Clinical effectiveness of chin cup treatment for the management of Class III malocclusion in pre-pubertal patients: a systematic review and meta-analysis
Maria I Chatzoudi
Moschos A Papadopoulos
Department of Orthodontics, School of Dentistry, Aristotle University of Thessaloniki
Kalamaria 55132 Thessaloniki
Background: Chin cup is regarded as the oldest orthodontic appliance for the management of Class III malocclusion. To assess its clinical effectiveness in pre-pubertal patients, a meta-analysis on specific cephalometric values is attempted. Methods: Detailed electronic and hand searches with no restrictions were performed up to July 2014. Only randomized controlled trials (RCTs) and cohort studies, i.e. prospective controlled trials (pCCTs) and (retrospective) observational studies (OS), were included. Analyses were performed by calculating the standard difference in means and the corresponding 95% confidence intervals, using the random effects model. Data heterogeneity and risk of bias assessment of the included studies were also performed. Study selection, data extraction and risk of bias assessment were performed twice. The level of significance was set at P 0.05 for all tests, except for heterogeneity (P 0.1). Results: Seven treated groups from five studies (no RCTs, four pCCTs, one OS) were eligible for inclusion, assessing only the short-term occipital pull chin cup effects. In total, 120 treated patients (mean age: 8.5 to 11 years) compared with 64 untreated individuals (mean age: 7.3 to 9.89 years) were assessed by means of 13 cephalometric variables. The overall quality of these studies was low to medium. In comparison to untreated individuals, the SNB and gonial angles decreased significantly following chin cup use, whereas ANB, Wits appraisal, SN-ML, N-Me and overjet increased. For the rest of the variables, no statistically significant differences were detected. Conclusions: Although the occipital chin cup affects significantly a number of skeletal and dentoalveolar cephalometric variables, indicating an overall positive effect for the treatment of Class III malocclusion, data heterogeneity and between-studies variance impose precaution in the interpretation of the results.
A number of appliances are available for the treatment
of Class III malocclusion [1-6]. Among them, chin cup
holds a premium position as a traditional appliance for
the early orthopaedic treatment of Class III malocclusion
[3,7,8]. However, a thorough and in-depth investigation
of the literature reveals controversies and contradictions
regarding both its appropriate use and its clinical
The suggested appropriate age for use varies from 4
 to 14  years of age. Patients' sex could also be a
factor to consider, since females mature earlier than males.
Force magnitude should be small in young patients [3,4]
and increase gradually, but the suggested force at the
centre of the chin cup ranges from 150 g  up to 1,200 g
. Suggested hours of wear also range between 8  and
18 h per day . Further, concomitant use of additional
Records identified through hand searching in the
journals: AJODO, AO, EJO, JOO, and OCR
Sum of articles identified (n=1308)
Records screened on basis of title and
abstract, after removal of duplicates
Full-text articles to be assessed for
Full-text articles assessed for eligibility
Records excluded from title, abstract or
non-existing/non English abstract
Records excluded from hand searched
articles for non English abstract
Records excluded for various reasons
according to the exclusion criteria
Figure 1 Flow diagram of the retrieved studies through the selection process.
appliances like maxillary protraction appliances could
significantly affect the results [10,12,13].
Clinical results achieved with the chin cup also
constitute a matter of debate. Retardation or even sometimes
restriction of mandibular growth is supported by some
authors [2,4,5], while such effects are questioned by
Since no standard protocol has been followed from
various clinicians, it is evident that the effectiveness of
the chin cup varies according to the exact and
individualized way of use and it ranges substantially between
investigators from minimal  to great [16,17]. Although
the approach has been investigated through the years,
there is still little evidence concerning its clinical
effectiveness under the scope of evidence-based medicine,
such as in the form of data synthesis derived from
systematic reviews (SRs) or meta-analyses (MAs).
