ONLINE ONLY
Three-dimensional analysis of pharyngeal
airway in preadolescent children with different
anteroposterior skeletal patterns
Yoon-Ji Kim,a Ji-Suk Hong,a Yong-In Hwang,a and Yang-Ho Parkb
Seoul, Korea
Introduction: In growing patients with skeletal discrepancies, early diagnosis, evidence-based explanations
of etiology, and assessment of functional factors can be vital for the restoration of normal craniofacial growth
and the stability of the treatment results. The aims of our study were to compare the 3-dimensional pharyngeal
airway volumes in healthy children with a retrognathic mandible and those with normal craniofacial growth,
and to investigate possible significant relationships and correlations among the studied cephalometric variables and the airway morphology in these children. Methods: Three-dimensional airway volume and crosssectional areas of 27 healthy children (12 boys, 15 girls; mean age, 11 years) were measured by using
cone-beam computed tomography volume scans, and 2-dimensional lateral cephalograms were created
and analyzed. The subjects were divided into 2 groups based on their ANB angles (group I: 2 # ANB # 5 ;
group II: ANB .5 ), and cephalometric variables, airway volumes, and cross-sectional measurements were
compared. Results: There were statistically significant differences in the following parameters: height of
the posterior nasal plane (P \0.05), pogonion to nasion perpendicular distance (P \0.01), ANB angle
(P \0.01), mandibular body length (P \0.01), facial convexity (P \0.01), and total airway volume (P \0.05).
No statistically significant differences between the 2 groups were found in the cross-sectional area and the
volumetric measurements of the various sections of the airway except for total airway volume, which had
larger values in group I (P \0.05). Conclusions: The mean total airway volume, extending from the anterior
nasal cavity and the nasopharynx to the epiglottis, in retrognathic patients was significantly smaller than
that of patients with a normal anteroposterior skeletal relationship. On the other hand, differences in volume
measurements of the 4 subregions of the airway were not statistically significant between the 2 groups.
(Am J Orthod Dentofacial Orthop 2010;137:306.e1-306.e11)
T
he effects of respiratory function on craniofacial
growth have been studied for decades, and most
clinicians now understand that respiratory function is highly relevant to the orthodontic diagnosis and
the treatment plan. In 1907, Angle1 showed that his
Class II Division 1 malocclusion is associated with obstruction of the upper pharyngeal airway and mouth
breathing. Clinical features related to impaired breathing have been observed by some authors, and Ricketts2
presented the main characteristics of the respiratory obstruction syndrome as adenoid and tonsil hypertrophy,
From the Department of Orthodontics, Kangdong Sacred Heart Hospital,
Hallym University Medical Center, Seoul, Korea.
a
Resident.
b
Associate professor.
The authors report no commercial, proprietary, or financial interest in the products or companies described in this article.
Reprint requests to: Yang-Ho Park, Department of Orthodontics, Kangdong
Sacred Heart Hospital, 445 Gil-Dong, Gangdong-Gu, Seoul, Korea, 134-701.
e-mail, dentpark64@hanmail.net.
Submitted, May 2009; revised and accepted, October 2009.
0889-5406/$36.00
Copyright Ó 2010 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2009.10.025
crossbite, open bite, narrow external nares, and tongue
thrusting.
Predisposing factors of nasal obstruction can include adenoid and tonsil hypertrophy, polyps, allergies,
infections, and nasal deformities. A common cause of
mouth breathing arises from the adenoids, which are
a conglomerate of lymphatic tissues located in the posterior pharyngeal airway. Infection and inflammation of
the adenoids leads to upper airway obstruction, and the
term ‘‘adenoid facies’’ is often used to describe a possible aberrant craniofacial growth pattern related to
mouth breathing characterized by lip incompetency, underdeveloped nose, increased anterior facial height,
constricted dental arches, and proclined maxillary incisors with a Class II occlusal relationship.3,4
In addition to studies that affirm nasal obstruction as
the major factor responsible for dentofacial anomalies,
other studies refute a significant relationship between
airway obstruction and the frequency of malocclusion.
In a study of 500 patients with upper airway problems,
Leech5 discovered that 60% of the mouth-breathing patients were Class I and concluded that mouth breathing
306.e1
306.e2
Table I.
