This document provides an overview of the Twin Block appliance. Some key points: - The Twin Block appliance was developed by William J. Clark in 1977 and consists of maxillary and mandibular bite blocks designed to be worn 24 hours a day. - The inclined planes on the upper and lower bite blocks are angled at 70 degrees to encourage forward mandibular growth. - Treatment involves an active phase to correct sagittal discrepancies followed by a support phase to maintain corrections until the occlusion is established. - Functional appliances like Twin Block are thought to stimulate mandibular growth through remodeling of the glenoid fossa and pterygoid response to the new functional demands placed on the mastic

1. TWIN BLOCK APPLIANCE
PRESENTED BY:
DR. SHEHNAZ JAHANGIR
FINAL YEAR MDS
DEPT. OF ORTHODONTICS & DENTOFACIAL
ORTHOPAEDICS

2. CONTENTS:
• Introduction
• Historical perspective
• Angulation of the inclined planes
• Bite Registration
• Evolution of appliance design
• Parts of the Twin Block appliance
• Standard twin block appliance
• Modifications

3. • Twin Block technique – (stages of
treatment)
• The influence of functional appliance therapy
on Glenoid fossa remodeling
• Pterygoid response
• Lateral pterygoid muscle hypothesis
• Contra indications
• Clark’s cephalometric analysis
• The Bite Guide
• Management of deep over bite.
• Soft tissue response.

4. • Reactivation
• Progressive activation
• Treatment in mixed dentition.
• Twin Block traction technique.
• Magnetic Twin Blocks
• The waveney goal post appliance
• Conclusion
• References

5. Introduction
• Twin Block appliance, developed by
William.J. Clark on 7 September 1977, is
perceived by most clinicians to be easier to
manipulate than the FR-2 appliance of
Frankel, and thus has had a substantial rise
in frequency of use during the 1990’s

6. • Twin block appliances are simple
bite blocks that are designed for
full- time wear.

7. • A functional equilibrium is established
under neurological control in response to
repetitive tactile stimulus.

8. • The proprioceptive sensory feedback mechanism
controls muscular activity and provides a
functional stimulus or deterrent to the full
expression of mandibular bone growth.

9. • Aims
• improve the functional relationship of the
dento-facial structures
• improving the muscle environment that
envelops the developing occlusion.

10. • Twin blocks are constructed to a protrusive bite
that effectively modifies the occlusal inclined
plane by means of acrylic inclined planes on
occlusal bite blocks.

11. • The Twin Block appliance is composed of
removable maxillary and mandibular plates
that fit tightly against the teeth, alveolus, and
adjacent supporting structures.

13. • The precise clasp configuration depends on the type
and number of teeth present at the time of appliance
construction. The use of two expansion screws in
the midpalatal region is recommended.

14. • Twin blocks are designed to be worn 24 hours
per day, including during meals to take full
advantage of all functional forces applied to the
dentition, including the forces of mastication.

15. • Upper and lower bite blocks interlock at a
70° angle when engaged in full closure.

17. • The first principle of appliance design is simplicity.
The patient’s appearance is noticeably improved
when twin Blocks are fitted.

18. • Eight Advantages:
1. The Twin Block is now recognized as the most
comfortable and the most aesthetic of all the
functional appliances.
2. Patients wear the appliance 24 hours a day
(even while eating).
• 3. Patient cannot remove the appliance if the
doctor desires it has not to be removed. (Construct
with crown contours or Clark Clasps.).

19. • 4. The doctor removes the appliance, for the first time,
two or three days after the insertion appointment.
5. Excellent appliance to increase the vertical dimension
in deep bite cases.
• 6. Appliance will close open bites, with proper
adjustments and on proper treatment plan.
7. Mandibular repositioning and vertical results
accomplished rapidly, because of 24 hour wear, even
while eating.

20. • 8. By placement of screws in the appliances,
lateral development or sagittal movement is
readily accomplished.
• Patient cooperation is excellent, because the
tongue has freedom for speech.
• In most cases, the final detailing of the teeth is
accomplished with six months of fixed
appliances.

