Biomechanics of Headgears

Center of Resistance
 The center of resistance of a tooth is dependent on the root length and
morphology, the number of roots, and the level of alveolar bone support.
 The exact location of the center of resistance is not easily identified.
Analytical studies have determined that the center of resistance for single
rooted tooth with normal alveolar bone levels is about one fourth to one
third the distance from the cementoenamel junction to the root apex.
 Miki and Hirato found that the location of the center of resistance of the
midface of the human skull was between the first and second upper
premolars anteroposteriorly, and between the lower margin of orbitale and
distal apex of the first molar vertically in the sagittal plane.
 It is distal to the lateral incisor roots for intrusive movements of maxillary
anterior teeth.

BIOMECHANICS
 In 1971 Armstrong demonstrated the importance of the precise
control of magnitude, direction, and duration of extraoral force to
increase its efficiency and effectiveness in treating malocclusions
in the late mixed dentition.
 Gould has shown how changes in the inclination of the facebow
affect the direction of the force and ultimately the direction of
tooth movement.
 Greenspan presented reference charts elaborating the different
moments and forces produced with the various headgear
designs.

Timing of Headgear Treatment
 The most optimum treatment time is between maturational stages
SMI 4 to 7, a very high velocity period of growth.
 The next most desirable time to treat is during the accelerating
velocity period between stages SMI 1 to 3
 The least desirable time is during the decelerating velocity period
between maturational stages SMI 8 to 11. This information is
clinically useful for all growth related mechanics of treatment,
retention, and ortho-surgical timing of therapy.

Force systems with cervical headgear.
OB (Outer bow)-A lies along the LFO and
therefore only vertical and horizontal
forces will be produced, no M. The
position of OB-B will produce an extrusive
F, posteriorly directed F and
counterclockwise M since it is above CR.
Outer bows located below the LFO will
produce posterior forces and smaller
extrusive forces since they are closer
vertically to the neckstrap and clockwise
moments.
CERVICAL HEADGEAR

 The different moments and forces produced by the cervical headgear
depend on the situation of the outer bow in relation to the LFO. By
definition, when the outer bow lies along the LFO, no moment
occurs, and the force system will be reduced to a bodily movement in
a posterior and extrusive direction.
 If the outer bow is placed above this line (angle of above 20-30
degree above occlusal plane), the moment produced by the force will
be in a counterclockwise direction. On the other hand, if the outer
bow is adjusted below this line the moment created will be clockwise.
However, the direction of the forces are the same – extrusive and
posterior. It should be noted though that there is an exception to this
rule.

 If the outer bow is located below (angle of less than 20 degree to
occlusal plane) the neckstrap, the resultant force will be a small
intrusive one, instead of extrusive. Of course, a distal force and large
clockwise moment will also be produced.
 The direction of pull provided by the cervical headgear is especially
advantageous in treating short-face Class II maxillary protrusive
cases with low mandibular plane angles and deep bites, where it is
desirable to extrude the upper posterior teeth.
 Also, the clockwise moment that is so readily produced with this
headgear is very effective in helping conserve anchorage in
extraction cases.
 Outer bow is short -- steepen the occlusal plane
 Outer bow is long -- flatten the occlusal plane

Indications:
• Short face, class II maxillary protrusive cases with a low mandibular
plane angle and deep bite.
• Anchorage conservation.
• Early correction of class II malocclusion as it helps to distalize the
molar.
Contraindications:
• Open bite cases.
• High MP angle.
• Long faces cases with an increase in lower anterior face height.

If the teeth are banded and
stabilized, cervical pull
appliance, produces a force
below both center of
resistance of maxilla and the
dentition. The distances of
the force vector to A and B
determine the center of
rotation (x).

Cervical headgear (neckstrap) to the first
molar. Bodily movement is produced by
an outer bow length and position that
places the line of force (LFO) through
the center of resistance of the molar; but
with a lower direction of pull, the tooth is
extruded as well as moved backward.
Note that the outer bow of a facebow
used with cervical traction nearly always
is longer than the outer bow used with a
high-pull headcap. If the line of force is
above or below its center of resistance,
the tooth will tip with the root or crown,
respectively, going distally as indicated
by the dotted arrows.

