CRANIOMAXILLOFACIAL DEFORMITIES/COSMETIC SURGERY
Does Upper Premolar Extraction Affect the Changes of Pharyngeal Airway Volume After Bimaxillary Surgery in Skeletal Class III Patients? Min-Ah Kim, DDS, MSD,* and Yang-Ho Park, DDS, MSD, PhDy Purpose:
The purpose of this study was to assess the pharyngeal airway volume change after bimaxillary surgery in patients with skeletal Class III malocclusion and evaluate the difference in postoperative pharyngeal airway space between upper premolar extraction cases and nonextraction cases.
Materials and Methods:
Cone-beam computed tomographic scans were obtained for 23 patients (13 in extraction group and 10 in nonextraction group) who were diagnosed with mandibular prognathism before surgery (T0) and then 2 months (T2) and 6 months after surgery (T3). Using InVivoDental 3-dimensional imaging software, volumetric changes in the pharyngeal airway space were assessed at T0, T2, and T3. The Wilcoxon signed-rank test was used to determine whether there were significant changes in pharyngeal airway volume between time points. The Mann-Whitney U test was used to determine whether there were significant differences in volumetric changes between the extraction and nonextraction groups.
Results:
Volumes in all subsections of the pharyngeal airway were decreased (P < .05) except for changes in the oropharyngeal airway volume in the nonextraction group from T0 to T2. There were significant differences between the extraction and nonextraction groups in the changes of oro- and total pharyngeal airway volumes from T0 to T3.
Conclusion:
The null hypothesis was rejected. The extraction of upper premolars rather than nonextraction decreased the pharyngeal airway space more in patients with mandibular prognathism who planned to have bimaxillary surgery. Ó 2014 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 72:165.e1-165.e10, 2014
For growing patients with skeletal Class III malocclusion, there are various treatment options, such as orthopedic treatment, camouflage treatment, distraction osteogenesis, and orthodontic treatment with orthognathic surgery.1-3 For adults with severe Class III skeletal deformity, orthognathic surgery is usually chosen to restore proper dental occlusion and facial disharmony, because these patients are unaffected by growth modification or camouflage treatment.4,5 As the techniques and knowledge of orthognathic surgery have advanced, there has been an increase
in the rate of choosing bimaxillary surgery as a treatment6 instead of isolated mandibular setback surgery, which was more common.7,8 With isolated mandibular setback surgery or bimaxillary surgery, it is generally accepted that the position of the hyoid bone and the tongue are changed and the pharyngeal airway space is narrowed.8,9 Most reports have stated that the pharyngeal airway space is narrowed immediately after orthognathic surgery and then changes continually over time.10-13 However, bimaxillary surgery rather than isolated
Received from the Department of Orthodontics, Kangdong Sacred
Received June 13 2013
Heart Hospital, Hallym University Medical Center, Seoul, Korea.
Accepted September 13 2013
*Resident.
Ó 2014 American Association of Oral and Maxillofacial Surgeons
yProfessor. Address correspondence and reprint requests to Dr Park: Depart-
0278-2391/13/01209-3$36.00/0 http://dx.doi.org/10.1016/j.joms.2013.09.020
ment of Orthodontics, Kangdong Sacred Heart Hospital, Hallym University Medical Center, Gil-dong 445, Gangdong-gu, Seoul 134-701, Republic of Korea; e-mail: [email protected]
165.e1
165.e2
PREMOLAR EXTRACTION AND PHARYNGEAL AIRWAY
mandibular setback surgery enables better airflow, because clockwise rotation of the maxilla and maxillary advancement make the pharyngeal airway space wider, whereas mandibular setback causes narrowing of the pharyngeal airway space.7,8,10 Once the growth of patients with mandibular prognathism is completed, orthognathic surgery is primarily planned in addition to orthodontic treatment.14 Extraction of teeth before orthognathic surgery can be an effective method to secure space for dental alignment and to decompensate labioversed upper incisors and linguoversed lower incisors.15,16 However, when deciding whether extraction of upper premolars in patients with skeletal Class III malocclusion who plan to undergo bimaxillary surgery, some factors, such as dental arch width and crowding, should be considered.17 Some studies have assessed airway volume with 3dimensional (3D) images,10 but none have reported the difference of the change in the pharyngeal airway space between extraction and nonextraction cases in patients with skeletal Class III malocclusion treated with bimaxillary surgery. The purpose of this study was to assess the pharyngeal airway volume change after bimaxillary surgery in patients with skeletal Class III malocclusion and evaluate the difference between upper premolar extraction and nonextraction. The null hypothesis was that the change in pharyngeal airway volume would not differ between the 2 groups.
