Surgically assisted rapid maxillary expansion has been used for the treatment of transverse maxillary deficiency. This prospective study aimed to evaluate the effect of this surgery (with or without pterygomaxillary disjunction) on the upper airway volume. The patients were randomly divided into two groups: without pterygomaxillary disjunction (−PD) and with pterygomaxillary disjunction (+PD). Eleven patients per group were estimated to obtain a representative sample (90% of power and 95% of confidence level). Volumetric images of cone beam computed tomography scans were obtained preoperatively, immediately after Hyrax screw stabilization and 6 months after Hyrax screw stabilization. Volumetric measurements of the nasal cavity, maxillary sinuses, nasopharynx, and oropharynx, and of the minimum oropharynx cross-sectional area were obtained using Dolphin 3D Imaging Software. The final sample consisted of 25 adult individuals (+PD group, n = 12; −PD group, n = 13). In the +PD group, we observed a statistically significant increase immediately after Hyrax screw stabilization for the nasopharynx volume ( P = 0.003), oropharynx volume ( P = 0.007) and oropharynx cross-sectional area ( P = 0.001). Pterygomaxillary disjunction resulted in a significant ( P < 0.05) increase in volumetric measurements of the nasopharynx and minimum oropharynx cross-sectional area 6 months after the expander device stabilization.
Dentofacial deformities can lead to changes restricted to the maxilla, mandible, or reach both jaws. When they take place, they can occur in the vertical, horizontal, and transverse facial planes . From the facial deformities that affect the middle third, the transverse maxillary compression is the most prevalent one , and it can occur alone or linked to other skeletal changes . Such a condition is characterized by the presence of skeletal constriction of the palate, dental crowding, dental rotations, and unilateral or bilateral posterior crossbite, with deficit in the arc perimeter. It is usually associated with nasal breathing difficulties, hypertrophy of adenoids, mouth breathing, and middle ear diseases .
The treatment of this condition was initially described by Angell , in 1860, and was reintroduced 100 years later by Hass . It advocated the expansion of the median palatine suture by orthopaedic devices . The procedure was called rapid maxillary expansion (RME) .
Surgically assisted rapid maxillary expansions (SARMEs) are performed by osteotomies involving the areas of bone strength of the facial skeleton, such as the median palatine suture, the zygomatic pillars and the piriform aperture. Despite being considered a resistance area, the pterygomaxillaries junctions may or may not be separated during SARME . Such separation, when associated with the other osteotomies, allows a greater maxillary posterior expansion . Sygouros et al. concluded that non-performing pterygomaxillary disjunction (PD) can result in greater risks to the periodontium and to the maxillary bone. Laudemann et al. recommended PD in patients above 20 years old.
In 2016, Buck et al. conducted a meta-analysis to assess the influence of SARME in the upper airway. The authors observed a substantial volumetric increase in the nasal cavity in the short term and a weak evidence of absence of effect on the oropharynx volume. They warned about the high risk of biases in many articles and stated that SARME must not be indicated to breathing gain.
Periago et al. compared the accuracy of cephalometric measurements carried out directly on human skulls with those obtained using 3D volumetric reconstructions by cone beam computed tomography (CBCT), employing Dolphin Imaging software (version 2.3; Dolphin Imaging Management Solutions, Chatsworth, CA, USA). They concluded that the data obtained could present statistically significant differences in anatomical dimensions, although the software was accurate for clinical use (−1.13 ± 1.47%) on craniofacial analysis.
El and Palomo , when studying the use of software in 3D measurement of airways, concluded that the Dolphin Imaging 3D (version 11, Dolphin Imaging Management Solutions) presented low accuracy but a high level of confidence and high correlation of results with other software.
Abramson et al. conducted a study with the aim of evaluating the anatomy of the upper airways three-dimensionally. To do so, they compared the cephalometric findings with data obtained from computed tomography (CT) images, employing 3D Slicer software. The following parameters were considered: volume, surface area, length, average cross-section area, minimum retroglossal area, minimum retropalatal area and minimum cross-section area. The authors concluded that the measures obtained by cephalometry and by using the software from images obtained by CT were reliable and reproducible. They also concluded that the measure of the posterior airway space was the only one that showed correlation with the parameters obtained by CT.
Given the absence of studies that assess the influence of pterygomaxillary disjunction in the airways and based on the hypothesis that the changes resulting from SARME can result in dimensional changes in the upper airways, the aim of this study was to test the hypothesis that the performance of pterygomaxillary disjunction associated with SARME promotes an increase in the volume of the upper airways.
