Download Computed Tomographic Evaluation of Three

JIOS
10.5005/jp-journals-10021-1294
Computed Tomographic Evaluation of Three-dimensional Changes in Pharyngeal
Airway in Class II Division 1 Patients
ORIGINAL RESEARCH
Computed Tomographic Evaluation of Three-dimensional
Changes in Pharyngeal Airway in Class II Division 1
Patients treated with Twin Block Appliance
1
Parul Temani, 2Pradeep Jain, 3Seema Chaudhary, 4Pooja Rathee, 5Yashpal Pachori, 6Ruchira Temani
ABSTRACT
Objective: Recent years have witnessed a renewed interest
to determine a quantifiable relationship between mandibular
advancement performed with an orthodontic appliance and
the resulting airway dimensions and volume. The study was
conducted to evaluate the changes in dimensions of pharyngeal
airway space using computed tomography (CT) in Class II
division 1 patients with retrognathic mandible treated by twin
block appliance and to compare them with untreated controls.
Materials and methods: Twenty-five patients with Class II
division 1 malocclusion of age group 9 to 15 years were selected
randomly and evaluated for changes in pharyngeal airway
dimensions with and without twin block. Patients in each group
underwent CT scan of head and neck region at pretreatment
stage and 6 months after the initial scan. Institutional approval
for the project was obtained from the ethical committee. Volume,
area, transverse and anterioposterior (AP) dimensions of upper
(oropharynx) and lower (hypopharynx) pharyngeal airways
were measured on scanogram using computer software and
intragroup as well as intergroup comparisons were done.
Results: There was a statistically significant increase in
the volume of both hypopharynx and oropharynx in patients
treated with twin block. Area, transverse and AP dimensions of
oropharynx also increased significantly. In hypopharynx, area
and transverse dimensions increased markedly but no increase
in AP dimension was observed. Three-dimensional (3D)
reconstruction of the airway also demonstrates a considerable
increase in pharyngeal airway space.
Conclusion: Twin block can be a promising appliance for
improving pharyngeal airway space in Class II division 1 patients
with retrognathic mandible. However, the long-term implications
of this treatment modality needs further consideration and a
longer period of follow-up.
Keywords: Pharyngeal airway, Twin block, Computed
tomography.
How to cite this article: Temani P, Jain P, Chaudhary S, Rathee
P, Pachori Y, Temani R. Computed Tomographic Evaluation of
1,4
Assistant Professor, 2Professor and Head, 3Professor
Reader, 6Intern
5
1-4,6
Department of Orthodontics, Government Dental College
Jaipur, Rajasthan, India
5
Department of Orthodontics, Jodhpur Dental College and
General Hospital, Jodhpur, Rajasthan, India
Corresponding Author: Pooja Rathee, Assistant Professor
Depart­ment of Orthodontics, Government Dental College, Jaipur
Rajasthan, India, Phone: 9602732190, e-mail: drpoojarathee@
rediffmail.com
Three-dimensional Changes in Pharyngeal Airway in Class II
Division 1 Patients treated with Twin Block Appliance. J Ind
Orthod Soc 2014;48(4):439-445.
Source of support: Nil
Conflict of interest: None
Received on: 2/4/14
Accepted after revision: 15/5/14
INTRODUCTION
Retrognathia has been found to be a contributing factor in
obstructive sleep apnea (OSA) and other respiratory problems
with patients having a shorter mandibular body length.1
As the mandible opens, the tongue is carried downward
and the soft palate moves forward. Encroachment of the
soft palate on the posterior oropharyngeal wall contributes
to snoring and to obstructive events. In skeletal Class II
patients, the problem is likely caused by a posteriorlyorien­ted mandible that is displacing the soft tissues attached
to it, impinging on the airway space.2 There is a tremendous
spurge in the systemic problems like cardiac and respiratory
ailments in such patients, leading to decreased lifespan of
an individual.3
An increase in superior-posterior airway space, as seen
with functional appliance in place, allows a larger lumen for
air to pass through during inspiration, thereby decreasing
the likelihood of an obstructive event. The soft palate,
supra­­hyoid muscles and the genioglossus are displaced
anteriorly together with mandibular advancement. Other
than positional changes, mandibular displacement also stret­
ches the palatoglossal and palatopharyngeal arches which
increases upper airway muscular activity.4
Computed tomography (CT) is a radiologic ima­ging
tech­ni­que based upon computer assessment of the radia­tion
absor­bing characteristics of the various tissues of the body.