Materials and Methods STUDY DESIGN AND SAMPLE
This study protocol was approved by the ethics review committee at Kangdong Sacred Heart Hospital, Hallym University Medical Center (Seoul, Korea; institutional review board 12-1-011-2), and informed consent was obtained from all patients involved in this study. The inclusion criteria for this study consisted of patients with mandibular prognathism who visited the Department of Orthodontics, Kangdong Sacred Heart Hospital, Hallym University Medical Center for orthognathic surgery and patients who underwent cone-beam computed tomographic (CBCT) scanning
Table 1. TIME POINTS USED IN THIS STUDY
Definition T0 T1 T2 T3 T4
Initial examination Immediately before bimaxillary surgery 2 mo after bimaxillary surgery 6 mo after bimaxillary surgery Debonding
Kim and Park. Premolar Extraction and Pharyngeal Airway. J Oral Maxillofac Surg 2014.
at least 3 times, before and after surgery. The time points used in this study are listed in Table 1. All patients involved in this study had pre- and postoperative orthodontic treatment. Of 23 consecutive patients who underwent bimaxillary surgeries, 13 patients who had their maxillary premolars extracted as part of preoperative orthodontic treatment were included in the extraction group (EG), and the remaining 10 patients were included in the nonextraction group (NG; Table 2). In the EG, 8 patients were treated with extraction of the 2 maxillary first premolars, 3 patients were treated with extraction of the 2 maxillary second
Table 2. CHARACTERISTICS OF PATIENTS IN THE EG AND NG
EG
NG
Demographics Sample size (n) 13 10 Mean age (yr) 24.33 23.65 Women 6 5 Measurements at initial examination ANB ( ) 3.00 2.95 1.82 3.36 APDI 97.83 5.11 96.23 7.82 Overjet (mm) 2.66 3.12 1.35 3.30 FMA ( ) 32.72 18.24 28.32 5.14 Palatal plane 2.29 2.66 2.88 2.09 angle ( ) Occlusal plane 9.62 4.84 10.56 3.66 angle ( ) 28.11 5.93 28.32 5.14 Mandibular plane angle ( ) Arch length 6.67 4.39 0.25 1.90 discrepancy ( ) Surgical change PNS AP (mm) 2.52 1.87 2.24 2.93 Pogonion 8.14 3.83 3.80 6.40 AP (mm) Menton 3.78 3.74 5.20 2.56 (vertical) (mm) 2.90 2.89 2.12 2.64 Palatal plane angle ( ) Mandibular 2.45 3.97 0.87 2.87 plane angle ( )
P Value
.26 .42 .39 .71 .58 .60 .80 .01*
.93 .13 .26 .46 .32
Abbreviations: ANB, difference between the line connecting the sella to the nasion to the A point and the line connecting the sella to nasion to the B point; APDI, subtotal of facial plane angle, palatal plane angle, and AB (the line connecting A point and B point) to facial plane angle; EG, extraction group; FMA, angle between Frankfort horizontal plane and mandibular plane; NG, nonextraction group; PNS AP, anteroposterior position of posterior nasal spine; pogonion AP, anteroposterior position of pogonion. * P < .05. Kim and Park. Premolar Extraction and Pharyngeal Airway. J Oral Maxillofac Surg 2014.
