Download Factors affecting buccal bone changes of maxillary posterior teeth

ORIGINAL ARTICLE
Factors affecting buccal bone changes of
maxillary posterior teeth after rapid
maxillary expansion
Kitichai Rungcharassaeng,a Joseph M. Caruso,b Joseph Y. K. Kan,c Jay Kim,d and Guy Taylore
Loma Linda, Calif
Introduction: The purpose of this study was to use cone-beam computed tomography (CBCT) images to
determine the factors that might affect buccal bone changes of maxillary posterior teeth after rapid maxillary
expansion (RME). Methods: Thirty consecutive patients (17 boys, 13 girls; mean age, 13.8 ⫾ 1.7 years) who
required RME as part of their orthodontic treatment and had the pre-RME (T1) and post-RME (T2) CBCT
images available were included in the study. The T1 and T2 measurements of interdental distance, interdental
angle (IA), buccal bone thickness (BBT), and buccal marginal bone levels (BMBL) of the first premolar (P1),
the second premolar (P2), and the first molar (M1) were compared with the Friedman and the Wilcoxon
signed rank tests. To determine which variables were associated with the changes in IA, BBT, and BMBL, the
Spearman rank correlation analysis was performed (␣ ⫽ .05). Results and Conclusions: The results suggest
that buccal crown tipping, and reduction of BBT and BMBL of the maxillary posterior teeth are the expected
immediate effects of RME. There were no significant differences in dental expansion among P1, P2, and M1
(P ⬎.05). P2 had clinically more buccal crown tipping (P ⫽ .116) but statistically less reduction in BBT and
BMBL (P ⬍.0001 and P ⫽ .001) than P1 and M1. Buccal bone changes and dental tipping on P2 were not
affected by any other variables. Factors that showed significant correlation to buccal bone changes and
dental tipping on P1 and M1 were age, appliance expansion, initial buccal bone thickness, and differential
expansion (P ⬍.05), but rate of expansion and retention time had no significant association (P ⬎.05). (Am J
Orthod Dentofacial Orthop 2007;132:428.e1-428.e8)
R
apid maxillary expansion (RME) is a commonly
used method to correct maxillary constriction and
arch length discrepancy. RME appliances are
meant to produce orthopedic expansion; ie, the changes
are produced primarily in the underlying skeletal structures rather than by movement of the teeth through
alveolar bone.1-6 Orthopedic expansion is achieved
through RME not only by separation of the midpalatal
suture, but also by its effects on the circumzygomatic and
circumaxillary sutural systems.7 An implant study on
orthopedic expansion, however, showed that only 50% of
skeletal movement was achieved in young children, and
the rest of the expansion was attributed to dental movement. In addition, in adolescents, only 35% of the move-
From the School of Dentistry, Loma Linda University, Loma Linda, Calif.
a
Associate professor, Department of Orthodontics.
b
Associate professor and chair, Department of Orthodontics.
c
Associate professor, Department of Restorative Dentistry.
d
Professor of statistics, Department of Dental Education Services.
e
Assistant professor, Department of Orthodontics.
Reprint requests to: Kitichai Rungcharassaeng, Department of Orthodontics,
Loma Linda University, School of Dentistry, Loma Linda, CA 92354; e-mail:
[email protected].
Submitted, November 2006; revised and accepted, February 2007.
0889-5406/$32.00
Copyright © 2007 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2007.02.052
ment was skeletal, and 65% was dental.8 Therefore, as a
patient grows older, dental tipping becomes more likely;
this puts the teeth at higher risk of being moved through
the envelope of the alveolar process. This can result in
reduction of alveolar bone height, bone dehiscence, and
gingival recession.8-15
Studies of RME generally measured the changes
observed of the dental casts or the 2-dimensional
cephalometric radiographs (lateral or posteroanterior
radiographs) before and after treatment to evaluate the
short- and long-term skeletal and dental effects of
RME.15-18 Incidences of buccal marginal bone loss and
cortical fenestrations have been reported in conjunction
with gingival recession,19-21 but without quantitative
data. With low-dose cone-beam computed tomography
(CBCT) technology (NewTom 3G, AFP Imaging,
Elmsford, NY), it is possible to obtain accurate radiographic images that allow clinicians and researchers to
quantitatively evaluate hard-tissue changes in 3 dimensions.22-25
The purpose of this study was to use CBCT images
to quantitatively evaluate buccal bone changes of the
maxillary first premolar (P1), second premolar (P2),
and first molar (M1) after RME and the variables
associated with it.
428.e1
428.e2 Rungcharassaeng et al
Fig 1. Occlusal view of 4-banded hyrax appliance.
American Journal of Orthodontics and Dentofacial Orthopedics
October 2007
Fig 2. Occlusal view of 2-banded hyrax appliance with
expansion arms extended to P1.
