Introduction to Twin Blocks 7

Chapter 2

Introduction to Twin Blocks

THE OCCLUSAL INCLINED PLANE

The occlusal inclined plane is the fundamental functio-
nal mechanism of the natural dentition. Cuspal inclined
planes play an important part in determining the rela-
tionship of the teeth as they erupt into occlusion.
If the mandible occludes in a distal relationship to
the maxilla, the occlusal forces acting on the mandibular
teeth in normal function have a distal component of A
force that is unfavorable to normal forward mandibular
development. The inclined planes formed by the cusps of
the upper and lower teeth represent a servomechanism
that locks the mandible in a distally occluding functional
position.
Twin Block appliances are simple bite blocks that
are designed for full-time wear. They achieve rapid func-
B
tional correction of malocclusion by the transmission of
Figs. 2.1A and B: The occlusal inclined plane is the functional
favorable occlusal forces to occlusal inclined planes that mechanism of the natural dentition. Twin Blocks modify the occlusal
cover the posterior teeth. The forces of occlusion are used inclined plane and use the forces of occlusion to correct the maloc-
clusion. The mandible is guided forwards by the occlusal inclined
as the functional mechanism to correct the malocclusion
plane.
(Figs. 2.1A and B).
Malocclusion is frequently associated with discre-
PROPRIOCEPTIVE STIMULUS TO GROWTH pancies in arch relationships due to underlying skeletal
and soft-tissue factors, resulting in unfavorable cuspal
The inclined plane mechanism plays an important part guidance and poor occlusal function. The proprioceptive
in determining the cuspal relationship of the teeth as sensory feedback mechanism controls muscular activity
they erupt into occlusion. A functional equilibrium is and provides a functional stimulus or deterrent to the
established under neurological control in response to full expression of mandibular bone growth. The unfa-
repetitive tactile stimulus. Occlusal forces transmitted vorable cuspal contacts of distal occlusion represent an
through the dentition provide a constant proprioceptive obstruction to normal forward mandibular translation in
stimulus to influence the rate of growth and the trabecular function, and as such do not encourage the mandible to
structure of the supporting bone. achieve its optimum genetic growth potential.
8 Twin Block Functional Therapy—Applications in Dentofacial Orthopedics

Transverse Maxillary Development pattern is established that can support a new position
of equilibrium.
Transverse maxillary development is restricted as a result
of a distally occluding mandible. In a retrusive mandible
TWIN BLOCKS
the lower dentition does not offer support to the maxillary
arch, therefore the maxillary intercanine width and inter- The goal in developing the Twin Block approach to treat-
premolar width is reduced accordingly. The constricted ment was to produce a technique that could maximize
width of the maxillary dentition has the effect of locking the growth response to functional mandibular protrusion
the mandible in a distal occlusion and prevents normal by using an appliance system that is simple, comfortable
mandibular development. and aesthetically acceptable to the patient.
Functional appliance therapy aims to improve the Twin Blocks are constructed to a protrusive bite
functional relationship of the dentofacial structures by that effectively modifies the occlusal inclined plane by
eliminating unfavorable developmental factors and means of acrylic inclined planes on occlusal bite blocks.
improving the muscle environment that envelops the The purpose is to promote protrusive mandibular func-
developing occlusion. By altering the position of the tion for correction of the skeletal Class II malocclusion
teeth and supporting tissues, a new functional behavior (Figs. 2.2A to F).

A B

C D
Figs. 2.2A to D: (A and B) Upper Twin Block—occlusal and frontal; (C and D) Lower Twin Block—occlusal and rear views.
 Introduction to Twin Blocks 9

E F
Figs. 2.2E and F: Twin Blocks.

