The purpose of this study was to assess the stability of changes in the upper airways 4 years after orthognathic surgery in patients with skeletal Class II malocclusion.
A retrospective clinical study was conducted including 33 cone-beam computed tomography images from 11 patients (average age of 35.91 years) followed up longitudinally for 4 years. The airways were measured with the help of the Dolphin Imaging software (Dolphin Imaging and Management Systems, Chatsworth, Calif) at 3 points: T1 (preoperative), T2 (6 months after surgery), and T3 (4 years after surgery). The parameters assessed were surface area (SA), minimum axial area, and volume (VOL) of the pharyngeal airway space. The times were compared using analysis of variance and Tukey’s test. Pearson’s analysis was performed to assess the correlation with surgical changes and age ( P <0.05).
Four years after operating on the airway spaces, the means of SA and VOL were significantly higher than those observed before the surgery ( P <0.05). The means at 6 months were intermediate, with no significant difference before the surgery and 4 years after it ( P >0.05). There was no significant correlation of the changes in SA, VOL, and minimum axial area with the amount of mandibular advancement, counterclockwise rotation of the occlusal plane, and age of the patient ( P >0.05).
Four years after mandibular advancement surgery in patients with skeletal Class II malocclusion, the increases in the airways remained stable.
Changes in the upper airway were assessed 4 years after orthognathic surgery.
Measurements were performed before, after, and 4 years after surgery.
Four years after surgery, the increases in the airways remained stable.
Orthognathic surgery combined with orthodontic treatment promotes the correction of dentoskeletal and facial deformities, representing a major treatment alternative. It is known that patients with skeletal Class II malocclusion present reduced upper airway dimensions in comparison to patients with skeletal Class I or III malocclusion. This occurs because of a mandibular retropositioning, which might play an important role in the development of obstructive sleep apnea syndrome (OSAS) and compromise respiratory function. The literature reports that orthognathic surgery performed in patients with skeletal Class II malocclusion with anteroposterior maxillomandibular deficiency increases the airway space during the surgical correction of this malocclusion, , , which might benefit the respiratory function. This raises great interest among the scientific community.
However, the long-term stability of airway changes has long remained unknown. Recently, the behavior of airways 5 years after surgery was verified and showed substantial volume gains with progressive reduction. However, the standardization of the method might have affected these results because of the references used for the anatomic limits in the cone-beam computed tomography (CBCT) images, which could have changed during the surgical procedure.
Formerly, longitudinal studies used lateral teleradiography to assess the dimensional changes of airways before surgery, but this only allowed for visualizing the sagittal plane with multiple overlaps of the anatomic structures, which provided limited data with linear and angular measurements for a complex 3-dimensional structure. , The possibility of visualizing the upper portion of the airways with CBCT in the sagittal, coronal, and axial planes and the computed analysis with a specific software allowed for understanding the normal and abnormal airways and observing their pre- and postoperative changes with increased precision. CBCT combines high precision of images, fairly low exposure to radiation, lower cost, and improved accessibility, representing an excellent alternative for airway assessment, provided it follows the rigor of the method.
Considering the importance of the longitudinal study of airways for the surgical movements of maxillary bones with the CBCT standardized method and the lack of studies with adequate methodological protocols that follow the dimensional changes of airways for long periods, the present study assessed the stability of changes in the upper airways 4 years after orthognathic surgery to correct skeletal Class II malocclusion.
Material and methods
This study was approved by the Ethics Committee (#690121117.9.0000.5385). It was a retrospective and longitudinal clinical study performed with tomographic images from patients subjected to surgical orthodontic treatment for skeletal Class II malocclusion. The sample was calculated based on a previous pilot study, and 11 patients were required to achieve a test power higher than 80%, a significance level of 5%, and a large effect size (0.40).
From a sample universe of 23 patients, patients with skeletal Class II malocclusion (Wits appraisal >+3 mm) were selected. All patients were required to need orthognathic surgery with counterclockwise rotation of the maxillomandibular complex and mandibular advancement. The surgeries were performed in private hospital, under general anesthesia and following the same protocol. The surgery was performed between the years of 2011 and 2012 by the same team, headed by the same oral and maxillofacial surgeon, and it followed the same surgical and rigid internal fixation protocols. Orthognathic surgery was done using a standard Bilateral Sagittal Osteotomy and LeFort I osteotomies. The maxillomandibular advancement was performed with counterclockwise rotation and internal rigid fixation: the maxilla was stabilized with 4 bone plates and at least 4 2.0 mm-screws, and the sagittal split osteotomies were fixed with 1 or 2 bone plates in the body, followed by 2 or 3 bicortical positioning 2.0 mm bone screws in the retromolar region, on each side. , Patients with craniofacial anomalies and subjected to previous orthognathic surgeries were excluded. The final sample presented 11 patients, including 9 women and 2 men, with an average age of 35.91 years (±16.71).