21. • The Europeans are now using the Twin Block for TMJ
treatment, with great results. The Twin Block is excellent
for:
1. Relieving pain.
2. Decompressing the TM joints.
3. Permanently increasing the vertical dimension in deep
bite cases.
4. Repositioning the Mandible.
5. Easy for the patient to wear.

22. Historical perspective
• The concept of advancing the mandible by way of
inclined planes is not new, with the notion of “jumping
the bite” being traced back to the 1880 writings of
Kingsley.

23. • One of the few direct descends of this approach was the
“Vorbissplatte” of Schwarz.
• The Oliver “guide plane” also was used to jump the bite in
association with the labiolingual technique.

24. Angulation of the inclined planes
• During the evolution of the technique, the
angulation of the inclined plane varied from 90° to
45° to the occlusal plane, before arriving at an angle
of 70° to the occlusal plane as the final compromise
angle that proved most suitable in the majority of the
cases.

25. • It was reasoned that this may encourage
more forward mandibular growth.

26. • In treatment of class II malocclusion, the
inclined planes are positioned mesial to the
upper and lower first molars with the upper
block covering the upper molars and second
premolars or deciduous molars, and the lower
block extending mesially from the second
premolar or deciduous molar region.

27. • In the treatment of class II division 2
malocclusion, appliance design is modified by
the addition of sagittal screws to correct the
upper anterior teeth.

29. • Treatment of class III malocclusion is achieved by
reversing the occlusal inclined planes to apply a
forward component of force to the upper arch and
a downward and distal force to the mandible in the
lower molar region.

31. Bite Registration
• The Exactobite or Projet Bite
Gauge is designed to record a
protrusive interocclusal record
or ‘bite registration’ in wax for
construction of Twin Blocks.

32. • In a growing child, an overjet of up to
10mm can be corrected on the initial
activation by registering an edge to edge
bite with 2mm interincisal clearance.

33. • This is provided that the patient can
comfortably tolerate the mandible being
protruded so the upper and lower
incisors align vertically edge to edge.

34. • Inter incisal clearance- 2 mm
• In first premolar region- 5 to 6 mm
• In molar region- 1- 2 mm

35. Step 1 Step 2

36. • Step 3
Step 4

37. •Step 5

38. • According to Woodside (1997) – a bite registration used
commonly throughout the world registers the mandible
in a position protruded approximately 3.0 mm distal to
the most protrusive position that the patient can achieve,
while vertically the bite is registered within the limits of
the patients freeway space.

39. EVOLUTION OF APPLIANCE
DESIGN:
The earliest Twin Blocks were designed with
–
• A midline screw to expand the upper arch.
• Occlusal bite blocks.
• Clasps on the upper molars and premolars.

40. • Clasps on the lower premolars and incisors.
• A labial bow to retract the upper incisors.
• Springs to move individual teeth and to improve
the arch form as required.
• Provision for extraoral traction in some cases.

41. • Twin Block appliances are tooth and tissue
borne.
• One important difference compared to the
bionator, is that the Twin Block is worn for
eating. Oral hygiene is therefore an important
factor during treatment, and because of the risk
of decalcification incisal capping was
abandoned.

42. • In the Twin Block treatment a good lip seal is
achieved naturally without additional lip
exercise, as the appliance is worn for eating and
drinking, making it necessary to form a good
anterior seal.

43. • The construction bite should be taken in
modelling wax that retains its dimensional
stability after it is removed from the mouth.

44. • In the laboratory the models are mounted on an
articulator to register the construction bite before the
occlusal bite blocks are constructed. A plasterless
articulator may be used, with adjustable screws to
position the models in the correct relationship.
• The percentage of breakages was 10% for the modified
arrowhead clasp and 1% for the delta clasp.

45. Appliance design (Twin Blocks for
correction of uncrowded class II division 1
malocclusion)
• It is necessary to widen the upper arch to
accommodate the lower arch in the
corrected protrusive position. The upper
arch incorporates a mid line screw to
expand the upper arch.

47. Parts of the Twin Block appliance
• Maxillary Appliance: The maxillary
part of the twin block typically consists
of a split plate design, with one or two
midline screws.

48. • Clark also suggests the incorporation
of sagittal screws in instances of
retroclination of the maxillary incisors.