HIGH-PULL HEADGEAR
Force systems with high-pull headgear.
High-pull headgears produce intrusive
and posterior forces. Locating the outer
bow in front of the LFO (A and D) will
produce a counterclockwise M while an
OB behind (B and C) will create a
clockwise M. An OB located on the LFO
would of course produce no M.

 The direction of the moment that is produced is dependent on the
position of the outer bow. If the outer bow is placed anterior to the
LFO (angulated > 45 degree to occlusal plane) moment produced will
be counterclockwise.
 On the other hand, if the outer bow is placed posterior to this line
(angulated less than 45 degree to occlusal plane), the moment
produced will be in a clockwise direction.
 This force system would be beneficial in a long-face Class II patient
with a high mandibular plane angle, where intrusion of maxillary
molars would decrease facial height and improve the facial profile.

Indications:
• Long face patient to control further increase in facial height.
• Open bite cases.
• Anchorage control in vertical plane.
• To intrude and distalize molar.
Contraindications:
• Short face class II malocclusion.

Short outer bow angulated high to
create the headgear force line of
action that is far anterior to the unit’s
centre of resistance. This results in a
force system at the unit’s center of
resistance with a moment that tends
to flatten the occlusal plane and distal
and intrusive force components.

With long outer bow such that the
headgear force’s line of action passes
through the unit’s center of resistance
and therefore no change in the cant
of occlusal plane.

Long outer bow. The equivalent force
system at the unit’s center of
resistance has a moment that tends
to steepen the occlusal plane and a
force with intrusive and distal
components. May be necessary for
Class II open bite patients.

High-pull headgear (headcap) to the first
molar. To produce bodily movement of
the molar (no tipping), the line of force
(black arrow) must pass through the
center of resistance of the molar tooth.
This will produce both backward and
upward movement of the molar. Note
that the line of force is affected by the
length and position of the outer bow, so
that a longer outer bow bent up or a
shorter one bent down could produce
the same line of force. If bow length or
position produces a line of force above
or below the center of resistance (dotted
red), the tooth will tip with the root or the
crown, respectively, going distally
because of the moment that is produced.

 This style headgear is a combination of the high-pull and cervical
headgear, with the advantage of increased versatility. Depending on
the force system desired, the orthodontist has the opportunity to
change the location of the LFO.
 The prime advantage of this headgear is its ability to produce an
essentially pure posterior translatory force.
 This is accomplished by placing the LFO through the center of
resistance, parallel to the occlusal plane.
 Clinically, this means bending the outer bow to the same level as
CR, and hooking the elastic to a notch at the same vertical level.
COMBINATION-PULL or STRAIGHT
PULL or INTERLANDI HEADGEAR

The straight-pull headgear is
versatile in that the clinician has
many optional LFO's. In this case,
an OB located on the LFO would
cause translation in a posterior and
slightly superior direction. OB's
above the LFO will produce
posterior and extrusive forces and
clockwise moments. Placing the
outer bow along an LFO that Is
parallel to the maxillary occlusal
plane will produce a pure posterior
translation.

 The relation of the outer bow to the LFO dictates the direction and
magnitude of forces and moments. Placing the outer bow above the
LFO will produce a posterior force, counterclockwise rotation, and
most often an intrusive force.
 However, if the LFO cants up anteriorly (attachment site of elastic is
lower on headcap than at outer bow), an extrusive force will be
produced. If the outer bow is below the LFO, the force produced will
be posterior and superior, and the moment will be in a clockwise
direction.
 The straight-pull is the headgear of choice in a Class II malocclusion
with no vertical problems.
 It is also the headgear of preference when the main thrust of
headgear wear is to prevent anterior migration of maxillary teeth, or
possibly even translate them posteriorly.

