Effects of rapid palatal expansion on the sagittal and vertical dimensions of the maxilla a study on cephalograms derived from cone-beam computed tomography
The purpose of this study was to use cone-beam computed tomography imaging to examine the skeletal and dental changes in the sagittal and vertical dimensions after rapid palatal expansion.
2011 clinical outcome of dental implants placed with high insertion torques
Similar a Effects of rapid palatal expansion on the sagittal and vertical dimensions of the maxilla a study on cephalograms derived from cone-beam computed tomography
Similar a Effects of rapid palatal expansion on the sagittal and vertical dimensions of the maxilla a study on cephalograms derived from cone-beam computed tomography (20)
Effects of rapid palatal expansion on the sagittal and vertical dimensions of the maxilla a study on cephalograms derived from cone-beam computed tomography
1. Effects of rapid palatal expansion on the sagittal
and vertical dimensions of the maxilla: A study
on cephalograms derived from cone-beam
computed tomography
Miriam Habeeb,a
Normand Boucher,b
and Chun-Hsi Chungc
Nashville, Tenn, and Philadelphia, Pa
Introduction: The purpose of this study was to use cone-beam computed tomography imaging to examine
the skeletal and dental changes in the sagittal and vertical dimensions after rapid palatal expansion.
Methods: Twenty-eight healthy children (mean age, 9.9 years; range, 7.8-12.8 years; 17 boys, 11 girls) who
required rapid palatal expansion treatment were included. For each patient, a bonded Haas-type expander
with full occlusal and palatal acrylic coverage was cemented in place. Cone-beam computed tomography
images were obtained as part of the pretreatment orthodontic records and at the completion of rapid palatal
expansion for all patients. The mean interval between pretreatment and completion of rapid palatal expansion
was 52 days (range, 19-96 days). The average skeletal age of the patients, determined from hand-wrist films
also obtained before treatment, was 10.1 years. The mean expansion of the expander was 8.0 mm (range,
5.9-9.6 mm). Each cone-beam computed tomography image was compressed from the outer portion of the
right side of the patient's head to the center of the left central incisor into a 2-dimensional synthesized
cephalogram, which was then traced and measured. Results: The results showed that from pretreatment to
completion of rapid palatal expansion, SNA, FH-NA, and A-Nperp increased by means of 1.04
, 0.92
, and
0.87 mm, respectively (P 0.05). In addition, 1/-NA, 1/-SN, 1/-NA, 1/-Nperp, and 1/-PP showed mean
decreases of 3.74
, 2.53
, 1.17 mm, 0.49 mm, and 2.69
, respectively (P 0.05). Both ANS and PNS moved
significantly downward (ANS, 2.05 mm; PNS, 1.16 mm). Conclusions: There was forward movement of the
maxilla as a result of rapid palatal expansion treatment. Bonded rapid palatal expansion treatment resulted in
downward displacement of the maxilla with a greater displacement of ANS than PNS and posterior movement
of the maxillary central incisors. (Am J Orthod Dentofacial Orthop 2013;144:398-403)
T
he treatment to open the midpalatal suture with
rapid palatal expansion (RPE) has been widely
used in orthodontics to orthopedically increase
the transverse dimension of the maxilla in children.1-3
Because the palatal suture is often fused in adults, RPE
becomes less effective and may produce more
dentoalveolar changes rather than the desired
transverse craniofacial skeletal changes.4-6
Several studies have reported on the sagittal and
vertical skeletal and dental effects of RPE on the maxilla,
but their results were inconclusive. Haas1
and Davis and
Kronman7
reported that the maxilla moved downward
and forward with the use of Haas-type RPE. However,
Silva Filho et al8
found that the maxilla did not change
sagittally but moved downward after RPE, displaying
downward and backward rotation in the palatal plane.
Wertz9
found that the maxillary incisors were retroclined
after RPE (1/-SN decreased), whereas Sandlkc¸loglu and
Hazar10
reported that the maxillary incisors became
more proclined (1/-SN increased). Chung and Font11
found that the maxilla was displaced downward and for-
ward after RPE; however, the amount of forward move-
ment was small and might not be clinically significant.
Additionally, they found that the palatal plane was
a
Private practice, Nashville, Tenn.
b
Clinical associate professor, Department of Orthodontics, School of Dental
Medicine, University of Pennsylvania, Philadelphia.
c
Chairman and associate professor, Department of Orthodontics, School of
Dental Medicine, University of Pennsylvania, Philadelphia.
