PHARYNGEAL AIRWAY VOLUME FOLLOWING ...

PHARYNGEAL AIRWAY VOLUME FOLLOWING MAXILLOMANDIBULAR 

ADVANCEMENT SURGERY UTILIZING CONE BEAM 

COMPUTED TOMOGRAPHY 

Brandy Lee Burgess, D.D.S. 

An Abstract Presented to the Faculty of the Graduate School 

of Saint Louis University in Partial Fulfillment 

of the Requirements for the Degree of 

Master of Science in Dentistry 

2008

Abstract 

Purpose: The purpose of this study was to examine the 

effects of maxillomandibular advancement surgery on the 

pharyngeal airway volume in the short-term and longer-term 

and determine if a relationship exists between the amount 

of advancement and airway volume change. Materials and 

Methods: Records of 55 patients who had undergone combined 

orthodontic treatment and maxillomandibular advancement 

osteotomies were collected and analyzed. Cone beam 

computed tomography scans were taken within three days pre- 

surgery and at least eight weeks post-surgery. The 

pharyngeal airway volume was measured at pre-surgery (T0), 

2-3 months post-surgery (T1), and 4-12 months post-surgery 

(T2). Results: There was a significant increase in 

airway volume between T0 and T1 and between T0 and T2. No 

significant differences were found between T1 and T2. 

Correlations between the amount of surgical advancement and 

percentage of volumetric change were confounding and 

inconsistent between patients. Conclusion: In this study, 

maxillomandibular advancement osteotomies resulted in a 

significant increase in airway volume 2-3 months after 

surgery, and this change appeared to be stable up to one 

year following surgery. 

1

PHARYNGEAL AIRWAY VOLUME FOLLOWING MAXILLOMANDIBULAR 

ADVANCEMENT SURGERY UTILIZING CONE BEAM 

COMPUTED TOMOGRAPHY 

Brandy Lee Burgess, D.D.S. 

A Thesis Presented to the Faculty of the Graduate School 

of Saint Louis University in Partial Fulfillment 

of the Requirements for the Degree of 

Master of Science in Dentistry 

2008

COMMITTEE IN CHARGE OF CANDIDACY 

Assistant Professor Ki Beom Kim, 

Chairperson and Advisor 

Assistant Clinical Professor Steve Harrison, 

Assistant Clinical Professor Donald Oliver 

i

ACKNOWLEDGEMENTS 

I would like to thank the following individuals for 

their assistance in this thesis: 

Dr. Ki Beom Kim for serving as chairman of my thesis 

committee. Dr. Steve Harrison and Dr. Donald Oliver for 

their contributions as committee members. 

Dr. G. William Arnett and Dr. Michael Gunson for 

access to the surgery sample. 

Dan Kilfoy, Dr. Heidi Israel, and Celia Giltinan for 

their assistance with this project. 

ii

TABLE OF CONTENTS 

List of Tables...........................................iv 

List of Figures...........................................v 

CHAPTER 1: INTRODUCTION...................................1 

CHAPTER 2: REVIEW OF THE LITERATURE...................... 3 

Pharyngeal Airway Anatomy.................................3 

Obstructive Sleep Apnea...................................4 

Treatment.................................................5 

Non-surgical Therapy................................6 

Weight Loss....................................6 

Nasal Continuous Positive Airway Pressure......6 

Oral Appliances................................7 

Surgical Therapy....................................8 

Uvulopalatopharyngoplasty......................8 

Tongue-Reduction Procedures....................9 

Advancement Osteotomies/Hyoid Myotomy..........9 

Maxillomandibular Advancement Osteotomies.....10 

Cephalometric Studies....................................11. 

Computed Tomography Study................................13 

Cone Beam Computed Tomography............................14 

Purpose of the Study.....................................16 

Literature Cited.........................................17 

CHAPTER 3: JOURNAL ARTICLE...............................23 

Abstract.................................................23 

Introduction.............................................24 

Materials and Methods....................................28 

Sample.............................................28 

Imaging............................................29 

Isolating the Pharyngeal Airway and Volumetric 

Measurements.......................................30 

Determining Amount of Surgical Advancement.........33 

Statistics.........................................35 

Results..................................................35 

Discussion...............................................42 

Conclusions..............................................47 

Literature Cited.........................................48 

Vita Auctoris............................................52 

iii

LIST OF TABLES 

Table 3.1: Descriptive Statistics for Patients 

Measured at T0, T1, and T2 (n=18).........37 


Measured at T0 and T1 (n=29)..............38 


Measured at T0 and T2 (n=8)...............38 

Table 3.4: Pearson’s Correlation for Surgical 

Advancement Vs. Percentage of Airway Volume 

Change for Patients Measured at T0, T1, 

and T2 (n=18).............................41 

Table 3.5: Pearson’s Correlation For Surgical 


Change for Patients Measured at T0 and T1 

(n=29)....................................41 

Table 3.6: Pearson’s Correlation For Surgical 


Change for Patients Measured at T0 and T2 

(n=8).....................................42 

iv

LIST OF FIGURES 

Figure 2.1: Pharyngeal Airway Anatomy..................4 

Figure 3.1: Borders of Measured Pharyngeal Airway.....31 

Figure 3.2: Sculpted Pharyngeal Airway Volume of a 

Patient at T0, T1, and T2.................32 

Figure 3.3: Highlighted Pharyngeal Airway Volume with 

Superior and Inferior Aspects Identified..33 

Figure 3.4: 3D Skull Depicting X, Y, Z Axis...........34 

Figure 3.5: Airway Volume T0-T1-T2 (n=18).............39 

Figure 3.6: Airway Volume T0-T1 (n=29)................39 

Figure 3.7: Airway Volume T0-T2 (n=8).................39 

v

CHAPTER 1: INTRODUCTION 

Combined orthodontic-orthognathic surgical treatment 

has made it possible to treat skeletal and dental 

dysplasias in patients where orthodontics alone cannot 

produce a desirable result. By altering the position of 

the jaws, the size and shape of the external and internal 

surrounding soft tissues are affected, including the 

pharyngeal airway, which could influence respiration. This 

is of particular importance for patients who suffer from 

obstructive sleep apnea. For these patients, surgical 

advancement of both the maxilla and mandible is often 

performed to intentionally increase the size of the 

pharyngeal airway to eliminate or improve symptoms of the 

disorder. 