Force’s line of action passes
through center of resistance. No
moment acting to change the
cant of occlusal plane, and there
is pure distal force passing
through the center of resistance.

 This configuration is typical for redirecting maxillary horizontal growth
in class II patients and /or to move maxillary molars distally via
translation.
 When a force is applied to a headgear with inner and outer bows,
one side effect is buccal expansion component of forces, which act
bilaterally.
 This side effect is often helpful in class II malocclusions because it is
often necessary to expand the posteriors to maintain proper
intercuspation as the buccal segment class II interrelationship is
corrected.
 If such expansion is not required, it can be prevented by using a
transpalatal arch.

 The main purpose of this headgear is to produce an intrusive
direction of force to maxillary teeth, with posteriorly directed forces.
 If the outer bow is hooked to the headcap so that the line of force is
perpendicular to the occlusal plane and through the CR, pure
intrusion may take place. Due to the multiple notches in the headcap,
this headgear is also very versatile, as the LFO orientation may be
changed.
 However, upon establishing the LFO, our principles of determining
force systems produced remains unchanged.
VERTICAL PULL HEADGEAR

The vertical-pull headgear is used
primarily when a large magnitude
of pure intrusion is needed. The
outer bow must be located on the
LFO to obtain pure intrusion (A).
An OB located anterior to the LFO
will produce an intrusive force and
a smaller posterior force and a
counterclockwise moment (B and
C). Locating the OB posterior to
LFO will cause intrusion a small
anterior force and a clockwise
moment (D and E).

 The head is divided into two components: the anterior component
from the LFO forward and the posterior component located behind
the LFO. If the outer bow is placed anywhere in the anterior
compartment, the moment created will be counterclockwise, and the
forces produced will be intrusive and posterior.
 If the outer bow is placed anywhere in the posterior section, the
moment will be clockwise and the vertical force will be intrusive, but
the horizontal force will be forward.
 If this latter force system is desired, it will require inserting the inner
bow into the buccal headgear tube from the distal.
 The vertical-pull headgear is not as commonly used as are the
others.
 However, it is very useful when pure intrusion of buccal segments is
required, as in the Class I open-bite patient.

Extrusion of teeth and steepening of OP Cervical gear : OB even or low
Extrusion of teeth and flattening of OP Cervical gear : OB very high
Intrusion of teeth and steepening of OP Occipital gear : OB posterior to CRes
Intrusion of teeth and flattening of OP Occipital gear : OB anterior to CRes
Good distal force and flattening of OP Combi gear : OB above CRes
Good distal force and steepening of OP Combi gear : OB below CRes
Good distal force and no change in OP Combi gear : OB through CRes

 Right versus left asymmetries can be corrected using transpalatal or
lingual arches to correct asymmetric molar axial inclinations. The
same mechanism can be used to correct asymmetric molar rotations.
 If buccal occlusion is asymmetric, e.g. Class I on one side and class
II on the other side, without asymmetries either in molar axial
inclinations or in rotations, then it is most logical to achieve the
correction with asymmetric headgear.
 Distal forces exist on both sides, but they are three times greater on
the long outer bow side than on the short outer bow side.
ASYMMETRIC HEADGEAR

 Lateral forces, directed toward the short outer bow side exist with this
headgear. Crossbite development should be kept in mind.
 These are usually cervical or combination type.
 Suggestions to be noted with regard to the use of the asymmetric cervical
gear:
1. The differential in length of arms of face-bow need not be great, only
sufficient to alter the geometry so that the resultant bisector crosses the
molar line closer to the more anteriorly positioned molar than to the other.
Excessive difference in arm lengths could increase the lateral forces.
2. The diameter of wires can be increased for greater rigidity; it is
suggested that the inner bow of 0.055 inch and the outer bow of 0.075
inch (the 0.075 inch face-bow is approximately five times as stiff as the
0.50 inch one).
3. The arms of the face-bow should clear the cheeks so as not to
introduce more undesirable lateral forces.

