pharyngeal wall (RV-NPW) Along a horizontal plane at the narrowest distance between the BoT and the posterior pharyngeal wall (BoT-PPW) Along a horizontal plane at the tip of the epiglottis Airway formed by the roof of the airway and RV-NPV plane Airway formed by the RV-NPV and BoT-PPW planes Airway formed by the BoT-PPW and the plane passing through the upper border of larynx and perpendicular to sagittal plane (V-LPW) Airway extending from roof of the airway to the upper border of larynx

reformatted images were generated and measured. The software used in this study to build the 3D virtual models and perform the 3D analysis of the PAS was SimPlant OMS (Materialise Medical, Leuven, Belgium). SimPlant imported 2D stacked CT images and displayed the data in several ways by dividing the screen into 4 views: original axial, coronal, sagittal, and 3D. The airway and craniofacial structures were visualized in 3 dimensions; the sagittal and transversal linear measurements, and the cross-sectional areas and volumes were measured and calculated. Landmarks, linear distances, cross-sectional areas, and volumetric measurements used in this study are

shown in Tables I and II and Figure 1. The same investigator (H.S.G.) evaluated all CT images and performed all measurements. The following parameters were measured. Linear distances on the sagittal and transversal planes: (1) the narrowest part of the nasopharynx, (2) retropalatal airway space, (3) retroglossal airway space, and (4) hypopharynx. Cross-sectional areas: (5) nasopharyngeal, (6) retropalatal, (7) oropharyngeal, and (8) hypopharyngeal. Three-dimensional volumes: (9) superior pharyngeal airway, (10) middle pharyngeal airway, (11) inferior pharyngeal airway, and (12) total airway volumes.

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All parameters were measured by 1 author (S.M.G.). Because of the investigation of the reliability of the measurements, 15 patients were selected randomly, and their CT images were measured again 10 days later. The Wilcoxon signed rank test was applied to the first and second measurements of these images; this was not statistically significant (P .0.05). RESULTS

Fig 1. Landmarks and reference lines used in the study: AWRP, Retropalatal anterior pharyngeal wall; UPW, upper pharyngeal wall; NPW, narrowest pharyngeal wall; BoT, base of the tongue; PPW, posterior pharyngeal wall; V, vallecula; LPW, lower pharyngeal wall; RVW, retrovelar wall; U, uvula.

The levels for the linear and cross-sectional area measurements were settled on the midsagittal CT scan through the nasal septum. Cross-sectional areas were calculated automatically by the software at determined levels on the axial slices in square millimeters. The preoperative and postoperative upper airway volumes of each patient were studied in 3 levels of the upper airway by segmenting the region of interest in the CT scans. The borders of the PAS were formed as follows: (1) anterior, a vertical plane through the distal margin of the vomer, the soft palate, the base of the tongue, and the anterior wall of the pharynx; (2) posterior, the posterior wall of the pharynx; (3) lateral, the lateral walls of the pharynx; (4) upper, the roof of the nasopharynx; and (5) lower, a plane passing through the upper border of the larynx perpendicular to the sagittal plane (Fig 2).14 Statistical analysis

The descriptive statistics of the preoperative and postoperative measurements were analyzed using SPSS software (version 12.0.1 for Windows; SPSS, Chicago, Ill). The before and after treatment PAS measurements and the PSG variables were compared with paired samples t tests. Additionally, the Pearson correlation analysis was conducted between airway parameters and PSG data to determine the association between airway dimensions and objective indicators of sleep apnea severity. P \0.05 was considered statistically significant.

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The mean maxillary advancement achieved at T1 compared with T0 was 5 6 2.2 mm at A-point. For mandibular movement, a mean setback of 6.5 6 2.7 mm was found at T1 at B-point. The paired samples t test results comparing the preoperative and postoperative measurements are shown in Tables III through VIII. The linear, cross-sectional area, and volumetric measurements at T0 and T1 are presented in Figures 3 through 6. The consistency from all statistical tests of the oropharyngeal distance measurements on the sagittal and transversal planes showed statistically significant differences between T0 and T1 in the subjects who received bilateral sagittal split osteotomy combined with LeFort I maxillary advancement for the treatment of a Class III anteroposterior discrepancy (P \0.05) (Tables III and IV). In the sagittal plane, all subjects showed statistically significant increases in the narrowest part of the nasopharynx (2.06 6 1.28 mm) and the retropalatal airway space (1.26 6 1.01 mm) measurements related to the maxillary advancement (P \0.01 and P \0.05, respectively), and decreases in retroglossal airway space (1.46 6 1.29 mm) and hypopharynx (1.73 6 1.15 mm) measurements related to the mandibular setback (P \0.05 and P \0.01, respectively). However, in the transversal plane, there were statistically significant increases at all levels of the PAS (narrowest part of the nasopharynx, 1.47 6 1.18 mm; retropalatal airway space, 1.97 6 1.11 mm; retroglossal airway space, 1.1 6 1.2 mm; and hypopharynx, 1.69 6 1.15 mm; P \0.05). Statistically significant differences were found in all cross-sectional area measurements of the PAS between T0 and T1 (Table V). In the evaluation of the pharyngeal cross-sectional areas, it was observed that those of the superior region (nasopharyngeal and retropalatal) were statistically significantly increased on average by 170.58 6 50.28 and 171.7 6 54 mm2, respectively, whereas the cross-sectional areas of the inferior region (oropharyngeal and hypopharyngeal) were statistically significantly decreased on average by 55.34 6 17.8 and 65.88 6 18.19 mm2, respectively (P \0.05). In the 3D volumetric analysis, a significant increase in the volume of the superior pharyngeal region was found