The occlusal inclined plane acts as a guiding mecha- Class II division 1 malocclusion. This basic principle still
nism causing the mandible to be displaced downward and applies but over the years many variations in appliance
forward. With the appliances in the mouth, the patient design have extended the scope of the technique to treat
cannot occlude comfortably in the former distal position a wide range of all classes of malocclusion. Appliance
and the mandible is encouraged to adopt a protrusive design has been improved and simplified to make Twin
bite with the inclined planes engaged in occlusion. Blocks more acceptable to the patient without reducing
The unfavorable cuspal contacts of a distal occlusion their efficiency.
are replaced by favorable proprioceptive contacts on the In the treatment of Class II division 2 malocclusion,
inclined planes of the Twin Blocks to correct the maloc- appliance design is modified by the addition of sagittal
clusion and to free the mandible from its locked distal screws to advance the upper anterior teeth. Control of the
functional position. vertical dimension is achieved by sequentially adjusting
Twin Blocks are designed to be worn 24 hours per
the thickness of the posterior occlusal inclined planes to
day to take full advantage of all functional forces applied
control eruption (Figs. 2.3A to C).
to the dentition, including the forces of mastication.
Treatment of Class III malocclusion is achieved by
Upper and lower bite blocks interlock at a 70° angle
reversing the occlusal inclined planes to apply a forward
when engaged in full closure. This causes a forward
component of force to the upper arch and a downward
mandibular posture to an edge-to-edge position with
and distal force to the mandible in the lower molar
the upper anteriors, provided the patient can comfortably
maintain full occlusion on the appliances in that position. region. The inclined planes are set at 70° to the occlusal
In treatment of Class II malocclusion, the inclined planes plane with bite blocks covering lower molars and upper
are positioned mesial to the upper and lower first molars deciduous molars or premolars, with sagittal screws to
with the upper block covering the upper molars and advance the upper incisors (Figs. 2.4A to C).
second premolars or deciduous molars, and the lower The first principle of appliance design is simplicity.
blocks extending mesially from the second premolar or The patient’s appearance is noticeably improved when
deciduous molar region. Twin Blocks are fitted. Twin Blocks are designed to be
In the early stages of their evolution, Twin Blocks comfortable, aesthetic and efficient. By addressing these
were conceived as simple removable appliances with requirements, Twin Blocks satisfy both the patient and
interlocking occlusal bite blocks designed to posture the the operator as one of the most “patient friendly” of all
mandible forward to achieve functional correction of a the functional appliances.
10 Twin Block Functional Therapy—Applications in Dentofacial Orthopedics

Treatment of Class II Division 2 Malocclusion

A B C
Figs. 2.3A to C: Correction of Class II division 2 malocclusion by advancing the mandible and proclining the upper incisors with sagittal
screws. Vertical control is important in management of Class II division 2 malocclusion. The bite registration for this type of malocclusion
is edge to edge on the upper and lower incisors. The overbite is reduced by progressive trimming of the upper blocks to allow eruption of
lower molars. At the end of the Twin Block phase the molars are in Class I occlusion and the overbite is fully reduced.

Treatment of Class III Malocclusion

A B C
Figs. 2.4A to C: Reverse Twin Blocks for correction of Class III malocclusion with sagittal screws to advance upper incisors. The upper
block may also incorporate an occlusal screw for progressive activation.
 Introduction to Twin Blocks 11

DEVELOPMENT OF TWIN BLOCKS The appliance mechanism was designed to harness the
forces of occlusion to correct the distal occlusion and also
Case Report: CG Aged 7 Years 10 Months to reduce the overjet without applying direct pressure to
It is true that ‘necessity is the mother of invention’. The the upper incisors.
Twin Block appliance evolved in response to a clinical The upper and lower bite blocks engaged mesial to
problem that presented when a young patient, the son the first permanent molars at 90° to the occlusal plane
of a dental colleague, fell and completely luxated an when the mandible postured forward. This positioned
upper central incisor. Fortunately, he kept the tooth, the incisors edge-to-edge with 2 mm vertical separation
to hold the incisors out of occlusion. The patient had to
and presented for treatment within a few hours of the
make a positive effort to posture his mandible forward to
accident. The incisor was reimplanted and a temporary
occlude the bite blocks in a protrusive bite. Fortunately,
splint was constructed to hold the tooth in position
the young patient was successful in doing this consistently
(Figs. 2.5A to L).
to activate the appliance for functional correction. Had
Before the accident the center line was displaced
he not made this effort the technique may have been
to the right and the luxated incisor had a pronounced
stillborn.
distal angulation with a central diastema of 3 mm. When
The first Twin Block appliances were fitted on
the tooth was reimplanted the socket was enlarged to
7 September 1977, when the patient was aged 8 years
reposition the incisor as near as possible to the midline. 4 months. The bite blocks proved comfortable to wear
Complete correction of the midline was not possible, and treatment progressed well as the distal occlusion
recognizing that enlarging the socket too much might corrected and the overjet reduced from 9 mm to 4 mm
reduce the prognosis for reattachment of the tooth. in 9 months.
After 6 months with a stabilizing splint, the tooth had During the course of treatment radiographs confirmed
partially reattached, but there was evidence of severe that the reimplanted incisor had severe root resorption
root resorption and the long-term prognosis for the and an endodontic pin was placed to stabilize this tooth
reimplanted incisor was poor. after 4 months of treatment. This was successful in stabi-
The occlusal relationship was Class II division 1 lizing the incisor.
with an overjet of 9 mm and the lower lip was trapped At a later stage, in the permanent dentition, a simple
lingual to the upper incisors. Adverse lip action on upper fixed appliance was used to complete treatment. It
the reimplanted incisor was causing mobility and root was not possible to correct the centre line fully in replacing
resorption. To prevent the lip from trapping in the overjet the luxated tooth, and the central incisor ankylosed
it was necessary to design an appliance that could be during the process of reattachment. Consequently, a
worn full time to posture the mandible forward. At that slight displacement of the center line had to be accepted.
time no such appliance was available and simple bite The reimplanted incisor was crowned successfully, and
blocks were therefore designed to achieve this objective. the result is stable at age 25 years.
12 Twin Block Functional Therapy—Applications in Dentofacial Orthopedics

