Andreas Matsagkos
5th Course, group 13THREE DIMENSIONAL COMPARISON OF BIMAXILLARY
ORTHOGNATHIC VERSUS MANDIBULAR SETBACK
SURGERY IMPACT ON UPPER AIRWAY SPACE FOR
CLASS III PATIENTS.
A SYSTEMATIC REVIEW
Master‟s Thesis
Supervisor: Prof., PhD Arūnas Vasiliauskas
FINAL MASTER‘S THESIS IS CONDUCTED
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3 LITHUANIAN UNIVERSITY OF HEALTH SCIENCES
MEDICAL ACADEMY
FACULTYOFODONTOLOGY
THECLINICOFORTHODONTICS
THREE DIMENSIONAL COMPARISON OF BIMAXILLARY ORTHOGNATHIC VERSUS MANDIBULAR SETBACK SURGERY IMPACT ON UPPER AIRWAY SPACE FOR CLASS III
PATIENTS.
A SYSTEMATIC REVIEW Master‟s Thesis
The thesis was done
by student ………... supervisor ………... (name surname, year, group) (degree, name surname) ……….. ……… (signature) (signature)
……… 20…. ……… 20…. (day/month) (day/month)
4
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OF THE TYPE OF SYSTEMIC REVIEW OF SCIENTIFIC LITERATURE
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Compliance with MT
No. MT parts MT evaluation aspects requirements and
evaluation
Yes Partially No
1 Is summary informative and in compliance with the 0.3 0.1 0
Summary thesis content and requirements?
2 (0.5 point) Are keywords in compliance with the thesis 0.2 0.1 0
essence?
3 Introduc- Are the novelty, relevance and significance of the 0.4 0.2 0
work justified in the introduction of the thesis?
tion, aim
Are the problem, hypothesis, aim and tasks formed
4 and tasks 0.4 0.2 0
clearly and properly?
(1 point)
5 Are the aim and tasks interrelated? 0.2 0.1 0
6 Selection Is the protocol of systemic review present? 0.6 0.3 0
criteria of Were the eligibility criteria of articles for the
7 the studies, selected protocol determined (e.g., year, language, 0.4 0.2 0
search publication condition, etc.)
methods and Are all the information sources (databases with
8 strategy dates of coverage, contact with study authorsto 0.2 0.1 0
(3.4 points) identify additional studies) described and is the last
search day indicated?
Is the electronic search strategy described in such a way that it could be repeated (year of search, the
9 last search day; keywords and their combinations; 0.4 0.1 0
number of found and selected articles according to the combinations of keywords)?
Is the selection process of studies (screening,
10 eligibility, included in systemic review or, if 0.4 0.2 0
applicable, included in the meta-analysis)
described?
Is the data extraction method from the articles
11 (types of investigations, participants, interventions, 0.4 0.2 0 analysed factors, indexes) described?
Are all the variables (for which data were sought
12 and any assumptions and simplifications made) 0.4 0.2 0 listed and defined?
Are the methods, which were used to evaluate the
5 information is to be used in data synthesis,
described?
14 Were the principal summary measures (risk ratio,difference in means) stated? 0.4 0.2 0 Is the number of studies screened: included upon
15 assessment for eligibility and excluded upon giving 0.6 0.3 0 the reasons in each stage of exclusion presented?
Are the characteristics of studies presented in the
16 Systemiza- included articles, according to which the data wereextracted (e.g., study size, follow-up period, type of 0.6 0.3 0
tion and respondents) presented?
analysis of Are the evaluations of beneficial or harmful
data outcomes for each study presented? (a) simple
17 (2.2 points) summary data for each intervention group; b) effect 0.4 0.2 0
estimates and confidence intervals)
Are the extracted and systemized data from studies
18 presented in the tables according to individual 0.6 0.3 0
tasks?
19 Arerelevance indicated?the main findings summarized and is their 0.4 0.2 0
20 Discussion Are the limitations of the performed systemic 0.4 0.2 0
(1.4 points) review discussed?
