Original article
Effects of bonded rapid palatal expansion
on the transverse dimensions of the maxilla:
A cone-beam computed tomography study
Kimberly F. Christie,a Normand Boucher,b and Chun-Hsi Chungc
Philadelphia, Pa
Introduction: The purpose of this study was to examine the maxillary response on the transverse dimensions
to rapid palatal expansion (RPE) by using cone-beam computed tomography (CBCT). Methods: Twenty-four
children (average age, 9.9 years) who had RPE treatment with a bonded expander were included. Pretreatment orthodontic records (T1) and immediately after expansion (T2) CBCT images were taken for all patients.
For each patient, the width of the nasal cavity at the level of the maxillary first permanent molar and second
deciduous molar (or second permanent premolar), the width of the maxillary basal bone, and the width of
the midpalatal suture at the level of the second deciduous molar (or the second permanent premolar), the
first deciduous molar (or first permanent premolar), and the deciduous canine (or permanent canine) at T1
and T2 were measured. In addition, the amount of tipping for both the maxillary right and left first permanent
molars was measured. Results: From T1 to T2, mean increases in nasal width, related to the mean jackscrew opening (8.19 mm), occurred at the levels of the first permanent molars of 33.23% (2.73 mm, P <0.05)
and the second deciduous molars of 37.32% (3.06 mm, P <0.05). Significant increases in basal bone of the
maxilla were found at all levels (P <0.05), with mean increases of 40.65% (3.33 mm), 44.08% (3.49 mm),
46.73% (3.83 mm), and 46.83% (3.62 mm) of the mean jackscrew opening at the levels of the first permanent
molars, and the second deciduous molars, first deciduous molars, and deciduous canines, respectively. Significant openings in the midpalatal sutures was found at all levels (P <0.05), with mean increases of 52.82%
(4.33 mm), 53.23% (4.36 mm), 54.35% (4.46 mm), and 52.77% (4.33 mm) of the jackscrew opening at the levels of the first permanent molars, and the second deciduous molars, first deciduous molars, and deciduous
canines, respectively. The right first molar tipped buccally an average of 6.2° (P <0.05), and the left first molar
tipped buccally 5.6° (P <0.05). Conclusions: After RPE, significant increases in the transverse dimensions
of the nasal cavity, the maxillary basal bone, and the midpalatal suture opening occurred, with the greatest
increase in the midpalatal suture followed by basal bone and nasal cavity. The midpalatal suture opened in
a parallel fashion. Moreover, significant buccal tipping occurred on both maxillary first molars. (Am J Orthod
Dentofacial Orthop 2010;137:S79-85)
R
apid palatal expansion (RPE) has been widely
used by many orthodontists to increase the maxillary transverse dimension in young patients.
Throughout the years, many types of palatal expanders
and their effects on facial structures have been studied.
Historically, these studies have been conducted by using
Private practice, Media, Pa.
Clinical associate professor, Department of Orthodontics, School of Dental
Medicine, University of Pennsylvania, Philadelphia.
c
Associate professor, Department of Orthodontics, School of Dental Medicine,
University of Pennsylvania, Philadelphia.
The authors report no commercial, financial, or proprietary interest in the products or companies described in this article.
Reprint requests to: Chun-Hsi Chung, Department of Orthodontics, Robert
Schattner Center, University of Pennsylvania School of Dental Medicine, 240 S
40th St, Philadelphia, PA 19104-6030; e-mail, chunc@pobox.upenn.edu.
Submitted, August 2008; revised and accepted, November 2008.
0889-5406/$36.00
Copyright © 2010 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2008.11.024
a
b
traditional lateral and posteroanterior (PA) cephalograms, occlusal films, and dental casts. More recently,
computed tomography (CT) scanning has been used
by investigators to study the effects of RPE on facial
structures.
