Abstract
Background
To evaluate changes in airway dimensions following mandibular setback with conventional orthognathic approach (COA) and surgery-first orthognathic approach (SFOA).
Materials and Methods
Treatment records of 20 patients who underwent mandibular setback with SFOA/COA were divided into two groups (COA and SFOA, ten patients in each group). Acoustic pharyngometry values were obtained at T0 (01 week prior to surgery), T1 (01-month post-surgery) and T2 (01-year post-surgery). Percentage change in mean volume and area was obtained at T1 (T1–T0) to evaluate airway changes and at T2 (T2–T1) to compare relapse of airway changes in both groups. Changes in airway per mm setback at T1 (T1–T0) and T2 (T2–T1) were also obtained in both groups.
Results
For both parameters, SFOA showed greater reduction at T1 and greater relapse at T2 as compared to COA. The reduction in airway volume at T1 was 0.56 mm/mm setback in COA compared to 1.06 mm/mm setback in SFOA (P-value > 0.05). The relapse in airway volume at T2 was 0.15 mm/mm setback in COA compared to 0.25 mm/mm setback in SFOA (P-value > 0.05). The reduction in area at T1 was 0.062 mm/mm setback in COA compared to 0.110 mm/mm setback in SFOA (P-value > 0.05). The relapse in area at T2 was 0.016 mm/mm setback in COA compared to 0.034/mm setback in SFOA (P-value < 0.05).
Conclusion
In setback cases, SFOA has greater airway reduction immediate post-surgically and greater relapse at 01-year follow-up. Predicting these changes at diagnostic and treatment planning stage may prevent potential adverse events on airway.
Keywords: Surgery-first orthognathic approach (SFOA), Upper airway dimensions
Background
The literature reveals that posterior positioning of the mandible after mandibular setback surgery may compromise pharyngeal airway and predispose the patient to upper airway sleep disorders (UASD) like obstructive sleep apnoea (OSA). Though there exist contradicting evidence in this regard, it seems clear that the possible effect of orthognathic surgery on upper airway must be taken into consideration at all stages of treatment from diagnosis to treatment planning and treatment execution to prevent any possible adverse event post-surgically [1–4]. On the other hand, mandibular advancement with orthognathic surgery may have beneficial effects on airway, and studies have documented a success rate greater than 90% with surgical advancement of maxilla/mandible in management of OSA [4, 5].
The conventional orthognathic approach (COA), though a time tested and efficient method in improving smile aesthetics and oral functions, has faced criticism due prolonged treatment duration mainly due to a longer phase of pre-surgical orthodontics. Recently, this has been overcome by introduction of surgery-first orthognathic approach (SFOA) which drastically reduces the treatment time by eliminating the phase of pre-surgical orthodontics completely or partially and also by utilizing the post-surgical rapid tooth movement due to regional acceleratory phenomenon (RAP) [6–8]. The literature has documented an increased skeletal relapse with SFOA as compared to COA. This has mainly been attributed to an unstable interim transitional occlusion (ITO) post-surgically in SFOA as compared to COA, wherein the post-surgical occlusion is meticulously planned in the pre-surgical orthodontics in order to provide a stable occlusion immediate post-surgically. The changes in airway dimensions are commensurate with the amount of advancement/setback and also with the quantum of skeletal relapse [9, 10].
Though various studies have evaluated changes in airway dimensions post-mandibular setback surgery by conventional approach, there is no study which compares airway changes between COA and SFOA. Therefore, the present study was undertaken with primary objective to compare changes in pharyngeal airway dimensions after mandibular setback with COA and SFOA. The secondary objectives were (1) to compare and quantify changes in airway per mm mandibular setback 01-month post-surgically and (2) to compare and quantify relapse in airway per mm setback 01-year post-surgery. This quantification of airway changes would assist the clinician in predicting the same at the diagnosis and treatment planning stage in order to prevent potential airway related-adverse events.
Materials and Methods
Sample Selection
The sample for this retrospective observational study was obtained from the archives of a tertiary care post-graduate teaching institute. Complete set of orthodontic treatment and medical records of 20 patients matching the inclusion criteria of this study were selected. These patients underwent mandibular setback with bilateral sagittal split osteotomy (BSSO) with COA (ten patients) or SFOA (ten patients) with standard treatment protocol. Mean airway volume and mean area measurements were obtained from the acoustic pharyngometry (AP) records of the patients (Eccovision® Acoustic Pharyngometer™). AP readings were recorded by a single operator with a standard protocol. The amount of setback done was obtained from the treatment records.
