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Int J Paediatr Dent. 2020;00:1–8. wileyonlinelibrary.com/journal/ipd
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© 2020 BSPD, IAPD and John Wiley & Sons A/S.
Published by John Wiley & Sons Ltd
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INTRODUCTION
Maxillary arch expansion through a fixed appliance is a well-
known and consolidated practice in clinical orthodontics,
but current findings of ‘evidence-based dentistry’ have not
yet identified an ideal clinical expansion protocol. Recent
systematic reviews1,2 have shown that both rapid and slow
expansion protocols are clinically effective on the primary
outcome (ie, the resolution of the crossbite with a significant
increase of skeletal transversal dimension in the maxillary
transverse deficiency subjects). So, the choice of appliance
type solely based on its ability to solve maxillary constriction
issues is no longer the main selection criteria and the relevant
choice of the orthodontist should, therefore, be based on tim-
ing3,4 and on a ‘patient-oriented’ device, that can minimize
the various possible side effects, such as appliance break-
ages, functional impairments, injuries to the periodontal tis-
sues, and, of course, pain.5-12
Received: 1 July 2019
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Revised: 22 December 2019
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Accepted: 29 December 2019
DOI: 10.1111/ipd.12612
ORIGINAL ARTICLE
A multicenter, prospective, randomized trial of pain and
discomfort during maxillary expansion: Leaf expander versus
hyrax expander
AlessandroUgolini1
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GianguidoCossellu2
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MarcoFarronato2
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ArmandoSilvestrini-Biavati1
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ValentinaLanteri2
1Department of Surgical and Diagnostic
Sciences, University of Genova, Genoa,
Italy
2Department of Biomedical Surgical and
Dental Sciences, University of Milan,
Milan, Italy
Correspondence
Alessandro Ugolini, Department of
Orthodontics, University of Genoa, Largo
Rosanna Benzi 10, Pad. IV - 16132 Genova,
Italy.
Email: alessandro.ugolini@unige.it
Abstract
Background: Pain suffered by the young patient is the most frequent symptom
during orthodontic treatment and is the one that most frightens children and causes
worry in their families.
Aim: To investigate pain perception and function impairment during the first week
of activation of two palatal expansion screws.
Design: A total of 101 subjects were randomly divided into two groups: RME group
included patients treated with the standard hyrax expansion screw and LEAF group
included patients treated with Leaf Expander appliance. Pain intensity was assessed
via the Wong-Baker scale. A questionnaire on oral function impairments was also
compiled by the patients.
Results: The Pain Scale analysis showed that patients in the RME group suffered
from a significantly higher level of pain than those in the LEAF group (88.6% vs 25%,
P<.01). RME group showed highest pain indexes from day 1 to day 4 (51.4% RME
vs 9.7% LEAF suffered at least once from strong pain in the first 4days, P<.01).
Furthermore, oral functions were similarly affected in both groups.
Conclusions: Pain reported during maxillary arch expansion is influenced by clini-
cal activation protocol and by the screw type. Patients treated with Leaf Expander
reported significantly lower pain level in the first 7days of treatment.
KEYWORDS
leaf expander, maxillary expansion, pain, palatal expansion
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UGOLINI et aL.
In orthodontic daily practice, pain suffered by the young
patient is the most frequent symptom during treatment and
is the one that most frightens children and causes worry in
their families.13 Available literature shows that rapid maxil-
lary arch expansion is, among the early orthodontic therapies,
the one with the highest incidences of pain (up to 98%) as an
adverse symptom reported by patients.5-9 Pain could be re-
lated to the rapid expansion protocol, during which, for each
activation of the screw (0.2 or 0.25mm) the force expressed
can reach up to 10 pounds. 14-18
In the relevant literature, prevention and management of
pain during palate expansion is a poorly analysed topic, de-
spite being a daily occurring problem in orthodontic clinical
practice5,6,19-21; thus, the present study aims at investigating
and analysing the perception of pain and function impairment
during the first week of activation with two palatal expan-
sion screws to identify the effect of different maxillary arch
expansion protocol on the pain perception and discomfort in
young patients.