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Fig 2. Digital airway model with upper and lower boundaries displayed with overlaying skeletal model reconstructions at A, preoperative and B, postoperative periods.

at T1 compared with T0, and a reduction in volume of the inferior anatomic region at T1 (Table VI). At T1, the mean superior pharyngeal airway increased significantly from 10,232 6 1225 to 14,976 6 1987 mm3, with a mean increase of 4744 6 567 mm3 from the maxillary advancement, which represented a gain of 46.36% in the superior pharyngeal airway compared with T0 (P \0.001). Conversely at T1, the mean middle pharyngeal airway and inferior pharyngeal airway volumes decreased significantly from 7625 6 865 to 6176 6 786 mm3 and from 5762 6 767 to 4179 6 489 mm3, respectively, with mean decreases of 1449 6 287 and 1583 6 338 mm3, respectively, which represented mean decreases of 19.01% for the middle pharyngeal airway and 27.47% for the inferior pharyngeal airway volumes at T1 because of the mandibular setback (P \0.05). The changes in these volumetric

measurements showed a considerable gain (7.24%) in total airway volume between the preoperative and postoperative periods. The mean total airway volume increased from 23,619 6 2712 to 25,331 6 2925 mm3, with a mean increase 1712 6 566 mm3 according to the surgery (P \0.05) (Figs 7 and 8). As a result of the PSG evaluation, the postoperative sleep quality of the subjects was found to be improved compared with the preoperative data (Table VII). Nine of the 25 subjects were habitual snorers preoperatively (AHI \5). Habitual snoring completely disappeared in 6 of them, and a satisfactory improvement in sleep quality was declared by 3 subjects at T1. Five patients in the nonsnoring group at T1 began to snore after surgery, but the problem of subjective snoring was resolved after 6 months. Five patients were diagnosed mild OSA at

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Table III. Oropharyngeal distance measurements on sagittal plane T0

T1 95% CI

AWRP-UPWsag RV-NPWsag BoT-PPWsag V-LPWsag

Mean 16.05 9.55 11.81 11.65

SD 4.23 2.45 3.03 4.11

Lower bound 14.24 8.97 9.24 10.04

Upper bound 18.32 11.23 13.45 13.87

T0-T1 95% CI

Mean 18.11 10.81 10.34 9.92

SD 5.29 3.56 3.78 2.97

Lower bound 16.47 9.23 9.99 7.86

Upper bound 21.24 13.77 14.02 13.54

95% CI MD 2.06 1.26 1.46 1.73

SD 1.28 1.01 1.29 1.15

Lower bound 3.33 2.38 0.19 0.54

Upper bound 0.8 0.14 2.73 2.92

Test statistics t 5 3507 t 5 2433 t 5 2475 t 5 3117

P 0.003y 0.029* 0.027* 0.008y

MD, Mean difference; sag, sagittal. *P \0.05; yP \0.001.

T0; AHI scores decreased in 3 patients after surgery, and they became healthy (AHI \5). When the changes of the AHI between T0 and T1 were compared, the mean AHI scores decreased statistically significantly from 5.15 6 3.01 to 2.91 6 1.09, with a mean decrease of 2.24 6 1.91 (P \0.05). Sleep efficiency improved significantly from 85.4% 6 2.13% to 91.77% 6 3.12%, with a mean increase of 6.39% 6 2.3% after the surgery (P \0.001). In all patients, sleep stages weakness (3.89% 6 1.98%), first stage (4.65% 6 2.01%), and second stage (10.83% 6 3.76%) shortened after bimaxillary orthognathic surgery (P \0.01), and the insufficient third and fourth stages and rapid eye movement scores significantly increased postoperatively (3.34% 6 1.65%, 3.57% 6 1.89%, and 7.25% 6 2.67%, respectively; P \0.001). Mean oxygen saturation values during sleep increased significantly after bimaxillary orthognathic surgery (5.44% 6 2.69%; P 5 0.001). For the correlations between distances, crosssectional areas, volumetric measurements, and PSG variables, the oropharyngeal distance measurements in the sagittal plane showed significant correlations with some PSG measurements. In the sagittal plane, the nasopharyngeal, retropalatal, retroglossal, and hypopharyngeal distance measurements showed significant negative correlations with AHI (r, 0.493; r, 0.436; r, 0.445; and r, 0.424, respectively). All oropharyngeal distance measurements in the sagittal plane also had significant positive correlations with sleep efficiency (r, 0.403; r, 0.381; r, 0.344, and r, 0.399, respectively) and mean oxygen saturation (r, 0.389; r, 0.432; r, 0.478; and r, 0.455, respectively), but not with the other PSG variables (all P .0.05) (Table VIII). Oropharyngeal distance measurements in the transversal plane (narrowest part of the nasopharynx, retropalatal airway space, retroglassal airway space, and hypopharynx) did not correlate with any variables of PSG.

