INTRODUCTION
Obstructive sleep apnoea hypopnea syndrome (OSAHS) is a clinical
disorder characterized by complete or partial collapse of upper airway
during sleep resulting in cessation or reduction of respiratory function
and abnormal sleep1. Apnoea refers to cessation of
airflow for more than 10 seconds, while hypopnea is the reduced airflow
below 50% for a minimum of 10 seconds or longer with a 3% blood oxygen
saturation2.
A recent systematic review reports the overall prevalence of OSAHS
ranged from 9-38% in the general adult population with a prevalence of
13-33% in adult men and 6-19% in adult women3.
However, many OSAHS patients remain undiagnosed due to lack of identical
clinical symptoms and lack of accurate diagnosis. The risk factors for
OSAHS includes, higher BMI, increased neck circumference, smoking,
alcohol use and family history4. The Apnoea-Hypopnea
index (AHI), which is the total number of apnoea and hypopnea per hour
of sleep is used to diagnosis the severity of OSAHS. AHI of 5-15 per
hour is regarded as mild, between 15-30 as moderate, and greater than 30
as severe OSAHS5.
As a result of disturbed sleep, the OSAHS patients are at greater risk
of motor vehicle accidents, cardiovascular, pulmonary diseases, insulin
resistance and metabolic syndrome6. Also, the OSAHS
patients are affected by adverse health consequences including excessive
day time sleepiness, frequent nocturnal arousal, mood disturbance,
cognitive impairment and decreased quality of life7.
Continuous Positive Airway Pressure (CPAP) remains the gold standard
treatment for OSAHS8. However, poor patient compliance
limits the effectiveness of CPAP9. Currently, oral
appliances are used as an alternative to CPAP, as they help in forward
movement of the tongue and mandible and prevents collapse of upper
airway. Mandibular Advancement Device (OAm) are commonly used oral
appliances and evidence suggests that these devices are highly
acceptable due to its portability, effectiveness and
cost10.
Traditionally 2-dimensional (2D) lateral cephalograms have been used for
the evaluation of the upper airway changes in OSAHS patients. However,
2D imaging results in superimposition of adjacent structures and
provides only a 2D view of the upper airway space, thereby decreasing
the accuracy of diagnosis and prognosis. In order to overcome these
shortcomings of 2D imaging, a 3-dimensional (3D) imaging technique is
recommended11.
Currently 3D imaging techniques, especially the Cone Beam Computed
Tomography (CBCT) has proven its accuracy in easy visualization of
volumetric measurements of complex maxillofacial structures. It aids in
the assessment of cross-sectional areas of the coronal, sagittal and
axial planes of the airway anatomy12. The ability to
assess 3-Dupper airway structures along with the reduction in patient
exposure to radiation compared to convention CT, larger field of vision
(FOV), improved image quality with short scanning
time13 has made CBCT an potential tool for the
assessment of OSAHS patients14.
CBCT has proven its efficacy in the evaluation of upper airway
especially in relation to the hard tissue structures of the
skull14,15. However, a recent systematic review
reported that further research is needed to establish the reliability in
assessment of upper airway volume using CBCT5.
Whereas, the results of several other studies have reported the use of
CBCT in upper airway measurement was fairly
accurate16.
Even though CBCT has been used in the evaluation of upper airway, there
is paucity of literature pertaining to the use of CBCT in assessing
treatment outcomes in OSAHS patients in Asian population, especially in
the Chinese population. Hence, the aim of the study was to evaluate the
upper airway changes before and after the use of OAm of the patients
with mild to moderate OSAHS using CBCT in Chinese population and to
serve as a reference for providing theoretical guidance for the clinical
diagnosis and treatment of OSAHS.
MATERIAL AND METHODS
Study Design and Subjects
This was a single center, prospective study conducted at the ‘[removed
for blind peer review]’. All the consecutive patients with a diagnosis
of OSAHS who were treated with OAm in the Stomatology department from
February 2015 to January 2017 were included in the study.