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MATERIALS AND METHODS
The present multicentric randomized study was conducted
at the Departments of Orthodontics of the Universities of
Milan and Genoa (Italy). The trial was first approved by the
Institutional Ethical Review Board (Fondazione IRCSS Ca'
Granda n° 936-1666/13) and published on Clini calTr ials.gov
(Clini calTr ials.gov Identifier: NCT03757468, https ://clini
caltr ials.gov/ct2/show/NCT03 757468). CONSORT docu-
ments, including a checklist and a flow chart, have been used
to report the findings.
One hundred and sixteen consecutive subjects with trans-
versal maxillary deficiency (intermolar width <30mm, with
or without crossbite) were randomly assigned to RME group
(treated with the standard hyrax expansion screw) or LEAF
group (treated with Leaf Expander appliance). The treating
clinician was blinded from the randomization procedure, but
because of clear differences in appliance design, blinding was
not possible during the treatment period itself. The data ex-
aminer was also blinded from the treatment protocol. Both
appliances were anchored on the second primary molars. All
subjects had a Class I or Class II dental malocclusion with
unilateral or bilateral crossbite and/or constricted maxilla
and were selected before the pubertal peak (cervical vertebral
maturation stage 1-3).
Patients with previous orthodontic treatment, hypodontia in
any quadrant excluding third molars, inadequate oral hygiene,
craniofacial syndromes, or cleft lip or palate were considered
ineligible for the study and thus duly excluded from it.
One hundred and one patients completed the study: 48
subjects were included in the RME group (23 males and
26 females, mean age 9.4years, range 6-13years) and 53
subjects in the LEAF group (25 males and 28 females, mean
age 9.1years, range 6-13years) (Table 1).
The RME group was treated with the standard hyrax expan-
sion screw anchored on second primary molars (Figure 1A).
When the appliance was in situ, the screw was initially turned
two times at chairside and then patients started the screw acti-
vation (Lancer Orthodontics) of two-quarter turns a day, one
in the morning and one in the evening (0.40mm/d) until over-
correction was achieved. Then, the RME remained in place
for approximately 9months.
The LEAF group was treated with Leaf Expander appliance
(Figure 1B) anchored on the second primary molars. A detailed
appliance description was reported elsewhere.22,23 Briefly, de-
sign of the Leaf Expander is similar to that of a conventional
rapid palatal expander with a double nickel-titanium leaf spring
instead of a midline jackscrew. The screws deliver a maximum
expansion of 6 or 10mm, by activating (compressing) the leaf
spring, which generates a constant force of 450g. The screw
was pre-activated in the laboratory to deliver the first 3mm
expansion, and then, re-activation was performed in the office
by 10-quarter turns of the screw per month until expansion has
been completed. One-quarter turn corresponds to 0.1 mm of
activation (10 activations of the screw generate 1mm of acti-
vation). The Leaf Expander was activated by the clinician only
and requires no compliance from the patients and their par-
ents. Active expansion and overcorrection generally take about
5-6 months after which the Leaf Expander should be main-
tained passively in place for 3months and then removed (after
a total time of 9months).
A questionnaire regarding oral/masticatory function
and a Wong-Baker Faces Pain Scale with a complemen-
tary numeric rating scale from 0 to 10 were compiled by
Why this paper is important to paediatric
dentists
• Pain is the most frequent symptom during maxil-
lary arch expansion treatment and is the one that
most frightens children and causes worry in their
families.
• More than 50% of patients treated with the rapid
maxillary expander reported strong pain at least
once in the first 4days of treatment, whereas in
the Leaf Expander group, <10% of the subjects
suffered at least once from a level of pain indi-
cated as strong and the first 2days only.
• Pain suffered during maxillary arch expansion is
influenced by the choice of screw and activation
protocol, and Leaf Expander proved itself as an
effective and efficient expansion appliance in the
prevention of pain.