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The cross-sectional areas of the PAS variables tended to be correlated with some PSG measurements. There were significant negative correlations between all cross-sectional area variables (nasopharyngeal, retropalatal, oropharyngeal, and hypopharyngeal) and AHI (r, 0.424; r, 0.466; r, 0.554, and r, 0.428, respectively). All cross-sectional area variables also correlated positively with sleep efficiency (r, 0.414; r, 0.436; r, 0.385; and r, 0.387, respectively) and mean oxygen saturation (r, 0.529; r, 0.416; r, 0.517; and r, 0.438, respectively). In the other PSG parameters, no significant relationship was identified with the cross-sectional area measurements (P .0.05) (Table VIII). Oropharyngeal airway volumetric measurements (superior pharyngeal airway, middle pharyngeal airway, inferior pharyngeal airway, and total airway volumes) correlated negatively with AHI (r, 0.579; r, 0.548; r, 0.566; and r, 0.543, respectively). All volumetric variables also had positive correlations with sleep efficiency (r, 0.668; r, 0.333; r, 0.402; and r, 0.523, respectively), rapid eye movements (r, 0.373; r, 0.366; r, 0.331; and r, 0.342, respectively), and mean oxygen saturation (r, 0.654; r, 0.554; r, 0.637; and r, 0.568, respectively). No correlation was found between volumetric measurements and the other PSG variables (P .0.05) (Table VIII). DISCUSSION

To our knowledge, this study is the first to evaluate the changes in PAS after bimaxillary orthognathic surgery in patients with Class III malocclusion using a spiral CT-based 3D software program and the correlations between the measurements of PAS and PSG parameters. PAS narrowing after orthognathic surgery has drawn increasing attention in recent decades. The main reason is that PAS narrowing might be a predisposing factor for developing OSA.5,8,20,21 Many investigators have highlighted an important limitation of airway studies: the 2D technique.4,13,14,22 The 2D technique does not

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Table IV. Oropharyngeal distance measurements on transversal plane T0

T1 95% CI

Lower bound 19.13 21.24 24.34 23.12

Upper bound 28.65 25.03 30.43 32.34

T0-T1 95% CI

Lower bound 18.33 19.45 20.22 23.86

Upper bound 21.25 18.75 23.74 28.42

95% CI Lower bound 2.56 3.03 2.83 2.32

Upper bound 0.23 1.38 0.45 0.99

Test statistics t 5 4874 t 5 3674 t 5 2745 t 5 2813

P 0.043* 0.039* 0.044* 0.042*

Lower Upper Lower Upper Lower Upper SD bound bound Mean SD bound bound MD SD bound bound Test statistics 95.34 145.89 326.78 403.46 116.84 502.48 389.45 170.58 50.28 217.8 119.23 t 5 5534 62.47 89.54 203.69 311.3 102.49 414.23 297.46 171.70 54.00 220.40 121.80 t 5 5685 83.78 196.32 323.24 224.52 65.81 173.12 301.49 55.34 17.8 37.15 84.33 t 5 2621 77.15 222.45 325.98 230.14 69.18 199.53 299.53 65.88 18.19 48.17 84.66 t 5 3713

P 0.011* 0.012* 0.04* 0.03*

AWRP-UPWtrans RV-NPWtrans BoT-PPWtrans V-LPWtrans

Mean 23.05 20.89 26.78 29.66

SD 6.57 5.22 4.65 7.32

Mean 25.04 22.86 27.88 31.35

SD 8.32 5.97 7.12 9.21

MD 1.47 1.97 1.1 1.69

SD 1.18 1.11 1.2 1.15

MD, Mean difference; trans, transversal. *P \0.05.

Table V. Cross-sectional area of the pharyngeal airway measurements T0

T1 95% CI

Mean NPa 230.91 RPa 139.25 OPa 278.53 HPa 295.41

T0-T1 95% CI

95% CI

MD, Mean difference. *P \0.05.

represent exactly the nasopharyngeal space, and it is difficult to identify the exact soft-tissue contours on traditional lateral cephalograms. The spiral CT-based 3D technique uses standard scanning protocols that are noninvasive4 and has the advantage that details of hard-tissue and soft-tissue anatomies not otherwise discernible can be detected, and all measurements are real size. This technique allows visualization of crosssectional areas of the airway at any position along its length, comparison of 3D distances, and accurate volume measurements, linear projections, and orthogonal airway assessments.22 One other advantage of CT is that it allows a better delineation of soft tissues and air using different densities of Hounsfield units.4,14 CT scans might be a valuable tool for investigating the 3D changes in hard and soft tissues in terms of increased volume, which 2D radiographs cannot provide. Additionally, some critical CT parameters (retropalatal and retroglossal cross-sectional areas) did not correlate with the cephalometric parameters in patients with OSA.18 However, the increasing use of the CT technique in dentistry carries the risk of patient overexposure to radiation, which must be one of the dentist's greatest concerns.23-29 The effective doses of conventional dental imaging techniques in the literature are less than 1.5 mSv for intraoral radiographs,30 2.7 to 24.3 mSv for

