Tissue response functional appliance

TISSUE RESPONSE TO
FUNCTIONAL APPLIANCE
TREATMENT
www.indiandentalacademy.com

INTRODUCTION
• Functional appliance is a device that changes the posture
of the mandible,holding it open or open and forward to
alter the growth of the mandible by transmitting muscle
forces to the teeth and dentoalveolar structures in the
predetermined direction.
• An increasing recognition of the interrelationship of form
and function,the realisation that neuromuscular
involvement is vital in treatment and a growing
understanding of head posture and the accomplishment
of dentofacial pattern changes are all factors producing
growth in the use of functional appliance.

Functional appliances can be
classified as
• REMOVABLE FUNCTIONAL APPLIANCES
• FIXED FUNCTIONAL APPLIANCES

•In the late 1960's Petrovic and co-workers produced
the first rigorous demonstration that the condylar
cartilage's growth rate and amount can be modified
using appropriate functional and orthopedic
appliances.
•Also that the lateral pterygoid muscle (LPM)
apparently plays a regulating role in the control of the
condylar cartilage's growth rate.
•Stutzmann et al (1976)discovered that the
retrodiscal pad apparently has a mediator role in the
efforts of the LPM to control condylar growth.
•Stutzmann emphasises that secondary cartilages
exist in condylar and coronoid processes and
sometimes in sutureswww.indiandentalacademy.com

The dividing cells, prechondroblasts,are not surrounded by
a cartilaginous matrix and thus are not isolated from local
factor influences.

• Charlier,petrovic and Stutzmann put forward the
servosystem theory stating that if growth results
from cell division of prechondroblasts,it is
somewhat subject to local extrinsic factors.
• In this case the amount of growth can be
modulated by appropriate orthopedic devices and
if growth resulted from cell division of
differentiated chondroblasts, like that of cartilages
of the synchondroses of the cranial baseand
nasal septem, it appears to be subject to general
extrinsic factors and more specifically to
somatotropic hormone-somatomedin, sexual
hormones and thyroxinel.

• The effect of local biomechanic factors is reduced
to modulation of the direction of growth with no
effect on the amount of growth.
• Condylar cartilage growth is integrated into an
organised,functional whole that has the form of a
servosystem and is able to modulate the
lenghthening of the condyle so that the lower jaw
adapts to the upper jaw during growth.
• Variation in the postural activity of the LPM and
the iterative activity of the retrodiscal pad modify
the condylar cartilage growth rate and condylar
growth direction,producing a more anterior or
posterior growth rotation of the mandible

Regardless of the differences in mode of action of various
functional appliances, the following causal chain is
involved :
Functional appliance
Increased contractile activity of the LPM
Intensification of the repetitive activity of the retrodiscal pad (bilaminar zone)
Increase in growth-stimulating factors
- Enhancement of local mediators
-Reduction of local regulators.(factors having negative feed back effects on
cell multiplication rate)
- Change in condylar trabecular orientation
- Additional growth of condylar cartilage
-Additinal subperiosteal ossification of the posterior border of the mandible
Supplementary lenghthening of the mandiblewww.indiandentalacademy.com

EFFECTS OF REMOVABLE FUNCTIONAL
APPLIANCE
MUSCLE
• Graber suggested that one of the basic
objectives of a functional appliance is "to train
the perioral musculature to assist in optimal
dentofacial development by the elimination of
abnormal perioral muscle function, the
stimulation of normal functional patterns, and
the relief of abnormal muscle forces on the
developing dentition and basal structures.
• When the functional appliance is placed in the
mouth, the elevator muscles become elongated
and the amount of elongation is proportional to
the amount of bite raising and mandibular
protrusion caused by the appliance

• Ahlgren and Bendéus postulated that the temporal
muscles were stretched more than the masseter
muscles when the mandible was repositioned anteriorly
by jumping the bite with an activator.
• If it is assumed that the muscles respond according to
the amount and direction of repositioning, then one
would expect less elongation of the temporal muscle
when the mandible is repositioned posteriorly to an
edge-to-edge bite by approximately 3 mm.
• Thus the temporal muscles are affected more when the
mandible is positioned forward, but less when the
mandible is positioned backward.