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UGOLINI et aL.
each subject. Pain intensity was assessed using the Wong-
Baker scale24 from the first to the seventh day of the screw
activation, reporting a double registration per day (in the
morning and evening). The Wong-Baker scale is a tool for
self-assessment of pain intensity and is used in children
from 3years of age. The emojis range from the most smil-
ing, corresponding to ‘no pain perceived’, up to the cry-
ing emoji, corresponding to ‘worst pain imaginable’.9 Each
emoji is also paired with a number, from 0 to 10, which
coincides with the intensity of the pain. Verbal instructions
were given to the parent and child about how to correctly
assess pain. The child's pain response was measured 5min-
utes after each turn.5 Questionnaires also asked the patients
about eventual difficulties in swallowing and speaking, hy-
persalivation, analgesic consumption, and pain localization
(anterior teeth, anchored/posterior teeth, palatal vault, and
head) (Table 2).
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Statistical analysis
Shapiro-Wilk's test showed that pain intensity data were
normally distributed, and parametric statistics were thus
applied. Descriptive statistics, median value, standard
deviation, and confidence interval (95% CI) were calcu-
lated. Differences between groups in pain intensity were
tested with parametric Student's t test, and risk ratio (RR)
analysis was performed to assess the questionnaire data.
Probabilities of <.05 were accepted as significant in all sta-
tistical analyses.
The sample size was calculated ‘a priori’ to obtain a sta-
tistical power of the study >.85 at an α of .05, using the mean
values and standard deviations of pain intensity during maxil-
lary arch expansion therapy found by Baldini and co-authors
(‘overall pain’: mean 0.80± 1.22 and 1.88±2.15)9 and re-
sulted in a minimum of 47 subjects for each group. Moreover,
TABLE 1 Flow of participants
Assessed for eligibility (n = 116)
Excluded (n = 0)
♦Other reasons (n = 0)
Analysed (n = 53)
♦Excluded from analysis (give reasons) (n = 0)
Lost to follow-up
♦Notcomplete the questionnaire (n = 3)
Allocated to intervention (LEAF) (n = 58)
Received allocated intervention (n = 56)
♦
♦
Did not receive allocated intervention (n = 2,
missed appointment)
Lost to follow-up
♦Not complete the questionnaire (n = 2)
♦Not follow the prescribed activation protocol) (n = 8)
Allocated to intervention (RME) (n = 58)
♦Received allocated intervention (n = 58)
♦Did not receive allocated intervention (give
reasons) (n = 0)
Analysed (n = 48)
♦Excluded from analysis (give reasons) (n = 0)
Allocation
Anal
y
sis
Follow-Up
Randomized (n = 114)
Enrollment
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UGOLINI et aL.
a dropout of 20% was considered and the final sample size
comprised a minimum of 58 subjects for each group. The ef-
fect size (ES) coefficient (d)25 was also calculated. An ES
of .2-.3 might be a ‘small’ effect and thus a small clinically
significant difference, about .5 a ‘medium’ effect, and .8 to
infinity a ‘large’ effect.
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RESULTS
Three patients in the LEAF group and two patients in the
RME group did not complete the questionnaire, and eight
subjects, all in the RME group, did not follow the pre-
scribed activation protocol at home. Two subjects in the
LEAF group missed the appointment and did not receive
the allocation. Fifteen subjects were thus excluded from
the study and the final sample comprised 101 subjects.
Crossbites and traversal maxillary discrepancy were en-
tirely corrected in 100% of the subjects at the end of the
expansion active phase.
The Wong-Baker Faces Pain Scale analysis showed
that patients in the RME group suffered from a signifi-
cant generalized sensation of pain during the first week
of screw activation compared to those in the LEAF group
(88.6% vs 25%, P< .01); moreover, in the RME group
25.2% of the patients reported analgesic consumption
(Table 3). Table 4 reports the pain perceived in the first
7 days of activation from both groups: patients treated
with the rapid maxillary expander reported a statistically
significant higher amount of pain in the first 4 days of
treatment (Table 4). In detail, RME group reported higher
pain indexes recorded on the Wong-Baker scale from day
1 to day 4 with a 51.4% of the patients indicated they suf-
fered at least once from a strong pain in the first 4days.