panoramic radiographs,30-32 less than 6 mSv for cephalometric radiographs,30 30 to 1073 mSv for dental cone-beam CT,31-34 and 280 to 1410 mSv for maxillomandibular multislice CT.31-35 The radiation doses of CT scans are generally higher than those for conventional dental radiography. The dose depends on equipment type and exposure parameters, especially the field of view selected. In particular, low-dose protocols on modern CT equipment can lower the doses significantly.36 In our study, we used CT equipment that enabled us to reduce the patient dose up to 40% without loss of image quality, so that the radiation dose for the full cranium ranged from approximately 650 to 950 mSv. In this study, the SimPlant OMS software used the entire data sets to produce a color-contrasted and blended view of PAS changes before and after bimaxillary orthognathic surgery. Excellent segmentation was achieved, and it was possible to make linear, crosssectional, and volumetric assessments. The posture and position of the head can also modify the PAS.23-25 PAS narrows in supine position; in contrast, both the tongue and soft palate thicken owing to gravitational force or the changes in the upper airway reflexes; this might increase the risk for PAS collapsibility.25,26 The pharyngeal cross-sectional

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Table VI. Oropharyngeal volumetric measurements T0

T1

T0-T1

95% CI

SPAV MPAV IPAV TAV

Mean 10232 7625 5762 23619

SD 1225 865 767 2712

Lower bound 8916 6823 5011 20156

Upper bound 1297 9102 6589 29345

95% CI Mean 14976 6176 4179 25331

SD 1987 786 489 2925

Lower bound 12999 5239 3816 22314

95% CI

Upper bound 17021 7023 4967 30377

MD 4744 1449 1583 1712

SD 567 287 338 566

Lower bound 5234 1116 1184 2158

Upper bound 4012 1932 2012 1032

Test statistics t 5 5016 t 5 1523 t 5 1597 t 5 1681

P \0.001z 0.032* 0.043* 0.002y

MD, Mean difference. *P \0.05; yP \0.005; zP \0.001.

Table VII. PSG measurements before (T0) and after (T1) bimaxillary orthognathic surgery T0

T1 95% CI

Mean AHI 5.15 Sleep efficiency (%) 85.4 Sleep stage weakness (%) 11.13 Sleep stage 1 (%) 8.14 Sleep stage 2 (%) 70.96 Sleep stage 3 (%) 4.01 Sleep stage 4 (%) 11.53 REM (%) 7.77 Mean oxygen saturation (%) 91.28

SD 3.01 2.13 2.92 2.23 4.23 2.2 2.45 2.87 2.34

Lower bound 2.45 83.29 9.86 6.94 67.55 3.11 10.81 5.86 85.2

Upper bound 11.33 87.75 13.05 10.44 74.13 6.43 14.15 9.32 96.85

T0-T1 95% CI

Mean 2.91 91.77 7.15 3.45 60.11 7.35 15.12 15.02 96.76

SD 1.09 3.12 2.34 1.16 3.99 2.34 2.88 3.21 3.45

Lower bound 0.23 88.56 5.33 2.31 57.23 5.12 13.21 12.96 91.27

Upper bound 4.11 94.12 9.01 5.02 63.07 9.87 17.94 17.97 99.45

95% CI MD 2.24 6.39 3.89 4.65 10.83 3.34 3.57 7.25 5.44

SD 1.91 2.3 1.98 2.01 3.76 1.65 1.89 2.67 2.69

Lower bound 0.34 8.75 2.34 2.32 7.11 4.88 5.06 9.79 9.98

Upper bound 3.15 4.15 4.91 6.23 13.65 2.15 2.23 5.54 3.23

Test statistics t 5 2.816 t 5 5.437 t 5 3.577 t 5 6.711 t 5 8.516 t 5 6.905 t 5 11.237 t 5 5.835 t 5 5.362

P 0.04* \0.001z 0.003y \0.001z \0.001z \0.001z \0.001z \0.001z 0.001y

MD, Mean difference; REM, rapid eye movement. *P \0.05; yP \0.005; zP \0.001.

area was decreased with a change from the upright to the supine position.24,25 A change in body posture has an effect on PAS size because of the postural effects of the tongue.25,26 A supine CT scan thus provides more physiologic information, since it is obtained in the usual sleeping posture. The cross-sectional areas can also differ according to changes in head posture; thus, the 3D image was built using the CT scans in a supine position, which the head posture did not change.24,25 All CT scans in this study were obtained with the patient in a supine position to minimize differences in the size of the PAS from changes in body and head posture. To obtain a standardized position of the head during CT scanning, the subject's head and neck were in a neutral position with the Frankfort horizontal plane perpendicular to the floor, as described before.25 Additionally, a cephalostat was not used during the CT data acquisition to allow for a natural position that was unique for each subject.25,26 To avoid exposing the subject to multiple high doses of radiation, duplicate measurements of a subject's natural head position in different occasions have not been tested for