MATERIAL AND METHODS
This study was approved by the Institutional Review Board of Loma Linda University, Loma Linda,
Calif. Thirty consecutive patients, treated since January
2005 at the Graduate Orthodontic Clinic, Loma Linda
School of Dentistry, who required RME with the hyrax
appliance as part of their comprehensive orthodontic
treatment and had before (T1) and after (T2) RME
images made with CBCT available, were included in
the study. The T1 images were obtained before orthodontic treatment, and the T2 images were obtained
within 3 months after the end of activation. The hyrax
appliances used were either 4-banded (supported by
bilateral first premolars and first molars) (Fig 1) or
2-banded (supported by bilateral first molar with expansion arms and mesial rest bonded to first premolars)
(Fig 2).
General information about each patient was collected from the patient’s record and included sex, age at
start of treatment, type of appliance, activation time (in
weeks), and retention time (in weeks, from tie-off to the
time of the CBCT).
The CBCT data of each patient were reconstructed
at 0.5 mm increments, and the DICOM (Digital Imaging and Communications in Medicine) images were
assessed with software (Open-Source, OsiriX Medical
Imaging Software, http://homepage.mac.com/rossetantoine/osirix/Index2.html). The following parameters
were evaluated on P1, P2, and M1 and recorded.
1. Buccal marginal bone level and bone thickness.
From the axial section of the T1 images, at the root
level of the tooth of interest (P1, P2, or M1), an
open-polygon cut was made buccolingually so that
it bisected the root bilaterally. On the coronal image
derived from the open-polygon cut, reference lines
(RL) were constructed from the buccal cusp tips to
Fig 3. T1 coronal image derived from the open-polygon
cut. RL, Reference line; PL1, perpendicular line 1; PL2,
perpendicular line 2; BMBL is depicted in yellow; BBT is
depicted in pink; BTL is depicted in red.
the buccal root tips bilaterally (Fig 3). A straight
line connecting the buccal cusp tips was then
drawn. A perpendicular line (PL1) to the RL was
made at the most coronal point where the bone was
in contact with the tooth. The buccal marginal bone
level (BMBL) was defined as the distance on the
RL from PL1 to the cusp tip. A second perpendicular line (PL2) was made at the level where the
buccal bone deflected. The buccal bone thickness
(BBT) was the distance from the root surface to the
most buccal bone surface on PL 2. The distance on
RL from PL2 to the cusp tip was the bone thickness
level (BTL), where the BBT of the T2 image would
be measured. The procedure was repeated for the
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 132, Number 4
Fig 4. T2 image. Note significant ⌬BMBL (yellow) and
the use of BTL (red) to determine the level where BBT
would be measured.
T2 measurements, except that PL2 on the T2 image
was determined by the BTL at T1 (Fig 4). For M1,
only BMBL and BBT of the mesiobuccal root were
evaluated, because it is usually more prominent and
likely to exhibit more changes than the distobuccal
area.26 The change in BBT (⌬BBT) was obtained
by subtracting the T1 value from the T2 value
(BBTT2-BBTT1); whereas the change in BMBL
(⌬BMBL) was derived by subtracting the T2 value
from the T1 value (BMBLT1-BMBLT2). Negative
⌬BBT and ⌬BMBL values signified bone loss.
2. Interdental distance. From the axial section of the
T1 images, at the crown level of the tooth of
interest (P1, P2, or M1), an open-polygon cut was
made buccolingually so that it passed through the
central fossae bilaterally. On the coronal image
derived from the open-polygon cut, an interfossal
measurement was made and termed the interdental
distance (ID) (Fig 5). The procedure was repeated
for the T2 measurements, and their difference
(IDT2-IDT1) was the amount of dental expansion
(⌬ID).
3. Interdental angle. From the axial section of the T1
images, at the level of the cusp tips of the tooth of
interest (P1, P2, or M1), an open-polygon cut was
made buccolingually so that it passed through the
buccal and lingual (for M1, mesiobuccal and mesiolingual) cusp tips bilaterally. On the coronal
image derived from the open-polygon cut, lines
were drawn across the buccal and lingual cusp tips
of both left and right teeth. The interdental angle
(IA) was the angle formed by their intersection
Rungcharassaeng et al 428.e3
Fig 5. Coronal image derived from the open-polygon
cut. Interfossal measurement was made (yellow line),
which signified interdental distance (ID).
Fig 6. Coronal image derived from the open-polygon
cut. Interdental angle (IA), depicted in yellow, is the
angle formed by the intersection of the lines drawn
across the mesiobuccal and mesiolingual cusp tips of
the first molars bilaterally.
(Fig 6). The procedure was repeated for the T2
measurements, and their difference (IAT2-IAT1)
signified the amount of dental tipping (⌬IA). A
negative ⌬IA value indicated buccal crown tipping.