Patients treated with the Leaf Expander have instead a
statistically lower pain where only 9.7% of the subjects
of the LEAF group suffered from a level of pain indicated
as strong and in any case limited to the first 2days after
cementation and activation of the device, whereas the re-
maining 90% of the subjects report that they did not per-
ceive any pain in the first 2days of therapy. From the fifth
to the seventh day, the amount of pain reported was small
and did not differ significantly between the two groups
(Table 4). There were also no differences between the two
centres in the analysed variables.
Overall high scores of discomfort values in different oral
functions were reported (more than 80% of the sample re-
ported hypersalivation and difficulty in swallowing and
speaking) but did not differ between the groups (Table 3).
Subjects treated with RME have a significantly higher risk
of suffering pain from posterior teeth (RR=2.54, 95% IC:
1.51-4.28, P<.001), incisors (RR=3.3, 95% IC: 1.14-9.58,
P=.02), and taking pain medications (RR=11.14, 95% IC:
1.62-90.60, P<.01).
FIGURE 1 (A) Hyrax expansion appliance; (B) Leaf Expander
appliance
(A)
(B)
TABLE 2 Self-reported questions concerning pain and
discomfort, analgesic consumption in the first week of treatment
(modified from Feldman and Bazagani23)
1—Pain intensity
Do you now have pain? And for how many days?
Do you have pain from the molars?
Do you have pain from the incisors?
Do you have pain from the upper jaw?
Do you have pain from the palate?
Do you have pain from head?
Do you have pain during appliance activation?
2—Analgesic consumption
Have you used analgesics for pain from your jaws, teeth, or face?
If yes, what kind of analgesic and dosage did you use?
3—Jaw function impairment
If you have pain or discomfort in your teeth and jaws, how much
does that affect
Speaking
Salivation (hypersalivation)
Swallowing
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UGOLINI et aL.
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DISCUSSION
From a clinical point of view, correction of crossbites and
traversal maxillary discrepancy were achieved in all pa-
tients with both appliances. The jackscrew and the shape
memory leaf spring expander have different methods of
activation: the jackscrew or expansion screw (eg, hyrax) is
a telescoping appliance that requires several patient activa-
tions to achieve the maxillary arch expansion. The memory
leaf springs instead, due to their superelastic nature, re-
quired only a few activations or no activation at all because
of its reliance upon elastic restoration forces to achieve the
desired expansion. In the jackscrew, to a given amount of
screw turn corresponds a determined amount of expansion
(from 0.20 to 0.25 mm), so this allows clinicians to cal-
culate the number of activations required to achieve the
desired expansion. But it also suffers from several disad-
vantages because with each subsequent jackscrew activa-
tion the maxilla is subjected to a rapid increase in forces
and this is not only uncomfortable for the patient, but it
has also been suggested that high magnitude forces (up to
10 pounds) may result in a less pronounced physiologic
expansion of the suture.26 Another disadvantage for this
type of screw activation method is that it requires the pa-
tient (and parents) compliance to achieve the expansion:
in the present study, we had to exclude 14% (eight out 58)
of the subject of the RME initial sample because they did
not follow the recommended activation protocol in the first
week.27 Other complications during treatment (besides
those reported in the questionnaire) included mainly ap-
pliance breakage and decementation. All the complications
reported were lower in the LEAF group.
The main advantage with the shape memory leaf spring
is the continuous force application, similar to those of su-
perelastic NiTi wires. In fact, superelasticity is ‘the transfor-
mation from austenitic to martensitic that occurs by stress
application within a temperature range and is manifested by a
flat or nearly flat plateau in a force-deflection curve’.28 This
superelastic behaviour minimizes the number of rapid force
increments exerted on the tissue (and their magnitude as well)
which may lead to a more physiologic expansion and to an
increased feeling of comfort for the patients, as reviewed by
Romanyk et al.26 One disadvantage of the leaf-type activation
method is that longer time is required to achieve the expan-
sion (up to 6months), but the total time amount (9 months,
active expansion plus retention period) is equal to that with
rapid maxillary arch expansion.
