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Volume 12 No. 11
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Scientific Investigations

Surgical Maxillary Advancement Increases Upper Airway Volume in Skeletal Class III Patients: A Cone Beam Computed Tomography-Based Study

Henrique Damian Rosário, DDs, MSc, PhD1; Bruno Gomes de Oliveira, DDS2; Daniela Daufenback Pompeo, DDS, MSc, PhD3; Paulo Henrique Luiz de Freitas, DDS, PhD4; Luiz Renato Paranhos, DDS, PhD4
1Department of Orthodontics, UNISUL, Tubarão, SC, Brazil; 2Graduate Program in Dentistry, Federal University of Sergipe at Aracaju, SE, Brazil; 3Department of Dental Radiology, UNISUL, Tubarão, SC, Brazil; 4Department of Dentistry, Federal University of Sergipe at Lagarto, SE, Brazil

ABSTRACT

Study Objectives:

Although volumetric changes of the upper airway occur following surgical advancement of the maxilla, few studies investigated these changes using three-dimensional imaging techniques. Thus, the goal of this study was to verify whether the surgical advancement of the maxilla affects the volume of the upper airway and to determine any association of these volume changes with sex and age.

Methods:

Preoperative and postoperative cone-beam computed tomography (CBCT) scans of 14 patients (8 male and 6 female) who underwent maxillary advancement to correct skeletal class III deformities were assessed to determine the postoperative volumetric changes in the upper airway. Preoperative and postoperative airway volume measurements were compared by means of paired t-test, which was also used to compare airway volume between genders. Pearson correlation coefficient was used to verify whether a correlation between age and upper airway volume was present.

Results:

Maxillary advancement produced significant upper airway volume increases (mean 20.94%, p < 0.05) on nearly half of our sample. However, sex and age did not seem to influence upper airway volume in our sample of skeletal class III patients.

Conclusions:

Surgical advancement of the maxilla may produce significant volume increases in the upper airway of skeletal class III patients regardless of sex and age.

Citation:

Rosário HD, de Oliveira BG, Pompeo DD, de Freitas PH, Paranhos LR. Surgical maxillary advancement increases upper airway volume in skeletal class III patients: a cone beam computed tomography-based study. J Clin Sleep Med 2016;12(11):1527–1533.


INTRODUCTION

For decades, the profile cephalogram was the only imaging modality of use for the perioperative airway evaluation of orthognathic patients.13 However, as with any bidimensional (2D) representations of three-dimensional (3D) objects, radiographs are imprecise in terms of portraying overlapping structures, especially in complex anatomical regions such as the head and neck.4

In light of those disadvantages, the use of cone-beam computed tomography (CBCT) has been on the rise since the 1990s for the perioperative assessment of the upper airway in orthognathic surgery. The rationale behind this shift was that CBCT offered better visualization of the anatomic structures and allowed for more accurate 3D linear and volumetric measurements.5 More importantly, image segmentation of the upper airway became possible, which enabled proper 3D image reconstruction and volume calculation.6

The concern about the airway in the context of planning for orthognathic surgery grew strong as awareness of obstructive sleep apnea (OSA) increased. Indeed, maxillary advancement is a useful procedure for treating OSA patients because it enlarges the pharynx in terms of volume, which in turn decreases the resistance to inspiratory airflow.7 Although it has been reported that the oropharynx and the retropalatal and retroglossal regions are blocked during sleep apnea, the real contribution of maxillary advancement to address these blockades is not completely understood.2,8,9

BRIEF SUMMARY

Current Knowledge/Study Rationale: To date, few studies investigated the volumetric changes of the upper airway that occur following surgical advancement of the maxilla by means of three-dimensional imaging techniques. This study used cone-beam computed tomography to verify whether surgical advancement of the maxilla affects upper airway volume and to determine associations of any existing volume changes with sex and age.

Study Impact: By showing that maxillary advancement resulted in significant volumetric increase of the upper airway in nearly half the study's subjects, our results strengthen the role of isolated maxillary advancement as a fair alternative for the treatment of skeletal class III patients with OSA.

Orthognathic surgery is the standard of care in the correction of moderate and severe dentofacial deformities.10 Techniques such as maxillary advancement, surgical posterior repositioning of the mandible, or even a combination of both procedures might be used to treat patients with skeletal class III deformities depending on the type of the deformity.11 Although these patients often have large pharyngeal spaces, surgical backward movement of the mandible may displace the tongue in a posterior direction, which is not a desirable surgical outcome.12 If the tongue moves posteriorly, its contact surface with the soft palate increases, reducing the pharyngeal airway.13 This anatomic alteration may induce sleep breathing disorders, which are relatively common in skeletal class II patients.5,14

Considering all the aforementioned factors, this study attempted to determine whether maxillary advancement alone promotes an enlargement of the upper airway in patients with skeletal class III suffering with or at risk of the development of OSA, as well as to determine any association of these volume changes with sex and age.