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KIM AND PARK
FIGURE 1. A process for obtaining 3-dimensional images of the pharyngeal airway. A, Volume-rendered image of soft tissue. B, Inverse image of A. C, Cropped image of the pharyngeal airway. Kim and Park. Premolar Extraction and Pharyngeal Airway. J Oral Maxillofac Surg 2014.
premolars, and 1 patient was treated with extraction of the maxillary right second premolar and the left first premolar. Another patient lost his 2 maxillary second premolars when he was young. SURGICAL PROCEDURES
All patients involved in this study underwent bilateral sagittal split ramus osteotomy and Le Fort I osteotomy. Posterior impaction of maxilla was treated simultaneously, resulting in clockwise rotation of the jaws using the anterior nasal spine or upper incisal tip as the center of rotation. Eight patients in the EG
and 10 in the NG underwent advancement genioplasty as the adjunctive procedure. Rigid fixation of the maxilla and mandible was achieved by miniplates and miniscrews. Surgical wafers were placed for 3 to 4 weeks after surgery, and interarch elastics were used to stabilize the interarch relation after the surgical wafers were removed. IMAGE ACQUISITION
CBCT scans were acquired at initial examination (T0), 2 months after surgery (T2), and 6 months after surgery (T3). All CBCT images were obtained using
165.e4
PREMOLAR EXTRACTION AND PHARYNGEAL AIRWAY
FIGURE 2. Three sections comprising the pharyngeal airway. A, Reference planes and each pharyngeal airway space on a lateral cephalometric image acquired from a cone-beam computed tomographic image. B, Reference planes and each pharyngeal airway on the inverse image of soft tissue. H, hypopharyngeal airway; N, nasopharyngeal airway; O, oropharyngeal airway. Kim and Park. Premolar Extraction and Pharyngeal Airway. J Oral Maxillofac Surg 2014.
the Master 3D dental imaging system (Vatech Inc, Seoul, South Korea), with the following parameters: 90 kV, 3.6 mA, 15-second scan time, and 20- 19-cm field of view. A slice thickness of 0.3 mm was set, and the voxels were isotropic. The 3D graphic rendering was performed using InVivoDental 3D imaging software (Anatomage, San Jose, CA). For the 2-dimensional (2D) analysis of dental characteristics, lateral cephalographs also were obtained at T0, immediately before surgery (T1), at T2, at T3, and at debonding (T4; Table 1).
VOLUMETRIC CHANGES
To visualize the pharyngeal airway, it was necessary to convert the negative value of the void space to a positive value. In the lateral view of the CBCT images, the internal structure cut by the midsagittal plane was visualized. Then, the CBCT images were set to soft tissue mode using the rendering software, which stressed the soft tissue rather than the hard tissue, followed by the converting process, which enabled clear imaging of the pharyngeal airway. To calculate the airway volume, the pharyngeal airway space had to be cropped from the images. Using the software, the pharyngeal airway section was isolated from the surrounding structures. The threshold values were set at a range of 1,024 to 300 HU to eliminate any artifacts in the images and refine the
images. The volume of each pharyngeal airway section was calculated in cubic millimeters (Fig 1). The airway was divided into 3 sections: 1) the nasopharyngeal airway, from the top of the pharyngeal airway to the plane parallel to the Frankfort horizontal (FH) plane passing through the posterior nasal spine (PNS), 2) the oropharyngeal airway, from the bottom of the nasopharyngeal airway to the plane parallel to FH plane passing through the end of the soft palate, and 3) the hypopharyngeal airway, from the bottom of the oropharyngeal airway to the plane parallel to the FH plane passing the epiglottis. The total pharyngeal airway was the subtotal of these 3 sections (Fig 2). Each pharyngeal airway volume was measured at T0, T2, and T3 using CBCT images, and the changes in each airway volume were calculated (Fig 3). STATISTICAL ANALYSIS
SPSS 17.0 for Windows (SPSS, Inc, Chicago, IL) was used for all statistical analyses. The means and standard deviations of each measurement for each group were calculated. The Wilcoxon signed-rank test was used to determine significant differences in pharyngeal airway volume among time points. The MannWhitney U test was used to determine significant differences in volumetric changes between the EG and NG. All results in these analyses were considered significant at a P value less than .05 and much more significant at a P value less than .01.
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FIGURE 3. Example of pharyngeal airway volume changes after bimaxillary surgery in the same patient. A, Cone-beam computed tomographic image at initial examination. B, Cone-beam computed tomographic image at 2 months after bimaxillary surgery. C, Cone-beam computed tomographic image at 6 months after bimaxillary surgery. Kim and Park. Premolar Extraction and Pharyngeal Airway. J Oral Maxillofac Surg 2014.
