Changes in the midpalatal and pterygopalatine sutures induced by micro-implant-supported skeletal expander, analyzed with a novel 3D method based on CBCT imaging
Cantarella et al. Progress in Orthodontics
Changes in the midpalatal and pterygopalatine sutures induced by micro- implant-supported skeletal expander, analyzed with a novel 3D method based on CBCT imaging
Daniele Cantarella 2
Ramon Dominguez-Mompell 0
Sanjay M. Mallya 1
Christoph Moschik 0
Hsin Chuan Pan 0
Joseph Miller 3
Won Moon 0
0 Division of Growth and Development, Section of Orthodontics, School of Dentistry, Center for Health Science, University of California , Room 63-082 CHS, 10833 Le Conte Avenue, Box 951668, Los Angeles, CA 90095-1668 , USA
1 Division of Diagnostic and Surgical Sciences, Section of Oral and Maxillofacial Radiology, School of Dentistry, Center for Health Science, University of California , Room 53-068 B CHS, 10833 Le Conte Avenue, Box 951668, Los Angeles, CA 90095-1668 , USA
2 Division of Oral Biology and Medicine, School of Dentistry, Center for Health Science, University of California , 10833 Le Conte Avenue, Box 951668, Los Angeles, CA 90095-1668 , USA
3 Division of Integrative Anatomy, Department of Pathology and Laboratory Medicine, Geffen School of Medicine, Center for Health Science, University of California , Room 52-068 CHS, 10833 Le Conte Avenue, Box 951668, Los Angeles, CA 90095-1668 , USA
Background: Mini-implant-assisted rapid palatal expansion (MARPE) appliances have been developed with the aim to enhance the orthopedic effect induced by rapid maxillary expansion (RME). Maxillary Skeletal Expander (MSE) is a particular type of MARPE appliance characterized by the presence of four mini-implants positioned in the posterior part of the palate with bi-cortical engagement. The aim of the present study is to evaluate the MSE effects on the midpalatal and pterygopalatine sutures in late adolescents, using high-resolution CBCT. Specific aims are to define the magnitude and sagittal parallelism of midpalatal suture opening, to measure the extent of transverse asymmetry of split, and to illustrate the possibility of splitting the pterygopalatine suture. Methods: Fifteen subjects (mean age of 17.2 years; range, 13.9-26.2 years) were treated with MSE. Pre- and post-treatment CBCT exams were taken and superimposed. A novel methodology based on three new reference planes was utilized to analyze the sutural changes. Parameters were compared from pre- to post-treatment and between genders non-parametrically using the Wilcoxon sign rank test. For the frequency of openings in the lower part of the pterygopalatine suture, the Fisher's exact test was used. Results: Regarding the magnitude of midpalatal suture opening, the split at anterior nasal spine (ANS) and at posterior nasal spine (PNS) was 4.8 and 4.3 mm, respectively. The amount of split at PNS was 90% of that at ANS, showing that the opening of the midpalatal suture was almost perfectly parallel antero-posteriorly. On average, one half of the anterior nasal spine (ANS) moved more than the contralateral one by 1.1 mm. Openings between the lateral and medial plates of the pterygoid process were detectable in 53% of the sutures (P < 0.05). No significant differences were found in the magnitude and frequency of suture opening between males and females. Correlation between age and suture opening was negligible (R2 range, 0.3-4.2%). (Continued on next page)
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Conclusions: Midpalatal suture was successfully split by MSE in late adolescents, and the opening was almost perfectly
parallel in a sagittal direction. Regarding the extent of transverse asymmetry of the split, on average one half of ANS
moved more than the contralateral one by 1.1 mm. Pterygopalatine suture was split in its lower region by MSE, as the
pyramidal process was pulled out from the pterygoid process. Patient gender and age had a negligible influence on
suture opening for the age group considered in the study.