METHODS

Ethical Aspects

The Ethics in Research with Human Beings Committee of Sagrado Coração University, Bauru, São Paulo, Brazil, approved this study without restrictions (protocol #19796213.0.0000.5502).

Study Design, Sample, and Surgical Procedures

This was an observational analytical study based on data from 28 CBCT scans obtained from a sample of 14 Brazilian patients (8 males and 6 females) with Caucasian background who underwent maxillary advancement for the treatment of skeletal class III deformities (mean age 27.7 y). Patients with history of facial trauma or previous facial surgeries were excluded, as well as patients with cleft lip and palate or uncontrolled systemic diseases. One maxillofacial surgeon performed all surgical procedures.

Image Acquisition

One pair (one preoperative and one postoperative) of CBCT scans (one preoperative and one postoperative) was acquired for each patient. All patients underwent total CBCT scans of the head at least 5 days before orthognathic surgery for treatment planning. Follow-up CBCT scans were performed 10 to 18 w after surgery. Images were acquired with the same imaging device and protocol (ICat Vision, Imaging Sciences International, Hatfield, PA, USA; 120 kVp, 37 mAs, acquisition time 14.7 sec, voxel 0.2, power settings 12Vdc, 20 mA, 220V∼ 5A) and overseen by the same operator in a private radiology clinic. Head and cervical posture was standardized as described by Muto et al.,15 whereby patients should be seated, maintain a steady head position, and refrain from swallowing during scanning. In addition, the laser beams of the scanning device ensured that the head was positioned so that Frankfurt horizontal plane was parallel to the ground and the facial midline coincided with the vertical laser beam.

Handling of Image Data

CBCT data were reconstructed as DICOM (Digital Imaging and Communication in Medicine) files. The data were digitally stored and analyzed using the OsiriX software (version 5.8 64-bit, Pixmeo, Geneva, Switzerland).

All measurements were taken by one of the authors, who is a trained dental radiologist. Preoperative measurements were reassessed after 15 days to determine the degree of systematic error. According to the instructions of Panou et al.,10 clear delimitation of the pharyngeal space in the sagittal view was procured as follows:

  • the upper limit included the glandular soft palate, the region above the adenoid pad and the choanae, representing the roof of the nasopharynx (Figure 1A, a);

  • the anterior limit was defined as a plane perpendicular to the sella-nasion line passing through the point of transition between the hard and the soft palate (Figure 1A, b);

  • the inferior limit was a horizontal plane passing through the most anterior and inferior point of C3 (Figure 1A, c); and

  • the posterior limit was a plane perpendicular to the sella-nasion tangential to the posterior pharyngeal wall (Figure 1A, d).

Figure 1B and 1C show the corresponding limits in the axial and coronal views, respectively.

(A) Delimitation of the pharyngeal space in the sagittal view: the upper limit includes the glandular soft palate, the region above the adenoid pad and the choanae, representing the roof of the nasopharynx (a), the anterior limit is defined as a plane perpendicular to the sella-nasion line passing through the point of transition between the hard and the soft palate (b), the inferior limit was a horizontal plane passing from the most anterior and inferior point of C3 (c), and the posterior limit was a plane perpendicular to the sella-nasion tangential to the posterior pharyngeal wall (d). (B) and (C) show the corresponding limits in the axial and coronal views, respectively.

jcsm.12.11.1527a.jpg

jcsm.12.11.1527a.jpg
Figure 1

(A) Delimitation of the pharyngeal space in the sagittal view: the upper limit includes the glandular soft palate...

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After rough delimitation, a new DICOM image was created to enable finer delimitation of the pharyngeal contour, slice by slice, in increments of 2 mm (Figure 2). Then, a 3D image was reconstructed to allow volumetric calculation of the pharyngeal air space (Figure 3).

Sagittal (A) and axial (B) views of the DICOM image in 2-mm increments, which enables finer delimitation of the pharyngeal contour (C).

jcsm.12.11.1527b.jpg

jcsm.12.11.1527b.jpg
Figure 2

Sagittal (A) and axial (B) views of the DICOM image in 2-mm increments, which enables finer delimitation of the pharyngeal contour (C).

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Three-dimensional reconstruction of the airway in the software window, which shows the numerical information for the volume of interest.

jcsm.12.11.1527c.jpg

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Figure 3

Three-dimensional reconstruction of the airway in the software window, which shows the numerical information for the volume of interest.

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Data Analysis

Intraexaminer systematic error was assessed using a two-tailed paired Student t-test. Casual error was assessed using Dahlberg error16 with the following formula:

jcsm.12.11.1527a-e1.jpg
where d is the difference between the first and second measurements and n is the number of repetitions. All measurements were performed twice with a time interval of 15 days.