Kim et al
American Journal of Orthodontics and Dentofacial Orthopedics
March 2010
Sample characteristics
Group I
Subjects (n)
Age (y) (mean 6 SD)
Range (y)
Group II
Male
Female
Male
Female
Total
7
11.46 6 0.69
10.50-12.58
7
11.71 6 0.86
10.67-12.92
5
10.23 6 0.73
9.42-12.33
8
11.09 6 1.03
9.08-12.17
27
11.19 6 1.28
9.08-12.92
has no influence on craniofacial growth. Similarly,
Gwynne-Evans6 determined that facial growth is constant regardless of the mode of breathing. Additionally,
Humphreys and Leighton7 found no significant difference in the anteroposterior relationship of the jaws between nose and mouth breathers.
In growing patients with skeletal discrepancies and
clinical signs of adenoid facies, early diagnosis, evidence-based explanations of etiology, and assessment
of the functional factors might be vital for the restoration of normal craniofacial growth and the stability of
treatment results. Morphometric evaluation of the pharyngeal airway has been mostly performed on lateral
cephalometric headfilms, by identifying specific landmarks and measuring various lengths and areas in the
pharyngeal region.8-10
Despite the vast amount of research concerning airway anatomy and its influence on craniofacial growth
and development, most studies have been 2-dimensional (2D) and have used lateral or frontal cephalograms with limited evaluation of lengths and areas.
New 3-dimensional (3D) technology of computed tomography (CT) has expanded diagnostic capacities,
making volumetric analysis and accurate visualization
of the airway possible. Most 3D studies of the airway
used multislice CT to evaluate the airway; this has the
advantage of high-quality images to discern hard- and
soft-tissue anatomies, but, because of the high radiation
dose, it is restricted to patients with severe craniofacial
deformities and those undergoing orthognathic surgeries.11,12 Recently, cone-beam CT (CBCT) systems
have been developed specifically for the maxillofacial
region. Because a CBCT scan uses a different type of
acquisition than traditional multislice CT, radiation is
reduced and can be used in a wider range of patients,
eg, those having maxillofacial surgery, implantology,
and orthodontics.13 Cross-sectional and volumetric investigations of the pharyngeal airway have been possible by using CBCT scans to analyze the complex
airway anatomy, and previous studies have confirmed
that volumetric measurements of airways with CBCT
are accurate with minimal error.14
The aims of our retrospective, cross-sectional study
were (1) to compare the 3D pharyngeal airway volumes
in healthy children with a retrognathic mandible and
those with normal craniofacial growth and (2) to investigate possible significant relationships and correlations
among the studied cephalometric variables and the airway morphology in these children.
MATERIAL AND METHODS
Pharyngeal airway structures were studied in 27
healthy children (12 boys, 15 girls) with a mean age
of 11.19 6 1.28 years (Table I) who were referred to
the Department of Orthodontics of Kangdong Sacred
Heart Hospital, Hallym University Medical Center,
Seoul, Korea, for treatment. Those who had symptoms
of upper respiratory infection, pharyngeal pathology
such as adenoid hypertrophy and tonsillitis or a history
of adenoidectomy or tonsillectomy were excluded.
The study protocol was approved by the Ethics
Review Committee of the hospital (IRB 09-57).
CBCT volume scans of all subjects were obtained
by using the Master 3D dental-imaging system (Vatech,
Seoul, Korea), and the imaging protocol used a 12-in
field of view to include the entire craniofacial anatomy.
The axial slice thickness was 0.3 mm, and the voxels
were isotropic.
Patients sat upright with natural head position, and
their jaws were at maximum intercuspation with the
lips and tongue in a resting position. The patients
were asked not to swallow and not to move their heads
or tongues. Almost all 3D imaging modalities (eg, conventional CT or magnetic resonance imaging) require
patients to be supine; this causes significant morphologic changes of the airway, since gravity affects the
soft tissues surrounding the oropharyngeal cavity.15 It
might be reasonable to examine patients in the supine
position for diagnosing such disorders as obstructive
sleep apnea. In most cases (including orthodontic diagnosis and treatment planning), however, patients do not
need to be analyzed in the supine position. Recent advances in CBCT permit the acquisition of axial CT images in the upright sitting position, which is more valid
for our study.
The axial images were imported to InVivoDental
software (Anatomage, San Jose, Calif), and volumetric
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 137, Number 3
Kim et al 306.e3
Fig 1. A volumetric rendering of a subject’s craniofacial skeleton: A, lateral view right; B, frontal view;
C, lateral view left.
Fig 2. For the horizontal reference plane, the FH plane
was constructed from the right and left porions and the
right orbitale, which was set as the origin.
rendering was done for airway and cephalometric analysis (Fig 1). To standardize the measurements and minimize errors, the 3D image was reoriented, by using the
Frankfort horizontal (FH) plane as its reference plane.