The undesirable side effects in conventional rapid
maxillary expansion (RME) are limited skeletal movement,
dentoalveolar tipping, root resorption, detrimental
periodontal consequences, and lack of long-term stability
]. To moderate these effects, clinicians in recent years
have utilized micro-implant-assisted rapid palatal
expansion (MARPE) [
]. The Maxillary Skeletal Expander
(MSE) is a particular type of MARPE appliance that
differs from the others because it promotes bi-cortical
engagement of the four micro-implants into the cortical
bone of the palate and nasal floor [
Due to the higher interdigitation of the midpalatal
suture after puberty, some authors affirm that expansion of
the maxilla in post-pubertal patients is not feasible [
surgically assisted rapid palatal expansion (SARPE) is
]. However, recent evidence has suggested that
a successful expansion of the midpalatal suture in late
adolescents can be possible with bone-borne and
toothborne palatal expanders [
3, 4, 9
]. Although MARPE
appliances have been developed with the aim of enhancing the
orthopedic effect of maxillary expansion, comparisons
between tooth-borne and bone-borne expanders led to
different results. In fact, Lin et al.  found greater skeletal
expansion with a bone-borne appliance, while Lagravère
et al. [
] reported that the two types of expanders generate
similar skeletal effects.
In regard to the pterygopalatine suture, it has been shown
that the attempt to disarticulate it in dry skulls in late
juvenile and early adolescent periods is always accompanied
by fracture of heavily interdigitated osseous surfaces, as a
result of rigid interdigitation and high resistance to
separation of articulating bones [
]. Ghoneima et al. in a clinical
study conducted with CBCT imaging in early adolescents
concluded that this suture cannot be split when
toothborne palatal expanders are utilized [
]. To the authors’
knowledge, no investigation has been conducted on the
modifications induced on the pterygopalatine suture by
bone-borne maxillary expanders.
Traditionally, analysis of the midpalatal suture during
rapid palatal expansion was conducted using study
], two-dimensional imaging [
more recently, three-dimensional imaging based on
computed tomographic data [
]. The introduction
of cone beam computed tomography (CBCT) in the
orthodontic field and the development of new computer
software allows for multiplanar, 3-dimensional (3D)
reconstructions, and, thus, more possibilities in
diagnosis of the craniofacial complex in living subjects [
The aim of the present study is to investigate the
effects on midpalatal and pterygopalatine sutures induced
by a bone-borne expander (MSE) in late adolescents,
using high-resolution CBCT. Specific aims are to define
the magnitude and sagittal parallelism of midpalatal
suture opening, to measure the extent of transverse
asymmetry of split, and to illustrate the possibility of splitting
the pterygopalatine suture.
The present retrospective study received approval from
the Institutional Review Board (IRB) at University of
California, Los Angeles (UCLA).
Participants and intervention
The study included 15 consecutively debonded patients
(6 males, 9 females) with a mean age of 17.2 ± 4.2 years
(range 13.9–26.2 years) of dominant Hispanic ethnicity,
who were treated with MSE (BioMaterials Korea, Inc.)
and who met the inclusion criteria. Nine patients
presented a bilateral posterior crossbite, five patients
presented a unilateral crossbite, and one patient presented a
maxillary transverse deficiency without dental crossbite.
All patients were treated at the Orthodontic Clinic of
the UCLA School of Dentistry. Treatment with MSE
was started and completed before bonding of
orthodontic brackets in all patients.
The inclusion criteria were the following: (1) transverse
maxillary deficiency based on a modification of Andrews’
analysis of six elements [
], described below; (2)
treatment with MSE as part of the overall treatment; (3)
CBCT taken before and within 3 weeks of completion of
active expansion; (4) absence of any craniofacial
syndromes; and (5) lack of previous orthodontic treatment.
Regarding point 1, the method adopted consists in
analyzing the relationship between the maxillary and the
mandibular width (Fig. 1). Maxillary width is defined as
the distance between the right and left most concave point
on maxillary vestibule at the level of the mesio-buccal
cusp of first molars. Mandibular width is defined as the
distance between the right and left mandibular WALA
ridge at the level of the mesio-buccal groove of first
molars. WALA ridge represents the most prominent portion
of the buccal alveolar bone. In a normally developed
maxilla, the maxillary width should be equal to the mandibular
width. Maxillary transverse deficiency is calculated as the
difference between mandibular and maxillary width, and
represents the amount of maxillary skeletal expansion
required for the patient, as shown in Fig. 1.
