Airway changes in patients with unilateral cleft lip/palate (UCL/P) after maxillary advancement

Cleft lip and palate (CL/P) is the most common craniofacial congenital malformation, with an occurrence of approximately 1 in 1000 infants in the United States.¹  A fusion defect limited to the nasal processes is considered a cleft lip (CL), while a cleft palate (CP) is defined as a fusion defect of the palatal shelves. These conditions occur together in approximately 45% of cases, CP only in 30%, and CL only in 25%.²  The congenital condition has a multifactorial etiology and disrupts the function of the stomatognathic system and dentofacial esthetics. The characteristic presentations of CL/P include a retrognathic and posteriorly inclined maxilla, greater flattening of the cranial base, a larger mandibular plane and gonial angle, larger anterior facial height, and decreased posterior facial height.³ 

The structural abnormalities of the dentofacial complex in combination with the dysfunction of muscles controlling the soft palate place patients with CL/P at high risk for sleep-disordered breathing.⁴  Patients from this population have been shown to have more complaints of respiratory difficulties and snoring during sleep compared with control populations.^5,6  Other studies reported that patients who experience CL/P had an increased frequency of hypopnea and mouth breathing during sleep.^7,8  Respiratory difficulties increase the risk for hypertension, excessive sleepiness during the daytime, and cardiovascular and cerebrovascular diseases.⁹  For these reasons, the study of the pharyngeal airway space (PAS) in patients affected by CL/P has the potential to improve patient treatment outcomes.

Patients with CL/P often require correction of various forms of malocclusion, especially a Class III skeletal malocclusion due to maxillary deficiency. Treatment involves a combination of orthodontics and orthognathic surgery to achieve optimal results. After presurgical orthodontics is complete, a Le Fort I osteotomy with advancement of the maxilla is commonly indicated. Orthognathic surgery not only improves occlusion and facial balance but can also provide the further benefit of enlarging the patient's airway. However, the literature is limited regarding the effects on the airway after single jaw surgery in this patient population. Yatabe-Ioshida et al.¹⁰  reported an upper airway increase in patients with CL/P after orthognathic surgery using cone-beam computed tomography (CBCT) scan data. However, only nine subjects were included in the CL/P group, and two different surgical procedures were involved: maxillary advancement and mandibular setback together and maxillary advancement only. To further study the effects of maxillary advancement surgery on the airway in UCL/P patients, the effects of maxillary advancement surgery on the retropalatal airway (RPA), retroglossal airway (RGA), total airway (TA) volumes, and cephalometrics (SNA, SNB, ANB, PP-SN, Occl-SN, N-A, A-TVL, B-TVL) were assessed in patients with UCL/P using data from CBCT scans. The null hypothesis was that there would be no statistically significant change for each of the parameters of airway and cephalometrics in this study.

This retrospective study protected the rights of human subjects and was approved by the Marquette University Institutional Review Board for research under the jurisdiction of the university (HR-3485). The inclusion criteria were patients with unilateral cleft lip and palate (UCL/P), skeletal Class III malocclusion, treated with a Le Fort I maxillary advancement only, and perioperative CBCT scans. Exclusion criteria were patients with additional orthognathic surgeries (ie, bilateral sagittal split osteotomy and genioplasty). Presurgical and postsurgical orthodontic treatment was provided by various providers, although a team of experienced surgeons at Shriners Hospitals for Children, Chicago, was responsible for all maxillary advancement operations.

A power analysis for a one-tailed paired-samples t-test indicated that the minimum sample size to yield a statistical power of at least .8 with an alpha of .05 and a medium effect size (d = 0.5) was 30 (G*power, Düsseldorf, Germany).

The CBCT scans of 30 patients (13 males and 17 females, 17–20 years old) were evaluated at two time points: preoperative (T1) and postoperative (T2). The interval between T1 and T2 ranged from 9–14 weeks, except for two patients in whom the interval was 24 weeks. All CBCT scan images were previously obtained for surgical planning and treatment outcome purposes using an i-CAT Next Generation scanner (Imaging Science International Inc., Hatfield, Penn). All scans were taken using the following clinical protocol; field of view at least 16 × 13 cm, exposure time of 26.9 seconds, 120-kV tube voltage, 5-mA tube current, and a 0.3-mm³ voxel size.

