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twin block
THE OCCLUSAL INCLINED PLANE
•The occlusal inclined plane is the fundamental functional
mechanism of the natural dentition.
•Cuspal inclined planes play an important part in determining
the
relationship of the teeth as they erupt into occlusion.
•Occlusal forces transmitted through the dentition
provide a constant proprioceptive stimulus to influence
the rate of growth and the trabecular structure of the
supporting bone.
TWIN BLOCKS
•Twin blocks are bite-blocks that effectively modify
the occlusal inclined plane to induce favorably directed
occlusal forces by causing a functional mandibular displacement
•Upper and lower bite-blocks interlock at a 45” angle
•Designed for full-time wear to take advantage
of all functional forces applied to the dentition including
the forces of mastication.
•give greater freedom of movement in anterior and lateral excursion
•cause less interference with normal function.
twin block
ORTHOPEDIC TRACTION
•In cases in which the skeletal discrepancy is severe,the addition of an
orthopedic traction system to support the action of occlusal inclined
planes provides a versatile appliance technique that is effective in the
treatment of a wide range of malocclusions.
•The indications for treatment include maxillary protrusion,mandibular
retrusion, and vertical growth discrepancies
•A functional orthopedic approach eliminates the uncertainty of
treatment response that is sometimes associated
with purely functional techniques
• The technique achieves rapid correction of malocclusion even
in cases with severe malocclusions that are unfavourable
for conventional fixed or functional appliance therapy.
THE CONCORDE FACE-BOW
•The twin block technique uses a new method of applying inter-maxillary
traction.
•The Concorde facebow combines intermaxillary and extraoral traction
by the addition of a recurved labial hook to a conventional face-bow.
• Intermaxillary traction is applied as a horizontal force from the labial
hook to the lower appliance, eliminating the unfavorable upward
component of force associated with conventional intermaxillary
traction.
•The traction components are worn only at night to reinforce the action
of the occlusal inclined plane.
.
•If the patient fails to posture the mandible to the corrected occlusal
position during the night, the intermaxillarytraction force is automatically
increased to compensateso that favorable intermaxillary forces are applied
continuously
•Extraoral traction is added when orthopedic force to the maxilla is
indicated-for example, in correction of maxillary protrusion
•A vertical component of extraoral traction applies an intrusive force to the
upper posterior teeth and the palate via the upper appliancen to limit
downward maxillary growth
•This facilitates correction of Class II arch relationships in vertical growth
discrepancies.
• The Concorde face-bow effectively combines extraoral and
intermaxillary traction in the treatment of severe skeletal
discrepancies.
•A recurved labial hook is added to a conventional
face-bow. Outer bow is 1.5 mm; inner bow is 1.13 mm reinforced with
tubing; labial hook is 1.13 mm
• Intraoral views showing twin blocks in open and closed positions.
• The Concorde face-bow is illustrated with detail of the recurred
labial hook and intraoral attachment of the intermaxillary
elastic.+
• Simple twin block appliances are shown in conjunction with fixed
appliances.
• This combination produces rapid correction of arch relationships that
can counteract a slow response to treatment in cases with unfavorable
growth patterns
•Twin blocks may be either removable or fixed to the
teeth
APPLIANCE DESIGN
Removable twin blocks
•The upper appliance is retained by modified arrowhead clasps.
•The clasps incorporate a coiled tube for attachment of a face-bow if traction
is to be applied.
•Retention may be increased by adding ball-ended clasps in the labial or buccal
segments.
•A midline expansion screw provides compensatory lateral expansion of the
upper arch to accommodate a functional protrusion of the lower arch from its
retruded position.
•Labial and lingual bows (as needed) are included to control upper incisor
angulation.
•In the lower arch, retention is often obtained by l-mm interdental ball
clasps in the lower incisor region combined with clasps in the buccal
segments.
•The delta clasp was specifically designed bythe author to extend the
area of contact of the clasp in the undercut and to improve retention with
a closed triangle to increase resistance to fatigue.
•This combination of clasps gives excellent retention and is very effective
in limiting proclination of lower incisors during the twin block stage
•In mixed dentition treatment, clasps are placed on the lower incisors and on
deciduous molars or first permanent molars.
•The lower appliance may be split anteriorly with the addition of a screw or helical
spring to expand and develop the lower arch, if desired.
•The upper bite-blocks cover the lingual cusps of the upper posterior teeth,
extending to the mesial ridge of the upper second premolar.
•This allows the clasp to be more flexible and improves retention of the appliance
•Full occlusal cover is necessary in the lower premolar region to compensate for
the discrepancy in arch width and to allow the inclined planes to interlock in
occlusion.
