PHARYNGEAL AIRWAY EVALUATION FOLLOWING ISOLATED MANDIBULAR
SETBACK SURGERY UTILIZING CONE BEAM COMPUTED TOMOGRAPHY
Shireen K. Irani, D.D.S.
A Thesis Presented to the Graduate Faculty of
Saint Louis University in Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Dentistry
2014
COMMITTEE IN CHARGE OF CANDIDACY:
Associate Professor Ki Beom Kim,
Chairperson and Advisor
Assistant Clinical Professor Reza Movahed
Associate Clinical Professor Donald R. Oliver
i
DEDICATION
This work is dedicated to my wonderful husband, Firdosh. You have done
nothing but encourage and support me through this journey. You know how
much I love and appreciate you.
To my family, who listened to all of my heartaches and stresses
throughout this time in my life. Thanks for always being there.
Lastly, to the faculty of Saint Louis University, whose guidance and
instruction have built a strong foundation for me to grow a fulfilling practice and
future. Thank you all for always believing in me.
ii
ACKNOWLEDGEMENTS
This project was not possible without the help and support of the following
individuals:
Dr. Ki Beom Kim. Thank you for your guidance during my thesis preparation
and for enriching my education with your help and guidance in the classroom as
well as the clinic.
Dr. Rolf Behrents. Thank you for allowing me to be a part of the heritage at
Saint Louis University’s orthodontic program.
Dr. Donald Oliver. Thank you for your attention to detail during my thesis
preparation and revisions. I learn from your patience every day. The value of
your clinical guidance cannot be measured.
Dr. Reza Movahed. Thank you for taking the time to assist in the thesis
progression and for being a constant motivator.
Dr. Yong-II Kim. Thank you for the use of your long-term records in this
study.
Dr. Heidi Israel and Dr. Tomazic. Thank you for your assistance with the
statistical analysis for this thesis.
iii
TABLE OF CONTENTS
List of Tables ........................................................................................................ vi
List of Figures ...................................................................................................... vii
CHAPTER 1: INTRODUCTION ............................................................................ 1
CHAPTER 2: REVIEW OF THE LITERATURE
Pharyngeal airway anatomy........................................................... 3
Obstructive sleep apnea ................................................................ 4
Treatment for obstructive sleep apnea .......................................... 8
Nonsurgical treatment .............................................................. 8
Diet and lifestyle modification ........................................... 8
Pharmacologic agents ...................................................... 9
Positive airway pressure devices ................................... 10
Oral appliances .............................................................. 11
Surgical Treatment ................................................................. 12
Stage I surgical treatment ............................................... 14
Adenotonsillectomy/tonsillectomy……………………….14
Nasal surgery................................................................15
Uvulopalatopharyngoplasty……………………………...15
Base of tongue surgery…………………………………..16
Genioglossal advancement/genioplasty………………16
Radiofrequency ablation………...……………………...16
Laser midline glossectomy….………….…………........17
Hyoid myotomy suspension……….…..………………..17
Stage II surgical treatment.............................................. 17
Maxillomandibular advancement surgery………………17
Tracheotomy………………………..……………………..18
Airway Imaging ............................................................................ 19
Lateral cephalometric radiography ......................................... 19
Magnetic resonance imaging.................................................. 20
Standard computed tomgraphy .............................................. 20
Fast computed tomography .................................................... 21
Cone beam computed tomography ........................................ 21
Airway volume change following mandibular setback surgery ..... 22
Cephalometric studies ............................................................ 23
Computed tomography studies............................................... 27
Cone beam computed tomography studies ............................ 27
Sleep related disorders........................................................... 29
Statement of Thesis ..................................................................... 30
Literature Cited ............................................................................ 32
CHAPTER 3: JOURNAL ARTICLE
Abstract ....................................................................................... 40
Introduction .................................................................................. 42
iv
Materials and Methods ................................................................ 43
Sample ................................................................................... 43
Cone Beam Computed Tomography (CBCT) technique ........ 44
Calculation of surgical movement ........................................... 45
Isolating the pharyngeal airway .............................................. 46
Statistical analysis .................................................................. 48
Results ......................................................................................... 49
Cephalometric data..........………………………………………..49
Volumetric data……………………………………………………49
Discussion……………………………………………………………..53
Conclusion…………………………………………….......................57
Literature Cited………………………………………………………..58
Appendix ............................................................................................................ 62
Vita Auctoris ....................................................................................................... 68
v
LIST OF TABLES
Table 3.1 Descriptive statistics for volumes ....................................................... 50
Table 3.2 Descriptive statistics for TR and AP dimensions ............................... 50
Table 3.3 Pair wise comparison table ................................................................ 52
Table 3.4 Volume percent change .................................................................... 53
Table A.1 Within-subjects effects for volumes and dimensions ........................ 62
Table A.2 Multivariate Analysis for volumes and dimensions ........................... 63
vi
LIST OF FIGURES
Figure 2.1 Pharyngeal Airway Anatomy .............................................................. 4
Figure 3.1 Measurement of surgical movement................................................. 45
Figure 3.2 Segmentation of OP and HP boundaries.......................................... 47
Figure 3.3 Segmentation of TR and AP lenghts ................................................ 48
Figure 3.4 Graph of change in means of volumes ............................................. 50
Figure A.1 Estimated marginal means of volume OP ........................................ 64
Figure A.2 Estimated marginal means of volume HP ........................................ 64
Figure A.3 Estimated marginal means of total volume ...................................... 65
Figure A.4 Estimated marginal means of TR at OP ........................................... 65
Figure A.5 Estimated marginal means of TR at HP ........................................... 66
Figure A.6 Estimated marginal means of AP at OP ........................................... 66
Figure A.7 Estimated marginal means of AP at HP ........................................... 67
vii
CHAPTER 1: INTRODUCTION
A severe Class III skeletal relationship poses both esthetic and functional
problems. Its correction typically involves a combination of orthodontic and
orthognathic surgical treatment where orthodontics alone cannot produce a
desirable result. The surgical procedures that alter the facial skeleton also affect
the soft tissues that are attached to the bones to effect the facial changes. The
soft palate, tongue, hyoid bone and muscles are directly or indirectly attached to
the maxilla and mandible, and surgical movements of the jaws will affect the
tension of these muscles. One aspect of the surgery which has recently raised
awareness is the effect of the surgical movements on the pharyngeal airway
space (PAS). The result is an alteration in the volume of the nasal and oral
cavities, and PAS dimensions depending on the type and magnitude of surgery.
Research in the area of pharyngeal airway has been important in elucidating the
possible link of potential airway obstruction and the development of obstructive
sleep apnea (OSA). Certain orthognathic procedures to correct a skeletal Class
III relationship may induce an adverse change to the jaws and PAS that can
promote or aggravate breathing disorders or even perpetuate OSA.
OSA is a breathing disorder that could have potential life threatening
consequences. Typically patients diagnosed with OSA will pursue the first phase
of non-surgical treatment that includes weight loss, smoking cessation, or
continuous positive airway pressure and in some cases oral appliances. In
severe cases, surgical intervention is necessary with maxillomandibular
1
advancement (MMA) surgery providing the highest success rates. Studies have
been done to show the positive effect of MMA surgery on the airway volume, but
very few have shown the effect on the airway volume with correction of a skeletal
Class III via a mandibular setback surgery or combined with a maxillary
advancement.
Most of these studies have been done using lateral cephalograms which
allow a 2-dimensional evaluation of a 3-dimensional object. This proves to be a
disadvantage and to better understand how the airway is affected, it is important
to study the entire structure rather than a segment of it. The advent of 3dimensional imaging and advancement in the utilization with cone beam
computed tomography (CBCT), permits the accuracy and reliability of the airway
volume as a whole to be examined.
By utilizing CBCT to evaluate the changes in pharyngeal airway volume
following correction of skeletal Class III relationships via a mandibular setback
surgery alone, a better understanding of the impact of this procedure can be
determined. If a detrimental effect on the airway is determined then a
modification in treatment protocol for patients needs to be undertaken to prevent
the onset of OSA and more importantly for patients already diagnosed with OSA,
the prevention of a life threatening outcome.
2
CHAPTER 2: REVIEW OF THE LITERATURE
Pharyngeal Airway Anatomy
The upper airway is an intricate structure composed of soft tissue and muscles
that work in a dynamic relationship to perform many different physiologic
functions including respiration, deglutition, and vocalization.1 The upper airway is
divided into three regions: the nasopharynx, oropharynx, and the hypopharynx
(Figure 2.1). The nasopharynx is the area between the hard palate and nasal
turbinates. The oropharynx is a region that is subdivided into the retropalatal area
at the level of the hard palate to the caudal margin of the soft palate and the
retroglossal region at the caudal margin of the soft palate to the epiglottis base.
The hypopharynx is a region from the base of the tongue to the cervical
esophagus.1
The pharyngeal airway lies posterior to the nasal cavity, oral cavity, and larynx
and extends inferiorly posterior to the nasal turbinates towards the esophagus.