21 Doesresults?author present the interpretation of the 0.4 0.2 0 22 Do the conclusions reflect the topic, aim and tasks 0.2 0.1 0
Conclusions of the Master’s thesis?
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Additional sections, which may increase the collected number of points
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dations
Were additional methods of data analysis and their
31 results used and described (sensitivity analyses, +1 +0.5 0 meta-regression)?
6 Was meta-analysis applied? Are the selected
32 statistical methods indicated? Are the results of +2 +1 0
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General requirements, non-compliance with which reduce the number of points
33 Is the thesis volume sufficient (excludingannexes)? 15-20 pages <15 pages (-2 points) (-5 points)
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39 Amount of plagiarism in the thesis. >20%
require-
(not evaluated)
ments Is the content (names of sections and sub-
40 sections and enumeration of pages) incompliance with the thesis structure and -0.2 point -0.5 points
aims?
Are the names of the thesis parts in
41 compliance with the text? Are the titles ofsections and sub-sections distinguished -0.2 point -0.5 points
logically and correctly?
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TABLE OF CONTENTS
1. SUMMARY ... 8
2. INTRODUCTION ... 9
3. MATERIALS AND METHODS ... 12
3.1 Protocol ... 12
3.2 Selection criteria ... 12
3.2.1 Inclusion criteria for selection were the following... 12
3.2.2 Exclusion criteria were the following: ... 13
3.3 Literature search strategy ... 13
3.4 Selection of studies ... 14
3.5 Search results ... 14
3.6 Assessment of Quality of included studies ... 16
4. RESULTS ... 18
4.1. Segmental volumetric comparison of upper airway. ... 18
4.2. Minimum axial area comparison of the upper airway ... 20
4.3. Evaluation of the stability of upper airway dimension after orthognathic surgery... 21
5. DISCUSSION ... 22
6. CONCLUSION ... 26
7. PRACTICAL RECOMMENDATIONS ... 27
8. REFERENCES ... 28
8
SUMMARY
Title: Three dimensional comparison of bimaxillary orthognathic versus mandibular setback surgery impact on upper airway space for class III patients. A systematic review
Introduction: This systematic review was aimed to compare three dimensionally the impact of bimaxillary orthognathic versus mandibular setback surgery on upper airway space for Class III patients.
Materials and methods: PubMed/Medline, Science Direct and Cochrane library databases were searched. Seven combinations including the three main keywords were utilized and based on inclusion and exclusion criteria, the applicable articles were selected.
Results: A total of 628 articles were retrieved, after duplicate removal and eligibility criteria were evaluated, the final articles were selected. A total of five articles were included in this review. The threestudies included in the review were used to compare volumetric changes in three segments of the upper airway, two of them wereutilized to compare minimum axial area in two segments and two articles were used to evaluate the postoperative stability of upper airway after orthognathic surgery in different follow up sequences as well. Majority of the studies had a moderate risk of bias. Conclusion: Significant decrease in the retropalatal segment of the upper airway is observed in Class III patients after bimaxillary orthognathic and mandibular setback surgery. In addition, mandibular setback combined with maxillary advancement, showed more favorable results in accordance to postoperative airway constriction than mandibular setback technique.