Meta-analyses, being important components of SRs,
attempt to combine and summarize both qualitative and
quantitative data from multiple studies using
sophisticated statistical methodology [18,19]. Such a strategy
strengthens evidence, giving the results more statistical
power and, therefore, more credibility than the
individual studies . According to Victor , this kind of
approach is recommended when existing literature data
is both contradictory and confusing and when clinical
benefit could be derived.
The null hypothesis investigated in this study is that
the chin cup has no clinical effectiveness on Class III
Therefore, the main (PICO) question this MA aims to
answer is as follows: for growing patients presenting
Class III malocclusion and/or open bite, could chin cup,
as compared with no treatment at all, be beneficial for
the improvement of their facial, skeletal and
dentoalveolar characteristics in the short and long term?
The present MA was undertaken after an a priori
designed protocol according to the Cochrane Handbook
for Systematic Reviews of Interventions version 5.1.0
 and presented according to the guidelines of the
PRISMA Statement for reporting SRs and MAs of
studies evaluating health-care interventions .
Data sources and searches
Systematic searches were conducted for published,
unpublished and ongoing studies up to July 2014 to identify
potentially relevant studies reporting data from growing
patients with Class III malocclusion and/or open bite
Table 1 Contribution of the original studies to the investigation of the individual cephalometric variables
aAuthors in alphabetical order.
leaS2ubm ilrsaaeb ()AN ()BN ()BN iil(rtssaaappm ()-noGmm )(-LNM ill(aaenong ()-eMmm ()FHmm ()FAHmm ()-ooGmm j()rtveemm i()rtveebmm iillitttsscyaaSgn
T V S S A W C S G N U L C O O *
Figure 2 Cephalometric variables examined in current investigation.
having received treatment with chin cup appliance
(occipital or vertical) for the improvement of their facial, skeletal
and dentoalveolar characteristics. Every effort to minimize
any possible bias in the location of studies was made, and
citations to potentially relevant studies from journal
articles, dissertations or conference proceedings were located
by searching the corresponding electronic databases.
In addition to the electronic searches, manual searching
was also performed for the following journals: American
Journal of Orthodontics and Dentofacial Orthopedics,
Angle Orthodontist, European Journal of Orthodontist,
Journal of Orofacial Orthopedics and Orthopedics and
Craniofacial Search, as well as in the reference list of
the full-text articles eligible for inclusion, in an effort to
identify and retrieve all possible relevant data. Existing
SRs and MAs relevant to this study were identified,
and their reference lists were also scanned for additional
trials. Conference abstracts were additionally searched and
Figure 3 Forest plot of the cephalometric variable SNA.
Figure 4 Forest plot of the cephalometric variable SNB.
inquired on their current status. Articles published in
journals, dissertations and conference proceedings were located
from several electronic databases following the use of an
appropriately adjusted search strategy for each individual
database as shown in Additional file 1: Table S1.
No restrictions were applied concerning publication
year, language or status. Grey literature (i.e. informally
published written material by searching the Digital
Dissertations, Conference Paper Index and metaRegister
of Controlled Trials databases)  was also included in
our search. If additional information was needed, authors
were to be contacted.
Selection of studies
Studies eligible to be included in this MA were (a)
randomized controlled trials (RCTs) and (b) cohort studies,
i.e. prospective controlled clinical trials (pCCTs) and
(retrospective) observational studies (OS), with matching control
samples, investigating the clinical effectiveness of the chin
cup used for orthodontic/orthopaedic treatment alone or
in combination with removable disocclusion or transversal
expansion appliances (such as maxillary bite planes,
mandibular bite planes, removable palatal cribs or quad helices)
in patients being in the pubertal or pre-pubertal growth
spurt (6 to 14 years old) at the start of their treatment.
Additional file 2: Table S2 presents in detail the eligibility
criteria used in this MA.
Figure 5 Forest plot of the cephalometric variable ANB.
