Three-dimensional pharyngeal airway space changes after bimaxillary advancement

ABSTRACT Introduction: The probability of improvement in the upper airway space (UAS) with orthognathic surgery should be considered during the surgical-orthodontic treatment decision, providing not only an esthetic, but also a functional benefit for the patient. Objective: The purpose of this study was to evaluate the 3D changes in the upper airway space after maxillomandibular advancement surgery (MMA). Methods: A retrospective analysis of 56 patients, 21 male and 35 female, with a mean age of 35.8 ± 10.7 years, who underwent MMA was performed. Pre- and postoperative cone-beam computed tomography scans (CBCT) were obtained for each patient, and the changes in the UAS were compared using Dolphin Imaging 11.7 software. Two parameters of the pharyngeal airway space (PAS) were measured: airway volume (AV) and minimum axial area (MAA). Paired t-test was used to compare the data between T0 and T1, at 5% significance level. Results: There was a statistically significant increase in the UAS. Bimaxillary advancement surgery increased the AV and the MAA, on average, by 73.6 ± 74.75% and 113.5 ± 123.87%, respectively. Conclusion: MMA surgery tends to cause significant increase in the UAS; however, this increase is largely variable.


INTRODUCTION
Harmonious facial esthetics and great functional occlusion have been recognized as the two most important goals of orthodontic treatment. For the correct indication of treatment, an accurate malocclusion and skeletal discrepancy diagnosis is needed. This care leads to adequate planning and multidisciplinary treatment with the objective of an esthetic and functional correction. 1 Dissatisfaction with facial esthetics is considered the most common motivating factor in the search for orthognathic surgery, since this is the procedure indicated in cases of severe dental and skeletal discrepancies in adult patients. 2 Airways effects caused by skeletal movements of the basal bones after orthognathic surgery are essential because they produce a change in the position of the hyoid bone and tongue. 3 Upper Airway Space (UAS) is formed by soft tissue structures: tonsils, soft palate, uvula, tongue and lateral pharyngeal wall.
The mandible and the hyoid bone are the main craniofacial bone structures that determine the airway size. Thus, the UAS anatomical conformation allows factors such as obesity, muscle hypotonicity and mandibular deficiency to favor the obstruction, generating Obstructive Sleep Apnea (OSA), which has been the subject of numerous studies. [4][5][6][7] Rocha TL, Lima L, Pinzan A, Sant'Ana E, Nogueira RLM, Bronfman CN, Janson G Three-dimensional pharyngeal airway space changes after bimaxillary advancement Changes in the upper airway space caused by orthognathic surgery have been a concern, because the quality of sleep can be increased or aggravated by these changes. The main concern involving these dimensional changes caused by orthognathic surgery is the sleep quality. 3,[9][10][11] Thus, the orthodontist should be aware of changes that may occur in the upper airway before proposing orthognathic surgery for patients. It is important to assess whether the patient with mandibular retrusion has associated symptoms of obstructive sleep apnea, such as obesity, excessive daytime sleepiness and snoring. The reason for this is that the Rocha TL, Lima L, Pinzan A, Sant'Ana E, Nogueira RLM, Bronfman CN, Janson G Three-dimensional pharyngeal airway space changes after bimaxillary advancement 6 possibility of improvement or not with orthognathic surgery should be considered during the decision for surgical orthodontic treatment, providing not only esthetic but also functional benefits for the patient. 3,9,12,13 Although there is clear evidence that bimaxillary advancement surgery can effectively increase the upper airway, 14,15 most studies have a limited number of patients. [16][17][18][19][20] Besides, they have not individually quantified the amount and percentages of upper air volume and minimum axial area increase. Therefore, the purpose of this study is to evaluate, in 3D images, the changes in the pharyngeal airway space (PAS) in skeletal Class I or Class II malocclusion patients, submitted to bimaxillary advancement surgery using bilateral sagittal split osteotomy for mandibular advancement, associated with maxillary advancement with Le Fort I maxillary osteotomy.   Male) as subgroups were performed with Mann-Whitney U tests.

MATERIAL AND METHODS
The statistical analyses were performed with Statistica software (Statistica 7, StatSoft Inc., Tulsa, OK). Results were considered significant at p < 0.05.

