CASE REPORT

Severe Class II Division 1 malocclusion

in an adolescent patient, treated with a novel
sagittal-guidance Twin-block appliance
Peilun Li,a Jing Feng,b Gang Shen,c and Ning Zhaob
Shanghai, China

Class II malocclusion is a challenging anomaly in orthodontic practice. Various types of functional appliances are
used to correct Class II skeletal and occlusal disharmonies in growing patients, including the Twin-block. We
used a modified sagittal-guidance Twin-block appliance combined with a fixed appliance and microimplant
anchorage to treat a 13-year-old Chinese boy with a severe skeletal Class II malocclusion and mandibular retro-
gnathia. Normal overjet and a Class I molar relationship were achieved because of the advancement of mandib-
ular development, the restriction of maxillary growth, and dentoalveolar modifications in both the maxilla and the
mandible. Favorable skeletal, dental, and soft tissue relationships were accomplished after 24 months of treat-
ment. After 2 years of retention, the results remained stable. (Am J Orthod Dentofacial Orthop 2016;150:153-66)

C
lass II malocclusion is a challenging anomaly in The SGTB consists of a bonded maxillary component
orthodontic practice. The development of this and a mandibular removable counterpart. The maxillary
malocclusion is due to mandibular retrognathia, component, which was bonded to the maxilla, has
maxillary protrusion, or both. It has been reported that occlusal planes that cover the bilateral buccal dentition
retrusion of the mandible is the factor that most and often has a screw expansioner incorporated pala-
commonly contributes to a Class II malocclusion.1 tally. The mandibular piece, which is removable via
Various types of functional appliances (eg, activator, Adams clasps on the first premolars and the first molars
bionator, Fr€ankel, and Herbst) are used for the correction and ball clasps between the mandibular incisors for
of Class II skeletal and occlusal disharmonies in growing retention, has occlusal planes that bilaterally cover
patients. Over recent decades, Twin-block appliances, only the area of the premolars combined with a lingual
which were originally developed by Clark2 in the late acrylic pad that extends posteriorly. The angulation of
1970s, have increased in popularity.3 the interface between the upper and lower occlusal
In this case report, we used a renovated sagittal- planes is 70 . Two brackets are embedded into the
guidance Twin-block appliance (SGTB) combined buccal facade of the upper occlusal planes and serve as
with a fixed appliance and microimplant anchorage anchorage for the further placement of a maxillary par-
for the treatment of a 13-year-old Chinese boy with a tial fixed appliance.
severe skeletal Class II malocclusion and mandibular The cephalometric analysis of Pancherz4 showed that
retrognathia. the normal overjet and a Class I molar relationship were
From the Department of Orthodontics, Shanghai Ninth People's Hospital,
achieved because of the advancement of mandibular
Shanghai Jiao Tong University, Shanghai, China. development, the restriction of maxillary growth, and
a
b
Postgraduate student. dentoalveolar modifications in both the maxilla and
Assistant professor.
c
Department chair.
the mandible. Favorable skeletal, dental, and soft tissue
All authors have completed and submitted the ICMJE Form for Disclosure of relationships were accomplished after 24 months treat-
Potential Conflicts of Interest, and none were reported. ment. After 2 years of retention, the stability of the treat-
Address correspondence to: Ning Zhao, Department of Orthodontics, Shanghai
Ninth People's Hospital, Shanghai Jiao Tong University, Shanghai, China;
ment was pronounced.
e-mail, zhaon1995@126.com.
Submitted, January 2015; revised and accepted, July 2015.
0889-5406/$36.00 DIAGNOSIS AND ETIOLOGY
Copyright Ó 2016 by the American Association of Orthodontists. All rights
reserved. The patient was a 13-year-old Chinese boy with a
http://dx.doi.org/10.1016/j.ajodo.2015.07.046 convex facial profile, protrusive and everted lips, and a
153
154 Li et al

Fig 1. Pretreatment extraoral and intraoral photographs showing the convex profile that resulted from
the retrusive mandible and Class II molar relation.

