Cephalometric evaluation of the effects of the Twin Block appliance in subjects with Class II, Division 1 malocclusion amongst different cervical vertebral maturation stages

Abstract

Objectives:
To evaluate the cephalometric changes in skeletal, dentoalveolar and soft tissue variables induced by Clark's Twin Block (CTB) in Class II, Division 1 malocclusion patients and to compare these changes in different cervical vertebral maturation stages.

Methods:
Pre- and post-treatment/observation lateral cephalograms of 53 Class II, Division 1 malocclusion patients and 60 controls were compared to evaluate skeletal, dentoalveolar and soft tissue changes. Skeletal maturity was assessed according to cervical vertebral maturation stages. Pre- and post-treatment/observation mean changes and differences (T2-T1) were compared by means of Wilcoxon sign rank and Mann-Whitney U-tests, respectively. Intergroup comparisons between different cervical stages were performed by means of Kruskal-Wallis test and Mann-Whitney U-test (p ≤ 0.05) .

Results:
When compared with controls, there was a significant reduction in ANB angle (p < 0.001), which was due to a change in SNB angle in CS-2 and CS-3 (p < 0.001), and in SNA (p < 0.001) and SNB (p = 0.016) angles in the CS-4 group. There was significant increase in the GoGn-SN angle in CS-2 (p = 0.007) and CS-4 (p = 0.024), and increase in Co-Gn and Go-Gn amongst all cervical stages (p < 0.05). There was significant decrease in U1-SN and increase in IMPA amongst all cervical stages (p < 0.05). There was significant retraction of the upper lip in CS-3 (p = 0.001), protrusion of the lower lip in CS-2 (p = 0.005), increase in nasolabial angle in CS-4 (p = 0.006) and Z-angle in CS-3 (p = 0.016), reduction in H-angle in CS-2 (p = 0.013) and CS-3 (p = 0.002) groups. When pre- and post-treatment mean differences were compared between different cervical stages, significant differences were found for SNA, SNB and UI-SN angles and overjet. .

Conclusions:
The Twin-Block along with the normal craniofacial growth improves facial esthetics in Class II, Division 1 malocclusion by changes in underlying skeletal and dentoalveolar structures. The favorable mandibular growth occurs during any of the cervical vertebral maturation stages, with more pronounced effect during CS-3 stage.

Full text

© 2016 Dental Press Journal of Orthodontics Dental Press J Orthod. 2016 May-June;21(3):73-8473
original article
Cephalometric evaluation of the effects of the Twin Block
appliance in subjects with Class II, Division1 malocclusion amongst
different cervical vertebral maturation stages
Aisha Khoja1, Mubassar Fida2, Attiya Shaikh3
1
Resident in Orthodontics, The Aga Khan University Hospital, Section of
Dentistry, Department of Surgery, Karachi, Pakistan.
2
Associate Professor, Program Director Orthodontics Residency Program,
TheAga Khan University Hospital, Section of Dentistry, Department of
Surgery, Karachi, Pakistan.
3
Assistant Professor, Program Coordinator Orthodontics Residency Program,
Section of Dentistry, Department of Surgery, The Aga Khan University
Hospital, Karachi, Pakistan.
» The authors report no commercial, proprietary or financial interest in the products
or companies described in this article.
Objectives: To evaluate the cephalometric changes in skeletal, dentoalveolar and soft tissue variables induced by Clark’s Twin Block (CTB) in Class II, Division 1
malocclusion patients and to compare these changes in different cervical vertebral maturation stages. Methods: Pre- and post-treatment/observation lateral cepha-
lograms of 53 Class II, Division 1 malocclusion patients and 60 controls were compared to evaluate skeletal, dentoalveolar and soft tissue changes. Skeletal maturity
was assessed according to cervical vertebral maturation stages. Pre- and post-treatment/observation mean changes and differences (T2-T1) were compared by means
of Wilcoxon sign rank and Mann-Whitney U-tests, respectively. Intergroup comparisons between different cervical stages were performed by means of Kruskal-
Wallis test and Mann-Whitney U-test (p ≤ 0.05). Results: When compared with controls, there was a significant reduction in ANB angle (p<0.001), which was
due to a change in SNB angle in CS-2 and CS-3 (p<0.001), and in SNA (p<0.001) and SNB (p=0.016) angles in the CS-4 group. There was significant increase
in the GoGn-SN angle in CS-2 (p=0.007) and CS-4 (p=0.024), and increase in Co-Gn and Go-Gn amongst all cervical stages (p<0.05). There was significant
decrease in U1-SN and increase in IMPA amongst all cervical stages (p<0.05). There was significant retraction of the upper lip in CS-3 (p=0.001), protrusion of
the lower lip in CS-2 (p=0.005), increase in nasolabial angle in CS-4 (p=0.006) and Z-angle in CS-3 (p=0.016), reduction in H-angle in CS-2 (p=0.013) and
CS-3 (p=0.002) groups. When pre- and post-treatment mean differences were compared between different cervical stages, significant differences were found for
SNA, SNB and UI-SN angles and overjet. Conclusions: The Twin-Block along with the normal craniofacial growth improves facial esthetics in Class II, Divi-
sion 1 malocclusion by changes in underlying skeletal and dentoalveolar structures. The favorable mandibular growth occurs during any of the cervical vertebral
maturation stages, with more pronounced effect during CS-3 stage.
Keywords:
Twin Block. Class II, Division 1 malocclusion. Cervical vertebral maturation.
DOI: http://dx.doi.org/10.1590/2177-6709.21.3.073-084.oar
How to cite this article: Khoja A, Fida M, Shaikh A. Cephalometric evaluation
of the effects of the Twin Block appliance in subjects with Class II, Division 1
malocclusion amongst different cervical vertebral maturation stages. Dental Press
J Orthod. 2016 May-June;21(3):73-84.
doi: http://dx.doi.org/10.1590/2177-6709.21.3.073-084.oar
Submitted: January 13, 2015 - Revised and accepted: October 23, 2015
Contact address: Aisha Khoja
E-mail: dr.aisha86@gmail.com
Objetivo: avaliar as alterações em variáveis cefalométricas esqueléticas, dentoalveolares e do perfil tegumentar, induzidas pelo aparelho TwinBlock de Clark (TBC),
em pacientes com má oclusão de Classe II, divisão 1, e comparar as alterações nos diferentes estágios de maturação das vértebras cervicais. Métodos: telerradio-
grafias laterais pré- e pós-tratamento de 53 pacientes com má oclusão de Classe II, divisão 1, foram comparadas às telerradiografias de 60 pacientes controle, para
avaliar as alterações esqueléticas, dentoalveolares e no perfil tegumentar. A maturação esquelética foi avaliada de acordo com os estágios de maturação das vértebras
cervicais. As alterações médias e as diferenças entre o pré- e o pós-tratamento (T2
– T1) foram comparadas por meio do teste de postos sinalizados de Wilcoxon e do
teste U de Mann-Whitney, respectivamente. Foram realizadas comparações intergrupos para os diferentes estágios de maturação das vértebras cervicais, por meio
do teste de Kruskal-Wallis e teste U de Mann-Whitney (p ≤ 0,05). Resultados: em comparação aos pacientes do grupo controle, constatou-se que houve uma
redução significativa do ângulo ANB (p<0,001), em virtude de alterações no ângulo SNB nos estágios CS2 e CS3 (p<0,001), e nos ângulos SNA (p<0,001)
e SNB (p=0,016) no estágio CS4. Houve um aumento significativo do ângulo GoGn-SN nos estágios CS2 (p=0,007) e CS4 (p=0,024), e um aumento em
Co-Gn e Go-Gn em todos os estágios de maturação das vértebras cervicais (p< 0,05). Houve redução significativa em U1-SN e um aumento do IMPA em
todos os estágios de maturação das vértebras cervicais (p<0,05). Houve retração significativa do lábio superior em CS3 (p=0,001), protrusão do lábio inferior
em CS2 (p=0,005), aumento do ângulo nasolabial em CS4 (p=0,006) e do ângulo Z em CS3 (p=0,016), além de redução do ângulo H em CS2 (p=0,013) e
CS3(p= 0,002). Quando as diferenças médias entre pré- e pós-tratamento foram comparadas entre os diferentes estágios de maturação das vértebras cervicais,
foram identificadas diferenças significativas para os ângulos SNA, SNB e UI-SN, assim como para o overjet. Conclusões:ouso do aparelho Twin-Block, associado
ao crescimento craniofacial normal, melhora a estética facial em pacientes com má oclusão de Classe II, divisão 1, por meio de alterações nas estruturas esqueléticas
e dentoalveolares subjacentes. Esse crescimento mandibular mais favorável pode ocorrer durante qualquer um dos estágios de maturação das vértebras cervicais,
com um efeito mais acentuado durante o estágio CS3.
Palavras-chave: TwinBlock. Má oclusão de Classe II, divisão 1. Maturação das vértebras cervicais.