Results CHARACTERISTICS OF PATIENTS
The subjects consisted of 13 patients in the EG and 10 patients in the NG. Skeletal and dental characteristics were measured using cephalograms and CBCT images. Using cephalograms at T0, the difference between the line connecting the sella to the nasion to the A point and the line connecting the sella to the nasion to the B point; the subtotal of the facial plane angle, the palatal plane angle, and AB (the line connecting A point and B point) to the facial plane angle; the
angle between the FH plane and the mandibular plane; overjet; palatal plane angle; occlusal plane angle; and mandibular plane angle were measured. To evaluate the effect of bimaxillary surgery on skeletal measurements, anteroposterior changes in the PNS and pogonion, vertical changes in the menton, and the change in the palatal plane angle and the mandibular plane angle were assessed. As a result of surgery, the amount of posterior impaction in the EG was 3.75 1.40 mm on average and that in the NG was 4.00 0.56 mm. The mean amount of mandibular setback was 9.00 1.65 mm in the EG and 7.44 2.52 mm in the NG.
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Table 3. DENTAL CHANGES IN PRESURGICAL ORTHODONTIC TREATMENT (T0 TO T1) AND TOTAL ORTHODONTIC TREATMENT (T0 TO T4)
T0
T1
T4
T0-T1
P Value
T0-T4
P Value
.31
3.09 7.03
.10
.16
2.56 1.94
.05), except for arch length discrepancy (P < .05). The arch length discrepancy of the EG ranged from 14.3 to 0.2 mm (mean, 6.67 mm) and that of the NG ranged from 2.4 to 4.4 mm (mean, 0.25 mm). DENTAL CHANGES IN PROGRESS OF ORTHODONTIC TREATMENT
To evaluate changes in the inclination of maxillary central incisors, the degrees between the maxillary central incisor (U1) and the FH plane were measured
at T0, T1, and T4. Also, the distances between the U1 and the line connecting the nasion to the A point at T0, T1, and T4 were measured to assess the changes in the anteroposterior position of maxillary central incisors (Table 3). The inclination and anteroposterior position of U1 at T0 were not statistically significant (P < .05). There were no significant changes in the inclination and anteroposterior position of U1 during presurgical orthodontic treatment (P > .05) in the EG and NG. The inclination of the U1 increased somewhat in the EG, which meant the upper incisors were decompensated. In contrast, there were significant decreases from T0 to T4 in the anteroposterior position of U1 (P < .05) in the 2 groups. In addition, there was no significant difference in dental changes between the EG and the NG.
Table 4. MEANS AND STANDARD DEVIATIONS OF EACH AIRWAY SPACE VOLUME AT T0 AND SIGNIFICANT DIFFERENCES BETWEEN EG AND NG
T0
Nasopharyngeal airway (mm3) Oropharyngeal airway (mm3) Hypopharyngeal airway (mm3) Total pharyngeal airway (mm3)
EG
NG
P Value
8,624.08 1,327.92 14,672.69 6,079.29 22,269.69 6,087.95 45,566.46 11,865.90
7,444.30 2,737.01 11,385.60 3,650.64 18,231.00 3,383.50 37,060.90 8,413.83
.17 .34 .06 .08
Note: The Mann-Whitney U test was performed. Abbreviations: EG, extraction group; NG, nonextraction group; T0, initial examination. P > .05 means no significant difference between two groups. Kim and Park. Premolar Extraction and Pharyngeal Airway. J Oral Maxillofac Surg 2014.
165.e7 DIFFERENCE IN AIRWAY VOLUME CHANGES BETWEEN EG AND NG
Kim and Park. Premolar Extraction and Pharyngeal Airway. J Oral Maxillofac Surg 2014.
Note: The Wilcoxon signed-rank test was performed. Abbreviations: Hypo-V, hypopharyngeal airway volume; Naso-V, nasopharyngeal airway volume; Oro-V, oropharyngeal airway volume; T0, initial examination; T1, immediately before surgery; T2, 2 months after surgery; T3, 6 months after surgery; Total-V, total pharyngeal airway volume. * P < .05. y P < .01.