Screening of titles, abstracts and full-text citations was
performed by two review authors independently (MC and
II). Any disagreement was resolved by consulting the third
reviewer (MAP). Inter-reviewer agreement on study
eligibility was assessed by means of the unweighted Cohen's
kappa . Levels of agreement were classified as poor
(kappa < 0.00), slight (0.00 < kappa < 0.20), fair (0.21 <
kappa < 0.40), moderate (0.41 < kappa < 0.60),
substantial (0.61 < kappa < 0.80) and almost perfect (0.81 <
kappa < 1.00).
The process of study selection, as well as of data
extraction and risk of bias assessment, was not performed
blinded, since scientific evidence does not strongly
recommend masked assessment .
Data extraction and management
Two reviewers (MC and II) extracted independently study
characteristics and outcomes from the included studies in
an a priori developed extraction form. Any disagreements
were resolved after consulting the third reviewer (MAP).
The Cohen's kappa statistic was used to assess the level of
agreement between the two reviewers.
Risk of bias (quality evaluation) analysis of the included
The risk of bias (quality analysis) for all included studies
was performed independently by two reviewers (MC and
Figure 6 Forest plot of the cephalometric variable Wits appraisal.
II), with respect to pre-established characteristics. The
risk of bias of RCTs was planned to be assessed with the
Cochrane risk of bias tool . The risk of bias of
nonrandomized studies (pCCTs and OS) was assessed with the
Downs and Black checklist . The criteria were grouped
in five main domains: reporting, external validity, internal
validity - bias, internal validity - confounding, and power.
All items were given one point when the respective
criterion was fulfilled, except for the power domain, in which
up to five points could be given, summing up to a
maximum of 30 points per article. Serious methodological
limitations were judged to exist when a non-randomized
study collected less than 17 points on the checklist. Again,
any disagreements were resolved by discussion after
consulting the third reviewer (MAP), and inter-reviewer
agreement for both methods was evaluated by the Cohen's
Data synthesis and analysis
Data were summarized and considered suitable for
pooling if the corresponding RCTs and cohort studies,
i.e. pCCTs or (retrospective) OS, used similar
exposures in the same way and reported similar outcomes
as provided by lateral cephalometric radiographs. The
standard difference in means (SDM) and the
corresponding 95% confidence intervals (CIs) were
calculated, (a) since possibly different magnification factors
of the original lateral cephalometric radiographs might
have been used or (b) since cephalometric landmarks
used in the primary studies for the common variables
Figure 7 Forest plot of the cephalometric variable Co-Gn.
examined might have not been defined and measured
identically for some cephalometric variables, such as the
gonial angle. Soft tissue, cast model and perioral muscular
electromyography data analyses were also to be performed,
if data were available. The pooled estimate (SDMs) of the
examined variables and the corresponding 95% CIs were
used to construct a forest plot.
Weighting of the pooled estimates was performed with
the random effects model since it was expected that one
or more non-RCTs would be included in the analysis
[27,28] and because this model takes into account the
heterogeneity of the data . In addition, since the
observed effect was expected to differ across studies due
to sample and implementation differences, the use of
this model was regarded as more appropriate [29-31].
If the included studies were less than five, exploratory
analyses were to be performed instead. Their derivatives
are regarded as secondary in validity and should be viewed
with caution [31,32].
Analyses were performed by means of the statistical
software Comprehensive Meta-Analysis version 2.0
(Biostat Inc., Englewood, NJ, USA). The level of
significance was set at P 0.05 except for heterogeneity which
was set at P 0.10. P-values were two-sided.
To identify the extent of data heterogeneity, the Cochran
Q test for homogeneity with the corresponding P-value
was calculated [33-35]. Results were statistically significant
where P 0.10 [34,35]. In addition, the I2 index was
Figure 8 Forest plot of the cephalometric variable Co-Go.
applied to measure the within-studies variability, where
a value of 0% for the I2 index equals with no observed
heterogeneity, while values of 25%, 50% and 75% equal
with low, medium and high heterogeneity, respectively
. Due to the random effects model application, T2
was also used to quantify the impact of heterogeneity
between studies .