Inclusion Criteria
Age—18 to 30 years (both sexes inclusive).
Availability of complete set of medical and orthodontic treatment records.
Skeletally mature patients with a prognathic mandible (negative overjet > 2 mm and ANB < − 2°).
Medical history indicating no evidence of any systemic condition/syndrome/pathology which can affect bone metabolism or contradict general anaesthesia and orthognathic surgery.
Cases treated with non-extraction treatment protocol with tooth size arch length discrepancy ≤ 5 mm.
Exclusion Criteria
Patients treated with bi-jaw orthognathic surgery.
History of previous orthodontic/ortho-surgical treatment or trauma to the jaw bones.
The presence of any respiratory disease, airway constriction, enlarged tonsils, nasal septum deviation, enlarged adenoids, tongue lesions, severe pharyngitis, asthma or any other disease/condition compromising airway.
Categorization of Study Sample
The study sample consisted of 20 patients (ten males and ten females aged 18-30 years, mean age-25 years). These patients were divided into two groups:
Group 1 Conventional orthognathic surgery (COA) group (ten patients, five males and five females)
Group 2 Surgery-first orthognathic approach (SFOA) group (ten patients, five males and five females)
Equal number of males and females were selected in both groups to avoid gender bias. The COA patients underwent three standard stages during their treatment, i.e. pre-surgical orthodontics, setback surgery and post-surgical orthodontics, whereas the SFOA patients underwent two stages, i.e. setback surgery and post-surgical orthodontics. All cases were operated under general anaesthesia by the same ortho-surgical team. 0.022 MBT pre-adjusted edgewise appliance with standard wire sequencing was used in all cases. The mean airway volume and mean area were obtained at three time frames as below:
T0 01 week prior to surgery
T1 01 month post-surgery
T2 01 year post-surgery
The data collected were compiled in MS Excel work sheet and subjected to statistical analysis. The percentage (%) change in these parameters was recorded between T1 and T0 to ascertain and compare the changes in upper airway after setback surgery in both groups. The % change between T2 and T1 was obtained to ascertain and compare the relapse of airway changes in both groups.
Quantification of changes in airway (T1–T0) was done for per mm setback of mandible by the following formula:
Quantification of relapse in airway (T2–T1) was done for per mm setback of mandible by the following formula:
Statistical Analysis
The categorical variable-related data are represented as n (number of cases) and continuous variable-related data are shown as mean and standard deviation (SD) across both the study groups. The inter-group statistical comparison of means of continuous variables was done using independent sample t test. The intra-group statistical comparison of continuous variables was done using repeated measures ANOVA. The underlying normality assumption was tested before subjecting the study variables to t test and analysis of variance (ANOVA). The P-values < 0.05 were considered to be statistically significant. All the hypotheses were formulated using two-tailed alternatives against each null hypothesis (hypothesis of no difference). The entire data were statistically analysed using Statistical Package for Social Sciences (SPSS version 21.0, IBM Corporation, USA) for MS Windows.
Results
The results of this study are as below:
Comparison of Mean Volume (Table 1, Figs. 1, 2)
Table 1.
Inter-group and intra-group comparison of mean volume
| Volume (cc) | Group 1 (n = 10) | Group 2 (n = 10) | P-value (Inter-group) | ||
|---|---|---|---|---|---|
| Mean | SD | Mean | SD | ||
| T0 | 36.08 | 3.60 | 30.57 | 4.89 | 0.010** |
| T1 | 32.44 | 5.52 | 23.78 | 4.73 | 0.001*** |
| T2 | 33.41 | 5.23 | 25.36 | 4.52 | 0.030* |
| % change at T1 from T0 | − 10.56% | – | − 21.89% | – | 0.002** |
| % change at T2 from T1 | 3.31% | – | 7.05% | – | 0.024* |
| Airway change per mm setback at T1 from T0 | − 0.56 | – | − 1.06 | – | 0.076NS |
| Airway change (relapse) per mm setback at T2 from T1 | 0.15 | – | 0.25 | – | 0.105NS |
| P-value (Intra-group) | |||||
| T0 versus T1 | 0.005** | 0.001*** | |||
| T1 versus T2 | 0.001*** | 0.001*** | |||
Values are mean and SD, P-value (inter-group) by independent sample t test. P-value (intra-group) by repeated measures ANOVA. P-value < 0.05 is considered to be statistically significant
*P-value < 0.05, **P-value < 0.01, ***P-value < 0.001
NS statistically significant
Fig. 1.