4. Appliance expansion. From the axial section of the
T2 images, at the level of the hyrax appliance, an
open-polygon cut was made, bisecting the appliance transversely. On the coronal image derived
from the open-polygon cut, the separation distance
of the appliance and the thickness of the middle
portion of the appliance was measured (Fig 7). The
difference was the amount of expansion activated to
the appliance (AE).
428.e4 Rungcharassaeng et al
American Journal of Orthodontics and Dentofacial Orthopedics
October 2007
Table I. Means, standard deviations, and ranges of age,
appliance expansion, activation time, rate of appliance
expansion, and retention time
Age (y):
Overall (n ⫽ 30)
Male (n ⫽ 17)
Female (n ⫽ 13)
Appliance expansion (mm)
Activation time (wk)
Rate of appliance expansion
(mm per week)
Retention time (wk)
Fig 7. Coronal image derived from the open-polygon
cut. AE is the difference between the separation distance of the appliance and the thickness of the middle
portion of the appliance.
5. Rate of AE. The rate of AE was defined as the
amount of AE divided by the activation time (mm
per week).
6. Differential expansion (DifE) was defined as the
difference between ⌬ID and AE (⌬ID-AE).
Statistical analysis
The intraexaminer reliability of the measurements
was determined by using triple assessments of each
parameter on M1 taken at least 2 weeks apart and
expressed as the intraclass correlation coefficient.
Means and standard deviations were calculated for each
parameter. T1 and T2 data were analyzed by using the
Friedman and the Wilcoxon signed rank tests. To
determine which variables were associated with the
changes in BMBL, BBT, and IA, the Spearman rank
correlation analysis was performed. The significance
level of ␣ ⫽ .05 was used for all statistical analyses.
RESULTS
Seventeen boys and 13 girls (mean age, 13.8 years;
range, 10.3-16.8 years) were included in this study.
Seventeen 4-banded and thirteen 2-banded appliances
were used. The mean AE, activation time, rate of
expansion, and retention time were 4.96 mm, 4.4
weeks, 0.83 mm per week, and 3.6 weeks, respectively
(Table I). In 4 patients, bilateral P1 extractions were
performed before the T2 images were taken, and, in 7
patients, the P2 teeth (4 bilateral and 3 unilateral) were
not erupted at the time the T1 images were taken.
Intraclass correlation coefficients for the measurements were higher than 0.90, indicating that the measurement methods were reliable and reproducible. Tables II through IV give the means and standard
deviations of all T1 and T2 measured parameters, their
differences, and the results of the statistical analyses.
Mean ⫾ SD
Range
13.8 ⫾ 1.7
14.1 ⫾ 1.8
13.3 ⫾ 1.5
4.96 ⫾ 1.88
7.8 ⫾ 4.4
10.3-16.8
10.3-16.8
10.3-15.8
1.93-10.6
2-18
0.83 ⫾ 0.56
3.6 ⫾ 4.1
0.22-2.43
0-12
Table II.
Comparison of T1 and T2 measurements with
Wilcoxon signed rank test (␣ ⫽ .05)
ID P1 (mm)
ID P2 (mm)
ID M1 (mm)
IA P1 (°)
IA P2 (°)
IA M1 (°)
BBT P1 (mm)
BBT P2 (mm)
BBT M1 (mm)
BMBL P1 (mm)
BMBL P2 (mm)
BMBL M1 (mm)
T1
(mean ⫾ SD)
T2
(mean ⫾ SD)
P value
33.30 ⫾ 3.10
38.06 ⫾ 3.20
43.92 ⫾ 3.46
197.07 ⫾ 17.23
183.08 ⫾ 16.08
169.61 ⫾ 8.62
1.70 ⫾ 0.65
2.27 ⫾ 0.63
1.96 ⫾ 0.56
8.68 ⫾ 1.03
8.04 ⫾ 0.86
8.25 ⫾ 0.82
39.33 ⫾ 3.56
44.02 ⫾ 3.64
50.58 ⫾ 3.92
190.67 ⫾ 12.36
172.17 ⫾ 14.83
162.96 ⫾ 10.31
0.56 ⫾ 0.65
1.42 ⫾ 0.85
0.72 ⫾ 0.76
13.10 ⫾ 4.73
9.41 ⫾ 2.44
11.17 ⫾ 3.21
⬍.0001
⬍.0001
⬍.0001
.009
⬍.0001
.003
⬍.0001
⬍.0001
⬍.0001
⬍.0001
⬍.0001
⬍.0001
ID, Interdental distance; IA, interdental angle; BBT, buccal bone
thickness; BMBL, buccal marginal bone level; P1, first premolar; P2,
second premolar; M1, first molar.