•The lower bite-block extends to the distal marginal ridge of the lower second
premolar
•For correction of deep overbite, it is an advantage to leave the lower molars
free of the appliance, allowing their eruption to be controlled in relation to the
overbite
•It is very important to prevent molar eruption in cases in which there is
reduced overbite or anterior openbite.
• All erupted posterior teeth must occlude on the bite-block to prevent
overeruption.
, Diagram showing details of twin blocks combined with fixed
appliances. Occlusalinclined planes are outlined in black. Clasps
on 655 55 6
7
are shown in black. In this example the upper
fixed appliance is confined to 3211123 at this stage until arch
relationships are corrected, allowing A
easy transition into a full fixed appliance. In the lower arch, a
utility arch accommodates clasps in the
buccal segments. The fixed appliances are shown in red.
BITE REGISTRATION
•For Class II problems, the proper construction bite is taken and the models are
articulated with mandibular protrusion.
• The amount of mandibular protrusion depends on the ease with which the
patient can posture forward.
• As a general rule, the initial activation should reduce the overjet by 5 to 7 mm
leaving 3 to 5 mm interocclusal clearance in the first premolar
region.
•The interocclusal clearance is increased where there is increased overbite and
the bite-blocks are designed to allow the free eruption of the lower molars to
reduce the overbite by increasing the lower facial height
•The registration bite should allow for correction of midlines in cases in which
they are displaced by functional occlusal interference or guidance into habitual
occlusion.
• Twin blocks may be activated unilaterally to correct postural mandibular
displacement with center line displacement and asymmetric buccal segment
relationships.
•The occlusal inclined plane is particularly well suited to the correction of
functional abnormalities associated with asymmetric mandibular development.
•For correction of asymmetry, the lower appliance requires maximum retention
in the lower arch to minimize dental movement and to encourage asymmetric
compensatory growth.
twin block
Intraoral views before treatment
Intraoral views after treatment
twin block
twin block
FIXED TWIN BLOCKS
•Twin block appliances may be designed for direct fixation to the teeth by
bonding.
•The appliances resemble the Herbst appliance, substituting occlusal inclined
planes for telescopic tubes to provide the functional component to guide the
mandible into a protrusive position.
•Preformed wedge attachments are being designed at present for direct
fixation to molar bands to allow simpler application in fixed appliance technique
CLINICAL MANAGEMENT
•This report refers to the treatment of an uncrowdedClass II, Division 1
malocclusion primarily, using removabletwin blocks.
• The patient had a combination of maxillary protrusion and mandibular
retrusion.
•The technique is described in two stages, an ,active phase with twin blocks
and traction attachments, and a support phase with a guide plane after
correction of arch relationships.
STAGE 1 -ACTIVE PHASE
•Twin blocks are combined with intermaxillary and extraoral traction for
rapid correction of arch relationships
•The initial activation is checked when twin blocks are fitted to confirm that
the patient can comfortably maintain the altered postural position.
•Twin blocks are removed for eating for the first 3 days until the initial
discomfort from appliance wear has been resolved
•Thereafter, the appliances are worn avoid soft-tissue irritation. The upper midline
screw is continuously.
•It is important for the patient to understand that wearing twin blocks for eating
increases the orthopedic forces and improves the response to treatment; this
makes it a true functional appliance.
•It may be necessary to trim or relieve the flange the lower appliance, lingual to the
lower incisors, to avoid soft tissue irritation
•The upper midline screw is continuously turned a one-quarter turn every week to
10 days until the the arch width is adequate to accommodate the lower
arch in its corrected position.
•It is important to check the expansion of the upper arch at each visit to avoid
excessive expansion
•The Concorde face-bow is adjusted so that it lies just below the level of
the upper lip at rest, with the ends of the outer bow sloping slightly
upward above the level of the inner bow.
•The resulting extraoral traction applies an upward component of force
that helps to retain the upper appliance
•The intermaxillary elastic is attached under the ball clasps in the lower
labial segment and passes to the labial hook on the face-bow (Fig. 1, C). If
lower incisors are already proclined, less elastic traction will be tolerated.
•Avoid prolonged elastic traction in slow vertical-growing patterns.
•The retention of the appliance must be checked after the traction
assembly is fitted
•Extraoral traction is applied by a straight pull toa conventional headcap
worn every night for 8 to 10 hours using 200 g distal extraoral force on
each side and approximately 150 g intermaxillary force.
•At each monthly visit, the occlusion is checked for
•correction of arch relationships
Clinical response in active phase
•Within a few days of fitting the appliances, theposition of muscle balance is
altered so that it becomes painful for the patient to retract the mandible.