Among 1,308 initially identified relevant records (940
through electronic searching and 368 through manual
searching of the aforementioned journals), 262 unique
citations remained after duplicate removal. From them,
213 were excluded on the basis of the title and abstract,
and therefore, 49 articles remained to be assessed on a
full text basis. Hand searching on their reference lists
revealed five additional relevant records, three from which
were excluded due to non-English abstract. Thus, a sum
of 51 articles remained for full text eligibility assessment.
Application of the detailed inclusion and exclusion
criteria resulted in the exclusion of another 46 articles as
seen in Additional file 3: Table S3. The numbers of
excluded articles, according to the exclusion criteria, are
listed in summary in Additional file 4: Table S4. In total,
five studies [9-11,13,16] remained for qualitative and
quantitative synthesis. All of them were cohort studies
and were categorized according to study design into four
pCCTs and one OS. Two studies [9,10] examined two
independent treated groups versus a control group each,
Figure 9 Forest plot of the cephalometric variable Gonial angle.
and therefore, the total number of examined
independent treated groups versus their corresponding control
groups was seven. No RCT was found to be eligible for
inclusion in this MA. The flow diagram of the retrieved
studies is presented in Figure 1.
Cohen's kappa between the two investigators before
reconciliation for data selection was 0.838 (standard
error: 0.042) and for data extraction 0.898 (standard
error: 0.100), both of which represent an almost perfect
Description of studies and baseline characteristics
The characteristics of the included studies [9-11,13,16]
are presented in Additional file 5: Table S5.
Although the initial plan was to investigate the
shortand long-term effects of both the occipital and the vertical
pull chin cup, due to the limited data provided from the
included articles, only the short-term occipital pull chin
cup effects were finally examined. Consequently, where
the term chin cup is used thereafter, it is referred to the
occipital pull chin cup, and where the term clinical effects
is used, it is limited to the short-term ones.
Soft tissue, model cast and perioral muscular
electromyography data analyses were also not possible to be
performed because no such data could be retrieved as
appropriate for inclusion and analysis in the present
study. Thus, treatment effect comparisons between the
experimental groups were considered just for skeletal
and dentoalveolar alterations as measured on lateral
Figure 10 Forest plot of the cephalometric variable N-Me.
Risk of bias (quality evaluation) analysis of the included
The risk of bias analysis of the included studies according
to the Downs and Black  checklist is presented in
Additional file 6: Table S6.
Cohen's kappa between the two investigators for quality
evaluation was 0.750 (standard error: 2.100) for reporting,
which is substantial, and 1 (standard error: 0.000) for
external validity, internal validity and power, which is
perfect. Details can be seen in Additional file 7: Table S7.
Effectiveness of chin cup treatment
The common cephalometric variables retrieved from the
seven included treated groups and possible to be
examined in current MA were the following: (a) skeletal
variables in the sagittal plane: SNA (), SNB (), ANB (), Wits
appraisal (mm) and Co-Gn (mm); (b) skeletal variables in
the vertical plane: SN-ML (), gonial angle (), N-Me
(mm), UFH (mm), LAFH (mm) and Co-Go (mm) and (c)
dentoalveolar variables: overjet (mm) and overbite (mm).
These are all presented schematically in Figure 2. The
contribution of the original studies to the investigation of each
individual cephalometric variable is presented in Table 1.
Meta-analyses were performed for the variables SNA,
SNB, ANB, Wits appraisal, SN-ML and gonial angle,
where data from five or more treated groups derived from
the included studies contributed in the analysis. For the
Figure 11 Forest plot of the cephalometric variable UFH.
rest of the variables, namely Co-Gn, N-Me, UFH, LAFH,
Co-Go, overjet and overbite, where data from four or less
treated groups contributed in the analysis, exploratory
analyses were performed. The summary of pooled
estimates of all cephalometric variables under investigation
performed with the random effects model is presented in
Table 2 and in Figures 3-15. The detailed results of the
statistical elaboration of the variables that presented
statistically significant differences are presented below.