Descriptive analysis was used to report mean volumes, standard deviations, and mean volume changes, as well as minimum and maximum volumetric values. Comparison between preoperative and postoperative volumes was performed using a two-tailed paired Student t-test, which was also used for volume comparison between sexes. Correlation between patient age and upper airway volume was performed using Pearson correlation, which was also used to assess concordance between measurements for craniocervical inclination (SNC2), which is the acute angle between the sella-nasion line and a tangent line extending from the posterior border of the second cervical vertebrae used to determine whether there is significant neck flexion or extension that could taint the measurements.17 All tests were performed with significance level set at 5% (p < 0.05). The statistical analysis was performed using the Statistica software (version 5, StatSoft Inc., Tulsa, OK, USA).

RESULTS

Intra-examiner Systematic Error for Volumetric and Angular Data

Means (in cm3) for the first and second measurements were very similar (22.54 ± 9.05 vs. 22.56 ± 9.08), which resulted in low values for p (0.36, NS) and Dalbergh error (0.08). Means (in degrees) for the first and second measurements regarding SNC2 were similar before (65.23 ± 4.44 versus 65.34 ± 4.07, p = 0.68) and after surgery (65.40 ± 4.41 versus 65.16 ± 4.11, p = 0.41), with low Dalbergh error values at both time points (pre, 0.003; post, 0.014). Values for Pearson correlation coefficients for the two measurements at each surgical time point and for the mean craniocervical inclination angle preoperatively and postoperatively are shown in Table 1.

Values (mean ± standard deviation in degrees) for the craniocervical inclination angle (SNC2).

jcsm.12.11.1527.t01.jpg

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Table 1

Values (mean ± standard deviation in degrees) for the craniocervical inclination angle (SNC2).

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Postoperative Upper Airway Volume Changes and Sample Size Power

Mean values (in cm3) for upper airway volume were significantly different pre- and postoperatively (20.94 ± 9.48 versus 24.16 ± 8.67, p < 0.005). Postoperative mean volume increase was 3.22 ± 3.17 cm3, ranging from −1.42 cm3 (−4.14%) to 6.84 cm3 (67.5%). Considering such standard deviation for the volume increase and a significance level of 5%, our sample (n = 14) has a discriminative power of 91% to detect postoperative volume changes of 3 cm3 or above.

Influence of Sex and Age on Upper Airway Volume Changes

Table 2 presents the data for age, upper airway volume, and surgical movements used in each procedure for all patients. Means and modes are presented, respectively, for numerical and categorical variables. Comparison between upper airway volume measurements and changes according to patients' sex showed that sex might not be an important modifier of those dependent variables (Table 3).

Individual data for age, upper airway volume, and surgical movements.

jcsm.12.11.1527.t02.jpg

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Table 2

Individual data for age, upper airway volume, and surgical movements.

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Comparison between upper airway volume measurements and changes according to patients' sex.

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Table 3

Comparison between upper airway volume measurements and changes according to patients' sex.

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In addition, correlation between age and upper airway volume changes was considered negligible (r = 0.04), as was the correlation between age and preoperative upper airway volume (r = −0.29). Correlation between age and postoperative upper airway volume was barely considered as weak (r = −0.31).

DISCUSSION

Morphological changes of the upper airway following orthognathic surgery have been reported by several studies.15,7,9,10,12,13 Still, the understanding of how and to what extent these changes occur is limited especially in skeletal class III deformities. In these patients, surgical treatment often requires a combination of mandibular retraction and maxillary advancement.18 Although some authors9,13,19 alerted about reductions of the pharyngeal airway after mandibular retraction, Park et al.20 suggested that there are no volumetric alterations but instead a compensatory expansion of the airway, which grows laterally.

Our study was formulated after we verified that the literature assessing changes of the upper airway in patients treated solely with maxillary advancement is scarce. Specifically, we intended to elucidate the role maxillary advancement plays in the consequent volumetric airway changes, which has not been clearly established.21 In addition, one the one hand, the current study had a problem-based approach, which considered that surgical posterior repositioning of the mandible is not indicated for patients with skeletal class III deformities who are also affected by obstructive sleep apnea, whereas, on the other hand, isolated maxillary advancement may not be the best option if the sagittal dentoskeletal discrepancy persists. Taking the aforementioned into consideration, assessing the influence of maxillary advancement alone on airway changes appears to be an issue of clinical significance.