The upper airway is bounded superiorly by the basilar portion of the occipital
bone and body of the sphenoid; anteriorly by the nasal turbinates, soft palate,
tongue, and epiglottis; posteriorly by the superior, middle and inferior pharyngeal
constrictor muscles; and laterally by soft tissue and several muscles
(hypoglossus, stylogossus,stylohyoid, palatoglossus and palatopharyngeus),2 the
palatine tonsils, and other pharyngeal fat pads.1
3
Figure 2.1 – Pharyngeal Airway Anatomy – adopted from Burgess3
Obstructive Sleep Apnea
Obstructive Sleep Apnea (OSA) is characterized by repeated increases in
resistance to airflow within the upper airway causing obstruction.4 OSA is
characterized by the periodic partial or complete collapse of the upper airway
during rapid eye movement (REM) and non-REM sleep that results in episodes
of hypopnea (diminished airflow of at least 30% lasting at least 10 seconds) or
apnea (absent airflow).4-6 A predominant factor in the etiology of OSA is the
collapse of soft tissues in the upper airway, including the retropalatal and
retroglossal regions of the oropharynx.1 The lateral pharyngeal walls are also a
cause for airway obstruction in patients with OSA, and an increase in thickness
4
of the walls predisposes to the development of OSA.4 While sites of airway
obstruction vary from patient to patient, obstructions typically can occur at
multiple levels in the airway.7
Epidemiologic estimates of OSA prevalence is about 4% for men and 2% for
women in the age group 30-60 years for those living in the United States when
considering subjective day-time sleepiness.8 Approximately 1 in 5 adults has
at least mild OSA and 1 in 15 adults has OSA of moderate or worse severity.8
According to the Wisconsin Sleep Cohort Study, OSA prevalence is 24% for men
and 9% for women when using only Apnea Hypopnea Index (AHI) greater than 5
as an objective measure.5, 9-13
OSA prevalence also increases with age and obesity.8 Risk factors for OSA
include smoking,8 obesity14 and or those with a high body mass index
(BMI>25),15 snoring, increased neck circumference (collar size greater than 16
inches for women and 17 inches for men),16 a modified Mallampati grade III or IV,
where the anatomy of the oral cavity is visualized; specifically, whether the base
of the uvula, faucial pillars and soft palate are visible. Grade III or IV are difficult
to intubate.15 In addition factors that decrease respiratory muscle tone, such as
excessive alcohol intake, respiratory depressing drugs,15 or neurological
disorders.15
Anatomic or physiologic factors can cause increased airway resistance. While
obesity is the main predisposing factor for OSA,14 at a greater risk for OSA are
non-obese patients with craniofacial dysplasias, such as micrognathia and
5
retrognathia.17, 18 Although mandibular body length appears to be an associated
factor, it does not support causality.18
Orofacial characteristics that include high-arched palate, nasal septal
deviation, long anterior facial height, steeper and shorter anterior cranial base,
inferiorly displaced hyoid bone, large and retropositioned tongue, a long soft
palate, large parapharyngeal fat pads, and decreased posterior airway space are
additional predisposing factors in adults.4, 15 A meta-analysis evaluating
craniofacial and upper airway morphology in pediatric sleep-disordered breathing
determined that children with obstructive sleep apnea have a reduced
anteroposterior width of the upper airway at the level of the posterior nasal spine
and superiorly at the level of the adenoidal mass.19 Physiologic factors are those
that functionally reduce dilation of airway muscles, such as the decreased
response by the tongue or soft palate in response to4 negative airway pressure
and increased pharyngeal collapsing forces and pharyngeal compliance. 15, 20 The
balance of constricting forces from the negative inspiratory intraluminal suction
generated by the diaphragm and dilating forces of the pharyngeal musculature is
dysfunctional in obstructive sleep apnea.21
The collapse of the airway can be impacted by patient sleep positioning.15 The
supine position is the most susceptible position to airway collapse due to the
posterior positioning of the tongue and or soft palate against the posterior
pharyngeal wall or the medial collapse of the lateral soft tissue walls of the
pharynx.20, 22 With air flow consequently reduced, the patient must increase the
speed of the airflow to maintain the required oxygen supply to the lungs. This
6
increase in airflow velocity causes vibration of soft tissues, which produces
snoring.4 Mouth opening may also exacerbate upper airway resistance due to the
increased collapsibility and or decreased efficacy of dilator muscles.4 The gold
standard in the diagnosis of OSA is nocturnal attended polysomnography, which
aims to measure the number of apneas and hypopneas during sleep along with
monitoring brain activity, eye movement, muscle activity, cardiac rhythm, and
pulse oximetry.23 The apnea-hypopnea index (AHI) 6 is the average number of
apneas and hypopneas per hour of sleep. The AHI index is used to classify the
severity of OSA on the basis of 3 categories: (1) Mild OSA (5-15 events/hour)
(2) Moderate OSA (15-30 events/hour) and (3) Severe OSA (more than 30
events/hour).23 Another index used is the respiratory disturbance index (RDI),
which in addition to hypopneas and apneas, includes respiratory effort-related
arousals (RERAs).15 A RERA event is described as an increase in respiratory
effort for 10 or more seconds leading to an arousal from sleep, but not meeting
the criteria for a hypopneic or apneic event.15 OSA is diagnosed if the RDI
reaches a threshold typically 5 or 10.7
Reduction in the amount of air and thus oxygen reaching the lungs can lead to
recurrent airway obstructions which can have life-threatening consequences.
This leads to an increase in carbon dioxide accumulation and reduction in blood
oxygen saturation.7 Disturbances in normal sleep patterns, dry mouth, excessive
daytime sleepiness, cognitive impairment, morning headaches, absence of
dreams, fatigue, decreased libido, depression, pulmonary and systemic
hypertension, polycythemia, stroke, cardiac arrhythmias, and myocardial
7
infarction are all potential negative effects of untreated OSA.5, 7, 9 Thus, the study
of OSA and the characteristics of pharyngeal airflow9 are both important for
proper diagnosis and appropriate treatment that could potentially be life-saving.
Treatment for Obstructive Sleep Apnea
Non-surgical and surgical therapies can be used in the treatment of OSA. Nonsurgical therapies include diet and lifestyle modification,24-26 pharmacologic
agents,26-28 nasal positive airway devices,2, 29-31 and oral appliances.25, 32-35
Surgical options for the treatment of OSA include nasal reconstruction,
uvulopalatopharyngoplasty (UPPP),36 uvulopalatopharyngo-glossoplasty,
uvulopalatal flap,36 radiofrequency ablation to the base of the tongue,28, 36
mandibular osteotomy with genioglossus advancement,36 hyoid myotomy and
suspension,36 tracheotomy,36 tonsillectomy and adenoidectomy,28 distraction
osteogenesis, and maxillomandibular advancement osteotomy.25, 37
Nonsurgical Treatment
Diet and Lifestyle Modification
Although the amount of weight loss needed to improve sleep disordered
breathing and daytime sleepiness is unclear, obese patients should be
encouraged to lose weight. It is clear however, that weight-loss should be
mandatory in OSA treatment as an increase in BMI by one standard deviation is
associated with a 4 times increased risk of having an AHI greater than 5 per
hour.25 Reduced AHI scores were noted in patients with moderate to severe OSA
8
following weight reduction after bariatric surgery, but moderate sleep apnea
persisted.24
Smoking and alcohol consumption, have been shown to increase airway
resistance. Smoking has been shown to produce upper airway edema that
results in upper airway resistance. Thus, OSA patients are advised to avoid
smoking tobacco.8, 25 Alcohol is a respiratory depressant that may exacerbate
pre-existing OSA, and thus should be avoided at least four hours prior to sleep.8,
25
Stabilizing the upper airway through body positioning during sleep may help to
reduce the AHI by up to eight events per hour.26 The preferred sleep position is
an avoidance of the supine position with a preference for lateral recumbent
posture or a 30° or 60° head-elevated position.25
Pharmacologic Agents
Some pharmacologic treatment has been aimed at improving the quality of
sleep by targeting underlying medical conditions that may contribute to OSA. The
approach to date has involved drug therapies which include selective serotonin
reuptake inhibitors26 such as fluoxetine with no statistically significant reduction in
AHI and paroxetine which did not improve subjective sleepiness. The other
category is rapid eye movement (REM) sleep suppressants such as protriptylline
and clonidine both showing insufficient improvement in AHI to justify their use.26
Drugs can potentially improve OSA by increasing respiratory drive, maintaining
patency of the upper airway during sleep, reducing the proportion of REM sleep,
facilitating cholinergic tone during sleep or decreasing upper airway resistance. 27
Typically, treating the underlying medical condition can have pronounced effects
9
on the AHI. It has been demonstrated that stimulant therapy with caffeine leads
to a small improvements in objective daytime sleepiness, but overall
improvement is limited.26 Currently, there are no widely effective
pharmacotherapies for individuals with OSA, except in cases of individuals with9
hypothyroidism or with acromegaly.
Positive Airway Pressure Devices
Positive airway pressure devices, such as continuous positive airway pressure
(CPAP), automatic positive airway pressure (APAP), and bi-level positive airway
pressure (BPAP) devices, can be all be used in the treatment of OSA. CPAP is
the most commonly used non-surgical therapy and was first introduced in 1981
as a treatment modality for OSA.29 CPAP is considered to be the most effective
method in managing OSA and is considered the gold standard of treatment.15
By continuously pumping room air under pressure through a sealed nose or face
mask into the upper airway and lungs, CPAP acts in a non-invasive manner as a
pneumatic splint that elevates and maintains a constant pressure during
inspiration and expiration.15
Along with increases in airway area and volume, improvements in subjective
and objective measures of sleepiness have been documented as a result of
CPAP therapy.4 Kuna et al. and Schwab et al. found that upper pharyngeal
airway dimensions improved more in the lateral aspect than in the anteriorposterior dimension.2, 30, 38 Upper airway dimensions increased 8% to 16% in
lateral dimensions with CPAP compared to a 2% to 4% increase in
anteroposterior dimension.30 Other significant improvements include: snoring, dry
10
mouth, morning headaches, daytime function, perceived health status, and
quality of life.15 A lack of CPAP therapy compliance, however, can diminish the
improvements shown with long-term treatment.