This has been described as the “pterygoid response”
(McNamara*) or the formation of a “tension zone” distal to the condyle
(Harvold5). It is rare for such a responseto be observed with functional
appliances that are not worn full-time.
•The rapid clinical response confirms the summary of adaptive responses in
functional protrusion experiments with fixed inclined planes by McNamara.
The placement of appliances results in an immediate change
in the neuromuscular proprioceptive response. Provided all
phasic and tonic muscle activity is affected, the resulting
muscular changes are very rapid, and can be measured in
terms of minutes, hours and days. Structural alterations are
more gradual and are measured in months, whereby the dento
skeletal structures adapt to restore a functional equilibrium to
support the altered position of muscle balance.’
•The patient’s rate of growth should be taken into account in timing the
reactivation of the bite-blocks by the addition of cold cure acrylic to the
mesial inclined plane of the upper blocks.
• However, an overjet of up to 10 mm can be corrected without reactivating
the biteblocks if the rate and direction of mandibular growth are favorable.
•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.
•Full correction of sagittal arch relationships can be achieved in as little as 2
to 6 months, giving a normal incisor relationship with the buccal segments out
of
•occlusion due to the presence of the bite-blocks.
• It is a consistent feature in functional techniques that sagittal correction
of arch relationships is achieved before compensatory vertical development
in the buccal segments is complete
Management of overbite
•Deep overbite is reduced by overcorrecting the incisors to an edge-to-edge
relationship before reducing the height of the bite-blocks.
•Vertical development of the lower molars is encouraged from the beginning of the
active phase of treatment by progressively trimming the upper bite-block
occlusodistally to allow the lower molars to erupt.
•At the end of the active phase, the incisors and the molars should be in correct
occlusion.
•At this stage an open bite is still present in the premolar region because of the
presence of the biteblocks.
•The lower block is trimmed over a period of 2 or 3 months to reduce the open bite
in the premolar region.
•It is important to maintain adequate interlocking wedges to maintain
anteroposterior correction of arch relationships.
•This method of reducing overbite by controlled eruption of posterior teeth
supported by occlusal biteblocks results in favorable changes in facial balance by
increasing lower facial height.
•Conversely, if the overbite is reduced before treatment, it is important to
prevent overeruption of posterior teeth, which would further reduce the
overbite.
• All erupted teeth must then be in occlusal contact with the bite-blocks.
•If second molars erupt during the active phase, occlusal cover or occlusal
rests must be extended to prevent overeruption of these teeth.
•When the overbite is reduced, clasps are placed on the posterior teeth and
the appliances are left clear of the anterior teeth to encourage eruption of
the incisors.
•In addition, a vertical-pull headgear may be used to apply an intrusive force
to the upper molars to reduce the vertical component of growtha
STAGE 2-SUPPORT PHASE
The aim of the second stage of treatment is to retain the corrected
incisor relationship until the buccal segment occlusion is fully
established, using an upper Hawley-type removable appliance with an
inclined guide plane to retain the sagittal relationship.
twin block
twin block
twin block
twin block
twin block
twin block
twin block
twin block
twin block
CASE SELECTION
•The technique has a wide application in those cases in which
anteroposterior correction of arch relationship . For the neophyte,
the technique should be used to treat intially class 2 div 1 with an
uncrowded lower arch.
•In cases with crowding arch relationships arecorrectd first with twin
block before crowdin is relieved.
•In the treatment of Class II, Division 2 , twin blocks are designed to
procline upper incisors and align the labial segments while correcting
the sagittal malrelationship.
•The inclined planes are shaped to encourage molar eruption and the
labial segments are aligned while correcting the distal mandibular
occlusion
•An integrated approach with fixed appliances allows alignment, intrusion, and
torque to be carried out for the maxillary labial segments during the active
phase of treatment when arch relationships and skeletal discrepancies are
treated simultaneously.
• The presence of bite-blocks prevents traumatic occlusion on the fixed
attachments and avoids breakage as a result of excessive overbite.
•The necessity to combine a functional orthopedic phase of treatment with a
subsequent orthodontic phase is recognized in cases in which additional dental
correction is required.
•Reverse twin blocks may be used to correct sagittal arch relationships in
Class III malocclusion.
•The upper twin block is designed to procline upper incisors and Class III
intermaxillary or extraoral traction may also be applied.
•The technique is effective in the mixed or permanent dentition and may
also be successful in adult treatment except that only dentoalveolar
correction occurs as opposed to skeletal adaptation in the growing child.