.01* .01*
Does Upper Premolar Extraction Affect the Changes of Pharyngeal Airway Volume After Bimaxillary Surgery in Skeletal Class III Patients? Min-Ah Kim, DDS, MSD,* and Yang-Ho Park, DDS, MSD, PhDy Purpose:
The purpose of this study was to assess the pharyngeal airway volume change after bimaxillary surgery in patients with skeletal Class III malocclusion and evaluate the difference in postoperative pharyngeal airway space between upper premolar extraction cases and nonextraction cases.
Materials and Methods:
Cone-beam computed tomographic scans were obtained for 23 patients (13 in extraction group and 10 in nonextraction group) who were diagnosed with mandibular prognathism before surgery (T0) and then 2 months (T2) and 6 months after surgery (T3). Using InVivoDental 3-dimensional imaging software, volumetric changes in the pharyngeal airway space were assessed at T0, T2, and T3. The Wilcoxon signed-rank test was used to determine whether there were significant changes in pharyngeal airway volume between time points. The Mann-Whitney U test was used to determine whether there were significant differences in volumetric changes between the extraction and nonextraction groups.
Results:
Volumes in all subsections of the pharyngeal airway were decreased (P < .05) except for changes in the oropharyngeal airway volume in the nonextraction group from T0 to T2. There were significant differences between the extraction and nonextraction groups in the changes of oro- and total pharyngeal airway volumes from T0 to T3.
Conclusion:
The null hypothesis was rejected. The extraction of upper premolars rather than nonextraction decreased the pharyngeal airway space more in patients with mandibular prognathism who planned to have bimaxillary surgery. Ó 2014 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 72:165.e1-165.e10, 2014
For growing patients with skeletal Class III malocclusion, there are various treatment options, such as orthopedic treatment, camouflage treatment, distraction osteogenesis, and orthodontic treatment with orthognathic surgery.1-3 For adults with severe Class III skeletal deformity, orthognathic surgery is usually chosen to restore proper dental occlusion and facial disharmony, because these patients are unaffected by growth modification or camouflage treatment.4,5 As the techniques and knowledge of orthognathic surgery have advanced, there has been an increase
in the rate of choosing bimaxillary surgery as a treatment6 instead of isolated mandibular setback surgery, which was more common.7,8 With isolated mandibular setback surgery or bimaxillary surgery, it is generally accepted that the position of the hyoid bone and the tongue are changed and the pharyngeal airway space is narrowed.8,9 Most reports have stated that the pharyngeal airway space is narrowed immediately after orthognathic surgery and then changes continually over time.10-13 However, bimaxillary surgery rather than isolated
Received from the Department of Orthodontics, Kangdong Sacred
Received June 13 2013
Heart Hospital, Hallym University Medical Center, Seoul, Korea.
Accepted September 13 2013
*Resident.
Ó 2014 American Association of Oral and Maxillofacial Surgeons
yProfessor. Address correspondence and reprint requests to Dr Park: Depart-
0278-2391/13/01209-3$36.00/0 http://dx.doi.org/10.1016/j.joms.2013.09.020
ment of Orthodontics, Kangdong Sacred Heart Hospital, Hallym University Medical Center, Gil-dong 445, Gangdong-gu, Seoul 134-701, Republic of Korea; e-mail: [email protected]
165.e1
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PREMOLAR EXTRACTION AND PHARYNGEAL AIRWAY
mandibular setback surgery enables better airflow, because clockwise rotation of the maxilla and maxillary advancement make the pharyngeal airway space wider, whereas mandibular setback causes narrowing of the pharyngeal airway space.7,8,10 Once the growth of patients with mandibular prognathism is completed, orthognathic surgery is primarily planned in addition to orthodontic treatment.14 Extraction of teeth before orthognathic surgery can be an effective method to secure space for dental alignment and to decompensate labioversed upper incisors and linguoversed lower incisors.15,16 However, when deciding whether extraction of upper premolars in patients with skeletal Class III malocclusion who plan to undergo bimaxillary surgery, some factors, such as dental arch width and crowding, should be considered.17 Some studies have assessed airway volume with 3dimensional (3D) images,10 but none have reported the difference of the change in the pharyngeal airway space between extraction and nonextraction cases in patients with skeletal Class III malocclusion treated with bimaxillary surgery. The purpose of this study was to assess the pharyngeal airway volume change after bimaxillary surgery in patients with skeletal Class III malocclusion and evaluate the difference between upper premolar extraction and nonextraction. The null hypothesis was that the change in pharyngeal airway volume would not differ between the 2 groups.