When comparing ID, IA, BBT, and BMBL at T1
and T2 on P1, P2, and M1 using the Wilcoxon signed
rank test, we found statistically significant differences
in all parameters (P ⬍.05) (Table II).
When comparing the effect of RME on P1, P2, and
M1 using the Friedman test, we found no statistically
significant differences in the ⌬ID, the DifE, and dental
tipping (P ⫽ .522, .215, and .116, respectively). However, the changes in BBT and BMBL were statistically
significantly less in P2 than in P1 and M1 (P ⬍.0001
and P ⫽ .001, respectively). By using the Wilcoxon
signed rank test, no statistically significant differences
were found in the changes in BBT and BMBL between
P1 and M1 (P ⫽ .219 and P ⫽ .094, respectively)
(Table III). In addition, since there were no statistically
significant differences in ⌬BBT and ⌬BMBL between
the right and left P1, P2, and M1 (Table IV; P ⬎.05),
only the measurements on the right side were used for
correlation analyses.
Rungcharassaeng et al 428.e5
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 132, Number 4
Table III.
Comparison of RME effect on first premolar (P1), second premolar (P2), and first molar (M1) with
Friedman and Wilcoxon signed rank tests (␣ ⫽ .05)
P1 (mean ⫾ SD)
P2 (mean ⫾ SD)
M1 (mean ⫾ SD)
P value
4.96 ⫾ 1.88
6.02 ⫾ 2.27
1.01 ⫾ 1.94
⫺6.39 ⫾ 10.30
⫺1.14 ⫾ 0.65
⫺4.42 ⫾ 4.61
5.97 ⫾ 2.31
0.94 ⫾ 2.05
⫺10.90 ⫾ 10.97
⫺0.84 ⫾ 0.57*
⫺1.37 ⫾ 2.14*
6.66 ⫾ 2.69
1.71 ⫾ 1.41
⫺6.64 ⫾ 9.49
⫺1.24 ⫾ 0.56
⫺2.92 ⫾ 3.11
.522
.215
.116
⬍.0001*
.001*
AE (mm)
⌬ID (mm)
DifE (mm)
⌬IA (°)
⌬BBT (mm)
⌬BMBL (mm)
AE, Appliance expansion; ⌬ID, dental expansion; DifE, differential expansion; ⌬IA, dental tipping; ⌬BBT, change in buccal bone thickness;
⌬BMBL, change in buccal marginal bone level.
*Statistically significant.
Table IV. Comparison of buccal bone changes between right and left first premolar (P1), second premolar (P2), and
first molar (M1) with Wilcoxon signed rank test (␣ ⫽ .05)
P1 (mean ⫾ SD)
Right
⌬BBT (mm)
P value
⌬BMBL (mm)
P value
⫺1.06 ⫾ 0.58
P2 (mean ⫾ SD)
Left
Right
⫺1.23 ⫾ 0.71
⫺0.82 ⫾ 0.56
.127
⫺4.10 ⫾ 4.46
M1 (mean ⫾ SD)
Left
Right
⫺0.86 ⫾ 0.58
⫺1.27 ⫾ 0.62
.761
⫺4.75 ⫾ 4.83
⫺1.31 ⫾ 2.21
.151
Left
⫺1.21 ⫾ 0.49
.959
⫺1.44 ⫾ 2.10
.749
⫺3.27 ⫾ 3.34
⫺2.56 ⫾ 2.87
.111
⌬BBT, Change in buccal bone thickness; ⌬BMBL, change in buccal marginal bone level.
For P1, ⌬BBT and initial BBT (BBTT1) showed
strong correlations with ⌬BMBL (r ⫽ 0.43 and 0.39;
P ⫽ .031 and .048, respectively). BBTT1 also showed
a significant correlation with ⌬BBT (r ⫽ ⫺0.41; P ⫽
.036). No variable had a significant correlation with
⌬IA (P ⬎.05).
For P2, a significant correlation was found between
⌬BBT and ⌬BMBL (r ⫽ 0.61; P ⫽ .001). Similar to
P1, no variable had a significant correlation with ⌬IA
(P ⬎.05).
For M1, ⌬BBT, BBTT1, ⌬ID, and DifE demonstrated strong correlations with ⌬BMBL (r ⫽ 0.62,
0.50, ⫺0.38 and ⫺0.44; P ⫽ .000, .005, .037, and .015,
respectively). Age and DifE also showed significant
negative correlations with ⌬IA (r ⫽ ⫺0.42 and ⫺0.41;
P ⫽ .023 and .026, respectively).