•The response to treatment is always related to the patient’s growth
pattern
DISCUSSION
•In many respects the occlusal inclined plane is a significant improvement
on existing appliance mechanisms in the functional guidance of facial
growth and development.
•Significant changes in facial appearances are seen within 2 or 3 months
of starting treatment with twin blocks as a result of altered muscle
balance and continuous wear, even during eating. Rapid soft-tissue
adaptation occurs in response to an improved occlusal relationship.
•Soft-tissue compensation occurs to assist the primary functions of mastication
and swallowing, which require an effective anterior oral seal.
•The twin block appliance positions the mandible downward and forward,
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 spontaneously adopt a natural lip seal for
deglutition without exercises when twin blocks are fitted.
•The lip seal is maintained throughout treatment and improved facial balance is
evident within a few months of starting treatment.
•Twin blocks have been described by patients as the most comfortable of all the
functional appliances.
• Although the appliances are removable, they produce rapid improvements in
facial appearance that encourage good patient motivation.
CEPHALOMETRIC ANALYSIS
Changes during the active phase of treatment.
•Reduction in the anteroposterior apical base discrepancy on angular
assessment of ANB angle
•Increase in effective mandibular length (articulare to gnathion)
•Increase in length of the facial axis (cc to gnathion)
•Increase in facial height (nasion to menton). The majority of patients in
the control sample had deep overbite and the aims of treatment were
consistent with increasing facial height.
•Reduction in facial convexity (A point to facial plane)
•Reduction in the distance from the distal outline of the upper first
molar to the pterygoid vertical
LOWER INCISOR ANGULATION
In the study of 70 consecutively treated cases, the lower incisor was shown
to procline in the active phase of treatment and to upright in the support
phase.
After treatment the angulation of the lower incisor to the mandibular plane
had decreased slightly by a mean value of less than 1”. This had no statistical
significance, but is important in evaluating the stability of the lower
anterior segment after treatment.
REFERENCES
1. Charlier JP, Petrovic A, Herman-Stutzman J. Effects of mandibular
hyperpropulsion on the prechondroblastic zone of young
rat condyle. AM J ORTHOD 1969;55:71-4.
2. McNamara JA Jr. Functional determinants of crania-facial size
and shape. Eur J Orthod 1980;2:131-59.
3. Howe RP. The bonded Herbst appliance. J Clin Orthod
1982;10:663-7.
4. Howe RP, McNamara JA Jr. Clinical management of the bonded
Herbst appliance. J Clin Orthod 1983;7:456-63.
5. Harvold EP. Bone remodelling and orthodontics. Eur J Orthod
1985;7:217-30.
6. Harvold EP. Primate experiments on oral sensation and morphogenesis.
Transactions of 3rd International Congress of the
European Orthodontic Society. 1973;43 1:4.
7. Clark WJ. The twin block traction technique. Eur J Orthod
1982;4: 129-38.
8. McNamara JA, Bookstein FL, Shaughnessy TG. Skeletal
and dental changes following functional regulator therapy on
Class II patients. AM J ORT~IOD 1985;88:91-110.
9. Riolo ML, Moyers RE, McNamara JA Jr, Stuart Hunter W. An
atlas of craniofacial growth. Cephalometric standards from the
University School Growth Study, the University of Michigan.
Ann Arbor: 1974. Center for Human Growth and Development,
University of Michigan.

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twin block

  • 2. THE OCCLUSAL INCLINED PLANE •The occlusal inclined plane is the fundamental functional mechanism of the natural dentition. •Cuspal inclined planes play an important part in determining the relationship of the teeth as they erupt into occlusion. •Occlusal forces transmitted through the dentition provide a constant proprioceptive stimulus to influence the rate of growth and the trabecular structure of the supporting bone.
  • 3. TWIN BLOCKS •Twin blocks are bite-blocks that effectively modify the occlusal inclined plane to induce favorably directed occlusal forces by causing a functional mandibular displacement •Upper and lower bite-blocks interlock at a 45” angle •Designed for full-time wear to take advantage of all functional forces applied to the dentition including the forces of mastication. •give greater freedom of movement in anterior and lateral excursion •cause less interference with normal function.
  • 5. ORTHOPEDIC TRACTION •In cases in which the skeletal discrepancy is severe,the addition of an orthopedic traction system to support the action of occlusal inclined planes provides a versatile appliance technique that is effective in the treatment of a wide range of malocclusions. •The indications for treatment include maxillary protrusion,mandibular retrusion, and vertical growth discrepancies •A functional orthopedic approach eliminates the uncertainty of treatment response that is sometimes associated with purely functional techniques • The technique achieves rapid correction of malocclusion even in cases with severe malocclusions that are unfavourable for conventional fixed or functional appliance therapy.