The sensitivity of CT makes it possible to identify hard
and soft tissues in multiple, sequential, radiographic slices
(tomograms). Computed tomography could help resolve
some of the issues of brea­thing patterns, airway anatomy, the
resistance to nasal airflow and the form of facial structures
and the dental arches.
Although, cone beam computed tomography allows
for accu­rate assessment of the entire volume of the upper
airway, it cannot quantify the upper airway changes caused
The Journal of Indian Orthodontic Society, October-December 2014;48(4):439-445
439
Parul Temani et al
by pre- and post-treatment 3D registration due to the lack
of stable references with a 3D craniofacial model.
The purpose of this study was to evaluate changes
in the pharyngeal airway space in growing patients with
retro­gnathic mandible and small airway dimensions, treated
with myofunctional orthodontic appliance, in the form of
‘twin block’, designed by William Clark in 1977.5 The
null hypothesis was that there was no significant increase
in oropharyngeal airway between patients treated with or
without twin block.
MATERIALS AND METHODS
The present study was conducted with a sample consisting
of 25 patients with Class II division 1 malocclusion of age
group 9 to 15 years selected randomly from the patients of
North Indian origin to evaluate the changes in pharyngeal
airway dimensions with and without myofunctional
appliance therapy (twin block). Institutional approval for
the project was obtained from the ethical committee. The
sample was divided into two groups as follows:
• Group A (treatment group—15 subjects): Treated with
twin block appliance for correction of Class II division
1 malocclusion.
• Group B (control group—10 subjects): Patients with
Class II division 1 malocclusion in which no treatment
was given.
All patients gave their consent as per the forms and
regulations decided by the ethical committee of the institute
after being notified of potential risks and radiation damage
associated with CT radiation. Group B patients were delayed
as the best time for functional and/or fixed appliance therapy
was justified as per skeletal maturity and the vacations of
the patient who himself/herself was not ready to start the
treatment immediately. Groups A and B were matched as
per the inclusion criteria.
Selection Criteria
Inclusion Criteria
• Skeletal Class II division 1 malocclusion (ANB > 4°)
with a clinically diagnosed retrognathic mandible.
• Class II division 1 dental malocclusion (with the first
molars at least one-half unit Class II).
• Mandibular plane angle (Go-Me to FH plane) of 25° ± 5°
• Overjet > 5 mm.
• Age group: 9 to 15 years with significant growth potential
at the beginning of treatment period.
Exclusion Criteria
• No sex difference taken into account.
• No prior orthodontic treatment and no permanent teeth
extracted before and during myofunctional appliance
treatment.
440
• Patients having no congenital anomalies or facial
asymmetries.
• Patients with no history of any serious trauma or surgery
of orofacial region.
Fitting Twin Blocks
Upper and lower blocks were placed in the patient’s mouth
and patient was motivated to bring the lower jaw forward to
engage the appliance and bite on the blocks. Patients were
followed up after every month. The overjet was measured
with the mandible fully retruded and this measurement was
recorded in the patient’s notes and checked at every visit to
monitor the progress.
Methods
Patients’ details were recorded in a pre-designed proforma
and the following records at the beginning of treatment were
taken for the study:
• Study models in dental stone
• Intra- and extraoral photographs
• Lateral cephalogram with teeth in centric occlusion
• Panoramic radiographs
• CT scan in supine position
Twin block appliance was delivered to the patients in
Group A.