Case Report: CG

A B

D E F

G H I

J K L
Figs. 2.5A to L: Treatment: (A and B) Before treatment: 1 was completely luxated and was reimplanted. An endodontic pin was fitted
to stabilize the incisor. This was successful in achieving bony reattachment; (C) Profiles at ages 7 years 10 months (before treatment),
9 years 7 months (after 9 months of treatment) and 24 years; (D and E) Dental views before treatment at age 7 years 10 months;
(F) After 9 months of treatment, the overjet has reduced, and the distal occlusion is corrected; (G and H) The first Twin Blocks were
simple bite blocks occluding in forward posture. The blocks were angled at 90° to the occlusal plane; (I) A simple fixed appliance is used
to improve alignment in permanent dentition. The damaged upper incisor is now ankylosed; (J to L) The occlusion remains stable 5 years
out of retention.
 Introduction to Twin Blocks 13

MODIFICATION FOR TREATMENT OF The original Twin Block prototype appliances were
CLASS II DIVISION 2 MALOCCLUSION modified from the standard design for correction of
Case Report: AK Aged 11 Years 1 Month Class II division 1 malocclusion by the addition of springs
lingual to the upper incisors to advance retroclined upper
Two years later, having developed a protocol for Twin
incisors. At the same time the mandible was translated
Block treatment of Class II division 1 malocclusion, atten-
tion was turned to Class II division 2 malocclusion. The forwards to correct the distal occlusion and the appliance
first patient of this type presented a severe malocclu- was trimmed to encourage eruption of the posterior teeth
sion with an excessive overbite and an interincisal angle to reduce the overbite.
approaching 180° (Figs. 2.6A to I). As an indication of the The Class II division 2 Twin Blocks were worn for
depth of the overbite the intergingival height from the 6 months, at which stage brackets were fitted on the
gingival margin of the upper incisors to the gingival mar- upper anterior teeth and activated with a sectional arch-
gin of the lower incisors was 7 mm, suggesting that the wire to correct individual tooth alignment. This combina-
upper incisors were impinging on the lower gingivae. The tion fixed/functional appliance treatment continued for
lower archform was good but the mandible was trapped 6 months. Completion of treatment was then effected
in distal occlusion by the retroclined upper incisors. with a simple upper fixed appliance.

Case Report: AK

A B C

D E F

G H I
Figs. 2.6A to I: A patient with a Class II division 2 malocclusion treated with Twin Blocks: (A to C) Excessive overbite and severely retroclined
incisors; (D and E) After 8 months the distal occlusion is corrected and the overbite is reduced; (F) A simple upper fixed appliance to
correct alignment; (G to I) The occlusion is stable 3 years later. A diagrammatic interpretation of the treatment is given on case report AK.
14 Twin Block Functional Therapy—Applications in Dentofacial Orthopedics