Patients aged ≥20 years were included in the study if they had
polysomnographic (PSG) diagnosis of mild to moderate OSAHS. Patients
were referred to the Stomatology department, by the Respiratory Medicine
specialist after performing PSG examination and confirming the diagnosis
of mild to moderate OSAHS. The other inclusion criteria included
presence of at least 10 teeth with no mobility in each arch so as to
ensure device retention and those willing to wear the device
continuously for more than 5 hours every night. Patients with history of
craniomaxillofacial trauma and operation, active periodontal disease,
TMD and nocturnal bruxism and those who were mentally unfit were
excluded from the study.
Following a CBCT scan, all the included patients were instructed to wear
OAm (SCHEU, Germany) at night and were monitored till they were adapted
with the device [figure 1]. The mandibular advancement achieved with
OAm was 75% of maximum protrusion.
The study protocol was approved by the institutional review board while
confirming to the standards of the Declaration of Helsinki and its
subsequent revisions. The patients were explained about the study and
informed consent was obtained.
CBCT Analysis
All CBCT examinations were performed using i- CAT 17-19 CBCT (KaVo 3D
eXam). All the patients underwent two CBCT examinations, one before
wearing the OAm and the other while wearing the device.
During imaging procedure, the patients were positioned upright with
Frankfurt plane perpendicular to the floor. The scanning parameters were
as follows: field-of-vision: 16 cm x 13 cm, tube current 5mA, tube
voltage 120kV, scanning time 25 seconds, exposure time 3.6 seconds and
the reconstruction <2 minutes.
To obtain a standardized respiratory phase during CBCT scanning, all the
patients were asked to hold the breath at the end of the expiration
(Muller breathing) and then breathe in. Scanning data were stored in
workstations and converted to DICOM (Digital Imaging and Communications
in Medicine). The CBCT images of patients were imported into InVivo
Dental 5.2 software for three-dimensional airway reconstruction.
Study Outcomes
The study outcomes include assessing the sagittal and coronal diameters
of the hard palate plane, the soft palate lower edge plane and the
epiglottis upper edge plane [figure 2]. We also assessed the volume
of posterior soft palate area, posterior lingual area, posterior
epiglottis area, total airway volume, and the minimum cross-sectional
area (MCA). Furthermore, sleep related indicators such as snoring
frequency, AHI and minimum oxygen saturation (SaO2)
before and during the use of OAm were also assessed.
The measurement work was centralized by the same surveyor for a period
of time. Each measurement item was measured three times and its average
value was taken.
Statistical Analysis
The experimental data were analyzed by SPSS 21.0 software. Paired t test
was used to compare the number of snoring before and after wearing. The
number of snoring did not obey the normal distribution. The results were
expressed by P50 (P25, P75). The difference before and after wearing OAm
was analyzed by rank sum test. P value of <0.05 was
considered statistically significant.
RESULTS
Study subjects
A total of thirty patients were enrolled in this study, comprising of 21
males and 9 females, with a mean age of 49.53±6.62 years, and average
body mass index (BMI) of 24.82 ± 2.13 kg/m2. Minimum
oxygen saturation observed was 0.78 ± 0.08 (Supplementary table 1).
Primary outcomes
Sagittal and coronal diameter of the different planes in OSAHS patients
were analyzed before initiating and during OAm treatment [figure 3].
There was a statistically significant increase
(P <0.001) in the sagittal diameter of the lower margin
of soft palate from 7.01±1.43 to 14.78±1.36 and the upper epiglottis
margin plane from 9.58±0.95 to 13.75±0.77 after wearing OAm. However,
there was no significant increase in the diameter of hard palate plane
after wearing OAm (P >0.05). Similar to the sagittal
diameter, the coronal diameter has statistically significant improvement
in the lower margin of the soft palate from 20.46±1.24 to 28.35±1.85 and
the upper epiglottis margin planes from 19.86±2.06 to 26.72±2.25 with
the use of OAm and no statistically significant improvement
(P >0.05) was observed in the diameter of the hard
palate plane [figure 4] (Supplementary table 2).
The MCA of the posterior soft palate, the posterior lingual, and the
posterior epiglottis area showed an increase after the OAm treatment
with a statistically significant difference (P <0.001)
[figure 5 & 6]. A statistically significant difference
(P <0.001) was also observed with the increase in the
volume of the upper airway segments and total airway volume
(Supplementary table 3) [Supplementary figure 1].