All authors have completed and submitted the ICMJE Form for Disclosure
of Potential Conflicts of Interest, and none were reported.
Reprint requests to: Chun-Hsi Chung, University of Pennsylvania School of
Dental Medicine, Department of Orthodontics, Robert Schattner Center, 240 S
40th St, Philadelphia, PA 19104; e-mail, chunc@dental.upenn.edu.
Submitted, December 2012; revised and accepted, April 2013.
0889-5406/$36.00
Copyright Ó 2013 by the American Association of Orthodontists.
http://dx.doi.org/10.1016/j.ajodo.2013.04.012
398
ORIGINAL ARTICLE
2. displaced downward in almost a parallel manner. Akkaya
et al12
reported that the maxilla moved forward, and the
mandible moved backward.
Previous studies regarding the effects of RPE in
the sagittal and vertical dimensions focused on
conventional lateral cephalograms, which are limited
by factors such as magnification, superimposition of
structures, and distortion caused by head position.
Cone-beam computed tomography (CBCT) technology
offers a reproducible 3-dimensional image without the
limiting factors of magnification and distortion.13
Kumar et al14
compared cephalometric measurements
from CBCT synthesized lateral cephalograms using
orthogonal and perspective projections with those
from conventional cephalograms and dry skulls. They
found that orthogonal CBCT synthesized cephalograms
provided measurements closest to the actual skull
measurements and were significantly more precise
than the other image modalities. These results were
consistent with those of Lamichane et al,15
who found
significant accuracy in orthogonal projections that
were more representative of actual anatomy than were
perspective projections. Thus, this technology inevitably
results in more accurate information to examine the
effects of RPE in the sagittal and vertical dimensions.
The purpose of this study was to examine the vertical
and sagittal dental and skeletal effects of bonded RPE
using orthogonal lateral cephalograms synthesized
from CBCT.
MATERIAL AND METHODS
This study was approved by the institutional review
board of the University of Pennsylvania. Twenty-eight
healthy children (mean age, 9.9 years; range, 7.8-12.8
years; 17 boys, 11 girls) who required RPE treatment
at a private orthodontic practice were included in this
study. The need for RPE was determined by the treating
orthodontist (N.B.), and the inclusion criterion was that
the patient had a maxillary transverse deficiency diag-
nosed from the Andrews' 6 elements transverse anal-
ysis.16
No patient had either craniofacial syndromes or
previous orthodontic treatment.
A pretreatment CBCT image (T1) was taken as a
standard initial record for all patients. The scans were
obtained with an i-CAT machine (Imaging Sciences
International, Hatfield, Pa). The field of view was
22 3 16 cm, including the whole head, to provide a
complete diagnosis for the patient; the voxel size
was 0.4 mm; and the amount of radiation was 68 mSv.
The skeletal age of each patient was determined
from a hand-wrist film also obtained at T1
according to the standards of Greulich and Pyle.17
The mean skeletal age of the patients was 10.1 years
(range, 7.3-14.8 years). For each patient, a bonded
maxillary expander with full occlusal and palatal acrylic
coverage was cemented in place, with coverage from the
deciduous or permanent canine to the first molar. The
rationale for this appliance was to have some control
of the buccal tipping and eruption of the posterior teeth.
The same orthodontic laboratory fabricated all
expanders.
The expansion protocol consisted of 2 turns per day
(0.25 mm per turn) until the required expansion
(including 2 mm of overexpansion) was achieved; this
was determined according to Andrews' 6 elements
transverse analysis.16
The amount of expansion was
determined by measuring the distance between the
2 acrylic halves of the expander before and after
expansion with a digital caliper. Then a postexpansion
CBCT image (T2) was taken of each patient with half
the amount of radiation (34 mSv) of the T1 image by
reducing the imaging time from 20 to 10 seconds.
The voxel size was 0.4 mm, and the field of view was
13 3 16 cm to evaluate the changes to the maxilla
from RPE. The mean interval between T1 and T2 was
51.9 days (range, 19-96 days). All patients did not
have brackets or wires placed in the maxillary arch until
after the T2 records were taken.
All CBCT images were oriented and standardized
using Dolphin Imaging software (version 10.5; Dolphin
Imaging Management Solutions, Chatsworth, Calif).
Each head was oriented by the frontal and lateral views.
In the frontal view, the head was oriented with the floor
of the orbits parallel to the floor; in the right lateral view,
the Frankfort horizontal line was parallel to the floor
(Fig 1).