With regard to the skeletal cephalometric changes in
the sagittal plane, it was revealed that there was
statistically significant reduction in the SNB angle of the patients
treated with the chin cup in comparison to the untreated
individuals (SDM = 1.97, CI = 3.09 to 0.84, P = 0.001),
indicating a restriction effect on mandibular growth. This
is explicitly shown in Figure 4. In addition, Class III
malocclusion of treated patients was significantly improved
since there was a statistically significant increase following
chin cup use in comparison to untreated individuals to (a)
the ANB angle (SDM = 2.48, CI = 1.36 to 3.61, P = 0.000)
and (b) the Wits appraisal (SDM = 3.62, CI = 1.32 to 5.92,
P = 0.002) as shown in Figures 5 and 6, respectively.
However, for all these three variables, the observed data
heterogeneity as well as the between-studies variance was
With regard to the skeletal cephalometric changes in
the vertical plane, the results of the MA revealed that
the SN-ML angle increased significantly as depicted in
Figure 12 Forest plot of the cephalometric variable LAFH.
Figure 13 whereas the gonial angle (Figure 9) decreased
significantly in the patients treated with the chin cup as
compared with the untreated individuals (SDM = 1.17,
CI = 0.48 to 1.86, P = 0.001 and SDM = 0.80, CI = 1.52
to 0.08, P = 0.030, respectively), indicating a tendency
towards an increase of the vertical growth pattern and/
or posterior rotation of the mandible. However, data
heterogeneity of the included studies was moderate to
high, and the between-studies variance was moderate.
The tendency towards increase of the anterior face
height is further supported by the statistically significant
increase of the linear variable N-Me according to the
exploratory analysis performed (Figure 10) (SDM =
1.39, CI = 0.59 to 2.18, P = 0.001). Moderate data
heterogeneity of the included studies and small
betweenstudies variance were also observed here.
As far as the dentoalveolar changes are concerned, the
results of the exploratory analysis revealed that there
was a statistically significant increase of overjet in the
patients treated with the chin cup in comparison to the
untreated individuals, clearly depicted in Figure 14 (SDM
= 2.62, CI = 1.06 to 4.19, P = 0.001), indicating an
improvement of the antero-posterior relations of the
maxillary and mandibular incisors. Yet, data heterogeneity
observed in the included studies, as well as the
betweenstudies variance, was high.
For the rest of the variables, namely SNA, Co-Gn,
UFH, LAFH, Co-Go and overbite, no statistically significant
Figure 13 Forest plot of the cephalometric variable SN-ML.
differences were derived. This is also presented in the
relevant forest plots, depicted in Figures 3, 7, 11, 12, 8 and
Finally, due to the limited data provided from the
included articles, no long-term effects following the
use of the occipital chin cup, as well as no short- and
long-term effects of the vertical pull chin cup, could
According to the results of the current investigation,
the null hypothesis was rejected since many of the
variables of lateral cephalometric radiographs that
were possible to be evaluated presented statistically
Patients treated with the chin cup presented, in
comparison to untreated individuals, a clockwise rotation of
the mandible and an increase in their anterior facial
height, both beneficial in solving their skeletal problem.
In detail, statistically significant reduction of the
variable SNB indicates a restriction effect on the mandibular
growth of growing patients and/or an intense clockwise
The pooled statistically significant increase of the ANB
angle entails an improvement of the Class III skeletal
relationship of the maxilla and mandible. In the Altu
et al.  study, a much further increase in ANB than in
Figure 14 Forest plot of the cephalometric variable overjet.
the rest was found. Perhaps this is associated with the
individualized protocol applied in that study.
