Mandibular response after rapid maxillary expansion in class II growing patients: a pilot randomized controlled trial
Lione et al. Progress in Orthodontics
Mandibular response after rapid maxillary expansion in class II growing patients: a pilot randomized controlled trial
Roberta Lione 0 1
Valerio Brunelli 0 1
Lorenzo Franchi 2 4
Chiara Pavoni 0 1
Bernardo Quiroga Souki 3
Paola Cozza 0 1
0 Department of Dentistry UNSBC , Tirana , Albania
1 Department of Clinical Sciences and Translational Medicine, University of Rome “Tor Vergata” , Viale Oxford, 81, 00133 Rome , Italy
2 Department of Surgery and Translational Medicine, University of Florence , Florence , Italy
3 School of Dentistry, Orthodontics, Pontifical Catholic University of Minas Gerais , Belo Horizonte , Brazil
4 Thomas M. Graber Visiting Scholar, Department of Orthodontics and Pediatric Dentistry, School of Dentistry, The University of Michigan , Ann Arbor, MI , USA
Background: The aim of this pilot randomized controlled trial (RCT) was to evaluate the sagittal mandibular response induced by rapid maxillary expansion (RME) therapy in mixed dentition patients with class II malocclusion, comparing the effects of bonded RME and banded RME with a matched untreated class II control group. Methods: This RCT was designed in parallel with an allocation ratio of 1:1:1. The sample consisted of 30 children with a mean age of 8.1 ± 0.6 years who were randomly assigned to three groups: group 1 treated with bonded RME, group 2 treated with banded RME, and group 3 the untreated control group. All patients met the following inclusion criteria: early mixed dentition, class II molar relationship, transverse discrepancy ≥ 4 mm, overjet ≥ 5 mm, and prepubertal skeletal maturity stage (CS1-CS2). The expansion screw was activated one quarter of a turn per day (0.25 mm) until overcorrection was reached. For each subject, lateral cephalograms and plaster casts were obtained before treatment (T1) and after 1 year (T2). A randomization list was created for the group assignment, with an allocation ratio of 1:1:1. The observer who performed all the measurements was blinded to group assignment. The study was single-blinded in regard to statistical analysis. Results: RME was effective in the correction of maxillary deficiency. Class II patients treated with both types of RME showed no significant improvement of the anteroposterior relationship of the maxilla and the mandible at both skeletal and occlusal levels. The acrylic splint RME had significant effects on reducing the skeletal vertical dimension and the gonial angle. Conclusions: The orthopedic expansion did not affect the sagittal relationship of class II patients treated in the early mixed dentition when compared with the untreated control group. Additional studies with a larger sample are warranted to elucidate individual variations in dento-skeletal mandibular response to the maxillary expansion protocol in class-II-growing patients. Trial registration: ClinicalTrials.gov NCT03159962.
Rapid maxillary expansion; Mandibular response; Class II malocclusion; Growing subjects
Class II malocclusions are commonly observed in
orthodontic patients [
]. During treatment planning among
the several dento-skeletal pattern combinations of class
II malocclusion, it is important to consider the maxillary
transverse deficiency, which is often overlooked [
Tollaro et al. [
] showed an underlying posterior
interarch transverse discrepancy of 3 to 5 mm in subjects in
early mixed dentition with class II malocclusions
without posterior crossbites in centric occlusion. When these
class II patients are asked to posture their lower jaw
forward in a class I molar relationship, this transverse
discrepancy (i.e., maxillary constriction) can be observed
]. It was postulated that in these subjects, the
mandible is kept in a distal position relative to centric
relation because the constricted maxilla is holding it
]. The presence of a primitive transverse
discrepancy between the dental arches induces a backward
position of the mandible, as the occlusal goal is to obtain
the highest number of functional contacts .
As reported by several authors [
], widening the
maxilla with rapid maxillary expansion often leads to
spontaneous forward posturing of the mandible during
the retention period. The orthopedic expansion removes
occlusal interferences, allowing the mandible to posture
forward, thus improving the sagittal relationships [
The mandibular arch acts as a “foot” that moves forward
after the “shoe” is widened [
]. Caprioglio et al. reported
that patients with smaller mandibular length and more
acute superior gonial angles are expected to show greater
improvement in class II molar relationship .