Patients in Group B were not given any appliance and
they were followed every month.
In Group A, CT scans were again taken 6 months after
the insertion of twin block.
In Group B, CT scans were taken 6 months after the
initial records.
A cut off period of 6 months was chosen as it is the appro­
priate time period during which significant changes in airway
can be noticed. All cases were evaluated for any lymphoid
abnormalities prior to treatment. Ethical clearance for taking
radiographs was obtained from the Ethical committee.
COMPUTED TOMOGRAPHY
Each subject had an awake supine CT scan (Light speed
advantage helical CT: 16 multislice scanner with advanced
windows workstation, General Electric Medical Systems,
USA) of the pharyngeal airway at 120 kVp and 220 mA at
a tilt of zero degree. The patient’s head was positioned with
the soft tissue Frankfort plane (tragus of the ear to soft tissue
orbitale) perpendicular to the floor.6 Scans were performed
during tidal breathing.7 The patient was instructed to relax
with the back teeth lightly contacted, and not to swallow
during anyone scan. Contiguous scans were obtained at
5 mm intervals from the Frankfort plane to a level below
the sixth cervical vertebra.8 The resulting image data were
JIOS
Computed Tomographic Evaluation of Three-dimensional Changes in Pharyngeal Airway in Class II Division 1 Patients
stored in digital imaging and communications in medicine
(DICOM) format.
The pharynx is located behind the nasal and oral cavity
and the larynx, extending from the cranial base to the level
of the sixth cervical vertebra and the lower border of the
cricoid cartilage. It can be divided into three parts—naso­
pharynx, oropharynx and hypopharynx. The naso­pharynx
extended from the rostral limit of the airway to the level of
the hard palate, the oropharynx extended from the hard palate
to the rostral tip of the epiglottis, and the hypopharynx
extended to the level of the lower border of the sixth cervical
vertebra.8
Volume Measurement
In this study, for the volumetric analysis of the airway on
CT, the volume of the oropharynx and hypopharynx were
assessed. Measurements were done on the pharyngeal
cross-sections as these sections are parallel to the Frankfort
hori­zontal (FH) plane. To digitally excise the airway, a
distin­ctive high contrast border was defined using threshold
seg­mentation. In the resulting set of masks (highlighted
areas representing the region of interest within each slice),
the areas occupied by air corresponded to a range of CT
units below the ranges for the denser soft tissue and bone,
i.e. from the number of voxels ranging from the minimum
value (–1024 HU) to (–600 HU).9,10 The threshold limits
were modified to an appropriate range that adequately
captured all spaces filled by air within the volume of each
particular CT scan.
Upper and lower landmarks for oropharynx were taken
as posterior most tip of hard palate and tip of epiglottis
respectively. Hypopharynx was taken from the next slice
below epiglottis to the lower border of sixth cervical vertebra
(Fig. 1). Airway was defined at each slice level with the
help of segmentation tool (Fig. 2). Once all the slices were
reconstructed, they were recombined into a single volume for
visualization. After finishing the markings, volume viewer
of the software measures the entire volume of the segmented
region of the oropharynx and hypopharynx (Fig. 3).
Fig. 1: Divisions of pharyngeal airway space
Fig. 2: Demarcation of the airway at different slice levels
Area and Linear Measurements
Cross-sectional measurements including width, length,
and area were calculated in the sectional views, because
they provide precise two-dimensional (2D) visualization
and linear accuracy of 2D measurements. Area and linear
dimensions were measured at the level of lower border of
second cervical vertebra for oropharynx and at the level of
lower border of sixth cervical vertebra for hypopharynx.
Linear measurement in mm was made with the help of ruler
marking tool at the largest anterioposterior (AP) dimension
Fig. 3: Measured volume
and the largest lateral or transverse dimension (Figs 4 and 5).
Area was measured at the same levels with the help of airway
measurement tool.