9
INTRODUCTION
Facial aesthetics and face harmony was and will be one of the main concerns of humans. Many people with dentofacial deformities experience facial disharmonies and asymmetries and are therefore seeking treatment. Skeletal Class III malocclusion is one of those deformities which is characterized by disharmony in the anterio-posterior direction, with either maxillary deficiency, mandibular excess or both. If is not possible to compensate those disharmonies orthodontically, surgical treatment combined with orthodontic treatment is a therapeutic alternative, usually mandibular setback combined or not with maxillary advancement. [1]
Mandibular setback osteotomy has been routinely used as an orthognathic surgical procedure for mandibular prognathism and bimaxillary orthognathic surgery in conjunction with mandibular setback, and maxillary advancement procedures are commonly used to correct Class III malocclusion. [2]
In addition to its positive effects for treatment of malocclusion, these kinds of surgical procedures can reposition the facial skeletal components together with soft tissue components, such as the soft palate, muscles around the jaw and the tongue base. [3] Through the genioglossus, geniohyoid, and mylohyoid muscles the mandible is related to the hyoid. The tongue is linked to the hyoid bone and to the mandible, in such a way that movement of the muscle attachment points or the mandible results in dimensional alternations of the posterior airway space (PAS). [4] After setback, mandibular spatial position is shifted to a region closer to the posterior pharyngeal wall. This new relation to the composing structures of the upper airways may compromise air space and predispose the individual to developing obstructive sleep apnea-hypopnea (OSAH) [5].
The concern about the airway in the context of planning for orthognathic surgery grew strong as awareness of snoring and obstructive sleep apnea (OSA) increased. [5] In cases that the airway is or becomes narrow, the probability of snoring and sleep apnea occurring increases, sincethe airflow resistance increases. During facial growth and development, significant relationships between the pharyngeal structures and the development of the face and occlusion establish. Orthognathic surgery for skeletal deformity alters the skeletal and soft- tissue components.
10 The use of cone-beam computed tomography (CBCT) has been on the rise in the last two decades for the perioperative assessment of the upper airway in orthognathic surgery. The rationale behind this shift was that CBCT offers very precise and reliable data in relative low radiation. Its combination with specialized software allows for more accurate 3D linear and volumetric measurements and more detailed investigation of possible changes that can occur in the pharyngeal airway. More importantly, image segmentation of the upper airway became possible, which enabled proper 3D image reconstruction and volume calculation [6]. It is therefore an important tool to assist in the clinical diagnosis.
Recent studies [7-9] have suggested that the upper airway dimensions do not undergo major alterations following bimaxillary surgery, including maxillary advancement and maxillary setback as it can reduce the amount of mandibular setback. As a result, diminishing the negative effects of mandibular setback on upper airway dimensions. This study was therefore conducted to compare three dimensionally the postoperative changes between mandibular setback versus bimaxillary surgery in the upper airway for Class III patients. The novelty of this study is accredited to the fact that it aims to clarify the disparity created by methodological heterogeneity of the research studies. In this study the anatomical landmarks defining the segments of upper airway between the included articles were selected to be identical or as close as possible for a more accurate comparison.
Aim:
The aim was to compare three dimensionally impact of bimaxillary orthognathic versus mandibular setback surgery on upper airway space for Class III patients.
Tasks:
1. To compare an impact on upper airway volume between bimaxillary surgery and mandibular setback surgery in the treatment of Class III individuals.
2. To compare an impact on minimum axial area in two segments of the upper airway, between bimaxillary surgery and mandibular setback surgery in the treatment of Class III individuals.
3. To evaluate the stability of upper airway dimension after orthognathic surgery for Class III patients in different follow-up sequences.
11
Abbreviations:
Abbreviations presented in this review are explained below: P=prospective study,
R=retrospective study, M=Male
F=Female
MdS=Mandibular setback Surgery, BSSO=Bilateral sagittal split osteotomy MxA=Maxillary advancement surgery
MdS MxA=Mandibular setback combined with Maxillary advancement MinAA= Minimum axial area
P value=0, 05
SD=standard deviation
12
MATERIALS AND METHODS
3.1 Protocol
The protocol of this systematic review was conducted following the statement of PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) [10]. Approval was acquired by the local bioethics committee (No.BEC-OF (U)-124).
Establishment of focus question
With the implement of PICOS framework, a meticulous review question was established (Table 1). Table 1. PICOS table
Component Description
Population (P) Non-growing patients with skeletal Class III
pattern.