© 2016 Dental Press Journal of Orthodontics Dental Press J Orthod. 2016 May-June;21(3):73-8474
Cephalometric evaluation of the eects of the Twin Block appliance in subjects with Class II, Division1 malocclusion amongst dierent cervical vertebral maturation stagesoriginal article
INTRODUCTION
Physical attractiveness plays a vital role in social inter-
action and in dealing with people in society.
1
Theface
is the rst structure to be noticed and people with well-
proportioned and attractive faces are perceived as being
more outgoing, friendly, socially competent, optimistic,
intelligent, and condent.
2
Subjects with Class II, Division 1 malocclusion typi-
cally present with an increased overjet, lower lip trapped
behind maxillary incisors and an unfavorable facial pro-
le, which may predispose children towards a negative
feeling of self-image and self-esteem.
3-6
The goal of
orthodontic treatment for these patients is to achieve a
harmonious relationship of dentoskeletal subunits along
with an esthetically pleasing facial prole.
3,5
Class II malocclusion is commonly observed by or-
thodontists in daily practice.
7
In a local study conducted
by Gul-e-Erum and Fida,
8
70.5% of patients had Angle
Class II, and amongst them 64.7% had Class II, Divi-
sion1 malocclusion. On a global scale, an approximate
estimation shows over 20% prevalence of Class II maloc-
clusion in North America, Europe and North Africa.
9
Various treatment modalities can be instituted to
treat these patients, amongst which functional ap-
pliance has been found to be a suitable treatment op-
tion in growing individuals.
10,11
These appliances work
by changing the activity of the various muscle groups
that inuence function and position of the mandible.
12
Altering sagittal and vertical mandibular position gener-
ates pressure due to stretching of muscles and surround-
ing so tissues. The resultant force is transmitted to the
underlying dental and skeletal tissues and brings about
orthodontic and orthopedic changes.
13
Twin Block is
the most preferred type of functional appliance in the
United Kingdom.
3,10
It was rst introduced by Clark,
in 1982,
14
and has been increasingly popular because of
its uncomplicated design and ease of use.
10
It consists of
two separate upper and lower acrylic units which po-
sition the mandible forward through interlocking oc-
clusal bite blocks.
10,13
The independent units facilitate
speech and mastication and are proved to be associated
with good patient compliance.
12,13
A multitude of evidence-based studies have described
the role of the Twin Block appliance on skeletal, dental
and so tissue structures.
3,10,11,15,16
Some studies
3,16,17
sug-
gest that functional appliance can increase mandibular
growth, provided it is used in the growing age, whereas
others
18,19
did not nd any real change in the length of
the mandible.
Nevertheless, dental changes have been
observed by most researchers.
3,10,16,17,20
To the best of our
knowledge, no prospective clinical trials have been con-
ducted in Pakistan to investigate the clinical eects of
functional appliances in Class II, Division 1 malocclusion
patients. However, there was a review article by Sukhia
21
on the jasper jumper appliance, its usage, eects and mod-
ications. Therefore, the primary aim of this research is
to assess the mean changes in skeletal, dentoalveolar and
so tissue variables on lateral cephalogram at a one-year
interval in growing individuals with Class II, Division 1
malocclusion following Twin Block appliance therapy.
Early intervention in these patients promotes the growth
of the mandible in a favorable manner, thereby resulting
in a pleasing facial prole. This will provide children with
psychosocial advantage; in addition, the subsequent need
for orthodontic tooth extractions and orthognathic sur-
gery will be minimized. Moreover, these children may
also exhibit less signs and symptoms of temporoman-
dibular joint dysfunction by repositioning the condyles
downward and forward.
22
The eectiveness of functional appliances at induc-
ing skeletal changes largely depends on the growth rate
of the mandible. The stages of cervical vertebral matu-
ration are directly related to mandibular growth changes
that occur during puberty. The stages include obser-
vations during the accelerated growth phase (CS-1 and
CS-2) and observations during the decelerated phase
(stages CS4, CS-5 and CS-6).
23
The peak in pubertal
growth occurs on average between vertebral stages 3
and4. Evidence has been gathered from the literature,
suggesting that the greatest eect of functional appliance
is produced when it is used during the peak in mandib-
ular growth.
23,24
However, there is variable response to
treatment in dierent subjects at dierent cervical verte-
bral maturation stages. Hence, it is important to evalu-
ate the cervical stage of an individual before intervening
with the functional appliance. Therefore, the secondary
goal of this study is to evaluate the eects of the Twin
Block appliance on skeletal, dental and so tissues in
Class II, Division 1 patients treated at dierent cervical
vertebral maturation stages (CS-2, CS-3, and CS-4).
MATERIAL AND METHODS
Sample size was calculated keeping α = 0.05, power
of study (β) as 81% and by using the ndings of a study