Haas,1 and Memikoglu and Iseri2 demonstrated increases in the width of the nasal cavity after RPE by using PA cephalograms. Podesser et al3 found an increase
in nasal cavity width at the level of the maxillary first
molars using CT scanning. Garib et al4 reported an increase in the width of the nasal floor after RPE using
CT scanning and found it to be one-third of the amount
of the jackscrew opening of the expander. Using conebeam CT (CBCT), Garrett et al5 found a nasal width increase of 37.2% of the mean hyrax appliance expansion.
Haas6 suggested that the midpalatal suture opens
after RPE in a parallel manner anteroposteriorly and triangularly infero-superiorly, with the apex in the nasal
S79
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American Journal of Orthodontics and Dentofacial Orthopedics
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especially the first premolars compared with the toothborne expander. Kilic et al13 reported that both hyrax
(tooth borne) and acrylic bonded (tooth tissue-borne)
palatal expanders produced significant buccal tipping of
supporting teeth, but the amount of tipping was less in
the tooth tissue-borne appliance.
The purpose of this study was to use CBCT to examine the effects of RPE on the widths of the nasal cavity,
maxillary basal bone, and midpalatal suture, and the inclination of maxillary first molars with a bonded Haastype expander.
Fig 1. Bonded palatal expansion appliance. The occlusal coverage included the deciduous canines (or permanent canines if in the arch) through the first molars.
cavity. However, Wertz and Dreskin7 reported that after RPE the midpalatal suture opening was not parallel, with the widest opening at the anterior nasal spine
(ANS) and diminishing posteriorly. Using CT scanning,
Habersack et al8 found a parallel opening of the midpalatal suture in a young patient after RPE, whereas
an older patient had a pyramidal opening of the suture
with jigsaw-like rupture lines indicating greater suture
interdigitation. Silva Filho et al9 found that the posterior
nasal spine (PNS) opened to a lesser extent than did the
ANS in children in the deciduous and mixed dentition
stages on CT images after RPE. Podesser et al3,10 evaluated the effects of RPE in 9 children using CT imaging.
They reported that the average expansion measured at
the molar crowns was 3.6 mm, whereas the actual midpalatal sutural opening was as low as 1.6 mm. Using
CBCT, Garrett et al5 found more skeletal expansion of
the maxilla in the first premolar region and less in the
first molar region: 55% and 38% of the hyrax appliance
expansion, respectively.
Chung and Font11 examined 20 adolescents expanded with Haas-type expanders. They found that 9.7% of
interpremolar expansion and 4.3% of intermolar expansion were due to buccal crown tipping, but the degree
of tipping was not determined because of the inability
to measure the axial inclination from PA cephalograms.
Haas12 suggested that more bodily movement and less
dental tipping were produced when acrylic palatal coverage was added to support the appliance. Garib et al4
examined the dentoskeletal effects of tooth tissue-borne
and tooth-borne expanders, and concluded that RPE
led to buccal movement of the maxillary posterior teeth
by tipping and bodily translation in both groups. However, the tooth tissue-borne expander produced greater
changes in the axial inclination of the supporting teeth,
S79-85_AAOPRG_3053.indd 80
Material and methods
Twenty-four healthy children (mean age, 9.9 years;
range, 7.8-12.8 years; 14 boys, 10 girls) who required
RPE treatment, from a private orthodontic practice,
were included for the study. The skeletal age of each
patient was determined from a hand-wrist radiograph,
according to the standards of Greulich and Pyle.14 The
mean skeletal age of the patients was 10.3 years (range,
7.5-13 years).
A pretreatment CBCT image (T1) was taken as part
of the initial orthodontic records of all patients. The scans
were obtained with an I-CAT machine (Imaging Sciences
International, Hatfield, Pa). For each patient, a bonded
Haas-type maxillary expander was cemented in place. The
design of the expander was full occlusal and palatal acrylic
coverage. The occlusal coverage included the deciduous
canine (or the permanent canine if in the arch) through
to the first molar (Fig 1). The appliances were all made
by the same orthodontic laboratory. Before cementation,
2 small holes were drilled on either side of the expander
in both anterior and posterior regions. Once the expander
was cemented in place, the distance between the 2 holes
was measured with a digital caliper. Expansion was carried
out as 2 turns per day (0.2 mm per turn) until the required
expansion was complete.