Patients were excluded from tooth-borne maxillary
expansion and assigned to MSE treatment, based on the
following criteria: patient maturity (appearance of
secondary sexual characteristics such us facial hair, voice
change, onset of menstruation cycle, cervical vertebral
maturation stage higher than CS4) [
vertical biotype (determined with SN-GoGn and FMA
angles on lateral cephalometric analysis) and history of
nasal airway obstruction. At UCLA Section of
Orthodontics, dolicofacial patients are preferably treated with
MSE rather than with a tooth-borne maxillary expander
because, based on our experience, bone-borne
appliances lead to lesser dentoalveolar tipping and lower
posterior mandibular rotation.
Expander design and activation rates
MSE (Fig. 2a) elaboration and delivery was as proposed
by Carlson [
]. The rate of expansion was two turns
(.25 mm per turn) per day until inter-incisal diastema
appeared and then one activation per day was applied.
The expansion was completed when the maxillary width
was equal to the mandibular width, as defined in Fig. 1.
After the expansion, MSE remained blocked for at least
3 months to stabilize the expansion.
In order to calculate the average amount of activation
of the expansion jackscrew received by the patients, the
distance between the two halves of the expansion screw
was measured on the post-expansion CBCT (Fig. 2b),
and the pre-expansion distance, measured 10 times on a
CBCT of the expansion device before activation, was
then subtracted. The values were averaged to determine
the mean and the standard deviation.
CBCT scans were taken before expansion and within
3 weeks of completion of active maxillary expansion on
all patients. The duration of active maxillary expansion
ranged between 12 and 36 days, while the average time
period between the pre-expansion and post-expansion
CBCT was 5 ± 2 months, as this included the time for
insurance clearance, scheduling of appointments,
appliance fabrication, and delivery. Secondary CBCT was
taken before bonding of orthodontic brackets and within
3 weeks of completion of active expansion, in order to
analyze suture openings before bone formation may
occur. All CBCT scans were taken by a NewTom 5G
scanner in an 18 × 16 field of view with a 14-bit gray
scale and with a voxel size of 0.3 mm. Scan times were
18 s (3.6 s emission time), with 110 kV, and utilized an
automatic exposure control that adjusted the
milliampere based upon the patient’s anatomic density. Five
hundred thirty-eight axial slices with 609 × 609
resolution and a slice thickness and increment of 0.3 mm
and pixel spacing of 0.3 mm were obtained.
Utilizing the fusion module of OnDemand3D software
from Cybermed Inc. company, the post-expansion CBCT
was superimposed on pre-expansion CBCT using the
anatomical structures of the whole anterior cranial base, as
proposed by Cevidanes et al. for non-growing patients [
]. The superimposition method utilizes the voxel gray
scale and is fully automated by the software through the
“Automatic Registration” tool, to avoid errors related to
the operator. The accuracy of the method has been
recently validated by Weissheimer et al. .
Three novel reference planes have been identified in
the present study in order to orient the skull: maxillary
sagittal plane (MSP), axial palatal plane (APP), and
Vcoronal plane (VCP) (Fig. 3). Maxillary sagittal plane
passes through the anterior nasal spine (ANS), posterior
nasal spine (PNS), and nasion (N) on the pre-expansion
CBCT; the axial palatal plane is perpendicular to the
maxillary sagittal plane and passes through ANS and
PNS (Fig. 4); the V-coronal plane is perpendicular to the
other two planes and passes through the most posterior
point of the vomer (V point). The three reference planes
can be utilized to analyze the lateral, sagittal, and vertical
displacement of the maxilla and surrounding structures
induced by maxillary expansion. An axial section parallel
to the axial palatal plane (APP) and passing through
sella turcica was checked in every patient before taking
the measurements in order to verify the accuracy of
automated software superimposition on the anterior
cranial base (Fig. 5e).