DISCUSSION
Although the effective radiation dose of CBCT (45-59
␮Sv) is about 4 to 7 times greater than that of the
panoramic radiographs (6.3-13.3 ␮Sv),27 it is comparable
to that of film-based periapical radiographs (14-100
␮Sv).22,28 In addition, when compared with conventional
computed tomography (CT) (314 ␮Sv),27,29 CBCT produces a much lower effective radiation dose and can still
produce clear images of highly contrasting structures.22,30,31 All CBCT units provide voxel resolutions
that are isotropic— equal in all 3 dimensions; this pro-
duces submillimetric resolution from 0.4 to 0.125
mm.22 Furthermore, CBCT images also have a substantially lower level of metal artifacts than conventional
CT images.22,32 Therefore, with its ability to produce
3-dimensional data, which can be manipulated to generate images representing clinical situations, and comparatively low effective radiation doses, CBCT is an
appealing alternative to conventional CT. CBCT has
been used for 3-dimensional orthodontic diagnosis and
assessment of treatment outcomes.23-25
In addition to dental expansion, the immediate
effects of RME include dental tipping, reductions of
alveolar bone height, and bone dehiscence.9-15,26 This
study demonstrated similar results with significant dental expansion, buccal crown tipping, and loss in BMBL
and BBT of maxillary posterior teeth in the short term
(within 3 months) after RME (P ⬍.05; Table II).
In this study, the mean ⌬ID values on P1 (6.02
mm), P2 (5.97 mm), and M1 (6.66 mm), although not
significantly different from each other, were greater
than the mean AE (4.96 mm) (Table II). These results
were comparable with the findings of Chung and Font33
and Garib et al.34 They attributed DifE to the inherent
buccal crown tipping effect of RME, which was also
observed in this study. However, only in M1, and not in
P1 and P2, was there a significant correlation between
DifE and ⌬IA (the greater the DifE, the greater the
buccal crown tipping; r ⫽ ⫺.41, P ⫽ .026).
428.e6 Rungcharassaeng et al
Buccal crown tipping occurred in about 80% of the
posterior teeth in this study; this closely corresponded
to the 75% of the sample measured immediately after
expansion reported by Thorne.35 The mean ⌬IA values
observed in this study were ⫺6.39, ⫺10.90, and ⫺6.64
mm with ranges of ⫺24.79 to 7.78, ⫺39.22 to 5.53, and
⫺24.52 to 6.58 mm for P1, P2, and M1, respectively
(Table II). Although there was no statistically significant difference in ⌬IA of P1, P2, and M1 due to high
variability in the measurements (P ⫽ .116; Table III),
the clinically greater mean buccal inclination observed
on P2 when compared with P1 and M1 coincided with
the finding of Garib et al.34 The most logical explanation would be the difference in how the teeth were
attached to the appliance. P1 and M1 were rigidly
fixated to the appliance with bands or bonded occlusal
rests and therefore had more bodily movement during
expansion. On the other hand, the expansion force
applied to P2 via the lingual bar would most likely
create a buccal moment that resulted in the buccal
crown tipping of P2.34
Adkins et al36 also reported highly variable measurements in dental tipping after rapid palatal expansion and found no significant relationships of buccal
crown tipping with age, initial palatal width, amount of
expansion, and crossbite. They concluded that buccal
tipping of anchor teeth is a factor to be considered as a
part of the rapid palatal expansion procedure. Similar
findings were observed in this study on P1 and P2; no
significant correlations were found between ⌬IA and
the other parameters recorded (P ⬎.05). Nevertheless,
in addition to DifE, ⌬IA on M1 was also significantly
correlated to the subject’s age (buccal crown tipping
increases as age increases; r ⫽ ⫺0.42; P ⫽ .023). This
result supports the idea that, with increased age, more
dental expansion and less skeletal expansion can be
expected during RME procedures.8,17
Significant buccal bone losses were observed in
both horizontal (BBT) and vertical (BMBL) dimensions in all posterior teeth (P1, P2, and M1) after RME
(Table II; P ⬍.0001). Although the bone losses (BBT,
BMBL) around P1 (⫺1.14, ⫺4.42 mm) and M1
(⫺1.24, ⫺2.92 mm) were not significantly different
from each other (P ⬎.05), they were statistically
significantly greater than the bone losses observed
around P2 (⫺0.84, ⫺1.37 mm) (Table III; P ⬍.0001
and P ⫽ .001). Garib et al26 reported similar results;
they found significantly more buccal bone losses (BBT,
BMBL) around P1 (⫺0.6, ⫺7.1 mm) and M1 (⫺0.7,
⫺3.8 mm) than P2 (⫺0.2, ⫺0.2 mm) (P ⬍.05).
However, they did not find significant bone changes
around P2 after RME (P ⬎.05). No significant differences were found in the amount of bone changes
American Journal of Orthodontics and Dentofacial Orthopedics
October 2007
between the left and right P1, P2, and M1 (Table IV;
P ⬎.05), indicating that the effect of RME on buccal
bone is relatively symmetrical.