In addition, the Wits appraisal of the treated patients
presented a statistically significant increase in comparison
to that of the untreated individuals, and this is in
accordance with all included studies providing the corresponding
treated groups [9,10,16]. Once again, in the study of Altu
et al. , a much greater increase than in the rest was
found. Improvement of the Wits appraisal depicts the
true and favourable underlying skeletal alterations in
the lower face.
The angular variable SN-ML also presented a
statistically significant increase in patients treated with chin
cup [10,11,13,16]. This is indicative of the increase of
the anterior face height that takes place probably due
to the backwards and downwards rotation of the
Regarding the statistically significant decrease of the
gonial angle, although it is in accordance with the four
participating studies providing the corresponding treated
groups [9-11,16], in the study of Altu et al. , a much
further reduction was observed than in the others,
standing as an outlier. This might indicate that different
protocols in the use of the appliance (i.e. different force
levels and/or different hours of wear) produce the same
result (reduction in this case) but in a very different
Figure 15 Forest plot of the cephalometric variable overbite.
Finally, the statistically significant increase of N-Me
and overjet, as derived from the corresponding
exploratory analyses ([10,13] and [9,11], respectively), further
justifies the beneficial use of the chin cup towards the
development of a Class I skeletal profile. The observed
increase of the anterior facial height could be the result
of the clockwise rotation of the mandible whereas the
increased overjet might indicate the physiological
adaptation of the patients' masticatory system in the new
mandibular position where lip and tongue pressures
tend towards normal. Yet, although statistical
significance was found in these results, exploratory analysis of
linear measurements with high heterogeneity imposes
precautions in the validity of these results.
A thorough search of the literature revealed that other
studies as well, performed under different protocols
from the ones implemented in this MA, support many
of the aforementioned findings.
The redirection, inhibition and backwards rotation of
the mandible and the subsequent decrease of the SNB
angle are also supported by the literature [12,36-40].
Increase of the ANB angle supported by many authors
in the literature [12,36,37,39,41] may not indicate where
exactly the changes were affected , but it does mirror
the resolution of the skeletal malocclusion that was seen
clinically. Sugawara and Mitani  however in their
study found no significant differences in ANB angle
when they compared their Class III subjects with a Class
I control group.
Regarding the possible changes in the size of the
mandible, the literature supports the opinion that the high
density of the bone that forms the mandible seems to
react strongly to the chin cup efforts to restrict its
growth, permitting only changes to its shape and
redirection of its growth [5,12,14,42-46]. Lu et al.  after
having examined their patients for 5 years found that in
the first third of this period, there was a remarkable
reduction in the dimension of their mandibles. During
the following two thirds of the observation period
though, the mandibles increased to their original sizes.
On the contrary, Graber  found that there was an
actual reduction of the size of the mandible.
The closure of the gonial angle due to chin cup use is
widely supported by the literature as well [2,12,36,39-43,46]
and could be partly explained if the direction of the force
applied through the chin cup is considered. The direction
of the force passes through the occipital area and the
glenoid fossa either via or underneath the condyle and seems
to work as a fulcrum, around which the ramus of the
mandible tends to rotate . Due to the engagement of
the condyle to the articulation and apart from the condyle
remodelling to a more forward direction , the gonial
area also has some freedom to remodelling; thus, it
becomes less obtuse .
Nevertheless, the N-Me distance seems to increase
and many studies in the literature support this finding
[2,12,15,39,41,43]. It seems therefore that the
simultaneous closure of the gonial angle cannot withstand the
increase in anterior face height measured through the
variable N-Me. It is possibly the antegonial notch that
absorbs much of the applied pressure from the chin cup,
thus allowing the deformation of the mandible .
Pros and cons of this MA
The current investigation presents a number of strengths
and weaknesses, which are detailed in the following.
Firstly, none of the included studies was a RCT. In
addition, from the CCTs included in the analysis, three
were appraised as of medium quality [9,10,13] and two
as of low [11,16], while the overall estimate was low.