deep mentolabial fold. The frontal view did not show any No symptoms of temporomandibular disorder were
facial asymmetry or deviation between the dental and detected.
facial midlines (Fig 1). Based on these findings, the patient was diagnosed
Intraoral, dental cast, and 3-dimensional (3D) model with a Class II Division 1 malocclusion, a low mandibular
examinations showed full-unit Class II molar relation- plane angle, a deep overbite, a deep overjet, and a local-
ships on both sides. A deep overjet of 12.7 mm, a com- ized scissors-bite.
plete deep overbite, and a resultant deep curve of Spee
were also found. Furthermore, there was a scissors-bite TREATMENT OBJECTIVES
of the premolars on the right side. The maxillary arch
The treatment objectives for this patient were the
had spread spacings of 4.5 mm (Figs 1 and 2).
following: (1) amend the skeletal discrepancy with a
The lateral cephalometric analysis showed a Class II
SGTB, (2) retract the maxillary front teeth, (3) create
skeletal pattern that resulted from maxillary protrusion
ideal overjet and overbite, (4) correct the scissors-bite
and mandibular retrusion (ANB, 7.6 ; Wits appraisal,
of the premolars on the right side, (5) improve the facial
8.8 mm) and a decreased mandibular plane angle (MP-
profile, and (6) ultimately achieve long-term stability.
FH, 18.3 ). Both the maxillary and mandibular incisors
were labially proclined (U1-SN, 122.2 ; L1-MP, 109.9 ).
TREATMENT ALTERNATIVES
A panoramic radiograph showed root morphology that
appeared normal, and 4 third molars were developing. Ex- Orthopedic treatment with headgear alone to distal-
aminations of the cephalometric and cervical vertebrae ize the maxillary buccal segment could have corrected
suggested that the patient was in a pubertal growth spurt the molar relationship and reduced the overjet and
(Fig 3; Table I), which indicated optimal timing for ortho- may also have restrained the maxilla, but the efficacies
pedic therapy for a Class II disharmony.5 of these removable appliances and headgear depend

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Li et al 155

Fig 2. Pretreatment study casts depicting the proclined maxillary incisors and the increased overjet
and spacing in the frontal segment.

Fig 3. Pretreatment cephalogram, tracing, and panoramic radiograph.

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156 Li et al

exercises by pressing his lips together as much as

Table I. Cephalometric analysis from lateral radio-
possible.
graphs
The brackets were bonded on the maxillary front
After teeth in the fourth month, and a 0.012-in nickel-
Twin-block titanium wire was engaged for the initial alignment
Variable Pretreatment appliance Posttreatment D
(Fig 5). After 8 months of treatment, the maxillary fron-
SNA ( ) 85.3 85.2 85.3 0
SNB ( ) 77.8 79.5 80.9 3.1 tal segment was retracted backward with an 0.018-in
ANB ( ) 7.5 5.7 4.4 3.1 stainless steel archwire. The bonded maxillary device
Wits (mm) 8.8 5.4 4.0 4.8 served as solid anchorage for the retraction of the ante-
ANS-PNS 52.6 51.8 51.7 0.9 rior teeth (Fig 6). At this time, the spaces between the
(mm)
maxillary canines and the acrylic blocks were approxi-
Go-Me 74.6 75.9 77.4 2.8
(mm) mately 2 mm, which indicated that the SGTB appliance
Ar-Go 51.4 53.8 55.1 3.7 produced favorable molar distalization in the maxillary
(mm) buccal segment.
ANS-Me 64.1 66.6 66.0 1.9 After 11 months of treatment, the patient obtained a
(mm)
stabilized and forward mandible position. Next, we
MP-FH ( ) 18.3 19.2 18.5 0.2
U1-L1 ( ) 104.3 116.6 122.6 18.3 removed the SGTB and took records for reassessment
U1-SN ( ) 122.2 108.4 104.6 17.6 (Figs 7 and 8). Based on the straight profile and the
L1-MP ( ) 109.9 112.2 112.1 2.2 spacing in the maxillary arch after the SGTB treatment,
Overjet 12.7 4.8 2.8 9.9 we decided not to treat this patient with extractions of
(mm)
any premolars in the second stage. Because any
Overbite 6.1 3.7 2.8 3.3
(mm) anchorage loss might have jeopardized the reduced
overjet and the improved molar relationship, we
planned to reinforce the anchorage using
on patient compliance.4 Moreover, the unesthetic microimplant anchorage in the maxilla and preferred
appearance can embarrass the patient and result in to extract the maxillary third molars.
poor cooperation. In the 16th month, during the placement of
Camouflage therapy by removing the maxillary pre- 0.018 3 0.025-in stainless steel archwires in both
molars in patients with mandibular retrognathia requires arches, microimplant anchorage devices (diameter,
a more thorough assessment6; otherwise, it can lead to 1.6 mm; length, 10 mm; Cibei Medical Treatment Appli-
detrimental changes in the soft tissue profile.7 ance, Ningbo, China) were inserted into the apical root
The treatment of Class II adolescent patients requires regions between the maxillary first molars and second
careful diagnosis and treatment planning. The family premolars on both sides under local anesthesia (Fig 9).
was shown a simulation of the results of protruding The maxillary front teeth were retracted with elastic
the mandible forward, and they preferred this profile. chains from the microimplant anchorage to the archwire
with a force of approximately 150 g per side. Meanwhile,
TREATMENT PROGRESS we instructed the patient to use the elastics full time in
The patient and his parents agreed with the treat- the right buccal segment to correct the scissors-bite.
ment plan after receiving detailed explanations about The overall treatment time was 24 months (Fig 10).
the SGTB, microimplant anchorage, and related clinical After debonding, the microimplant anchorage devices
procedures. This protocol was accepted by the patient's were removed, and clear retainers were issued for full-
family and approved by the ethics committee of time wear over the next year.
Shanghai Ninth People's Hospital.
The SGTB appliance was issued after oral hygiene
instructions and scaling (Fig 4). For the spaced and TREATMENT RESULTS
proclined maxillary incisors, early retraction of the Favorable skeletal, dental, and soft tissue relation-
anterior teeth was selected. Therefore, 2 embedded ships were obtained. The severe deep overjet was cor-
preadjusted straight-wire brackets for the buccal sur- rected. Class I canine and molar relationships on both
faces of the maxillary first premolars were designed, sides were also achieved. The scissors-bite of the premo-
and the maxillary component was fixed to the arch lars on the right side was corrected, and the posterior
to serve as a strong anchorage for anterior teeth occlusal interdigitation was improved. The profile was
alignment. The patient was instructed to wear the greatly improved by repositioning of both the maxilla
SGTB 24 hours per day and perform musculature and the mandible (Figs 10 and 11).