49. • The lateral aspects of the posterior teeth are not
covered, so that the clasps can be adjusted during
treatment. Both upper and lower parts of the
appliance fit tightly against the dentition, so that
the parts do not “float” during normal activities,
like speech and mastication.

51. • Mandibular Appliances: Original Design of Clark:
• The original design of Clark is a horseshoe of acrylic
that extends posteriorly to the mandibular second pre-
molars bilaterally. The lingual surfaces of the
mandibular molars are not connected by the appliance
to allow for the unimpeded eruption of those teeth
during treatment.

52. • The lower appliance is anchored to the
dentition by means of a delta clasps that
contact the mandibular first premolars
bilaterally. In addition a series of ball
clasps lie in the interproximal areas
between the canines and mandibular
incisors.

53. STANDARD TWIN BLOCKS
Standard twin blocks are essentially for treatment of
an uncrowded class II div 1 malocclusion with a
good arch form.
Appliance design
Clark’s Twin Block appliance consists of
1. Base plate
2. Occlusal inclined plane or bite blocks
3. Retentive components - Delta and ball end clasps
4. Active components- screw ,springs and bows

54. Base plate/bite blocks
• Appliances may be heat-cure or self
cure.
• Heat cure is preferred because of
strength
CLASPS
Delta clasp
Routinely placed on upper first molars and
on lower first premolars.

55. Ball-ended clasps
Routinely employed mesial to lower
canines and in the upper premolar or
deciduous molar region.
C-clasps
Additional c-clasps may be placed to improve
retention.

56. Occlusal inclined planes
Initially the angulation between the blocks
were made at 90 degrees
since it was difficult to hold the mandible
forward at this angle, the angulation was
changed to a 45 degree one
the angulation was changed to 70 degrees to
the occlusal plane to apply a more horizontal
force encouraging a more forward mandibular
growth.

58. Position
The inclined plane on lower bite block is angled from
the mesial surface of the second premolar or
deciduous molar whichever present. The lower bite
block does not extend distally to the marginal ridge
on the lower second premolar.
This allows the leading edge of the inclined plane on
the upper appliance to be positioned mesial to the
lower first molar so as not to obstruct eruption.

60. • Buccolingually the lower bite block covers the
occlusal surfaces of the lower premolars .
• In canine region it has to be thinner.
• Upper inclined plane is angled from the mesial
surface of the upper second premolar to the
mesial surface of the first molar.

61. • Since the upper arch is wider than the
lower, it is necessary to cover only lingual
cusps of upper posterior teeth rather than
the full occlusal surface.
• Mistakes in the appliance can lead to
treatment failure.

62. • Modified design: The original design of
Clark has been modified by placing a
labial bow anterior to the mandibular
incisors that has labial acrylic similar to
that of a lower spring retainer.

64. • Posteriorly the acrylic must be trimmed so
as to not impede the eruption of the
mandibular permanent molars, as the
maxillary bite blocks are contoured.

65. Other Mandibular Designs:
• If a modest increase in mandibular arch is
desired, the lower appliance can be fabricated
with a Schwarz type design. Here, a labial bow is
not present because of the desired expansion in
the mandibular incisor region.

66. Twin Block For Transverse Development
• By combining twin-block with schwarz
appliance.
• Screws in upper & lower twin block to
develop arch form in mixed dentition.
OTHER MODIFICATIONS

67. TWIN-BLOCK WITH SCHWARZ
APPLIANCE.

68. Twin block for sagittal development
For anteroposterior arch development
two screws which are aligned antero
posteriorly.

69. Twin block for sagittal development

70. For both transverse and sagittal
3 way screws

71. With habit breakers

72. FOR CLASS III
REVERSE TWIN BLOCKS

73. Magnetic twin blocks

74. Attachment in TWIN BLOCK
for advancement

75. Twin block bio finisher
Extruding lower molars by vertical traction to stabilize
the TMJ

77. Twin Block technique – (stages of
treatment): Active Phase
• Twin Block treatment is described in two
stages. Twin Blocks are used in the active
phase to correct the anteroposterior
relationship and establish the correct
vertical dimension.

78. • In all functional therapy, sagittal
correction is achieved before vertical
development of the posterior teeth is
complete.