Intervention (I) Orthognathic surgery
Comparison (C) Mandibular setback orthognathic surgery versus
bimaxillary orthognathic surgery
Outcomes (O) Changes of the upper airway
Focus Question Is there any difference in the changes of the upper airway between mandibular setback surgery and bimaxillary surgery?
Types of publications:
The systematic review included studies on humans published in the English language.
Types of studies:
Prospective clinical studies or retrospective cohort studies.
3.2 Selection criteria
3.2.1 Inclusion criteria for selection were the following: -Publications written in English language.
-Studies performed on humans only.
13 -Randomized clinical trials and controlled prospective clinical studies, retrospective cohort studies assessing the impact of orthognathic surgery for Class III individuals on upper airway using cone-beam computed tomography
-Orthognathic surgical procedure for treatment of Class III malocclusion including mandibular setback with or without maxillary advancement.
3.2.2 Exclusion criteria were the following: -Publications in languages other than English. -Case reports, systematic reviews, Meta-Analyses. -Studies performed on animals.
-Patients with cleft lip and/or palate, facial asymmetries, obese patients and patients with obstructive sleep apnea
-Studies using evaluation tools other than Cone-Beam Computed Tomography
3.3 Literature search strategy
For this review PubMed/Medline, Science Direct and Cochrane library were searched. Seven combinations including the three main keywords were used and based on inclusion and exclusion criteria, the applicable articles were selected. Table 2 was created providing information concerning each combination, its results and the date of search.
Table 2. Keyword combinations
Search dates Keyword combination Results
First date of search: 24/01/2020
“Mandibular setback” and “Airway”
88
“Bimaxillary surgery” and “airway”
96
“Bimaxillary surgery” and “Class III malocclusion”
87
“Pharyngeal airway” and “Class III malocclusion”
63
14
05/02/2020 “Cone-Beam Computed
Tomography”
“Bimaxillary surgery” and
“Cone-Beam Computed
Tomography”
87
“Pharyngeal airway” and
“Cone-Beam Computed
Tomography”
148
3.4 Selection of studies:
Articles were assessed according to inclusion and exclusion criteria. First titles and abstracts were examined primarily in order to determine full articles evaluating volumetric and linear changes of upper airway following mandibular setback or bimaxillary surgery that includes mandibular setback combined with maxillary advancement. The articles that evaluated the airway alternations using any other radiographic tool except of Cone-Beam Computed Tomography were not included in this review. Consecutively, these articles were subjected to inclusion and exclusion criteria. For the inclusion criteria it was requisite that studies published during the period of 1st 2017 until December 31 st 2019 and were performed on humans only, who underwent orthognathic surgery for treatment of Class III malocclusion. The exclusion criteria were studies performed in patients with cleft lip and/or palate, facial asymmetries, obese patients and patients with obstructive sleep apnea. Moreover systematic reviews and Meta analyzes as well as case studies were excluded.
3.5 Search results:
15
Figure 1: PRISMA flow chart
PubMed/MEDLINE, Science Direct, and Cochrane Library database advanced search
Search keywords: „Pharyngeal airway‟, „Maxillary Surgery‟, „Mandibular set
back‟ Publication period:01/01/2017-31/12/2019 (n = 628 ) S cr ee n in g Incl ud ed E li g ibi li ty Id en tif icat
ion Additional records identified
through other sources (n = 0)
Records after duplicates removed (n = 331) Records screened (n =331 ) Records excluded -Systematic reviews: (n=3)
-Not applicable results: (n=316)
Full-text articles assessed for eligibility
(n =12)
Full-text articles excluded -Maxillomandibullar setback: (n=3)
16
3.6 Assessment of Quality of included studies
The quality of the incorporated studies were based on quality assessment used by Mattos et al [16] which he used to evaluate similar studies (Annex 1). Studies from 6 to 8 points are classified as high quality studies hence low risk of bias, from 4 to 6 points are classified as moderate thus having
moderate risk of bias and less than 4 points studies are classified as low quality studies therefore having high risk of bias (Table 3). Systematization of data presented in Table 4.