Materials and Methods STUDY DESIGN AND SAMPLE
This study protocol was approved by the ethics review committee at Kangdong Sacred Heart Hospital, Hallym University Medical Center (Seoul, Korea; institutional review board 12-1-011-2), and informed consent was obtained from all patients involved in this study. The inclusion criteria for this study consisted of patients with mandibular prognathism who visited the Department of Orthodontics, Kangdong Sacred Heart Hospital, Hallym University Medical Center for orthognathic surgery and patients who underwent cone-beam computed tomographic (CBCT) scanning
Table 1. TIME POINTS USED IN THIS STUDY
Definition T0 T1 T2 T3 T4
Initial examination Immediately before bimaxillary surgery 2 mo after bimaxillary surgery 6 mo after bimaxillary surgery Debonding
Kim and Park. Premolar Extraction and Pharyngeal Airway. J Oral Maxillofac Surg 2014.
at least 3 times, before and after surgery. The time points used in this study are listed in Table 1. All patients involved in this study had pre- and postoperative orthodontic treatment. Of 23 consecutive patients who underwent bimaxillary surgeries, 13 patients who had their maxillary premolars extracted as part of preoperative orthodontic treatment were included in the extraction group (EG), and the remaining 10 patients were included in the nonextraction group (NG; Table 2). In the EG, 8 patients were treated with extraction of the 2 maxillary first premolars, 3 patients were treated with extraction of the 2 maxillary second
Table 2. CHARACTERISTICS OF PATIENTS IN THE EG AND NG
EG
NG
Demographics Sample size (n) 13 10 Mean age (yr) 24.33 23.65 Women 6 5 Measurements at initial examination ANB ( ) 3.00 2.95 1.82 3.36 APDI 97.83 5.11 96.23 7.82 Overjet (mm) 2.66 3.12 1.35 3.30 FMA ( ) 32.72 18.24 28.32 5.14 Palatal plane 2.29 2.66 2.88 2.09 angle ( ) Occlusal plane 9.62 4.84 10.56 3.66 angle ( ) 28.11 5.93 28.32 5.14 Mandibular plane angle ( ) Arch length 6.67 4.39 0.25 1.90 discrepancy ( ) Surgical change PNS AP (mm) 2.52 1.87 2.24 2.93 Pogonion 8.14 3.83 3.80 6.40 AP (mm) Menton 3.78 3.74 5.20 2.56 (vertical) (mm) 2.90 2.89 2.12 2.64 Palatal plane angle ( ) Mandibular 2.45 3.97 0.87 2.87 plane angle ( )
P Value
.26 .42 .39 .71 .58 .60 .80 .01*
.93 .13 .26 .46 .32
Abbreviations: ANB, difference between the line connecting the sella to the nasion to the A point and the line connecting the sella to nasion to the B point; APDI, subtotal of facial plane angle, palatal plane angle, and AB (the line connecting A point and B point) to facial plane angle; EG, extraction group; FMA, angle between Frankfort horizontal plane and mandibular plane; NG, nonextraction group; PNS AP, anteroposterior position of posterior nasal spine; pogonion AP, anteroposterior position of pogonion. * P < .05. Kim and Park. Premolar Extraction and Pharyngeal Airway. J Oral Maxillofac Surg 2014.
