Introduction
The objective of this study was to investigate the 2-year postoperative change and influencing factors of the upper airway after mandibular advancement with maxillary setback surgery for patients with a skeletal Class II relationship.
Methods
Fifty-seven participants who underwent mandibular advancement with maxillary setback surgery were enrolled consecutively. Cone-beam computed tomography was performed preoperatively, 3 months postoperatively (T1), and 2 years (T2) postoperatively. All parameters were measured using Dolphin Imaging software (Dolphin Imaging and Management Solutions, Chatsworth, Calif).
Results
The total volume (V), minimum cross-sectional area (CSA min ), and glossopharynx increased significantly in both the short-term (V, 13.33%; CSA min , 33.03%; glossopharynx, 26.73%) and long-term (V, 10.19%; CSA min , 23.18%; glossopharynx, 18.27%) after the surgery. Mandibular advancement, mandibular width increase, preoperative CSA min , and body mass index (BMI) significantly affected 2-year postoperative V increases. Mandibular advancement and BMI significantly affected 2-year postoperative glossopharynx increases. Backward movement of point PNS may lead to a reduction of the nasopharynx; however, downward movement of point PNS, upward movement of point A, and increased maxillary width may compensate for this effect by increasing the likelihood of the nasopharynx opening. Furthermore, mandibular body length at T1 is positively associated with relapse rate ([T2 − T1] / T1) of V and CSA min .
Conclusions
Mandibular advancement amount, mandibular width increase, preoperative CSA min , and BMI are the 4 factors for long-term V changes. Patients with a longer mandibular body length might have a lower relapse rate.
Highlights
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Mandibular advancement with maxillary setback surgery is beneficial to the airway.
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We evaluated 2-year postoperative changes of the airway after the surgery.
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We explored influencing factors of 2-year postoperative airway changes.
Obstructive sleep apnea (OSA) is defined as the absence of inspiratory airflow for at least 10 seconds during sleep, which is a common disease in the clinical work of orthodontists and orthognathic surgeons. Multiple studies using a variety of imaging techniques consistently show that a crowded, narrow upper airway is the key cause of OSA. Therefore, more and more orthodontists and orthognathic surgeons pay attention to the changes in the upper airway in their work and are vigilant for problems such as narrow upper airways during treatment.
Orthognathic surgery is the most established treatment to correct severe Class II or Class III malocclusion, which is widely accepted because of its improvement of craniofacial deformities and occlusal function. , Some studies have found that orthognathic surgery can not only improve craniofacial deformities but also have certain effects on the upper airway. A comparative study including 25 patients treated with mandibular advancement surgery and 25 patients treated with mandibular setback surgery found that mandibular advancement surgery contributed to the opening of the upper airway, whereas mandibular setback surgery showed the reverse effects. Another study related to maxillomandibular advancement surgery reported that this surgical approach helps to better open the upper airway, reduce apnea-hypopnea index, and treat OSA.
Although previous studies have revealed that orthognathic surgery is emerging as a treatment option for OSA, some problems remain. First, many patients with a skeletal Class II relationship have a maxillary protrusion and mandibular advancement with maxillary setback is a common operative method to solve the problem. However, there is relatively limited research on evaluating the changes in the upper airway after this specific surgical method. Second, some studies have demonstrated that the relationship between postoperative maxillomandibular movement and upper airway changes on a qualitative level, there is still a lack of quantitative analysis. Such detailed quantitative analyses can help orthognathic surgeons plan surgeries from the perspective of the upper airway. In addition, in reports of long-term postoperative airway changes, it has been observed that postoperative airway remodeling is a gradual process with time. Most studies evaluating postoperative changes in the airway are limited to 1 year, with only a few studies considering longer-term follow-ups of 2 years. By assessing the changes in the upper airway over 2 years, researchers can gather more evidence and insights about the gradual process of airway remodeling after surgery. Moreover, comparing the preoperative, 3-month postoperative, and 2-year postoperative time points can provide a better understanding of the factors influencing the stability of the upper airway after surgery.
Considering the issues in this particular field, we conducted this study. The main objective was to evaluate the changes in the upper airway over 2 years, as well as identify the factors that influence these changes. We gathered 57 patients with a Class II skeletal malocclusion who underwent mandibular advancement with maxillary setback surgery (MAWMS).