Case Report: AK

AK Age 11.1 13.1 16.8

Cranial Base Angle 26 26 26
Facial Axis Angle 32 30 33
F/M Plane Angle 13 15 12
Craniomandibular Angle 39 42 38
Maxillary Plane –3 0 1
Convexity 4 0 2
U/Incisor to Vertical –5 22 17
L/Incisor to Vertical 16 29 26
Interincisal Angle 169 129 137
6 to Pterygoid Vertical 18 20 28
L/Incisor to A/Po –8 0 –1
L/Lip to Aesthetic Plane –4 –6 –6
 Introduction to Twin Blocks 15

Angulation of the Inclined Planes this may encourage more forward mandibular growth. If
the patient has any difficulty in posturing forward, it is
During the evolution of the technique, the angulation of preferable to reduce the angulation of the inclined planes
the inclined plane varied from 90° to 45° to the occlusal to 45° to guide the mandible forward and make it easier
plane, before arriving at an angle of 70° to the occlusal for the patient to maintain a forward posture.
plane. An angle of 45° may be used for patients who have
more difficulty in maintaining a forward mandibular Bite Registration
posture.
The Exactobite or Projet Bite Gauge (the name differs in the
The earliest Twin Block appliances were constructed
USA and the UK) is designed to record a protrusive wax in
with bite blocks that articulated at a 90° angle, so that
wax for construction of Twin Blocks (Fig. 2.7). Typically,
the patient had to make a conscious effort to occlude in
in a growing child, an overjet of up to 10 mm can be
a forward position. However, some patients had difficulty
corrected on the initial activation by registering an inci-
maintaining a forward posture and, therefore, would
sal edge-to-edge bite with 2 mm interincisal clearance
revert to retruding the mandible back to its old distal
(Figs. 2.8A and B). This is provided that the patient can
occlusion position, occluding the bite blocks together
comfortably tolerate the mandible being protruded so
on top of each other on their flat occlusal surfaces. This
the upper and lower incisors align vertically edge-to-
was detectable at an early stage of treatment when it
edge. Larger overjets invariably require partial correction,
could be observed that the patient was not posturing
followed by reactivation after the initial partial correction
forwards consistently. A significant posterior open bite
is accomplished.
was caused by biting on the blocks in this fashion. This
complication was experienced in approximately 30% of
the earliest Twin Block cases. It was resolved by altering
the angulation of the bite blocks to 45° to the occlusal
plane in order to guide the mandible forwards. This was
immediately successful in eliminating the problem.
An angle of 45° to the occlusal plane applies an equal
downward and forward component of force to the lower
dentition. The direction of occlusal force on the inclined
planes encourages a corresponding downward and for-
ward stimulus to growth. After using a 45° angle on the
blocks for 8 years, the angulation was finally changed to
the steeper angle of 70° to the occlusal plane to apply a
more horizontal component of force. It was reasoned that Fig. 2.7: Projet bite gauge.

A B
Figs. 2.8A and B: The blue bite gauge registers 2 mm vertical clearance between the incisal edges of the upper and lower incisors. This
generally proves to be an appropriate interincisal clearance in bite registration for most Class I division 1 malocclusions with increased
overbite.
16 Twin Block Functional Therapy—Applications in Dentofacial Orthopedics

Appliance Design—Twin Blocks for dimension. Once this phase is accomplished, the Twin
Correction of Uncrowded Class II Blocks are replaced with an upper Hawley type of appli-
ance with an anterior inclined plane, which is then used
Division 1 Malocclusion
to support the corrected position as the posterior teeth
It is usually necessary to widen the upper arch to accom- settle fully into occlusion.
modate the lower arch in the corrected protrusive posi-
tion. The upper appliance incorporates a midline screw Stage 1: Active Phase
to expand the upper arch. Twin Blocks achieve rapid functional correction of man-
Delta clasps are placed on upper molars, with addi- dibular position from a skeletally retruded Class II to
tional ball-ended clasps distal to the canines, or between Class I occlusion using occlusal inclined planes over the
the premolars or deciduous molars. posterior teeth to guide the mandible into correct rela-
The lower appliance is a simple bite block with delta tionship with the maxilla. In all functional therapy, sagit-
clasps on the first premolars and ball clasps mesial to the tal correction is achieved before vertical development of
canines (Figs. 2.9A and B). the posterior teeth is complete. The vertical dimension is
controlled first by adjustment of the occlusal bite blocks,
THE TWIN BLOCK TECHNIQUE— followed by use of the previously mentioned upper
STAGES OF TREATMENT inclined plane appliance.
In treatment of deep overbite, the bite blocks are
Twin Block treatment is described in two stages. Twin trimmed selectively to encourage eruption of lower poste-
Blocks are used in the active phase to correct the antero- rior teeth to increase the vertical dimension and level
posterior relationship and establish the correct vertical the occlusal plane (Fig. 2.10). Throughout the trimming