STATISTICAL ANALYSIS
Mean, standard deviation and standard error were calculated,
with the t-test used to determine the level of significance.
The Journal of Indian Orthodontic Society, October-December 2014;48(4):439-445
441
Parul Temani et al
Table 1: Distribution of study participants
according to age and sex
Age
Male
Female
Total
No.
%
No.
%
No.
%
10
2
8
2
8
4
16
11
3
12
4
16
7
28
12
5
20
0
0
5
20
13
4
16
1
4
5
20
14
3
12
1
4
4
16
Total
17
68
8
32
25
100
Chi-square: 4.944 with 3° of freedom; p: 0.234
Table 2: Comparison of Group A with respect to
oropharyngeal measurement
Fig. 4: Area and linear measurements (oropharynx)
N
Mean
Std. deviation
p-value*
Pre
Post
15
15
12.4267
13.0333
2.29081
2.43711
<0.001
Transverse Pre
Post
15
15
20.9800
22.0067
5.37696
5.31473
<0.001
Area
15
15
258.6220
284.5740
80.94989
86.37219
<0.001
AP
Pre
Post
*Paired t-test
Table 3: Comparison of Group A with respect to
hypopharyngeal measurement
N
Mean
Std.
deviation
p-value*
Pre
Post
15
15
13.3800
13.3067
2.09700
2.13992
0.683
Transverse Pre
Post
15
15
12.9667
14.3333
2.44501
5.31473
<0.001
Area
15
15
175.0380
192.3040
51.42381
54.16400
<0.001
AP
Fig. 5: Area and linear measurements (hypopharynx)
RESULTS
In this study, participation of male patients was more (68%)
as compared to female patients (32%). Majority of the male
patients were 12 years. of age (20%) and female patients
were 11 years of age (28%) (Table 1).
It was seen that the difference in age and sex distribution
among cases and controls was not statistically significant
(p > 0.05). Thus with respect to age and sex, cases and
controls were comparable to each other.
The changes in area, AP, transverse dimensions and
volume measurements of upper and lower pharyngeal
airway in case and control group have been summarized in
(Tables 2 to 10 and Figs 6 to 9).
DISCUSSION
Class II division 1 malocclusion is by far a major and
challenging problem in orthodontics. McNamara11 stated
that 60% of the skeletal Class II malocclusions are as
a consequence of mandibular retrognathism. Over the
442
Pre
Post
*Paired t-test
Table 4: Comparison of Group A with respect to volume
N
Mean
Std.
deviation
p-value*
Upper
pharyngeal
Pre
Post
15
15
7.9430
9.3459
2.44977
2.33271
<0.001
Lower
pharyngeal
Pre
Post
15
15
8.9822
10.5499
2.61625
2.70919
<0.001
Area
Pre
Post
15
15
16.9252
19.8958
4.56617
4.44702
<0.001
*Paired t-test
years, mandibular advancement appliances in the form of
functional appliances are used in the dentofacial orthopedic
treatment of growing children with hypoplastic and/or
retrognathic mandible.12
Through this study, it was intended to evaluate the
change in dimensions of pharyngeal airway space in all the
3D in Class II division 1 patients with retrognathic mandible
JIOS
Computed Tomographic Evaluation of Three-dimensional Changes in Pharyngeal Airway in Class II Division 1 Patients
Table 5: Comparison of Group B with respect to
oropharyngeal measurement
N
Mean
Std.
deviation
p-value*
Table 6: Comparison of Group B with respect to lower
pharyngeal measurement
N
Mean
Std.