McNamara concept
• During functional jaw orthopedic treatment, the orofacial system
undergoes considerable change and the mandible presumably
attains an altered functional position.
• The Positional alteration have been attributed to morphologic
adaptations to an altered muscular tone and to changes in the
direction of the traction exerted by the masticatory muscles.
• On the basis of our findings, the hypothesis is proposed that
A) During the first phase of functional treatment reflexes in jaw
muscles are transiently brought into imbalance. This phase of
imbalance could act as a trigger for the mandible to attain a
new functional position that subsequently leads to morphologic
changes
• The neuromuscular changes might have occurred first and
triggered the morphologic changes which was observed an
interval of 2 weeks between the onset of the muscular response
and the morphologic changes in histologic preparations of the
mandibular condyle of Macaca mulatta.www.indiandentalacademy.com

• It may well be that full-time wearing of the
appliance is of importance in this respect since a
continuous anterior functioning might elicit the
muscle response more rapidly than a
discontinuous one.
• B) The larger the anterior positioning by the
appliance, the larger the (1) muscle response
• (2) the positional response, and (3) probably the
morphologic changes.
• McNamara and his colleagues also pointed out
from their experiments in Macaca mulatta
• primates that anterior displacement of the
mandible was capable of inducing altered
postural activity in the lateral pterygoid musclewww.indiandentalacademy.com

Petrovic concepts
• From their experiments on rats, Petrovic and his
colleagues also claimed the enhanced activity in the
pterygoid muscle during mandibular hyperpropulsion
• This change in the activity of the pterygoid muscle is
indeed a "new pattern of function," which in
experimental animals leads to a "new morphologic
pattern."
• The "new pattern of function" can refer to different
functional components of the orofacial system, for
example, the tongue, the lips, the facial and
masticatory muscles, the ligaments, and the
periosteum.
• Depending on the type of appliance, its proponent puts
more emphasis on one of these different functional
components. www.indiandentalacademy.com

• The "new morphologic pattern" includes a
different arrangement of the teeth within the jaws,
an improvement of the occlusion, and an altered
relation of the jaws.
• It also includes changes in the amount and
direction of growth of the jaws, and differences in
the facial size and proportions.
• Although it has been generally accepted that the
orofacial musculature has a profound influence
on the development of the face and dentition’ it
may be very difficult to evaluate and quantify this
effect as it relates to the morphology, to the
relative position, and to the functional behavior of
the muscular components.www.indiandentalacademy.com

• The importance of the lateral pterygoid muscle has
conclusively been demonstrated in the experiments of
McNamara, Petrovic, and their respective colleagues,
but it must be kept in mind that 20 other facial or
masticatory muscles are attached to the mandible and
that these muscles are all mechanically linked by
means of the mandible.
• Thus, a change in the activity of one muscle, giving rise
to a change in mandibular posture, must always be
accompanied by lengthening or shortening of other
muscles attached to the mandible.
• Consequently, since the distribution of force in the
muscles and at the bone-muscle interface is changed,
the process of adaptation can begin in both systems:
the muscle-adaptation to a new functional length and
the bone remodeling to new stress distribution at its
surface. www.indiandentalacademy.com

H - Activator
• According to Andresen and Haupl,the activator
induces musculoskeletal adaptation by introducing a
new pattern of mandibular closure.
• The neuromuscular adaptation to the increased
distance and change in direction is the basic
requirement for reeducating the orofacial
musculature.
• According to them the bite does not open the
mandible more than 4 mm(beyond postural rest
position).
• Myotatic reflex activity is stimulated,causing
isometric muscle contraction.
• This muscle force transmitted by the appliance
moves the teeth.
• Thus the appliance works by using kinetic energy.www.indiandentalacademy.com

• According to Mcnamara the stimuli from the
activator and muscle receptors and periodontal
mechanoreceptors promote displacement of the
mandible.
• The superior head of the lateral
pterygoidmuscles have the most important role
in this adaptation because they assist in skeletal
adaptation.

V - Activator
• Harvold and Woodside opens the mandible as much
as 10 to 15 mm beyond postural rest vertical
dimension.
• According to them the viscoelastic properties of
muscles and the stretching of soft tissues are decisive
for activator action.The viscoelastic reaction can be
divided into
• Emptying of vessels
• Pressing out of interstitial fluid
• Stretching of fibres
• Elastic deformation of bone
• Bioplastic adaptation
• According to them ,eliciting a stretch of soft tissues
primarily requires dislocating the mandible anteriorly
or opening beyond the postural rest vertical dimensionwww.indiandentalacademy.com