B
Figs. 2.9A and B: Twin Blocks for correction of uncrowded class II Fig. 2.10: Sequence of trimming blocks.
division 1.
 Introduction to Twin Blocks 17

sequence it is important not to reduce the leading edge

of the inclined plane, so that adequate functional occlusal
support is given until a three-point occlusal contact is
achieved with the molars in occlusion.
The upper block is trimmed occlusodistally to leave
the lower molars 1–2 mm clear of the occlusion to encou-
rage lower molar eruption and reduce the overbite. By
maintaining a minimal clearance between the upper bite
block and the lower molars the tongue is prevented from
spreading laterally between the teeth. This allows the
molars to erupt more quickly. At each subsequent visit
the upper bite block is reduced progressively to clear the
occlusion with the lower molars to allow these teeth to
erupt, until finally all the acrylic has been removed over
A
the occlusal surface of the upper molars allowing the
lower molars to erupt fully into occlusion.
Conversely, in treatment of anterior open bite and
vertical growth patterns, the posterior bite blocks remain
unreduced and intact throughout treatment. This results
in an intrusive effect on the posterior teeth, while the
anterior teeth remain free to erupt, which helps to
increase the overbite and bring the anterior teeth into
occlusion.
At the end of the active stage of Twin Block treatment
the aim is to achieve correction to Class I occlusion and
control of the vertical dimension by a three-point occlusal
contact with the incisors and molars in occlusion. At this
stage the overjet, overbite and distal occlusion should be
fully corrected.

Stage 2: Support Phase

The aim of the support phase is to maintain the corrected
incisor relationship until the buccal segment occlusion
is fully interdigitated. To achieve this objective an upper
removable appliance is fitted with an anterior inclined
plane with a labial bow to engage the lower incisors and
canines (Figs. 2.11A and B).
The lower Twin Block appliance is left out at this
stage and the removal of posterior bite blocks allows
the posterior teeth to erupt. Full-time appliance wear is
necessary to allow time for internal bony remodelling to
support the corrected occlusion as the buccal segments B
settle fully into occlusion. Figs. 2.11A and B: Support phase—anterior inclined plane.
18 Twin Block Functional Therapy—Applications in Dentofacial Orthopedics

RETENTION RESPONSE TO TREATMENT

Treatment is followed by retention with the upper anterior Rapid improvements in facial appearance are seen
inclined plane appliance. Appliance wear is reduced to
consistently even during the first few months of Twin
night time only when the occlusion is fully established.
Block treatment. These changes are characterized by the
A good buccal segment occlusion is the cornerstone of
development of a lip seal and a noticeable improvement
stability after correction of arch-to-arch relationships. The
in facial balance and harmony. Lip exercises are not
appliance-effected advanced mandibular position will
not be stable until the functional support of a full buccal necessary to achieve this change in soft-tissue behavior.
The patient develops a lip seal naturally as a result of
segment occlusion is well established.
eating with the appliances in the mouth. When the
Timetable of Treatment: Average mandible closes in a forward position it is easier to form
Treatment Time an anterior oral seal by closing the lips together than
to support the lips with an anterior tongue thrust. In
r
"DUJWF
QIBTF: average time 6–9 months to achieve full
growing children, the facial muscles adapt very quickly
reduction of overjet to a normal incisor relationship
to an altered pattern of occlusal function. The changes in
and to correct the distal occlusion.
appearance are so significant that the patients themselves
r
4VQQPSU
QIBTF: 3–6 months for molars to erupt into
occlusion and for premolars to erupt after trimming frequently comment on the improvement in the early
the blocks. The objective is to support the corrected stages of treatment.
mandibular position after active mandibular trans- The facial changes are soon accompanied by equivalent
lation while the buccal teeth settle fully into occlusion. dental changes and it is routine to observe correction of
r
3FUFOUJPO: 9 months, reducing appliance wear when a full unit distal occlusion within the first 6 months of
the position is stabilized. treatment. The response to treatment is noticeably faster
An average estimate of treatment time is 18 months, compared to alternative functional appliances that must
including retention. be removed for eating.
 Introduction to Twin Blocks 19