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reliability. In this study, the subjects' dentofacial and pharyngeal growths were complete, and only men were selected, because sex differences in PAS changes have been previously described.15,21 Many studies have assessed time-dependent PAS changes after orthognathic surgery. Some of them reported no significant changes in PAS between early (1 week to 3 months) and late (1 to 2 years) follow-ups postoperatively.5,7 Kawamata et al2 found significant PAS narrowing 3 months after surgery and no significant tendency to recover at 6 months or 1 year after surgery. In light of these results, we selected more than 1 year as the postsurgical time frame. There is no consensus in the literature for an established standard pattern of airway segmentation. The airway distance and volume in our study were difficult to compare with the results of other studies because of variations in the locations of the boundaries. Various anteroposterior airway distance measurements were found to be common in bimaxillary orthognathic surgery studies, especially posterior nasal spine to the pharyngeal wall5,14,23; soft palate (or specifically, the uvula)

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Table VIII. Correlations between distance, cross-sectional areas, and volumetric measurements and PSG variables Definition AWRP-UPWsag RV-NPWsag BoT-PPWsag V-LPWsag AWRP-UPWtrans RV-NPWtrans BoT-PPWtrans V-LPWtrans NPa RPa OPa HPa SPAV MPAV IPAV TAV

Pearson correlation r P value r P value r P value r P value r P value r P value r P value r P value r P value r P value r P value r P value r P value r P value r P value r P value

AHI 0.493 0.002y 0.436 0.009y 0.445 0.007y 0.424 0.012* 0.05 nc 0.073 nc 0.313 nc 0.324 nc 0.424 0.003y 0.466 0.004y 0.554 0.032* 0.428 0.033* 0.579 \0.001z 0.548 \0.001z 0.566 \0.001z 0.543 0.004y

Sleep efficiency 0.403 0.017* 0.381 0.02* 0.344 0.043* 0.399 0.02* 0.124 nc 0.109 nc 0.182 nc 0.101 nc 0.414 0.01* 0.436 0.009y 0.385 0.021* 0.387 0.027* 0.668 \0.001z 0.333 0.048* 0.402 0.015* 0.523 0.001y

Sleep stage weakness 0.01 nc 0.073 nc 0.345 nc 0.084 nc 0.07 nc 0.033 nc 0.275 nc 0.126 nc 0.09 nc 0.133 nc 0.109 nc 0.006 nc 0.143 nc 0.163 nc 0.145 nc 0.047 nc

Sleep stage 1 0.1 nc 0.65 nc 0.055 nc 0.121 nc 0.052 nc 0.092 nc 0.321 nc 0.308 nc 0.352 nc 0.338 nc 0.005 nc 0.288 nc 0.142 nc 0.151 nc 0.063 nc 0.069 nc

Sleep stage 2 0.351 nc 0.343 nc 0.224 nc 0.188 nc 0.172 nc 0.272 nc 0.27 nc 0.202 nc 0.312 nc 0.391 nc 0.401 nc 0.382 nc 0.234 nc 0.267 nc 0.299 nc 0.301 nc

Sleep stage 3 0.113 nc 0.143 nc 0.176 nc 0.142 nc 0.165 nc 0.231 nc 0.212 nc 0.242 nc 0.115 nc 0.118 nc 0.091 nc 0.101 nc 0.297 nc 0.276 nc 0.168 nc 0.199 nc

Sleep stage 4 0.238 nc 0.244 nc 0.211 nc 0.232 nc 0.177 nc 0.189 nc 0.231 nc 0.201 nc 0.042 nc 0.063 nc 0.021 nc 0.162 nc 0.187 nc 0.143 nc 0.291 nc 0.248 nc

REM 0.032 nc 0.015 nc 0.076 nc 0.023 nc 0.124 nc 0.235 nc 0.266 nc 0.203 nc 0.302 nc 0.295 nc 0.315 nc 0.322 nc 0.373 0.029* 0.366 0.032* 0.331 0.049* 0.342 0.04*

Mean oxygen saturation 0.389 0.029* 0.432 0.012* 0.478 0.001* 0.455 0.009y 0.231 nc 0.239 nc 0.288 nc 0.201 nc 0.529 0.001y 0.416 0.017* 0.517 0.001y 0.438 0.009y 0.654 \0.001z 0.554 0.001y 0.637 \0.001z 0.568 \0.001z

REM, Rapid eye movement; sag, sagittal; trans, transversal; nc, not correlated. *P \0.05; yP \0.005; zP \0.001.

to the pharyngeal wall4,5,12,14,20,21,24,27; base of the tongue to the posterior pharyngeal wall2,4,8,18,20; vallecula to the pharyngeal wall5,14,24; and minimal PAS.14,21 The authors also described PAS volume in different ways: the region between the planes tangent to the posterior nasal spine and the tip of the epiglottis in the midsagittal plane,14 the volume between the planes parallel to the Frankfort horizontal plane passing through cervical vertebrae 1 and 2,28 the region from the frontal plane passing through the anterior nasal spine to the axial plane passing through the superior margin of the epiglottis,29 the volume between the roof of the pharynx and a horizontal plane passing from the most anterior and inferior point of cervical vertebra 3,37 the region between the plane through the posterior nasal spine to the posterior pharyngeal wall, and the horizontal plane through the base of the epiglottis.24 Thus, the PAS was defined according to the specific borders described previously; these were

formed after evaluation and modification of the borders defined in other similar studies.13,27,37 We assessed all 4 distance measurements in the sagittal and transversal planes at the narrowest part of the nasopharynx, retropalatal, and retroglossal regions; the hypopharnx; and also 4 cross-sectional area measurements at the same levels for each interval (T0 and T1). Additionally, total airway volume was defined as the airway extending from the roof of the airway to the upper border of the larynx. In this study, bimaxillary orthognathic surgery had effects on the PAS with significant decreases in the narrowest oropharyngeal and hypopharyngeal regions, and significant increases in the narrowest nasopharyngeal and retropalatal airway space when compared with the preoperative period, according to cross-sectional area and distance measurements in the sagittal plane. Unexpectedly, the distance measurement in the transversal plane showed significant increases at all 4 levels. Based