• The proponent of this concept contend that the use of
myotatic reflex along with attemptsto increase the
frequency of biting and swallowing should be largely
ignored,letting passive tension (visco elastic properties)
in the stretched labial and oral musculature deliver the
primary force to the appliance.
• The power to produce alveolar remodeling is obtained
from the inherent elasticity of muscle, tendinous tissues
and skin without motor stimulation.
• Muscle spindle have not been clearly demonstrated in
the labial muscles and therefore there seems to be no
mechanism for turning off reflex muscle activity through
a modification of the myotactic reflex.
• Thus,more these muscles are stretched,greater is the
force delivered to the activator.
• The reason that bite registered for 3 mm to 4 mm distal
to the most protruded position is to avoid the possibility
of initiating golgi tendon organ activity and thus
eliminate any undesirable myotatic reflex

• Eschler (1952) opens the vertical dimension
beyond 4mm and according to him muscle
stretching method works alternately with isotonic
and isometric muscle contractions.
• At Insertion of the appliance mandible is elevated
by isotonic muscle ontractions.
• When the mandible assumes a static position in
contact with the appliance, isometric contractions
arise.
• Because the mandible cannot reach the postural
rest position,the elevators remain stretched.
• When fatigue occurs,the contracting muscles relax
and the mandible drops.
• As soon as the muscles have recovered,the cycle
begins again. www.indiandentalacademy.com

Herren (L.S.U) activator
• According to Herren L.S.U activator,during the
time the appliance is worn,the forward
positioning of the mandible is the cause of the
reduced increase in length of the LPM.At the
same time a sensory engram is formed for the
new positioning of the mandible.
• During the period in which the activatoer is not
worn,the mandible is functioning in a more
forward position so that the retrodiscal pad is
much more stimulated than in controls.
• The increased repetitive activity of the pad
produces an earlier onset of hypertrophy of the
condylar chondroblasts.

• This earlier commencement and the
simultaneous decrease in the number of
functional chondroblasts implies that the
decrease of the negative feedback signal has a
restraining effect on the prechondroblast
multiplication rate consequently the growth rate
of the condylar cartilage is accelerated.
• In,.otherwords,the LPM partly mediates the
action of the applance.
• In the case of Herren or L.S.U activator the
stimulating effect on condylar growth appears
to be produced mostly during the time
appliance is not worn.

Frankel Appliance
• Frankel appliance is an exercise device,
stimulating normal function while eliminating the
lip trap,hyperactive mentalis and aberrant
buccinator and orbicularis oris action by means
of buccal shields and lip pad.
• The shields and pad can be extended into the
depth of the vestibule putting the tissue under
tension.
• This tension exerts a pull on the periosteal
tissue of the maxillary bone.
• Periosteal pull elicits increased bone activity in
contiguous osseous structures and the
maxillary basal bone is widened.

Twin block technique - Clark
• Within a few days of fitting the appliances, the
position 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.
• It is rare for such a response to 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.

BONE
• Petrovic,Mcnamara and their co-authors
demonstrated increase in condylar growth in
animals treated with appliances designed to force
the mandible into an anterior position.
• An implant study by Stephen williams and Birte
Melsen in AJO 82 on activator therapy indicates
that the induction of a condylar growth pattern in
an upward/posterior direction will result in a
centre of mandibular rotation that is favourable
for sagittal changes.

• The results obtained through a laminographic
study of activator patients indicated that a
temporary change towards a more sagittal
growth of the condyle was observed during
treatment but that a return to the original
growth pattern took place subsequent to
treatment..
• The existing condylar growth can be used in
an optimal manner,bringing the mandible
forward if the sutural and dentoalveolar
growth can be minimised.

• Harvold et al in AJO 85 in a cephalometric study
with activator showed that all mandibular
structures measured to SNP including mandibular
molars,incisors,soft tissue chin ,lower lip and
labiomental sulcus came forward significantly
more during treatment.
• The position of the condylion become more
inferior and anterior as evidenced by decreased
Co-S-N angle and unchanged condyle position in
the glenoid fossa was verified.
• It appeared due to an effect on the location of
glenoid fossa that resulted in a relocation of the
mandible in an anterior direction.

• Baltromejus et al in EJO 2002 in a comparison of
Activator and Herbst showed biologically significant
stimulation of condylar growth seems to be possible
with Activator mainly in the vertical direction,whereas
in Herbst TMJ growth changes were directed mainly
posteriorly.
• Analysis of the treatment effects suggest a strong
vertical condylar growth stimulation induced by
Activator therapy.
• This increase of vertical growth component might be
due to the intermittent forces generated by Activator
in contrast to the continuous forces delivered by
Herbst appliance.