Regarding our image acquisition choices, postoperative CBCT scans were performed at least 10 w after surgery to avoid unreliable information,9 which could be a consequence of evaluating images taken from patients that were still healing and could have shown airway changes due to inflammation and edema. Since our image acquisition protocol did not abide to the principles of ALARA, or as low as reasonably achievable,22 for methodological reasons, CBCT was chosen instead of multislice computed tomography to minimize the amount of radiation to which patients were exposed.23

Although several studies13,19,2426 investigated the anatomic variation of the oropharynx and the nasopharynx using lateral teleradiographs, they were haunted by the effect that 2D representations of 3D structures have on the reliability and precision of pharyngeal morphological assessments. With CBCT scans, however, 3D images may be examined in real size, without magnifications or distortions.4

According to Alves et al.27 and Tso et al.,28 volumetric analysis of the airway is a challenging task because its success and reliability depend on the phase of breathing and on head positioning. Here, image acquisition was performed in only 14.7 sec, an interval too short to allow for deep breathing. Importantly, standardized head posture was assured according to the instructions of Muto et al.15

The mean volumetric increases detected in this study (20.47%) were compatible with those reported by Jakobsone et al.3 (13% to 21%) and Pereira-Filho et al.29 (18.84%), but lower than those presented by Aydemir et al.30 (30%). Here, however, we did not perform bidimensional analyses. An interesting approach to examine the volumetric changes of the upper airway was reported by Pourdanesh et al.31 who, by means of acoustic rhinometry, showed a 33% increase in air flow; unfortunately, we cannot establish any comparisons with our data due to the significant methodological differences.

Higher volumetric airway increases were reported by Hernández-Alfaro et al.32 (37.7%) in a CBCT-based study. However, delimitation of the airway was achieved through automated segmentation, which, according to El and Palomo,14 is less reliable than the manual delimitation performed in our methodology. Specifically, Alves et al.27 highlight the lack of standardized thresholds, which ultimately affects measurements accuracy. Moreover, according to Riley et al.33 this difference may be explained by the extent of maxillary advancement, because pharyngeal changes become relevant only when the maxilla is advanced between 8 and 12 mm, which is not an usual movement in routine orthognathic cases. Interestingly, the degree of volumetric increase varied greatly within our sample, which may reflect differences that already existed preoperatively. Moreover, different surgical movements such as occlusal plane rotation—which is possible with bimaxillary surgery only—appear to affect the degree of volumetric gain. For instance, when patients were grouped according to presence or absence of occlusal plane rotation, volume changes seemed significantly higher in those subjected to counterclockwise rotation (data not shown). Counterclockwise rotation appears to increase airway volume by advancing the mandibular symphysis, and along with it the genioglossus and geniohyoid muscles and the base of the tongue; in addition, counterclockwise rotation of the hard palate causes the soft palate to move forward and downward, which leads to an additional volumetric gain in the upper airway.34 Not surprisingly, the use of counterclockwise occlusal plane rotation was reported as a valid alternative for treating patients with obstructive sleep apnea.35

Concerning the influence of sex on airway dimensions, Chiang et al.36 suggested that men have larger and longer airways. We were unable to verify such a phenomenon; sample size and composition may be determinant considering that sampling patients with similar surgical needs and using inclusion and exclusion criteria reinforces the uniqueness of the individuals included in a given study.

As for sex, we were unable to establish any correlations between airway volume and age. Chiang et al.36 explained that the airway grows significantly during puberty. However, our sample consisted of adults, which may justify the absence of an airway volume versus age association.

One drawback of this study is the fact that patients were awake during image acquisition, for airway dimensions are different in conscious and in sleeping individuals.37 Another limitation is the lack of data on body mass index, because obesity shows an association with collapsibility and volumetric decrease of the upper airway.38

Although it seems that maxillary advancement results in airway volume increase in some patients, is not possible to determine the long-term stability of such gain. The surgical benefit may be lost with ageing, mainly due to reduced muscle elasticity and weight gain.39 The influence of occlusal plane rotation is yet another matter that is worthy of further exploration. Therefore, large-sampled, longitudinal studies that look into different variables must be performed for further clarification of the role of surgical maxillary advancement in promoting airway volume increases.

CONCLUSIONS

In this study, maxillary advancement resulted in significant volumetric increase of the upper airway in nearly half of our subjects. Our results suggest that isolated maxillary advancement may be a reasonable alternative for the treatment of skeletal class III patients at risk or already suffering from obstructive sleep apnea.

DISCLOSURE STATEMENT

This was not an industry supported study. The authors have indicated no financial conflicts of interest. All authors participated, to different extents, in the literature search, data acquisition, data analysis, statistical analysis, manuscript preparation, manuscript editing, and manuscript review.

ABBREVIATIONS

2D

two-dimensional

3D

three-dimensional

CBCT

cone-beam computed tomography

CCW

counterclockwise

DICOM

Digital Imaging and Communication in Medicine

OSA

obstructive sleep apnea

SNC2

craniocervical inclination angle

UAV

upper airway volume

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