The CBCT image files were exported in Digital Imaging and Communication in Medicine format into Dolphin Imaging software version 11.95 Premium (Dolphin Imaging & Management Solutions, Chatsworth, Calif). Each three-dimensional (3D) image was spatially oriented in Dolphin through a standardized protocol. The axial plane was positioned coincidently with the Frankfort horizontal plane (FP), and then the midsagittal plane was aligned perpendicular to the FP while passing through nasion. In patients with an asymmetry, the orientation was set so that these planes were as close to the original plane orientation as possible.¹¹  Once the image was properly oriented, a lateral cephalometric image at the midsagittal plane was created using the “Build X-Rays” tool in Dolphin. The lateral cephalogram for each time point was traced using the “Digitize” tool and the following angles: SNA, SNB, ANB, palatal plane–SN (PP-SN), occlusal plane–SN (Occl-SN). Distances nasion–A point (N-A), A-true vertical line (A-TVL), and B-true vertical line (B-TVL), were recorded (Figures 1 and 2). For A-TVL and B-TVL distances, when the A or B point was distal/posterior to TVL, the distance value was defined as negative, while it was positive when the point was mesial/anterior to TVL.

To evaluate the volume (mm³) of the RPA, RGA, and TA (Figures 3 and 4), the Dolphin sinus/airway tool was used to outline the areas of interest and calculate the airway space and respective minimum cross-sectional areas (MCAs). First, the boundaries were traced using a protocol outlined by Chang et al.¹²  The superior border of the PAS, in this study, was the variable TA and was defined as the line connecting the posterior nasal spine to basion. The inferior border of the PAS was defined as a horizontal line passing through the most superior point of the epiglottis. The PAS was divided into the superior portion (the RPA) and the inferior portion (the RGA). The line differentiating these segments was defined as a horizontal line through the most posteroinferior point of the soft palate.

Within the defined boundaries, a seed point was placed with a standardized threshold value of 55 Hounsfield units. The MCA was the smallest cross-sectional area of each segment, in square millimeters, for the RPA, RGA, and TA—in other words, the area of greatest PAS constriction.

The measurements of the RPA, RGA, TA volumes, and cephalometrics (SNA, SNB, ANB, PP-SN, Occl-SN, N-A, A-TVL, B-TVL) were analyzed using a paired t-test to compare between T1 and T2. SPSS statistical software (SPSS Statistics 28.0.0.0, IBM, Armonk, NY) was used for all statistical analyses. Data were expressed as means ± standard deviations, with a P value of .05 considered significant. In addition, one patient was randomly selected to be reevaluated by the same investigator. Each measurement was performed three times at 1-week intervals to evaluate intraexaminer reliability using the intraclass correlation coefficient test (Table 1).

Significant changes were observed in all measured cephalometric measurements except for SNB (Table 2). Increased values were found in the PP-SN, SNA, ANB, Occl-SN, N-A, and B-TVL measurements. A point in reference to TVL moved significantly anteriorly (from –3.9 ± 5.0 to 1.5 ± 5.3, P = .000), indicating the A point moved anteriorly about 5.4 mm on average after maxillary advancement. The cephalometric measurements showing the largest and most significant changes were SNA (from 74.6 ± 5.5 to 80.3 ± 5.4, P = .000), ANB (from –0.6 ± 15.3 to 2.6 ± 2.3, P = .000), and A-TVL (from –3.9 ± 5.0 to 1.5 ± 5.3, P = .000; Figure 5).

The volumetric changes increased significantly in each studied area: RPA (from 9574 ± 4573 to 10,472 ± 4767, P = .019), RGA (from 9736 ± 5314 to 11,358 ± 6588, P = .019), and TA (from 19,121 ± 8480 to 21,750 ± 10,078, P = .002) (Figure 6). For the corresponding MCAs, only the RPAm increased significantly (from 173 ± 115 to 272 ± 129, P = .002), and the RGAm and TAm had no or inconsequential changes. In the sagittal plane, the area in mm² of the RGAs (from 385 ± 134 to 427 ± 165, P = .020) and TAs (from 730 ± 213 to 772 ± 238, P = .016) showed significant changes, and the RPAs had no increase (Table 3).