© 2016 Dental Press Journal of Orthodontics Dental Press J Orthod. 2016 May-June;21(3):73-8475
original article
Khoja A, Fida M, Shaikh A
conducted by Toth and McNamara.
25
They reported
pre- and post-treatment mean dierences for the vari-
able Co-Gn (mandibular unit length) in the Twin
Block group (5.7±2.4mm) and in the control group
(2.7 ± 1.5 mm). Power analysis showed a minimum
sample of 51 subjects. Aer considering the rate of lost
to follow-up as well as non compliant patients, we in-
cluded 65 consecutive patients.
Ethical approval to conduct this study was obtained
from the Ethical Review Committee of Aga Khan Uni-
versity Hospital (AKUH), Karachi Pakistan (2910-Sur-
ERC-14). Aer taking informed consents from the par-
ents and assents from the children, a total of 65 consecu-
tive children were recruited for this study. All of them
met the following inclusion criteria:
1) Skeletal Class II relationship measured on cepha-
lometric radiograph (ANB > 5°).
2) Mandibular retrognathism measured on cephalo-
metric radiograph (SNB <78°).
3) Class II incisor, canine and molar relationships.
4) Overjet ≥ 6mm.
5) Patients of growing age (9-16 years)who were in
CS-2, CS-3 and CS-4 of cervical vertebral maturation
stages, according to Baccetti et al.
23
The exclusion criteria of this study were subjects
with any craniofacial anomaly or syndrome, noncom-
pliant or uncooperative patients who failed to wear the
appliance for more than 12 hours/day, and subjects with
history of orthodontic treatment. The compliance to
wear the appliance for a minimum of 12 hours/day was
monitored by asking the patient and his/her parents on
every visit and later conrming it with the help of an
overjet change. If there was no improvement in overjet
for two consecutive months, it clearly indicated failure
to wear the appliance.
A total of 12 patients were excluded from the total
sample. Seven patients failed to wear the appliance for
more than 12 hours/day, three patients did not follow up
aer appliance delivery and an additional two presented
with frequent appliance breakage. Hence, we ended up
with a nal sample of 53 patients among which 25 were
males and 28 were females.
The control group consisted of 60 subjects (30 males,
30 females) selected from the Bolton Brush growth
study and had no history of orthodontic treatment.
These subjects were matched in skeletal age (according
to the cervical vertebral maturation stages), sex, dental
malocclusion, overjet and ANB angle with the experi-
mental subjects. The mean observation period for the
control group was taken at one-year interval to match
with the post-treatment readings of the study group.
For the experimental group, data were obtained
from the lateral cephalograms taken at the beginning
(T
1
) and at the end (T
2
) of full time appliance wear of
patients presented at AKUH dental clinics. The Twin
Block appliance was manufactured according to the
original design described by Clark, with the modica-
tion of mandibular incisor capping. Construction bite
was recorded with the mandible postured forward into
an edge-to-edge incisal relationship with 2-3mm of
interincisal clearance and 5-6mm of bite opening in
the rst premolar region. Patients with pretreatment
overjet greater than 7 mm had stepwise mandibular
advancement performed. Initially, the bite was regis-
tered in the range of 4-6mm, followed by reactivation
of an appliance in an end-to-end incisal position aer
a few months. Reactivation of appliance was carried
out by adding cold cure acrylic on the anterior incline
of upper Twin Block halfway through treatment.
25,26
All patients were instructed to wear the appliance
full time for a period of 8-12 months, except during
brushing and meal times. In addition, all appliances
incorporated a midline expansion screw which was
activated 0.25mm every alternate day by means of a
slow expansion technique.
Pre- and post-treatment cephalograms were manu-
ally traced on acetate paper over an illuminator by
the main investigator, according to the conventional
method. Several landmarks were marked, over which
various linear and angular measurements were taken to
evaluate skeletal, dental and so tissue changes (Figs 1-3).
Overjet was measured clinically on each visit, as the dis-
tance from the labial surface of mandibular central inci-
sor to the labial surface of the most prominent maxil-
lary incisor, with the help of an overjet scale. Skeletal
maturity stages were assessed on lateral cephalogram by
observing the morphological and dimensional changes
of the bodies of second through sixth cervical vertebrae,
according to the evaluation method by Baccetti et al.
23
In order to ensure a high degree of precision, the
pre- and post-treatment lateral cephalograms of sub-
jects were routinely taken with the sagittal plane at right
angle to the path of x-ray beams, the head in an erect
position, Frankfort horizontal plane being parallel to the