Case Report: CH Aged 14 Years 1 Month Clinical Management

An example of treatment for a boy with an uncrowded At the first adjustment visit 2 weeks after the appliance is
Class II division 1 malocclusion with good archform and fitted, it is noted that the patient is not always posturing
a full unit distal occlusion (Figs. 2.12A to D). forward, and is sometimes simply biting together on the
flat occlusal surfaces of the blocks. This would tend to
Diagnosis, Skeletal Classification produce a posterior open bite, and it is important to avoid
this complication by detecting this at an early stage in
r
Moderate Class II.
treatment. The problem is resolved simply by trimming
r
'BDJBM
UZQF: moderate brachyfacial (horizontal growth).
the acrylic slightly from the anterior incline of the upper
r
.BYJMMB: mild protrusion.
block until the patient bites comfortably and consistently
r
.BOEJCMF: mild retrusion.
on the inclined planes of the blocks. This reduces the
r
Convexity = 6 mm.
initial forward activation to 7 mm with 2 mm interincisal
clearance. In spite of the slight upper block reduction,
Diagnosis, Dental Classification
this activation reduces the overjet from 12 mm to 4 mm
r
Severe Class II division 1. in 5 months.
r
6QQFS
JODJTPST: severe protrusion. Nevertheless, as a general principle, if the overjet is
r
-PXFS
JODJTPST: normal. greater than 10 mm it is usually necessary to correct the
r
Overjet = 12 mm. occlusion in a two-stage forward activation of the Twin
r
Overbite = 5 mm (deep). Blocks. After the initial partial correction, the Twin Blocks
r
No crowding. are reactivated to produce an upper to lower incisal edge-
to-edge occlusion with 2 mm vertical clearance by adding
Treatment Plan cold cure acrylic to the anterior aspect of the upper
inclined plane. This second activation by means of the
Functional correction to Class I occlusion by means of
longer upper block completes the mandibular correction
a combination of maxillary retraction and mandibular
to Class I occlusion. The blocks are trimmed occlusally
advancement, with reduction of overjet and overbite.
as before to reduce the overbite and encourage vertical
development.
Bite Registration
The initial bite registration with the blue Exactobite Duration of Treatment
aims to correct the overjet to edge-to-edge with a 2 mm
r
ActiWF
QIBTF: 8 months with Twin Blocks.
interincisal clearance.
r
4VQQPSU
QIBTF
BOE
SFUFOUJPO: 6 months.
Lower third molars were potentially impacted and
Appliances on completion of treatment all four second molars
Twin Blocks for correction of uncrowded Class II division 1 were extracted to accommodate third molars, which
malocclusion. subsequently erupted in good position.
20 Twin Block Functional Therapy—Applications in Dentofacial Orthopedics

Case Report: CH

B C D
Figs. 2.12A to D: Treatment: (A) Profiles at ages 14 years 1 month (before treatment), 14 years 6 months (after 5 months of treatment)
and 19 years 7 months; (B) Occlusion before treatment at age 14 years 1 month; (C) Occlusal change after 5 months of treatment, at
age 14 years 6 months; (D) Occlusion at age 19 years 7 months. A diagrammatic interpretation of the treatment is given case report CH.
 Introduction to Twin Blocks 21

Case Report: CH

CH Age 14.1 15.2 19.7

Cranial Base Angle 26 26 25
Facial Axis Angle 26 27 26
F/M Plane Angle 25 25 23
Craniomandibular Angle 51 51 48
Maxillary Plane –1 –3 –3
Convexity 6 4 4
U/Incisor to Vertical 38 26 27
L/Incisor to Vertical 31 30 30
Interincisal Angle 111 124 123
6 to Pterygoid Vertical 14 14 16
L/Incisor to A/Po 0 1 1
L/Lip to Aesthetic Plane –7 –8 –10
22 Twin Block Functional Therapy—Applications in Dentofacial Orthopedics