Inter-group comparison of mean volume
Fig. 2.
Intra-group comparison of mean volume
Inter-group Comparison of Mean Volume at T0
The mean ± SD of mean volume at T0 in Group 1 and Group 2 was 36.08 ± 3.60 cc and 30.57 ± 4.89 cc, respectively. This distribution of mean volume at T0 was significantly higher in Group 1 compared to Group 2 (P-value < 0.01).
Inter-group Comparison of Mean Volume at T1
The mean ± SD of volume at T1 in Group 1 and Group 2 was 32.44 ± 5.52 cc and 23.78 ± 4.73 cc, respectively. This distribution of mean volume at T1 was significantly higher in Group 1 compared to Group 2 (P-value < 0.001).
Inter-group Comparison of Mean Volume at T2
The mean ± SD of volume at T2 in Group 1 and Group 2 was 33.41 ± 5.23 cc and 25.36 ± 4.52 cc, respectively. This distribution of mean volume at T2 was significantly higher in Group 1 compared to Group 2 (P-value < 0.05).
Inter-group Comparison of Mean % Change in Volume at T1 from T0
The mean % change (decrease) in volume at T1 from T0 in Group 1 and Group 2 was − 10.56% and − 21.89%, respectively. This distribution of mean % change in volume at T1 from T0 was significantly higher in Group 2 compared to Group 1 (P-value < 0.01).
Inter-group Comparison of Mean % Change in Volume at T2 from T1
The mean % change in volume (increase) at T2 from T1 in Group 1 and Group 2 was 3.31% and 7.05%, respectively. This distribution of mean % change in volume at T2 from T1 was significantly higher in Group 2 compared to Group 1 (P-value < 0.05).
Inter-group Comparison of Mean Change in Volume per mm Setback at T1 from T0
The mean change in volume (decrease) per mm setback at T1 from T0 in Group 1 and Group 2 was − 0.56 cc and − 1.06 cc, respectively. This distribution of mean change in volume per mm setback at T1 from T0 did not differ significantly between two study groups (P-value > 0.05).
Inter-group Comparison of Mean Change in Volume per mm Setback at T2 from T1
The mean change in volume (increase) per mm setback at T2 from T1 in Group 1 and Group 2 was 0.15 and 0.25, respectively. This distribution of mean change in volume per mm setback at T2 from T1 did not differ significantly between two study groups (P-value > 0.05).
Intra-group Comparison of Mean Volume
In both groups, the distribution of mean volume was significantly lower at T1 compared to T2 (P-value < 0.01 for both). The distribution of mean volume in both groups was significantly higher at T2 compared to T1 (P-value < 0.001 for both).
Comparison of Mean Area (Table 2, Figs. 3, 4)
Table 2.
Inter-group and intra-group comparison of mean area
| Mean area (cm2) | Group 1 (n = 10) | Group 2 (n = 10) | P-value (Inter-group) | ||
|---|---|---|---|---|---|
| Mean | SD | Mean | SD | ||
| T0 | 3.66 | 0.33 | 3.08 | 0.50 | 0.007** |
| T1 | 3.26 | 0.54 | 2.38 | 0.47 | 0.001*** |
| T2 | 3.37 | 0.57 | 2.59 | 0.49 | 0.005** |
| % change at T1 from T0 | − 11.46% | – | − 22.43% | – | 0.035* |
| % change at T2 from T1 | 3.63% | – | 9.39% | – | 0.001*** |
| Airway change per mm setback at T1 from T0 | − 0.062 | – | − 0.110 | – | 0.092NS |
| Airway change per mm setback at T2 from T1 | 0.016 | – | 0.034 | – | 0.014* |
| P-value (Intra-group) | |||||
| T0 versus T1 | 0.003** | 0.001*** | |||
| T1 versus T2 | 0.002** | 0.310NS | |||
Values are mean and SD, P-value (inter-group) by independent sample t test. P-value (intra-group) by repeated measures ANOVA. P-value < 0.05 is considered to be statistically significant
*P-value < 0.05, **P-value < 0.01, ***P-value < 0.001
NS statistically significant
Fig. 3.