deviation
p value*
AP
Pre
Post
10
10
12.7100
12.7400
2.85013
2.89682
0.468
AP
Pre
Post
10
10
12.0300
11.9100
2.28719
2.27764
0.568
Transverse
Pre
Post
10
10
18.2500
17.2500
5.76546
5.81000
0.364
Transverse
Pre
Post
10
10
11.8900
11.9700
1.80398
1.84695
0.223
Area
Pre
Post
10
10
234.7840
223.1370
97.14139
99.97149
0.412
Area
Pre
Post
10
10
145.7710 43.33848
145.0560 42.84172
*Paired t-test
0.781
*Paired t-test
Table 7: Comparison of Group B with respect to volume
N
Mean
Std. deviation
p-value*
Upper
pharyngeal
Pre
Post
10
10
5.6932
5.6865
1.04386
0.92631
0.952
Lower
pharyngeal
Pre
Post
10
10
6.8281
6.8844
2.01784
1.98766
0.299
Area
Pre
Post
10
10
12.5213
12.5709
2.24846
2.32892
0.688
*Paired t-test
Table 8: Comparison of groups with respect to difference in
oropharyngeal measurements
N
Mean
Std. deviation p-value*
Control
Case
10
15
0.0300
0.6067
0.12517
0.32175
<0.001
Transverse Control
Case
10
15
–1
1.0267
3.30555
0.80929
0.031
Area
10
15
–11.6470 42.84725
25.9520 12.73565
AP
Control
Case
0.004
*Paired t-test
Table 9: Comparison of groups with respect to difference in
hypopharyngeal measurements
Group
N
Mean
Control
Case
10
15
–0.1200 0.64083
–0.0733 0.68187
0.864
Upper
Control
pharyngeal Case
10 –0.0067 0.34132
15 1.4029
1.11880
<0.001
Transverse Control
Case
10
15
0.0800
1.3667
<0.001
Lower
Control
pharyngeal Case
10 0.0563
15 1.5677
0.16144
0.75450
<0.001
Area
10
15
–0.7150 7.87994
17.2660 12.50508
0.001
Total
10 0.0496
15 2.9706
0.37867
1.36933
<0.001
AP
Control
Case
Std. deviation
Table 10: Comparison of groups with respect to difference in
volume
0.19322
1.10238
p-value*
*Unpaired t-test
Group
Control
Case
N
Mean
Std. deviation
p-value*
*Unpaired t-test
Fig. 6: Pretreatment volume (oropharynx) in Group A
Fig. 7: Post-treatment volume (oropharynx) in Group A
trea­ted by twin block appliance and to compare them with
untreated controls.
The importance of the third dimension and the use of
CT have been emphasized as early as 1979, highlighting
important limitations of 2D airway studies.13 Previous studies
were conducted taking the same patient as the experimental
subject and the control. Computed Tomography scan was
made at the same time, one without the appliance, serving
as a control and the second was made with the removable
appliance in place.14 In this study, untreated patients were
The Journal of Indian Orthodontic Society, October-December 2014;48(4):439-445
443
Parul Temani et al
Fig. 8: Pretreatment volume (hypopharynx) in Group A
Fig. 9: Post-treatment volume (hypopharynx) in Group A
taken as control and airway was measured before and after
6 months to find out, if growth has any effect on the
pharyngeal airway space.
This also primarily dealt with use of CT for volumetric
ima­ging of patients. Previous 2D studies were limited
to cephalometrics,15,16 whereas previous CT and MRI
studies were limited to cross-sectional area and linear
measure­ments. These studies could not produce volumetric
measurements.This study used pre-released software from
GE healthcare (Advantage Workstation 4.4). In this study,
it was found that it is possible to predict the volume gained,
the amount of cross-sectional area gained and the lateral and
AP linear dimensions gained at various levels of pharynx
after mandibular advancement. In addition, change in shape
of pharyngeal airway can also be visualized.
The purpose of this study was to try to understand the
effect of functional appliances; specifically twin block in
Class II division 1 patients on airway dimensions, including
cross-sectional areas, transverse and AP dimensions and
volume of oropharynx (upper pharynx) and hypopharynx
(lower pharynx) by 3D imaging and their efficacy in
reducing obstructive respiratory problems in future.
It was seen that there was a significant increase
(p < 0.001) in upper pharyngeal, lower pharyngeal and total
airway volume in treated cases after 6 months of twin block
therapy.