Each image was compressed from the outer portion of
the right side of the patient's head to the center of the left
central incisor into a 2-dimensional orthogonal projec-
tion (Fig 2). Then the CBCT-synthesized cephalograms
were built using orthogonal projections. The definition
of the landmarks corresponded to those given by Riolo
et al.18
Each image was traced by 1 examiner (M.H.)
and verified by an orthodontic professor (C.-H.C.). Both
examiners agreed on all cephalometric landmarks. To
minimize tracing errors, the lateral cephalograms at T1
and T2 were superimposed on the cranial base to match
the landmarks of porion and orbitale. The following mea-
surements were made (Fig 3).
1. Sagittal skeletal: SNA angle (in degrees), Frankfort
horizontal plane to NA angle (FH-NA, in degrees),
and A-N perpendicular (A-Nperp, in millimeters).
Increases in angular measurements were considered
positive, and decreases were considered negative.
Habeeb, Boucher, and Chung 399
American Journal of Orthodontics and Dentofacial Orthopedics September 2013 Vol 144 Issue 3
3. For the linear measurements, forward displacement
of the skeletal structure from T1 to T2 was given a
positive value, whereas backward displacement
was considered negative.
2. Sagittal dental: 1/NA (in degrees and millimeters),
1/SN (in degrees), 1/-Nperp (in millimeters),
and 1/-PP (in degrees). Increases in angular
measurements from T1 to T2, indicating maxillary
incisor proclination, were considered positive;
decreases in angular measurements, indicating
incisor retroclination, were considered negative.
For the linear measurements, forward movement
of the maxillary incisor was considered positive,
and posterior movement was considered negative.
3. Vertical: anterior nasal spine (ANS) difference
(in millimeters) and posterior nasal spine (PNS)
difference (in millimeters). The values of these
differences were calculated by superimposing the
lateral cephalograms (T1 and T2) on the anterior
cranial base and measuring the distance between
the positions of ANS and PNS at T1 and their
positions at T2. The difference was considered
positive if ANS and PNS moved downward from
T1 to T2, and negative if ANS and PNS moved
upward from T1 to T2.
All tracings, measurements, and data were completed
by the same examiner (M.H.) and verified by the same
orthodontic professor (C.-H.C.). All data were tested
for reliability and reproducibility by conducting intra-
examiner trials. To test intraexaminer reproducibility,
14 patient records were randomly selected, reoriented,
retraced, and remeasured by the same examiner and
compared with the original measurements. A paired
Fig 1. A, Frontal view: the head was oriented with the floor of the orbits parallel to the floor;
B, right lateral view: Frankfort horizontal was parallel to the floor.
Fig 2. Created 2-dimensional orthogonal image from the
outer portion of the right side of the patient's head to the
center of the left central incisor.
400 Habeeb, Boucher, and Chung
September 2013 Vol 144 Issue 3 American Journal of Orthodontics and Dentofacial Orthopedics
4. Student t test was used to determine whether there was a
significant difference between the 2 measurements
taken at the 2 times.
Descriptive statistics including means, standard
deviations, and ranges were calculated for the measure-
ments at T1 and T2. A 2-tailed Student t test was used to
determine whether there was a difference in the
measurements from T1 to T2. The significance was
predetermined at P 0.05.
RESULTS
The intraexaminer reproducibility test showed
that only 1 (1/-NA [mm]) of the 10 measurements
had significant differences (P 0.05) between the orig-
inal data set and the data set that was remeasured.
However, the Pearson correlation coefficient for all
measurements varied between 0.99 and 0.97. There-
fore, the measurements in this study were highly repro-
ducible and reliable.
The mean amount of expansion measured from the
expander was 8.0 6 0.8 mm (range, 5.9-9.6 mm).
Table I details the sagittal skeletal effects from the
data. SNA, FH-NA, and A-Nperp increased by means of
1.04
, 0.92
, and 0.87 mm, respectively, after RPE.
All 3 measurements were statistically significant at
P 0.05.
The sagittal dental effects are listed in Table II;
1/-NA, 1/-SN, 1/-NA, 1/-Nperp, and 1/-PP showed
mean decreases of 3.74
, 2.53
, 1.17 mm, 0.49 mm,
and 2.69
, respectively. All sagittal dental changes
were statistically significant at P 0.05.