Materials and methods
Outline of the study and participants
This is a clinical, prospective, unicentric, randomized and double-blind test, approved by the Research Ethics Committee (Protocol no. 064.06.11), in accordance with the Helsinki Protocol. All patients gave free and informed consent. The study was conducted with patients of both sexes, aged between 18 and 45 years, with skeletal transverse maxillary deficiency superior to 5 mm, unilateral or bilateral skeletal crossbite, without active periodontal disease or tooth mobility in the teeth considered as pillars for fixing the Hyrax screw, and needing SARME under general anaesthesia. We excluded patients who were syndromic, smokers, with a history of facial middle third fractures, with chronic systemic diseases, or using medications with influence on the bone metabolism, as well as patients with tumours or acute diseases in airways viewed by nasofibroscopy (J.L.B., otolaryngologist collaborator) and CT. In addition, patients who did not return for the revaluations were removed from this study.
All patients went submitted to SARME under general anaesthesia, and were operated by the same team of oral and maxillofacial surgeons (E.C.S.S. and J.R.M.). The operative technique consisted of osteotomy type Le Fort I, using no. 703 drills, without promoting the lowering of the maxilla, in addition to the use of osteotomy in midline with drill no. 701, and a chisel and hammer. One group (+PD) had surgical pterygomaxillary disjunction but the other group (−PD) did not. The Hyrax screw was activated in the perioperative period until the maximum opening and emergence of diastema; then it was disabled, with a permanent four-quarters of a turn .
The progressive Hyrax screw activations were initiated 6 days after the surgical procedures, following a value of 0.5 mm/day and a rate of one-quarter of a turn of the screw, twice a day. After the total uncrossing of the bite with overcorrection, the devices were stabilized for 6 months using a 0.25-mm ligature wire .
Assessment of outcomes
The primary outcome adopted for this study was the increase in the upper airways volume, and the secondary outcome was the increase in the oropharynx cross-sectional area.
For the measurement of outcomes, all patients underwent tests by cone beam CT using an i-CAT device (Imaging Sciences International, Hatfield, PA, USA) with the following parameters: 3–8 mA, 120 kVp, field of view 22 × 16 cm, and voxel 0.4 mm. The tests had a field of view comprising the glabella to the fourth cervical vertebra (vertical) and from the acoustic meatus to point A (horizontal). The tomographic tests were performed with the patients in a natural head position, with the tongue resting on the palate, avoiding breathing or swallowing during the examination. The patients underwent CT at three times: preoperative (T1), after the activation period post-SARME, which was verified with the total uncrossing of the bite with overcorrection (T2), and after 6 months of Hyrax screw stabilization (T3). The DICOM (Digital Imaging and Communications in Medicine) files obtained in each test were imported to the Dolphin Imaging 3D software, version 11.5 (Dolphin Imaging & Management Solutions); measurements were taken blindly, by a dental surgeon collaborator and imaging specialist (C.R.A.A.). Two measurements of each CT were carried out, with an interval of 15 days, of each volume and area of interest.
We obtained the nasal cavity volume (NCV), the right (RMSV) and left (LMSV) maxillary sinus volume, the nasopharynx volume (NPV), the oropharynx volume (OPV), and the oropharynx minimum cross-sectional area (OMCSA). Volumetric measures were given in cubic millimetres (mm 3 ) and area measures in square millimetres (mm 2 ). Before greyscale variation was found in the images, we adopted a sensitivity (slice airway sensitivity) of 25 for the establishment of the airway space. The limits (boundaries) of each measure were defined and standardized according to Table 1 . The process of generating volumes and OMCSA can be seen in Fig. 1 .
|Region||Anterior limit||Posterior limit||Superior limit||Inferior limit|
|Nasal cavity||Line that connects point N to point A, in the MSP||Line that connects point S to the posterior nasal spine, in the MSP||Line that connects point S to point N, in the MSP||Line that connects the anterior nasal spine to point S, in the MSP|
|Based on the more anterior sagittal plane of the lateral wall of the right orbit, the nasal cavity was also delineated in the coronal plane|
|Maxillary sinuses||Based on the more anterior sagittal and coronal planes of the lateral wall of the right orbit, the maxillary sinuses were delineated individually. They were also delineated individually on the axial plane, coincident with the Frankfort plane|
|Nasopharynx||Line that connects the posterior nasal spine to point S, in the MSP||Line that connects point S to the more superior point of the Atlas, in the MSP||–||Line that connects the more superior point of the Atlas to the posterior nasal spine, in the MSP|
|Oropharynx||Line that connects the posterior nasal spine to the more superior and posterior point of the hyoid bone, in the MSP||Line that connects the more inferior and anterior point of the C3 to the more superior point of the body of the Atlas, in the MSP||Line that connects the more superior point of the body of the Atlas to the posterior nasal spine, in the MSP||Line that connects the more superior and posterior point of the hyoid bone to the more inferior and anterior point of the C3, in the MSP|