Most studies that examine changes in the pharyngeal 

airway size utilize lateral cephalograms, which allow 2- 

dimensional measurements of a 3-dimensional object. 

Measurements are taken of the sagittal, or anteroposterior, 

dimension. In order to better understand how the airway is 

affected, it is important to study the size and shape of 

the entire airway rather than a section or segment of it. 

With the development of 3-dimensional imaging, the airway 

volume can be examined as a whole. By studying airway 

1

volume, we can more accurately determine how the airway 

changes following maxillomandibular advancement surgery, 

determine whether or not there is a significant increase in 

airway volume, and if the results are stable over time. In 

addition, we can determine if there is a correlation 

between the amount of advancement and the degree of 

volumetric change. 

2

CHAPTER 2: REVIEW OF THE LITERATURE 

Pharyngeal Airway Anatomy 

The pharyngeal airway is an intricate structure. In 

conjunction with its surrounding structures, it is 

responsible for the physiologic processes of swallowing, 

vocalization, and respiration. 1 The airway lies posterior 

to the nasal cavity, oral cavity, and larynx. It begins 

posterior to the nasal turbinates and extends inferiorly to 

the esophagus. The superior wall is formed by the body of 

the sphenoid bone and the basilar part of the occipital 

bone. 1 The nasal turbinates, soft palate, tongue, and 

glottis make up the anterior border. The posterior wall is 

formed by the pharyngeal constrictor muscles. The lateral 

walls contain adipose tissue, lymphoid tissue, and numerous 

muscles. 1 

The airway is subdivided into three anatomical 

regions: the nasopharynx, oropharynx, and hypopharynx 

(Figure 2.1). The nasopharynx is the area between the 

nasal turbinates and the hard palate. The oropharynx 

contains two areas: retropalatal (from the hard palate to 

the tip of the soft palate) and retroglossal (from the tip 

of the soft palate to the epiglottis). The hypopharynx 

extends from the epiglottis to the esophagus. 1 

3

Retropalatal 

Retroglossal 

Figure 2.1: Pharyngeal Airway Anatomy 

Obstructive Sleep Apnea 

The pharyngeal airway is extensively studied in 

patients suffering from obstructive sleep apnea. 

Obstructive sleep apnea is a condition characterized by 

recurring episodes of pharyngeal airway obstruction during 

sleep that results from collapse of the surrounding soft 

tissues. 2-4 This obstruction reduces the amount of air, and 

therefore oxygen, into the lungs. 2 In the supine position, 

the soft palate and/or tongue can fall posteriorly against 

4 

Nasopharynx 

Oropharynx 

Hypopharynx

the posterior pharyngeal wall, 2 or the lateral walls of the 

pharynx can collapse medially, 3 thereby obstructing the 

airway. Sites of obstruction vary between patients and 

typically occur at multiple levels of the airway. 4 

Obstructive sleep apnea affects approximately 2% of 

middle-aged women and 4% of middle-aged men. 5 Risk factors 

include smoking, excessive alcohol consumption, snoring, 

obesity, 6 and increased neck circumference. 7 In addition, 

functional and structural abnormalities also play a role. 

Cephalometric studies have identified anatomical (skeletal 

and soft tissue) abnormalities in sleep apnea patients. 

When compared to normal controls, these patients have 

elongated soft palates, large tongues, retrusive tongue 

positions, retrognathic maxillas and mandibles, retrusive 

chins, short anterior cranial bases, long anterior facial 

heights, inferiorly positioned hyoid bones, narrow 

posterior airway spaces, and narrowed lateral pharyngeal 

walls. 3,8-15 

Treatment 

Treatment for obstructive sleep apnea consists of non- 

surgical and surgical therapies. Non-surgical modalities 

include weight loss, nasal continuous positive airway 

pressure (CPAP), and dental appliances. 1 Surgical 

5

treatments include uvulopalatopharygoplasty (UPPP), laser 

midline glossectomy, lingualplasty, radiofrequency 

volumetric tissue reduction, inferior sagittal mandibular 

osteotomy and genioglossal advancement, hyoid myotomy and 

suspension, and maxillomandibular advancement. 16 

Non-surgical Therapy 

Weight Loss 

In obese patients or patients with increased neck 

circumference, weight loss can reduce sleep apnea 17-20 by 

decreasing the airway collapse. 21 Overly obese patients 

might consider gastric bypass surgery to aid in weight 

loss. 19 

Nasal Continuous Positive Airway Pressure (CPAP) 

The gold standard for treating sleep apnea is nasal 

CPAP. 16 A CPAP machine delivers pressurized air through a 

nose mask into a patient’s airway, preventing collapse of 

the surrounding soft tissues, thereby keeping the airway 

patent. 22 This therapy is non-invasive 1 and has been shown 

to increase airway area and volume within the oropharynx. 23 

The most notable changes are seen in the lateral rather 

than the anteroposterior (A-P) dimension. 23 Although nasal 

CPAP has been shown to be effective, users have reported 

6

mask discomfort, nasal dryness, and congestion, 24 which may 

lead to compliance issues. Compliance rates range from 

less than 50% 16 to as high as 75%, 24 leaving a large number 

of patients in need of another form of therapy. 