The vertical skeletal effects are listed in Table III. Both
ANS and PNS moved downward (ANS, 2.05 mm; PNS,
1.16 mm). When we compared ANS with PNS movement,
there was greater downward movement at ANS than at
PNS by 10.89 mm from T1 to T2; this was statistically
significant (P 0.05).
DISCUSSION
The objective of this study was to evaluate the
skeletal and dental effects of bonded RPE in the sagittal
and vertical planes using CBCT. The mean interval
between T1 and T2 was 52 days (range, 19-96 days).
The reason for the wide range of values from T1 to T2
was that some patients did not start treatment until 2
months after the T1 records were taken. Thus, some of
the skeletal change from T1 to T2 in this study could
be attributed to growth during this waiting period,
although the amount was estimated to be small.
In our study, different amounts of radiation were
used at T1 and T2. At T1, the whole head was included
in the CBCT image to provide a complete diagnosis
(including any pathologic findings) for the patient, so a
larger field of view was used (22 3 16 cm) with 68 mSv
of radiation of. At T2, the CBCT image was taken to eva-
luate the changes to the maxilla from RPE; therefore,
the field of view was reduced to 13 3 16 cm with half
of the imaging time and half of the radiation (34 mSv).
Our data clearly showed forward displacement of the
maxilla in the sagittal plane that was statistically
significant. This result concurs with previous finding
by Haas,1
Davis and Kronman,7
Chung and Font,11
Akkaya et al,12
and Basciftci and Karaman.19
On the
other hand, our findings disagreed with reports by Sarver
and Johnston,20
Asanza et al,21
and Silva Filho et al.8
Additionally, Chung et al22
found that the maxilla
displaced forward to a statistically significant amount
Fig 3. Landmarks and reference lines for the linear and
angular measurements.
Table I. Sagittal skeletal effects of RPE from T1 to T2
n
Mean
difference
from T1 to T2 SD Range P value
SNA (
) 28 11.04 1.1 À1.2 to 15.1 0.05*
FH-NA (
) 28 10.92 1.41 À1.7 to 14.6 0.05*
A-Nperp
(mm)
28 10.87 1.97 À0.9 to 14.2 0.05*
Increases in angular measurements were considered positive,
and decreases were negative. For linear measurements, forward
displacement of the skeletal structure was considered positive, and
backward displacement was negative.
*Statistically significant.
Habeeb, Boucher, and Chung 401
American Journal of Orthodontics and Dentofacial Orthopedics September 2013 Vol 144 Issue 3
5. immediately after surgically assisted RPE in adults;
however, the movement was minimal (10.6
). All of
these studies used conventional lateral cephalograms,
but we used lateral cephalograms synthesized from
CBCT; this eliminated the magnification factor.
Although our data showed that forward displacement
of the maxilla after RPE is statistically significant, it
might not be clinically significant because the
amount is small. Thus, for the treatment of Class III
malocclusions in children, one should not expect
spontaneous correction from RPE; other orthopedic
appliances (such as a protraction facemask) might be
needed. From a different perspective, McNamara
et al23
found that the use of a bonded RPE results in sig-
nificant sagittal Class II correction in the early mixed
dentition from mandibular forward displacement. How-
ever, Volk et al24
concluded that maxillary expansion
might help Class II correction in some patients but is un-
predictable in determining which patients would benefit
from maxillary expansion. They found improvement in
Class II malocclusions about 50% of the time, but in
some cases the Class II malocclusion became worse.
They recommended a similar study with a larger sample
size to definitely resolve this issue. We did not examine
the mandibular changes after RPE in this study, but
our data showed, from the maxillary point of view,
that the maxilla moved forward after RPE, and this did
not help Class II correction.
Our data regarding the sagittal dental effects showed
that the maxillary incisors were more retroclined after
RPE. These results agreed with those of Wertz,9
Chung
and Font,11
and Sarver and Johnston.20
On the contrary,
Sandlkc¸loglu and Hazar10
reported that maxillary
incisors became more proclined (increase in 1/-SN) after
RPE. Basciftci and Karaman19
found a significant
increase in overjet that was attributed to a combination
of anterior movement of the maxilla and posterior
rotation of the mandible. They found that the maxillary
incisors were more proclined after RPE, but not to the
extent that it was statistically significant.