Tolerance problems, psychological problems, and lack of instruction
categorize the reasons for poor compliance.31 Mask discomfort, congestion,
nasal dryness, chest pain, dry mouth, conjunctivitis, rhinorrhea, pressure sores,
epistaxis, skin rash, mask leaks, difficulty exhaling, aerophagia, and bed partner
intolerance include patient reports of tolerance problems.15 Psychological
problems include claustrophobia, lack of motivation, and anxiety.15
Study design will determine the definition of compliance with CPAP therapy.
Some research suggests compliance ranges from 50% to 89% for nasal
CPAP.39-41 When patient compliance is defined as greater than 4 hours of nightly
use, 46% to 83% of patients with OSA have been reported to be non-adherent to
treatment.42 Mounting evidence indicates that CPAP use for greater than 6 hours
16
reduces sleepiness, improves daily functioning, and re-establishes memory to
normal levels.42 Other modalities of non-surgical OSA treatment come to the
forefront when patients are unable to tolerate CPAP for a period of time, even
though the effectiveness of CPAP therapy is well-established when compliance is
good.
Oral Appliance
Patients who are intolerant of CPAP therapy or those who refuse surgery are
candidates for oral appliances, and are most commonly used for patients with
mild to moderate OSA.15 Increase in the posterior oropharyngeal airway space
11
and reduction in the collapsibility of the upper airway during sleep is the goal of
oral appliance therapy.15
Tongue-retaining or mandibular-repositioning are the two categories for oral
appliances. Tongue-retaining oral appliances position the tongue in an anterior
direction through negative pressure, and are indicated for patients for those who
have few or no teeth, macroglossia, or cannot adequately posture their mandible
forward.15, 32 Mandibular-repositioning devices help to posture the mandible and
associated structures, such as the tongue and hyoid bone, in an anterior
direction, thus 15 increasing both the anterior-posterior and lateral dimensions of
the upper airway. 15, 33, 34 While these devices are effective with success rates at
54% defined as reducing AHI to less than 10 and a resolution of symptoms, they
are not without negative side-effects.34
The most common dental side effects from oral devices includes proclination
of the mandibular incisors, retroclination of the maxillary incisors, mesial
movement of the mandibular molars, and a decrease in the SNB angle after long
term usage.35 Changes of a minor and temporary nature include excess
salivation, temporomandibular joint pain, dental pain, facial muscle pain, dry
mouth, and occlusal changes.5
Surgical Treatment
Surgery is most indicated when conservative therapeutic approaches are
unsuccessful or not tolerated well. The goal of surgical treatment for OSA is to
target site specific areas that are causes for upper airway obstruction. Typically
12
surgery should increase the upper airway size resulting in a decrease in airway
resistance, thereby reducing the pressure effort to breath.15 Patients that have
well-identified underlying skeletal abnormalities in cases of moderate to severe
OSA14 are also indicated for surgery22 Surgical prerequisites include an apneahypopnea index greater than 15 (AHI), or apnea index greater than 5 (AI), 22 a
respiratory disturbance index (RDI) greater than 15-20,16 lowest oxyhemoglobin
desaturation less than 90%, and excessive daytime sleepiness. Patients must be
psychologically and medically stable and willing to accept surgery. 37
Three categories typically govern upper airway surgical procedures for the
treatment of OSA: (1) procedures that directly enlarge the upper airway; (2)
changing the soft tissue elements and or skeletal anatomy by specialized
procedures that increase the upper airway and as a last resort option, (3) a
tracheotomy that bypasses that pharyngeal portion of the upper airway.4 Surgical
treatment is typically staged into 2 phases. Stage I surgery is considered to be
more conservative and site-specific and addresses obstructions in the palatal
and tongue base area without movement of the jaw(s) or teeth. A multi-level
approach may target areas such as: the nose, the oropharynx (the retropalatal
and retroglossal airway) and the hypopharynx. This stage also includes nasal
surgery, uvulopalatopharyngoplasty (UPPP), and base of tongue surgery (which
includes genioglossal advancement, modified genioplasty, radiofrequency
ablation, and hyoid myotomy).15, 17
Stage I therapy is usually conducted in a stepwise manner according to a
methodical protocol where less invasive surgical procedures are first attempted
13
and progressively treated with more surgery based on clinical symptoms.37 This
may result in unnecessary additional surgery, which may be painful and
expensive, and behave as a deterrent for patients to look for definitive surgical
treatment.37
Stage II surgery includes maxillomandibular advancement (MMA). MMA is an
invasive procedure that surgically moves the maxilla and mandible anteriorly,
along with their muscular attachments, to increase the airway space of the
nasopharynx, oropharynx, and hypopharynx15 to enhance the neuromuscular
tone of the dilator muscles.37
Stage I Surgery
Adenotonsillectomy/Tonsillotomy
The most common reason for OSA in children is hypertrophic adenotonsilar
tissue in the presence of a narrow airway and decreased muscular tone of the
oropharyngeal complex. The goal of maximizing the upper airway size and
preventing soft palate and lateral pharyngeal wall collapse makes
adenotonsillectomy first-line therapy for OSA in children.36 Curative rates greater
than 90% for children has been shown to be a result of adenotonsillectomy. A
common complication associated with adenotonsillectomy is excessive bleeding,
and a laser-assisted tonsillotomy can be undertaken that leads to similar curative
rates, but with significantly less pain and bleeding.28 When adenotonsillectomy is
unsuccessful for OSA treatment in children, they remain at risk for worsening
OSA into adulthood.28
14
Nasal Surgery
Nasal airway surgery, such as septoplasty or turbinectomy may be the initial
surgical therapy option for the treatment of OSA. It should be included in the
treatment plan because it has been shown to reduce mouth breathing which
leads to subjective improvement of sleep quality and increase patient compliance
with CPAP although nasal surgery alone typically does not improve or correct
OSA.15, 18
Uvulopalatopharyngoplasty and Laser- Assisted Uvulopalatoplasty
Uvulopalatopharyngoplasty (UPPP) is a procedure undertaken to reduce the
degree of pharyngeal obstruction that occurs during an apneic event by surgically
removing the uvula and surrounding redundant mucosal tissue20 including the
posterior pillar and posterior pharyngeal wall, while preserving the muscular
layer.43 The success rate for UPPP was 44% according to Braga et al., which
also concurs with the findings of 40-50%, found by Won et al. at 12 months postsurgery.36, 44 While UPPP can be curative in some patients, a combination of
treatment modalities must be considered.44 The uvulopalatal flap, is preferred
over UPPP in most cases because it reduces the risk of nasopharyngeal
incompetence due to it being a potentially reversible procedure.36 Laser-assisted
uvulopalatoplasty (LAUP) is a less-invasive alternative to UPPP that can be
performed under local anesthesia in an out-patient setting with similar success
rates as UPPP and should be considered during treatment planning.45 The
procedure progressively shortens and tightens the uvula and palate through a
series of carbon dioxide laser incisions and vaporizations.36 Studies evaluating
15
LAUP for OSA suggest a near 50% success rate in reducing the RDI to less than
10 events per hour.46
Base of Tongue Surgery
Genioglossal Advancement and Genioplasty
Anterior reposition of the genial tubercle and genioglossus muscle is the goal
of a genioglossal advancement. The procedure places tension on the base of
tongue, and thus tends to reduce prolapse into the posterior airway during
sleep.15 The patient cure rates from a genioglossal advancement 21 varies from
35-60% depending upon OSA severity.36 Potential compliactions from
genioglossal advancement surgery include mandibular fracture, lower incisor root
lesions, infection, permanent anesthesia, and seromas.36 A modified genioplasty
is a technique that advances the genioglossus muscle and chin used for patients
with microgenia. The primary goal of a genioplasty is improvement in facial
esthetics, a secondary benefit of surgery is an increase in airway volume, thus
decreasing the likelihood of hypopharyngeal airway collapse.15
Radiofrequency Ablation
Radiofrequency ablation (RFA) is a procedure that uses radiofrequency
energy to reduce tongue volume.47 By heating the tongue base and or soft palate
to 70-85°C, tissue lesions are created which leads to scarring, tissue volume
reduction, and a reduction in upper airway collapsibility.15, 28 Currently, RFA is not
considered a primary procedure in the treatment of OSA, but considered
adjunctive therapy.22, 36
16
Laser Midline Glossectomy, Lingualplasty, & Epiglottidectomy
Tongue reduction surgery through laser midline glossectomy or lingualplasty is
used to treat OSA for patients with macroglossia that obstruct the airway and
may be combined with epiglottidectomy to increase the hypopharyngeal
volume.15 Success rates are highly variable especially for morbidly obese
patients and thus tongue volume reduction surgery is rarely used due to
postoperative edema and excessive bleeding as morbidities.
Hyoid Myotomy Suspension
The advancement of the hyoid bone along with the epiglottis, the tongue base,
and the suprahyoid muscles helps to increase the upper airway space, mainly in
the retroglossal area.15 This technique involves suturing the hyoid bone to the
thyroid cartilage using resorbable sutures after myotomy and dissection of the
stylohyoid ligaments.28 Potential complications of hyoid myotomy suspension
include seromas, intermittent23 aspiration, and the loss of a resorbable suture.