Oral Appliances 

Oral appliances are an available alternative 

treatment, especially in patients who find nasal CPAP too 

cumbersome to tolerate. 25 These appliances cover the 

dentition and position the mandible forward and/or advance 

the tongue, and increase the posterior airway space in the 

sagittal and lateral dimensions. 1 Although these 

positioners are well-tolerated by patients, they have 

undesirable effects on the dentition. Otsuka et. al 25 found 

significant decreases in occlusal contact area and biting 

force in patients who used oral appliances for 5 years. 

Proclination of the mandibular incisors, retroclination of 

the maxillary incisors, mesial movement of mandibular 

molars, and a decrease in the SNB angle have been reported 

with long-term usage, 26 as well as temporomandibular joint 

problems. 27 

7

Surgical Therapy 

Surgical treatment is indicated with a respiratory 

distress index (RDI) greater than 20, 28 oxyhemoglobin 

desaturation below 90%, excessive daytime sleepiness, 

significant cardiac arrhythmias associated with 

obstruction, when a specific anatomic abnormality is 

identified, non-surgical treatments are rejected, patients 

are medically stable, and they desire surgical therapy. 16 

The respiratory distress index is also known as the apnea- 

hypopnia index (AHI). 28 It is a measurement of airflow and 

is calculated as the total number of apnea (complete 

obstruction of airflow) and partial apnea (partial 

obstruction of airflow) episodes per hour of sleep. 28 

Uvulopalatopharyngoplasty 

Uvulopalatopharyngoplasty (UPPP) is a surgical 

procedure introduced by Fujita et al. in 1981, 29 involving 

“shortening the soft palate, amputating the uvula, and 

removing redundant lateral and posterior wall mucosa from 

the oral pharynx.” 4 Even though the soft palate is 

shortened, it can thicken, resulting in a narrower airway. 4 

UPPP has a 50% success rate, 30 possibly because it only 

addresses the retropalatal region of the airway, when many 

patients experience obstruction at multiple sites. 31 

8

Tongue-Reduction Procedures 

Other surgical procedures are aimed at reducing the 

size of the tongue and soft tissues in the inferior 

oropharynx. Laser midline glossectomy (LMG) involves an 

excision at the midline of the tongue of 2.5cm by 5cm. 16 

Lingualplasty is similar to LMG, but includes removal of 

tissue laterally and posteriorly in addition to the area 

removed by LMG. Radiofrequency tissue reduction shrinks 

the size of the tongue by using a probe to induce 

“coagulation necrosis and healing by scar and muscle 

contraction”. 16 

Advancement Osteotomies/Hyoid Myotomy 

Advancement of bones and bone segments has also been 

performed to enlarge the pharyngeal airway space. Inferior 

sagittal mandibular osteotomy and genioglossal advancement 

involve an advancement osteotomy of the bone where the 

genioglossus muscle attaches at the genial tubercles. 16 

After advancement, the bone segment is fixated to the lower 

border of the mandible. Hyoid myotomy and suspension is a 

procedure that advances the hyoid bone and its surrounding 

muscles in order to enlarge the hypopharyngeal airway. 16 

The surgical procedures discussed above are often 

referred to as Phase I surgery. They are performed alone 

9

or in combination depending upon the site(s) of airway 

constriction or collapse. Given that surgical procedures 

focused solely on one area of the airway do not have a high 

success rate, various surgical procedures have been 

performed simultaneously to address airway obstruction in 

multiple areas. 16 The success rates vary by procedure(s) 

and by patient. Traditionally, patients who undergo Phase 

I surgery without success are recommended for Phase II 

surgery. 

Maxillomandibular Advancement Osteotomies 

Advancement osteotomies of both the maxilla and the 

mandible have traditionally been considered Phase II 

surgery when non-surgical therapies and single-site 

surgeries, such as UPPP, hyoid suspension, and mandibular 

advancement, have been unsuccessful. 28 Many advocates of 

maxillomandibular advancement surgery are now recommending 

this procedure as a first surgical option in patients who 

have been diagnosed with multiples levels of airway 

collapse and those with craniofacial skeletal 

abnormalities. 28,32,33 

Maxillomandibular advancement (MMA) osteotomies have 

had success in treating obstructive sleep apnea. It has 

been proposed that advancing the surrounding skeletal 

10

structures causes the airway muscles to elongate, become 

more tense, and have a lesser tendency towards collapse 

during sleep. 34 

The success rate of MMA surgery has largely been 

measured by the Respiratory Distress Index (RDI). Criteria 

for success vary between an RDI of less than 10 and an RDI 

of less than 20. Utilizing an RDI criteria of less than 

10, the success rates of MMA have been reported as 65%, 35 

80%, 32 and 97%. 36 Success rates of 83%, 37 90%, 38 97%, 39 and 

100% 33 have been documented when an RDI of less than 20 was 

the treatment goal. 

Cephalometric Studies 

Several researchers have quantified the amount of 

surgical advancement and measured the structural 

anteroposterior (A-P) airway changes following MMA 

osteotomy utilizing a lateral cephalogram. The most 

frequently measured site is the posterior airway space 

(PAS), which is the distance between the base of the tongue 

and the posterior pharyngeal wall (PPW). 40 A reference line 

from point B through gonion to the PPW is typically used. 41 

Other measurements include the upper retropalatal airway 

space, narrowest retropalatal space, lowest retropalatal 

space, and narrowest retroglossal airway space. The upper 

11

etropalatal airway space is the airway distance from the 

posterior nasal spine (PNS) perpendicular to the PPW or 

perpendicular to a line drawn from sella (S) to basion 

(Ba). 42 The lowest retropalatal airway space is measured 

from the tip of the uvula to the PPW. 42 

Following an average maxillary advancement of 7.3mm 

and mandibular advancement of 12.5mm, Waite et al. 35 

reported a mean increase in PAS of 7mm at six weeks post- 

surgery. Following maxillary advancement of 6mm and 

mandibular advancement of 16mm, Riley et al. 43 showed a 187% 

increase in PAS measured at time points ranging between 4 

and 16 months after surgery. With a mean skeletal 

advancement of 10.2mm, Li et al. 37 measured a 73% increase 

in PAS and a 20% increase in the upper pharyngeal airway 

space at 3-6 months post-surgery. 