Inter-group comparison of mean area
Fig. 4.
Intra-group comparison of mean area
Inter-group Comparison of Mean Area at T0
The mean ± SD of area at T0 in Group 1 and Group 2 was 3.66 ± 0.33 cm2 and 3.08 ± 0.50 cm2, respectively. This distribution of mean area at T0 was significantly higher in Group 1 compared to Group 2 (P-value < 0.01).
Inter-group Comparison of Mean Area at T1
The mean ± SD of area at T1 in Group 1 and Group 2 was 3.26 ± 0.54 cm2 and 2.38 ± 0.47 cm2, respectively. This distribution of mean area at T1 was significantly higher in Group 1 compared to Group 2 (P-value < 0.001).
Inter-group Comparison of Mean Area at T2
The mean ± SD of area at T2 in Group 1 and Group 2 was 3.37 ± 0.57 cm2 and 2.59 ± 0.49 cm2, respectively. This distribution of mean area at T2 was significantly higher in Group 1 compared to Group 2 (P-value < 0.01).
Inter-group Comparison of Mean % Change in Area at T1 from T0
The mean % change in area (decrease) at T1 from T0 in Group 1 and Group 2 was − 11.46% and − 22.43%, respectively. This distribution of mean % change in area at T1 from T0 was significantly higher in Group 2 compared to Group 1 (P-value < 0.05).
Inter-group Comparison of Mean % Change in Area at T2 from T1
The mean % change in area (increase) at T2 from T1 in Group 1 and Group 2 was 3.63% and 9.39%, respectively. This distribution of mean % change in area at T2 from T1 was significantly higher in Group 2 compared to Group 1 (P-value < 0.001).
Inter-group Comparison of Mean Change in Area per mm Setback at T1 from T0
The mean change in area (decrease) per mm setback at T1 from T0 in Group 1 and Group 2 was − 0.062 and − 0.110, respectively. This distribution of mean change in area per mm setback at T1 from T0 did not differ significantly between two study groups (P-value > 0.05).
Inter-group Comparison of Mean Change in Area per mm of Amount of Setback at T2 from T1
The mean change in area per mm setback at T2 from T1 in Group 1 and Group 2 was 0.016 and 0.034, respectively. This distribution of mean change in area per mm setback at T2 from T1 was significantly higher in Group 2 compared to Group 1 (P-value < 0.05).
Intra-group Comparison of Mean Area
In Group 1 and Group 2, the distribution of mean area was significantly lower at T1 compared to T0 (P-value < 0.01 for both). In Group 1, the distribution of mean area was significantly higher at T2 compared to T1 (P-value < 0.01). In Group 2, the distribution of mean area at T2 did not differ significantly compared to T1 (P-value > 0.05).
Discussion
The constriction of pharyngeal airway after mandibular setback surgery has gained considerable attention in the recent past. This is mainly attributed to the posterior positioning of tongue and associated hard and soft tissues subsequent to mandibular setback surgery which narrows the upper airway space and predisposes the patient to snoring and OSA [1, 2, 4, 10–14]. Though the effects on airway after mandibular setback with COA has been well-researched in the literature [1–4, 10–15], the immediate post-surgical and long-term effects of setback on airway with SFOA have not been adequately researched. Also, the authors could not find any study correlating the airway changes post-surgically and relapse during follow-up period with per mm setback. Therefore, this study was designed to aid the ortho-surgical team in deciding the surgical technique and predicting the airway changes post-surgery.
Lateral cephalogram is an essential diagnostic radiograph used in orthodontic practice which also helps in airway estimation. However, the precision of its measurements are often questioned since this modality is a two-dimensional (2D) representation of three-dimensional (3D) structures. Similarly, computed tomography (CT) and magnetic resonance imaging (MRI) produces accurate 3D images of airway but are associated with limitations like increased cost and radiation exposure (in CT scans). This limits their use in routine clinical practice [3]. AP overcomes the above shortcomings by providing volume and area measurements at no radiation exposure and lesser cost to the patient. It is presently an accepted modality for assessment of airway obstruction and changes post-orthognathic surgery or mandibular advancement devices to relieve OSA. Its accuracy is comparable to CT and MRI scans [16–18]. Hence, AP was used as a modality to evaluate upper airway volume and area changes in this study.