© 2016 Dental Press Journal of Orthodontics Dental Press J Orthod. 2016 May-June;21(3):73-8476
Cephalometric evaluation of the eects of the Twin Block appliance in subjects with Class II, Division1 malocclusion amongst dierent cervical vertebral maturation stagesoriginal article
ground, teeth in centric occlusion and lips lightly closed
in a relaxed position. These radiographs were recorded
with rigid head xation and a 165-cm lm-to-tube dis-
tance by means of Orthoralix
TM
9200 (Kavo Gendex,
Milan, Italy).
STATISTICAL ANALYSIS
Statistical analyses were performed with Statistical Pack-
age for the Social Sciences (SPSS) for Windows (version 19.0
Chicago Inc. USA). Descriptive statistics (mean and SD)
were computed for all quantitative variables. Shapiro-Wilk
test was used to check for normality of data, showing a non-
normal distribution for most variables. Wilcoxon signed
rank test was applied to compare changes in skeletal, dento-
alveolar and so tissue cephalometric variables from T
1
to T
2
in the treatment and control groups. Themean dierences
were then compared by means of Mann-Whitney U-test
between treatment and control groups.
The sample was further stratied into three cervical
vertebral maturation groups (CS-2, CS-3 and CS-4).
Pre- and post-treatment (T
2
-T
1
) mean dierences for
Figure 1 - Skeletal variables.37
Figure 3 - Soft tissue variables.37
Figure 2 - Dentoalveolar variables.37
Go
Ba
Po
Ar
Cd
Se
B
Pt
ANS
Gn
Na
Pg
Me
PNS
A
Or
Go
Ba
Po
Ar
Cd
Se
B
Pt
ANS
Gn
Pg
Me
PNS
A
Po
Gn
B
Pog Pog’
N
Or
Go
PNS A
Me
Pr
Na
Or
S
ANS
ANS’

© 2016 Dental Press Journal of Orthodontics Dental Press J Orthod. 2016 May-June;21(3):73-8477
original article
Khoja A, Fida M, Shaikh A
each variable were calculated amongst these groups and
were later compared with untreated controls which were
also selected on the basis of cervical vertebral maturation
stages using the same nonparametric tests.
To assess the eects of the Twin Block appliance, used at
dierent cervical vertebral maturation stages, pre- and post-
treatment mean dierences (T
2
-T
1
) were compared for skel-
etal, dental and so tissue variables by means of the Kruskal-
Wallis test. Intergroup comparisons (between CS-2 and
CS-3, CS-2 and CS-4, CS-3 and CS-4) were carried out
for the cephalometric variables by means of Mann-Whitney
U-test. Level of signicance was set at p ≤ 0.05.
ERROR ANALYSIS
To detect any error in locating dierent landmarks
on lateral cephalogram and in measuring pre- and post-
treatment skeletal, dental and so tissue changes, repli-
cated measurements separated by four weeks in 20 ran-
domly selected pre- and post-treatment cephalograms
were performed by the main investigator (intraexaminer
error). The intraclass correlation coecient denoted
that repeated measurements were strongly correlated
with correlation values greater than 0.90.
RESULTS
A total of 53 pre- and post-treatment cephalograms of
Class II, Division 1 malocclusion patients (28 males, 25
females) and 60 pre- and post observational cephalograms
of controls (24 males, 36 females) were compared to inves-
tigate the overall changes in skeletal, dentoalveolar and so
tissue variables. The mean age of males and females in the
treatment group was 11.4±1.71 and 11.8±1.62 years, re-
spectively. The mean age for males and females in controls
were 11.1±1.68 and 11.2±1.86 years, respectively.
Pre- and post-treatment/observation mean changes
in treatment and control groups in the total sample
Initial compatibility between treatment and control
groups was examined by comparison of cephalometric
variables at T
1
, as shown in Table 1.
Pre- and post-treatment/observation means and
standard deviations of the cephalometric skeletal, den-
toalveolar and so tissue variables in treatment and con-
trol groups are presented in Table 2.
From these measurements, the mean dierence (post-
treatment/observation – pretreatment) was then calcu-
lated for each variable in treatment and control groups.
The change in the study group was then compared to the
natural growth change in the control group by means of
Mann-Whitney U-test, asshowninTable3. Treatment
eect was calculated by subtracting natural craniofacial
growth from the treatment change. The results showed
a signicant increase in SNB angle (p<0.001), decrease
in ANB angle (p < 0.001), and increase in vertical jaw
relationship (p = 0.029), increase in mandibular unit
length and body (p<0.001). Amongst the dentoalveo-
lar structures, there was signicant reduction in overjet
(p<0.001) and maxillary incisor inclination (p<0.001),
whereas mandibular incisor incisors inclination increased
(p<0.001). There was statistically signicant retraction of
upper lip with respect to the E-line (p=0.015), increase
in N-L (p=0.001) and Z-angle (p< 0.021), and a de-
crease in the H-angle (p<0.001).
Comparison of pre- and post-treatment/obser-
vation mean changes in treatment and control
groups at different cervical stages
The sample was further stratied into three groups,
on the basis of cervical vertebral maturation stages, into
CS-2, CS-3 and CS-4 in both treatment and control
groups. Pre and post-treatment/observation mean dif-
ference (post-treatment/observation – pretreatment) for
each variable was then compared between treatment
and control groups by means of Mann-Whitney U-test,
so as to identify the actual treatment eect, as shown
in Table 4. The results showed an overjet correction of
5.0, 7.4 and 6.0mm in CS-2, CS-3 and CS-4 groups,
respectively. When compared with untreated subjects
at similar cervical stages, there was statistically signi-
cant reduction in ANB angle amongst the three cervi-
cal stage groups (p < 0.001). However, this reduction
was primarily due to change in SNB angle in CS-2
(p<0.001) and CS-3 (p<0.001) groups, and in both
SNA (p<0.001) and SNB (p=0.016) angles in the CS-4
group. In vertical dimension, there was a signicant in-
crease in the mandibular plane angle in relation to the
S-N plane in CS-2 (p=0.007) and CS-4 (p = 0.024)
groups. Thechange in mandibular unit length and body
was signicant in CS-2 (p<0.001), CS-3 (p<0.001,
p = 0.001) and CS-4 (p = 0.027, p = 0.004) groups.
Amongst the dentoalveolar variables, there was statisti-
cally signicant reduction in maxillary incisor inclina-
tion and increase in mandibular incisor inclination in
CS-2 (p<0.001, p=0.002), CS-3 (p=0.013, p=0.005)