Airway changes following MMA have also been evaluated 

in patients without sleep apnea. Mehra et al. 41 studied 

patients 2.5 years after maxillary advancement of 4.15mm 

and mandibular advancement of 7.5mm. They found a 39% 

increase in the pharyngeal airway posterior to the soft 

palate and a 63% increase in PAS measured in the sagittal 

dimension. 41 Goncalves et al. 42 evaluated airway changes at 

5 days and at 34 months after maxillary advancement of 

2.4mm and mandibular advancement of 10mm. Immediately 

12

after surgery, the upper retropalatal space significantly 

decreased 4.2mm while the narrowest retropalatal, lowest 

retropalatal, and narrowest retroglossal airway spaces 

increased 2.9mm, 3.7mm, and 4.4mm, respectively. 42 Over the 

average 34 month follow-up period (range= 6 months to 9 

years 3 months), the upper retropalatal space increased 

3.9mm, almost returning to presurgical value, while the 

other areas remained stable. 42 

Computed Tomography Study 

Recognizing that measurements taken from a lateral 

cephalogram do not evaluate changes in the transverse 

dimension, Fairburn et al. 44 examined transverse and 

sagittal airway changes 3 to 6 months after MMA. In all 

patients, the mandible was advanced 10mm following by 

advancement of the maxilla to achieve a Class I occlusion. 

Helical computed tomography (CT) scans were obtained before 

and after surgery. This radiography modality scans the 

airway via axial slices every 2.5mm from the base of the 

skull to the trachea. Measurements were taken every 10mm 

(or every 4 th axial slice) from the level of the hard palate 

to the hyoid bone. At each level, the transverse airway 

dimensions significantly increased except at the level of 

the hyoid bone with the greatest change at the retroglossal 

13

(posterior tongue) area. In the A-P, or sagittal, 

dimension, there was a significant increase in airway size 

at all levels except the retroglossal area. 44 

Cone Beam Computed Tomography 

Lateral cephalometry has traditionally been used in 

orthodontics and oral surgery to examine the craniofacial 

skeleton, dentition, growth effects, and airway. 

Cephalometry is widely available, low in patient radiation, 

and inexpensive compared to computed tomography (CT) and 

magnetic resonance imaging (MRI). 1 The main limitation of 

this imaging modality is the inability to measure airway 

volume or examine lateral soft tissue structures. 1 

In recent years, a new technology, cone beam computed 

tomography (CBCT) has been developed and is gaining 

popularity in the realm of orthodontics and oral surgery. 

When compared to traditional CT, CBCT scans are faster, 

less expensive, more readily available, and expose the 

patient to less radiation. 45 Utilizing a cone-shaped x-ray 

beam, a 3-dimension image is acquired with one 360 degree 

scan of a patient. 46 The x-ray beams are oriented in a 

parallel fashion with the patient close to the sensor, 

therefore producing an image that has a magnification ratio 

of 1:1. 46 CBCT allows a more accurate evaluation of 

14

skeletal tissues, soft tissues, and the pharyngeal airway 

than lateral cephalograms and are more assessable than 

traditional CTs. 

Presently, little information is known regarding the 

effects of orthognathic surgery on the pharyngeal airway 

volume. Utilizing the Hitachi MercuRay machine, Sears 47 

evaluated volumetric changes in 20 patients who received 

orthognathic surgery to correct skeletal and dental 

dysplasias. Two patients received MMA plus advancement 

genioplasty whereas the remaining patients received 

different types of orthognathic surgery that involved one 

or two-jaw procedures. Pharyngeal airway volume was 

examined at 1 month (T1) and 6-8 months (T2) post-surgery 

and compared to the pre-surgical values (T0). For each 

group of patients, the total airway volume did not 

significantly change following surgery. 47 

When all surgical groups were evaluated together, the 

total airway volume significantly increased immediately 

following surgery, but there was not a significant change 

between T0 and T2. Nasopharyngeal volume significantly 

increased at both short-term and long-term follow-ups. 

Oropharyngeal volume increased in the short-term, but there 

was no significant change between T0 and T2 or between T1 

15

and T2. Hypopharyngeal volume did not show a significant 

change at any time point. 47 

It is difficult to assess the changes as a result of 

maxillomandibular advancement in the study by Sears because 

patients receiving different types of surgery were grouped 

together when changes were evaluated. This was probably 

due to the small sample size. 

Purpose of the Study 

The purpose of this study is to evaluate pharyngeal 

airway volume changes following MMA surgery in a larger 

sample of surgical patients than previously investigated by 

others. Airway volume will be measured pre-surgically 

(T0), 2-3 months following surgery (T1), and 4-12 months 

post-surgery (T2). We will also determine if there is a 

correlation between the amount of skeletal advancement and 

airway volume change. 

16

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41. Mehra P, Downie M, Pita MC, Wolford LM. Pharyngeal 

airway space changes after counterclockwise rotation of the 

maxillomandibular complex. Am J Orthod Dentofacial Orthop 

2001;120:154-159. 