In order to describe the transverse and sagittal
movement of the maxilla and pterygoid plates and the
modifications in the pterygopalatine suture along its entire
length, three axial sections have been analyzed: the axial
palatal section (APS), lower nasal section (LNS), and
upper nasal section (UNS) (Fig. 5). The axial palatal
section (APS) passes through the axial palatal plane and is
the section analyzed in this article. The lower nasal
section (LNS) and upper nasal section (UNS) are parallel to
the axial palatal section and will be the object of future
Measurements in the axial palatal section
In the present study, the APS has been used to study the
split of the midpalatal and pterygopalatine sutures. The
utilized landmarks are shown in Fig. 6, and the evaluated
parameters were the following: distance of right and left
half of ANS and PNS from maxillary sagittal plane, sum
of lateral displacement of Rt ANS and Lt ANS, sum of
lateral displacement of Rt PNS and Lt PNS, and width of
opening in right and left pterygoid processes (Fig. 7). In
addition, the frequency of openings in the pterygoid
processes was calculated.
The split of the midpalatal suture generates two halves
of the ANS and PNS. The maxillary sagittal plane passes
through the ANS and PNS in the pre-expansion CBCT,
and the distance between the two halves from the
maxillary sagittal plane in the post-expansion CBCT
represents the lateral movement of each half (Fig. 7a).
The extent of transverse asymmetry of the split of the
midpalatal suture was calculated as follows: for each
patient, the lesser movement of one half of ANS was
subtracted from the larger movement of the contralateral
half. The values were then averaged. This parameter
shows on average how much more one half moves with
respect to the contralateral half. The movement of the
ANS and not the PNS was chosen as a parameter to
evaluate the asymmetry because changes at ANS reflect
modifications in the anterior part of the maxilla more
closely and therefore can have a larger impact on the
soft tissues of the face (Fig. 5b–d).
Furthermore, the axial palatal section cuts the
pterygopalatine suture in an area where the pyramidal process
of the palatine bone articulates with the pterygoid notch
located between the lateral and the medial plate of the
pterygoid process (Fig. 8). Changes in this area due to
the maxillary expansion are described as “openings”
between the lateral and medial pterygoid plates.
The average width and frequency of the openings (i.e.,
percentage of sutures presenting the openings) were calculated.
The width of the opening between the lateral and medial
pterygoid plates was measured as the distance from the
most medial point of the lateral pterygoid plate to the most
lateral point of the medial pterygoid plate (Figs. 6 and 7). In
the case of a partial disengagement of the pyramidal process
from the pterygoid notch, the width of the opening was
measured from the pyramidal process to the pterygoid plate
adjacent to the opening (Fig. 7b). The whole extension of
articulation between the pyramidal process of the palatine
bone and the pterygoid notch of the pterygoid process was
analyzed with consecutive axial sections parallel to the axial
palatal plane for each patient, and the section with the
widest opening was chosen as the measurement. In the
preexpansion CBCT, the frequency and width of the openings
were given a value equal to zero.
The landmarks shown in Fig. 6 could be detected only
in the post-expansion CBCT since in the pre-expansion
CBCT, the two halves of ANS and PNS are in contact.
In addition, there are no gaps between the lateral and
medial plates of the pterygoid processes since the
pterygoid notch is occupied by the pyramidal process of the
palatine bone (Fig. 8).
Sample size analysis was performed for 80% power with
an alpha value of 0.05.
The assessments of parameters were compared from
preto post-treatment non-parametrically using the Wilcoxon
sign rank test. A non-parametric test was chosen because
the pre-expansion values of all considered parameters were
equal to zero (non-normal distribution). The Wilcoxon sign
rank test was also utilized to compare the magnitude of
suture openings between males and females.
The Fisher’s exact test was used to compare the
frequency of openings in the lower part of the
pterygopalatine suture from pre-expansion to post-expansion, and
between males and females.
A correlation analysis between age and parameters of
suture opening was performed.
Reliability of skull orientation was evaluated by
reorienting 30% of randomly selected CBCT scans (n = 5
patients) and calculating the intra-class correlation
coefficient, using the posterior clinoid process and basion as
landmarks for comparison, similarly to the method
adopted by Woller et al. [
Reliability of measured parameters was obtained on 10
different patients by two raters. Each parameter was
measured twice by each rater. Reliability was evaluated by
computing the intra-class correlation coefficient (ICC) ρ.