An immediate postexpansion CBCT image (T2)
was taken of each patient on the day the appliance
was tied off when adequate expansion was achieved.
To decrease the amount of radiation, the posttreatment
scan had a smaller window, which decreased the imaging time from 20 to 10 seconds and halved the amount
of radiation. A digital caliper was used to measure the
distance between the 2 acrylic halves after expansion.
The amount of activation of the jackscrew was measured by averaging the difference in distance between
the T1 and T2 images in the anterior and posterior
areas. The mean interval between the T1 and T2 was
66 days (range, 21-152 days), but the mean active expansion period (from beginning of expansion to T2)
was 30 days (range, 21- 42 days). None of the patients
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Volume 137, Number 4, Supplement 1
Fig 2. Reference points 1 and 2 on the frontal view of
the skull, defined as the most superior aspects of the
concavity of the maxillary bone as it joined the zygomatic process.
received any brackets or wires in the maxillary arch
until the CBCT images were taken at T2.
All CBCT images were oriented and standardized
by using Dolphin Imaging (version 10.5, Dolphin Imaging & Management Solutions, Chatsworth, Calif). Each
head was oriented in 3 planes of space for frontal, right
lateral, and left lateral views. The head was oriented
in the frontal view with the floor of the orbits parallel
to the floor. The right lateral view allowed placement of
the head so that the Frankfort horizontal line (upper rim
of external auditory meatus, porion, to the inferior border of the orbital rim, orbitale) was parallel to the floor.15
Both the right and left posterior borders of the ramus
and the angle of the mandible were superimposed to the
best possible fit. The left lateral view was also examined
to ensure that the Frankfort horizontal was parallel to
the floor, and the borders of the ramus and the angle of
the mandible were superimposed as best fit.
The first set of data was calculated from the patient’s
3D skull view. Quantitative evaluation of the parameters was based on the identification and registration of
a series of points. Points 1 and 2 were reference points
that represented the levels of basal bone of the maxilla.
These landmarks were plotted from the frontal view of
the skull on both sides. These landmarks were defined
as the most superior aspect of the concavity of the maxillary bone as it joined the zygomatic process (Fig 2).
From point 1, a horizontal reference line parallel to the
floor was drawn. Points 3, 4, 5, and 6 were marked on the
right lateral view of the 3D skull on the horizontal reference line and above the center of the clinical crown of the
maxillary first molar, second deciduous molar (or second
S79-85_AAOPRG_3053.indd 81
Christie, Boucher, and Chung S81
Fig 3. Right lateral view of the skull showing the plotting
of points 3 through 6 by using a line passing through
point 1 and parallel to the floor as the horizontal reference line. Point 3 was marked on the same horizontal
plane as point 1 directly above the center of the clinical
crown of the maxillary first molar. Point 4 was marked on
the same horizontal plane as point 1 and directly above
the center of the clinical crown of the second deciduous
molar (or second premolar). Point 5 was marked on the
same horizontal reference plane as point 1 and directly
above the center of the clinical crown of the first deciduous molar (or first premolar). Point 6 was marked on the
same horizontal reference plane as point 1 and directly
above the center of the clinical crown of the canine.
premolar if in the arch), first deciduous molar (or first premolar if in the arch), and canine, respectively (Fig 3).
The same method was used for the left lateral view,
but using point 2 to make a horizontal reference line.
Points 7, 8, 9, and 10 were marked on the left lateral
view of the 3D skull on the horizontal reference line of
point 2 and above the center of the clinical crown of the
maxillary first molar, second deciduous molar (or second premolar if in the arch), first deciduous molar (or
first premolar if in the arch), and canine, respectively.
Once points 1 through 10 were plotted on the 3D
skull, the axial section was brought into view to ensure
that all points were plotted on the alveolar bone. The
maxillary base width and the width of the suture opening were calculated from the axial view.