Stage II Surgery
Maxillomandibular Advancement Surgery
Maxillomandibular advancement (MMA) is a Stage II surgical procedure by
which the maxilla and mandible are advanced typically 10-15 mm by means of
LeFort I and bilateral sagittal-split osteotomies.36 Patients usually undergo Stage
II surgical treatment for OSA after they have been unsuccessfully treated with
non-surgical or Stage I surgical therapy with persistent obstruction at the base of
the tongue.36
17
Advancement of the lower facial skeleton and surrounding structures in an
effort to pull forward and increase the tension of the attached soft tissues in
addition to anatomically enlarging the entire velo-oro-hypo-pharyngeal airway is
the main goal of MMA.37 OSA27 patients with craniofacial characteristics, such as
maxillary and mandibular deficiencies, influence pharyngeal airway obstruction
more than previously suspected.48 and are most appropriate for curative surgical
correction by MMA.4
A successful surgical outcome has been defined in some studies as having an
AHI or RDI less than 10.49 For those studies using an AHI or RDI of less than 10,
surgical success rates have been found to range from 65% to 97%.48-50 Other
studies define a successful surgery with an AHI or RDI of less21 because this
correlates with decreased patient mortality.51 These studies have found surgical
success rates from 83% to 100%.22, 52-55
Tracheotomy
A tracheotomy is a surgical procedure by which a tracheostomy tube is
inserted into an opening in the neck through the trachea bypassing the upper
airway allowing respiration.56 Patient acceptance is low however due to the social
implications and associated morbidity, despite being the most effective
treatment.36 Currently it is used as a temporary measure for patients with morbid
obesity or craniofacial anomalies that are a high risk due to the airway being
compromised.36
18
Airway Imaging
Airway imaging techniques used in the diagnosis of OSA have greatly
improved with the further understanding of OSA pathophysiology.57 Treatment
planning and evaluation of surgical and non-surgical therapies which target
specific areas of obstruction are now possible with newer imaging modalities.
Airway imaging can be done using numerous techniques such as acoustic
reflection, fluoroscopy, and nasopharyngoscopy.1 However, the most common
airway imaging modalities are lateral cephalometric radiography, magnetic
resonance imaging (MRI), and computed tomography (CT).
While panoramic radiography offers little diagnostic information specific for the
diagnosis of OSA, it can provide pre-operative records useful in surgical
treatment planning, postoperative assessment of the anatomic changes and its
allows one to monitor the periodontal and dental conditions of OSA patients
being treated with oral appliances.57
Lateral Cephalometric Radiography
Lateral cephalometric radiography is the most widely used imaging technique
for hard and soft tissue evaluation for patients with OSA.58 Orthodontists and oral
surgeons24 routinely use lateral cephalograms for evaluating the facial skeleton,
the dentition, the effects of growth on treatment, and the airway. The relatively
low cost, low-dose radiation and wide availability in dental offices allows lateral
cephalograms to be easily obtained in an office setting. The limitations of a
lateral cephalogram are that it is a static, two dimensional image that is gathered
with the patient in an upright position during a non-apneic event. Consequently,
19
three-dimensional volumetric data cannot be gathered from two-dimensional
images. Cephalometric data should be interpreted in light of the diagnostic
information from a sleep study, clinical history, and physical examination.57
Evaluating three-dimensional structures is better suited utilizing newer imaging
technologies such as MRI and CT. They provide greater detail in three
dimensions of hard and soft tissue structures of the head and neck. Standard CT
imaging not only provides three-dimensional images of the airway, but also
volumetric data as well.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) uses electromagnetic energy and radio
waves to assess various types of soft tissue without exposing the patient to
ionizing radiation.26 MRI has equal resolution, but much greater contrast than CT
scanning—this is especially useful in studying OSA as it allows more detailed
visualization of soft tissues of the pharyngeal airway. The limitations of using MRI
include: the large size of the MRI machine, noisy scans, taking several minutes
for a scan, claustrophobic effects of being inside the machine, and its relative
expense. These limitations negate its use as a routine imaging assessment for
patients with OSA.57
Standard Computed Tomography
Standard CT images are obtained as 1-2mm slices in axial or coronal planes
or both, from the patient in the supine position, which is the typical position of a
patient who is having an apneic event. The slices are combined and
reconstructed into three-dimensional images.57 If anatomic abnormalities are the
20
cause of OSA, CT scans should delineate them and allow better direct surgical
interventions.58 Increased cost and radiation exposure to the patient, static
images,29 poorer quality imaging of soft tissue, and are the shortcomings of
standard CT imaging.57
Fast Computed Tomography
Fast CT imaging is more useful in the study of OSA as it allows the active
capturing of images of the dynamic movement of the hard and soft tissues of the
pharyngeal airway during respiration. Like standard CT, fast CT imaging uses
two-dimensional images that are combined to create a three-dimensional image
by acquiring eight contiguous scans every 0.7 seconds. Fast CT provides a more
physiologically significant assessment of the upper airway compared with
standard CT imaging due to its ability to capture the dynamic component of sleep
apnea, while carrying the same drawbacks as standard CT.57
Cone Beam Computed Tomography
Cone beam computed tomography (CBCT) uses divergent x-rays that form a
cone to capture a three-dimensional image. The scanner rotates around a
patient’s head capturing up to 600 images that are reconstructed to create a
digital volume composed of three-dimensional voxels of anatomical data which
can be manipulated with software.59 Advantages of CBCT imaging include lower
radiation exposure to the patient with wide availability, relatively low cost
compared to standard CT, images can be captured in sitting or supine positions,
and it allows for accurate assessments of the upper airway.30 Disadvantages of
CBCT imaging include initial cost, static image, and poor soft tissue resolution. 57
21
In a study by Lenza et al.60, a CBCT study of patients was used to perform a 3D
evaluation of the upper airway to correlate linear measurements, cross-sectional
areas and volumes of the upper airway. The analysis showed a weak correlation
between most of the linear measurements, but the upper part of the velopharynx
showed a good correlation between area and volume. 60 Sears et al. compared
plain radiography with CBCT for the determination of pharyngeal airway changes
after orthognathic surgery and concluded that the lateral cephalogram cannot be
considered equal to a CBCT in terms of an imaging tool.61 In addition El et al.,
studied the reliability and accuracy of 3 commercially available digital imaging
and communications in medicine (DICOM) viewers and concluded that Dolphin
3D showed high correlation of results but poor accuracy in the airway volume
calculations.62
Airway Volume Change Following Mandibular Setback Surgery
The pharyngeal upper airway has attracted much attention because snoring
and sleep apnea are known to be closely linked to its size. If the airway is or
becomes narrow, the airflow resistance increases, heightening the risks of
snoring and sleep apnea. In facial growth and development, there are important
relationships between the pharyngeal structures and the development of the face
and occlusion. Orthognathic surgery for skeletal deformity alters the skeletal and
soft tissue components. Surgery can include any combination of maxillary
advancement and/or mandibular setback surgery, in conjunction with orthodontic
treatment. Narrowing of the pharyngeal airway space (PAS) after orthognathic
22
surgery has received attention in recent years.63-66 The great interest in this
subject arose because a small group of patients who receive mandibular setback
surgery may develop OSA.67 The jaws, tongue base, hyoid bone, and pharyngeal
walls are intimately connected by muscles and tendons. The tongue with its
muscles and ligaments is related to the hyoid bone and mandible. When the
mandible is posteriorly repositioned, the tongue assumes a more posterior
position, narrowing the PAS.
Cephalometric Studies
Several studies have evaluated the effects of maxillomandibular
advancements on airway volume, however there is insufficient data on the impact
of mandibular setback surgery on the nasopharyngeal, oropharyngeal and
hypopharyngeal airway volume. A review of the literature includes some of these
cephalometric studies. Riley et al. reported on 2 women who presented with OSA
after mandibular osteotomy for treatment of mandibular prognathism.67 Before
surgery neither patient had any signs and/or clinical symptoms of airway
obstruction. One patient developed loud snoring 5 months postoperatively. The
other reported similar signs 2 months after surgery. These 2 patients were
diagnosed with OSA. Hochban et al. evaluated the effect of mandibular setback
surgery on the PAS of patients with mandibular hyperplasia and showed that the
PAS decreased considerably at the oropharyngeal and hypopharyngeal levels,
but did not lead to sleep related breathing disorders.63 Athanasiou et al. studied
patients with Class III deformity who had bilateral vertical ramus osteotomy for
the correction of prognathism with preoperative and 1-year follow-up
23
radiographs.68 They found no statistical difference in the dimensions of the PAS
when comparing the initial and final radiographs. Gu et al. analyzed patients who
underwent mandibular setback surgery.69 The investigators concluded that there
is a relation across mandibular setback surgery, hyoid position, a decrease in the
PAS, and head posture that leads to extensive biomechanical adjustment of the
patient’s tongue and infrahyoid musculature to balance the stomatognathic
system.