Width of opening in Lt pterygoid process
The sample sizes needed for 80% power are given in
Table 1. The sample size of 15 provided at least 80%
power for all considered parameters, for confirming
treatment change using the usual 0.05 two-sided
The average amount of activation of MSE expansion
jackscrew was 6.8 ± 1.9 mm (range, 4.1–10.5 mm). The
duration of maxillary expansion ranged from 12 to
Regarding the midpalatal suture, the amount of split at
PNS (4.3 mm) was 90% of that at ANS (4.8 mm), as
shown in Table 2.
The split of the midpalatal suture was asymmetrical:
on average, one half of the ANS moved more than the
contralateral half by 1.1 (± 1.0) mm.
With regard to the pterygopalatine suture split, 16
sutures out of 30 (53%) presented openings between the
medial and lateral pterygoid plates (P < .01).
All measures are expressed in mm
Rt ANS right half of anterior nasal spine, Lt ANS left half of anterior nasal spine, Rt PNS right half of posterior nasal spine, Lt PNS left half of posterior nasal spine, Rt
right, Lt left
*P < .05; **P < .01
No significant differences were found in the magnitude
and frequency of suture opening between males and
females, as shown in Table 3.
The correlation analysis between age and parameters
of suture opening is given in Table 4. Correlation was
negligible for all considered parameters.
Skull orientation was highly reliable, as the obtained
Cronbach’s alpha value was 0.987.
For the considered parameters, the intra-class
correlation coefficient (ICC) ρ was at least 0.973 or more,
showing that measurements were very reliable (Table 5).
For the evaluation of facial structures in the frontal
plane, 2D postero-anterior cephalometric analyses
commonly utilize a reference line perpendicular to a line
connecting the right and left frontozygomatic sutures
and passing through Crista Galli of the ethmoid bone
(Fig. 9a, b), and reference planes based on the cranial
base have been described also in 3D cephalometric
]. However, reference lines or planes based on
the cranial base do not necessarily cross the midpalatal
suture so that ANS or PNS fall either on the one side or
on the other side of the vertical reference line/plane. In
the present study, the maxillary sagittal plane (MSP) has
been developed in order to establish a procedure that
allows to analyze the extent of transverse asymmetry of
the split of the midpalatal suture and the movement of
each maxillary bone (Fig. 9c, d).
Regarding the midpalatal suture, this was successfully split
by MSE in all patients in the present study. In the literature,
it is described that tooth-borne maxillary expanders produce
a V-shaped opening of the midpalatal suture, with the
greatest opening anteriorly and progressively less separation
towards its posterior part [
12, 18, 26
]. Lione et al. [
a tooth-borne maxillary expander activated by 7 mm on all
patients and found that the opening of the midpalatal suture
was 3.01 and 1.15 mm at ANS and PNS, respectively. The
split at PNS was about 40% of that at ANS, showing the
Vshaped expansion pattern. Conversely, in the patients treated
with MSE in the present study, the borders of the midpalatal
suture moved almost perfectly parallel to each other since
the amount of split at PNS (4.3 mm) was 90% of that at
ANS (4.8 mm) (Fig. 10a). This is probably due to the
different biomechanics in MSE compared to tooth-borne
maxillary expanders [
]. The use of four mini-implants in the
MSE, with a considerable antero-posterior distance between
them and positioned in the posterior part of the palate,
medial to the zygomatic buttress bones, allows the separation
force to be distributed along the entire suture length
(Fig. 10b). This promotes the more parallel split of the
midpalatal suture in an antero-posterior direction [
Rt ANS right half of anterior nasal spine, Lt ANS left half of anterior nasal spine, Rt PNS right half of posterior nasal spine, Lt PNS left half of posterior nasal spine
Furthermore, the magnitude of the separation of the
midpalatal suture with MSE was larger, compared to the
findings of Lione et al. [
] for a modified Hyrax-type
expander. In the present study, the expansion at the level of
the midpalatal suture was 71 and 63% at ANS (4.8 mm)
and PNS (4.3 mm), respectively, compared to the amount
of activation of the jackscrew (6.8 mm). This ratio is
higher than what has been reported by Lione et al. (43%
for ANS and 16% for PNS) [
], probably due to the
different anchorage modality of the expansion device
(boneborne versus tooth-borne). In fact, dentoalveolar tipping is
an important modification induced by tooth-borne
expanders since the expansion force is transmitted to the
maxillary bones via the dentition [
], while it is
negligible with MSE, even in late adolescents, as shown in a
recent case report .