These findings match with those observed by Haskell
and Bruce et al14 in their study on the effects of mandibular
advancement device (MAD) on airway dimensions. They
reported an average oropharyngeal volume increase of
approximately 2800 mm3 with MAD therapy.
Previous other authors have also suggested the improve­
ment in volume in the oropharynx with a mandibular
advance­ment device.17-19
Whereas, it was found that there was no significant
change (p > 0.05) in upper pharyngeal, lower pharyngeal and
total airway volume in control cases in which no treatment
was given.
There was a highly significant difference (p < 0.001)
between the two groups regarding changes in upper pharyn­
geal, lower pharyngeal and total airway volume after 6 months.
There was a significant (p < 0.001) increase in area and
transverse dimensions of upper and lower pharyngeal airway
after 6 months with no significant (p > 0.05) change in AP
dimension in lower pharyngeal airway.
No significant (p > 0.05) change in area, transverse and
AP dimensions were observed in control patients. It also
shows a significant difference (p < 0.05) regarding change
in transverse dimensions and area between the two groups.
It also shows a significant difference (p < 0.05) in change
in area between the two groups. But, the change in AP dimen­
sions between cases and controls was not significant (p > 0.05).
These findings are in accordance with previous studies
done on pharyngeal airway assessment. Ogutcen-Toller
et al20 conducted an experiment looking at changes in the
airway in 15 snoring subjects. They made a customized
acrylic block for each subject that advanced each mandible
3 mm less than maximum protrusion. By using CT scans, one
with and one without the mandibular advancement device,
they measured the cross-sectional area of the airway. The
dramatically differing measurement between the appliance
and nonappliance scans, was the minimum cross-sectional
area of the airway, which increased by 60 mm2 or 72%.
Ozbek MM et al15 studied the use of functional-orthopedic
devices in increasing oropharyngeal airway dimensions
in children with Class II skeletal patients and clinically
deficient mandible and concluded that oropharyngeal airway
dimensions increased significantly in treated patients as
compared with controls.
Conley and Legan2 found a significant increase on
the dimensions of the oropharynx by surgically assisted
bimaxillary advancement.
444
JIOS
Computed Tomographic Evaluation of Three-dimensional Changes in Pharyngeal Airway in Class II Division 1 Patients
Several authors measured the total airway volume, the
smallest cross-sectional area, and anterior-posterior and
lateral lengths of the smallest cross-sectional area after
mandibular advancement and observed similar findings.21,22
Thus, it was observed through this study that pharyngeal
airway space was increased in all the dimensions after the use
of twin block appliance and growth has a minimal influence
on airway space in the absence of a functional appliance.
CONCLUSION
• The null hypothesis was rejected.
• There was a statistically significant increase in the
volume of both hypopharynx and oropharynx in patients
treated with twin block.
• Area, transverse and AP dimensions of oropharynx also
increased significantly.
• In hypopharynx, area and transverse dimensions
increased markedly but no increase in AP dimension
was observed.
Hence, it can be concluded that twin block can be a
promising removable functional appliance for improving
pharyngeal airway space in class II division 1 patients with
retrognathic mandible. However, the long-term implications
of this treatment modality needs further consideration and
also a longer period of follow-up is required.
REFERENCES
1. Johal A, Conaghan C. Maxillary morphology in obstructive sleep
apnea: A cephalometric and model study. Angle Orthod 2004;
74(5):648-656.
2. Conley RS, Legan HL. Correction of severe obstructive sleep
apnea with bimaxillary transverse distraction osteogenesis and
maxillomandibular advancement. Am J Orthod Dentofac Orthop
2006;129(2):283-292.
3. Sharabi Y, Dagan Y, Grossman E. Sleep apnea as a risk factor
for hypertension (review). Curr Opin Nephrol Hypertens
2004;13(3):359-364.