Table 3. Risk of bias
Author/ year Type of study Eligible criteria for participants described Presence of a control group Blinding assessment stated Statistical treatment performed Reliability of measures tested Reporting drop-out Follow-up period reported
17
Table 4. Systematization of data Author and
year
Type of study Sample/ gender Mean age Type of surgery Evaluation Records Main Evaluation tool
Presentation of results Measurements
Jae Hwa An et.al(2019) Retrospective clinical study 11Males 12 Females 22.7 ± 4.7 Mandibular setback Maxillary advancement Preoperative, immediately after, 6 months after, 6 years after Cone Beam Computed Tomography Before-After Volumetric Segmental Total Linear S.-T. Lee et al(2019) Retrospective clinical study 11 Males 14 Females 23.0 ± 4.4 Mandibular setback Preoperative, immediately after, 1 year after Cone Beam Computed Tomography
Mean difference between before/after Volumetric Segmental Total Linear Tahsin Tepecik et.al(2018) Prospective clinical study 7 Males 14 Females 23.19 ± 6.53 Mandibular setback Maxillary advancement Preoperative, between 6 to 12 months after Cone Beam Computed Tomography
Mean difference between before/after Volumetric Segmental Total Linear Shireen K. Irani et al.(2018) Retrospective clinical study 17 Males 11 Females 23.88 ± 6.57 Mandibular setback Preoperative, 6 months after, 1 year after Cone Beam Computed Tomography Before-After Volumetric Segmental Total Linear Yuxue Yang et.al(2017) Retrospective clinical study 11 Males 18 Females 22.31 Mandibular setback with and without Maxillary advancement Preoperative, 3 months after Cone Beam Computed Tomography
Mean difference between before/after
Volumetric Segmental Total
18
RESULTS
4.1. Segmental volumetric comparison of upper airway.
Three dimensional comparisons of airway segments were performed and depicted in Table 5.
Starting from nasopharynx Yuxue Yang et al., 2017, with a sample size of 13 patients, using mandibular setback resulted in a slight decrease (-0.28 cm³) of volume, a result which was statistically insignificant. On the other hand in MdS MxA the same author showed extremely low decrease (-0.01 cm³) almost unchanged nasopharyngeal volume. On the contrary Tahsin Tepecik et al., 2018 recorded a slight increase in the volume of the same segment which was statistically insignificant.
Both studies performing MdS recorded a decrease of volume in the retropalatal segment but only in the study executed by Yuxue Yang et al., 2017, the result was statistically significant with the mean difference to be -4.7 cm³.
Comparing with the MdS MxA technique, the same author had also statistically significant decrease in the volume with the mean difference being -2.59 cm³. In comparison to the study executed by Tahsin Tepecik et al.2018, there was a decrease in the volume but not statistically significant -0.3 cm³.
19
Table 5. Volumetric comparison of three segments of upper airway (cm³)
Nasopharyngeal airway segment Retro palatal airway segment Retro lingual airway segment
Isolated Mandibular setback Mandibular setback With Maxillary advancement Isolated Mandibular setback Mandibular setback With Maxillary advancement Isolated Mandibular setback Mandibular setback With Maxillary advancement Author Sample ΔΤ1-Τ0 Sample ΔΤ1-Τ0 Sample ΔΤ1-Τ0 Sample ΔΤ1-Τ0 Sample ΔΤ1-Τ0 Sample ΔΤ1-Τ0 Mean ± SD P-value Mean ± SD P-value Mean ± SD P-value Mean ± SD P-value Mean ± SD P-value Mean ± SD P-value Yuxue Yang et al. 2017* 13 -0.28 ± 1.47 SI 16 -0.01 ± 0.1 SI 13 -4.71 ± 1.40 SS 16 -2.60 ± 3,10 SI 13 -1.61 ± 2.95 SI 16 -0.28 ± 2.53 SI Tahsin Tepecik et al.2018 21 0.11 ± 0.89 SI 21 -0.30 ± 1.48 SI 21 -0.48 ± 1.30 SI S.-T. Lee et al. 2019 25 -2.0 ± 2.8 SI 25 -2.2 ± 3.3 SI
Abbreviations: SD= standard deviation, SS=statistically significant, SI=statistically insignificant,ΔΤ1-Τ0=Mean difference between preoperative and first post-operative measurements
20
4.2. Minimum axial area comparison of the upper airway
The minimum axial area for the two most affected segments of pharyngeal airway was compared between single jaw surgery and MdS MxA surgery and depicted in Table 6. Both authors reported statistically significant decrease in both retropalatal and retrolingual segments.