Analyzing the transverse asymmetry of midpalatal split
(Fig. 11), on average one half of the ANS moved more
than the contralateral one by 1.1 mm. The reason why
the midpalatal suture splits with an asymmetrical pattern
is unknown. One reason could be related to external
forces, such as the presence of a unilateral crossbite that
hampers the movement of one maxilla. Another
hypothesis could be associated with circummaxillary sutures.
These sutures may not become loose in the same
proportion in both sides of the skull during RPE. Thus, one
maxillary bone could present more lateral displacement
and therefore explain asymmetrical expansion. In
addition to circummaxillary sutures, also discrepancies
in zygomatic buttress bone density and morphology can
play an important role in this phenomenon. The
movement of the anterior part of maxillary bones can affect
soft tissues in the midface during maxillary expansion
Table 5 Intra-class correlation coefficients (ICC) of the
parameters. Rt ANS right half of anterior nasal spine, Lt ANS left
half of anterior nasal spine, Rt PNS right half of posterior nasal
spine, Lt PNS left half of posterior nasal spine, Rt right, Lt left
Distance of Rt ANS from maxillary sagittal plane
Distance of Lt ANS from maxillary sagittal plane
Distance of Rt PNS from maxillary sagittal plane
Distance of Lt PNS from maxillary sagittal plane
Distance between two halves of expansion screw
], and this might lead to esthetic modifications in this
region that could become asymmetrical. The analysis of
the transverse asymmetry of midpalatal suture split was
performed for the first time in our study. Further
investigations with tooth-borne maxillary expanders and
different MARPE designs are recommended.
With regard to the pterygopalatine suture, Ghoneima
et al. in a clinical investigation conclude that the cited
suture cannot be split when tooth-borne expanders are
used for rapid palatal expansion [
]. However, MSE has
shown that the pterygopalatine suture was split, as the
pyramidal process of the palatine bone was pulled away
from the medial and lateral plates of the pterygoid
process, leaving detectable openings on the CBCT in 16
out of 30 sutures (53%) (Fig. 7). Seven patients showed
openings in both the right and left pterygopalatine
sutures, one patient in the right suture only, and one
patient in the left one only.
The average width of openings between pterygoid plates
was 1.4 and 2.2 mm for the right and left suture,
respectively. The width depends on the size of the pyramidal
process of the palatine bone that presents large variability
in shape and size among the population [
]. Also, if
partial disengagement of the pyramidal process from the
pterygoid process takes place, such in the case of a minor
movement of the maxilla, the opening is not complete
and hence presents a smaller width (Fig. 7b). In the case
of a complete disengagement, the width becomes larger
(Fig. 7a). The complete disengagement of the pyramidal
process from the pterygoid plates was the most common
finding, as it was present in 13 sutures, while the partial
disengagement was detected in 3 sutures only. From the
data above, it can be inferred that when the
pterygopalatine suture became disarticulated, it was most commonly
split bilaterally on the right and left side of the skull and
with a complete disengagement of the pyramidal process
from the pterygoid plates. The reason why the
pterygopalatine suture was disarticulated in some patients and not
in other can be related to anatomical factors such as the
size and shape of the pyramidal process that are largely
] and hence can influence the resistance to the
suture split. Other reasons can be the individual bone
density and thickness, the degree of suture interdigitation,
or complex interactions among various circummaxillary
sutures. In the present study, the patient gender and age
had no significant influence on the frequency of
pterygopalatine suture split.