© 2016 Dental Press Journal of Orthodontics Dental Press J Orthod. 2016 May-June;21(3):73-8478
Cephalometric evaluation of the eects of the Twin Block appliance in subjects with Class II, Division1 malocclusion amongst dierent cervical vertebral maturation stagesoriginal article
Table 2 - Pre- and post-treatment/observation changes in skeletal, dental and soft tissue variables.
Wilcoxon signed rank test.
*p<0.05; ** p<0.001.
Variables
Treatment group
(n =53)
Control group
(n =60)
T
1
Mean±SD
T
2
Mean±SD p value T
1
Mean±SD
T
2
Mean±SD p value
Skeletal variables
SNA 81.1±3.88 80.9±4.00 0.180 81.8±2.07 81.9±1.80 0.555
SNB 73.8±3.41 75.5±3.54 < 0.001** 74.7±2.15 74.8±2.19 0.072
ANB 7.31±1.99 5.37±1.99 < 0.001** 7.12±2.19 6.98±2.23 0.455
GoGn-SN 32.9±4.63 33.5±5.38 0.189 33.9±4.81 33.8±4.62 0.615
Co-A 86.7±4.81 87.8±5.06 < 0.001** 87.9±5.82 88.4±5.70 0.057
Co-Gn 106.3 ±6.92 110.9± 7.89 < 0.001** 106.4 ±7.29 107.7±7.06 < 0.001**
Go-Gn 67.4±4.24 70.8±4.22 < 0.001** 67.4±6.70 68.4±8.63 0.206
Dentoalveolar variables
UI-SN 109.8±9.82 105.1±8.60 < 0.001** 108.1±6.45 109.2±9.82 0.002*
IMPA 101.4±7.16 105.8±6.31 < 0.001** 100.2±5.70 101.3±5.60 0.124
Overjet 8.37±1.97 1.86±1.41 < 0.001** 7.87±2.98 7.56±3.43 0.067
Soft tissue variables
UL-E-line -0.23±1.67 -1.03±2.55 0.014* -0.27±2.85 -1.29±1.79 0.433
LL-E-line 0.83±2.74 1.21±2.58 0.095 -0.00±3.72 -0.56±3.34 0.194
N-L angle 102.8±13.3 106.4±11.6 0.022* 105.6±7.47 101.8±10.4 0.084
Z-angle 60.5±5.68 62.8±7.45 < 0.001** 62.3±5.10 61.3±5.59 0.585
H-angle 23.7±4.51 20.2±3.20 < 0.001** 23.0±3.31 22.8±3.11 0.620
Variables Treatment group (T
1
)
Mean±SD
Control group (T
1
)
Mean±SD p value
SNA 81.1±3.88 81.8±2.07 0.351
SNB 73.8±3.41 74.7±2.15 0.182
ANB 7.31±1.99 7.12±2.19 0.316
GoGn-SN 32.9±4.63 33.9±4.81 0.198
Co-A 86.7±4.81 87.9±5.82 0.134
Co-Gn 106.3±6.92 106.3±7.29 0.968
Go-Gn 67.4±4.24 67.4±6.70 0.266
UI-SN 109.7±9.82 108.1±6.45 0.109
IMPA 101.4±7.16 100.2±5.70 0.580
OJ (overjet) 8.37±1.97 7.87±2.98 0.146
UL-Eline -0.22±1.67 -0.27±2.85 0.764
LL-Eline 0.83±2.74 -0.01±3.72 0.221
N-L angle 102.8±13.3 105.6±7.47 0.552
Z-angle 60.5±5.68 62.3±5.10 0.352
H-angle 23.7±4.51 23.0±3.31 0.804
Table 1 - Comparison between treatment and control groups at T1.
Mann-Whitney U-test.
* p<0.05.