• Mandible rotated anteriorly in the Activator group
due to the fact that condylar growth was
stimulated predominently in a vertical direction
during Activator therapy.
• Hypodivergent subjects reacts more favourably to
activator treatment than hyperdivergent subjects
as the Activator stimulates mainly vertical
condylar growth ,which is the physiological
condylar growth direction in hypodivergent
individuals.

• Birkebaek, Melsen, and Terp in an implant study
that featured laminographs of the
temporomandibular joint, concluded that the major
effects of activator treatment were an increased
amount of condylar growth and a remodeling of the
articular fossa.
• Condylar growth during the 10 month period of
activator treatment increased 1.1 mm and was
redirected 12° in a more posterior direction
compared with untreated controls.
• They also found that treatment resulted in a slightly
forward displacement of the glenoid fossa as
compared with the slightly backward displacement in
the controls.

DENTOALVEOLAR
ACTIVATOR
Harvold in AJO 85 in a study on 120 children with Activator
therapy showed a significant reduction in forward growth of
the maxilla.
The maxillary dental arch became significantly wider during the
treatment which resulted in a larger dental arch.
But the activator used here was not effective in inhibition of
mesial migration of maxillary molars.
In persons with good and fast response to activator treatment,it
was found that maxillary alveolar height increase was
inhibited and mandibular alveolar height was increased.
But it was not consistent or large enough to become statistically
significant.
The longitudinal data on 18 subjects, demonstrate a significantly
greater mean mandibular unit length increase during the first
year of treatment than during the last treatment yearwww.indiandentalacademy.com

• The spline regression analysis of longitudinal changes
during 2 years of pretreatment and 2 years of treatment
in 33 subjects also demonstrate a significantly larger
increase in mandibular length during treatment than
during pretreatment period.
• Reports in the literature demonstrate conflicting
findings on treatment effects by functional appliance on
mandibular growth.
• Some indicate that increased mandibular growth results
from activator treatment,others maintain that the
mandible does not respond with increased growth in
length.
• The findings from this study do not demonstrate
conclusively that mandibular length can be increased by
this type of appliance therapy.
• Mandibular molars came forward significantly along
with relocation of the glenoid fossa and mandible.
• Labial movement or tipping of the mandibular incisors
occured during activator treatment.

BIONATOR
• Almeida et al in EJO 2004 in their cephalometric
human study with bionator showed that there was
no significant restriction of maxillary growth
whereas there was an anterior relocation of
mandible.
• A statistically significant increase in mandibular
protrusion and length was observed in patients
treated with bionator.
• Articulare to gnathion and condylion to gnathion
lengths increased 4.9 mm during a standardised
13 month period.
• There was no evidence of a morphological change
in the mandible,as measured by the gonial angle
between Bionator and control group.www.indiandentalacademy.com

• Improvement in the basal bone relationship resulted
from small changes in maxillary anterior growth and
by an increase in anterior growth of the mandible in
the Bionator group.
• There was no significant differences in craniofacial
growth pattern or LAFH between the groups.
• Posterior face height showed a greater increase in
Bionator group probably related to the posterior bite
opening effect when the mandible was brought
forward and the molars encouraged to erupt.
• Mandibular plane was not significantly affected.
• There was a greater tendency for a clockwise rotation
of the maxillary plane which did not adversely affect
LAFH.
• Bionator group demonstrated lingual tipping of the
maxillary incisors.www.indiandentalacademy.com

• This effect was expected as the labial bow
may come into contact with the incisors
during appliance wear,particularly during
sleep..
• Some proclination of the lower incisors was
found to be produced by Bionator.
• This effect is probably consequent to the
resultant mesialforce on the lower incisors
induced by protrusion of the mandible.
• Vertical eruption of lower first molars was
greater in the functional appliance group.
• Thus the contribution of dental and skeletal
changes was 65% to overall changes.
• The major effects were dentoalveolar with a
smaller significant skeletal effect.www.indiandentalacademy.com

FRANKEL APPLIANCE
• The Function regulator (FR1)was developed by
Frankel in 1967.
• Its conceptual method of action is based on
orthopedic principles that consider muscle exercise
as an important factor in bone development.
• Studies of the effects of the FR in the treatment of
Class II malocclusions have variously demonstrated
greater mandibular growth development, an
absence of maxillary growth changes,an increase in
Lower anterior face height, labial tipping of the
mandibular incisors and a greater vertical
development of mandibular incisors.
• Statistically significant increasein mandibular
intercanine and maxillary intermolar distances have
been reported.