80. • Throughout the trimming 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 molar in occlusion.

81. • The upper block is trimmed occlusodistally to
leave the lower molars 1-2mm clear of the
occlusion to enchorage lower molar eruption
and reduce the overbite.

82. • Conversely, in treatment of anterior open
bite and vertical growth patterns, the
posterior bite blocks remain unreduced
and intact throughout treatment.

83. Support phase:
The aim of this phase is to maintain the
corrected incisor relationship until the buccal
segment occlusion is fully interdigitated.

84. 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.
Time required is 4-6 months

85. anterior inclined plane

86. RETENTION
• Treatment is followed by retention
with upper anterior inclined plane
appliance.
• Appliance wear is reduced to night
time wear only when the occlusion is
fully established.

87. FIXED APPLIANCE PHASE
Final detailing of the occlusion
is completed using fixed
appliance therapy.

88. The influence of functional appliance
therapy on Glenoid fossa remodeling:
• Woodside et al (1987) examined – the influence of
functional appliance therapy on Glenoid fossa remodeling,
following a period of progressive activation, he concluded
that the skeletal jaw relationship may be altered by both
Glenoid fossa remodeling and condylar extension in
young primates, and thereafter by Glenoid fossa
relocation.

89. • Deposition of new bone on the posterior
wall of the Glenoid fossa is even more
significant than thickening of the
condylar cartilage, and is a major factor
in the repositioning of the mandible.

90. Pterygoid response
• Also called as tension zone by HARVOLD.
• These are clinical signs after fitting functional
appliance.
• The patient experiences adaptation of muscle
function immediately on insertion of the appliance,
in response to altered occlusal function..
• Within few days the patient experiences pain
behind the condyle when the appliance is
removed.

91. Cause
• From the studies of histological changes in
animal experiment , it may be deduced that
retraction of the condyle results in compression
of connective tissue & blood vessels and that
ischemia is the principal cause of pain.
• A new pattern of muscle behavior is quickly
established whereby patient finds it difficult and
later impossible to retract the mandible into its
former retruded position.

92. • After a few days it is comfortable to wear
the appliance than to leave it out.
• This change in muscle action has been
described by McNAMRA as the pterygoid
response & results from the altered
activity of the medial head of the lateral
pterygoid muscle

93. The lateral pterygoid muscle hypothesis
Suggests that both postural and functional
activity in the masticatory muscles increases
after functional appliance insertion. This
increased activity, especially in the superior
head of the lateral pterygoid muscle, then acts
as a stimulus to mandibular growth.
(McNamara JA. Neuromuscular and skeletal adaptations to altered function in
orofacial region. AJO 1973)

94. • John C. Voudouris et al (AJODO -2000) –
improved clinical use of Twin Block and Herbst
as a result of radiating viscoelastic tissue forces
on the condyle and fossa in treatment and long
term retention: Growth relativity –
• It was previously thought that the increased
activity in the postural masticatory muscles was
the key to promoting condyle-glenoid fossa
growth.

95. • This premise has its foundation on three key
specific findings-
• significant glenoid fossa bone formation occurs
during treatment that includes mandibular
displacement;
• glenoid fossa modification is a result of the
stretch forces of the retrodiscal tissues, capsules,
and altered flow of viscous synovium;
• glenoid fossa bone formation takes place from a
distance from the soft tissue attachment.

97. • The biodynamic factors are also capable of
reversing effects of treatment on mandibular
growth direction, size, and morphology.
• Relapse occurs as a result of release of the
condyle and ensuing compression against the
newly proliferated retrodiscal tissues together
with the reactivation muscle activity.

99. A comparison of Twin Block response
with animal experiments:
• Harvold (1983) confirms from histological study
in animal experiments that rapid adaptive changes
occur in the tissues surrounding the condyle when
a full-time functional appliance is fitted.

100. • Above and behind the condyle is an area of intense
cellular activity described as a ‘tension zone’ that
is quickly invaded by proliferating connective
tissue and capillary blood vessels, when mandible
functions in a protrusive position..
• The initial response to functional mandibular
protrusion is therefore, a change in the muscle of
mastication to establish a new equilibrium in
muscle behavior.