Our results showed that the maxillary incisors were
more retracted after RPE; this outcome might be
attributed to the pulling of the transseptal periodontal
fibers, when the space created between the central
incisors by the RPE might spontaneously close or
decrease. When retroclination of the incisors is not
desired, such as for Class III patients, the practitioner
should consider extending the acrylic of the expander
to the palatal aspect of the incisors or placing brackets
and stopped archwires immediately after expansion to
prevent the maxillary incisors from moving posteriorly.
The vertical effects in this study clearly demonstrated
downward displacement of the palatal plane after
bonded RPE treatment, with ANS displaced downward
more than PNS after treatment. This finding agrees
with the findings of Chung and Font,11
Chung et al,22
and Silva Fihlo et al.8
The data from our study
disagreed with those of Sarver and Johnston,20
who
found no downward movement of the maxilla after
bonded RPE, and Basciftci and Karaman,19
who reported
that PNS moved downward more than ANS after
modified acrylic bonded RPE. However, when used in
conjunction with a vertical chincup, the vertical position
of the maxilla did not change. Asanza et al21
found an
element of vertical control with bonded expanders over
banded with less inferior displacement at PNS in the
bonded group. On the other hand, Reed et al25
found
that the palatal plane dropped inferiorly by the same
amount in both the banded and bonded groups.
In our sample, most subjects were between 7.8 and
11.0 years of age (21 of 28); only 3 were older than
12.0 years. Further study is warranted to understand
whether older children of either sex, ages 12 to 15 years,
would have similar skeletal and dental effects from RPE
treatment as the younger children in this study.
CBCT imaging was used in our study because of its
high degree of accuracy for landmark identification and
elimination of distortion associated with magnification
and overlapping structures. To date, no published and
Table II. Sagittal dental effects of RPE from T1 to T2
n
Mean
difference
from T1 to T2 SD Range P value
1/-NA (
) 28 À3.74 2.42 À8.0 to 13.9 0.05*
1/-SN (
) 28 À2.53 2.33 À6.7 to 14.8 0.05*
1/-NA (mm) 28 À1.17 1.11 À0.9 to 0 0.05*
1/-Nperp
(mm)
28 À0.49 0.89 À3.1 to 11.2 0.05*
1/PP (
) 28 À2.69 2.21 À6.9 to 13.9 0.05*
Increases (1) in angular measurements indicate incisor proclination;
decreases (–) indicate incisor retroclination. For the linear
measurements, forward movement of incisor was considered
positive, and posterior movement was considered negative.
*Statistically significant.
Table III. Vertical effects of RPE
n
Mean
difference
from T1 to T2 SD Range P value
ANS (mm) 28 12.05 0.73 10.5 to 13.5 0.05*
PNS (mm) 28 11.16 0.58 10.5 to 13.0 0.05*
It was considered positive if ANS and PNS moved downward from T1
to T2.
*Statistically significant.
402 Habeeb, Boucher, and Chung
September 2013 Vol 144 Issue 3 American Journal of Orthodontics and Dentofacial Orthopedics
6. accepted 3-dimensional imaging norms allow for the
replacement of 2-dimensional cephalometic data. Never-
theless, using compressed orthogonal projections allows
for use of the technology to provide precise landmark
identification to acquire accurate cephalometric data.
Orthogonal projections are created by parallel rays and
generated with no magnification. This is different from
the perspective projection that has a center of projection
(focus) at a finite distance from the projection plane,
which has inherent magnification.14
It was decided to
compress the image from the outer portion of the right
side of the patient's head to the center of the left central
incisor to avoid overlapping structures and to ensure that
all necessary midline landmarks were incorporated into
the single 2-dimensional image.
Although the accuracy of CBCT imaging has been
well documented, tracing error is realistically inevitable.
Despite the clarity of the images obtained in our study,
ANS and PNS remained more difficult to determine.
Additionally, the maxillary molars were not clear in
many images, mainly because the acrylic coverage of
the expander obscured the teeth. Therefore, the
measurements of maxillary molars were not used in
our study. The mandibular response to bonded RPE
treatment was not considered because of the acrylic
coverage over the occlusal surface.
CONCLUSIONS
The effects of RPE on children were examined using
lateral cephalograms derived from CBCT images before
and after RPE treatment, and the conclusions are as
follows.
1. There was a slight forward movement of the maxilla
induced by RPE (P 0.05). However, the amount
was small and might not be clinically significant.
2. Bonded RPE resulted in posterior movement of the
maxillary central incisors: they became more
retroclined (P 0.05).
3. There was downward displacement of the maxilla
after RPE (P 0.05) with a greater displacement
at ANS than at PNS (P 0.05).
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