Samman et al. studied patients with Class III deformity who were treated with
mandibular setback, maxillary advancement , and bimaxillary surgery.70 The
study evaluated the regions of the nasopharynx, oropharynx, hypopharynx, and
pharyngeal minimal space on preoperative and 6-month postoperative
radiographs. For the group undergoing mandibular setback, a decrease in the
hypopharynx and nasopharynx was described; maxillary advancement resulted
in an increase in the PAS at the nasopharynx and oropharynx, and bimaxillary
surgery promoted a decrease at the oropharynx. Comparing the results among
these 3 groups, the investigators concluded that patients who underwent
mandibular setback surgery have an increased risk for developing OSA, but
believed that the risk is minimal, based on their experience. Compensatory
changes that occur in the morphology of the soft palate may explain the slight
risk
Eggensperger et al. evaluated patients with mandibular prognathism who
underwent mandibular setback surgery and noted that there was a decrease in
the PAS after this type of surgery.65 They used preoperative, 1-week, 6-month,
24
and at least 1-year postoperative radiographs. Until 1 year the PAS continued to
decrease in the region of the nasopharynx and oropharynx. Results showed that
the hypopharynx remained almost unchanged from the initial measurement, but
the nasopharynx and oropharynx showed a progressive decrease. Chen et al.
evaluated patients who had skeletal Class III deformity who underwent
mandibular setback and bimaxillary surgery.64 Radiographs were obtained 6
months preoperatively, 3 to 6 months postoperatively, and a minimum of 2 years
postoperatively. The PAS was studied at the nasopharynx, oropharynx, and
hypopharynx. The results showed that patients undergoing mandibular setback
surgery had a decrease in the PAS in the region of the oropharynx and
hypopharynx at 3-6 months and 2 years postoperatively. In the bimaxillary group,
changes in the PAS consisted of increases of the nasopharynx and oropharynx
and a decrease of the hypopharynx after 3-6 months. In the long-term, there
were no significant changes. The researchers concluded that bimaxillary surgery
has little effect on the reduction of the PAS compared with mandibular setback
surgery alone. They also believed that the few changes observed in the PAS
after 2 years in patients who underwent bimaxillary surgery occurred from the
advancement of velopharyngeal muscles caused by maxillary advancement,
which offsets constriction of the PAS created by mandibular setback.
Marsan et al. studied the PAS and hyoid position in patients with Class III
deformity treated with bimaxillary surgery and observed an increase in the
nasopharynx.71 The purpose of this study was to retrospectively evaluate the
PAS changes in patients with skeletal Class III deformity who were treated by
25
different skeletal repositioning. In this study, patients presented no PAS changes
at all 3 levels. Regarding the PAS and the changes promoted by orthognathic
surgery, mandibular setback did not result in changes at the nasopharynx and
oropharynx. The hypopharynx showed a slight reduction in the anteroposterior
dimension, although not statistically significant. In addition Tselnik and Pogrel
studied the lateral cephalograms of adults and found that the PAS was
constricted at the oropharyngeal level after mandibular setback surgery. 72 Muto
et al. evaluated the effect of bilateral sagittal split ramus osteotomy setback on
the morphology of the pharyngeal airway, especially structures of the soft palate
and pharyngeal airway space.73 Lateral cephalograms were traced before and 1
year after surgery. Not only did the morphology of the PAS and soft palate
change significantly but the mandibular setback surgery markedly decreased the
PAS.
Saitoh examined lateral cephalograms before treatment, 3-6 months after
surgery and also 2 years after surgery to assess the influence of mandibular
setback surgery on pharyngeal airway morphology.66 For up to 3-6 months after
surgery the pharyngeal airway constricted significantly. However from there to
the 2 year point the lower facial morphology showed no significant changes.
Thus the pharyngeal airway gradually relapsed with time.
If lateral cephalometry is to be used for upper airway imaging then two
modifications are recommended. Initially, because pharyngeal volume fluctuates
with phases of respiration, cephalometry should be standardized by obtaining the
films at both end-tidal volume and during a modified Mueller maneuver (that is,
26
forced inspiration against a closed mouth and nose, to simulate the upper airway
collapse associated with negative inspiratory forces generated during OSA
events). Further, because the most critical site of hypopharyngeal closure may
vary, the cephalometric posterior airway space should be measured at the most
narrow level of hypopharyngeal collapse, rather than at a level determined by
skeletal landmarks.37
Computed Tomography Studies
Degerliyurt et al. observed patients with Class III deformity with pre- and
postoperative computed tomographic (CT) scans.74 Patients were divided into
groups with mandibular setback and bimaxillary surgery. The study evaluated the
nasopharyngeal and oropharyngeal regions in the anteroposterior and lateral
dimensions. Results indicated a decrease in the PAS in both groups. Patients
who underwent bimaxillary surgery showed a smaller decrease in the PAS
compared with patients with mandibular setback alone. Kawamata et al.
evaluated patients after mandibular setback surgery and determined that 3
months after surgery the pharyngeal airway decreased by 90%, and also showed
significant decreases in the lateral and frontal widths.75
Cone Beam Computed Tomography Studies
Significantly fewer studies have utilized cone beam computed tomography
(CBCT) in the study of pharyngeal airway and changes with Class III skeletal
surgeries. Lee et al. investigated volumetric changes to the upper airway space
in patients with skeletal class III skeletal deformities who had undergone
mandibular setback surgery.76 All of the patients underwent a CBCT for
27
assessment of the upper airway volume and skeletal changes before surgery and
6 months after surgery. The patients with mandibular setback movement showed
decreases in oropharyngeal and hypopharyngeal volumes.
Park et al. evaluated the volumetric change of the upper airway space in Class
III patients who had undergone isolated mandibular setback.77 CBCT
examination was performed at three stages. The results showed that the
volumes of the oropharyngeal and hypopharyngeal airways decreased
significantly 4.6 months post-surgery in the mandibular setback group and these
diminished airways had not recovered 1.4 years post-surgery.
Kim et al. evaluated the longitudinal changes in the hyoid bone position and
the pharyngeal airway space following bimaxillary surgery in mandibular
prognathism patients.78 CBCT scans were acquired at an average of 2 weeks
before surgery, 2 months and then 6 months after surgery. The total volume,
nasopharyngeal and hypopharyngeal airway volumes decreased at 2months and
6 months after surgery, but oropharyngeal airway showed no significant changes
in volume.
In Panou et al. study, changes of the pharyngeal airway and maxillary sinus
volume after mandibular setback surgery combined with a maxillary
advancement and/or impaction were determined.79 CBCT scans were evaluated
prior to and on average 3.9 months after surgery. The results showed that there
was no significant change in the volume of pharyngeal airway after bimaxillary
surgery except for the lower and total volume for males. In addition there was
28
also no correlation between the amount of surgical movement and the change in
volume of the pharyngeal airway.
CBCT scans for 21 patients who were undergoing mandibular setback surgery
were obtained in a study by Hong et al.80 Scans were taken prior to surgery and
then 2 months after surgery for patients undergoing either mandibular setback or
bimaxillary surgery. The anteroposterior dimension, cross sectional area and the
pharyngeal volume were all decreased in patients with mandibular setback.
Mattos et al. conducted a meta-analysis on the effects of orthognathic surgery on
oropharyngeal airway.81 The comparison of anteroposterior changes after
mandibular setback surgery showed a highly significant decrease in
oropharyngeal airway at the level of the soft palate and the level of the base of
the tongue. There was also a significant decrease in the lateral width of the
oropharyngeal airway after mandibular setback surgery.74, 82 In summary there is
moderate evidence to conclude that mandibular setback surgery may lead to a
decrease in the oropharyngeal airway.81
Sleep Related Disorders
Some studies have tried to examine the relationship between sleep related
disorders and mandibular setback surgery. Hasebe et al. examined the effects of
mandibular setback surgery on pharyngeal airway space and respiratory function
during sleep.83 The subjects were patients in whom mandibular prognathism was
corrected by bilateral sagittal split ramus osteotomy; either one jaw or two jaw
surgery. Polysomnography was performed before surgery and 6 months after
surgery, and the AHI and arterial oxygen saturation during sleep were measured
29
to assess respiratory function during sleep. AHI was not changed significantly
after surgery, although two patients were diagnosed with mild OSA syndrome
after surgery. They were not obese, but the amounts of mandibular setback at
surgery were large. Kitagawara et al. studied the effects of mandibular setback
surgery on craniofacial and pharyngeal morphology and on respiratory function
during sleep.84 The subjects were patients with skeletal class III malocclusions
that were corrected by bilateral sagittal split ramus osteotomy. Arterial oxygen
saturation (SpO2) during sleep was measured by pulse oximetry, and
morphological changes were studied using cephalograms. Although there was no
significant change at the oropharyngeal level, decreased SpO2 during sleep was
found just after surgery but had improved 1 month after surgery. It seems that
almost all of the subjects adapted to the new environment in respiratory function
during sleep, but patients with obesity have the potential for sleep-disordered
breathing and a large amount of setback may suffer from OSA in the future.
Statement of Thesis
The purpose of this study is to evaluate how the pharyngeal airway volume
and dimensions change after mandibular setback surgery in patients with skeletal
Class III dysplasia utilizing cone beam computed tomography (CBCT). A
determination will also be made if there is a correlation between the amount of
skeletal setback and pharyngeal airway volume and dimensions. Thus the null
hypotheses would be that there is no difference in pharyngeal airway following
30
mandibular setback surgery and the alternative hypothesis would show that there
is a difference in the pharyngeal airway after mandibular setback surgery.
31
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69. Gu G, Gu G, Nagata J, Suto M, Anraku Y, Nakamura K, Kuroe K, Ito G.
Hyoid position, pharyngeal airway and head posture in relation to relapse
after the mandibular setback in skeletal Class III. Clin Orthod Res.
2000;3:67-77.
70. Samman N, Tang SS, Xia J. Cephalometric study of the upper airway in
surgically corrected class III skeletal deformity. Int J Adult Orthodon
Orthognath Surg. 2002;17:180-90.