However with MdS MxA, the decrease was lesser for both authors than with isolated mandibular setback. The difference between segments was similar in all cases except in Yuxue Yang et al. 2017. In the group that underwent bimaxillary surgery, minimum axial area for retropalatal segment was decreased by 0, 95 cm² and for retrolingual segment 0.2 cm².
21
4.3. Evaluation of the stability of upper airway dimension after orthognathic surgery
The airway dimensions were recorded and compared in different follow up periods and presented in Table 7. Two studies were selected from the literature that fulfilled the criteria of this review. In the study of Shireen K. Irani et al. (2018), 28 patients underwent bilateral sagittal split ramus osteotomy for mandibular setback. Three scans were obtained for each patient: before surgery, an average of 6 months after surgery and 1 year after surgery. Initially total airway volume was 30.5 cm³, six months after surgery it decreased to 22.9 cm³. Approximately 1 year after the procedure, it became 24.3 cm³.
In the study of Jae Hwa An et al. 2019, 23 patients underwent sagittal split ramus osteotomy for mandibular setback and Lefort 1 osteotomies for maxillary advancement. Initially the mean total airway volume was 22 cm³, immediately postoperative mean value was 15.9 cm³ and 6 months later mean volume became 18.3 cm³. On average, 6 years after operation, which is the longest follow up to date, regarding 3 dimensional pharyngeal airway dimensions showed the mean of 16.7 cm³.
Table 7. Total volume of upper airway in different follow up sequence (cm³)
Author Surgery performed
Sample
mean± standard deviation
22
DISCUSSION
In this review the 3 dimensional comparison of the impact of mandibular setback with or without maxillary advancement on the upper airway of Class III individuals was performed. For this comparison 5 articles that were published during 2017-2019 period were used.It was not possible to compare the total pharyngeal airway volume as the three authors did not process the same limits for total airway volume. Four studies qualified with moderate risk of bias and one study with high risk. Three segments were evaluated volumetrically in both groups: nasopharyngeal, retropalatal and retrolingual. In addition to the volumetric measurements, the minimum cross sectional area was evaluated at retropalatal and retrolingual level. Moreover 2 studies were selected in order to present total airway changes in different follow up sequences.
In recent decades, changes in the upper airway space after orthognathic surgery have attracted increasing attention. Due to the close proximity of jaws with upper airway, change of their position will inevitably alter dimensions of the upper airway.
Variations occurred in the surgical movements and their amplitude according to the individual needs of each patient to obtain the best results, as it is expected for surgical procedures that seek esthetic and especially functional improvement in patients who submit to orthognathic surgical procedures. [17]
Simultaneous retro position of maxilla and mandible will lead to upper airway narrowing [18-20]. On the other hand, maxillomandibullar advancement will result in expansion of the airway [17]. Both procedures are being performed infrequently for special cases of Class III malocclusion. Retro position of maxilla for Class III individuals is used when clockwise rotation of the maxilla (posterior impaction) is performed for the correction of acute nasolabial angle and stabilization of the occlusal plane [3]. The aforementioned procedures are only applied in very specific cases of Class III.