© 2016 Dental Press Journal of Orthodontics Dental Press J Orthod. 2016 May-June;21(3):73-8479
original article
Khoja A, Fida M, Shaikh A
Table 4 - Pre- and post-treatment/observation mean changes (T2-T1) between treatment and controls amongst different cervical stages.
Mann-Whitney U-test. *p<0.05; **p<0.001. CG=Control group; TG=Treatment group.
Variables
CS-2 CS-3 CS-4
Mean±SD Mean±SD Mean±SD
TG CG p value TG CG p value TG CG p value
n =18 n =20 n =22 n =20 n =13 n =20
SNA -0.47±0.81 -0.88±0.66 0.194 0.32±1.28 0.58±0.75 0.682 -0.69 ±0.75 0.41±0.90 < 0.001**
SNB 1.44±1.04 -0.39 ±1.07 < 0.001** 2.32±1.28 0.73±0.63 < 0.001** 1.15±0.98 0.18±1.03 0.016*
ANB -1.92±1.03 -0.48±1.28 0.001* -2.00±1.27 -0.15±1.27 < 0.001** -1.84 ±1.21 0.23±1.00 < 0.001**
GoGn-SN 0.27±2.02 -0.52±1.21 0.007* 0.14±2.55 -0.28±0.97 0.629 1.84±2.57 0.23±1.00 0.024*
Co-A 0.94±2.71 0.07±1.57 0.194 1.50±1.33 0.25±2.70 0.290 0.77±2.12 1.24±1.70 0.956
Co-Gn 3.72±1.74 1.03±1.93 < 0.001** 5.54±3.26 1.24±2.92 < 0.001** 4.15±3.53 1.65±1.93 0.027*
Go-Gn 3.38±1.68 0.10±1.57 < 0.001** 3.59±2.59 0.29±2.73 0.001* 3.31±2.46 1.17±1.62 0.004*
UI-SN -6.72±6.22 1.05±6.29 < 0.001** -1.68±4.30 1.30±2.90 0.013* -6.77 ±3.51 1.00±2.55 < 0.001**
IMPA 4.55±4.09 1.88±2.05 0.002* 3.00±3.10 0.61±2.38 0.005* 6.15±4.35 0.67±5.10 0.005*
OJ -5.59±2.96 -0.55±1.41 < 0.001** -7.25±2.20 0.14±1.01 < 0.001** -6.51 ±1.73 -0.52±1.24 < 0.001**
UL-E-line 0.05±2.76 0.04±1.54 0.597 -1.18±1.10 -1.26±5.64 0.001* -1.38 ±3.25 -0.65±1.54 0.096
LL-E-line 1.05±1.39 -0.76±2.04 0.005* 0.04±1.49 -0.25±7.03 0.630 0.00±1.73 -0.65±1.41 0.426
N-L angle 4.33±9.14 -2.55±15.3 0.208 2.31±10.53 -1.80±13.3 0.164 5.53±10.9 -6.80±14.4 0.006*
Z-angle 1.33±3.94 -0.10±5.24 0.407 2.30±3.89 -1.06±8.12 0.016* 2.46±4.96 -0.90±10.2 0.781
H-angle -3.50±3.89 -0.70±3.22 0.013* -4.54±6.35 -0.40±2.25 0.002* -2.00 ±2.41 -0.30±2.61 0.162
Table 3 - Mean change in cephalometric variables between treatment and control group (T2-T1).
Mann-Whitney U-test.
*p<0.05; **p<0.001.
Variables
Treatment group
(n =53)
Control group
(n =60) Treatment eect
p value
Mean±SD Mean±SD (Treatment – Control group)
SNA -0.19±1.10 0.04±1.01 -0.23 0.168
SNB 1.73±1.22 0.17±1.03 1.56 < 0.001**
ANB -1.96±1.16 -0.14±1.21 -1.82 < 0.001**
GoGn-SN 0.60±2.45 -0.19±1.09 0. 79 0.029*
Co-A 1.13±2.06 0.52±2.08 0.61 0.0 68
Co-Gn 4.58±2.97 1.31±2.28 3.27 < 0.001**
Go-Gn 3.45±2.24 0.52±2.06 2.93 < 0.001**
UI-SN -4.66±5.44 1.12±4.19 -5.78 < 0.001**
IMPA 4.30±3.91 1.05±3.45 3.25 < 0.001**
OJ (overjet) -6.50±2.46 -0.30±1.25 -6.20 < 0.001**
UL-E-line -0.81±2.41 -0.62±3.47 -0.19 0.015*
LL-E-line 0.37±1.57 -0.55±4.24 0.9 2 0.082
N-L angle 3.64±9.83 -3.72±14.17 7.36 0.001*
Z-angle 2.30±3.89 -1.07±8.12 3.37 0.021*
H-angle -3.56±4.86 -0.20±2.72 -3.36 < 0.001**

© 2016 Dental Press Journal of Orthodontics Dental Press J Orthod. 2016 May-June;21(3):73-8480
Cephalometric evaluation of the eects of the Twin Block appliance in subjects with Class II, Division1 malocclusion amongst dierent cervical vertebral maturation stagesoriginal article
and CS-4 (p<0.001, p=0.005) groups when compared
with their controls. Upper lip retraction was signicant
in CS-3 (p = 0.001), whereas lower lip became more
projected in CS-2 (p=0.005). The nasolabial angle in-
creased signicantly in CS-4 (p=0.006) and Z-angle in
CS-3 (p=0.016); whereas reduction in H-angle was sig-
nicant in CS-2 (p=0.013) and CS-3 (p=0.002) stages
when compared with their control groups, respectively.
Comparison of pre- and post-treatment mean
differences (T
2
-T
1
) in the treatment group at
different cervical stages
To assess variability in the eect of the Twin Block
appliance in Class II subjects treated at dierent cer-
vical stages, pre- and post-treatment mean dierences
(T
2
-T
1
) were compared for cephalometric skeletal,
dental and so tissue variables between CS-2, CS-3
and CS-4 stages of the treatment group. There was
statistically signicant dierence in the variables SNA
(p=0.010), SNB (p=0.020), UI-SN (p=0.003) and
overjet (p=0.035) between the three cervical vertebral
maturation groups. Intergroup comparisons were fur-
ther performed by means of multiple comparison tests
to evaluate pre- and post-treatment (T
2
-T
1
) changes at
dierent cervical stages, as shown in Table 5.
Cephalometric
variables p value
#
Multiple comparisons for the cephalometric variables
CS-2
(n =18)
Mean±SD
CS-3
(n =22)
Mean±SD
CS-4
(n =12)
Mean±SD
CS-2/CS-3
p
†
CS-2/CS-4
p
†
CS-3/CS-4
p
†
SNA -0.47±0.81 0.32±1.28 -0.69±1.73 0.010* 0.016* 0.435 0.011*
SNB 1.44±1.04 2.32±1.28 1.15±0.98 0.020* 0.037* 0.540 0.015*
ANB -2.00±1.02 -2.00±1.27 -1.84±1.21 0.910 0.735 0.885 0.699
GoGn-SN 0.27±2.02 0.14±2.55 1.84±2.57 0.0 96 0.339 0.266 0.026*
Co-A 0.94±2.71 1.50±1.33 0.77±2.12 0.617 0.363 0.792 0.490
Co-Gn 3.72±1.74 5.54±3.26 4.15±3.53 0.171 0.064 0.840 0.236
Go-Gn 3.38±1.68 3.59±2.59 3.31±2.46 0.900 0.890 0.625 0.769
UI-SN -7.16±6.67 -1.68±4.30 -6.76±3.51 0.003* 0.010* 0.904 0.002*
IMPA 4.55±4.09 3.00±3.10 6.15±4.35 0.065 0.056 0.387 0.055*
OJ -5.59±2.96 -7.25±2.20 -6.52±1.73 0.035* 0.018* 0.0 88 0.264
UL-E-line 0.05±2.76 -1.18±1.10 -1.38±3.25 0.244 0.475 0.183 0.128
LL-E-line 1.05±1.39 0.04±1.49 0.00±1.73 0.057 0.032* 0.057 0.696
N-L angle 4.88±9.79 2.32±10.53 4.92±10.05 0.431 0.261 0.936 0.295
Z-angle 1.33±3.94 3.00±3.10 2.46±4.96 0.480 0.227 0.559 0.619
H-angle -3.50±3.89 -4.54±6.35 -2.00±2.41 0.44 1 0.701 0.162 0.437
Table 5 - Pre- and post-treatment changes (T2-T1) in cephalometric variables at different cervical stages.
# =Kruskal-Wallis test; † =Mann-Whitney U-test.
*p ≤ 0.05
CS-2 =Cervical stage 2; CS-3 =Cervical stage 3; CS-4 =Cervical stage 4.