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Fig 3. CT airway views using 3D simulation and modeling program: axial view, the region of interest, nasopharyngeal PAS; coronal view, image for cross-sectional and transversal linear measurements; sagittal view, linear measurement of the region extends from AWRP to UPW; 3D view, 3D volumetric reconstruction and superimposition of preoperative and postoperative nasopharyngeal PAS.

on these data, we observed substantial increases in superior pharyngeal airway and total airway volumes, whereas the middle and inferior pharyngeal airway volumes showed significant decreases after surgery. These changes in the PAS in patients were considered to result from anterior displacement of the maxilla and backward movement of the mandible after bimaxillary orthognathic surgery. The reason for the increase in total airway volume might be that advancement of the velum and the velopharyngeal muscle caused by the LeFort I osteotomy partly decreased the constricting effect of the associated mandibular setback.5,27 The positional changes resulting from the movements of the jaws have been shown to be responsible for airway narrowing and associated with sleep-related breathing disorders, such as OSA.5,8,10,21 Maxillary advancement has been shown to be effective in the elimination of OSA because it enlarges the PAS and tightens the upper airway muscles and tendons.7,13,21 Mandibular setback is known to be a cause of PAS narrowing,5-8,13,21 especially at the oropharyngeal and hypopharyngeal levels.5,7,9 Conversely, it has been reported that there is no decrease

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of the upper airway with bimaxillary orthognathic surgery of Class III malocclusion, and that total airway volume is increased as a result of the surgery.5,38 Some investigators have affirmed that bimaxillary orthognathic surgery to correct a Class III skeletal deformity might have a lesser effect in decreasing the PAS than does 1-jaw surgery.4,5,13,17,24,25,28,39 Most authors agree with a significant linear increase in the nasopharynx and oropharynx and a decrease or no alteration in the hypopharynx after 6 or 24 months in patients who underwent bimaxillary orthognathic surgery.5,13,21,27 Demetriades et al17 showed an increase in PAS after bimaxillary orthognathic surgery (PAS .11 mm). PereiraFilho et al38 found increases in the nasopharyngeal space and the oropharynx and a decrease in the hypopharynx for bimaxillary orthognathic surgery patients with a Class III pattern. Jakobsone et al14 observed a substantial increase in the volume of the oropharynx after bimaxillary orthognathic surgery. These results are close to our findings, with small variations. Conversely, Park et al28 found a significant linear decrease in the area or volume in the measurements of the soft palate and base of the tongue. In the

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Fig 4. CT airway views using 3D simulation and modeling program: axial view, the region of interest, retropalatal PAS; coronal view, image for cross-sectional and transversal linear measurements; sagittal view, linear measurement of the region extends from RVW to NPW; 3D view, 3D volumetric reconstruction and superimposition of preoperative and postoperative retropharyngeal PAS.

study of Panou et al,37 upper PAS volume had an insignificant increase with a significant decrease of lower PAS, and total airway volume were observed in only 6 male subjects. We concluded that the findings about the decrease in the nasopharyngeal region are meaningless because only maxillary advancement has an increasing effect on the region.5,13,21 Jakobsone et al suggested that clinically a maxillary advancement of 2 mm or more causes a significant increase in the airway dimensions at the nasopharyngeal level. Furthermore, Tselnik and Pogrel9 reported that the nasopharyngeal airway space is not affected by mandibular setback. Maxillary advancement causes autorotation of the mandible, which positions the hyoid bone and the genioglossus muscle, and the tongue, in more anterior and superior locations, thus increasing the PAS dimensions.17 A small cross-sectional area of the airway is likely to explain the presence of OSA events.4 De gerliyurt et al4 found that the part of the PAS most narrowed was the sagittal dimension at the level of the soft palate and the posterior pharyngeal wall and the retroglossal airway space for men who had bimaxillary orthognathic

surgery. We observed no statistically significant reductions in transversal and cross-sectional area dimensions at the same levels between preoperative and postoperative measurements. Jakobsone et al14 demonstrated that cross-sectional areas increased at the retropalatal area, decreased at the oropharyngeal area, and remained unchanged at the hypopharyngeal area after surgery, although all the changes were insignificant. Panou et al37 observed that the minimal cross-sectional area of the PAS had an insignificant increase after bimaxillary orthognathic surgery in men. In our study, the average postoperative cross-sectional area at the retropalatal area (nearly the same level as the soft palate and the posterior pharyngeal wall) increased, whereas at the oropharygeal area (same level as the retroglossal airway space) decreased significantly. Previous investigations with CT have demonstrated that the changes in PAS after bimaxillary orthognathic surgery occurred mostly in the anteroposterior direction, whereas the lateral width remained unchanged after the surgery or slightly reduced after isolated mandibular setback.2,4 In this study, significant increases in the