The measurement of the width of the maxillary base
at the level of the maxillary first molars, second deciduous molars, first deciduous molars, and canines were
measured as the distances between points 3 and 7, 4 and
8, 5 and 9, and 6 and 10, respectively (Fig 3).
On the T2 images, once the maxillary base width had
been recorded, the axial slice with points 1 through 10 plotted was used to measure the width of the suture opening.
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S82 Christie, Boucher, and Chung
Point 6
Point 5
Point 4
Point 3
Point 17
Point 18
Point 15
Point 16
Point 13
Point 14
Point 11
Point 12
American Journal of Orthodontics and Dentofacial Orthopedics
April 2010
Point 10
Point 9
Point 8
Point 7
Fig 4. Axial slice showing how the suture opening was
recorded. Points 11 and 12 were plotted on the same
horizontal line as point 3, which represented the basal bone of the maxillary right first molar. Point 11 was
placed on the right border of the suture, and point 12
was placed on the left border of the suture. The distance between points 11 and 12 was recorded as the
suture opening for the maxillary first molar. This process
was repeated for the second deciduous molar (second
premolar), first deciduous molar (first premolar), and canine by using the horizontal reference lines of points 4,
5, and 6, respectively.
The image was adjusted at slice thickness distance 1.0 mm
until the entire suture opening could be seen. Points 11 and
12 were marked at the horizontal level of point 3, which
marked the maxillary right first molar. Point 11 was placed
on the right border of the suture, and point 12 was placed
on the left border of the suture. Point 13 was placed on the
right border of the suture following the horizontal line of
point 4 (right second deciduous molar), and point 14 was
placed on the left border of the suture in the same horizontal plane. Point 15 was placed on the right border of
the suture following the horizontal line of point 5 (right
first deciduous molar), and point 16 was placed on the left
border of the suture in the same horizontal plane. Point 17
was placed on the right border of the suture following the
horizontal line of point 6 (right canine), and point 18 was
placed on the left border of the suture in the same horizontal plane. The distances between points 11 and 12, 13 and
14, 15 and 16, and 17 and 18 were calculated, representing
the distances between the suture opening at the level of the
maxillary first permanent molar, second deciduous molar,
first deciduous molar, and canine, respectively (Fig 4).
The second set of data for the coronal sections was
collected and analyzed according to the guidelines of Podesser et al.10 For the molar slice, the most anterior slice
showing the entire palatal root of the maxillary first molar was chosen. The second deciduous molar (or second
premolar if present), and the first deciduous molar (or first
premolar if present) were chosen as the most anterior slice
on which the crown and root could be seen in their entire
length, regardless of whether the tooth was the deciduous
one or its permanent successor.
S79-85_AAOPRG_3053.indd 82
Fig 5. Points 1 and 2 represented the lateral limits of the
nasal cavity. Point 1 was the lateral point on the lateral
wall of the right nasal cavity with a line perpendicular to
the floor. Point 2 was constructed on the lateral wall of
the left nasal cavity from point 1 by using a line perpendicular to the floor. Points 3 and 4 represented the apices of the palatal roots of the right and left first molars,
respectively. Points 5 and 6 represented the tips of the
mesiobuccal cusps of the maxillary right and left first
molars, respectively.
Quantitative evaluation of the parameters was based
on the identification and registration of a series of points,
as suggested by Podesser et al.10 Points 1 and 2 were the
lateral limits of the nasal cavity: point 1 was the lateral
point on the lateral wall of the right nasal cavity with a line
perpendicular to the floor. Point 2 was constructed on the
lateral wall of the left nasal cavity from point 1 by using a
line perpendicular to the floor. Points 3 and 4 represented
the apices of the palatal roots of the first molars, right and
left, respectively. Points 5 and 6 represented the tips of the
mesiobuccal cusps of the maxillary first molars, right and
left, respectively (Fig 5). The following measurements
were taken on each coronal section.
1.On the first molar: (1) nasal cavity width, the distance between points 1 and 2; (2) right molar inclination, points 5 to 3 to the floor; (3) left molar
inclination, points 6 to 4 to the floor; and (4) intermolar angle, the angle of intersection of lines from
points 5 to 3 and points 6 to 4.