© 2016 Dental Press Journal of Orthodontics Dental Press J Orthod. 2016 May-June;21(3):73-8481
original article
Khoja A, Fida M, Shaikh A
DISCUSSION
Class II malocclusion can manifest in various com-
binations of skeletal and dental disharmony that aect
the overlying so tissue facial prole. However, the ma-
jority of patients have anteroposterior deciency of the
mandible.
27
Gillmore
28
reported a retropositioned, small
mandible in patients with Class II, Division 1 maloc-
clusion. Therefore, an ideal treatment plan for these pa-
tients is primarily directed towards functional appliance.
In this study, changes in skeletal, dentoalveolar
and soft tissue variables were measured on lateral
cephalograms following Twin Block appliance thera-
py. Inorder to assess the influence of normal growth
that would have occurred without the appliance in
place, it is important to have a control group.
29
Var i-
ous authors have used different control groups, such
as Class II, Division 1 malocclusion patients,
5,19
Class
I patients who did not require treatment,
30,31
patients
whose pretreatment records have been done, but
they refused to continue treatment,
3
and published
normative data using Bolton and Michigan growth
standards.
25,29
An ideal control group should be simi-
lar in terms of malocclusion, age, sex, race, skeletal
maturity and an equal observation period to that of
the treatment group. Therefore, in order to match the
control group with the study group as precise as pos-
sible, published normative growth data were used and
retrieved from the Bolton Brush study.
In order to determine the sole effects of the Twin
Block appliance, multi-banded fixed orthodontic ap-
pliances were not placed during the active and sup-
porting phase of treatment. The results of this study
showed that the Twin Block appliance has a short
term effect in treating Class II, Division 1 maloc-
clusion by a combination of skeletal (instant forward
shift of the mandible, increase in mandibular unit
length and body, gonial angle changes) and dental ef-
fects (maxillary incisor retroclincation and by loss of
anterior anchorage of mandibular incisors).
Effects on the maxilla
O’Brien et al
16
found minimal restraining effect
on maxillary growth with the Twin Block appliance,
which constituted 13% of overall skeletal changes.
Similarly, Illing et al
20
also demonstrated a small
mean reduction in SNA angle. Due to the stretch of
the muscles and surrounding soft tissues of the facial
skeleton, the forwardly placed mandible tends to re-
turn to its original position. This creates a recipro-
cal restraining effect on the maxilla, which is called
headgear effect.
13,27
However, several other studies
did not find any significant orthopedic effect exerted
on the maxilla with this appliance.
27,28
The results
obtained in the present study are in concordance
with their study results, with no statistically signifi-
cant reduction in SNA angle. In addition, change in
maxillary unit length (Co-A) was also insignificant.
Nevertheless, on stratification of sample into dif-
ferent cervical stages, significant reduction in SNA
angle was found in the CS-4 stage when compared
with controls. Toth and McNamara
25
reported that
the studies supporting maxillary growth restriction
have included extraoral force along with functional
appliance. In addition, construction bite, when reg-
istered in a single step, produces headgear effects due
to stretch of the retractor muscles.
Effects on the mandible
The eect of functional appliance on mandibular
growth is controversial. Several studies have suggested
that functional appliance can increase the SNB angle by
anterior relocation of point B and pogonion.
10,20
Baysal
and Uysal
3
found a signicant increase in SNB angle af-
ter treatment with the Twin Block appliance. Illing et al
20
found an increase in mandibular unit length measured
from point condylion and articulare to gnathion. Toth and
McNamara
25
found an increase in mandibular unit length
(Co-Gn) of 3.0mm during a 16-month period when com-
pared with controls. Our results are similar to the afore-
mentioned studies, with signicant increase in SNB angle
by 1.56˚ and mandibular unit length of 3.27 mm over a
12-month period. Growth stimulation by the Twin Block
appliance produced a greater change over a short treatment
duration, which is of benet to the patients.
27
However, it
was not possible to identify whether the increase in point
condylion to gnathion was due to true increase in man-
dibular length or merely a repositioning of the mandible.
In addition, no actual measurements of mandibular fossa
adaptation or relocation were made in this study. There-
fore, it is recommended that further studies be conducted
to assess the long term eects of the Twin Block appliance
on mandibular growth increments as well as to see the role
of mandibular fossa adaptation and possible relocation with
the functional appliance.