The results of this study show increased volume and area measurements at T0 in COA group as compared to SFOA group. This may be attributed to the fact that the decompensated occlusion involving maxillary dentoalveolar expansion and incisor proclination in COA cases favours forward positioning of tongue and associated soft tissues, thereby improving airway, whereas in SFOA cases, surgery is performed on non-decompensated arches [19].
The results of this study indicate a statistically significant reduction in airway volume and area at T1 in both modalities. However, this reduction was more in SFOA. These findings are similar to other studies in the literature [1, 3, 4, 10–14]. However, all these studies were based on COA, and most of these studies used 2D modalities like lateral cephalogram for airway assessment with inherent disadvantages. AP has been used in the present study to obtain 3D volume and area assessment. Airway parameters increased at 01-year follow-up (T2) showing relapse in airway which was also increased in SFOA. This is an important aspect to be studied since airway relapse may commensurate with the skeletal relapse. A systematic review observed similar results at 1-year follow-up [3]. However, most of the studies selected in this systematic review utilized linear parameters measured on lateral cephalogram, and volume and area estimation were not done in these studies.
The results of the present study show 10.56% reduction in airway volume in COA group as compared to 21.89% in SFOA group at T1. Similarly, the % relapse in airway volume at T2 was also greater in SFOA group (7.05%) as compared to COA group (3.31%) owing to ITO and lesser control in post-surgical phase in SFOA compared to COA. The reduction in airway volume at T1 was 0.56 mm/mm setback in COA cases compared to 1.06 mm/mm setback in SFOA cases. However, this was not statistically significant indicating a similar effect of setback on airway in both modalities. The relapse in airway volume at T2 was 0.15 mm/mm setback in COA cases compared to 0.25 mm/mm setback in SFOA indicating a greater potential of relapse in SFOA cases. The changes in mean area parameters were similar to mean volume as described above. These findings may be validated with further prospective studies before application in clinical practice.
Conclusions
The airway reduction immediate post-surgically is greater in SFOA compared to COA owing to non-decompensated pre-surgical occlusion in SFOA cases.
The airway relapse 1-year post-surgical is greater in SFOA cases owing to an unstable ITO in these cases.
The findings regarding % change in airway and change in airway per mm setback in the present study may help the clinicians predict the airway changes post-treatment to prevent potential adverse events like OSA.
Prospective studies with larger sample size correlating the airway and skeletal changes are recommended to substantiate the findings of this study.
Compliance with Ethical Standards
Conflict of interest
The authors declare that they have no competing interests.
Ethical Standard
The study design was approved by the Institutional Ethical Committee.
Footnotes
Publisher's Note
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Contributor Information
S. S. Agarwal, Email: docshivagarwal@rediffmail.com
Sanjeev Datana, Email: drdatana@gmail.com.
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References
- 1.Tan SK, Leung WK, Tang TH, Zwahlen RA. Effects of one or two jaw osteotomies on pharyngeal airways: overview of systematic reviews. Int J Oral Maxillofac Surg. 2017;46(1):168–178. doi: 10.1016/j.ijom.2017.02.576. [DOI] [Google Scholar]
- 2.Hasebe D, Kobayashi T, Hasegawa M, et al. Changes in oropharyngeal airway and respiratory function during sleep after orthognathic surgery in patients with mandibular prognathism. Int J Oral Maxillofac Surg. 2011;40:584–592. doi: 10.1016/j.ijom.2011.01.011. [DOI] [PubMed] [Google Scholar]
- 3.Zayer MA, Leung YY. Skeletal and airway stability after mandibular setback in patients with mandibular prognathism: a systematic review. Int J Oral Maxillofac Surg. 2017;46(1):152–159. doi: 10.1016/j.ijom.2017.02.525. [DOI] [Google Scholar]