RESULTS
The random errors were within acceptable limits 24,25 (AV = 686.48mm 3 ; MAA = 0.21mm 2 ), and there was no significant systematic error for both variables (p-values were 0.155 and 0.468 for AV and MAA, respectively).
There were significant increases in volume and minimum axial area in the airways after surgery ( Table 2). The mean percent- The amount of maxillary and mandibular advancement did not show significant influence on the airway volume and minimum axial area (Table 3).
Rocha TL, Lima L, Pinzan A, Sant'Ana E, Nogueira RLM, Bronfman CN, Janson G Three-dimensional pharyngeal airway space changes after bimaxillary advancement  Similar airway volume and minimum axial area changes were observed between skeletal Class I and Class II, and between female and male patients (Tables 4 and 5).     in exposing patients to unnecessary radiation. 14 The most common period of follow-up was 6 months. 3,9 Patients in the present sample had a mean mandibular advance- for volumetric measurements, as performed in other studies. [31][32][33] Hyoid bone and PNS were used because they are hard tissues, which consist of more precise and consistent form of identification, compared to soft tissue palate and epiglottis, which could vary after surgery. 25,30,34 The different measurements adopted by the authors to evaluate the oropharyngeal airway changes make it impossible to compare all studies among themselves, regardless of the type of surgery adopted. 3,14 PNS was used as the airway limit for volumetric measurements, as in most studies. 25,32,33,35 Small variations in the anatomical limits and calibration and training of examiners did not seem to have great influence on the results. 14,26 The present study evaluated only the changes in the oropharyngeal region, due to the difficulty of evaluating the nasopharyngeal region. In a study evaluating the reliability and accuracy of airway measurement in three dimensions of three different software, the authors observed a precision discrepancy in the volume quantification between the different evaluated software. According to them, the nasopharyngeal volume evaluation was more challenging and showed lower reliability, due to the presence of some anatomical structures (turbinate and the concha region) that create intricate anatomy. 35 For the oropharyngeal evaluation, there was a smaller difference in the results found in different software. 9 Dolphin 3D software was used because it showed high accuracy and reliability for the volumetric assessment of airspace in previous studies, and was therefore used in this study. 9, 26,35,36 This software provides greater accuracy because it is a tool for inclusion of reference points in the images, which allows quantification control of volume limits, with few errors (1%). 35,36 Variations in the soft palate and tongue positions between pre-and post-surgical exams may significantly influence the outcome of this variable. 26 Thus, patients who presented visible differences in the position of these structures in T 0 and T 1 periods were excluded from the sample.
The literature shows that there is no difference in the upper airway when comparing patients with Class I and Class II malocclusion, unlike the patient with Class III malocclusion. 37 In the present study, there was significant increase in the airway volume and minimum axial area in almost all patients, regardless of sex and sagittal relationship (Tables 2, 3 and 4). These variables were analyzed to indirectly contribute to the surgical treatment of patients with OSA. Many surgical treatments used for patients with OSA, such as turbinectomies, uvulopalatopharyngoplasty, and reduction glossectomies, are associated with low success rates, between 17% and 40%, when performed alone, because they act only on the airway obstruction. [38][39][40][41][42] Bimaxillary advancement has the benefit of optimizing airway gain, increasing success rate in OSA treatment, and correcting the patients' dentofacial and esthetic deformities. 43,44 Although a retrusive craniofacial profile is predictive of OSA, there is still controversy among authors. 45,46 Comparisons performed at the preoperative stage between OSA patients and control patients without OSA showed significant less volume in the OSA group, as expected. Nevertheless, the control group without OSA had relatively (but not statistically significant) more bimaxillary retrusion, when compared with the OSA group, indicating that the craniofacial profile may not reliably predict the presence of OSA. 19 In this research, bimaxillary advancement surgery provided significant volumetric increases in the upper airways, as well as in the minimal axial area, corroborating with the literature. 13,18 After assessing the airway morphological changes, the bimaxillary advancement leads to airway increase in all dimensions, anteroposterior or latero-medial. 25,26,47,48 Another study observed statistically significant increases in all airway dimensions in the analysis of minimal axial area and volume, 9 and in the oropharyngeal airway at the soft palate level. 3 Some studies have evaluated the effects of single-jaw orthognathic procedures on the upper airways, and have also found significant increases in upper airway volume. 17,49,50 There was no volumetric gain in the oropharyngeal region in only one patient of the sample (Table 5). This can occur because bimaxillary advancement causes an increase in airway width, Rocha TL, Lima L, Pinzan A, Sant'Ana E, Nogueira RLM, Bronfman CN, Janson G Three-dimensional pharyngeal airway space changes after bimaxillary advancement decreasing its constriction and air passage resistance, and may lead to a decrease in height in this area. 47 In the current study, nine patients had MAA values below 67mm², and presented a postoperative mean gain of 143.26% (Table 5). There is a statistically significant relationship between the narrower cross section of the upper airway and the OSA probability. Small airway area of about 40 to 67mm² is associated with OSA, 30 so the patients in this sample left the range of predisposition to OSA.
In this research, the minimum axial area and volume presented considerable gains. One study concluded that the airway resistance decrease after this type of surgery was secondary to a shorter and wider area. 16 Poiseuille's law demonstrates that as the radius of a tube (or an airway) increases and height decreases, there is a resulting significant decrease in airway resistance. 16,51 Based on this evidence, it could be thought that increasing the surface area due to increases in anteroposterior and transverse dimensions could lead to a decrease in airway resistance. Despite this outcome, four patients presented a decrease in MAA (Table 6); yet, still maintaining normal values. Individual anatomical changes and soft tissue adaptations (hyoid bone position, pharyngeal airway space narrowing and tongue position) may justify this decrease. 30,52,53 Due to a representative number of patients, it was possible to ascertain that bimaxillary advancement actually produces significant increase in the UAS regardless of sex and skeletal sagittal relationship, and to individually quantify the amount and percentages of AV and MAA increases. As a result, balance between function restoration and esthetic optimization is extremely important in the treatment of these types of patients.

LIMITATIONS
The main limitation of this retrospective study was the great variability in the amount of maxillary and mandibular vertical and horizontal surgical displacements, due to including skeletal Class I and Class II malocclusions patients.

CONCLUSIONS
Bimaxillary advancement surgery to correct skeletal Class I and Class II malocclusions had a tendency to produce significant increase in the UAS (AV and MAA).

AP.
The authors report no commercial, proprietary or financial interest in the products or companies described in this article.