CASE SELECTION FOR Case Report: JMcL Aged 12 Years

SIMPLE TREATMENT A girl with a Class II division 1 malocclusion and mild
In starting to use any new technique it is important to crowding in the upper labial segment due to narrowing
select suitable cases from which to learn the fundamentals of the upper arch (Figs. 2.13A to G).
of treatment without complications. This is especially
important when the practitioner is not experienced in Diagnosis, Skeletal Classification
functional therapy. Case selection for initial clinical use r
Moderate Class II.
of Twin Block should, therefore, display the following r
'BDJBM
UZQF: mesognathic.
criteria: r
.BYJMMB: slight protrusion, contracted laterally.
r
Angle’s Class II division 1 malocclusion with good r
.BOEJCMF: normal.
archform. It is easier to learn the management of the
r
Convexity = 6 mm.
technique first by treating uncrowded cases before
progressing to crowded dentitions. Diagnosis, Dental Classification
r
A lower arch that is uncrowded or decrowded and
aligned. r
Severe Class II division 1.
r
An upper arch that is aligned or can be easily aligned. r
6QQFS
JODJTPST: mild protrusion.
r
An overjet of 10–12 mm and a deep overbite. r
-PXFS
JODJTPST: normal.
r
A full unit distal occlusion in the buccal segments. r
Overjet = 9 mm.
r
On examination of the models in occlusion with the r
Overbite incomplete due to tongue thrust.
lower model advanced to correct the increased overjet,
the distal occlusion is also corrected and it can be Treatment Plan
seen that a potentially good occlusion of the buccal Slight functional protrusion of the mandible to reduce
teeth will result. A good buccal segment occlusion is skeletal and dental Class II relationships.
the cornerstone of stability after correction of Class II
arch relationships. Appliances
r
On clinical examination the profile should be notice-
ably improved when the patient advances the mandibl r
Twin Blocks with labial bow to align the upper incisors.
voluntarily to correct the overjet. This factor is fun- r
Anterior guide plane to support the corrected occlu-
damental in case selection for functional appliance sion and retain.
therapy, and is a clinical indication that the Class II
arch relationship is skeletal in origin. Bite Registration
To achieve a favorable skeletal change during treat- The construction bite is registered with a blue Exactobite
ment, the patient should be growing actively. A more edge-to-edge with 2 mm vertical interincisal clearance.
rapid growth response may be observed when treatment
coincides with the pubertal growth spurt. Conversely, the Clinical Management
response to treatment is slower if the patient is growing
Progress in this case proved to be slow because the
more slowly. Although the rate of growth will influence
patient did not always posture forward. After 7 months
progress, it is not necessary to plan treatment to coincide
the thickness of the blocks was increased slightly to dis-
with the pubertal growth spurt, as the Twin Block system
courage the patient from dropping out of contact with the
is effective in mixed dentition, transitional dentition and
inclined planes. This appliance adjustment was effective
permanent dentition.
in completing the remaining skeletal correction and the
In experienced hands, Twin Blocks are very effective
overjet was fully reduced after 4 more months.
in the treatment of complex malocclusions that are due to
a combination of dental and skeletal factors. Twin Blocks
Duration of Treatment
integrate more easily with fixed appliances than any other
functional appliance in a combined approach to ortho- r
"DUJWF
QIBTF: 11 months with Twin Blocks.
pedic and orthodontic treatment. r
4VQQPSU
QIBTF
BOE
SFUFOUJPO: 5 months.
 Introduction to Twin Blocks 23

Case Report: JMcL

B C D

E F G
Figs. 2.13A to G: Treatment: (A) Profiles before treatment at age 12 years and 1 year out of retention at age 14 years 7 months;
(B to D) Occlusion before treatment; (E to G): Occlusion 1 year out of retention. A diagrammatic interpretation of the treatment is given
case report JMcL.
24 Twin Block Functional Therapy—Applications in Dentofacial Orthopedics

Case Report: JMcL

JMcL Age 12.0 15.2

Cranial Base Angle 31 31
Facial Axis Angle 27 28
F/M Plane Angle 24 23
Craniomandibular Angle 55 54
Maxillary Plane 0 1
Convexity 6 5
U/Incisor to Vertical 33 28
L/Incisor to Vertical 27 25
Interincisal Angle 120 127
6 to Pterygoid Vertical 15 18
L/Incisor to A/Po –1 1
L/Lip to Aesthetic Plane 0 –3