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Li et al 157

Fig 4. Modified Twin-block appliance design. Anterior, lateral, and occlusal views showing the
following components. Maxillary appliance: (1) occlusally inclined planes occluded at a 70 angle in first
premolar region, (2) 2 preadjusted straight-wire brackets on the buccal surface of the acrylic plates at
the position of the first premolar, and (3) transpalatal arches (1.0 mm) that served as connectors. When
necessary, an expansion appliance can replace the transpalatal arches for compensatory lateral
expansion. Mandibular appliance: (1) ball clasps (0.8 mm) in the incisor region, (2) Adams clasps
(0.8 mm) on the first premolars and first molars, and (3) inclined planes in the first premolar region.

Fig 5. In the fourth month, the straight-wire appliance was bonded to the maxillary front teeth, and a
0.012-in nickel-titanium wire was engaged for the initial alignment.

The cephalometric analysis indicated a significant backward (the A-OLp changed from 81.1 to 80 mm),
skeletal anteroposterior reduction. The ANB angle which indicated the successful restriction of maxillary
decreased by 3.2 , and the Wits value decreased by growth and dentoalveolar changes. Large increments
4.8 mm from 8.8 to 4.0 mm. The length of the maxillary in total mandibular length (Go-Me increased from 74.6
base (ANS-PNS) decreased from 52.6 mm to 51.7 mm, to 77.4 mm) and in ramus height (Ar-Go increased
and the position of maxillary base had been retracted from 51.4 to 55.1 mm) indicated favorable growth of

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158 Li et al

Fig 6. Eight months into treatment, an 0.018-in stainless steel archwire was placed, and the maxillary
frontal segment was retracted backward with a solid anchorage supported by the maxillary device.

Fig 7. Eleven months into treatment. Extraoral and intraoral photographs. The Twin-block appliance
was removed, and the fixed appliance was fully bonded. The spaces between the maxillary canines
and the first premolars were approximately 2 mm, indicating favorable molar distalization in the buccal
segment because of the Twin-block appliance.

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Li et al 159

Fig 8. Eleven months into treatment: cephalogram, tracing, and panoramic radiograph after the Twin-
block appliance had been removed.