On the other hand mandibular setback surgery (BSSO or IVRO) for skeletal Class III patients has been the traditional method in which, these last twenty years, there is a big controversy between scientists whether it can reduce the upper airway dimension, and consequently provoke sleep-related breathing disorders such as obstructive sleep apnea (OSA). At present, it is generally acknowledged that a relative reduction of the pharyngeal airway space (PAS) could be resulted from mandibular setback [21]. Τhe first report in which 2 patients had developed OSA following mandibular setback surgery for the treatment of mandibular prognathism was reported by Guilleminault et al in 1985 [22].
23 symptoms such as extreme day-time sleepiness, severe snoring, obstruction of the pharyngeal airway, and hypoxemia during sleep. Obstruction that causes episodes of apnea is the result of collapse of the pharyngeal airway and usually occurs at the oropharynx or velo-pharynx. The development of obstructive sleep apnea has been associated to both genetic and environmental factors some of which include obesity, skeletal conditions such as a short mandibular body and mandibular retreat, large tongue or uvula, shape of the airway, age, and ethnicity [23-24].
According to Katsantonis et al., [25] the pharyngeal regions that are the most responsible for the collapse in OSAS patients are the posterior regions of the soft palate and tongue. Taking this into consideration some authors used reference points on soft tissues instead of vertebral reference points when separating air segments. When vertebral points are used for reference, the retropalatal and retrolingual regions, which are the most responsible for OSAS, are not exactly matched to their boundaries. Moreover, vertebral lengths, locations and upper or lower limits do not accord to the same region in each patient, and, consequently, different and unrelated regions are compared. Therefore, it is more reasonable to measure retropalatal and retrolingual regions using points determined from the anatomical structures that make up or are adjacent to the borders of these very structures.
In our results, the volumes in nasopharyngeal segment for mandibular setback remain almost unchanged and for group bimaxillary group it increases slightly, but both changes were statistically insignificant. Hatab et al., [7] using equivalent reference points for segmentation of airway reported similar results regarding that segment. On the contrary Jakobsone et al., [8] reported a statistical increase for the nasopharyngeal segment for bimaxillary group. For the retropalatal segment in both groups there was a decrease in the mean value, however only in the study of Yang et al. both groups showed statistically significant decrease in volume whereas bimaxillary group showed less decrease compared mandibular setback. The rest of the results from the same category showed also difference between the groups favoring the bimaxillary group. Lastly the retrolingual segments showed decrease in the mean for both groups. Although not statistically significant, between the two groups bimaxillary surgery resulted in lesser decrease showing that it can compensate in some degree the negative impact of retro position of mandible.
24 the most significant factor in resistance to air flow is the extent of contraction. More over according to Schendel et al., [28] as the axial area narrows, the risk of apnea and OSAS tendency is also increasing. Therefore, the minimum axial areas are the potential areas where collapse and resistance are most likely to occur in the development of OSAS. Making them very important factor to investigate and compare between those two surgical procedures. In this review for both surgical procedures, minimum axial area for both segments of PAS (Retropalatal, retrolingual) were significantly decreased but with lesser degree in bimaxillary group. Our results were consistent with findings of Kim et al., [29] which reported that the minimal axial area of PAS decreased significantly after treatment in patients who had undergone bimaxillary surgery. On the other hand, Panou et al., [30] and Hart et al., [9] reported that minimal axial area of PAS did not undergo significant changes after bimaxillary orthognathic surgery.
25
Limitations:
26
CONCLUSION
1. Significant decrease in retropalatal segment of upper airway was observed after bimaxillary surgery and mandibular setback surgery in the treatment of Class III individuals. The mandibular setback combined with maxillary advancementwas more favorable to minimize the postoperative reduction of the airway instead of performing only mandibular setback. 2. Minimum axial area for two segments was significantly decreased after bimaxillary surgery
and mandibular setback surgery in the treatment of Class III individuals.
27
PRACTICAL RECOMMENDATIONS
28
REFERENCES
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