71. Marsan G, Vasfi Kuvat S, Oztas E, Cura N, Susal Z, Emekli U.
Oropharyngeal airway changes following bimaxillary surgery in Class III
female adults. J Craniomaxillofac Surg. 2009;37:69-73.
72. Tselnik M, Pogrel MA. Assessment of the pharyngeal airway space after
mandibular setback surgery. J Oral Maxillofac Surg. 2000;58:282-5;
discussion 5-7.
37
73. Muto T, Yamazaki A, Takeda S, Sato Y. Effect of bilateral sagittal split ramus
osteotomy setback on the soft palate and pharyngeal airway space. Int J
Oral Maxillofac Surg. 2008;37:419-23.
74. Degerliyurt K, Ueki K, Hashiba Y, Marukawa K, Nakagawa K, Yamamoto E.
A comparative CT evaluation of pharyngeal airway changes in class III
patients receiving bimaxillary surgery or mandibular setback surgery. Oral
Surg Oral Med Oral Pathol Oral Radiol Endod. 2008;105:495-502.
75. Kawamata A, Fujishita M, Ariji Y, Ariji E. Three-dimensional computed
tomographic evaluation of morphologic airway changes after mandibular
setback osteotomy for prognathism. Oral Surg Oral Med Oral Pathol Oral
Radiol Endod. 2000;89:278-87.
76. Lee JY, Kim YI, Hwang DS, Park SB. Effect of maxillary setback movement
on upper airway in patients with class III skeletal deformities: cone beam
computed tomographic evaluation. J Craniofac Surg. 2013;24:387-91.
77. Park SB, Kim YI, Son WS, Hwang DS, Cho BH. Cone-beam computed
tomography evaluation of short- and long-term airway change and stability
after orthognathic surgery in patients with Class III skeletal deformities:
bimaxillary surgery and mandibular setback surgery. Int J Oral Maxillofac
Surg. 2012;41:87-93.
78. Min-Ah Kim B-RK, Jin-Young Choi, Jong-Kuk Youn, Yoon-Ji R. Kim, YangHo Park. Three-dimensional changes of the hyoid bone and airway
volumes related to its relationship with horizontal anatomic planes after
bimaxillary surgery in skeletal Class III patients. Angle Orthodontist.
2013;83:623-29.
79. Panou E, Motro M, Ates M, Acar A, Erverdi N. Dimensional changes of
maxillary sinuses and pharyngeal airway in Class III patients undergoing
bimaxillary orthognathic surgery. Angle Orthod. 2013;83:824-31.
80. Hong JS, Park YH, Kim YJ, Hong SM, Oh KM. Three-dimensional changes in
pharyngeal airway in skeletal class III patients undergoing orthognathic
surgery. J Oral Maxillofac Surg. 2011;69:e401-8.
81. Mattos CT, Vilani GN, Sant'Anna EF, Ruellas AC, Maia LC. Effects of
orthognathic surgery on oropharyngeal airway: a meta-analysis. Int J Oral
Maxillofac Surg. 2011;40:1347-56.
82. Kawamata A, Ariji Y, Langlais RP. Three-dimensional computed tomography
imaging in dentistry. Dent Clin North Am. 2000;44:395-410.
38
83. Hasebe D, Kobayashi T, Hasegawa M, Iwamoto T, Kato K, Izumi N, Takata
Y, Saito C. Changes in oropharyngeal airway and respiratory function
during sleep after orthognathic surgery in patients with mandibular
prognathism. Int J Oral Maxillofac Surg. 2011;40:584-92.
84. Kitagawara K, Kobayashi T, Goto H, Yokobayashi T, Kitamura N, Saito C.
Effects of mandibular setback surgery on oropharyngeal airway and
arterial oxygen saturation. Int J Oral Maxillofac Surg. 2008;37:328-33.
39
CHAPTER 3: JOURNAL ARTICLE
Abstract
Introduction: An aspect of mandibular setback surgery which has raised
awareness is the possible link of reduction in airway and the development of
obstructive sleep apnea (OSA).Purpose: This study investigates volumetric and
dimensional changes to the pharyngeal airway space (PAS) following isolated
mandibular setback surgery for patients with Class III skeletal dysplasia utilizing
cone beam computed tomography (CBCT). Materials and Methods: Records of
31 patients who had undergone combined orthodontic and mandibular setback
surgery was obtained. The sample comprised of 20 males and 11 female
subjects. The mean age was 23.67± 6.28 years, range of 18 to 52 years. CBCT
scans were obtained at three time points T1 (before surgery), T2
(average of 6 months after surgery) and T3 (average of 1 year after surgery).
Oropharyngeal (OP), hypopharyngeal (HP) and total volumes (TV) were
calculated. The lateral surface (TR) and anteroposterior (AP) dimensions at the
minimal axial area for OP and HP and mean mandibular setback were
determined. Results: The mean mandibular setback was 8.16 ± 7.74 mm.
Repeated measures ANOVA determined an overall significant decrease between
the means for 6 months and up to 1 year after surgery
(F(1.560,46.801) = 21.755, P < 0.001) for OP, (F(1.744,52.325) = 10.768,
P < 0.001) for HP and (F(1.590,47.706) = 17.699, P < 0.001) for TV,
(F(1.818,54.527) = 12.526, P < 0.001) for TR at OP and (F(1.762,52.861) =
9.051, P < 0.01) for AP at HP. No significant correlation between mandibular
40
setback surgery and pharyngeal airway volumes or dimensions was determined.
Conclusions: Following mandibular setback surgery pharyngeal airway volume,
transverse and anteroposterior dimensions were decreased. Patients undergoing
mandibular setback surgery should be evaluated for OSA and the proposed
treatment plan modified according to the risk for potential airway compromise.
41
Introduction
In patients with severe skeletal Class III dysplasia, combined orthodonticorthognathic surgical treatment provides an esthetic and functional solution.
Isolated mandibular setback surgery is a treatment option for the correction of
this dysplasia. An important aspect of this surgical correction is that it causes a
change in the position of the hyoid bone and base of tongue. 1-4 The posterior
shift of the tongue base creates an increase in contact length between the soft
palate and tongue base and can decrease the pharyngeal airway space
(PAS).1, 4-6 The resultant changes in hard and soft tissue following mandibular
setback surgery have been noted to produce a shift in oropharyngeal
characteristics to a morphology associated with sleep-disordered breathing,
typical of obstructive sleep apnea (OSA).7
OSA is characterized by repeated increases in resistance to airflow within the
upper airway causing obstruction.8 It is also characterized by the periodic partial
or complete collapse of the upper airway that results in episodes of hypopnea
(diminished airflow of at least 30% lasting at least 10 seconds) or apnea (absent
airflow).8-10 The collapse of soft tissues in the upper airway, including the
retropalatal and retroglossal regions of the oropharynx play a role in the etiology
of OSA.11 Epidemiologic estimates of OSA prevalence is about 4% for men and
2% for women in the age group 30-60 years for those living in the United States
when considering subjective day-time sleepiness.12-16 Approximately 1 in 5 adults
have at least mild OSA and 1 in 15 adults have OSA of moderate or worse
severity.12, 17, 18
42
Initial research performed to evaluate the effect of mandibular setback
surgeries on the PAS have been evaluated with lateral cephalograms. 7, 19-24 The
limitations of a lateral cephalogram are that it is a static, two dimensional image
that do not adequately represent the three-dimensional volumetric data.25
Recently CBCT has been utilized to evaluate the airway changes in a three
dimensional manner.26 The majority of CBCT studies examining pharyngeal
airway volume changes have patients undergoing a combination of maxillary
advancement and mandibular setback surgery.27-30 Thus limited evidence is
present in the literature describing the effect of isolated mandibular setback
surgeries on PAS utilizing CBCT. Further research may elucidate if a setback
alone contributes to a negative impact on the airway and lead to the possibility of
exacerbating obstructive sleep apnea.
The aim of this study was to evaluate volumetric and dimensional changes in
the PAS for patients who have undergone isolated mandibular setback surgery
utilizing CBCT, and also determine if a correlation exists between mandibular
setback surgery and pharyngeal airway volumes or dimensions.
Materials and Methods
Sample
For this study, records of 31 patients who had undergone combined
orthodontic and isolated mandibular setback surgery to correct Class III skeletal
dysplasia was obtained. The sample comprised of 20 males and 11 female
subjects. The mean age was 23.67± 6.28 years, range of 18 to 52 years. The
43
sample was retrieved from the Department of Orthodontics at Pusan National
University Hospital, Busan, South Korea. The setback surgery consisted of
sagittal split ramus osteotomy of the mandible with rigid fixation. CBCT scans
were obtained at three time points T1 (before surgery), T2 (an average of 6
months after surgery) and T3 (an average of 1 year after surgery). The inclusion
criteria for this study will include adult subjects with Class III skeletal deformities
who have undergone mandibular setback surgery and orthodontic treatment. The
exclusion criteria governing subject selection are: no severe facial asymmetry or
presence of syndromes, and no symptoms of temporomandibular disorders or
respiratory disease.
Cone Beam Computed Tomography (CBCT) Technique
All patients underwent CBCT examination (DCTpro, Vatech, Seoul,Korea) for
assessment of the upper airway volume and skeletal changes. The patients were
seated in the upright position with maximum intercuspation. The Frankfort
horizontal plane of the patients was parallel to the floor. Head orientation was the
same for each CBCT image performed by the same experienced operator. The
patients were asked not to swallow during the scan. The maxillofacial regions
were scanned for 24seconds using a CBCT machine with a field of view of
20cmX19cm, a tube voltage of 90 kVp, and a tube current of 4.0 mA. Images
were imported into Dolphin 11.5 3D Imaging software (Dolphin Imaging Systems
LLC, Chatsworth, CA) and used to view, analyze and manipulate the CBCT
scans.