42. Goncalves J, Buschang P, Goncalves D, Wolford L. 

Postsurgical Stability of Oropharyngeal Airway Changes 

Following Counter-Clockwise Maxillo-Mandibular Advancement 

Surgery. J Oral Maxillofac Surg 2006;64. 

43. Riley RW, Powell NB, Guilleminault C, Nino-Murcia G. 

Maxillary, mandibular, and hyoid advancement: an 

alternative to tracheostomy in obstructive sleep apnea 

syndrome. Otolaryngol Head Neck Surg 1986;94:584-588. 

44. Fairburn SC, Waite PD, Vilos G, Harding SM, Bernreuter 

W, Cure J et al. Three-dimensional changes in upper airways 

of patients with obstructive sleep apnea following 

maxillomandibular advancement. J Oral Maxillofac Surg 

2007;65:6-12. 

21

45. Mozzo P, Procacci C, Tacconi A, Martini PT, Andreis IA. 

A new volumetric CT machine for dental imaging based on the 

cone-beam technique: preliminary results. Eur Radiol 

1998;8:1558-1564. 

46. Mah J, Hatcher D. Three-dimensional craniofacial 

imaging. Am J Orthod Dentofacial Orthop 2004;126:308-309. 

47. Sears C. Pharyngeal Airway Change After Orthognathic 

Surgery as Assessed by Conebeam Computed Tomography. 

Department of Growth and Development. San Francisco: 

University of California; 2006: p. 1-23. 

22

CHAPTER 3: JOURNAL ARTICLE 

Abstract 

Purpose: The purpose of this study was to examine the 

effects of maxillomandibular advancement surgery on the 

pharyngeal airway volume in the short term and longer term 

and determine if a relationship exists between the amount 

of advancement and airway volume change. Materials and 

Methods: Records of 55 patients who had undergone combined 

orthodontic treatment and maxillomandibular advancement 

osteotomies were collected and analyzed. Cone beam 

computed tomography scans were taken within three days 

pre-surgery and at least eight weeks post-surgery. The 

pharyngeal airway volume was measured at pre-surgery (T0), 

2-3 months post-surgery (T1), and 4-12 months post-surgery 

(T2). Results: There was a significant increase in 

airway volume between T0 and T1 and between T0 and T2. No 

significant differences were found between T1 and T2. 

Correlations between the amount of surgical advancement and 

percentage of volumetric change were confounding and 

inconsistent between patients. Conclusion: In this 

study, maxillomandibular advancement osteotomies resulted 

in a significant increase in airway volume 2-3 months after 

23

surgery, and this change appeared to be stable up to one 

year following surgery. 

Introduction 

Combined orthodontic-orthognathic surgical treatment 

has made it possible to treat skeletal and dental 

dysplasias in patients where orthodontics alone cannot 

produce a desirable result. By altering the position of 

the jaws, the size and shape of the external and internal 

surrounding soft tissues are affected, including the 

pharyngeal airway, which could influence respiration. One 

of the goals of orthognathic surgery is to maintain or 

increase the size of the pharyngeal airway as not to 

predispose a patient to obstructive sleep apnea. 1 For sleep 

apnea patients, surgical advancement of both the maxilla 

and mandible is often performed to intentionally increase 

the size of the pharyngeal airway 2 to alleviate or reduce 

symptoms of the disorder. 

Obstructive sleep apnea is known to affect 

approximately 2-4% of middle-age adult women and men, 

respectively. 3 Risk factors include smoking, excessive 

alcohol consumption, snoring, obesity, 4 and increased neck 

circumference. 5 When compared to normal controls, apneic 

24

patients often have elongated soft palates, large tongues, 

retrusive tongue positions, retrognathic maxillas and 

mandibles, retrusive chins, short anterior cranial bases, 

long anterior facial heights, inferiorly positioned hyoid 

bones, narrow posterior airway spaces, and narrowed lateral 

pharyngeal walls. 6-14 

In patients with sleep apnea, it is known that the 

surrounding soft tissues and musculature of the airway can 

collapse or constrict during sleep in the oropharyngeal 

region of the airway. 15 Sites of airway collapse and 

constriction are not identical in all patients, and some 

have multiple sites of obstruction. 16 

Treatment for obstructive sleep apnea consists of non- 

surgical and surgical therapies. Non-surgical modalities 

include weight loss, nasal continuous positive airway 

pressure (CPAP), and dental appliances. 15 Surgical 

treatments include, but are not limited to, 

uvulopalatopharygoplasty (UPPP), laser midline glossectomy, 

lingualplasty, radiofrequency volumetric tissue reduction, 

inferior sagittal mandibular osteotomy and genioglossal 

advancement, hyoid myotomy and suspension, and 

maxillomandibular advancement (MMA). 17 

Advancement osteotomies of both the maxilla and the 

mandible have traditionally been considered when non- 

25

surgical therapies and single-site surgeries have been 

unsuccessful. 18 Many advocates of MMA surgery recommend 

this procedure as a first surgical option in patients who 

have been diagnosed with multiples levels of airway 

collapse and those with craniofacial skeletal 

abnormalities. 18-20 

Analyzing lateral cephalograms in patients following 

maxillomandibular advancement surgery, significant 

increases in airway size have been reported in patients 

with sleep apnea 21-23 and in patients without sleep apnea. 24,25 

Following an initial increase in airway size, some studies 

reported a decrease in airway size 3.5 years 26 and 4 years 

post-surgery, 27 although the airway did not return to pre- 

surgical values. 

Recognizing that measurements taken from a lateral 

cephalogram do not evaluate changes in the transverse 

dimension, Fairburn et al. 28 examined transverse and 

sagittal airway changes and showed a significant increase 

in airway size 2-dimensionally at multiple levels of the 

pharyngeal airway. 