101. Muscle response to the Twin Block
appliance –
• Aggarwal (1999) provides important information on the
adaptive changes during treatment. Bilateral
electromyography activity of elevator muscles of the
mandible was monitored longitudinally with bipolar
surface electrodes to determine changes in the postural,
swallowing and maximum voluntary clenching activity
during an observation period of 6 months.

102. • The results revealed a significant increase in
postural and maximum clenching
electromyography activity in masseter and an
increase in anterior temporalis activity.

103. • Voudouris and Kuftinec (2000) present a further
explanation to account for growth changes in Twin
Block and Herbst treatment, following recent
research in Toronto.
• They observed that it was previously thought that
increased activity in the postural masticatory
muscle was the key to promoting condyle – glenoid
fossa growth.

104. • By analyzing the results from several studies
they postulated a non-muscular hypothesis
as a result of radiating viscoelastic forces on
the condyle and fossa in treatment and long
term retention.

105. ‘Richter Scale’:
Helpful in treatment planning to classify
the malocclusion as mild, moderate or severe.
This is a sliding scale expressing degree of
difficulty for dental correction by non-extraction
therapy. The higher the value, the more difficult
it is to resolve crowding permanently without
extraction.

106. Contraindication for Twin Block
therapy
• Careful case selection is the most important
aspect of diagnosis and treatment planning
in order to achieve a successful outcome.

107. • Examination of the profile is the most
important clinical guideline. If the profile
does not improve when the mandible is
advanced, this is a clear contraindication
for functional mandibular advancement,
and an alternative approach should be
considered.

108. Clark Cephalometric Analysis
• Cephalometric analysis attempts to define the
pattern of craniofacial growth by examining the
angular and linear relationships of clearly
defined skeletal landmarks on cephalogram.

109. • Growth of the head is observed more accurately by
superimposition at basion.
• The Clark analysis lends itself well to the
expression of Coben’s interpretation of facial growth
by horizontal orientation of the head and evaluation
of the growth changes from basion.

110. • The same method of superimposition has been
selected to demonstrate facial growth changes
with Twin Block treatment, using basion as a
fulcrum point for analysis of growth changes in
the facial rectangle, with the Frankfort plane
horizontal.

111. FACIAL RECTANGLE :
A facial rectangle helps to define the relative
position and angulation of cranial, maxillary,
mandibular and dentoalveolar structures. The
rectangular framework makes it easier to identify
areas where growth departs from normal in the
facial pattern.

112. RICKETTS TRIANGLE: (facial wedge): The
Rickets triangle defines the face in profile as a
wedge-shaped triangle attached to the under
surface of cranial base.
• The base of the triangle extends from basion to
nasion and defines the cranial base plane.
• The facial plane extends from nasion tangent to
the chin at the pogonion to define the angulation
of the face in the anterior plane

113. • The mandibular plane is the third leg of the
triangle defining the angulation of the lower
border of the mandible.
• The triangle is bisected by the facial axis,
extending from pterygoid to gnathion to
define the direction of growth of the chin.

114. RICKETS TRIANGLE:

115. THE BITE GUIDE:
• The development of a lingual attachment, the bite
guide is a significant factor, not only related to
Twin Block Technique, but also relevant in many
clinical situations where vertical control of
increased overbite is an important aspect of
treatment.

116. • When vertical control is necessary during the transition
– to - support phase in order to maintain the corrected
overjet and overbite. The bite guide acts as a fixed
retainer to maintain the corrected vertical dimension
after the molars have erupted into occlusion.

118. • when the overjet is more than 3mm then the
lower incisors would bite lingually to the bite
guide. Therefore it is necessary to fully correct
the overjet before the bite guide is fitted.

119. • Twin Blocks may also be bonded directly
to the teeth by applying composite around
the clasps. This is a useful approach in
mixed dentition when ball clasps may be
bonded directly to deciduous molars to
improve fixation.

120. MANAGEMENT OF DEEP OVER
BITE:
• Overbite reduction is achieved by trimming the occlusal
blocks on the upper appliance, so as to enchorage
eruption of the lower molars.
• The objective is to increase lower facial height and
improve facial balance by controlling the vertical
dimension.