The results of the present study on the pain perceived
during the maxillary arch expansion reflected the differences
between appliances in their biomechanical work and in the
release of the forces; in fact, overall pain during the first week
of the screw activation was significantly higher in the RME
group compared to the LEAF group (88.6% vs 25%, P=.01).
In detail, the subjects treated with the Leaf Expander reported
low pain level in the first 7days of activation (the appliance
was pre-activated to deliver the first 3 mm expansion) and
9.7% of the subjects suffered from a pain indicated as strong
at least once for the first 2days only after activation (the re-
maining 90.3% of subjects reported that they did not experi-
ence pain in the first 2days of therapy). Instead, the patient
in the RME (the screw activation was about 3mm in a week)
reported high pain level in the first 4days with a 51.4% (max-
imum peak in the second day) of the subjects that indicated
they suffered from severe pain at least once in the first 4days;
moreover, 25.2% of the patients in the RME group reported
analgesic consumption.
The results reported in the RME group were in accord
with those found in the literature 5,8,9,20,21 that found that
rapid maxillary expander was generally well tolerated with a
peak of pain perceived during the first 4days of the screw ac-
tivation with a complementary analgesic consumption (usu-
ally paracetamol or ibuprofen).21
TABLE 3 Discomfort and analgesic consumption in the first week of therapy
RME (%) LEAF (%)
Relative risk
ratio 95% CI Significance level
Difficulty in swallowing 79.2 84.9 0.93 0.77-1.12 .74
Hypersalivation 81.3 79.2 1.02 0.84-1.24 .8
Difficulty in speaking 87.5 92.5 0.94 0.82-1.07 .41
Pain—posterior teeth 62.5 24.5 2.54 1.51-4.28 <.001***
Pain—incisors 25.0 5.7 3.31 1.14-9.58 .02*
Pain—palatal vault 12.5 3.8 3.12 0.70-15.63 .13
Pain—head 8.3 0.0 4.43 0.51-38.15 .17
Analgesic consumption 25.2 0.0 11.14 1.62-90.60 .01**
*P=.05;
**P=.01;
***P=.001.
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UGOLINI et aL.
TABLE 4 Pain intensity reported on the Wong-Baker Faces Pain Scale; Student's t test for independent samples
Day 1 M Day 1 E Day 2 M Day 2 E Day 3 M Day 3 E Day 4 M Day 4 E Day 5 M Day 5 Day 6 M Day 6 E Day 7 M Day 7 E
RME group
Mean 1.9 2.1 2.7 2.9 2.4 2.2 1.6 1.5 0.9 1.0 0.9 0.7 0.7 0.9
SD 1.0 1.1 1.2 1.1 1.0 1.0 1.0 1.1 1.2 0.9 0.9 0.8 0.5 0.6
CI 95% 0.2 1.8 2.3 2.6 2.1 1.9 1.3 1.1 0.6 0.7 0.6 0.5 0.5 0.8
0.3 2.4 3.1 3.2 2.7 2.5 1.8 1.8 1.3 1.3 1.1 0.9 0.9 1.1
LEAF group
Mean 0.8 1.3 1.2 1.2 0.8 0.8 0.7 0.7 0.6 0.7 0.6 0.6 0.6 0.7
SD 0.9 0.8 0.8 0.7 0.6 0.6 0.5 0.6 0.9 0.8 0.7 0.9 0.6 0.5
IC 95% 0.6 1.1 1.0 1.0 0.6 0.6 0.7 0.5 0.4 0.5 0.4 0.3 0.4 0.2
1.1 1.5 1.4 1.4 0.9 0.9 0.5 0.8 0.9 0.9 0.8 0.9 0.8 0.7
Test T
RME vs LEAF 0.001*** 0.020** 0.000*** 0.000*** 0.000*** 0.000*** 0.000*** 0.000*** 0.15 0.08 0.07 0.55 0.36 0.08
Cohen effect size 1.7 L 0.8 L 1.4 L 1.8 L 1.9 L 1.7 L 1.1 L 0.9 L – – – – – –
Note: M=morning questionnaire registration, E=evening questionnaire registration. Cohen effect size: S indicates small clinical significance; M, medium clinical significance; L, large clinical significance.