  • 6. THE CONCORDE FACE-BOW •The twin block technique uses a new method of applying inter-maxillary traction. •The Concorde facebow combines intermaxillary and extraoral traction by the addition of a recurved labial hook to a conventional face-bow. • Intermaxillary traction is applied as a horizontal force from the labial hook to the lower appliance, eliminating the unfavorable upward component of force associated with conventional intermaxillary traction. •The traction components are worn only at night to reinforce the action of the occlusal inclined plane. .
  • 7. •If the patient fails to posture the mandible to the corrected occlusal position during the night, the intermaxillarytraction force is automatically increased to compensateso that favorable intermaxillary forces are applied continuously •Extraoral traction is added when orthopedic force to the maxilla is indicated-for example, in correction of maxillary protrusion •A vertical component of extraoral traction applies an intrusive force to the upper posterior teeth and the palate via the upper appliancen to limit downward maxillary growth •This facilitates correction of Class II arch relationships in vertical growth discrepancies.
  • 8. • The Concorde face-bow effectively combines extraoral and intermaxillary traction in the treatment of severe skeletal discrepancies. •A recurved labial hook is added to a conventional face-bow. Outer bow is 1.5 mm; inner bow is 1.13 mm reinforced with tubing; labial hook is 1.13 mm
  • 9. • Intraoral views showing twin blocks in open and closed positions. • The Concorde face-bow is illustrated with detail of the recurred labial hook and intraoral attachment of the intermaxillary elastic.+
  • 10. • Simple twin block appliances are shown in conjunction with fixed appliances. • This combination produces rapid correction of arch relationships that can counteract a slow response to treatment in cases with unfavorable growth patterns
  • 11. •Twin blocks may be either removable or fixed to the teeth APPLIANCE DESIGN Removable twin blocks •The upper appliance is retained by modified arrowhead clasps. •The clasps incorporate a coiled tube for attachment of a face-bow if traction is to be applied. •Retention may be increased by adding ball-ended clasps in the labial or buccal segments. •A midline expansion screw provides compensatory lateral expansion of the upper arch to accommodate a functional protrusion of the lower arch from its retruded position. •Labial and lingual bows (as needed) are included to control upper incisor angulation.
  • 12. •In the lower arch, retention is often obtained by l-mm interdental ball clasps in the lower incisor region combined with clasps in the buccal segments. •The delta clasp was specifically designed bythe author to extend the area of contact of the clasp in the undercut and to improve retention with a closed triangle to increase resistance to fatigue. •This combination of clasps gives excellent retention and is very effective in limiting proclination of lower incisors during the twin block stage
  • 13. •In mixed dentition treatment, clasps are placed on the lower incisors and on deciduous molars or first permanent molars. •The lower appliance may be split anteriorly with the addition of a screw or helical spring to expand and develop the lower arch, if desired. •The upper bite-blocks cover the lingual cusps of the upper posterior teeth, extending to the mesial ridge of the upper second premolar. •This allows the clasp to be more flexible and improves retention of the appliance
  • 14. •Full occlusal cover is necessary in the lower premolar region to compensate for the discrepancy in arch width and to allow the inclined planes to interlock in occlusion. •The lower bite-block extends to the distal marginal ridge of the lower second premolar •For correction of deep overbite, it is an advantage to leave the lower molars free of the appliance, allowing their eruption to be controlled in relation to the overbite •It is very important to prevent molar eruption in cases in which there is reduced overbite or anterior openbite. • All erupted posterior teeth must occlude on the bite-block to prevent overeruption.
  • 15. , Diagram showing details of twin blocks combined with fixed appliances. Occlusalinclined planes are outlined in black. Clasps on 655 55 6 7 are shown in black. In this example the upper fixed appliance is confined to 3211123 at this stage until arch relationships are corrected, allowing A easy transition into a full fixed appliance. In the lower arch, a utility arch accommodates clasps in the buccal segments. The fixed appliances are shown in red.
  • 16. BITE REGISTRATION •For Class II problems, the proper construction bite is taken and the models are articulated with mandibular protrusion. • The amount of mandibular protrusion depends on the ease with which the patient can posture forward. • As a general rule, the initial activation should reduce the overjet by 5 to 7 mm leaving 3 to 5 mm interocclusal clearance in the first premolar region. •The interocclusal clearance is increased where there is increased overbite and the bite-blocks are designed to allow the free eruption of the lower molars to reduce the overbite by increasing the lower facial height
  • 17. •The registration bite should allow for correction of midlines in cases in which they are displaced by functional occlusal interference or guidance into habitual occlusion. • Twin blocks may be activated unilaterally to correct postural mandibular displacement with center line displacement and asymmetric buccal segment relationships. •The occlusal inclined plane is particularly well suited to the correction of functional abnormalities associated with asymmetric mandibular development. •For correction of asymmetry, the lower appliance requires maximum retention in the lower arch to minimize dental movement and to encourage asymmetric compensatory growth.