The FH plane was constructed from the right and left
porions located in the most laterosuperior point of the
external auditory meatus and the right orbitale (Fig 2).
Cho16 proposed a 3D analysis system from a CBCT volumetric image with a set of landmarks, reference lines,
and reference planes. In his system, the 3D image is reoriented according to the nasofrontozygomatic plane
and the FH plane. Lagravère et al17 designated reference
points such as the midpoint between the foramen lac-
erum and the middorsum foramen magnum, since they
are easily viewed in the 3D images.
The 2D cephalometric images were derived from
the 3D CT scans by creating an orthogonal projection
with parallel rays, and the images were imported into
V-ceph software (Osstem Implant, Seoul, Korea) for
conventional 2D analysis. Landmark identifications
and physical measurements were performed by the
same investigator (Y.J.K). For the cephalometric analysis, 13 conventional hard-tissue cephalometric landmarks were identified, and 5 anteroposterior and 5
vertical measurements were calculated (Table II, Fig
3). The subjects were assigned to 2 groups based on
their ANB angles: 14 subjects (7 boys, 7 girls) whose
ANB angles ranged from 2 to 5 were allocated to
group I, and 13 subjects (5 boys, 8 girls) who had
ANB angles greater than 5 were allocated to group II
(Table I).
Five cross-sectional planes (2 frontal and 3 axial
sections) and 5 volumes of the pharyngeal airway
were developed in this study based on the FH plane
and soft-tissue landmarks (Table III; Figs 4 and 5).
Cross-sectional planes of the nasal cavity are perpendicular to the FH plane, whereas the pharyngeal cross-sections are parallel to the FH plane. Although these crosssections are not directly perpendicular to the long axis
of the airway, the FH plane was used as a reference
plane to standardize the plane orientation and minimize
error in identifying the studied cross-sectional planes of
the subjects. Various dimensions of the airway were calculated by the same examiner. Cross-sectional measurements including width, length, and area were calculated
in the sectional views (frontal and axial) because they
provide precise 2D visualization and linear accuracy
of 2D measurements (Fig 5).
306.e4
Table II.
Kim et al
American Journal of Orthodontics and Dentofacial Orthopedics
March 2010
Two-dimensional cephalometric variables used in this study
Variable
Vertical skeletal pattern
Gonial angle
AFH
PFH
FMA
AFH/PFH
Anteroposterior skeletal pattern
A to N-perp
Pog to N-Perp
ANB
Mn body length
Facial convexity
Definition
The angle formed by the junction of the posterior and lower borders of the mandible
Distance between nasion and menton
Distance between sella and gonion
The angle formed by the FH plane and the mandibular plane (Go-Me)
Ratio of AFH to PFH
The linear distance from Point A to nasion perpendicular
The linear distance from pogonion to nasion perpendicular
The difference between SNA and SNB
The linear distance of the mandibular plane (Go-Me)
The angle fomed by nasion, Point A, and pogonion
the selected airway region. Finally, the volume of the
designated airway was calculated in cubic millimeters.
Lateral cephalometric variables and airway dimensions of 15 randomly selected CT scans were remeasured by the same investigator 2 weeks after the first
measurements. A paired t test was used to estimate systemic error, and all measurements were free of systemic
error.18 Random error was estimated by using Dahlberg’s formula19 (ME2 5 Sd2/2 n). Random errors varied from 0.49 to 2.24 mm in linear measurements, from
11.33 to 36.12 mm2 in area measurements, and from
57.36 to 91.37 mm3 in volume measurements.
Descriptive statistics including the mean and standard deviation for each group were calculated by using
SPSS for Windows software (version 12.0, SPSS, Chicago, Ill). Differences between groups I and II, and
between the sexes, were tested by using independent
t tests. Pearson’s correlation coefficient test was used
to detect any relationship of different parts of the airway
and between airway volume and 2D cephalometric
variables.
Fig 3. Landmarks, anteroposterior measurements, and
vertical measurements used in this study.