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KIM AND PARK
FIGURE 1. A process for obtaining 3-dimensional images of the pharyngeal airway. A, Volume-rendered image of soft tissue. B, Inverse image of A. C, Cropped image of the pharyngeal airway. Kim and Park. Premolar Extraction and Pharyngeal Airway. J Oral Maxillofac Surg 2014.
premolars, and 1 patient was treated with extraction of the maxillary right second premolar and the left first premolar. Another patient lost his 2 maxillary second premolars when he was young. SURGICAL PROCEDURES
All patients involved in this study underwent bilateral sagittal split ramus osteotomy and Le Fort I osteotomy. Posterior impaction of maxilla was treated simultaneously, resulting in clockwise rotation of the jaws using the anterior nasal spine or upper incisal tip as the center of rotation. Eight patients in the EG
and 10 in the NG underwent advancement genioplasty as the adjunctive procedure. Rigid fixation of the maxilla and mandible was achieved by miniplates and miniscrews. Surgical wafers were placed for 3 to 4 weeks after surgery, and interarch elastics were used to stabilize the interarch relation after the surgical wafers were removed. IMAGE ACQUISITION
CBCT scans were acquired at initial examination (T0), 2 months after surgery (T2), and 6 months after surgery (T3). All CBCT images were obtained using
165.e4
PREMOLAR EXTRACTION AND PHARYNGEAL AIRWAY
FIGURE 2. Three sections comprising the pharyngeal airway. A, Reference planes and each pharyngeal airway space on a lateral cephalometric image acquired from a cone-beam computed tomographic image. B, Reference planes and each pharyngeal airway on the inverse image of soft tissue. H, hypopharyngeal airway; N, nasopharyngeal airway; O, oropharyngeal airway. Kim and Park. Premolar Extraction and Pharyngeal Airway. J Oral Maxillofac Surg 2014.
the Master 3D dental imaging system (Vatech Inc, Seoul, South Korea), with the following parameters: 90 kV, 3.6 mA, 15-second scan time, and 20- 19-cm field of view. A slice thickness of 0.3 mm was set, and the voxels were isotropic. The 3D graphic rendering was performed using InVivoDental 3D imaging software (Anatomage, San Jose, CA). For the 2-dimensional (2D) analysis of dental characteristics, lateral cephalographs also were obtained at T0, immediately before surgery (T1), at T2, at T3, and at debonding (T4; Table 1).
VOLUMETRIC CHANGES
To visualize the pharyngeal airway, it was necessary to convert the negative value of the void space to a positive value. In the lateral view of the CBCT images, the internal structure cut by the midsagittal plane was visualized. Then, the CBCT images were set to soft tissue mode using the rendering software, which stressed the soft tissue rather than the hard tissue, followed by the converting process, which enabled clear imaging of the pharyngeal airway. To calculate the airway volume, the pharyngeal airway space had to be cropped from the images. Using the software, the pharyngeal airway section was isolated from the surrounding structures. The threshold values were set at a range of 1,024 to 300 HU to eliminate any artifacts in the images and refine the
images. The volume of each pharyngeal airway section was calculated in cubic millimeters (Fig 1). The airway was divided into 3 sections: 1) the nasopharyngeal airway, from the top of the pharyngeal airway to the plane parallel to the Frankfort horizontal (FH) plane passing through the posterior nasal spine (PNS), 2) the oropharyngeal airway, from the bottom of the nasopharyngeal airway to the plane parallel to FH plane passing through the end of the soft palate, and 3) the hypopharyngeal airway, from the bottom of the oropharyngeal airway to the plane parallel to the FH plane passing the epiglottis. The total pharyngeal airway was the subtotal of these 3 sections (Fig 2). Each pharyngeal airway volume was measured at T0, T2, and T3 using CBCT images, and the changes in each airway volume were calculated (Fig 3). STATISTICAL ANALYSIS
SPSS 17.0 for Windows (SPSS, Inc, Chicago, IL) was used for all statistical analyses. The means and standard deviations of each measurement for each group were calculated. The Wilcoxon signed-rank test was used to determine significant differences in pharyngeal airway volume among time points. The MannWhitney U test was used to determine significant differences in volumetric changes between the EG and NG. All results in these analyses were considered significant at a P value less than .05 and much more significant at a P value less than .01.
165.e5
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FIGURE 3. Example of pharyngeal airway volume changes after bimaxillary surgery in the same patient. A, Cone-beam computed tomographic image at initial examination. B, Cone-beam computed tomographic image at 2 months after bimaxillary surgery. C, Cone-beam computed tomographic image at 6 months after bimaxillary surgery. Kim and Park. Premolar Extraction and Pharyngeal Airway. J Oral Maxillofac Surg 2014.