Recent studies have examined airway volume in order to 

obtain a more accurate understanding of how the pharyngeal 

airway changes following orthognathic surgery. Two 

studies 2,29 have examined 3-dimensional airway changes 

26

subsequent to orthognathic surgery utilizing cone beam 

computed tomography (CBCT). Stigall 29 reported non- 

significant enlargement of the combined nasopharyngeal and 

oropharyngeal airways following surgery in 9 patients that 

had mandibular advancement osteotomies. Six of these 

patients also had accompanying maxillary advancement 

osteotomies. 

Sears 2 examined volumetric changes in 20 orthognathic 

surgery patients. Two patients received maxillary, 

mandibular, and genioplasty advancement whereas the 

remaining patients received different types of orthognathic 

surgical procedures. Pharyngeal airway volume was examined 

at 1 month (T1) and 6-8 months (T2) post-surgery and 

compared to the pre-surgical values (T0). For each group 

of patients, the total airway volume did not change 

significantly following surgery. 2 However, when all 

surgical groups were evaluated together, the total airway 

volume significantly increased immediately following 

surgery (T1), but there was not a significant change 

between T0 and T2. 2 

The majority of past research has measured airway 

changes in mainly one dimension (A-P) when the airway 

itself is a complex 3-dimensional structure. There are few 

studies with long-term data or data at multiple time points 

27

that allow a better understanding of what happens to the 

airway over time. The CBCT studies have been limited by 

small sample sizes and the fact that patients having 

different types of orthognathic surgery were analyzed 

together. 

The purpose of the current study was to evaluate 

pharyngeal airway volume changes following MMA surgery in a 

larger sample of surgical patients than previously 

investigated by others and at multiple time points to 

obtain a more accurate indication of how the airway volume 

is affected. In addition, we also wanted to determine if a 

correlation existed between the amount of skeletal 

advancement and the percentage of airway volume change. 

Materials and Methods 

Sample 

For this retrospective study, records of 55 patients 

who had undergone combined orthodontic treatment and 

maxillomandibular advancement surgery to correct skeletal 

dysplasias were collected. The sample was comprised of 35 

females and 20 males, including 7 patients with obstructive 

sleep apnea. Eighteen patients had a genioplasty procedure 

(14 advancements, 4 reductions). The mean age was 28.33 

28

years. Females had a mean age of 28.31 years (range = 17- 

60 years), and males had a mean age of 28.35 years (range = 

17-59 years). The inclusion criteria were combined 

orthodontic/orthognathic surgery patients who had undergone 

maxillomandibular advancement surgery, had pre-surgical 

CBCT scans taken within a week prior to surgery and at 

least one scan taken at a minimum of eight weeks following 

surgery. The exclusion criteria were patients possessing 

craniofacial syndromes. 

All surgeries were performed by one of two oral 

surgeons utilizing the same surgical technique, which 

consisted of a bilateral sagittal split advancement 

osteotomy (BSSO) of the mandible followed by a single or 

multiple piece maxillary advancement osteotomy. For large 

surgical movements, bone grafts were placed in the 

osteotomy site. Prior to rigid fixation of each jaw, the 

mandibular condyles were seated in centric relation. 

Imaging 

Pre-surgical and post-surgical CBCT scans were 

performed utilizing the same i-CAT CBCT machine (Imaging 

Sciences International, Hatfield, PA). The field of view 

was 23cm by 19cm. All scans were taken with the condyles 

seated in centric relation. 

29

Pharyngeal airway volume was measured at three time 

points: T0 (pre-surgery), T1 (2-3 months post-surgery), and 

T2 (4-12 months post-surgery, mean = 7 months). 18 

patients had data for all three time points, 29 patients 

only had data at T0 and T1, and 8 patients only had data at 

T0 and T2. CBCT scans were analyzed using V-Works 4.0 3D 

software (CyberMed Inc., Seoul, Korea) and the beta version 

of Dolphin 3D (Chatsworth, CA). 

Isolating the Pharyngeal Airway and Volumetric Measurements 

Volumetric data was obtained after importing images 

into V-Works 4.0 and isolating the pharyngeal airway space, 

which included the oropharynx and a portion of the 

nasopharynx (Figure 3.1). The anterior border was 

comprised of the posterior soft palate and base of the 

tongue. The superior/anterior border was defined by a line 

created from PNS to sella (S), and the superior border was 

a line along the inferior border of the body of the 

sphenoid bone. The posterior border was the posterior 

pharyngeal wall. The inferior border was a line created 

from the tip of the epiglottis perpendicular to the 

posterior pharyngeal wall. After the pharyngeal airway was 

isolated from the surrounding tissues, the total airway 

volume of the sculpted airway (Figure 3.2) was calculated. 

30

Line from Sella to 

PNS 

Posterior of Soft 

Palate 

Posterior of Tongue 

Figure 3.1: Borders of Measured Pharyngeal Airway 

31 

Sella 

PNS Line at Inferior 

Border of Sphenoid 

Bone 

Posterior Pharyngeal 

Wall 

Line at Tip of 

Epiglottis

T0 A T1 A 

T0 B 

Figure 3.2: Sculpted Pharyngeal Airway Volume of a Patient 

at T0, T1, and T2. (T0= Pre-surgery; T1= 2 mo. postsurgery; 

T2= 7 mo. post-surgery; A= A-P view of the airway; 

B= lateral view of the airway as viewed from the anterior) 

The pharyngeal airway was divided into superior and 

inferior aspects by creating a line from the maxillary 

incisal edge perpendicular to the inferior aspect of the 

posterior pharyngeal wall (Figure 3.3). Superior 

pharyngeal airway and inferior pharyngeal airway volumes 

were also calculated. 