From Haack DC, Weinstein S. The mechanics of centric and eccentric cervical
traction. Am J Orthod 44(5):346. 1958

 Rigorous force analysis of the several cervical gears of different
design using elastic straps shows that the fundamental principle
involved in the distribution of the forces to the right and left molars is
the geometry of the direction of the right and left forces emanating
from the cervical elastic band.
 If these forces are symmetrical with reference to the mid-sagittal line
of the head, then the distribution of the reactionary forces at the right
and left molars will be equal, irrespective of the design of the rigid
portions of the appliance (or the point of attachment of face-bow to
arch wire).

 If the direction of forces from the cervical elastic band is
asymmetrical with respect to the mid-sagittal line of the head, then
the anterior-posterior components of the reactionary forces on the
right and left molars will be unequal, the molar nearest the resultant
of the two elastic band forces receiving the greater force.
 Small lateral forces on the molars are always developed by this
eccentric design. These forces can be manipulated to cause all
lateral reaction to occur on one side or the other by springing the
labial arch inward or outward, respectively.

 Headgear bracket-tube combinations can be attached to either
lower first or second molar.
 If the bracket-tube combination is on the first molar, it is
advantageous to place the headgear tube occlusally.
 First molar is preferred since,
1) The lingual arch is on the first molar and gives better control.
2) It is easier for the patient.
 Possible directions are:
1. The posterior segments tend to move back.
2. A positive moment will be produced, which will steepen the
occlusal plane.
HEADGEAR TO LOWER JAW

J-hooks to archwire
 A line of pull attached to the incisor region of the arch wire and
passing occlusally to the center of the resistance will place a distally
directed force upon the maxillary teeth, but will also tip the occlusal
plane downwards at the incisor end of the arch.
 A line of pull through center of resistance will produce distal
movement of the maxillary arch without undesirable rotational effects.
 A more vertical direction of pull, mesial and apical to center of
resistance produces an anti-clockwise moment and an intrusive effect
upon the incisor end of the arch wire.
 Disadvantage is that the flexibility of arch wire results in unavoidable
deformations which subject the teeth near the attachment to diurnal
reversals of force application as the extraoral appliance is attached
or disengaged. Heavy arch wires minimize this rebound effect, but
not eliminated.
J-HOOK HEADGEAR

J-hooks to individual teeth
 If the center of resistance of a single tooth coincides with the
centroid, the line of force of a J-hook headgear intended to produce
upright bodily movement of an individual tooth should ideally pass
through this center of resistance.
 Most authorities suggest an occipitally directed line of force to move
maxillary canines distally.

Magnitude of Force
 When line of action is closer to center of resistance greater force of
450 – 500 gms/side may be applied for orthopedic changes.
 Forces away from center of resistance that produce a moment
should be restricted to 50 – 150 gm/side as in J – hook headgear to
prevent damage to periodontium during dentoalveolar changes that
take place during a moment.

Duration of Force
 Intermittent force for 12 – 14 hrs/day in preadolescent age from early
evening until next morning.
 Typical duration of treatment of about 12 to 18 months, depending on
rapidity of growth and patient cooperation.

CLINICAL APPLICATIONS OF
HEADGEAR FORCE
 There are four main uses of headgear force:
1. Anchorage control
2. Tooth movement
3. Orthopedic changes
4. Controlling the cant of occlusal plane

1. Anchorage Control
 In Class II treatment, headgear force can play a major role in
ensuring that buccal segment teeth do not move mesially when
anteriors are retracted.
 Intraoral mechanics often result in eruption of teeth.
 Headgear produces a vertical force greater than the force of side
effect.
 Inner and outer bows can be of any shape, and length.
 Only the angle and level of the final line of action after the strap
forces have been applied to know exactly the force of headgear
system.

 The reaction force from headgear is dissipated against the bones of
the cranial vault, thus adding the resistance of these structures to the
anchorage unit.
 The only problem with reinforcement outside the dental arch is that
springs within an arch provide constant forces, whereas elastics from
one arch to the other tend to be intermittent, and extraoral force is
likely to be even more intermittent.
 For first molar extraction cases - Interlandi headgear is suitable and
well tolerated.