RESULTS
Volumetric renderings of the subjects’ CT scans
were acquired with the InVivoDental software, and we
proceeded with volumetric analysis of the defined airways. Since airway is void space surrounded by hard
and soft tissues, inversion of the 3D-rendered image is
required; this converts a negative value to a positive
value, and vice versa. This process removes the hard
and soft tissues of the image and embodies the airway
spaces of the craniofacial region including the paranasal
sinuses and other empty spaces. Then sculpting was
dpme to isolate the desired airway section by removing
unnecessary structures; subsequently, threshold values
were adjusted to eliminate imaging artifacts and refine
Means and standard deviations for cephalometric,
cross-sectional, and volumetric variables were compared by sex; since no sex differences were found in
any measurement, the subjects were combined for subsequent analysis. Table IV gives the comparison results
of groups I and II. There were statistically significant
differences in the following parameters: height of the
posterior nasal plane (P\0.05), pogonion to nasion perpendicular distance (P \0.01), ANB (P \0.01), mandibular body length (P \0.01), facial convexity
(P \0.01), and total airway volume (P \0.05). According to the lateral cephalometric analysis, group II had
retruded mandibles and a greater skeletal anteroposterior discrepancy, as evidenced by the pogonion to nasion
Kim et al 306.e5
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 137, Number 3
Table III.
Cross-sectional planes and volumes of the 3D pharyngeal airway
Landmark
Definition
Cross-sectional plane
Anterior nasal plane
Ana plane
Posterior nasal plane
Pna plane
Upper pharyngeal plane
Uph plane
Middle pharyngeal plane
Mph plane
Lower pharyngeal plane
Lph plane
Volume
Nasal airway
Superior pharyngeal airway
Middle pharyngeal airway
Inferior pharyngeal airway
Total airway
A frontal plane perpendicular to the FH plane passing
through ANS
A frontal plane perpendicular to the FH plane passing
through PNS
An axial plane parallel to the FH plane passing
through PNS
An axial plane parallel to the FH plane passing
through the caudal margin of the soft palate
An axial plane parallel to the FH plane passing
through the superior margin of the epiglottis
Airway formed by the Ana and Pna planes
Airway formed by the Pna and Uph planes
Airway formed by the Uph and Mph planes
Airway formed by the Mph and Lph planes
Airway extending from Ana plane to Lph plane
perpendicular distance, ANB, and facial convexity
values. No statistically significant difference between
the 2 groups was found in the cross-sectional area and
volumetric measurements of the different parts of the
airway. However, total airway volume, which is the
sum of the 4 separate volumes of the airway, was significantly greater in group I (P\0.05). The linear measurements of the cross sections indicated that the height of
the posterior nasal plane was the only significant mean
found, with greater values in group I (P \0.05).
Tables V and VI show the correlations among the
studied variables. Table V shows the correlations of sections of the airway with each other, and Table VI shows
correlations between the 2D cephalometric variables
and the 3D volumetric measurements of the airway.
The nasal airway volume and the superior pharyngeal
airway volume had a positive correlation (P \0.01).
Some analyses from the lateral cephalograms tended
to be correlated with airway volume. The anterior facial
heights showed positive correlations to all volumetric
measurements except the middle pharyngeal airway
volume. Posterior facial height showed significant correlations with total airway volume and inferior pharyngeal airway volume (P \0.05). Additionally, total
airway volume was significantly correlated with ANB
angle and mandibular body length (P \0.05).
DISCUSSION
Although the impact of respiratory function on craniofacial growth and its relevance in orthodontics has
long been a controversial issue, many clinical studies
have presented good evidence with sound data supporting this hypothesis. To evaluate the airway, nasal resis-
tance and airflow tests, nasoendoscopy, and lateral
cephalometry have been the primary means used for
the last few decades.20,21 As new-generation CBCT supplements the diagnosis and treatment planning of orthodontic patients, 3D analyses of the maxillofacial
skeleton and the soft tissues are possible. Our study of
the pharyngeal airway with CBCT produced anatomically true images that are 3D reconstructed without
magnification or distortion, allowing accurate measurement in all 3 dimensions (sagittal, frontal, and transverse) to understand fully the pharyngeal morphology
in growing children.22-24
Because of the retrospective design of this study, direct examination of the patients’ nasopharyngeal functions was not possible; selection of subjects was based
on previous clinical chart information at their diagnoses
for orthodontic treatment, and CBCT images were used
additionally to screen subjects with severe adenoid and
tonsillar hypertrophy. Area measurements of adenoids
in lateral cephalograms have been reported to have clinically useful correlations with gold standards such as actual tissue volumes obtained by adenoidectomy and
direct observations through endoscopy.25-27 However,
Aboudara et al28 found that 2D measurements of the nasopharyngeal airway area lacks much of the structural
information, since the 3D structure is compressed into
a 2D image. In our study, subjective grading of the adenoid and tonsil sizes in the 3D image was done, and patients with severe adenoid or tonsillar hypertrophy were
considered as having infections or allergies, and they
were excluded in this study. As a result, we confirmed
that our patients were free of clinical signs and symptoms related to pharyngeal pathology and had no history
of treatment intervention (eg, tonsillectomy or
306.e6
Kim et al
American Journal of Orthodontics and Dentofacial Orthopedics
March 2010
Fig 4. Five cross-sectional planes of the pharyngeal airway used in this study: A, right lateral view
and B, frontal view of volume rendered images. a, Anterior nasal plane (Ana); b, posterior nasal plane
(Pna); c, upper pharyngeal plane (Uph); d, middle pharyngeal plane (Mph); e, lower pharyngeal plane
(Lph). C, The cross-sectional planes are shown in the lateral cephalogram.