- 4.Holty JC, Guilleminault C. Maxillomandibular advancement for the treatment of obstructive sleep apnea: a systematic review and meta-analysis. Sleep Med Rev. 2010;14:287–297. doi: 10.1016/j.smrv.2009.11.003. [DOI] [PubMed] [Google Scholar]
- 5.Li KK, Powell NB, Riley RW, Troell RJ, Guilleminault C. Long-term results of maxillomandibular advancement surgery. Sleep Breath. 2000;4(3):137–139. doi: 10.1055/s-2000-11564. [DOI] [PubMed] [Google Scholar]
- 6.Baek S, Ahn HW, Kwon YH, Choi JY. Surgery-first approach in skeletal class III malocclusion treated with 2-jaw surgery: evaluation of surgical movement and postoperative orthodontic treatment. J Craniofac Surg. 2010;21:332–338. doi: 10.1097/SCS.0b013e3181cf5fd4. [DOI] [PubMed] [Google Scholar]
- 7.Liou EJ, Chen PH, Wang YC, Yu CC, Huang CS, Chen YR. Surgery-first accelerated orthognathic surgery: postoperative rapid orthodontic tooth movement. J Oral Maxillofac Surg. 2011;69(3):781–785. doi: 10.1016/j.joms.2010.10.035. [DOI] [PubMed] [Google Scholar]
- 8.Nagasaka H, Sugawara J, Kawamura H, Nanda R. “Surgery first” skeletal class III correction using the skeletal anchorage system. J Clin Orthod. 2009;43(2):97–105. [PubMed] [Google Scholar]
- 9.Kim CS, Lee SC, Kyung HM, Park HS, Kwon TG. Stability of mandibular setback surgery with and without presurgical orthodontics. J Oral Maxillofac Surg. 2014;72:779–787. doi: 10.1016/j.joms.2013.09.033. [DOI] [PubMed] [Google Scholar]
- 10.Choi JW, Park YJ, Lee CY. Posterior pharyngeal airway in clockwise rotation of maxillomandibular complex using surgery-first orthognathic approach. Plast Reconstr Surg Glob Open. 2015;3:485–492. doi: 10.1097/GOX.0000000000000446. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Chen F, Terada K, Hua Y, Saito I. Effects of bimaxillary surgery and mandibular setback surgery on pharyngeal airway measurements in patients with class III skeletal deformities. Am J Orthod Dentofac Orthop. 2007;131:372–377. doi: 10.1016/j.ajodo.2005.06.028. [DOI] [PubMed] [Google Scholar]
- 12.Tselnik M, Pogrel MA. Assessment of the pharyngeal airway space after mandibular setback surgery. J Oral Maxillofac Surg. 2000;58:282–285. doi: 10.1016/S0278-2391(00)90053-3. [DOI] [PubMed] [Google Scholar]
- 13.Hochban W, Schurmann R, Brandenburg U, Conradt R. Mandibular setback for surgical correction of mandibular hyperplasic-does it provoke sleep disorder? Int J Oral Maxillofac Surg. 1996;25:333–338. doi: 10.1016/S0901-5027(06)80024-X. [DOI] [PubMed] [Google Scholar]
- 14.Liukkonen M, Vahatalo K, Peltomaki T, Tiekso J, Happonen RP. Effect of mandibular setback surgery on the posterior airway size. Int J Adult Orthod Orthognath Surg. 2002;17:41–46. [PubMed] [Google Scholar]
- 15.Nakagawa F, Ono T, Ishiwata Y, Kuroda T. Morphologic changes in the upper airway structure following surgical correction of mandibular prognathisn. Int J Adult Orthod Orthognath Surg. 1998;13:299–306. [PubMed] [Google Scholar]
- 16.Jackson AC, Butler JP, Millet EJ, Hoppin FG, Jr, Dawson SV. Airway geometry by analysis of acoustic pulse response measurements. J Appl Physiol. 1977;43:523–536. doi: 10.1152/jappl.1977.43.3.523. [DOI] [PubMed] [Google Scholar]
- 17.Tsolakis IA, Venkat D, Hans MG, Alonso AA, Palomo JM. When static meets dynamic: comparing cone-beam computed tomography and acoustic reflection for upper airway analysis. Am J Orthod Dentofac Orthop. 2016;150:643–650. doi: 10.1016/j.ajodo.2016.03.024. [DOI] [PubMed] [Google Scholar]
- 18.Deyoung PN, Bakker JP, Sands SA, Batool-Anwar S, Connolly JG, Butler JP, et al. Acoustic pharyngometry measurement of minimal cross-sectional airway is a significant independent predictor of moderate to severe obstructive sleep apnea. J Clin Sleep Med. 2013;9:1161–1164. doi: 10.5664/jcsm.3158. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Maria A, Guijjaro P, Guijjaro R, Alfaro AH. Surgery first in orthognathic surgery: a systematic review of the literature. Am J Orthod Dentofac Orthop. 2016;149(4):448–462. doi: 10.1016/j.ajodo.2015.09.022. [DOI] [PubMed] [Google Scholar]