Several studies already observed that a Le Fort I osteotomy with maxillary advancement created an increase in the nasopharyngeal and upper airway sagittal dimensions. Cakirer et al.¹³  analyzed the sagittal airway changes after maxillary advancement in patients with UCL/P. The study found significant increases in the nasopharyngeal airway and no changes in the oropharyngeal airway. In another study involving patients with UCL/P, Baez et al.¹⁴  also observed increases in the upper airway after maxillary advancement. However, in those studies, radiographic assessment was performed using lateral cephalograms. Lateral cephalograms are limited in the fact that they produce a static, two-dimensional (2D) image that cannot satisfactorily portray the 3D volumetric airway space.¹⁵  Major et al.¹⁶  found a weak correlation between linear 2D measurements and identifying airway restrictions. The study suggested that 2D cephalograms should be used only as a screening tool for airway obstruction. The Baez et al.¹⁴  study also recommended future research in patients with UCL/P to analyze airway changes using the airway volume capabilities of cone-beam technology.

It is important to note that the CBCT scans used for this research were performed as part of the standard of care for patients undergoing orthognathic surgery. Since its introduction into dentistry in 1997, CBCT has become an increasingly important source of 3D volumetric information for orthodontic diagnosis, surgical treatment planning, and research.¹⁷  However, it is important to ensure that the additional information garnered from CBCT is able to meaningfully aid in diagnosis, treatment planning, or for assessing progress during treatment.¹⁸  Kapila and Nervina¹⁹  confirmed that CBCT was indicated for CL/P and orthognathic surgery patients, as the CBCT data are likely to improve patient outcomes. Another benefit of CBCT is that lateral cephalograms and panoramic radiographs can be generated from the scan and used for traditional purposes, including cephalometric tracing. Cephalometric analysis allows for a quantitative assessment of the extent of the dentofacial deformity and provides valuable surgical planning information.²⁰ 

Using the 3D power of CBCT, the current study found significant changes in airway volume, sagittal area, and MCA after maxillary advancement. For the volume measurements, the RPA (P = .019), RGA (P = .019), and TA (P = .002) increased significantly. These findings were in agreement with another CBCT study conducted by Yatabe-Ioshida et al.,¹⁰  which reported an upper airway increase in patients with CL/P after orthognathic surgery. However, only nine subjects were included in the CL/P group, and two different surgical procedures were involved: maxillary advancement and mandibular setback together, and maxillary advancement only.

The sagittal airway area showed significant increases in the RGAs and TAs and no increase in the RPAs. The sagittal airway changes (RPAs, RGAs, TAs) were the smallest compared with the other dimensional changes measured. It seems that maxillary advancement moves the maxilla forward skeletally, but the effect on the airway is in the volume increase rather than the sagittal dimension of the airway. This finding, in a way, reflects the complex nature of airway changes in response to maxillary advancement.

The minimum cross-sectional airway had a significant change in the RPA. The MCA of the RGA and TA was essentially unaffected by maxillary advancement. This suggested that the MCA of the PAS in most patients was located in the area defined as the RGA. A similar study also found an increase in the lower airway MCA after orthognathic surgery (Yamashita et al.¹¹), although that group used data from combination surgeries (maxillary advancement and mandibular setback, maxillomandibular advancement).

Predictably, significant changes were found in all measured cephalometric measurements except for SNB. SNB represents the relative anteroposterior position of the mandible to the cranial base. The lack of significant change in SNB was expected since the surgical operation was performed only on the maxilla. Therefore, the only appreciable change was observed in data focused on the upper jaw.

An interesting finding was that the B-TVL (distance in millimeters from the B point perpendicular to the true vertical line) was increased after maxillary advancement. This may have been because the maxilla was moved downward during advancement, which was also reflected in the palatal plane to SN angle and the occlusal plane to angle increases, leading to a clockwise rotation of the mandible.

In analyzing pre- and postoperative CBCT images, we investigated the effects of single jaw surgery maxillary advancement on airway and cephalometric measurements in patients with UCL/P. The results were largely expected. Significant increases in the RPA, RGA, and TA volume were observed, along with significant changes in most cephalometric measurements. This research showed that performing a Le Fort I maxillary advancement in patients with UCL/P can improve PAS. However, because of the nature of the unilateral cleft, further studies are needed to answer whether the airway responses to maxillary advancement are symmetrical or asymmetrical, as well as for long-term follow-up.

• Maxillary advancement single jaw surgery successfully corrects the midface deficiency in UCL/P patients.

• Based on the data, the null hypotheses were rejected. Maxillary advancement produces statistically significant increases in the retropalatal (volumetric and MCA), retroglossal (volumetric and sagittal), and total (volumetric and sagittal) airways.