44
Calculation of Surgical Movement
The calculation of the anterior-posterior surgical movement was measured by
converting the CBCT scan from a three-dimensional volume to a lateral
cephalogram image. A reference plane was drawn through Sella and Nasion and
then 7° (SN-7°) was subtracted. A perpendicular line was drawn through the
corrected horizontal plane from Nasion and then the distance to B-point was
measured and compared pre- and post-surgery (Figure 3.1).
Figure 3.1: Lateral cephalogram demonstrating measurement of surgical
movement.
45
Isolating the Pharyngeal Airway and Volumetric Measurements
Orientation of the CBCT included the horizontal reference plane that was
defined bilaterally by porion with right orbitale. This condition was verified on the
mid sagittal plane. The transporionic plane was oriented vertically, defined
bilaterally by porion and perpendicular to the horizontal reference plane. The mid
sagittal plane was oriented vertically, defined by nasion, and perpendicular to the
other reference planes. The two defined volumes included the oropharyngeal
(OP) and hypopharyngeal (HP). The superior border of OP was bounded by a
line from the most superior anterior point of cervical vertebrae (CV) 1 to the
posterior tip of the hard palate. The inferior border was defined by a line parallel
to the superior border from the most inferior anterior point of CV2 to the base of
tongue. This inferior border also formed the superior border of the HP, and the
inferior border of the HP, was a line parallel to the superior border from the most
inferior anterior point of CV4 to the anterior border. The anterior border was
comprised of the posterior soft palate and base of tongue. The posterior border
was the posterior pharyngeal wall (Figure 3.2).
46
OP
HP
Figure 3.2: Segmentation of Oropharyngeal (OP) and Hypopharyngeal (HP)
volume
After isolation, the volume of each segment and total volume (TV) was
calculated. In addition the minimum axial area was determined and then the
lateral surface length (TR) and anterior posterior lengths (AP) were measured
(Figure 3.3).
47
TR
AP
Figure 3.3: Segmentation of Lateral surface (TR) and anterior posterior
length (AP).
Statistical Analysis
Data analysis was performed using IBM SPSS Statistics 20.0 (Armonk, NY,
USA). Descriptive statistics calculated the mean and standard deviation for
mandibular setback, and relapse, as well as the OP, HP and TV, TR and AP at
each time point. Repeated measures ANOVA, Multivariate analysis and
Greenhouse-Geiser correction tested for significant differences in the mean
airway volumes, the TR and AP measurements. Post hoc test with Bonferroni
correction was used to determine which time points had significant changes.
Pearson’s correlation was used to determine if a relationship existed between the
amount of mandibular setback and pharyngeal volumes and dimensions. For
reliability testing 10 percent of the variables were randomly selected and
48
remeasured. Cronbach’s alpha Inter-item Correlation was the statistic used to
determine reliability.
Results
Cephalometric Data
The mean mandibular setback is 8.16 ± 7.74 mm and the mean mandibular
relapse from T2 to T3 is 0.63 ± 3.41 mm.
Volumetric Data
Means and standard deviations for OP, HP, TV, TR and AP are presented
(table 3.1 and 3.2). Repeated measures ANOVA performed to measure the
change over time of OP, HP, TV, TR and AP. The Tests of Within-Subjects
Effects (appendix table A.1) takes into account the Greenhouse-Geisser
correction and denotes that there is an overall significant difference between the
means at the different time points (F(1.560,46.801) = 21.755, P < 0.001 ) for OP,
(F(1.744,52.325) = 10.768, P < 0.001) for HP and (F(1.590,47.706) = 17.699,
P < 0.001) for TV, (F(1.818,54.527) = 12.526, P < 0.001) for TR at OP and
(F(1.762,52.861) = 9.051, P < 0.01) for AP at HP. There was no significant
difference between the means for TR at HP and AP at OP.
49
Table 3.1: N = 31 Descriptive Statistics for oropharyngeal volume (OP), hypopharyngeal volume
(HP) and total volume (TV) (mm³), at T1= preop, T2= 6 months postop, T3= 1 year postop.
Volume
T1
T2
T3
OP
16440.72 ± 4457.04
12190.20 ± 5525.65
12463.31 ± 5410.12
HP
14566.51 ± 4474.52
11665.45 ± 5152.99
12298.19 ± 4312.07
TV
31007.11 ± 8241.44
23855.65 ± 9803.38
24761.29 ± 8693.05
Table 3.2: N = 31 Descriptive Statistics for lateral surface (TR) (mm) and anteroposterior (AP)
(mm) at oropharyngeal (OP) and hypopharyngeal (HP) regions. T1= preop, T2= 6 months postop,
T3= 1 year postop.
Variable
T1
T2
T3
TR OP
28.77 ± 5.40
24.20 ± 5.91
24.42 ± 5.81
TR HP
28.67 ± 8.79
27.77 ± 6.62
28.07 ± 7.23
AP OP
13.52 ± 3.33
10.23 ± 3.56
12.01 ± 8.40
AP HP
14.49 ± 3.21
11.61 ± 3.94
11.95 ± 4.06
35000
30000
(mm3)
25000
20000
Means of OP Vol
Means of HP Vol
15000
Means of Total Vol
10000
5000
0
T1
T2
T3
Figure 3.4: Graph representing change in means of volumes at T1= preop, T2= 6 months postop,
T3= 1 year postop.
50
Thus the null hypothesis can be rejected and the alternative hypothesis
accepted. There is a significant difference in the pharyngeal airway (OP, HP and
TV, TR at OP and AP at HP) after mandibular setback surgery.
Post hoc tests identify the intervals during which there are significant changes
for the OP, HP, TV, in addition to the TR and AP. Significant decrease was noted
from T1 to T2 and from T1 to T3, but no significant changes were noted from T2
to T3 (table 3.3). As a general rule, intra-class correlations greater than or equal
to 0.80 are considered adequate. A Cronbach’s value of 0.8 or greater was met
for all measurements.
51
Table 3.3: Pair- wise comparison table denoting significant change for time point T1 and T2, T1
and T3 but not T2 and T3. Oropharyngeal (OP), hypopharyngeal (HP), Lateral surface (TR),
Anteroposterior (AP). T1= preop, T2= 6 months postop, T3= 1 year postop.
Variable
Vol OP
Timepoint
Timepoint
T1
T2
4250.52*
769.96
0,000
T3
T1
T3
T2
T3
T1
3977.41*
-4250.52*
-273.12
2901.07*
2268.33*
-2901.07*
845.62
769.96
503.17
734.67
698.15
734.67
0.000
0.000
1.000
0.001
0.009
0.001
T3
T2
T3
T1
T3
T2
-632.74
7151.46*
6245.82*
-7151.46*
-905.64
4.57*
519.09
1441.93
1487.93
1441.93
920.38
1.09
0.697
0.000
0.001
0.000
0.999
0.001
T3
4.35*
1.12
0.002
T1
-4.57*
1.09
0.001
T3
T2
T3
T1
T3
-0.23
2.87*
2.54*
-2.87*
-0.34
0.85
0.78
0.82
0.78
0.59
1.000
0.003
0.013
0.003
1.000
T2
T1
Vol HP
T2
T1
Total Vol
T2
T1
TR at OP
T2
T1
AP at HP
T2
Mean Difference
Std. Error
Sig.
Calculations were done to determine the volume percentage change. All three
volumes showed a statistically significant percentage decrease from T1 to T2
and T1 to T3. However, T2 to T3 showed a non-significant percentage change
(table 3.4).
52
Table 3.4: Volume percent change over the three time points for OP, HP and TV where * indicate
statistically significant decrease. P < 0.05.
Volume Percent Change
T1 – T2
T2 – T3
T1 – T3
Oropharyngeal
-25.85%*
2.24%
-24.10%*
Hypopharyngeal
-19.91%*
5.42%
-15.57%*
Total Volume
-23.06%*
3.79%
-20.14%*
Pearson’s correlation was used to determine if a relationship existed between
the amount of mandibular setback and pharyngeal airway volumes or dimensions
between the time points. The results are not significant at the P < 0.01 level and
so no significant correlation exists between mandibular setback and pharyngeal
airway volumes or dimensions.
Discussion
In this study, we evaluated pharyngeal airway volume changes, lateral surface
and anteroposterior dimensional changes utilizing CBCT for 31 patients who had
undergone combined orthodontic and isolated mandibular setback surgery to
correct Class III skeletal dysplasia. Correlation analysis was performed to
ascertain a relationship between the amount of mandibular setback and
pharyngeal airway volumes or dimensions.
53
Statistical analysis determined that there was a significant decrease in volume
for OP, HP and TV for T1 to T2 and T1 to T3, but not for T2 to T3. Similar
significant decrease was noted for TR at OP and AP at HP.