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Fig 5. CT airway views using 3D simulation and modeling program: axial view, the region of interest, oropharyngeal PAS; coronal view, image for cross-sectional and transversal linear measurements; sagittal view, linear measurement of the region extends from BoT to PPW; 3D view, 3D volumetric reconstruction and superimposition of preoperative and postoperative oropharyngeal PAS.

transversal plane at all levels were found at the PAS. The explanation provided was that the pharyngeal lumen had an elliptical shape, with the lateral width being the longer axis.14 After bimaxillary orthognathic surgery, the soft palate was lengthened to preserve the oropharyngeal seal, and the tongue occupied the space provided by the maxillary advancement, as described earlier.13,14 Therefore, a consequent increase in lateral width occurred after surgery. To evaluate the potential risk of development of OSA, postoperative PAS values should be compared with healthy subjects' PAS dimensions based on lateral cephalogram studies; these range from 11 6 2 mm6 to 14.8 6 4.4 mm.14 In our study, the average postoperative PAS values at the retroglassal airway space and hypopharynx in the sagittal plane were 10.34 6 3.78 and 9.92 6 2.97 mm, respectively. These results were in the range of healthy subjects' PAS dimensions. The minimal cross-sectional area associated with breathing disturbances was reported to be about 50 mm2 or less.40 The minimal cross-sectional areas for healthy subjects were reported to be at least 134.2 mm2 at the

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nasopharyngeal level40 and 177.8 mm2 at the oropharyngeal level.10 These values were smaller than the mean postoperative cross-sectional areas in our study (403.46 and 224.52 mm2, respectively). The literature about the effects of bimaxillary orthognathic surgery on OSA is still controversial.17 It should be better to consider that maxillary advancement leads to biologic adaptation, inhibits OSA, and improves the airway of the patients.24 Some patients with a Class III pattern have an augmented PAS before surgery, so that a small setback will have no clinical repercussion; however, patients with a previously normal airway space should receive an even smaller setback.27,38 In the study of Becker et al,27 no patient had previous signs or symptoms of OSA or developed them in the postoperative period, even with great mandibular setback movements, showing the adaptive capacity of the pharyngeal musculature in patients with no predisposition to OSA. Hochban et al7 reported no evidence of postoperative OSA in patients who underwent mandibular setback, although the PAS decreased after surgery. In the PSG study of Hasebe et al,41 there were an insignificant

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Fig 6. CT airway views using 3D simulation and modeling program: axial view, the region of interest, hypopharyngeal PAS; coronal view, image for cross-sectional and transversal linear measurements; sagittal view, linear measurement of the region extends from V to LPW; 3D view, 3D volumetric reconstruction and superimposition of preoperative and postoperative hypopharyngeal PAS.

decrease in AHI and an increase in the lowest oxygen saturation and no sign of sleep-disordered breathing after bimaxillary orthognathic surgery, although 2 patients were diagnosed with mild OSA 6 months after surgery, because the amounts of mandibular setback were large. In the study of Demetriades et al,17 significantly more patients in the mandibular setback group were diagnosed with OSA compared with patients in the bimaxillary orthognathic surgery group. In addition, a significantly higher percentage of patients in the mandibular setback group experienced oxygen desaturation compared with patients in bimaxillary orthognathic surgery group.17 The mini-sleep study of Turnbull and Battagel16 showed no change in sleep quality after mandibular setback surgery; no patients became snorers or developed OSA, even though the lateral cephalograms identified significant reductions in their retrolingual airways after surgery. Foltan et al42 concluded that bimaxillary orthognathic surgery worsened breathing function during sleep, as reflected in the significant increase of the index of flow limitations and the decrease in oxygen saturation, although the AHI

was decreased insignificantly. In our study, there was a significant increase in the total airway volume, especially at the upper airway level; this means that maxillofacial surgery can immediately have an influence on the functional outcome (such as breathing). Perhaps somewhat surprising in our study was the finding that 5 of the 23 patients also demonstrated mild OSA preoperatively; AHI scores decreased after surgery, and they became healthy (AHI \5). Only 2 of them remained with a diagnosis of sleep apnea postoperatively. Bimaxillary orthognathic surgery, as demonstrated in these subjects, caused a significant improvement in sleep quality. The sleep stages weakness, first stage, and second stage decreased, whereas rapid eye movement, third stage, and fourth stage increased after surgery. These findings agree with our previous results, which demonstrated that bimaxillary orthognathic surgery significantly improved sleep quality in Class III patients by improving the nasopharyngeal and velopharyngeal airways and improved the nasal continuous positive airway pressure.13 It seems that almost all of the subjects adapted to the new environment in respiratory function during sleep, but

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Fig 7. 3D volumetric reconstruction of PAS, shown in lateral and coronal views at: A and B, preoperative, and C and D, postoperative periods. Green and red areas, 3D representations of SPAV; light green and pink areas, 3D representations of MPAV; brown and yellow areas, 3D representations of IPAV.