2. Tooth Movement
1. Intrusion in deep bite cases – 120 to 150 gm force is delivered.
2. Distalization of molars – 300 gm force on each side.

3. Orthopaedic Changes
If the headgear is applied through
the center of resistance of maxilla,
which is in the posterosuperior part
of maxilla. Determined clinically
by dropping a line vertically 10 mm
from the outer canthus of eye and
above the apex of distobuccal root
of maxillary 1st molar.

Effects of orthopedic forces on maxilla
• Cervical traction produces stresses along the frontal process of
maxilla, zygomaticofrontal suture, and the junction of the palatine
bones, areas where high-pull traction produce no observable effect.
Only the high-pull headgear produces stress at the anterior junction
of maxillae (anterior nasal spine).

Pterygoid plates of the sphenoid
 High stress develops upon activation.
 These stresses begin in the middle of the posterior curvature of the
plates and just superior to their anterior junction with the palatine
bone and maxilla.
 As the force increases, the stresses progress superiorly toward the
body of the sphenoid bone.

Zygomatic arches
 Cervical and high pull HGs both
produce similar stress.
 Starts at the inferior border
of the zygomaticotemporal
suture and proceeds posteriorly
along the zygomatic process of
temporal bone.
 Cervical force produces more
intensity at lower load level.

Junction of the maxilla with the lacrimal and ethmoid bones
 Both cervical and high pull produce a stress concentration at the
junction of the maxilla with the lacrimal bones and with the orbital
plates of ethmoid.
Maxillary teeth
 High stresses around maxillary molars with cervical traction. These
located around the middle third of the mesiobuccal root and around
distobuccal root at a position toward apex.
 Also distal to second molar.

Palate
 Cervical traction produces stress in posterior region developing in the
horizontal portion of palatine bones. High pull has no effect.
Anterior junction of left and right maxillae
 Only high pull produces forces below the anterior nasal spine and
just lateral to the suture between the two maxillae.
Frontal process of maxilla
• Stresses produced anterior to nasolacrimal foramen only with
cervical pull.

Sphenomaxillary suture - large compressive stresses.
Temporozygomatic suture - tensile normal stresses.
Sphenozygomatic suture - large tensile stresses.
Frontozygomatic suture - large compressive stresses.
Frontomaxillary suture - large tensile stresses.
 Sphenomaxillary and sphenozygomatic sutures, in particular, resist
the posterior displacement of the nasomaxillary complex.
 Stresses in the nasomaxillary sutures are varied by the direction of
headgear force, and the force applied in the direction closest to that
of the CRes may produce the most effective sutural modification for
controlling maxillary growth.

Headgear treatment can have several
side effects that complicate correction of
Class II malocclusion. If the child wears
the appliance, maxillary skeletal and
dental forward movement will be
restricted. Although this helps in
correction of the Class II malocclusion,
vertical control of the maxilla and
maxillary teeth is important, because this
determines the extent to which the
mandible is directed forward and/or
inferiorly. Downward maxillary skeletal
movement or maxillary and mandibular
molar eruption (all shown in dashed
arrows) can reduce or totally negate
forward growth of the mandible.

FABRICATION & DELIVERY OF
HEADGEAR
• First the correct size and length of the facebow is selected.
• It is then adjusted and adapted to the maxillary cast such that, the
inner bow is away from the maxillary teeth, and position comfortably
to rest in between the lips at rest.
• The inner bow is slightly expanded to facilitate correction of
constricted maxillary arch commonly seen in Class II.
• Molar stop is then made either with a U-loop or bayonet bend mesial
to molar tube.
• Patient is made to sit in an upright position or standing position, then
the facebow is inserted into the molar tube intraorally.