© 2016 Dental Press Journal of Orthodontics Dental Press J Orthod. 2016 May-June;21(3):73-8482
Cephalometric evaluation of the eects of the Twin Block appliance in subjects with Class II, Division1 malocclusion amongst dierent cervical vertebral maturation stagesoriginal article
When skeletal changes were compared among sub-
jects at dierent cervical vertebral maturation stages, in
a study conducted by Baccetti et al,
32
greater changes
were observed in the late treated groups (CS-3 and
CS-4), as compared to the early treated groups (CS-1
and CS-2).
The greater therapeutic eectiveness of func-
tional appliance occurs during the peak in the pubertal
growth spurt of an individual, which coincides with
the maximum growth rate of the mandible.
33
Similarly,
Malmgren et al
34
found greater skeletal eects of Bass
appliance in boys treated during the peak period than
those treated during the prepeak period.
In our study,
we also observed greater mandibular skeletal changes in
CS-3 and CS-4 groups, as compared to the CS-2 group.
However, this increase was statistically insignicant.
Maxillomandibular changes
In light of evidence, it was found that the reduction
in ANB angle following Twin Block appliance therapy
may occur by decrease in SNA and increase in SNB or
both. Toth and McNamara
25
found reduction in ANB
angle by 1.8˚ in patients treated with the Twin Block
appliance. Likewise, Illing et al
20
found statistically sig-
nicant reduction in ANB angle, as compared to con-
trols. Our results are similar to the above ndings, with
mean reduction in ANB angle by 1.82˚ in the total
sample. This reduction in ANB angle was primarily due
to an increase in SNB angle in CS-2 and CS-3 groups;
whereas, in CS-4, it occurred due to a combination of
decrease in SNA angle and increase in SNB angle.
Vertical relationship of the jaws
There is large variability in treatment response, with
a few studies showing an increase in total anterior facial
height and maxillary-mandibular plane angle (MMPA);
whereas other studies demonstrated a small mean re-
duction inmmPA angle.
16,17,25,35
The possible reason for
this decrease inmmPA is inhibition of molar eruption
by increasing the height of the posterior bite blocks or
by rotation of maxillary plane.
20
In this study, a signi-
cant increase in vertical jaw relationship (GoGn-SN)
was found, as compared to the controls following Twin
Block appliance therapy. However, on stratication of
sample into dierent cervical stages, this increase was
signicant at CS-2 and CS-4 stages, as compared to
controls. Since the authors of this study did not con-
sider the vertical dimensions of subjects prior to their
inclusion, this may have aected treatment results.
Therefore, it is advisable that subjects in future studies
be selected with regard to their facial heights and verti-
cal pattern of growth.
Dentoalveolar changes
Illing et al
20
found a mean reduction in the in-
clination of maxillary incisors, which was more
pronounced in the Twin Block group (-9.1 ± 6.2˚)
when compared to Bass and bionator. This effect is
greater by incorporation of labial bow into an appli-
ance. O’Brien et al
16
showed that maxillary incisor
retraction contributed significantly to overjet reduc-
tion and, therefore, Class II malocclusion is mainly
corrected by dentoalveolar movements rather than
mandibular growth. In our study, significant retro-
clination of maxillary incisors was found following
Twin Block appliance therapy amongst all cervical
stages. However, this reduction in maxillary inci-
sor inclination was greater in CS-2 and CS-4 stages
compared to CS-3 stage.
The effect on mandibular incisors is variable in
different studies. Lund and Sandler
35
found a sta-
tistically significant increase in mandibular incisor
inclination, while Illing et al
20
found no significant
change. In this study, a significant increase in man-
dibular incisor inclination was observed despite
mandibular incisor capping into an appliance, which
was found to be statistically significant amongst all
cervical stages when compared to controls. Procli-
nation of labial segment contributes to overjet re-
duction by limiting the potential for further growth.
In addition, proclination of mandibular incisors in-
crease the tendency towards relapse and, therefore,
must be corrected during the second phase of orth-
odontic treatment with interdental stripping or ex-
tractions.
36
Soft tissue changes
Upper and lower lip position
Quintão et al
5
found a significant change in up-
per lip position due to maxillary incisor retroclina-
tion after functional appliance treatment. In con-
trast, Morris et al,
17
in their study, demonstrated no
significant change in the sagittal position of upper
lip despite large reductions in overjet. In our study,
upper lip became significantly less projected in the

© 2016 Dental Press Journal of Orthodontics Dental Press J Orthod. 2016 May-June;21(3):73-8483
original article
Khoja A, Fida M, Shaikh A
treatment group when compared to the controls.
Baysal and Uysal
3
found greater advancement of the
lower lip, lower lip sulcus and soft tissue pogonion
in the Twin Block group. In contrast, Quintão et al,
5
in their study, did not find any significant changes
in any of the lower lip variables. In our study, lower
lip changes were observed only in the CS-2 group.
However, the E-line, as a reference plane to quantify
actual changes in lips, is not very reliable because of
the simultaneous growth of the soft tissue chin and
pronasale that may give a false impression of the ac-
tual lip position.
Nasolabial angle
Quintão et al,
5
in their study, did not nd any sta-
tistically signicant change in the nasolabial angle aer
treatment with the Twin Block appliance. Incontrast,
Varlik et al
11
found signicant increase in nasolabial
angle in the Twin Block group. Likewise, in our study,
we found signicant increase in the nasolabial angle,
which may be the result of the change in upper lip po-
sition. On stratication of sample into dierent cer-
vical stages, this increase was signicant at the CS-4
stage when compared to controls.
Z-angle
Varlik et al,
11
in their study, found a significant
increase in Z-angle in patients treated with the Twin
Block appliance due to forward movement of soft
tissue chin. Our results are similar to their study.
However, on stratification of sample into different
cervical stages, this increase was significant only at
the CS-3 stage when compared to controls.
H-angle
Holdaway
38
related H-angle decreases as the facial
convexity decreases. Baysal and Uysal,
3
in their study,
found a signicant reduction in this angle aer Twin
Block appliance treatment, which showed improve-
ment in facial convexity. In our study, we also found
signicant reduction in this angle at the CS-2 and CS-3
stages, with an overall improvement of facial prole.
The possible explanation for this reduction in H-angle
is the combination of upper lip retraction and forward
movement of the so tissue pogonion.
CONCLUSIONS
» The Twin Block appliance reduces overjet in ClassII,
Division 1 malocclusion by means of favorable skeletal
changes in bony bases and dentoalveolar compensations.
» Overlying so tissues change along with underly-
ing hard tissues, which improves overall facial esthetics.
» Mandibular growth changes were signicant amongst
all cervical stages. However, they are more pronounced
when appliance is placed during the CS-3 stage, as com-
pared to CS-2 and CS-4 stages. Any attempt to change
the growth is best achieved at the peak of pubertal
growth; therefore, it is better to wait for CS-3 to achieve
maximum skeletal eects as well as to reduce overall
treatment duration.
» Dentoalveolar changes were also minimal dur-
ing treatment in CS-3 stage, as compared to CS-2 and
CS-4 stages.

© 2016 Dental Press Journal of Orthodontics Dental Press J Orthod. 2016 May-June;21(3):73-8484
Cephalometric evaluation of the eects of the Twin Block appliance in subjects with Class II, Division1 malocclusion amongst dierent cervical vertebral maturation stagesoriginal article
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