Significant correlations between changes in BBT
and BMBL were observed in P1, P2, and M1 (P ⫽
.031, .001, and .000). These findings were anticipated
because, when the tooth is being moved buccally, the
loss in BMBL is usually the result of the loss in BBT.
Nevertheless, only BBTT1 of P1 had a significant
correlation with ⌬BBT (r ⫽ ⫺0.41, P ⫽ .036); this
means that greater bone loss could be expected with
greater BBTT1. This also can be interpreted as a higher
probability for bone dehiscence around P1 than P2 and
M1 after RME. This might be because P1 usually is
located in an area where bone becomes narrower
apically, and thus the root can perforate the bone more
easily when there is bodily buccal movement.26 No
other variables were associated with buccal bone changes
in P2 (P ⬎.05).
Regarding BBTT1, our results suggest that BMBL
was better preserved with thicker BBTT1. Garib et al26
reported a similar significant correlation between BBTT1
and ⌬BMBL, and concluded that, in patients with initially
thicker bone plates, RME did not have such negative
effects on the buccal periodontium. Significant correlations between ⌬BMBL and the amounts of ⌬ID (r ⫽
⫺0.38; P ⫽ .037) and DifE (r ⫽ ⫺0.44; P ⫽ .015) in M1
mean that greater loss in BMBL can be expected with
greater ⌬ID and DifE. These variables had no bearing on
⌬BMBL of P1 and P2.
The mean rate of appliance expansion in this study
was 0.83 mm per week (range, 0.22-2.43 mm). This
range encompasses the rates of both slow expansion
(0.4-1.1 mm per week) and rapid expansion (0.2-0.5
mm per day) of the maxilla.37 RME is believed to result
in maximum skeletal displacement and bodily tooth
movement with minimum dental tipping.7,37 Slow expansion, on the other hand, is supposed to produce less
tissue resistance in the circummaxillary structures and
better bone formation in the intermaxillary suture; these
help to minimize posterior relapse.37 Greater buccal
tipping of the molars has been reported in patients
treated with slow expanders such as the quad-helix or
the nickel-titanium expander compared with those
treated with RME appliances.38,39 In this study, there
were no significant correlations between the rate of
expansion and ⌬IA, ⌬BBT, and ⌬BMBL in P1, P2, and
M1 after RME (P ⬎.05). These results suggest that the
difference in force delivery system (hyrax delivers
heavy [3-10 lb] interrupted force with cumulative
residual force of 20 lb or more,40 and quad-helix
delivers lighter [about 400 g] continuous force at 8 mm
expansion),41 rather than the rate of expansion, influ-
Rungcharassaeng et al 428.e7
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 132, Number 4
ences how teeth respond to maxillary expansion (bodily
movement vs tipping). The long-term effect of the rate
of expansion on relapse is beyond the scope of this
study and will be reported when data are available.
Starnbach et al7 demonstrated, in their histologic
animal study, the incidence of buccal bone resorption
of posterior teeth after 2 weeks of orthodontic expansion. Evidence of bone formation was apparent after 3
months of retention; it further improved to “near
normal” 3 months later.7 Garib et al26 reported significant buccal bone reduction due to RME after 3 months
of retention and attributed their finding to the absence
of correspondent compensatory bone apposition under
the buccal periosteum. Timms and Moss42 demonstrated evidence of a reversal line well within the
buccal bone and also bone deposition 1 year after RME
therapy. Greenbaum and Zachrisson43 evaluated the
effect of rapid and slow palatal expansion therapy on
periodontal supporting structures on first molars after
orthodontic treatment. Although they found statistically
significant differences in alveolar bone level and attachment level among the rapid expansion, slow expansion,
and control groups (P ⬍.05), the mean differences were
less than 0.5 mm and deemed insignificant clinically.
They concluded that, regardless of the movement
pattern of the dentition involved, the posttreatment
response of the buccal tissues appears to have been
minimal when compared with similar tissues not
exposed to the forces of palatal expansion therapy.43
In our study, the retention time (0-12 weeks) did not
seem to influence the amount of ⌬IA, ⌬BBT, and
⌬BMBL in P1, P2, and M1 after RME (P ⬎.05).
Although the amount of bone loss observed (Table
III) seemed alarming, these results were comparable
to those in other studies and are considered the
immediate effects of RME.7,26 Follow-up study is
warranted to evaluate the postorthodontic tissue
response of the buccal bone.
This study involved data collection on consecutively
treated patients, and, therefore, many variables were not
controlled. However, this model allowed us to evaluate
these variables because of regular clinical setting and
incorporate them into the statistical analyses. Although
useful information was found in this study, its limitation
should be acknowledged. A larger sample size and a
long-term follow-up will undoubtedly provide more insightful evidence on the effect of RME.