adenoidectomy) in the pharyngeal area. Thus, we assumed that the subjects were relatively healthy and
showed normal patterns of nasorespiratory function.
Obviously, this method of patient selection is not ideal,
and we could have included patients with mild pharyngeal diseases that could not be detected. According to
a study by Laine-Alava and Minkkinen,29 however,
a history or symptoms of upper respiratory diseases
have no influence on variables related to nasorespiratory
function when the measurements are made during an
asymptomatic period.
The nasopharyngeal airway is mainly influenced by
the adenoids, which are known to follow the lymphoid
growth curve shown by Scammon et al.30 They increase
rapidly from infancy, reach a peak before adolescence,
and then gradually decrease to their adult sizes. Subtelny and Baker31 concluded that the growth peak of
the adenoids varies from 9 to 15 years of age. In our
study, children aged 9 to 12 years were selected. According to the curves of general growth of Scammon
et al,30 which the maxillomandibular growth is known
to follow, this period is the end of the second phase of
growth when the growth rate is steady and constant before the adolescent growth spurt. Therefore, children at
these preadolescent ages can have adenoids that have
reached their maximum size, and considerable facial
growth has occurred to reflect functional influences because they might be predisposed to the natural anatomic
conditions of narrower nasopharyngeal airways.
The 2D lateral cephalometric images were created
from the CBCT scans primarily to assign the subjects
to the 2 groups and also to ascertain significant correlations among the cephalometric variables and the airway
volumes. Linear accuracy of the CBCT-derived lateral
cephalometric images has been studied.32-34 Moshiri
et al35 compared linear measurements of lateral cephalograms derived from CBCT with those of conventional
cephalograms and direct measurements on a dry human
skull, which was considered to represent the anatomic
truth. For most linear measurements calculated in the
sagittal plane, they found that the CBCT-derived 2D lateral cephalograms were more accurate than conventional lateral cephalograms. Moreover, generation of
2D cephalometric images from CBCT data prevents unnecessary irradiation of the patients. Regarding patient
positioning, Hassan et al33 compared linear measurements on 3D surface-rendered images, 2D tomographic
multiplanar reformatted slices, and 2D projection images in both ideal and rotated positions of dry human
skulls. They concluded that linear measurements on
all 3 images were accurate in the ideal skull position;
however, the rotated skull provided linear accuracy
only for 3D surface-rendered images and 2D tomographic slices.
To classify the subjects based on their anteroposterior skeletal relationships, Korean norms for the ANB
angle were used.36 Several reports about the ANB angle
have indicated its lack of clinical significance and reliability in the determination of the anteroposterior jaw
position. Hussels and Nanda37 showed that the ANB angle is influenced by rotation and vertical growth of the
jaws, anteroposterior position of the nasion, and vertical
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 137, Number 3
Kim et al 306.e7
Fig 5. Cross-sectional views of the pharyngeal airway in the 5 planes: a represents the length (axial
slice) or height (frontal slice) of the airway defined by the greatest distance in the anteroposterior or
vertical direction of the airway cross section; b is the width of the airway defined by the greatest distance in the right and left directions of the airway cross section. The colored region indicates the
cross-sectional area of the airway.
distance between Points A and B. Ferrario et al38 suggested that the orthodontic diagnosis should be based
on more than 1 anteroposterior appraisal. However,
the ANB angle is a commonly used cephalometric parameter in clinical orthodontics,39 and Ishikawa et al40
corroborated that it is reliable for determining the anteroposterior relationship of the jaws. Additionally, these
authors showed that the ANB angle and the angle of
convexity in the prepubertal assessment have high prediction accuracy for postpubertal jaw relationships. In
our study, the anteroposterior analyses displayed statistically significant differences except Point A to nasion
perpendicular distance, reaffirming the reliability of
the ANB angle, which was used to classify our subjects.