  • 19. Intraoral views before treatment Intraoral views after treatment
  • 22. FIXED TWIN BLOCKS •Twin block appliances may be designed for direct fixation to the teeth by bonding. •The appliances resemble the Herbst appliance, substituting occlusal inclined planes for telescopic tubes to provide the functional component to guide the mandible into a protrusive position. •Preformed wedge attachments are being designed at present for direct fixation to molar bands to allow simpler application in fixed appliance technique
  • 23. CLINICAL MANAGEMENT •This report refers to the treatment of an uncrowdedClass II, Division 1 malocclusion primarily, using removabletwin blocks. • The patient had a combination of maxillary protrusion and mandibular retrusion. •The technique is described in two stages, an ,active phase with twin blocks and traction attachments, and a support phase with a guide plane after correction of arch relationships.
  • 24. STAGE 1 -ACTIVE PHASE •Twin blocks are combined with intermaxillary and extraoral traction for rapid correction of arch relationships •The initial activation is checked when twin blocks are fitted to confirm that the patient can comfortably maintain the altered postural position. •Twin blocks are removed for eating for the first 3 days until the initial discomfort from appliance wear has been resolved
  • 25. •Thereafter, the appliances are worn avoid soft-tissue irritation. The upper midline screw is continuously. •It is important for the patient to understand that wearing twin blocks for eating increases the orthopedic forces and improves the response to treatment; this makes it a true functional appliance. •It may be necessary to trim or relieve the flange the lower appliance, lingual to the lower incisors, to avoid soft tissue irritation •The upper midline screw is continuously turned a one-quarter turn every week to 10 days until the the arch width is adequate to accommodate the lower arch in its corrected position. •It is important to check the expansion of the upper arch at each visit to avoid excessive expansion
  • 26. •The Concorde face-bow is adjusted so that it lies just below the level of the upper lip at rest, with the ends of the outer bow sloping slightly upward above the level of the inner bow. •The resulting extraoral traction applies an upward component of force that helps to retain the upper appliance •The intermaxillary elastic is attached under the ball clasps in the lower labial segment and passes to the labial hook on the face-bow (Fig. 1, C). If lower incisors are already proclined, less elastic traction will be tolerated. •Avoid prolonged elastic traction in slow vertical-growing patterns. •The retention of the appliance must be checked after the traction assembly is fitted •Extraoral traction is applied by a straight pull toa conventional headcap worn every night for 8 to 10 hours using 200 g distal extraoral force on each side and approximately 150 g intermaxillary force. •At each monthly visit, the occlusion is checked for •correction of arch relationships
  • 27. Clinical response in active phase •Within a few days of fitting the appliances, theposition of muscle balance is altered so that it becomes painful for the patient to retract the mandible. This has been described as the “pterygoid response” (McNamara*) or the formation of a “tension zone” distal to the condyle (Harvold5). It is rare for such a responseto be observed with functional appliances that are not worn full-time.
  • 28. •The rapid clinical response confirms the summary of adaptive responses in functional protrusion experiments with fixed inclined planes by McNamara. The placement of appliances results in an immediate change in the neuromuscular proprioceptive response. Provided all phasic and tonic muscle activity is affected, the resulting muscular changes are very rapid, and can be measured in terms of minutes, hours and days. Structural alterations are more gradual and are measured in months, whereby the dento skeletal structures adapt to restore a functional equilibrium to support the altered position of muscle balance.’
  • 29. •The patient’s rate of growth should be taken into account in timing the reactivation of the bite-blocks by the addition of cold cure acrylic to the mesial inclined plane of the upper blocks. • However, an overjet of up to 10 mm can be corrected without reactivating the biteblocks if the rate and direction of mandibular growth are favorable. •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. •Full correction of sagittal arch relationships can be achieved in as little as 2 to 6 months, giving a normal incisor relationship with the buccal segments out of •occlusion due to the presence of the bite-blocks. • It is a consistent feature in functional techniques that sagittal correction of arch relationships is achieved before compensatory vertical development in the buccal segments is complete
  • 30. Management of overbite •Deep overbite is reduced by overcorrecting the incisors to an edge-to-edge relationship before reducing the height of the bite-blocks. •Vertical development of the lower molars is encouraged from the beginning of the active phase of treatment by progressively trimming the upper bite-block occlusodistally to allow the lower molars to erupt. •At the end of the active phase, the incisors and the molars should be in correct occlusion. •At this stage an open bite is still present in the premolar region because of the presence of the biteblocks. •The lower block is trimmed over a period of 2 or 3 months to reduce the open bite in the premolar region. •It is important to maintain adequate interlocking wedges to maintain anteroposterior correction of arch relationships. •This method of reducing overbite by controlled eruption of posterior teeth supported by occlusal biteblocks results in favorable changes in facial balance by increasing lower facial height.