CONCLUSIONS
With the limits of this study, the following conclusions can be made.
1. Buccal crown tipping, and reduction of BBT and
BMBL of P1, P2, and M1 are the expected
immediate effects of RME.
2. The response of buccal bone to RME is relatively
symmetrical bilaterally.
3. Dental expansion is uniform anteroposteriorly
(among P1, P2, and M1).
4. P2 exhibited more buccal crown tipping than P1
and M1, although it was not statistically significant.
5. P2 experienced significantly less reduction in BBT
and BMBL than P1 and M1.
6. Only ⌬IA on M1 (not P1 and P2) had a significant
correlation with DifE and patient age.
7. ⌬BBT was significantly associated with ⌬BMBL
in all teeth involved. Nevertheless, only in P1 was
⌬BBT significantly correlated to another variable
(BBTT1).
8. For P2, ⌬BBT and ⌬BMBL were not correlated to
any other variables in this study.
9. For M1, significant correlation was also observed
between ⌬BMBL and the amounts of ⌬ID and
DifE.
10. The rate of AE and retention time did not have
significant effects on ⌬IA, ⌬BBT, and ⌬BMBL.
REFERENCES
1. Haas AJ. Rapid expansion of the maxillary dental arch and nasal
cavity by opening the midpalatal suture. Angle Orthod 1961;31:7390.
2. Haas AJ. The treatment of maxillary deficiency by opening the
mid-palatal suture. Angle Orthod 1965;65:200-17.
3. Haas AJ. Palatal expansion: just the beginning of dentofacial
orthopedics. Am J Orthod 1970;57:219-55.
4. Haas AJ. Long-term posttreatment evaluataion of rapid palatal
expansion. Angle Orthod 1980;50:189-217.
5. Wertz RA. Skeletal and dental changes accompanying rapid
midpalatal suture opening. Am J Orthod 1970;58:41-66.
6. Timms DJ. An occlusal analysis of lateral maxillary expansion
with mid-palatal suture opening. Dent Pract 1968;18:435-41.
7. Starnbach H, Bayne D, Cleall J, Subtelny JD. Facioskeletal and
dental changes resulting from rapid maxillary expansion. Angle
Orthod 1966;36:152-64.
8. Krebs A. Midpalatal suture expansion studied by the implant
method over a 7-year period. Trans Eur Orthod Soc 1964;40:
131-42.
9. Wennstrom JL, Lindhe J, Sinclair F, Thilander B. Some periodontal tissue reactions to orthodontic tooth movement in monkeys. J Clin Periodontol 1987;14:121-9.
10. Batenhorst K, Bowers G, Williams J. Tissue changes resulting
from facial tipping and extrusion of incisors in monkeys. J
Periodontol 1974;45:660-8.
11. Karring T, Nyman S, Thilander B, Magnusson I. Bone regeneration in orthodontically produced alveolar bone dehiscences. J
Periodontol Res 1982;17:309-15.
12. Steiner G, Pearson J, Ainamo J. Changes of the marginal
periodontium as a result of labial tooth movement in monkeys. J
Periodontal 1981;52:314-20.
428.e8 Rungcharassaeng et al
13. Thilander B, Nyman S, Karring T, Magnusson I. Bone regeneration in alveolar bone dehiscences related to orthodontic tooth
movements. Eur J Orthod 1983;5:105-14.
14. Lindhe J. Clinical periodontology. 2nd ed. Copenhagen: Munksgaard; 1989.
15. Handelman CS, Wang L, BeGole EA, Haas AJ. Non-surgical
rapid maxillary expansion in adults: report of 47 cases using the
Haas expander. Angle Orthod 2000;70:129-44.
16. McNamara JA Jr, Baccetti T, Franchi L, Herberger TA. Rapid
maxillary expansion followed by fixed appliances: a long-term
evaluation of changes in arch dimensions. Angle Orthod 2003;
73:344-53.
17. Baccetti T, Franchi L, Cameron CG, McNamara JA Jr. Treatment timing for rapid maxillary expansion. Angle Orthod 2001;
71:343-50.
18. Garib DG, Henriques JFC, Jason GP. Longitudinal cephalometric appraisal of rapid maxillary expansion effects. Rev Dent Press
Ortod Ortop Facial 2001;6:17-30.
19. Vanarsdall RL. Periodontal/orthodontic interrelationships. In:
Graber TM, Vanarsdall RL, editors. Orthodontics: current principles and techniques. 3rd ed. St Louis: Mosby; 1994. p. 801-38.
20. Vanarsdall RL Jr. Commentary: non-surgical rapid maxillary
alveolar expansion in adults: a clinical evaluation. Angle Orthod
1997;67:306-7.