The sample sizes were adequate in three of the included
studies [10,13,16] and inadequate in the remaining two
studies [9,11]. In total, seven treated groups were derived
from the five included studies; however, two studies
contributed with two independent treated groups each [9,10],
whereas the remaining three studies contributed with just
one treated group each.
When examining the characteristics of each original
study, it was observed that not all treated groups were
identical with regard to the amount of force exercised,
additional appliances used, duration of treatment,
suggested hours of chin cup wear as well as the
chronological age of patients. Different protocols in the clinical
procedures might have led in different results, however.
For the lateral cephalometric radiographs of the included
studies, possibly different magnifications might have been
used, since they had been taken at different times in
different environments and with different equipment. However,
this possible source of bias affected mainly the linear
variables, namely Wits appraisal, Co-Gn, N-Me, UFH, LAFH,
Co-Go, overjet and overbite, and efforts were made to
reduce its impact by the use of the random effects model.
Not all included studies and not all independent treated
groups contributed to the statistical elaboration of each of
the variables examined. Thus, for the variables Co-Gn,
N-Me, UFH, LAFH, Co-Go, overjet and overbite, where
four or less treated groups were included, an exploratory
analysis was conducted instead of a formal MA. The small
number of included treated groups significantly attenuated
the validity of the corresponding results and imposed
precaution in their interpretation, since they are considered
as secondary in comparison with those derived from a
formal MA. In addition, high levels of heterogeneity, evident
in most of the variables examined, question the validity
and reliability of the results.
To balance the reported weaknesses as well as to
increase the strength of the current investigation, a strict
inclusion-exclusion protocol was applied, according to
which specific restrictions to the study designs of the
included trials, the participants' characteristics and the
principal outcome measures were imposed. Selection of
studies, data extraction and management and
assessment of the risk of bias of the included studies (quality
analysis) were independently performed by two
reviewers, while a third one was involved where in doubt
to remove subjectivity from the processes. Authors were
contacted where no precise information was given. With
regard to the statistical computations, the pooled
estimate SDM was used instead of the mean difference
(MD), to alleviate discrepancies derived from possibly
different magnification factors of the lateral
cephalometric radiographs evaluated in the original articles, as
well as from non-standardized and non-calibrated
measurements. Finally, in the current MA, the random
effects model was used instead of the fixed effects model
in order to take into consideration the data
heterogeneity of the included studies, as well as to counterbalance
the dominance of the studies with large sample sizes
over those with small ones.
Although the aim of this investigation was to assess the
short- and long-term effects of both the occipital and
the vertical pull chin cup, due to the lack of appropriate
data of the included articles, only the short-term occipital
pull chin cup effects were possible to be assessed. In
addition, soft tissue, model cast and perioral muscular
electromyography data analyses were also not possible to
be performed for the same reasons.
Thus, according to the results of this investigation, it
can be concluded that following the use of occipital pull
chin cup for the short-term management of growing
patients with Class III malocclusion before pubertal spurt,
an overall significant improvement of the skeletal and
dentoalveolar relationships takes place in comparison to
untreated individuals. In detail, data elaboration leaded to
the following conclusions:
The skeletal Class III sagittal relationships of the
maxilla and mandible are improved.
The skeletal Class III vertical relationships are also
affected towards an increase of the vertical growth
pattern, an increase of the anterior face height, and/
or posterior rotation of the mandible.
The antero-posterior relations of the maxillary and
mandibular incisors, as indicated by the increase of
overjet, are improved.
Nevertheless, the limited number of included studies, the
high heterogeneity observed in most of the variables and
the linear manner of many of them suggest some precaution
in the interpretation of these conclusions. It seems that
there is not enough evidence-based data to make definitive
recommendations about the chin cup treatment.
More high-quality evidence-based clinical trials with
proper design, sample size, appliance use and
measurements are needed in the future in order to reach more
reliable results concerning the chin cup treatment of
Class III malocclusion in the short and the long term.