The number of subjects in our study was limited and,
therefore, this investigation should be considered a pilot
study. Because of the small number of subjects, data
from both sexes were collected, and, fortunately, no sexual dimorphism in any cross-sectional and volumetric
measurements was observed. These findings agree
with those of Ceylan and Oktay41 and Freitas et al.42
Vertical cephalometric means of the 2 groups were
within normal limits, and no statistically significant
differences in the vertical measurements between
groups I and II were observed (Table IV), eliminating
the possible effects of the vertical skeletal pattern that
might have contributed to the variations of the airway
dimensions. In the longitudinal study of Akcam et
al,43 upper and lower pharyngeal airways were measured in preadolescents according to the different rotation types, and hyperdivergent subjects had narrower
lower pharyngeal airways.
All cross-sectional area and volumetric measurements of the subregions of the pharyngeal airway
were greater in group I. However, they were not statistically significant, indicating that segmental airway capacities are not related to mandibular deficiencies
(Table IV). This agrees with previous 2D studies that
claimed no association of airway dimensions with malocclusion types.12,41,42 Ceylan and Oktay41 asserted
that, as skeletal anteroposterior relationship changes,
pharyngeal structures undergo postural modifications,
and hence the size of the airway remains constant. Interestingly, total airway volume, the sum of the 4 subregions of the airway from the nasal cavity and the
nasopharynx to the oropharyngeal region above the
306.e8
Kim et al
Table IV.
Descriptive statistics of groups I and II
American Journal of Orthodontics and Dentofacial Orthopedics
March 2010
Group I (n 5 14)
Ana plane
Pna plane
Uph plane
Mph plane
Lph plane
Cephalometric analysis
Airway volume
Height
Width
Cross-sectional area
Height
Width
Cross-sectional area
Length
Width
Cross-sectional area
Length
Width
Cross-sectional area
Length
Width
Cross-sectional area
Gonial angle
AFH
PFH
PFH/AFH
FMA
Point A to nasion perpendicular
Pogonion to nasion perpendicular
ANB
Mandibular body length
Facial convexity
Nasal airway
Superior pharyngeal airway
Middle pharyngeal airway
Inferior pharyngeal airway
Total airway
Group II (n 5 13)
Mean
SD
Mean
SD
Intergroup difference
P
44.62
16.48
263.51
22.15
25.85
292.93
22.98
29.72
494.93
18.25
25.38
321.86
17.34
29.63
427.68
125.94
116.02
73.09
0.63
29.72
–1.15
–6.84
2.42
68.22
5.04
13479.62
2620.77
1581.23
3278.00
20959.62
6.03
1.55
71.47
1.17
2.14
70.77
5.61
5.55
159.05
5.65
5.68
129.11
4.96
3.12
183.11
5.90
5.06
5.61
0.04
4.05
2.87
5.05
1.10
4.99
3.33
2547.12
899.23
509.83
1101.55
3611.26
40.32
14.91
216.92
19.42
25.40
258.04
22.45
28.63
467.64
15.44
23.57
250.96
16.18
28.72
363.66
125.30
111.96
69.32
0.62
32.22
–1.16
–12.79
5.85
63.10
12.10
11124.00
2138.38
1402.92
2498.77
17164.08
8.67
3.07
95.07
2.01
2.25
77.46
4.64
5.12
161.03
4.44
4.11
99.99
5.39
4.14
148.17
5.26
6.81
5.49
0.02
2.25
2.29
3.91
1.15
3.03
3.18
3302.82
658.27
662.49
1095.03
4238.46
0.16
0.11
0.17
0.03*
0.61
0.24
0.79
0.61
0.67
0.17
0.36
0.13
0.57
0.53
0.34
0.77
0.10
0.10
0.41
0.06
1.00
0.01*
\0.01†
\0.01†
\0.01†
0.06
0.13
0.45
0.08
0.02*
Linear measurements (mm), area measurements (mm2), volumetric measurements (mm3), angular measurements ( ).