• Mark the centre of resistance of the maxilla on patient face and then
check the position of the outer bow with respect to the mark and then it
should be bend in the planned direction of force and moment to be
generated.
• The outer bow should be conformed to the cheeks. It should be at least
10 mm away from the cheeks.
• A safety release mechanism is recommended to prevent the facebow or
J-hook springing back and injuring the patient’s eye or face if it is pulled
away from the face while still connected to the attachment.
• Final position of the outer bow should be checked while patient is in an
upright sitting position from the front side of patient and clearance from
the cheeks from behind.
• Junction of the inner and outer bow should be away from maxillary
anterior teeth and lie between the lips.

• Once the clinician is satisfied with the final adjustment, it is best to
demonstrate the placement and removal of the headgear to the
patient with one of the parents present.
• This permits both the child and the parent to understand how to
manipulate the appliance in a safe and an efficient manner.
• In the first week of wear it is necessary for the child to have some
assistance.
• We should demonstrate how to carefully insert and remove the
facebow without applying vertical forces which may loosen the band.
• Similarly insertion and removal of J-hook should be demonstrated in
order to avoid deformation of the wire or debonding of the brackets.

• Patient is shown how to safely connect and disconnect the headgear
attachment to the facebow with an explanation and demonstration of
the safety release mechanism.
• Instruction is given for safe use and avoidance of wear during most
sports and other physical activity where child may vulnerable to blow
to the face.

In order to determine the proper length needed
for the outer bow, use the index fingers to apply
pressure in the direction of the headgear
selected. A, Pushing up and back in the direction
of a high-pull headgear. B, Pushing down and
back in the direction of a cervical headgear. As
the fingers are moved from the anterior portion of
the outer bow to the posterior portion, the
position of the bow between the lips will change.
C, If the bow moves up, the roots on the
maxillary first molar will move distally. D, If the
bow moves down on the lower lip the roots of the
maxillary first molar will move mesially and the
crown distally. E, If the bow does not move, the
force is through the center of resistance of the
maxillary first molar and the molar will move
bodily and not rotate. These rules hold true for
both high-pull and cervical-pull headgears. F,
After the correct length is chosen and the outer
bow cut with a pliers, a hook is bent at the end
with a heavy pliers.

USES OF HEADGEAR
1. To restrain the forward and downward growth of the maxilla and
re-directioning maxillary growth.
2. Molar distalization: Headgear may be used to distalize the
maxillary molar to correct the Class II molar relationship or to gain
space for relief of crowding.
3. Headgears can be used to reinforce molar anchorage in high
anchorage cases. Headgears should be worn for at least 10 hr /
day with a minimum force of 300 gm per side.
4. Headgear is an effective means of maintaining arch length by
preventing mesial migration of molars.
5. Molar rotation can also be brought about with the inner bow of the
headgear.

LIMITATIONS OF HEADGEARS
1. Headgears cannot apply force directly to the maxillary sutures. The
orthopedic forces have to be applied through the dentition and
therefore, dental changes are inevitably seen along with skeletal
effects.
2. Patient compliance is mandatory for headgear therapy to be
successful.
3. An adequate amount of mandibular growth is required to "catch
up" while maxilla is restrained. However, this may not always be
seen clinically.

HEADGEAR WITH FUNCTIONAL
APPLIANCES
Lehman appliance (Lehman activator):
• A combination activator-headgear appliance developed by R.
Lehman.
• It consists of a maxillary acrylic plate that carries two rigidly fixed
outer bows and a mandibular lingual shield.
• The acrylic plate covers the palate and it extends over the occlusal
and incisal surfaces of the maxillary teeth, upto the occlusal third of
their buccal and labial surfaces.
• Selective expansion of the maxillary arch is possible by appropriately
activating the two transverse expansion screws (one anterior and
one posterior) that are embedded in the plate.

• Occipital traction is applied through a headstrap attached on the
outer bows, which are fixed at the anterior aspect of the
appliance.
• The mandibular lingual shield is connected to the maxillary plate
by means of two heavy S-shaped wires.
• Unlike many activator type appliances which are constructed
with the mandible in a protruded position, this appliance is
made from a bite registration taken in centric occlusion.
• According to R. Lehman, the S-shaped wires are activated by
approximately 2 mm every 4 to 6 weeks, to achieve a gradual
advancement of the mandible.