  • 31. •Conversely, if the overbite is reduced before treatment, it is important to prevent overeruption of posterior teeth, which would further reduce the overbite. • All erupted teeth must then be in occlusal contact with the bite-blocks. •If second molars erupt during the active phase, occlusal cover or occlusal rests must be extended to prevent overeruption of these teeth. •When the overbite is reduced, clasps are placed on the posterior teeth and the appliances are left clear of the anterior teeth to encourage eruption of the incisors. •In addition, a vertical-pull headgear may be used to apply an intrusive force to the upper molars to reduce the vertical component of growtha
  • 32. STAGE 2-SUPPORT PHASE The aim of the second stage of treatment is to retain the corrected incisor relationship until the buccal segment occlusion is fully established, using an upper Hawley-type removable appliance with an inclined guide plane to retain the sagittal relationship.
  • 42. CASE SELECTION •The technique has a wide application in those cases in which anteroposterior correction of arch relationship . For the neophyte, the technique should be used to treat intially class 2 div 1 with an uncrowded lower arch. •In cases with crowding arch relationships arecorrectd first with twin block before crowdin is relieved. •In the treatment of Class II, Division 2 , twin blocks are designed to procline upper incisors and align the labial segments while correcting the sagittal malrelationship. •The inclined planes are shaped to encourage molar eruption and the labial segments are aligned while correcting the distal mandibular occlusion
  • 43. •An integrated approach with fixed appliances allows alignment, intrusion, and torque to be carried out for the maxillary labial segments during the active phase of treatment when arch relationships and skeletal discrepancies are treated simultaneously. • The presence of bite-blocks prevents traumatic occlusion on the fixed attachments and avoids breakage as a result of excessive overbite. •The necessity to combine a functional orthopedic phase of treatment with a subsequent orthodontic phase is recognized in cases in which additional dental correction is required.
  • 44. •Reverse twin blocks may be used to correct sagittal arch relationships in Class III malocclusion. •The upper twin block is designed to procline upper incisors and Class III intermaxillary or extraoral traction may also be applied. •The technique is effective in the mixed or permanent dentition and may also be successful in adult treatment except that only dentoalveolar correction occurs as opposed to skeletal adaptation in the growing child. •The response to treatment is always related to the patient’s growth pattern
  • 45. DISCUSSION •In many respects the occlusal inclined plane is a significant improvement on existing appliance mechanisms in the functional guidance of facial growth and development. •Significant changes in facial appearances are seen within 2 or 3 months of starting treatment with twin blocks as a result of altered muscle balance and continuous wear, even during eating. Rapid soft-tissue adaptation occurs in response to an improved occlusal relationship.
  • 46. •Soft-tissue compensation occurs to assist the primary functions of mastication and swallowing, which require an effective anterior oral seal. •The twin block appliance positions the mandible downward and forward, 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 spontaneously adopt a natural lip seal for deglutition without exercises when twin blocks are fitted.
  • 47. •The lip seal is maintained throughout treatment and improved facial balance is evident within a few months of starting treatment. •Twin blocks have been described by patients as the most comfortable of all the functional appliances. • Although the appliances are removable, they produce rapid improvements in facial appearance that encourage good patient motivation.
  • 48. CEPHALOMETRIC ANALYSIS Changes during the active phase of treatment. •Reduction in the anteroposterior apical base discrepancy on angular assessment of ANB angle •Increase in effective mandibular length (articulare to gnathion) •Increase in length of the facial axis (cc to gnathion) •Increase in facial height (nasion to menton). The majority of patients in the control sample had deep overbite and the aims of treatment were consistent with increasing facial height. •Reduction in facial convexity (A point to facial plane) •Reduction in the distance from the distal outline of the upper first molar to the pterygoid vertical
  • 49. LOWER INCISOR ANGULATION In the study of 70 consecutively treated cases, the lower incisor was shown to procline in the active phase of treatment and to upright in the support phase. After treatment the angulation of the lower incisor to the mandibular plane had decreased slightly by a mean value of less than 1”. This had no statistical significance, but is important in evaluating the stability of the lower anterior segment after treatment.