Fig 8. 3D volumetric superimposition of preoperative and postoperative PAS, shown in A, lateral and B, coronal views.

patients with a large mandibular setback would be at risk for developing OSA after surgery if it is difficult for the surrounding tissues to adapt to the new environment.41 The contradiction with the heterogeneous (including men and women) study of Foltan et al42 might be caused by the inaccuracy of the mini-sleep study compared with the much more detailed PSG methods of overnight monitoring that were used in this study. This study was conducted specifically to determine whether a more accurate multidimensional radiographic assessment of the airway in patients with bimaxillary orthognathic surgery might better predict the clinical parameters of OSA. There was no study in the literature evaluating the correlation between PAS performed on

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a population that received bimaxillary orthognathic surgery and sleep study parameters, so the findings could not be compared. In this study, significant correlations were found between AHI, sleep efficiency, mean oxygen saturation, and all airway parameters, except oropharyngeal airway measurements in the transversal plane. AHI decreased with increasing PAS distances in the sagittal plane, cross-sectional areas, and PAS volumes; however, sleep efficiency and mean oxygen saturation increased with increasing PAS distances in the sagittal plane, cross-sectional areas, and PAS volumes. Bhattacharyya et al43 studied 40 OSA patients with 3D airway CT, and correlation analysis was conducted between apnea index, respiratory disturbance index, lowest oxygen saturation, and minimum cross-sectional areas of the PAS. The authors were unable to find a correlation between cross-sectional areas and the PSG parameters.43 They attributed this result to other parameters including airway volumes, soft tissue and skeletal relationships, or other factors that might be more relevant to OSA. They studied the region of maximal narrowing, but this might be an oversimplification.43 Some investigators proved the correlation of airway length, genial tubercle to hyoid bone distance, minimum retroglossal crosssectional areas, and lateral/anteroposterior ratio with the presence and severity of OSA.5,18 In our study, some airway parameters determined by the CT correlated with sleep parameters; we would expect patients with a narrower airway lumina to have a greater tendency to have OSA. Rather than distinguishing between patients with and without bimaxillary orthognathic surgery, the true potential value of the airway CT and PSG values preoperatively

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would be realized if they could help to determine the degree of airway obstruction postoperatively. This correlation could then be used to accommodate airway surgery for Class III patients. CONCLUSIONS

The findings of our study indicate that 3D imaging techniques should be the methods of choice when analyzing the PAS structure. After bimaxillary orthognathic surgery, mandibular setback caused significant narrowing of the oropharyngeal and hypopharyngeal airways by positioning the tongue closer to the pharyngeal wall; this might be a predisposing factor in the development of OSA. Conversely, maxillary advancement combined with mandibular setback compensated for the PAS narrowing because maxillary advancement caused significant widening of the nasopharyngeal and oropharyngeal airways, which increased the total airway volume. This change could result in relaxation of the physiologic flow of air through the PAS to the lungs, causing improved sleep quality. Bimaxillary orthognathic surgery rather than only mandibular setback would be preferable to correct a Class III deformity to prevent narrowing of the PAS. The correlations between the PAS parameters and the PSG variables could be helpful to overcome the confounding effect of maxillomandibular surgery. Additional studies, with more patients, are required to document the benefits of these correlations. REFERENCES 1. Lye KW. Effect of orthognathic surgery on the posterior airway space (PAS). Ann Acad Med Singapore 2008;37:677-82. 2. Kawamata A, Fujishita M, Ariji Y, Ariji E. Three-dimensional computed tomographic evaluation of morphologic airway changes after mandibular setback osteotomy for prognathism. Oral Surg Oral Med Oral Pathol 2000;89:278-87. 3. Busby BR, Bailey LJ, Proffit WR, Phillips C, White RP Jr. Long term stability of surgical Class III treatment: a study of 5-year postsurgical results. Int J Adult Orthodon Orthognath Surg 2002;17:159-70. 4. Degerliyurt K, Ueki K, Hashiba Y, Marukawa K, Simsek B, Okabe K, et al. The effect of mandibular setback or two-jaws surgery on pharyngeal airway among different genders. Int J Oral Maxillofac Surg 2009;38:647-52. 5. Chen F, Terada K, Hua Y, Saito I. Effects of bimaxillary surgery and mandibular setback surgery on pharyngeal airway measurements in patients with Class III skeletal deformities. Am J Orthod Dentofacial Orthop 2007;131:372-7. 6. Guven O, Saracoglu U. Changes in pharyngeal airway space and hyoid bone positions after body osteotomies and sagittal split ramus osteotomies. J Craniofac Surg 2005;16:23-30. 7. Hochban W, Sch€ urmann R, Brandenburg U, Conradt R. Mandibular setback for surgical correction of mandibular hyperplasia—does it provoke sleep-related breathing disorders? Int J Oral Maxillofac Surg 1996;25:333-8. 8. Kawakami M, Yamamoto K, Fujimoto M, Ohgi K, Inoue M, Kirita T. Changes in tongue and hyoid position, and posterior airway space

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American Journal of Orthodontics and Dentofacial Orthopedics

Evaluation of pharyngeal airway space changes after bimaxillary orthognathic surgery with a 3-dimensional simulation and modeling program.

The aims of this study were to use 3-dimensional simulation and modeling programs to evaluate the effects of bimaxillary orthognathic surgical correct...
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