The finding of an almost perfectly parallel split of the
midpalatal suture with MSE indicates a large movement
of the posterior part of the maxilla that leads to the
disarticulation of the pyramidal process of the palatine bone
from the pterygoid process of the sphenoid. Conversely,
the typical V-shaped split of the midpalatal suture in
Hyrax patients is associated with a lack of disarticulation
of the pterygopalatine suture, as reported in a clinical
]. This posterior skeletal expansion with MSE
can offer certain advantages such as improving posterior
occlusion in patients with maxillary deficiency, providing
patent nasal airway with relieve of posterior constriction.
These findings can have important implications also in the
treatment of class III patients when MSE is followed by
facemask therapy; MSE loosens the pterygopalatine suture
and can reduce its resistance to maxillary protraction. In
fact, rapid palatal expansion is a procedure commonly
utilized to enhance maxillary advancement.
The correlation between age and parameters of suture
opening was negligible, as the R2 coefficient for the
considered parameters ranged from 0.3 to 4.2%. This can be
due to the fact that the analyzed patients were at
postpubertal age, when most significant changes in suture
interdigitation have already occurred [
One limitation of the present study is the small
number of patients. The statistical analysis showed that a
minimum sample size of 15 is needed to show the
effects on sutures with at least 80% power for the
considered parameters. However, further studies with a larger
sample would be beneficial.
The novel reference planes and novel methodology
allowed for quantification of the opening of the
midpalatal and pterygopalatine sutures produced by
maxillary expansion; this method also made it possible
to evaluate the extent of transverse asymmetry of split
of the midpalatal suture.
MSE efficiently split the midpalatal suture in late
adolescents, and separation at posterior nasal spine
(4.3 mm) was about 90% of that at anterior nasal spine
(4.8 mm), leading to an almost perfectly parallel split of
the suture in the sagittal direction.
The split of the midpalatal suture was asymmetrical
in the transverse direction; on average one half of ANS
moved more than the contralateral one by 1.1 mm.
Remarkably, this study shows that the
pterygopalatine suture can be split by an orthopedic
appliance without the need of surgery in late
adolescents; MSE was able to split the pterygopalatine
suture in its lower part in 53% of the sutures, as the
pyramidal process of the palatine bone was pulled out
of the pterygoid notch of the pterygoid process.
Patient gender and age had a negligible influence on
magnitude and frequency of sutures opening for the
age group considered in the study.
ANS: Anterior nasal spine; APP: Axial palatal plane; CBCT: Cone beam computed
tomography; ICC: Intra-class correlation coefficient; IRB: Institutional Review
Board; MARPE: Micro-implant-assisted rapid palatal expansion; MSE: Maxillary
Skeletal Expander; MSP: Maxillary sagittal plane; N: Nasion; PNS: Posterior nasal
spine; RME: Rapid maxillary expansion; RPE: Rapid palatal expansion;
SARPE: Surgically assisted rapid palatal expansion; V point: Most posterior
point of the vomer; VCP: V-coronal plane
Special thanks to Stephen Tran, from UCLA Department of Bioinformatics, for
conducting the statistical analysis.
The authors declare that they have not received any sources of funding for
Availability of data and materials
Data of the present study will not be shared because the same data and
materials will be used in further publications where the analysis of different
sutures will be presented.
DC participated in the study conception, participated in the data collection
and data interpretation, elaborated the novel methodology, carried out the
measurements, constructed the tables, elaborated the figures, and wrote the
manuscript. RDM participated in the study conception, participated in the
data collection and data interpretation, conducted the literature search,
elaborated the figures, and wrote the manuscript. SMM participated in the
study conception for factors related to radiology. HCP elaborated the figures.
JM participated in the study conception for factors related to anatomy of the
sutures. CM participated in manuscript writing and figures elaboration. WM
participated in the study conception, coordinated the study, and revised the
manuscript. All authors read and approved the final manuscript.
The micro-implant-supported skeletal expander used in the present study
has been developed and used since 2003. Nowadays, it is widely used at
UCLA Orthodontic Clinic where the study was performed.
Ethics approval and consent to participate
The present retrospective study received approval from the Institutional Review
Board at University of California, Los Angeles (UCLA), IRB number 16-001662.
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