Teuscher-Stockli activator/headgear combination appliance:
 A modified activator used in combination with a high-pull headgear.
 The appliance was introduced by U.M. Teuscher and P.W. Stockli
as a means to avoid the detrimental profile effects of cervical traction
while treating Class II malocclusions in growing individuals.
 Buccal headgear tubes are incorporated in the interocclusal acrylic at
the level of the maxillary second premolar or first molar.
 The vector of the high-pull headgear force is directed through a point
midway between the estimated center of resistance of the maxilla
and that of the maxillary dentition.

• In this way it is claimed that the best compromise is reached
between a resulting counter-clockwise rotation of the maxillary
occlusal plane and a clockwise rotation of the maxilla itself, possibly
maintaining the inclination of the maxillary occlusal plane.
• The design includes reduced palatal acrylic coverage to provide
more space for the tongue.
• The acrylic covers the occlusal and incisal surfaces of the maxillary
teeth to distribute the headgear force over the entire dentition.
• The labial bow can be substituted by torquing springs to counteract
palatal tipping of the maxillary incisors. Long lingual flanges extend
from the lower portion of the appliance to enhance forward
positioning of the mandible.
• In addition, Frankel-type lower lip pads may be added to enhance
normal perioral muscle function. Finally, a jackscrew is added
occasionally for controlled expansion.

Van Beek Appliance:
 A construction bite is taken in an end-to-end position, if possible, and
with the teeth approximately 5-8 mm apart.
 The upper part of the appliance covers the front teeth upto the
gingiva for torque control.
 The outer arms are short, ending just in front of the canines, and
extend far enough laterally to avoid soft tissue irritation from the
elastics.
 Molars and premolars are half covered, lateral grinding provides
optimum expansion.

The Twin Block Traction Technique:
• In most cases, full functional correction can be achieved with twin block
alone.
• In a minority of the cases,
1. Severe maxillary protrusion.
2. To control vertical growth pattern.
The Concorde Facebow:
• A method was developed to combine extraoral and intermaxillary traction.
• Concorde facebow helped in restricting maxillary growth, at the same
time encouraged mandibular growth in combination with the functional
appliance.
• Patient comfort and acceptance was similar to the conventional facebow.

1. W.J. Clarke. The twin block technique - A functional orthopedic appliance
system. Am J Orthod Dentofac Orthop. 93, 1988, 1-18.
2. W.J. Clarke. The twin block traction technique. European Journal of
Orthodontics 4 (1982) 129-138.

 The labial hook is positioned extraorally 1 cm clear of the lips.
 Traction component are worn only at night.
 Careful selection of case is very essential.

HEADGEAR INJURIES
• The results of headgear wear can be very beneficial to the patient,
but documented reports of headgear trauma to the face and eyes
demonstrate the potential for serious injury.
• In 1975, the American Association of Orthodontists (AAO) issued a
special bulletin to its members urging them to take precautionary
measures to eliminate accidental patient injuries. In that same year,
the AAO also contacted manufacturers to explore the feasibility of
making a safer headgear design.
• In 1984, the California State Society of Orthodontists highly
recommended the exclusive use of safety facebows and breakaway
headgear systems.

• The incidence is very low, but when an eye injury does occur it can
have serious consequences. Because wounds are contaminated by
oral bacteria and are difficult to treat, eye injuries may result in
impaired vision or even loss of the eye. Another serious
consequence can be sympathetic ophthalmitis.
• Injuries from headgear can occur due either to recoil, where the
appliance is actively pulled, or as a result of accidental
disengagement, particularly during sleep. The dangers arising from
accidents during play or incorrect use are known.
• Manufacturers now produce safety neck straps and anti-recoil
headgear, but even so, anti-recoil devices alone do not make
headgear totally safe. It has been reported that the greatest
incidence of disengagement occurs at night and it is therefore
essential when using headgear at night that the headgear is
securely attached to the appliance.