4. Lowe AA, Fleetham JA, Ryan F, et al. Effects of a mandibular
repositioning appliance used in the treatment of obstructive
sleep apnea on tongue muscle activity. Prog Clin Biol Res
1990;345:395-404.
5. Clark WJ. The twin block technique: a functional orthopaedic
appliance system. Am J Orthod Dentofac Orthop 1988;93(1):1-18.
6. Lowe AA, Fleetham, Adachi S, Ryan CF. Cephalometric and
computed tomographic predictors of obstructive sleep apnea
severity. 1995;107(6):589-595.
7. Bohlman ME, Haponik EF, Smith PL, Allen RP, Bleecker ER,
Goldman SM. CT demonstration of pharyngeal narrowing in
adult obstructive sleep apnea. AJR 1983;140(3):543-548.
8. Lowe AA, Glonhaku N. Three-dimensional CT reconstructions
of tongue and airway in adult subjects with obstructive sleep
apnea. Am J Orthod Dentofac Orthop 1986;90(5):364-374.
9. Glover GH, Pelc NJ. Nonlinear partial volume artifacts in X-ray
computed tomography. Med Phys 1980;7(3):238-248.
10. Shigeta Y, Ogawa T, et al. Gender and age based differences in
computerized tomographic measurements of the oropharynx.
Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2008;106(4):
563-570.
11. McNamara. Orthodontic and orthopaedic treatment in mixed
dentition. Needham Press Inc; 1995.
12. Graber TM, Rakosi T, Petrovic AG, editors. Dentofacial
Orthopedics with functional appliances. St Louis, CV Mosby
Company, 1985.
13. Aboudara C, Nielsen IB, et al. Comparison of airway space
with conventional lateral headfilms and three-dimensional
reconstruction from cone-beam computed tomography. Am J
Orthod Dentofac Orthop 2009;135(4):468-479.
14. Haskell JA, McCrillis J, Haskell BS, Sheetz JP, Scarfe FC,
Farman AG. Effects of mandibular advancement device (MAD)
on airway dimensions assessed with cone beam computed
tomography. Semin Orthod 2009;15(2):132-158.
15. Ozbek MM, Memikoglu TUT, et al. Oropharyngeal airway
dimensions and functional orthopaedic treatment in skeletal
class II cases. Angle Orthod 1998;68(4):327-336.
16. Gavish A, Vardimon AD, et al. Cephalometric and
polysomnographic analyses of functional magnetic system
therapy in patients with obstructive sleep apnea. Am J Orthod
Dentofac Orthop 2001;120(2):169-177.
17. Fransson AM, Tegelberg A, Johansson A, et al. Influence on the
masticatory system in treatment of obstructive sleep apnea and
snoring with a mandibular protruding device: a 2-year follow-up.
Am J Orthod Dentofac Orthop 2004;126(6):687-693.
18. Bonham PE, Currier GF, Orr WC, et al. The effect of a modified
functional appliance on obstructive sleep apnea. Am J Orthod
Dentofac Orthop 1988;94(5):384-392.
19. Clark GT, Arand D, Chung E, et al. Effect of anterior mandibular
positioning on obstructive sleep apnea. Am Rev Respir Dis 1993;
147(3):624-629.
20. Ogutcen-Toller M, Sarac YS, Cakr-Ozkan N, et al. Computerized
tomographic evaluation of effects of mandibular anterior
repositioning on the upper airway: a pilot study. J Prosthet Dent
2004;92(2):184-189.
21. Ogawa T, Enciso R, Memon A, Mah JK, Clark GT. Evaluation
of 3D airway imaging of obstructive sleep apnea with cone
beam computed tomography. Stud Health Technol Inform
2005;111:365-368.
22. Shi H, Scarfe WC, Farman AG. Upper airway segmentation and
dimensions estimation from cone-beam computed tomography
image data sets. Int J Cars 2006;1(3):177-186.
The Journal of Indian Orthodontic Society, October-December 2014;48(4):439-445
445