the mandible. The cephalometric superimposition primarily caused by the maxillary incisor retraction.
showed a slightly increased mandibular plane angle of The skeletal contribution to the molar correction was
0.2 . The positions of the maxillary incisors were signif- predominant (88%). The increments in the mandibular
icantly affected (U1-SN decreased from 122.2 to base measurement accounted for most of the skeletal
104.6 ), whereas the mandibular incisors were not changes, whereas the dental changes were due primarily
significantly proclined by the treatment (L1-MP slightly to the distal movement of the maxillary molars.
increased by 2.2 ). The molars in the maxillary arch were A posttreatment panoramic radiograph showed no
distalized by 1.8 mm (Ms-OLp changed from 58 to apparent root resorption. It was still necessary to extract
56.2 mm) (Figs 12 and 13; Tables I and II). the mesially impacted mandibular third molars (Fig 12).
The cephalometric analysis of Pancherz4 was used to A stable occlusion and a harmonious facial balance
show the therapeutic effects of the novel SGTB appli- were maintained after 2 years (Fig 15).
ance in this patient (Fig 14; Table II). The active treat-
ment phase produced an overjet correction of 9.9 mm
and a correction in the molar relationship of 6.0 mm. DISCUSSION
The skeletal and dentoalveolar contributions to the over- Regarding the therapeutic choices for growing skel-
jet correction were almost equivalent (54% skeletal and etal Class II patients, many studies have reported that
46% dentoalveolar). The skeletal component of the functional appliances are highly effective in achieving
overjet correction was primarily due to the mandibular better relationships between the maxilla and the
changes, and the dentoalveolar component was mandible.1,6-9 Twin-block appliances, among other

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160 Li et al

Fig 9. In the 16th month of treatment when the 0.018 3 0.025-in stainless steel archwires were placed
in both arches, microimplant anchorages were placed to enhance the anchorage for the retraction of
the maxillary labial segment.

Fig 10. Posttreatment extraoral and intraoral photographs showing the improved facial appearance
and Class I molar relationship.

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Li et al 161

Fig 11. Posttreatment study casts.

Fig 12. Posttreatment cephalogram, tracing, and panoramic radiograph.

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162 Li et al

Fig 13. Posttreatment cephalometric superimpositions. Red line, pretreatment; black line, after Twin-
block treatment; blue line, posttreatment. A, The overall superimposition was registered on SN at sella;
B, the maxillary superimposition was registered on the palatal plane at ANS; C, the mandibular super-
imposition was registered on the long axis of the mandible at protuberance menti.

functional appliances, have proven to be comfortable, The classic Twin-block appliance consists of maxil-
esthetic, and efficient.3 Twin-block appliances have lary and mandibular acrylic plates with bite-blocks that
several advantages; they are well-tolerated by patients,10 position the mandible forward on closure. These devices
robust, easy to repair, and suitable for use in the perma- have been demonstrated to be clinically efficient for
nent and mixed dentition.3,5,11-15 However, there are growing patients with mandibular retrognathia caused
also some potential disadvantages that include by a combination of dentoalveolar and skeletal ef-
proclination of the mandibular incisors and the fects.5,11-16 In our patient, we designed a novel
development of posterior open bites.16-18 appliance based on the classic Twin-block appliance of
In our patient, the cephalometric analysis indicated Clark.2 This novel appliance was a semifixed functional
mandibular retrusive positioning, reduced lower facial appliance with the following structural modifications:
height, flat mandibular plane, deep curve of Spee, flar- (1) the cemented maxillary component, (2) 2 preadjusted
ing maxillary incisors, and severe overjet and overbite. brackets embedded on the maxillary first premolar
Using the SGTB combined with a fixed appliance and buccal surfaces, and (3) the removable mandibular com-
microimplant anchorage devices, we achieved a favor- ponents with Adams clasps on both first molars as the
able result and a good sagittal jaw relationship with anchorage units.
the dentoalveolar changes. The main mechanisms One major problem associated with removable func-
included the distalization of the maxillary posterior tional appliances is patient cooperation. Clark2 also
segment, the lingual inclination of the maxillary inci- suggested that his classic Twin-block appliance should
sors, and the mild labial inclination of the mandibular be fixed in the mouth for the first 2 weeks of treatment.
incisors. Our patient was able to eat and speak with both the