21. Vanarsdall RL Jr. Transverse dimension and long-term stability.
Semin Orthod 1999;5:177-80.
22. Scarfe WC, Farman AG, Sukovic P. Clinical applications of
cone-beam computed tomography in dental practice. J Can Dent
Assoc 2006;72:75-80.
23. Maki K, Inou N, Takanishi A, Miller AJ. Computer-assisted
simulations in orthodontic diagnosis and the application of a new
cone beam x-ray computed tomography. Orthod Craniofac Res
2003;6(Suppl 1):95-101.
24. Baumrind S, Carlson S, Beers A, Curry S, Norris K, Boyd RL.
Using three-dimensional imaging to assess treatment outcomes
in orthodontics: a progress report from the University of the
Pacific. Orthod Craniofac Res 2003;6(Suppl 1):132-42.
25. Aboudara CA, Hatcher D, Nielson IL, Miller A. A threedimensional evaluation of the upper airway in adolescents.
Orthod Craniofac Res 2003;6(Suppl 1):173-5.
26. Garib DG, Henriques JFC, Janson G, de Freitas MR, Fernandes
AY. Periodontal effects of rapid maxillary expansion with
tooth-tissue-borne and tooth-borne expanders: a computed tomography evaluation. Am J Orthod Dentofacial Orthop 2006;
129:749-58.
27. Ludlow JB, Davies-Ludlow LE, Brooks SL, Howerton WB.
Dosimetry of 3 CBCT devices for oral and maxillofacial radiology: CB Mercuray, NewTom 3G and i-CAT. Dentomaxillofac
Radiol 2006;35:219-26.
American Journal of Orthodontics and Dentofacial Orthopedics
October 2007
28. Mah JK, Danforth RA, Bumann A, Hatcher D. Radiation
absorbed in maxillofacial imaging with a new dental computed
tomography device. Oral Surg Oral Med Oral Pathol Oral Radiol
Endod 2003;96:508-13.
29. Lecomber AR, Yoneyama Y, Lovelock DJ, Hosoi T, Adams
AM. Comparison of patient dose from imaging protocols for
dental implant planning using conventional radiography and
computed tomography. Dentomaxillofac Radiol 2001;30:255-9.
30. Sukovic P. Cone beam computed tomography in craniofacial
imaging. Orthod Craniofac Res 2003;6(Suppl 1):31-6.
31. Ziegler CM, Woertche R, Brief J, Hassfeld S. Clinical indications for digital volume tomography in oral and maxillofacial
surgery. Dentomaxillofac Radiol 2002;31:126-30.
32. Holberg C, Steinhauser S, Geis P, Rudzki-Janson I. Cone-beam
computed tomography in orthodontics: benefits and limitations. J
Orofac Orthop 2005;66:434-44.
33. Chung CH, Font B. Skeletal and dental changes in the sagittal,
vertical, and transverse dimensions after rapid palatal expansion.
Am J Orthod Dentofacial Orthop 2004;126:569-75.
34. Garib DG, Henriques JFD, Janson G, de Freitas MR, Coelho RA.
Rapid maxillary expansion—tooth tissue-borne versus toothborne expanders: a computed tomography evaluation of dentoskeletal effects. Angle Orthod 2005;75:548-57.
35. Thorne NH. Experiences on widening the median maxillary
suture. Eur Orthod Soc Trans 1956;31:279-90.
36. Adkins MD, Nanda RS, Currier GF. Arch perimeter changes on
rapid palatal expansion. Am J Orthod Dentofacial Orthop 1990;
97:194-9.
37. Bishara SE, Staley RN. Maxillary expansion: clinical implications. Am J Orthod Dentofacial Orthop 1987;91:3-14.
38. Herold JS. Maxillary expansion: a retrospective study of three
methods of expansion and their long term sequelae. Br J Orthod
1989;16:195-200.
39. Ciambotti C, Ngan P, Durkee M, Kohli K, Kim H. A comparison
of dental and dentoalveolar changes between rapid palatal
expansion and nickel-titanium palatal expansion appliances.
Am J Orthod Dentofacial Orthop 2001;119:11-20.
40. Isaacson RJ, Wood JL, Ingram AH. Forces produced by rapid
maxillary expansion. Angle Orthod 1964;34:256-70.
41. Chaconas SJ, Caputo AA. Observation of orthopedic force
distribution produced by maxillary orthodontic appliances. Am J
Orthod 1982;82:492-501.
42. Timms DJ, Moss JP. An histological investigation into the
effects of rapid maxillary expansion on the teeth and their
supporting tissues. Trans Eur Orthod Soc 1971;263-71.
43. Greenbaum KR, Zachrisson BU. The effect of palatal expansion
therapy on the periodontal supporting tissues. Am J Orthod
1982;81:12-21.