CBCT examinations were performed in the Kodak 9500 3D Cone Beam Radiography System tomograph (Carestream Health, Rochester, NY) at the following times: before orthognathic surgery (initial preoperative period: classified as T1), intermediate postoperative period (6 months after surgery: classified as T2), and longitudinal follow-up (4 years after surgery: classified as T3). The work regime was of 85 kV, 6.3 mA, exposure time of 11.30 seconds, and extended field of view with voxel set at 0.30 mm.
During the examination, the volunteer was standing up in maximal habitual intercuspation. The Frankfort horizontal plane was parallel to the ground. The head direction was the same for each CBCT image taken by the same experienced operator. The patients were instructed to not swallow during the test. , The images were stored in the Digital Image and Communication in Medicine format and imported to the Dolphin Imaging software (version 11.9; Dolphin Imaging and Management Systems, Chatsworth, Calif) to visualize and manage the CBCT examinations.
The images were measured by only 1 blind examiner, , and the intraexaminer error was assessed by repeating all the measures 30 days after the first ones were taken. The method allowed for applying the reproducibility test and intraclass correlation analysis, indicating excellent values with correlation analysis ≥0.75.
Specific tools of the Dolphin Imaging software commanded the sagittal, coronal, and axial planes to correct potential head movements that might have occurred during the test, described as follows: Frankfort horizontal plane parallel to the axial plane, median sagittal plane matching the bone facial midline of the individual, and coronal plane passing by the lower margin of the right and left orbits. This enabled obtaining the correct head rotation so that bilateral structures matched. The airway analysis tool of the Sinus/Airway software was used to determine the volume (VOL), surface area (SA), and minimum axial area (MAA) of the pharyngeal airway space in the preoperative examinations and at the postoperative and longitudinal follow-up periods ( Fig 1 ). ,
The following anatomic limits were applied to perform the measurements described previously: upper limit—from the uppermost point of the axis tooth, a line is drawn parallel to the Frankfort plane up to beyond the airway dimensions; anterior limit—includes the anterior oropharyngeal wall (cutaneous tissues); lower limit—a line parallel to the Frankfort plane between the lower limit of the fourth vertebra up to the anterior oropharyngeal wall ; and posterior limit—a line extending from the edge of the axis tooth up to the lower limit of the fourth vertebra ( Fig 2 ).
After delimiting the measured area, the Add Seed Points tool allowed for taking measurements. Subsequently, the sensitivity of detection of the airway space was standardized at 25%, and then the Update Volume tool enabled measuring the volume of the delimited airway. After obtaining the volume, the MAA tool was activated, enabling achievement of the value of the most constricted area of the airway using 2 parallel lines: one in the uppermost airway and another in the lower limit ( Fig 3 ).
The measurements were taken twice for each region, and the means were used for the descriptive and exploratory analyses of the data. Analysis of variance was applied for the measures repeated at the times selected for the study, and Tukey’s test was used for the comparison between the times. Pearson’s correlation analyses were performed to assess the relationships of changes in SA, VOL, and MAA with the amount of advancement, counterclockwise rotation, and age of the patient. The analyses were performed in the SAS (SAS, Cary, NC) and R (R Foundation for Statistical Computing, Vienna, Austria) statistical software, at a 5% significance level.
According to the results, 4 years after orthognathic surgery, the upper airways presented means of SA and VOL of the airway space that were significantly higher than those observed before the surgery ( P <0.05). The means at 6 months were intermediate, with no significant difference before the surgery and 4 years after it ( P >0.05). The MAA did not show significant differences over time ( P >0.05) ( Table I ).
|Surface area, mm 2||730.50 (243.75) B||788.23 (240.04) AB||879.05 (278.42) A|
|Volume of the pharyngeal airway space, mm 3||16,404.14 (7902.41) B||18,261.68 (8058.06) AB||22,033.05 (11,010.12) A|
|Minimum axial area, mm 2||128.68 (93.40) A||142.86 (94.46) A||184.14 (103.47) A|