Material and methods
Based on a study published in 2022 on the evaluation of the upper airway after orthognathic surgery, a sample size was calculated to show that 26 samples were needed for the study. Between January 2017 and January 2023, 61 patients with skeletal Class II malocclusion who had undergone MAWMS were recruited from Peking University Stomatological Hospital. Inclusion criteria required patients to have received a cone-beam computed tomography (CBCT) scan (DCT PRO Dentofacial CBCT System; Vatech Co, Seoul, South Korea) at 3 specific time points: preoperatively (T0), 3 months postoperatively (T1), and 2 years (± 4 months) postoperatively (T2). Patients with congenital syndromes, a history of previous orthognathic surgery, a history of OSA, and those lacking scans at the designated time points were excluded from the study. Two patients were excluded because of congenital syndromes, and 2 others were removed because of incomplete CBCT data. Ultimately, 57 patients (with an average age of 27.37 ± 6.27 years, including 14 men and 43 women, and an average body mass index [BMI] of 23.11 ± 2.15 kg/m 2 ) were included in the study. The study was approved by the Ethics Committee of the School of Stomatology, Peking University (approval no. No. 2021-08-67-09). Because this study is retrospective, informed consent was not required.
Each patient was scanned in the upright position with the head in the natural position, the teeth in centric occlusion, and the tongue against the palate. The patients were also instructed to breathe smoothly and not swallow. The CBCT device was set at 90 kVp, 7 mA, a field of view of 20 cm × 19 cm, 0.40-mm voxel resolution, and a scan time of 15 seconds. All CBCT data were saved in the digital imaging and communications format.
All measurements in the study were conducted using Dolphin Imaging software (version 19.5; Dolphin Imaging and Management Solutions, Chatsworth, Calif). The digital imaging and communications data obtained from the CBCT images were imported into the Dolphin Imaging software. To ensure consistency, the image was aligned tangent to the nasal base, after the suture line of the middle palate, and adjusted parallel to the Frankfort horizontal (FH) plane. The upper airway was divided into 3 segments: the nasopharynx, velopharynx, and glossopharynx. In addition, the minimum cross-sectional area (CSA min ) was evaluated. Detailed measurements and visual representations of the upper airway can be found in Figures 1 and 2 , and further information regarding these measurements is provided in Table I .
| Parameters | Definitions |
|---|---|
| Skeletal | |
| A | The deepest point on the concavity of the maxilla between ANS and the maxillary alveolus |
| B | The innermost point on the contour of mandible between mandibular incisor and chin |
| PNS | Posterior nasal spine |
| Me | Menton, the most interior point on the chin |
| H | Hyoidale: the most superior and anterior point on the body of the hyoid bone |
| Ba | Basion, median point of anterior margin of foramen magnum |
| Go | The most anterior and inferior point of the mandible |
| Gn | The most posterior and inferior points of the mandible |
| NF-10 | Maxillary width parallel to and 10 mm above the lowest line of the nasal base |
| FH | Frankfort horizontal plane |
| VFH | A plane perpendicular to the FHP, midsagittal plane and passing through Basion point |
| MP/FH | The angle between the Go-Gn plane and the FH plane |
| Mandibular body length | The distance from Gn to the left or right Go |
| Mandibular width | The distance between the left and right Go |
| Mandibular depth | The 2-dimensional distance from Gn to Go |
| Soft-tissue parameters | |
| Soft-palatal angle | The angle between the tip of uvula, PNS, and ANS |
| Soft-palatal length | The distance from the posterior and inferior point of soft palatal to PNS |
| Upper airway parameters | |
| V | The anterior border is the line passing through PNS and S; the inferior border is the line parallel to the FHP passing through the root of epiglottis, and the posterior border is the pharyngeal posterior wall |
| CSA min | Minimum cross-sectional area of the upper airway |
| Nasopharynx | The anterior border is the line passing through PNS and S, the inferior border is the line parallel to the FHP passing through PNS, and the posterior border is the pharyngeal posterior wall |
| Velopharynx | The superior border is the line parallel to the FHP passing through PNS, the inferior border is the line parallel to the FHP passing through the tip of uvula, and the posterior border is the pharyngeal posterior wall |
| Glossopharynx | The superior border is the line parallel to the FHP passing through the tip of uvula, the inferior border is the line parallel to the FHP passing through the root of epiglottis, and the posterior border is the pharyngeal posterior wall |
We established a coordinate system to facilitate the measurement and evaluation of various features. The x-coordinate was defined as the FH plane. To establish the y-coordinate (VFH), we created a plane that was perpendicular to both the x-coordinate and the midsagittal plane, and this plane passed through the Basion point, which is a specific anatomic landmark.