However, the effectiveness of rapid maxillary
expansion (RME) on the sagittal dental or skeletal parameters
is still controversial because very little has been written
regarding the behavior of anteroposterior mandibular
changes in class-II-growing subjects who underwent
RME as the phase 1 treatment intervention. The
reported significant occlusal improvement could be
attributed to other reasons, i.e., skeletal growth or the use of
additional appliances during the transition from mixed
to permanent dentition. Moreover, the majority of the
] show some limits: they are not
], they are not prospective, and they have no
control group or they use patients from growth studies
as a source for the control group.
Considering that it was not possible to estimate from
previous studies the standard deviation to be used for
sample size calculation of the main trial with special
regards to the type of intervention and observation
intervals, the primary objective of the present investigation was
to conduct a pilot randomized controlled trial (RCT)
evaluating the changes in the anteroposterior mandibular
position induced by bonded or banded RMEs compared
with an untreated class II control group.
The Consolidated Standards of Reporting Trials
(CONSORT) checklist was used as a guideline for conducting
and reporting this trial [
]. The present pilot RCT was
designed as a prospective three-arm parallel group
randomized clinical trial with a 1:1:1 allocation ratio.
The study was approved by the Ethics Committee at the
University of XXXX, (protocol number 130/14), and
informed consent was obtained from the patients’ parents.
The trial was registered on ClinicalTrials.gov (registration
A total of 30 subjects with a mean age of 8.1 ± 0.6 years
(range 6.6–9.1 years) who sought for an orthodontic
treatment, were enrolled in the Department of
Orthodontics at the University of XXXX. All children met the
following inclusion criteria: early mixed dentition with
first molars fully erupted, class II malocclusion (full-cusp
or end-to-end molar relationships), negative posterior
transverse interarch discrepancy ≥ 4 mm [
], overjet ≥
5 mm, and prepubertal stage of development (CS1–CS2
in cervical vertebral maturation) [
]. Exclusion criteria
included previous orthodontic treatment, extracted or
congenitally missing teeth, craniofacial syndromes or
clefts, and use of additional orthodontic devices during
the observation period.
Patients enrolled in the study were blindly assigned in
three groups. In the first group (TG1), all subjects
underwent a standardized treatment protocol with bonded RME
with a 13-mm screw (A0620-13, Leone, Sesto Fiorentino,
Firenze, Italy). The acrylic splints of the bonded expander
extended from the first deciduous molars through the first
permanent molars (Fig. 1a). In the second group (TG2), all
children were treated with a banded RME in the form of a
butterfly palatal expander with a 13-mm screw (A0620-13,
Leone, Sesto Fiorentino, Firenze, Italy) [
through bands on the second deciduous upper molars
(Fig. 1b), while subjects assigned to the third group served
as the untreated control group (CG). Both TGs were
consecutively treated by one clinician (R.L). The expansion
screw was activated one quarter of a turn per day (0.25 mm
per turn) until the palatal cusps of the maxillary posterior
teeth approximated the lingual cusps of the mandibular
posterior teeth. The expander was kept in place as a
passive retainer for 8 months. After expander
removal, patients were followed without performing any
additional treatment for 4 months.
For each treated patient, standard lateral
cephalometric radiographs were obtained before treatment (T1) and
after 1 year (T2) to evaluate the T2–T1 dento-skeletal
changes. The CG was followed up without treatment for
1 year and had lateral cephalograms before (T1) and
after a 1-year interval (T2).
The cephalograms were scanned using a professional
table scanner (Epson Perfection V700 Photo, CA, USA),
with resolution set to 150 dots per inch (dpi) gray scale.
Cephalograms were digitized by one investigator (V.B.).
A customized digitization regimen and analysis
(Viewbox 3.1; dHAL Software, Kifissia, Greece) were used
for all the cephalograms that were examined in this
study. All lateral cephalograms were at a
magnification of 0%. The examiner who analyzed the lateral
cephalograms of all children at T1 and T2 was
blinded to the origin of the films and the group to
which each subject belonged.
The cephalometric reference points, lines, and angles
used in the analysis are shown in Fig. 2.
The primary outcome was the change in the position
of point Pogonion to the Nasion perpendicular (Pg to
Nperp). Secondary outcomes were considered: (1)
occlusal improvement of class II molar relationship and (2)
treatment effects on a vertical dimension.