Safety Mechanisms
• It is important that, where possible, all headgear has two safety
mechanisms: one to prevent accidental disengagement and the
second to prevent recoil injuries. It is the orthodontist’s responsibility
to select the most appropriate combination of headgear safety
features for each case.
Safety Mechanisms and Fixed Appliances:
Prevention of accidental disengagement:
• Rigid neck strap:
• Prevents the forward movement of the face bow, but must be
correctly fitted to prevent the bow disengaging from the buccal tubes
and the safety strap from the bow. This may be too tight for some
patients to tolerate.

• Locking mechanisms: These ensure that the face bow cannot be
removed from the buccal tubes, but they may be difficult for the patient to
fit and remove.
• Locating Elastics: Short strong elastics may be used between hooks on
the inner bow and the buccal tubes to reduce the likelihood of
disengagement. They may be variable in effect, and may present
difficulties for the patent to fit and remove.
Prevention of recoil injuries:
• Anti-recoil devices: These are designed to 'break-away' when excessive
force is applied to the headgear. However, there is considerable variation
in the amount of force required to activate the break-away mechanism
and they do not prevent disengagement of the face bow from buccal
tubes.

• Rigid neck strap: prevents the forward movement of the face bow,
but must be correctly fitted to prevent disengagement from buccal
tubes - this may be too tight for some patients to tolerate.
Other Safety Mechanisms:
• 'Safe ends': These do not prevent the accidental removal of the
face bow from the buccal tubes, but provide a blunt end which may
reduce the incidence of penetrating injuries

Safety Mechanisms and Removable Appliances:
• Integral face bow: When practical, consideration should be made
to having the face bow constructed as an integral part of the
removable appliance.
• Locking mechanisms: Mechanisms similar to those used for fixed
appliances may be used to positively locate the face bow to the
appliance. When face bows are used in conjunction with removable
appliances, the patient should be instructed to fit the face bow with
the appliance out of the mouth
1. Chaushu, G, Chausu, S, Weinberger, T: Infraorbital abscess from orthodontic
headgear. Am J Orthod Dentofac Orthop. 112, 1997, 364–366.
2. Stafford, GD, Caputo, AA, Turley, PK: Characteristics of headgear release
mechanisms: Safety implications. Angle Orthod. 68, 1998, 319–326.

• Remove the headgear before the inner bow. Never remove or fit the
headgear in one piece by pulling the headgear over the face/head.
• Do not wear headgear while playing sports or rough games.
• At night always ensure that the safety mechanism(s) are in place to
prevent accidental removal of the headgear and face bow.
• If the headgear comes detached during sleep, stop wearing the
headgear and contact your orthodontist.
• If any eye injury associated with the headgear occurs, it must be
treated as a medical emergency. Attend your local Accident and
Emergency Department for an ophthalmic opinion as soon as
possible.
• Bring your headgear to each appointment and report any problems
to your orthodontist.

Safety release headgear with
spring mechanism which breaks
apart when excessive force is
applied.

Lee KG, Ryu YK, Park YC, Rudolph DJ. A study of holographic interferometry on
the initial reaction of the maxillofacial complex during protraction.
Am J Orthod Dentofacial Orthop. 1997; 111:623-32.

REFERENCES
• Biomechanics in orthodontics. Michael R. Marcotte (1st Edition).
• Orthodontics and Dentofacial Orthopaedics. James McNamara Jr
and William Brudon (1st Edition).
• Contemporary Orthodontics. William R. Proffit, Henry W. Fields
and David M. Sarver (5th Edition).
• Biomechanics in Clinical Orthodontics. Ravindra Nanda.
• 1001 Tips in Orthodontics and its Secrets. Esequiel Eduardo
Rodriguez Yanez.
• Textbooks of Orthodontics. Gurkeerat Singh (2nd Edition).

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