2.On the second deciduous molar (or second pre­molar):
nasal cavity width, the distance between points 1 and 2.
3.On the first deciduous molar (or first premolar): nasal
cavity width, the distance between points 1 and 2.
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Christie, Boucher, and Chung S83
American Journal of Orthodontics and Dentofacial Orthopedics
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Table I. Changes in nasal cavity, basal bone of the maxilla, and midpalatal suture after bonded RPE
n
Mean difference,
T1-T2 (mm)
SD (mm)
First molar
Second deciduous molar
Basal bone of maxilla First molar
Second deciduous molar
First deciduous molar
Canine
Midpalatal suture
First molar
Second deciduous molar
First deciduous molar
Canine
24
24
24
24
24
24
24
24
24
24
2.73
3.06
3.33
3.49
3.83
3.62
4.33
4.36
4.46
4.33
0.92
0.88
1.32
2.02
1.46
2
1.19
1.27
1.11
1.06
Nasal cavity
Statistical analysis
Descriptive statistics including means, standard deviations, and ranges were calculated for the measurements at
T1 and T2. The Student paired t test was used to evaluate whether the changes from T1 to T2 were significantly
different. To test intraexaminer reproducibility, all images
were remeasured by the same examiner (K.F.C.) a minimum of 2 weeks later and compared with the original measurements. The paired t test and the Pearson correlation
coefficients were run to determine whether the measurements at the 2 times showed significant differences. To test
interexaminer reproducibility, 12 patients were selected at
random and measured by an orthodontic resident. The Student paired t test and the Pearson correlation coefficients
were run to determine whether the measurements by the 2
examiners showed significant differences. Significance for
all statistical tests was predetermined at P <0.05.
Results
The intraexaminer reproducibility test showed that
only 2 (nasal cavity width at the second deciduous molar and intermolar angulation) of the 24 measurements
had significant differences (P <0.05). However, in each
case, the Pearson correlation coefficient varied between
0.99 and 0.97, indicating high reproducibility among
measurements, and the magnitudes of the difference
were only 0.26 mm and 0.33°, respectively.
The interexaminer reproducibility test showed that
5 (basal bone width of the maxillary first molar at T1,
right molar angulation at T1, left molar angulations at
T1 and T2, intermolar angulation at T2, and mid­palatal
suture opening at the first deciduous molar [or first
premolar] at T2) of the 24 measurements had statistically significant differences (P <0.05). In each case, the
Pearson correlation coefficient varied between 0.98 and
0.99, indicating high reproducibility among measurements. The differences were 0.84 mm, 0.78 mm, 1.33°,
1.08°, 0.38°, and 0.03 mm, respectively.
S79-85_AAOPRG_3053.indd 83
Range (mm)
0.75–4.35
1–4.65
.5–5.45
.03–6.1
0.2–5.45
0.7–8
1.9–7.25
1.9–8.2
2.15–7.3
2.7–6.2
Mean/mean screw
expansion (%)
P value
33.23
37.32
40.65
44.08
46.73
46.83
52.82
53.23
54.35
52.77
<0.00001
<0.00001
<0.00001
<0.00001
<0.00001
<0.00001
<0.00001
<0.00001
<0.00001
<0.00001
Table I shows the increase in the width of the nasal
cavity at the level of the maxillary first molar and second
deciduous molar (or second premolar) after RPE. The
mean increases were 2.73 mm at the maxillary first molar and 3.06 mm at the maxillary second deciduous molar. Because the actual mean expansion from the bonded
expander was 8.19 mm, the nasal width expansions of
2.73 mm at the first molar and 3.06 mm at the second
deciduous molar were 33.23% and 37.32%, respectively.
The increases in the width of the basal bone of the
maxilla at all levels as a result of RPE are given in Table I.
The mean increases in basal bone width at the levels of the
maxillary first molar, second deciduous molar, first deciduous molar, and canine were 40.65% (3.33 mm), 44.08%
(3.49 mm), 46.73% (3.83 mm), and 46.83% (3.62 mm) of
the amount of jackscrew opening (8.19 mm), respectively.