*P \0.05; †P \0.01.
epiglottis, appeared to be significantly greater in group
I. From these contrasting results, we inferred that each
subregion of the upper airway does not specifically represent a patient’s whole upper airway capacity, and,
therefore, comprehensive assessment of the entire upper
airway is needed in patients who require functional examination. Further studies with larger samples are
needed to investigate certain airway subregions that
might be significantly correlated to other skeletal patterns such as mandibular prognathism and vertical
growth pattern. Additionally, evaluation of discriminating capacities of airway parts limited by different anatomic landmarks might show specific regions of the
airway that are responsible for significant relationships
between the airway and the craniofacial structures.
Linear analysis of the cross-sections showed that the
nasal airway dimension is influenced by skeletal
pattern. The height of the posterior nasal cavity was significantly greater in group I, and the rest of the crosssectional dimensions showed greater values in group I,
but they lacked statistical significance. Alves et al12
compared 3D airways of adult skeletal Class II and
Class III patients, and concluded that nasal cavity width
had statistical significance between the 2 groups,
whereas the height of the nasal cavity did not. In contrast, Kikuchi11 found in his 3D airway study that the
oropharyngeal region of the airway was influenced by
the skeletal pattern. He maintained that airway morphology, rather than size, is influenced by the anteroposterior position of the mandible and suggested that
airway volume remains constant by horizontal and vertical compensation mechanisms of the muscles adjacent
to the pharynx.
Nasal airway volume and superior pharyngeal airway volume were positively correlated (Table V), indicating a close relationship of the anterior and posterior
parts of the upper airway. Located above the hard palate,
these 2 sections of the airway are not only anatomically
adjacent, but also their volumetric dimensions have
a direct relationship. Linder-Aronson3 studied the
Kim et al 306.e9
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 137, Number 3
Table V.
Correlations among airway volumes
Nasal airway
Superior pharyngeal airway
Middle pharyngeal airway
Inferior pharyngeal airway
Pearson correlation
P value
Pearson correlation
P value
Pearson correlation
P value
Pearson correlation
P value
Nasal
airway
Superior pharyngeal
airway
Middle pharyngeal
airway
Inferior pharyngeal
airway
1
0.542
0.004*
1
0.343
0.086
0.199
0.330
1
0.159
0.437
0.362
0.069
0.375
0.059
1
˙
0.542
0.004*
0.343
0.086
0.159
0.437
˙
0.199
0.330
0.362
0.069
˙
0.375
0.059
˙
*P \0.01.
Table VI.
Correlations between cephalometric variables and airway volumes
Gonial angle AFH PFH PFH/AFH FMA Pt A to N perp Pog to N perp ANB Mn body Facial conv
Nasal airway
Pearson
correlation
P value
Superior pharyngeal Pearson
airway
correlation
P value
Middle pharyngeal Pearson
airway
correlation
P value
Inferior pharyngeal Pearson
airway
correlation
P value
Total airway
Pearson
correlation
P value
0.01
0.57
0.37
0.00
0.00
–0.12
0.05
–0.36
0.33
–0.28
0.95
–0.13
\.01† 0.07
0.51 0.39
0.99
0.07
0.99
–0.10
0.56
–0.09
0.80
–0.07
0.07
–0.14
0.10
0.33
0.16
–0.09
0.53
0.15
\.01† 0.06
0.33 0.19
0.74
–0.04
0.63
–0.01
0.67
0.07
0.73
0.21
0.49
–0.31
0.10
0.22
0.66
–0.25
0.83
0.18
0.95
–0.37
0.73
–0.15
0.31
0.06
0.13
–0.32
0.27
0.32
0.23
–0.34
0.12
–0.42
0.11
0.42
0.09
–0.35
0.03*
0.08
0.46
–0.33
0.10
0.41
0.36
0.39
0.10
–0.08
0.03* 0.04*
0.66 0.47
0.39
0.05
0.06
–0.12
0.46
–0.13
0.77
0.07
0.70
\.01† 0.02*
0.80
0.57
0.52
0.74
0.03*
Pt, Point; N, nasion; perp, perpendicular; Pog, pogonion; Mn, mandibular; conv, convexity.
*P \0.05; †P \0.01.
relationship of the upper and lower parts of the airway,
and reported that a smaller nasopharyngeal airway is accompanied by a larger oropharyngeal airway. Ricketts2
and Dunn et al44 stated that oral breathing is related to
a narrow nasopharyngeal airway width because it is easily blocked by adenoid enlargement. In our study, no
significant correlations were found among the rest of
the airway volumes below the hard palate.
The relationship of conventional cephalometric
analyses and airway volumes were evaluated; anterior
and posterior facial heights were positively correlated
to nasal, superior pharyngeal, and inferior pharyngeal
airways, as well as to total airway volume (Table VI).