Additional file 1: Table S1. The electronic databases searched, the
search strategies used and the corresponding results. The table
presents the strategy followed for the electronic selection of relevant
studies at a first level. All the electronic databases searched, the
keywords/search strategies used and the results of each database can be
seen in this table. This table presents a qualitative evaluation.
Additional file 2: Table S2. Eligibility criteria used in this
metaanalysis. The table presents the inclusion and exclusion criteria for this
meta-analysis according to four separate criteria: outcome, study design,
participants' characteristics and principal outcome measures.
Additional file 3: Table S3. Articles excluded on the basis of the
full text from this study and reason for exclusion. The table presents
the full text screened articles that were excluded from the current
metaanalysis and the exact reason or study characteristic that leaded to their
Additional file 4: Table S4. Number of the excluded articles
according to the exclusion criteria. This table presents a quantitative
evaluation of the excluded articles on full text basis i.e., how many of
them were excluded according to the specific criteria.
Additional file 5: Table S5. Characteristics of the studies included
in the meta-analysis. This table presents the basic characteristics of the
included studies permitting their qualitative and quantitative evaluation.
More specifically it examines the included studies according to the
following sectors: study design, treated sample origin and/or
characteristics and sample size, subgroups formed within the study,
gender ratio (M / F), and mean age of the treated sample, control sample
origin and/or characteristics, control sample size, gender ratio (M / F) and
mean age, diagnosis, method of measurement, appliance used, possible
additional appliance used, suggested hours of appliance use, treatment
follow-ups, treatment duration, control observation and reported effects.
Additional file 6: Table S6. Risk of bias analysis of the included
studies - Downs and Black  scale. The table presents the assessment
of possible bias in the included studies in terms of reporting, external
validity, internal validity-bias, internal validity-confounding and power.
Additional file 7: Table S7. Kappa scores measuring levels of
agreement between the two reviewers. The table presents the levels
of agreement between the two reviewers according to kappa score
methodology in assessing quality scores of the included articles
according to the Downs and Black scale.
CCT: controlled clinical trial; CIs: confidence intervals; MA: meta-analysis;
MD: mean difference; OS: (retrospective) observational study;
pCCT: prospective controlled clinical trial; RCT: randomized clinical trial;
SDM: standard difference in means; SE: standard error; SR: systematic review;
SNA: angle formed between the cephalometric points S, N and A;
SNB: angle formed between the cephalometric points S, N and B;
ANB: angle formed between the cephalometric points A, N and B;
Wits appraisal: the perpendicular distance of the cephalometric points A and
B to the functional occlusal plane; Co-Gn: distance between the
cephalometric points Co and Gn; SN-ML: angle formed between the
cephalometric planes SN and Go-Me or Go-Gn; Gonial angle: angle formed
between the cephalometric points Ar, Go and Me; N-Me: distance between
the cephalometric points N and Me; UFH: distance between the
cephalometric points N and ANS; LAFH: distance between the cephalometric
points ANS and Me; Co-Go: distance between the cephalometric points Co
and Go; Overjet: horizontal distance between the cephalometric points
Upper incisor tip and Lower incisor tip; Overbite: vertical distance
between the cephalometric points Upper incisor tip and Lower incisor tip.
The authors declare that they have no competing interests.
MC made the research, collected the data for this study and performed the
statistical elaboration/analysis and interpretation of the results as well as the
draft of this paper. II helped in the design of the study, in the screening of
the collected data, in the data extraction and management and in the
statistical analysis and made corrections to the draft. MAP conceived and
designed this study, helped in choosing proper statistical methodology and
also helped in the statistical analysis when needed and critically appraised
and corrected the draft. All three authors have given final approval of this
study to be published.
We feel obliged to Dr. Gkalp H. for providing us with additional data
regarding the study: Gkalp H, Kurt G. Magnetic resonance imaging of the
condylar growth pattern and disk position after chin cup therapy: a
preliminary study. Angle Orthod. 2005;75:56875. which enabled us to fully
include this study in our qualitative and quantitative analysis.