Table I also shows the increases in width of the midpalatal suture at all levels as a result of RPE. The mean
increases at the levels of the maxillary first molar, second deciduous molar, first deciduous molar, and canine
were 52.82% (4.33 mm), 53.23% (4.36 mm), 54.35%
(4.46 mm), and 52.77% (4.33 mm) of the amount of
jackscrew opening (8.19 mm), respectively. There was
no significant difference for suture opening at each level
(P >0.05). This demonstrated the parallel effect of the
suture opening across all levels.
A statistically significant increase (11.82° ± 3.07°)
was seen in the intermolar angle after expansion, with
6.22° ± 2.5° of buccal tipping on the right first molar
and 5.60° ± 2.6° of buccal tipping on the left first molar (Table II).
Discussion
The objective of this study was to evaluate the effects of bonded RPE on nasal width, maxillary basal
bone, midpalatal suture opening, and first molar tipping
with CBCT. The mean time from the T1 to the T2 CT
images was 66 days (range, 21-152 days), but the mean
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Table II. Tipping effects on maxillary first molars after bonded RPE
n
Right molar angulation
Left molar angulation
Intermolar angle
24
24
24
Mean difference, T1-T2
(°)
6.22
5.6
11.82
active expansion period (from beginning of expansion
to T2) was only 30 days (range, 21-42 days). The reason
for the long interval between T1 and T2 was that some
patients did not start treatment until 3 or 4 months after
the T1 images (initial records) were taken. Thus, some
skeletal changes from T1 to T2 in this study could be
attributed to growth during this waiting period, although
the amount was estimated to be small.16-18
Our data clearly showed significant increases in nasal cavity width at the levels of the maxillary first molars
(mean, 2.73 mm; 33.23% of jackscrew expansion) and
the second deciduous molars (mean, 3.06 mm; 37.32% of
jackscrew expansion) after RPE. We did not measure the
width of the nasal cavity at the level of the first deciduous molar and canine because of distortion of the coronal
image, since the section was taken more anteriorly. Our
results agreed with those of Garib et al,4 who reported that
the transverse increase at the level of the nasal floor corresponded to one-third of the amount of jackscrew expansion after RPE. We measured the lateral limits of the nasal
cavity, which was at a higher level than the nasal floor as
described by Garib et al.4 This finding might support the
theory that maxillary expansion increases air flow and
improves nasal breathing.1,6,11,12,19 However, additional research is warranted in terms of how the volume of the nasal
airway is affected by RPE.
We found that, as a result of RPE, the midpalatal suture
opened in a parallel fashion. This was different from the
results of Wertz and Dreskin,7 who used occlusal films and
described the opening to be the widest at ANS and diminished posteriorly after RPE in subjects aged 8 to 29 years.
This was also different from the CT study by Silva Filho
et al,9 who reported that the opening of the midpalatal suture in the area of the PNS occurred to a lesser extent than
at ANS after RPE with a Haas-type expander in subjects
from 5.2 to 10.5 years of age. Our results compare with
those of Habersack et al,8 who used CT imaging to demonstrate complete parallel opening of the midpalatal suture in
a child in the mixed dentition (skeletal age, 10 years) after
RPE with an acrylic splint expansion appliance. Perhaps
the parallel nature of the midpalatal suture opening seen
at the levels of canine through the maxillary first molar in
this study was due to a combination of the rigid acrylic
bonded expander and the younger skeletal age (mean, 10.3
years) of our patients. In our study, we measured the suture
S79-85_AAOPRG_3053.indd 84
SD (°)
Range (°)
P value
2.5
2.6
3.07
2.2–11.7
0.95–10.65
3.4–17.05
<0.00001
<0.00001
<0.00001
opening at the level of the teeth, whereas in previous studies, such as that of Wertz and Dreskin,7 the measurements
were at ANS and PNS.