To represent specific anatomic landmarks, we selected 5 points: A, PNS, B, Me, and H. These points corresponded to the anterior maxilla, posterior maxilla, anterior mandible, submentum, and hyoid bone, respectively. We used the parameter NF-10 to determine the width of the maxilla. For vertical skeletal evaluation, we used the parameter MP-FH. In addition, we employed measurements of mandibular length, width, and depth to assess the 3-dimensional (3D) size of the mandible. Detailed definitions of all these measurements can be found in Table I , whereas visual representations of skeletal measurements are provided in Figures 3-6 .
In addition to skeletal measurements, we also conducted soft-tissue measurements. These included the length and angle of the soft palate, which were measured in the midsagittal plane using the same threshold setting. Descriptions and illustrations of the soft-tissue measurements can be found in Table I and Figure 7 .
In this study, we evaluated several changes among the T0, T1, and T2 time points. These changes encompassed various aspects, including alterations in all upper airway measurements, sagittal and vertical changes in points A, PNS, B, Me, and H, changes in NF-10, changes in the length and angle of the soft palate, changes in the MP/FH, as well as changes in mandibular body length, mandibular width, and mandibular depth.
Statistical analysis
All the data collected in this study were analyzed using SPSS software (version 23.0; IBM, Armonk, NY. To ensure the reliability of the data, 2 researchers independently measured the relevant parameters of the upper airway volume (V) and the parameters related to the sagittal and vertical distances of the 5 landmarks. After the measurements were taken, the intraclass correlation coefficient was calculated, resulting in values ranging from 0.96 to 0.99. This high intraclass correlation coefficient indicates that the data reliability was confirmed.
The normality of the distribution for all the parameters was assessed using the Kolmogorov-Smirnov test. The paired t tests and the Wilcoxon signed-rank test were used to evaluate the changes in the upper airway among the T0, T1, and T2 time points. The paired t test was employed to compare data that followed a normal distribution. In contrast, the Wilcoxon signed-rank test was used for analyzing data that did not exhibit a normal distribution. The Pearson correlation test and Spearman correlation test were employed to analyze the influencing factors of the upper airway section showing significant changes (V, CSA min , and glossopharynx). Pearson correlation was applied to analyze data that followed a normal distribution, whereas the Spearman test was used for data that did not conform to a normal distribution. In addition, binary logistic regression was employed to analyze factors related to the upper airway section without significant changes (nasopharynx and velopharynx). Multiple linear regression analyses were conducted to analyze factors related to the upper airway section with significant changes (total V and glossopharynx).
Results
On comparing the measurements of the upper airway at T0 with those taken at T1, we found significant increases in the total upper airway V, CSA min , and the glossopharyngeal airway V (V increasing rate, 13.33%; CSA min increasing rate, 33.03%; glossopharynx increasing rate, 26.73%). However, no significant changes were noted in the nasopharynx and velopharynx.
When comparing the measurements of the upper airway at T0 with those at T2, we found that the increases in V, CSA min , and glossopharynx remained significant, whereas there were no significant differences in the nasopharynx and velopharynx (V changing rate, 10.19%; CSA min changing rate, 23.18%; glossopharynx changing rate, 18.27%). Interestingly, we observed significant reductions in V, CSA min , and glossopharynx at T2 compared with T1 (V changing rate, −2.77%; CSA min changing rate, −7.40%; glossopharynx changing rate, −6.67%). More detailed data on the upper airway measurements can be found in Table II , whereas information regarding skeletal and soft-tissue changes is provided in Supplementary Table I .