A reduction in the dimensions of the retrolingual and hypopharyngeal airway
after mandibular setback surgery has been noted in several studies.2, 3, 5, 6, 20, 22, 31
Similar to the current study, other CBCT studies have also reported a decrease
in OP and HP volume after mandibular setback surgery with short and long term
follow up studies.27 28, 29, 32 After mandibular setback surgery, there is a
posteroinferior displacement of the hyoid bone, which moves the tongue in a
similar direction.2-4, 31 The posteriorly displaced tongue can now narrow the
retrolingual (part of the oropharyngeal) region and decrease the PAS. 4-6, 31 This
can lead to an increase in the contact angle between the soft palate and the
tongue and contribute to the decrease in the OP volume.4
The significant decrease in TR at the OP region and decrease in AP at the HP
region in this study has also been corroborated.27, 29 Hong et al.30 examined
CBCT before surgery and then 2 months after surgery and determined that the
anteroposterior dimension, cross sectional area and the pharyngeal volume were
all decreased in the patients with mandibular setback. Mattos et al.33 in a metaanalysis conducted to study the effects of orthognathic surgery on oropharyngeal
airway determined that anteroposterior changes after mandibular setback
surgery had a highly significant decrease in oropharyngeal airway at the level of
the soft palate (-2.7mm) and the level of the base of the tongue (-2.99mm). There
54
was also a significant decrease in the lateral width of the oropharyngeal airway
after mandibular setback surgery.
Concerns over the effect of mandibular setback surgery have received more
attention as the epidemic of obesity continues to rise, leading to an increasing
number of middle aged adults with OSA. Surgeons first noticed some patients
developing OSA following mandibular setback and published case reports about
this potential complication.5, 7 Riley et al. reported on 2 women who presented
with OSA after mandibular osteotomy for treatment of mandibular prognathism. 7
Before surgery neither patient had any signs and/or clinical symptoms of airway
obstruction. These 2 patients were diagnosed with OSA. Hasebe et al.34
conducted polysomnography before and 2 months after surgery and determined
no change in the patients apnea hypopnea index. However 2 patients were
diagnosed with mild OSA as the setbacks were large. Both patients were not
obese and had undergone mandibular setback surgeries only. Consecutive
cephalometric studies by Hochban et al.19 noted a decrease in PAS after surgery
but the polysomnographs taken before and after surgery noted no significant
changes and the surgery did not perpetuate sleep related breathing disorders.
Correlation analysis for this study showed no significant correlation between
mandibular setback surgery and pharyngeal airway volumes or dimensions at the
three timepoints. Similar to the findings from this study, Panou et al.28 utilized
CBCT and determined no correlation between the amount of surgical movement
and change in the pharyngeal volume. Conversely Kawamata et al.1 found a
correlation (r = 0.54) between the amount of mandibular setback and the
55
reduction in lateral pharyngeal width 3 months after surgery utilizing computed
tomography (CT) to study the effect of mandibular setback surgery. In addition
Hochban et al.19 determined a correlation (r= 0.5) between mandibular setback
and reduction in PAS. These correlation values do not substantiate a strong
causation or association.
Limitations of this study include a small sample size, lack of control of tongue
position, and inspiratory or expiratory phase during acquisition of the CBCT. It
would have been helpful to have more long term data, and to compare the results
between patients with smaller initial airways volumes. Additionally sleep apnea
patients could have been compared with non-apneic patients to determine if a
difference exists between the groups after mandibular setback surgery. Changes
in the amount of surgical repositioning may also influence results.
The literature continues to evolve on the effect of mandibular setback surgery
on the posterior airway. The evidence points to a detrimental effect on the airway
and further CBCT studies need to be pursued to elucidate the relationship
between airway volume changes after setback surgery and its implications in
terms of airway resistance, obstruction, collapsibility and the resultant effect on
obstructive sleep apnea. After screening for excessive daytime somnolence,
snoring, increased BMI and medical conditions related to OSA, and results from
a polysomnograph, surgical treatment recommendations for patients pursuing
Class III surgical correction need to be made to determine if a mandibular
setback or combination with maxillary advancement would provide the best
esthetic and functional goals, and in turn avoid OSA, a life threatening outcome.
56
Conclusion
1. There is a significant decrease in all pharyngeal airway volumes from preop
surgery to 6 months and 1 year after isolated mandibular setback surgery.
2. There is a significant decrease in the lateral surface and anteroposterior
dimension for up to 1 year following isolated mandibular setback surgery.
3. No significant correlation exists between the amount of mandibular setback
surgery and pharyngeal airway volumes or dimensions.
57
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Appendix
Table A.1: Within-Subject Effects for Oropharyngeal, Hypopharngeal, Total
Volumes, Lateral Surface and Anteroposterior Dimensions
Source
Vol OP
Error(Vol OP)
Vol HP
Error(vol HP)
Total Vol
Error(Total
vol)
TR at OP
Error(TR OP)
TR at HP
Error(TR HP)
AP at OP
Error(AP OP)
AP at HP
Error(AP HP)
Type III Sum of Squares
Df
Mean
Square
F
Sig.
Sphericity Assumed
350933043.1
2
175466521.6
21.755
0.000
Greenhouse-Geisser
350933043.1
1.560
224952072.7
21.755
0.000
Sphericity Assumed
483935227.9
60
8065587.1
Greenhouse-Geisser
483935227.9
46.801
10340266.2
Sphericity Assumed
144272645.5
2
72136322.7
10.768
0.000
Greenhouse-Geisser
144272645.5
1.744
82717210.5
10.768
0.000
Sphericity Assumed
401949991.5
60
6699166.5
Greenhouse-Geisser
401949991.5
52.325
7681793.9
Sphericity Assumed
940063068.3
2
470031534.1
17.699
0.000
Greenhouse-Geisser
940063068.3
1.590
591156651.3
17.699
0.000
Sphericity Assumed
1593458576
60
26557642.9
Greenhouse-Geisser
1593458576
47.706
33401434
Sphericity Assumed
411.5
2
205.7
12.526
0.000
Greenhouse-Geisser
411.5
1.818
226.4
12.526
0.000
Sphericity Assumed
985.6
60
16.4
Greenhouse-Geisser
985.6
54.527
18.1
Sphericity Assumed
12.9
2
6.5
0.275
0.761
Greenhouse-Geisser
12.9
1.766
7.3
0.275
0.734
Sphericity Assumed
1418.3
60
23.6
Greenhouse-Geisser
1418.3
52.973
26.8
Sphericity Assumed
168.2
2
84.1
3.367
0.041
Greenhouse-Geisser
168.2
1.270
132.5
3.367
0.065
Sphericity Assumed
1498.9
60
24.9
Greenhouse-Geisser
1498.9
38.088
39.3
Sphericity Assumed
153.1
2
76.6
9.051
0.000
Greenhouse-Geisser
153.1
1.762
86.9
9.051
0.001
Sphericity Assumed
507.5
60
8.5
Greenhouse-Geisser
507.5
52.861
9.6
Within-subjects effects table denoting overall significant differences between the means for all
except TR at HP and AP at OP.
62
Table A.2: Multivariate Analysis for Oropharnygeal, Hypopharyngeal, Total
Volumes, Lateral Surface and Anteroposterior Dimensions
OP Volume
HP Volume
Total
Volume
TR at OP
TR at HP
AP at OP
AP at HP
Effect
Wilk's
Lambda
Wilk's
Lambda
Wilk's
Lambda
Wilk's
Lambda
Wilk's
Lambda
Wilk's
Lambda
Wilk's
Lambda
Error df
Sig.
Partial
Eta
Squared
Value
F
Hypothesis
df
0.495
14.806b
2.000
29.000
0.000
0.505
0.655
7.654b
2.000
29.000
0.002
0.345
0.548
11.952b
2.000
29.000
0.000
0.452
0.61
9.283b
2.000
29.000
0.001
0.39
0.987
.195b
2.000
29.000
0.824
0.013
0.519
13.430b
2.000
29.000
0.000
0.481
0.685
6.675b
2.000
29.000
0.004
0.315
Multivariate tests determining significance of change in oropharyngeal volume (OP),
hypopharyngeal volume (HP), total volumes (mm³), lateral surface (TR) (mm) and anteroposterior
dimensions (AP) (mm).
63
Figure A.1: Difference between the means for Volume oropharynx (OP). 1= preop,
2= postop 6 months, 3= postop 1 year
Figure A.2: Difference between the means for Volume hypopharynx (HP). 1= preop,
2= postop 6 months, 3= postop 1 year
64
Figure A.3: Difference between the means for total volume. 1= preop,
2= postop 6 months, 3= postop 1 year
Figure A.4: Difference between the means for lateral surface (TR) at OP. 1= preop,
2= postop 6 months, 3= postop 1 year
65
Figure A.5: Difference between the means for lateral surface (TR) at HP. 1= preop,
2= postop 6 months, 3= postop 1 year
Figure A.6: Difference between the means for anteroposterior (AP) at OP. 1= preop,
2= postop 6 months, 3= postop 1 year
66
Figure A.7: Difference between the means for anteroposterior (AP) at HP. 1= preop,
2= postop 6 months, 3= postop 1 year
67
VITA AUCTORIS
Shireen Irani was born in Mumbai, India. Her family continues to reside in
India, while she pursued her education in Texas to attain her Bachelor of Science
in Molecular Biology in 2003.
Dr. Irani received a Doctor of Dental Surgery degree in May 2007, followed
by an Advanced Education General Dentistry certificate in May 2008. She
worked as a general dentist for four years, providing comprehensive dental care
and was awarded a Fellowship in Academy of General Dentistry. She began her
orthodontic training at Saint Louis University in June 2012.
Shireen has been married to her husband, Firdosh, since January of 2011.
She will complete her Masters of Science in Dentistry degree in December 2014.
Upon graduation, Dr. Irani plans to reside in Dallas, Texas where she will start
her own orthodontic practice.
68