Because of the previous limitations in technology,
the amount of basal bone change after RPE was never
clearly understood at the levels of the maxillary first
molar, second deciduous molar (second premolar if
present), first deciduous molar (first premolar if present), and canine. Traditionally, the width of the maxillary basal bone was measured on a PA cephalogram.
The radiographic landmark of jugale was plotted on PA
cephalograms and defined as the intersection of the outline of the tuberosity of the maxilla and the zygomatic
buttress of both sides.16 The distance between right and
left jugales was used to estimate the transverse dimension of the maxilla. However, jugale can be hard to
identify because of the superimposition of many structures on a PA cephalogram. There was also no way to
measure the width of the basal bone of the maxilla at
any other level because of the 2-dimensional limitations
of traditional PA cephalograms. CBCT allowed us to
clearly visualize and quantify the changes throughout
the basal bone of the maxilla from palatal expansion.
Our data showed that all levels of the maxillary basal
bone examined were significantly increased (P <0.05)
after RPE.
Our data also showed a significant buccal crown tipping effect on the first molars from RPE. Clinically, this
information is important, since it could help clinicians
to determine the appropriate amount of overexpansion
from RPE. The mean amounts of buccal tipping were
6.22° ± 2.5° for the right molar and 5.60° ± 2.6° for
the left molar; these amounts are similar to those found
by Ciambotti et al19 of 6.08° ± 6.25° of buccal crown
tipping of the maxillary molars after RPE using a toothborne appliance on children and measured on dental
models. Oliveira et al20 examined the various effects of
a tissue-borne appliance (Haas) and a tooth-borne appliance (hyrax) on children. The Haas group had more orthopedic movement and less dentoalveolar tipping than
did the hyrax group. Recently, Kilic et al13 compared
the dentoalveolar inclination of patients treated with either a hyrax expander (mean skeletal age, 13.9 years)
or an acrylic bonded expander similar to the type used
in our study (mean skeletal age, 13.6 years) using study
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models. They determined that both types of expander
produced significant tipping, but the dentoalveolar inclination was greater in the hyrax group. They reported
tipping amounts with means of 7.01° for the right molar and 6.79° for the left molar with a mean jackscrew
opening of 7.31 mm in the acrylic bonded group. These
results were slightly higher than our findings.
We found that, after RPE, at the level of the first molar, the mean nasal cavity width increase was 2.73 mm,
the mean basal bone width increase was 3.33 mm,
and the mean suture opening was 4.33 mm. This demonstrated that the expansion had a triangular pattern,
with the greatest increase in the suture, followed by basal bone width and the nasal cavity width. Previous studies reported similar patterns in the expansion of skeletal
structures after RPE.2,6,11,21,22
Conclusions
The effects of bonded RPE (mean jackscrew opening, 8.19 mm) on the transverse dimensions of the maxilla in children, examined by CBCT, are as follows.
1.There were significant nasal width increases (P
<0.05) at the levels of the maxillary first molar and
second deciduous molar (second premolar if present) with means of 33.23% (2.73 mm) and 37.32%
(3.06 mm) of the jackscrew opening, respectively.
2.There were significant increases in the width of the
basal bone (P <0.05) at the levels of the first molar,
second deciduous molar (second premolar if present), first deciduous molar (first premolar if present), and canine with means of 40.65% (3.33 mm),
44.08% (3.49 mm), 46.73% (3.83 mm), and 46.83%
(3.62 mm) of the jackscrew opening, respectively.
3.There were significant midpalatal suture openings (P <0.05) at the levels of the first molar, second deciduous molar (second premolar if present),
first deciduous molar (first premolar if present),
and canine with means of 52.82% (4.33 mm),
53.23% (4.36 mm), 54.35% (4.46 mm), and 52.77%
(4.33 mm) of the jackscrew opening, respectively.
The midpalatal suture opening was parallel.
4.There was significant buccal tipping of the first molars (P <0.05), with mean increases of 6.2° for the
right molar and 5.6° for the left molar.
We thank Solomon Katz and Sonal Dave for their help.
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