121. • The management of the deep over bite begins
even before the appliance is fitted –by placing
elastic separators in the molar region. When
the appliance is fitted, the separators are
removed and the appliance is adjusted to
encourage the molars to erupt.

122. • The final adjustment at the end of the Twin
Block stage aims to reduce the lateral open
bite by trimming the upper occlusal surface of
the lower bite block over the premolars by
2mm to maintain adequate inclined planes to
support the corrected arch relationships, the
lower bite block is shaped into a triangle
wedge distally in contact with the upper
block.

123. SOFT TISSUE RESPONSE
• The Twin Block appliance positions the
mandible downwards and forwards,
increasing the intermaxillary space. As a
result it is difficult to form an anterior oral
seal by contact between the tongue and the
lower lip, and patients adapt a natural lip seal
without instruction.

124. • As the appliance is worn full-time, even during
eating, rapid soft-tissue adaptation occurs to assist
the primary functions of mastication and
swallowing that necessitate an effective anterior
oral seal.
• A good lip seal is always achieved by normal,
function with Twin Blocks, without the need for
lip exercises.

125. REACTIVATION OF TWIN BLOCKS:
• Reactivation is a simple procedure that is achieved
by extending the anterior incline of the upper Twin
Block mesially to increase the forward posture.
• Even in cases with an excessive overjet, a single
reactivation of the Twin Blocks is normally
sufficient to correct most malocclusions.
• It is important that no acrylic is added to the distal
incline of the lower Twin Block, especially in the
treatment of deep overbite.

126. • If the patient’s rate of growth is slow or the
direction of growth is vertical rather than
horizontal, it is advisable to advance the mandible
more gradually over a longer period of time to
allow compensatory mandibular growth to occur.
• This can be taken into account by reactivating
Twin Blocks progressively to extend the inclined
plane of the upper bite block mesially. (Petrovic
and Stutzmann, 1977).

127. PROGRESSIVE ACTIVATION OF TWIN
BLOCKS:
Progressive activation of the inclined planes is
indicated as follows:
• If the overjet is greater than 10mm it is advisable
to step the mandible forwards, usually in two
stages.
• In any case where full correction of arch
relationships is not achieved after the initial
activation, an additional activation is necessary.

128. • If the direction of growth is vertical rather
than horizontal, the mandible may be
advanced more gradually to allow adequate
time for compensatory mandibular growth
to occur.

129. TREATMENT IN MIXED
DENTITION:
• Treatment of skeletal discrepancies should not
be delayed until the permanent dentition has
been established.
• Interceptive treatment is frequently indicated in
the mixed dentition to restore normal function
and correct arch relationships by means of
functional appliance therapy.

130. • Twin Block appliance design for class II
division 1 malocclusion in the mixed dentition
is similar to appliance design for the permanent
dentition.
• Delta clasps may be fitted on lower first or
second deciduous molars if they are suitably
shaped for retention. Alternatively C-clasps can
be used for retention on deciduous molars.

131. • The occluso-guide is an excellent functional
retainer during the transition from mixed to
permanent dentition. The occluso-guide should be
worn for 1 or 2 hours during the day and the
patient is instructed to actively bite into the
appliance.

132. • This is effective in maintaining the vertical
dimension after correction of deep over bite. The
material is sufficiently flexible to allow
correction of minor tooth irregularities, in
addition to acting as a retainer to reinforce the
sagittal and vertical correction.

133. TWIN BLOCK TRACTION
TECHNIQUE:
• In most of the cases, full functional correction of
occlusal relationship can be achieved with Twin
Blocks without the addition of any orthopedic or
traction forces, but where the response to
functional correction is poor, the addition of
orthopedic traction force may be considered.

134. Indication for cases with growth patterns
where maxillary retraction is the treatment
of choice:
• In the treatment of severe maxillary protraction.
• To control a vertical pattern by the addition of
vertical traction to intrude the upper posterior
teeth.
• In adult treatment where mandibular growth
cannot assist the correction of a severe
malocclusion.

135. The Concorde facebow:
• Before Twin Blocks were developed, the author
used extraoral traction with removable
appliances as a means of anchorage to retract
upper buccal segments to correct class II
malocclusion (Cousins & Clark 1965).