| Variables | T0 | T1 | Change | P value |
|---|---|---|---|---|
| T0 − T1 | ||||
| V (mm 3 ) | 29721.43 ± 8545.20 | 33686.26 ± 8985.95 | 3964.82 (13.33) | <0.001 ∗ |
| CSA min (mm 2 ) | 202.70 ± 90.27 | 269.66 ± 102.36 | 66.96 (33.03) | <0.001 ∗ |
| Nasopharynx (mm 3 ) | 9638.63 ± 2301.11 | 10145.68 ± 2443.44 | 507.05 (5.26) | 0.068 |
| Velopharynx (mm 3 ) | 11752.19 ± 4944.87 | 12617.73 ± 4865.54 | 865.54 (7.36) | 0.051 |
| Glossopharynx (mm 3 ) | 8419.31 ± 3677.83 | 10670.15 ± 7.75 | 2250.84 (26.73) | <0.001 ∗ |
| T0 − T2 | T0 | T2 | Change | |
| V (mm3) | 29721.43 ± 8545.20 | 32752.11 ± 9037.86 | 3030.97 (10.19) | <0.001 ∗ |
| CSA mi n (mm 2 ) | 202.70 ± 90.27 | 249.70 ± 94.59 | 46.99 (23.18) | <0.001 ∗ |
| Nasopharynx (mm 3 ) | 9638.63 ± 2301.11 | 10008.97 ± 2327.67 | 370.33 (3.84) | 0.159 |
| Velopharynx (mm 3 ) | 11752.19 ± 4944.87 | 12526.11 ± 4903.68 | 773.92 (6.58) | 0.072 |
| Glossopharynx (mm 3 ) | 8419.31 ± 3677.83 | 9958.35 ± 3858.90 | 1539.04 (18.27) | <0.001 ∗ |
| T1 – T2 | T1 | T2 | Change | |
| V (mm 3 ) | 33686.26 ± 8985.95 | 32752.11 ± 9037.86 | −933.85 (−2.77) | 0.029 ∗ |
| CSA min (mm 2 ) | 269.66 ± 102.36 | 249.70 ± 94.59 | −19.96 (−7.40) | 0.023 ∗ |
| Nasopharynx (mm 3 ) | 10145.68 ± 2443.44 | 10008.97 ± 2327.67 | −136.71 (−1.34) | 0.312 |
| Velopharynx (mm 3 ) | 12617.73 ± 4865.54 | 12526.11 ± 4903.68 | −91.62 (−0.72) | 0.719 |
| Glossopharynx (mm 3 ) | 10670.15 ± 4161.58 | 9958.35 ± 3858.90 | −711.80 (−6.67) | 0.010 ∗ |
We discovered that B-VFH exhibited a positive association with an increase in V and glossopharynx ( P <0.05). Further analyses of the upper airway and glossopharyngeal airway can be found in Supplementary Tables II and III .
Because the above results did not indicate a significant increase in the nasopharynx and velopharynx, we conducted bivariate logistic regression analyses to examine the relationship between these changes and surgical movement. The results revealed that a 1 unit decrease in PNS-VFH may increase the likelihood of nasopharyngeal narrowing by 425.6%, and an increase of 1 unit in PNS-FH and NF-10 may increase the likelihood of nasopharyngeal enlargement by 140.6% and 157.5%, respectively (PNS-VFH: odds ratio [OR], 5.256 [95% confidence interval {CI}, 1.750-15.784], P = 0.003; PNS-FH: OR, 2.406 [95% CI, 1.115-5.191], P = 0.025; NF-10: OR, 2.575 [95% CI, 1.217-5.448], P = 0.013). However, no significant associations were found between changes in the velopharyngeal airway and the selected influencing factors. For specific details, please refer to Supplemental Figures 1 and 2 .
We discovered that an increase in B-VFH, Me-VFH, and mandibular width was significantly and positively associated with an increase in V. In contrast, preoperative CSA min showed a significant negative association with an increase in V ( Table III , P <0.05). In addition, we observed that an increase in B-VFH was significantly and positively associated with an increase in the glossopharynx, whereas the preoperative glossopharynx showed a significant negative association with an increase in the glossopharynx ( Table III , P <0.05).
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