Objective indicators of OSAHS
PSG monitoring indexes including AHI and SaO2 had shown a significant
improvement with reduction in AHI from 20.61±5.19 to 10.86±4.31 and
increase in oxygen saturation from 78±8 to 92±3 after the use of OAm
(P <0.001). A significant reduction in snoring frequency
was also observed after wearing OAm (Supplementary table 4).
DISCUSSION
Since the introduction of CBCT in 1998 17 for dental
and maxillofacial diagnosis and treatment, the popularity of this 3D
imaging technique has increased due to low cost, shorter acquisition
time and less effective radiation dose compared to conventional
CT11.
As CPAP treatment is intolerant and non-compliant in OSAHS
patients18, OAm being non-invasive, cheap and portable
has proven its effectiveness in treating OSAHS with good patient
compliance.
All the patients in our study had an overnight PSG confirmed diagnosis
of OSAHS. In our study, a significant reduction in AHI, improvement in
blood oxygen saturation and also decreased frequency of snoring was
observed after the use of OAm. Our finding are comparable with the RCT’s
conducted to assess the effect of OAm on OSAHS patients on symptoms
associated with OSAHS with a significant improvement in sleep latency
test, Epworth Sleepiness Scale (ESS) scores, both frequency and
intensity of snoring, along with enhanced arterial oxygen saturation,
reduction in AHI, arousal index and Rapid Eye Movements (REM)
sleep19. OAm enhances the upper airway diameter by
traction of soft tissues achieved by mandibular protrusion. Despite the
growing debate on its effectiveness, device design, side-effects and
patients preferences for OAm treatment, the clinical practice guidelines
recommend the applicability of OAm20.
In our study, upper airway CBCT imaging showed, significant increase in
the MCA and volume of each airway segment after using OAm. Similar
results have been reported by Abi-Ramia et al., wherein they observed
the increase in mean airway volume from 7601±26 to 8710±28 as a result
of mandibular protrusion after the use of OAm21.
Various studies have suggested unusual upper airway anatomy as a key
factor for OSAHS16. Other risk factors include, male
gender, older age and upper airway dimensions of
<17mm22.
Controversy exist between the supine and upright position of patients
during CBCT. Due to limited availability of supine position CBCT
assessment units, upright position CBCT is currently used for the 3-D
imaging for OSAHS patients. However, the upright position cannot mimic
the exact morphology of upper airway as in a normal sleeping position.
In our study CBCT was done in upright position for the evaluation of
OSAHS. A study conducted by Wun Eng Hsu et al.23 to
evaluate the change in upper airway measurements comparing lateral
cephalogram in upright position and CBCT in supine position suggested
that, mean anterior-posterior distance in the oropharynx and mandibular
plane to hyoid bone distance can be influenced by the change in the body
posture23.
Other factors which could affect the CBCT findings is the respiratory
phase during the exposure. As the change in airway shape and dimensions
due to variation in the breathing pattern during the exposure has
already been reported24, in our study, all the
patients were instructed to hold the breath at the end of the expiration
(Muller’s breathing) to obtain consistency in all the CBCT scans.
In the present study, we have prospectively assessed the OSAHS patients
before and after OAm, which has enabled us to maintain the relationship
between the age, sex and BMI among the same patient cohort. However,
most of the studies have compared the OSAHS patients with healthy
individuals to assess the efficacy of OAm and failed to match the
patient variables25. Also, many studies were
retrospective in nature23. To the best of our
knowledge, this is the first study in Chinese population that explored
the feasibility of CBCT in OSAHS patients.
Strength and limitations
All the OSAHS patients were confirmed with PSG. We conducted a
prospective study and effectiveness of OAm in OSAHS patients was done in
the same patient cohort using CBCT. And also, we adopted Muller’s
breathing during CBCT exposure to standardize respiratory phase in all
patients for consistent CBCT scans. Smaller sample size could be the
limitations in our study, however the sample size used is in agreement
with other studies.
CONCLUSION
In conclusion, based on our study finding CBCT serves as an effective
tool in the assessment of OSAHA and OAm is beneficial in the treatment
of mild to moderate OSAHS by significantly increasing the sagittal and
coronal diameter of the airway planes along with the changes in the MCA
of each airway segment and total airway volume.