  • 50. REFERENCES 1. Charlier JP, Petrovic A, Herman-Stutzman J. Effects of mandibular hyperpropulsion on the prechondroblastic zone of young rat condyle. AM J ORTHOD 1969;55:71-4. 2. McNamara JA Jr. Functional determinants of crania-facial size and shape. Eur J Orthod 1980;2:131-59. 3. Howe RP. The bonded Herbst appliance. J Clin Orthod 1982;10:663-7. 4. Howe RP, McNamara JA Jr. Clinical management of the bonded Herbst appliance. J Clin Orthod 1983;7:456-63. 5. Harvold EP. Bone remodelling and orthodontics. Eur J Orthod 1985;7:217-30. 6. Harvold EP. Primate experiments on oral sensation and morphogenesis. Transactions of 3rd International Congress of the European Orthodontic Society. 1973;43 1:4. 7. Clark WJ. The twin block traction technique. Eur J Orthod 1982;4: 129-38. 8. McNamara JA, Bookstein FL, Shaughnessy TG. Skeletal and dental changes following functional regulator therapy on Class II patients. AM J ORT~IOD 1985;88:91-110. 9. Riolo ML, Moyers RE, McNamara JA Jr, Stuart Hunter W. An atlas of craniofacial growth. Cephalometric standards from the University School Growth Study, the University of Michigan. Ann Arbor: 1974. Center for Human Growth and Development, University of Michigan.

Editor's Notes

  1. Fig. 1. Twin blocks appliance design. A, Anterior and lateral views show the following components. Upper appliance: (1) labial bow (0.8 mm) from mesial 6&, (2) clasps (0.8 mm) incorporating coils to accommodate the Concorde face-bow, and (3) occlusal inclined planes occlude at a 45” angle in @ region. Lower appliance: (1) ball-ended interdental clasps (1 .O mm) in 21112 region, (2) delta clasps (0.8 mm) on q (the delta clasp, designed by the author, gives excellent retention on lower premolars and requires minimal adjustment), and (3) inclined planes in @ region. 8, Occlusal views. The upper appliance has a midline screw for compensatory lateral expansion. Where necessary, a midline screw or recurved lingual bow (as in a Jackson appliance) can be included in the lower appliance.
  2. The combination of traction and inclined planes is very effective and is readily accepted by patients who recognize that the corrective forces are logical and the appliance system easily understood. The labial hook presents no problems and patient acceptance is similar to that of a conventional face-bow
  3. Fig. 3. Patient with a Class II, Division 1 malocclusion, treated with the twin block appliances and Concorde face-bow combination. This combines functional therapy with extraoral traction and intraoral intermaxillary elastic force. The combined appliances were worn 10 months. The extraoral distal and high-pull headgear vector applied intrusive forces to the maxillary posterior teeth (8 to 10 hours per night extraoral force wear). A guide plane was used to support the corrected position and treatment during the retention period of 14 months. No fixed appliances were used. A, Beginning facial views at 10 years 7 months. B, Age 11 years 5 months, at end of active correction phase. C, At end of retention, age 13 years 9 months
  4. Fig. 4. The major skeletal correction was completed in this case with twin blocks and Concorde facebow. A severe Class II, Division 1 malocclusion presented a 16-mm overjet with maxillary protrusion and mandibular retrusion with E absent. The overjet was reduced to 2 mm after 6 months treatment with twin blocks and Concorde face-bow. The position was then retained. Treatment was completed with fixed appliances. A, Facial views, age 11 years 4 months. B, Age 11 years 6 months. C, Age 12 years 3 months.
  5. Fig. 5. Orthopedic correction of facial asymmetry with twin blocks and Concorde face-bow is followed by fixed appliances to complete orthodontic correction. Patient demonstrated facial asymmetry, showing correction of center line by unilateral activation in twin block phase. The facial asymmetry and profile are significantly improved after 2 months’ treatment with twin blocks. The improvement is maintained throughout treatment; treatment is completed with fixed appliances after 6 months treatment with twin blocks. A through D, Facial views. A, Age 10 years 6 months. 6, Age 10 years 8 months. C, Age 11 years 3 months. D, Age 12 years 8 months.
  6. Fig. 5 (Cont’d). E through I, Intraoral views. E, Beginning of treatment, age 10 years 6 months. F and G, Age 11 years (G is without appliance in place). H, Finishing and detailing with fixed appliances, age 12 years 8 months. I, Completed treatment, age 13 years 5 months