136. • Twin Block tubes were added to clasps for
extraoral traction on the upper appliance to
be worn at night so as to reinforce the
functional components for correction of a
class II buccal segment relationship.

138. Magnetic Twin Blocks:
• Clark used Samarium Cobalt and
Neodinum – Iron – Boron in his well
acclaimed and accepted, Twin Block.
These magnets were embedded in the
inclined surface of the twin blocks.

139. • When the magnets are used in the repelling mode
it reduces the need for reactivation by including
an additional forward posture of the mandible.
• These were used in different ways for treating
class II and class III malocclusions and also for
correction of facial asymmetry.

140. • Caldwell and Paul Cook (EJO 1999) –
Predicting the out come of Twin Block
functional appliance treatment: a prospective
study.
• This study was undertaken to investigate the
relationship between various measured pre-
treatment parameters and the reduction in overjet
achieved when using a twin block functional
appliance.

141. • Forty-three subjects were fitted with a twin block
appliance. The functional appliance wear was
monitored for 6 months and any individual who
did not co-operate with wear was excluded from
the subsequent analysis.

142. • There was a percentage reduction in the
overjet achieved by functional appliance
wear to any of the pre-treatment parameters.
• The overbite and the SNB angle were the
most strongly related variables to percentage
reduction in overjet.
• This present study confirms that co-operation
remains a problem in removable functional
appliance treatment.

143. • David Ian Lund et al (AJO-DO 1998) – The
effects of Twin Blocks: A prospective
controlled study.
• This study investigated the net effects of the
Twin Block functional appliance taking into
account the effect of normal growth in an
untreated control group.

144. • The treatment group consisted of 36 subjects,
mean age of 12.4 years. The control group
consisted of 27 subjects with a mean age of 12.1
years. In the treatment group, a reduction in the
ANB of 2° was observed largely because of an
increase in SNB of 1.9°.

145. • No statistically significant restraint in the
maxillary growth was observed. Treatment
increased in Ar-Pog of 5.1mm compared
with the control group increase in Ar-Pog of
2.7mm, resulting in a net gain of 2.4mm.

146. • Nazli Tumer and Ali S. Gultan (AJO-DO 1999)
– Comparison of the effects of monobloc appliances
on the skeletal and dentoalveolar structures.
Functional appliances, which are used in the early
treatment period of skeletal class II malocclusions,
induce the forward displacement of the mandible by
altering the postural activity of the muscles and
causing some changes in both the skeletal and
dentoalveolar structures.

147. Two treatment groups composed of 26 growing
patients with skeletal and dental class II division 1
malocclusions were compared to an untreated control
group of 13 patients .
• In the Twin block group, the mandibular plane angle
and the gonial angle increased, although a decrease in
the degree of overbite occurred. In the monobloc
group, upper incisor demonstrated a great degree of
retrusion. However within the twin block group, the
lower incisors showed a greater degree of proclination.

148. The Waveney Goal Post Appliance:
• The Waveney Goal Post Appliance was designed
to stabilize the second supportive phase of Clark’s
Twin Block therapy (1982). It is to be worn full
time and is simple to construct, and well tolerated.
It can be used to stabilize the dentition following
most forms of functional treatment.

149. • This appliance is an upper Hawley retainer
incorporating a palatally placed wire frame work
or goal-post designed to engage the cingula of
the lower incisor teeth in their corrected
occlusion.
• The Waveney Goal Post Appliance maintains the
forward functional posture of the mandible while
the premolar teeth establish an interdigitating
occlusion, so resolving the previously induced
lateral open bites.

150. • Patients have found this appliance to be easy to wear as
it is not bulky, is aesthetically acceptable, and causes
few problems at meal times.

151. Conclusion :
• Comfort and esthetics are crucial in appliance
design. Twin Blocks have the advantage of
versatility of design. They meet a wide range of
requirements for the correction of different
types of malocclusion in children as well as
adults.

152. • There is no disturbance in speech. Proper
function due to free movement of the mandible is
observed, but the principal advantage is the
simplicity of appliance design. Finishing the
treatment though, has to be integrated with a
fixed appliance.