T1 B 

32 

T2 A 

T2 B

Line from Maxillary 

Incisor to Posterior 

Pharyngeal Wall 

Figure 3.3: Highlighted Pharyngeal Airway Volume 

with Superior and Inferior Aspects Identified 

Determining Amount of Surgical Advancement 

In order to determine the amount of surgical 

advancement, or anteroposterior (A-P) movement, of each 

jaw, CBCT scans taken before surgery and 2 weeks after 

surgery were used. Each scan was imported into Dolphin 3D. 

Head position was oriented with Frankfort Horizontal 

parallel to the horizontal plane (x-axis, or axial plane) 

and the facial midline centered on the vertical plane (z- 

axis, or sagittal plane). A plane created through nasion 

33 

Superior 

Pharyngeal 

Airway 

Inferior 

Pharyngeal 

Airway

perpendicular to Frankfort Horizontal represented the y- 

axis, or coronal plane (Figure 3.4). 

Figure 3.4: 3D Skull Depicting X, Y, Z Axis 

Three skeletal landmarks (nasion, point A, and point 

B) were identified. The A-P surgical movement of each jaw 

was calculated using the z-axis coordinate. The relative 

position of point A and point B to nasion was recorded for 

the pre-surgical and 2 week post-surgical scans and 

compared to determine the amount of advancement. It should 

be noted that the surgical technique utilized involved 

34

counterclockwise rotation of the mandible; therefore the 

amount of mandibular advancement measured may not equal the 

size of the osteotomy gap. 

Statistics 

Data analysis was performed using SPSS 14.0 (SPSS 

Inc., Rainbow Technologies, Chicago, IL). Descriptive 

statistics calculated the mean, range, and standard 

deviation of the airway volume at each time point along 

with the percentage of volumetric change between time 

points. Paired t-tests and a Wilcoxon signed rank test 

were used to test for significant differences in airway 

volume. Pearson’s correlation was used to determine if a 

relationship existed between the amount of advancement of 

each jaw and the percentage of airway volume change between 

time points. For reliability testing, ten percent of the 

sample was randomly selected and remeasured. Cronbach’s 

alpha Inter-item Correlation was the statistic used to 

determine reliability. 

Results 

Descriptive statistics are summarized in Tables 3.1, 

3.2, and 3.3. Figures 3.5, 3.6, and 3.7 show the mean 

35

airway volume measurements over time. For patients 

measured at all three time points (n=18), there was a 

significant increase in total airway volume from baseline 

(T0) to T1 (t=-4.954, p

Table 3.1: Descriptive Statistics for Patients Measured at T0, T1, and T2 (n=18) 

Mean Minimum Maximum Standard 

Deviation 

Maxillary Advancement (mm) 3.66 1.00 9.50 2.32 

Mandibular Advancement (mm) 9.21 0.30 14.4 4.09 

T0 Total Airway Volume (mm³) 17156.24 8248.90 26222.27 4819.08 

T0 Superior Airway Volume (mm³) 11996.63 5949.76 17212.55 3647.96 

T0 Inferior Airway Volume (mm³) 5159.77 2245.95 9867.20 2256.17 







T0-T1 Total Volume Percent Chang (%) 51.93 -15.7 139.70 38.39 

T0-T1 Superior Volume Percent Change(%) 45.28 4.60 97.90 28.32 

T0-T1 Inferior Volume Percent Change(%) 89.43 -68.30 428.30 118.23 

T1-T2 Total Volume Percent Change (%) -1.91 -26.30 36.1 20.32 

T1-T2 Superior Volume Percent Change(%) -1.12 -18.00 29.40 12.54 

T1-T2 Inferior Volume Percent Change (%) 4.50 -60.50 201.80 63.43 

T0-T2 Total Volume Percent Change (%) 44.21 8.10 102.3 28.14 

T0-T2 Superior Volume Percent Change (%) 42.16 5.70 86.80 25.62 


37

Table 3.2: Descriptive Statistics for Patients Measured at T0 and T1 (n=29) 


Deviation 










T0-T1 Superior Volume Percent Change (%) 35.47 -11.37 101.97 26.59 


Table 3.3: Descriptive Statistics for Patients Measured at T0 and T2 (n=8) 


Deviation 










T0-T2 Superior Volume Percent Change (%) 34.52 -.69 119.42 38.56 

T0-T2 Inferior Volume Percent Change (%) 74.56 1.50 190.29 65.72 

38

Volume (cubic mm) 

30000.00 

25000.00 

20000.00 

15000.00 

10000.00 

5000.00 

0.00 

Pharyngeal Airway Volume T0-T1-T2 (n=18) 

T0 T1 T2 

Figure 3.5: Airway Volume T0-T1-T2 (n=18) 


30000 

25000 

20000 

15000 

10000 

5000 

Pharyngeal Airway Volume T0-T1 (n=29) 

0 

T0 T1 

Total 

Airway 

Superior 

Airway 

Inferior 

Airway 

Figure 3.6: Airway Volume T0-T1 (n=29) 


30000 

25000 

20000 

15000 

10000 

5000 

0 

Pharyngeal Airway Volume T0-T2 (n=8) 

T0 T2 

Figure 3.7: Airway Volume T0-T2 (n=8) 

39 

Total Airway 

Superior Airway 

Inferior Airway 

Total Airway 

Superior Airway 

Inferior Airway

Patients measured at T0 and T1 (n=29) had a 

significant increase in total airway volume (t=-8.220, 

p

percent change from T0 to T2 (r=.558, p

Table 3.6: Pearson’s Correlation for Surgical Advancement 

Vs. Percentage of Airway Volume Change for Patients 

Measured at T0 and T2 (n=8) 

Correlation Coefficient r p-value 

Maxillary Adv. vs. Total Volume % Change .585 .128 

Maxillary Adv. vs. Superior Volume % Change .599 .117 

Mandibular Adv. vs. Total Volume % Change .664 .073 

Mandibular Adv. vs. Inferior Volume % Change .852 **.007 

** p

surrounding soft tissues encroaching upon the airway space, 

with the airway size rebounding after post-surgical 

swelling subsided. All of the remaining patients showed an 

increase in total airway volume from T0 to T1 and from T0 

to T2. 