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Li et al 163

clasps were placed on the first molars, and ball clasps

Table II. Cephalometric values of the analysis of
4 were placed in the mandibular incisor region. This com-
Pancherz in this patient (mm)
bination of clasps provided excellent retention and was
Variable Pretreatment Posttreatment effective in reducing the proclination of the mandibular
Overjet Is-OLp–Ii-OLp 12.7 2.8 incisors during the orthopedic stage.
Molar Ms-OLp–Mi-OLp 2.3 3.7 After removal of the appliances, sagittal correction
relationship
was achieved with a normal incisor relationship and an
Position of A-OLp 81.1 80.0
maxillary open bite in the posterior region. However, with the
base development of different types of superelastic nickel-
Position of Pg-OLp 77.1 81.3 titanium archwires, such open-bite problems can easily
mandibular be solved in 2 months. During the early alignment stage,
base
we used glass ionomer cement as the occlusal plate on
Jaw A-OLp–Pg-OLp 4.0 1.3
relationship the maxillary first or second molar. With the alignment
Position of Is-OLp 91.7 86.1 and leveling of both the maxillary and mandibular pos-
maxillary terior teeth, the occlusal plate can be reduced by
central grinding, and the posterior open bite can be closed
incisor
with 1 or 2 wire changes. Both the maxillary and
Position of Ii-OLp 79.0 83.3
mandibular mandibular posterior teeth can continue to erupt until
central they come into contact with the opposing teeth. We pre-
incisor sumed that it might be advantageous to allow both the
Position of Ms-OLp 58.0 56.2 maxillary and mandibular molars to erupt nearly freely
maxillary
under the guidance of the nickel-titanium archwires.
first
permanent This process might have led to a more reliable result
molar with long-term stability. The mechanism of the creation
Position of Mi-OLp 55.7 59.9 of a stable occlusion requires continuing research.
mandibular The classic Twin-block appliance of Clark2,3,19 was
first
designed for full-time wear to take advantage of all
permanent
molar functional forces applied to the dentition including the
forces of mastication. During the development of
different Twin-block appliances, the maxillary and
maxillary and mandibular appliances in place after only mandibular bite-block interlock angles have varied
several days of adaptation. The bonded maxillary from 45 to 90 .19 In the SGTB, we set the bite-block
component might facilitate adaptation to this appliance angle to 70 . We chose this angulation for the
and guarantee nearly full-time wearing of the appli- maxillary-mandibular interface for several reasons. We
ance. attempted to set up a small interincisal distance to
Two preadjusted brackets embedded on the buccal encourage the patient to close his lips naturally; when
surfaces of the maxillary first premolars allowed 2 stages the bite-block interlock angle is lower, the maxillary-
of the treatment to be conducted simultaneously. After mandibular interface is separated farther when the pa-
the initial alignment, the maxillary front teeth were re- tient is in a resting position, and when the angle is
tracted backward with solid anchorage supported by greater, the interlock influences the normal rotation of
the device. With this combination of orthopedic and the mandible. We also attempted to change the force
fixed appliances, the overall treatment time could be vector to be more sagittal and less vertical to achieve
shortened. additional sagittal guiding effects. Figure 16 illustrates
In the treatment of deep overbites in patients with why a larger interface angulation is superior for
horizontal growth patterns, Clark3,19 thought that it achieving additional sagittal guiding effects.
was a mistake to place clasps on the mandibular Regarding the classic Twin-block of Clark3 and other
molars because this would not allow for the vertical orthopedic appliances that are used for Angle Class II ad-
development of the posterior teeth to reduce the olescents, functional retention, such as an anterior in-
overbite and might result in a large posterior open bite clined plane, is recommended after functional therapy.
when the blocks are removed. However, it might result For our SGTB, we use the appliance at the end of the
in proclination of the mandibular incisors. mixed and the early permanent dentition stages when
In our patient, the lingual base of the mandibular patients have growth potentials of 60% to 80% accord-
appliance extended to the molar region where the Adams ing to vertebral evaluations.5,12,20,21 We combined the

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164 Li et al

Fig 14. Diagram of the maxillary and mandibular skeletal and dentoalveolar changes that contributed
to the sagittal overjet and molar corrections.

functional appliance with a fixed appliance via the bonded maxillary component encouraged full-time wear-
design of the maxillary bonded component and the ing of the appliance. Moreover, the embedded brackets
preadjusted brackets that were embedded on the enabled the overlapping of the functional orthopedic
buccal surface. After removal of the orthopedic phase with the fixed appliance phase. The distalization
appliances, we were able to continuously set up fixed of the maxillary posterior teeth and the growth of the
appliances for patients without any time lag for mandible were most likely the primary mechanisms of
functional retention. the effects of this novel appliance. The posterior open
bite was quickly closed with the guidance of the superelas-
tic nickel-titanium archwires after bite jumping. More-
CONCLUSIONS over, this approach might lead to more reliable results
In this case report, a renovated SGTB appliance with a by allowing the free eruption of both maxillary and
specially designed maxillary component combined with mandibular molars. As rigid anchorage, microimplant
microimplant anchorage was used to effectively treat a anchorage can used to achieve normal dental and skeletal
teenage boy with a severe skeletal Class II diagnosis. The relationships as well as a pleasing soft tissue profile.

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Li et al 165

Fig 15. Follow-up after 2 years of retention.

Fig 16. Diagram showing the working principles of changes in the angulation of the inclined surface
from 45 to 70 . This change altered the force vector to be sagittal and less vertical and caused the po-
sition of mandible to be more anterior in resting positions.

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