This indicates that patients with vertical growth patterns
are likely to have an expanded airway; this is inconsistent with studies that reported an inverse relationship
between pharyngeal volume and vertical facial
height.2,3,42,44,45 However, the variables used to assess
vertical craniofacial patterns are different from those
used in previous studies; this makes the comparison
less compatible. Interestingly, anterior facial height
showed strong correlations (P \0.01) to the upper
part of the airway, and the nasal and superior pharyngeal
airway; this agrees with Freitas et al,42 who noted that
vertical growth patterns have significant correlations
with the upper part of pharyngeal airways.
Anteroposterior discriminants such as ANB angle
and mandibular body length showed significant correlations with total airway volume, supporting the intergroup comparison of different anteroposterior skeletal
patterns in this study. The negative correlation of the
ANB angle and the total airway can be explained by
group I (2 #ANB#5 ) having significantly greater airway volume than group II (ANB .5 ). Mandibular
body length and total airway volume were both significantly greater in group I (Table IV), demonstrating
a positive correlation. Hwang et al46 reported that a constricted nasopharyngeal airway is associated with
retruded mandible and maxilla. On the other hand,
Abu Allhaija and Al-Khateeb47 concluded that
306.e10
Kim et al
anteroposterior pharyngeal airway dimensions were not
affected by changes of the ANB angle. Since these previous studies were based on lateral cephalograms, more
3D studies are needed to clarify this conflicting issue.
The standard deviations of the airway dimensions
were significantly large in cross-sectional area and volumetric measurements. This agreed with the findings of
Ozbek et al,48 who analyzed airway dimensions including width, area, and angulation in lateral headfilms of
skeletal Class II growing children. The area measurement of the oropharnynx had large standard deviations,
whereas the rest of the measurements such as airway
width and angulation showed narrow ranges. The wide
ranges of certain airway data were also evident in another study of airway morphology in skeletal Class II
and Class III adults.12 Whereas angular and linear measurements on the 3D airway model were typical of the
designated lengths and angles, cross-sectional areas
and volumes showed markedly large standard deviations in both skeletal types.
In a comparative study of the nasopharyngeal airway size using a lateral cephalometric headfilm and
a CBCT scan, Aboudara et al14 found that volume has
a much wider range than area of the same region of
the airway, asserting that determination of airway volume from 2D lateral cephalograms is inaccurate because of inconsistencies of the 3D airway anatomy.
Determined as percentages of the means, the standard
deviations of the area and volume in our study ranged
from 24% to 43% and 17% to 47%, respectively, indicating great variability in both parameters. Since
a CBCT scan provides the most accurate dimensional
analysis, it could be interpreted that much anatomic information is lost when the imaging modalities are 2D,
and linear and angular measurements do not give
enough information about the targeted structure.14,22-24
We showed that healthy preadolescent children with
retruded mandibles have decreased total pharyngeal airway volumes. Therefore, orthodontists should be aware
of the pharyngeal morphologies that might predispose
these children to impaired craniofacial growth. Future
investigations of longitudinal airway changes in patients
with different skeletal patterns and assessment of their
craniofacial growth with 3D superimpositions will
allow better understanding of the relationship between
respiratory function and craniofacial morphology.
CONCLUSIONS
The number of subjects available for this investigation was small; therefore, it should be considered a pilot
study. It was conducted to examine a possible significant relationship between airway size and maxillom-
American Journal of Orthodontics and Dentofacial Orthopedics
March 2010
andibular growth patterns in healthy preadolescent
children without evident pharyngeal pathology. According to our results, we can conclude the following.
1.
2.
3.
4.
Accurate volumetric determination of 3D pharyngeal airway is possible in preadolescents by using
CBCT scans.
There is no sexual dimorphism in the 2D lateral
cephalometric analysis or the 3D airway measurements of preadolescents.
The mean total airway volume, extending from the
anterior nasal cavity and the nasopharynx to the
epiglottis, of retrognathic patients was significantly
smaller than that of patients with a normal anteroposterior skeletal relationship. On the other hand,
differences in volume measurements of the 4 subregions of the airway were not found to be significantly different between the 2 groups.
In preadolescents, volumetric measurements of the
airway are significanlty correlated to anteroposterior and vertical cephalometric variables, mainly
anterior facial height and ANB angle.
We thank Kyung-Min Oh for her contributions to
data collection for this study.
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