*P=.05;
**P=.01;
***P=.001.
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UGOLINI et aL.
To our knowledge, no other study investigated the pain in-
tensity and discomfort during maxillary arch expansion with
a memory leaf spring, and based on the present results, it can
be postulated that statistically significant differences in the
perception of pain found during the active phase of expan-
sion between RME and LEAF group were due to the different
biomechanical work carried out by the screws, which release
the force generated by activation with different patterns, as
reviewed by Romanyk et al.26
The LEAF screw is designed to compress a double nick-
el-titanium leaf spring that recovers its original shape during
deactivation, resulting in a calibrated expansion of the upper
arch.21,22 This slow and continuous activation significantly re-
duces the mechanical forces transmitted to the bone and sutural
complex, consequently decreasing the inflammatory response
and maintaining tissue integrity during repositioning and re-
modelling of the midpalatal suture, as postulated by Arndt.29
It has been observed that the forces generated by the
jackscrews, which can reach up to 10 pounds per turn,13,14
produced a series of reactions characterized by tissue dis-
placement, deformation, and development of cellular stress in
the palatine suture area with the formation of exudates, fibro-
blasts death, collagen fibres disruption, and acute inflamma-
tion.30 Human and animal studies have shown that following
a rapid expansion of the palatal suture, a disorganized and
highly vascularized connective inflammatory tissue is cre-
ated, which acts as the main receptor of the pain perceived
during the expansion.14,15,17 The transmission of the slow
and continuous force generated by the nickel-titanium screw
inhibits the establishment of these inflammatory processes
with the clinical effect of a limited and negligible perception
of pain during appliance activation, unlike the level of pain
reported with the traditional screw expander. To corroborate
this hypothesis, a significantly higher risk of suffering from
pain and tension in the anterior and in the anchored/posterior
teeth was found in the RME group only. The main limitation
of the present study is that the skeletal effects of the Leaf
Expander on the midpalatal suture have not yet been clari-
fied, even if some promising results were recently published
as reported by Manzella et al31 which found a mild sutural
disruption after Leaf Expander treatment. Anyway, our anal-
ysis did not evaluate the skeletal effects of the appliances and
further carefully designed studies taking into account the su-
tural opening are necessary to support this hypothesis. So,
based on our results, we can conclude the Leaf Expander is
an effective pain-free and compliance-free alternative treat-
ment for patients with maxillary arch constriction.
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CONCLUSION
Pain suffered during maxillary arch expansion is influ-
enced by the choice of screw and activation protocol, and
the use of continuous force through the nickel-titanium
spring allows avoiding the worst levels of pain in the first
7days of activation. Leaf Expander proved itself an effec-
tive and efficient expansion appliance in the prevention of
pain.
CONFLICT OF INTEREST
Alessandro Ugolini, Gianguido Cossellu, Marco Farronato,
Armando Silvestrini-Biavati, and Valentina Lanteri declare
that they have no conflict of interest.
AUTHORS' CONTRIBUTIONS
AU contributed to the design of the study, analysis, and in-
terpretation of data and drafted the manuscript; GC contrib-
uted to acquisition and interpretation of data and critically
revised the manuscript; MF contributed to interpretation of
data; VL contributed to acquisition and interpretation of data;
and ASB contributed to conception and design of the study
and critically revised the manuscript.
ORCID
Alessandro Ugolini https://orcid.
org/0000-0002-2062-6014
Gianguido Cossellu https://orcid.
org/0000-0001-6442-5591
Marco Farronato https://orcid.
org/0000-0002-6209-9873
Valentina Lanteri https://orcid.
org/0000-0003-2191-8673
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How to cite this article: Ugolini A, Cossellu G,
Farronato M, Silvestrini-Biavati A, Lanteri V. A
multicenter, prospective, randomized trial of pain and
discomfort during maxillary expansion: Leaf expander
versus hyrax expander. Int J Paediatr Dent.
2020;00:1–8. https ://doi.org/10.1111/ipd.12612