A sample size for this pilot trial was calculated
according to the method proposed by Whitehead et al. [
For a standardized effect size of 1 (a clinically relevant
change of 2.0 mm with a combined SD of 2.0 mm
derived from Guest et al. [
]) for the primary outcome
variable Pg to Nperp, a sample size of 10 subjects per
group was required for a type I error rate of 5% and a
power of 80%.
Allocation of patients to the three groups was
determined by a computer-generated randomization list using
Rv.0.1 software [
] and by a block size of 4 (Fig. 3).
Then, the allocation information (randomization results)
was concealed in opaque and sealed envelopes by the
The observer who performed all the measurements
was blinded to the group assignment. The study was
blinded in regard to the statistical analysis: blinding was
obtained by eliminating from the elaboration file every
reference to patient group assignment.
To determine the reliability of the method, 15
radiographs chosen at random were traced and digitized by
the same investigator on two separate occasions at least
1 month apart. A paired t test was used to compare the
two measurements (systematic error). The magnitude of
the random error was calculated by using the method of
moment’s estimator (MME) [
Exploratory statistics revealed that not all
cephalometric variables were normally distributed
(KolmogorovSmirnov test) with equality of variances (Levene’s test).
Kruskal-Wallis test or ANOVA with Tukey’s post-hoc
tests were used to compare the T2–T1 changes in the
three groups. All changes were considered significant
at P < 0.05.
Fig. 2 Cephalometric points, lines, and angles used in analysis: SNA
angle (maxillary sagittal position), SNB angle (mandibular sagittal
position), ANB angle (maxillomandibular sagittal discrepancy), point
Pg to Nasion perpendicular (sagittal mandibular position relative to
Frankfurt plane), mandibular total length (Co-Gn), SN to mandibular
plane (Me-Go), gonial angle (Ar-Go-Me), lower anterior facial height
(ANS-Me), overjet, overbite; molar relationship
All statistical computations were performed with SPSS
software (Statistical Package for the Social Sciences,
SPSS, Version 12, Chicago, IL, USA).
In this pilot trial, where 31 patients were randomly
assigned to the interventions, one drop-out was
observed in the CG. The final sample that received the
intended treatment and analysis was 30 patients (Fig. 3).
The recruitment started in December 2014 and the
observation period ended in June 2016.
The baseline age was 8.1 ± 0.6 years (range 6.6–9.1 years).
No significant between-group differences were found at T1
for any of the cephalometric variables (Table 1).
No systematic error was found between the repeated
cephalometric values. For the cephalometric variables, the
random error varied from 0.21° (SNA angle) to 0.32° (gonial
angle) for angular measurements and from 0.16 mm
(CoGn) to 0.24 mm (overbite) for linear measurements.
As for the T2–T1 changes (Table 2), no statistical
significant differences were pointed out for the sagittal position of
the maxilla and the mandible at the end of the treatment
with RME with respect to the untreated CG. The detectable
significant changes occurred in TG1 with greater decreases
of both facial divergency (TG1 vs TG2, − 1.1°; TG1 vs
CG, − 1.5°) and gonial angle (TG1 vs TG2, − 1.3°; TG1 vs
CG, − 1.5°). Treatment with RME did not affect
significantly either dental measurements or molar relationship
with respect to the untreated controls.
Additional studies with a larger sample are warranted to
elucidate individual variations in dento-skeletal mandibular
response to the maxillary expansion protocol in
class-IIgrowing subjects. However, the results of the present pilot
RCT showed that there should be no concerns about
the generalizability of results from a future definitive
RCT conducted in an identical way to the pilot trial
with a larger sample.
Transverse maxillary deficiency deserves to be
included in the distinctive occlusal pattern of class II
]. Therefore, the aim of the present pilot
RCT was to evaluate the sagittal mandibular response
induced by RME therapy in mixed dentition patients
with class II malocclusion, comparing the effects of
bonded RME and banded RME with a matched
untreated class II control group.
Several studies [
10, 19, 20
] investigated possible
spontaneous correction of class II malocclusion after
orthopedic maxillary expansion. Wendling et al. [
et al. [
], and Farronato et al. [
] reported for all class
II patients a statistically significant decrease in ANB
angle obtained during treatment as a result of a
significant increase in SNB angle [
10, 19, 20
As suggested by McNamara [
], during the
postRME period, mandibular anterior displacement may be
observed because of the overexpansion of the maxilla.
Thus, the spontaneous correction of patients with a
tendency toward a class II malocclusion cannot be expected
during the active expansion period but rather during the
retention period. For this reason, in the present study,
the mean T2–T1 interval was 12 months.