153. References:
• Twin Block Functional Therapy- Applications in dentofacial
orthopaedics : William J Clark, 3rd edition.
• Orthodontics and Dent facial orthopedics : McNamara and
Brudon; 2000.
• Heather M. Illing, David O. Morris and Robert T. Lee: A
prospective evaluation of Bass, Bionator and Twin Block
appliances. Part I - the hard tissues. EJO 1998; Vol 20: Page
501-516.

154. • David O. Morris, Heather M. Illing and Robert T.
Lee: A prospective evaluation of Bass, Bionator and
Twin Block appliances. Part II - the soft tissues. EJO
1998; Vol 20: Page 663-684.
• Kevin O’ Brien et al: Effectiveness of early
orthodontic treatment with Twin Block appliance: A
multicenter, randomized, controlled trial, Part 2:
Psychosocial effects. AJO-DO 2003; Vol 124: Page
488-495.

155. • Nicola Ann Parkin et al: Comparison of 2
modifications of the Twin – block appliance in
matched Class II samples: AJO-DO 2001; Vol 119:
Page 572-577.
• Christine M. Mills and Kara J. McCulloch: Post
treatment changes after successful correction of class
II malocclusions with the Twin Block appliance.
AJO-DO 2000; Vol 118: page 24-33.

156. • Tiziano Baccetti, Lorenzo Franchi, Linda Ratner Toth,
and James A. McNamara: Treatment timing for Twin
Block therapy. AJO-DO 2000; Vol 118: Page 159-170.
• Christine M. Mills and Kara J. McCulloch: Treatment
effects of the twin block appliance: A cephalometric
study. AJO-DO 1998; Vol 114: Page 15-24.

157. • Preeti Aggarwal, O.P.Kharbanda, Rashmi Mathur,
Ritu Duggal and H.parkash: Muscle response to the
Twin-Block appliance: An electromyographic study
of the masseter and anterior temporal muscles.
AJO-DO 1999; Vol 116: Page 405-414.
• Kanoknart Chintakanon, kemal S. Turker, Sampson,
Tom Wilkinson and Grant Townsend: Effects of
Twin-block therapy on protrusive muscle functions.
AJO-DO 2000; Vol 118: Page 392-396.

158. • G.D. Singh and W.J. Clark: Soft tissue changes in patients
with class II division 1 malocclusions treated using Twin
Block appliances: finite-element scaling analysis. EJO
2003; Vol 25: Page 225-230.
• Kevin O’Brien et al: Effective of early orthodontic
treatment with Twin Block appliance: A multicenter,
randomized, controlled trial, Part 1: Dental and Skeletal
effects. AJO-DO 2003; Vol 124: Page 488-95.

159. • Nora M. Stratford, and Jennifer A. Scott: Stabilization of
functional treatment: The Waveney Goal Post Appliances.
BJO 1988; Vol 15: Page 123-125.
• H.L. Moseley, E.N. Horrocks,and R.R. Welfare: Use of a
modified Twin Block appliance following partial
maxillectomy: Case Report. BJO 1996; Vol 23: Page 103-
108.

160. • G.J. Camichael, P.A. Banks, and S.M. Chadwick: A
modification to enable controlled progressive
advancement of the Twin Block appliance. BJO 1999; Vol
26: Page 9-13.
• Nali Tumer and Ali S. Gultan: Comparison of the effects
of monoblock and twin-block appliances on the skeletal
and dentoalveolar structures. AJO-DO 1999; Vol 116:
Page 460-8.

161. • M. Dixon, Y. Jones, I.E Mackie, and S.K. Derwent:
Mandibular incisal edge demineralization and caries
associated with Twin Block appliance design. JO 2005;
Vol 32: Page 3-10.
• Daljit S. Gill and Robert T. Lee: Prospective clinical
trial comparing the effects of conventional Twin-block
and mini-block appliances: Part 1. Hard tissue changes.
AJO-DO 2005; Vol 127: Page 465-72.

162. • H.M. Lawton, J.M. Battagel, and B. Kotecha: A
comparison of the Twin Block and Herbst mandibular
advancement splints in the treatment of patients with
obstructive sleep apnoea : a prospective study. EJO 2005;
Vol 27: Page 82-90.