When the airway volume was separated into superior and 

inferior components, the pattern of change was similar to 

the changes in overall volume, with a significant increase 

from T0 to T1 and a small, but insignificant, decrease from 

T1 to T2. 

The results of Pearson’s correlation were confounding. 

In patients measured at all three time points (n=18), 

significant moderate correlations were found between the 

amount of maxillary advancement and total volume percent 

change and between the amount of maxillary advancement and 

superior volume percent change between T0 and T2. For 

patients measured at T0 and T2 (n=8), significant high 

correlations were found between the amount of mandibular 

advancement and inferior volume percent change. No groups 

of patients exhibited similar correlations. Several 2- 

dimensional studies 26,27,30 and one CBCT study 2 also found 

airway changes to be unpredictable and not correlated to 

the amount of surgical advancement. A possible explanation 

for the results of the present study is that the method 

43

employed to divide the airway into superior and inferior 

components may not have been accurate since the maxillary 

incisal edge most likely changed vertical position as a 

result of surgery; therefore, the airway may not have been 

separated at the same point along the posterior pharyngeal 

wall. For future studies, a hard tissue landmark that is 

not surgically altered could be utilized. 

There are other variables that could have influenced 

individual surgical results, including differential patient 

response to surgery, soft tissue thickness, muscle 

tonicity, body mass index, age, gender, and the fact that 

both jaws were surgically repositioned rather than one jaw. 

The results of the current study differ from other 

studies that measured airway volume utilizing CBCT. 

Stigall found no significant differences in airway volume 

after mandibular advancement surgery. This may have been 

due to the small sample size (n=9, 6 patients also had a 

maxillary advancement surgery), soft tissue swelling of 

tissues adjacent to the airway since post-surgical scans 

were taken between 1 and 8 weeks post-surgery, and/or the 

small amount of mandibular advancement (mean = 3.25 mm). 

Sears 2 found a significant increase in airway volume 

one month following surgery, but volume decreased at 6-8 

months following surgery. Airway volume did not return to 

44

the pre-surgical values, but there was not a significant 

difference between the 6-8 month measurements and baseline 

values. The sample in Sears’s study consisted of 20 

patients who had undergone a variety of orthognathic 

surgical procedures, and only two of these patients 

received maxillomandibular advancement osteotomies. When 

these two patients were examines separately, no significant 

changes were found. 2 

The majority of previous studies examined two- 

dimensional changes in airway size. Even though the 

present study examined the 3-dimensional changes, the 

results support the 2-dimensional findings, which report an 

increase in airway size following maxillomandibular 

advancement osteotomies. However, previous studies 26,27 

showed a decrease in size over time whereas no significant 

differences in volume were found in the present study 

between T1 and T2. 

The present study had several limitations. Tongue and 

head position were not standardized, which could have 

influenced the results. As previously mentioned, the 

method of separating the superior and inferior airway 

components may not have been accurate due to utilizing a 

skeletal landmark that changed position with surgical 

movement. The sample was mainly a non-apneic sample, the 

45

mean age was 28 years old, and the majority of patients 

were females whereas sleep apnea patients are largely 

middle-age males. 

Another limitation is the small number of patients who 

had data for all time points (n=18). It would have been 

helpful to have more long-term data and to compare the 

results between patients with smaller initial airway 

volumes to those with larger initial volumes. 

Additionally, sleep apnea patients could have been compared 

with non-apneic patients to determine if a difference 

exists between the two groups. 

Although this study showed an increase in pharyngeal 

airway volume following maxillomandibular advancement 

surgery, it is unknown how much of an effect this has on 

patients’ ability to breath since the size of a structure 

may not accurately reflect its ability to function 

properly. It would be beneficial to evaluate the pre- and 

post-surgical functional airway capacity utilizing airflow 

or air resistance studies and to compare these findings to 

anatomic size and cross-sectional areas of the airway. 

46

Conclusions 

1. In this study, patients had a statistically 

significant increase in pharyngeal airway volume 

following maxillomandibular advancement surgery, and 

this change appeared to be stable up to one year 

following surgery. 

2. Correlation data between the amount of surgical 

advancement and airway change was inconsistent and, 

therefore, inconclusive. 

47

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51

VITA AUCTORIS 

Brandy Lee Burgess was born on June 25, 1977 in Lake 

Charles, Louisiana and grew up in Shreveport, Louisiana for 

the first twelve years of her life before moving to 

southern California. In 1995, she graduated as 

valedictorian of her high school graduating class at Quartz 

Hill High School. She earned a B.S. in Psychobiology from 

UCLA in 1999, graduating cum laude. 

While she was in college, Brandy decided she wanted to 

become an orthodontist. She was accepted into the UCLA 

School of Dentistry in 2000 and graduated with a Doctor of 

Dental Surgery degree in 2004. She was also elected into 

the prestigious Omicron Kappa Upsilon dental honor society. 

Following dental school, Brandy moved across the 

country to Gainesville, Florida to complete a year long 

fellowship in orthodontics. In 2005, she began the 

orthodontics residency program at Saint Louis University 

where she is completing a certificate in orthodontics and a 

M.S. in Dentistry. She is excited to enter private 

practice and begin her career as an orthodontist. 

52

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