Results CHARACTERISTICS OF PATIENTS
The subjects consisted of 13 patients in the EG and 10 patients in the NG. Skeletal and dental characteristics were measured using cephalograms and CBCT images. Using cephalograms at T0, the difference between the line connecting the sella to the nasion to the A point and the line connecting the sella to the nasion to the B point; the subtotal of the facial plane angle, the palatal plane angle, and AB (the line connecting A point and B point) to the facial plane angle; the
angle between the FH plane and the mandibular plane; overjet; palatal plane angle; occlusal plane angle; and mandibular plane angle were measured. To evaluate the effect of bimaxillary surgery on skeletal measurements, anteroposterior changes in the PNS and pogonion, vertical changes in the menton, and the change in the palatal plane angle and the mandibular plane angle were assessed. As a result of surgery, the amount of posterior impaction in the EG was 3.75 1.40 mm on average and that in the NG was 4.00 0.56 mm. The mean amount of mandibular setback was 9.00 1.65 mm in the EG and 7.44 2.52 mm in the NG.
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PREMOLAR EXTRACTION AND PHARYNGEAL AIRWAY
Table 3. DENTAL CHANGES IN PRESURGICAL ORTHODONTIC TREATMENT (T0 TO T1) AND TOTAL ORTHODONTIC TREATMENT (T0 TO T4)
T0
T1
T4
T0-T1
P Value
T0-T4
P Value
.31
3.09 7.03
.10
.16
2.56 1.94
.05), except for arch length discrepancy (P < .05). The arch length discrepancy of the EG ranged from 14.3 to 0.2 mm (mean, 6.67 mm) and that of the NG ranged from 2.4 to 4.4 mm (mean, 0.25 mm). DENTAL CHANGES IN PROGRESS OF ORTHODONTIC TREATMENT
To evaluate changes in the inclination of maxillary central incisors, the degrees between the maxillary central incisor (U1) and the FH plane were measured
at T0, T1, and T4. Also, the distances between the U1 and the line connecting the nasion to the A point at T0, T1, and T4 were measured to assess the changes in the anteroposterior position of maxillary central incisors (Table 3). The inclination and anteroposterior position of U1 at T0 were not statistically significant (P < .05). There were no significant changes in the inclination and anteroposterior position of U1 during presurgical orthodontic treatment (P > .05) in the EG and NG. The inclination of the U1 increased somewhat in the EG, which meant the upper incisors were decompensated. In contrast, there were significant decreases from T0 to T4 in the anteroposterior position of U1 (P < .05) in the 2 groups. In addition, there was no significant difference in dental changes between the EG and the NG.
Table 4. MEANS AND STANDARD DEVIATIONS OF EACH AIRWAY SPACE VOLUME AT T0 AND SIGNIFICANT DIFFERENCES BETWEEN EG AND NG
T0
Nasopharyngeal airway (mm3) Oropharyngeal airway (mm3) Hypopharyngeal airway (mm3) Total pharyngeal airway (mm3)
EG
NG
P Value
8,624.08 1,327.92 14,672.69 6,079.29 22,269.69 6,087.95 45,566.46 11,865.90
7,444.30 2,737.01 11,385.60 3,650.64 18,231.00 3,383.50 37,060.90 8,413.83
.17 .34 .06 .08
Note: The Mann-Whitney U test was performed. Abbreviations: EG, extraction group; NG, nonextraction group; T0, initial examination. P > .05 means no significant difference between two groups. Kim and Park. Premolar Extraction and Pharyngeal Airway. J Oral Maxillofac Surg 2014.
165.e7 DIFFERENCE IN AIRWAY VOLUME CHANGES BETWEEN EG AND NG
Kim and Park. Premolar Extraction and Pharyngeal Airway. J Oral Maxillofac Surg 2014.
Note: The Wilcoxon signed-rank test was performed. Abbreviations: Hypo-V, hypopharyngeal airway volume; Naso-V, nasopharyngeal airway volume; Oro-V, oropharyngeal airway volume; T0, initial examination; T1, immediately before surgery; T2, 2 months after surgery; T3, 6 months after surgery; Total-V, total pharyngeal airway volume. * P < .05. y P < .01.
.01* .01*