On the contrary, Chung et al. [
] and Volk et al. [
demonstrated that RME protocol did not predictably
improve the occlusal relationship in class II prepubertal
patients, not supporting the “foot in the shoe” theory.
The results reported in literature [
7, 8, 19–26
] are not
only contradictory, but also frequently based on deficient
methodology, or lack of clinical relevance. More solid
scientific evidence based on reliable methods and proper
study designs is still lacking to test whether dental
correction or mandibular anterior shift and/or
supplementary growth takes place after RME.
In order to have a better predictability of the
effectiveness of any therapy, it is advisable to consider not only
controlled groups, but also randomization [
Some authors [
] reported significant occlusal sagittal
improvements during the transition from mixed to
permanent dentition. That might have helped in occlusal
anteroposterior changes at the end of RME therapy. To skip
this factor, only early mixed dentition patients were
enrolled at the beginning of the study. The phase of dentition
was stable during the whole observational period referring
any outcomes to mandibular growth or anterior shift.
To our knowledge, the present study is the first pilot
RCT to analyze specifically whether maxillary expansion
spontaneously corrects or improves a class II
malocclusion. In the present investigation, the treatment with
RME did not affect significantly the anteroposterior
skeletal mandibular response as well as the molar relationship
with respect to the CG. The results indicated neither
mandibular shift nor supplementary growth occurred after
RME. Positive T2–T1 change greater than 1 mm for the
value Pogonion to N-perpendicular was considered as a
clinically significant mandibular advancement. Three
patients treated with bonded RME showed favorable changes
of sagittal mandibular position (Pg to NPerp > + 1 mm),
compared with only 1 of the 10 patients treated with
banded RME and with only 1 of the 10 untreated subjects.
This difference was not significant (P = 0.405), according
to Fisher’s exact probability test.
However, statistically significant changes were observed
in the TG1 as a result of the acrylic splint, with a greater
reduction of both facial divergency (TG1 vs TG2, − 1.1°;
TG1 vs CG −1.5°) and gonial angle (TG1 vs TG2, − 1.3°;
TG1 vs CG, − 1.5°) when comparing the TG1 both with
the TG2 and the CG.
In bonded RME, the acrylic coverage of the occlusal
surfaces, acting as a bite block, inhibited posterior dental
extrusion and might provide some intrusion of posterior
]. Bonded RME is then suggested for correction
of the transverse dimension in patients, who need to
better control the vertical growth pattern minimizing
tipping of the posterior maxillary teeth [
23, 24, 29, 30
Our results are in contrast with those reported by Guest
et al.  and McNamara et al. [
]. In these large-scale
investigations, the improvement in molar relationship in
RME group were of over 1 mm in 92% of the expansion
patients and over 2 mm in almost 50% of them without
definitive class II mechanics incorporated into the
protocol. When the authors compared the treated group with
the historical control group, the net molar relationship
improvement was 1.7 mm, mainly due to a significant
increase in mandibular length. However, the mean
observation interval in the previous studies was of 4 years,
while in the present study all treated and untreated
subjects were prospectively evaluated after 1 year.
Class II patients in early mixed dentition treated with
either bonded or banded RME showed no significant
improvement of the anteroposterior relationship of the
maxilla and the mandible at both skeletal and occlusal
level when compared with an untreated control group.
The treatment with bonded RME determined a
reduction of the facial divergency and of the gonial angle
when compared both with subjects treated with the
banded RME and with untreated subjects.
The future definitive RCT will be planned with a
larger sample without any changes from the pilot trial.
RL designed the study protocol, treated the patients, and revised the
manuscript critically for important intellectual content. VB acquired the data,
performed the tracings, and drafted the manuscript. LF revised the
manuscript and the statistical analysis. CP participated in the data acquisition
and manuscript drafting. BQS helped in the interpretation of the statistical
analysis and the results and drafting of the manuscript. PC coordinated the
research project and revised the manuscript critically for important
intellectual content and English language usage. All authors read and
approved the final manuscript.
Ethics approval and consent to participate
Signed informed consent for releasing diagnostic records for scientific
purposes was available from the parents of the patients. The protocol was
reviewed and approved by the Ethics Committee of the University of Rome
“Tor Vergata” (Rome, Italy) (protocol number 130/14), and procedures
followed adhered to the World Medical Organization Declaration of Helsinki.
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
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