• Hamilton et al in 1987 and Nielsen et al in
1984 have found no increase in mandibular
growth as a consequence of the use of the
FR in the treatment of Class II malocclusions.
• There was a greater maxillary forward growth
restriction and a greater increase in LAFH in
the fixed appliance/cervical headgear groups.
• Nelson et al 1993 and Stuber in1990 showed
the FR demonstrated greater mandibular
development,counter clockwise mandibular
rotation, and greater stability of mandibular
incisor position.

• G.R.P Janson in EJO 2003 in his cephalometric
study with FR demonstrated no statistically
significant influence on maxillary development.
• Also there was no statistically significant difference
in the effective mandibular length(Co-Gn).
• However changes in the mandibular body length
were statistically significant and 1.63 mm greater in
the treated group showing the bone remodelling of
the mandibular ramus.
• It could be expected that a significant increase in
mandibular body length would produce a significant
increase in mandibular effective length.

• Nevertheless,this did not occur, probably
because the difference in the increase in
mandibular ramus height was not significant.
• There was a slight decrease in Co.Go.Me.as
expected with mandibular development.
• The increase in mandibular body size could
contribute to an improvement in mandibular
protrusion(Pog-Nperp).
• The mandibular protrusion also was not
significant,probably because the greater
increase in mandibular body length was not
sufficiently large.

• The changes in the proportion between maxillary and
mandibular effective lengths(Co-A:Co-Gn) were
statistically significant.
• This indicate that the treatment effects are more
evident when the changes in different facial
components are simultaneously considered as
opposed to an analysis of single variables.
• The increase in LAFH in the treated group was
significantly larger than in the control groups.
• This increase is considered to be result of posterior
bite opening due to mandibular protrusion as induced
by the construction bite.
• In subjects with an excessive overbite,this allows
greater dento-alveolar vertical development of the
mandibular posterior teeth.
• There was a significant difference in the proportion
between the LPFH and LAFH.www.indiandentalacademy.com

• The treated group had significant palatal tipping and a
decrease in protrusion of the maxillary incisors.
• According to Frankel and Frankel(1989),this movement
is consequent to the unfavourable contact of the
maxillary incisors by the labial arch.
• They recommended that the labial arch should not
contact these teeth and should not be activated.
• Frankel and Frankel also stressed that antero-posterior
activations greater than recommended cause a greater
uprighting of maxillary incisors.
• Mcnamara(1982)stated that the labial arch should
barely touch the labial surfaces of the maxillary
incisors and recommended the use of the FR-2 in
Class II Div1 because the upper lingual wire would
help in controlling the tipping and vertical position of
the maxillary incisors.www.indiandentalacademy.com

• Uprighting of the maxillary incisors can be very
favourable in subjects with large overjets and
accentuated labial tipping of the maxillary
incisors,characteristic of Class II Div 1 malocclusion..
• Therefore,in these cases,contact of the labial arch on
the maxillary incisors might be desirable.
• There was no restriction of the vertical development of
the maxillary incisors in the treated group.
• The dento-alveolar height as well as the antero-
posterior position of the maxillary molars did not
present statistically significant differences.
• The effect of the FR on the maxillary first molars is
considered to result from the palatal arch that contacts
the mesial surface of the molars to provide the antero-
posterior stability of the appliance

• It would be expected that at least some of the
distal muscle force would be transmitted against
the maxillary molars,preventing the physiological
mesial displacement,which would help in
correcting the Class II relationship.
• When increased changes on the maxillary molars
are required, other more effective FOA are
recommended,especially in association with extra-
oral forces.
• The treated group did not present statistically
significant antero-posterior changes in the
mandibular incisors.It has been claimed that the
action of the two lower lingual wires in the
presence of a deep bite is to prevent further
eruption of the mandibular incisors.This did not
occur in the study.www.indiandentalacademy.com

• Other FOA's with an acrylic coverage of these teeth
present a restriction of their vertical development.
• There was greater vertical development of the
mandibular molars in the treated group.
• This vertical development is considered a determining
factor to correct the deep overbite and the curve of spee.
• Harvold(1974) considered that a greater vertical
development of the mandibular molars,as compared with
the maxillary
• molars is essential to correct the molar relationship
because it induces a more anterior positioning of the
mandibular molars as compared with the maxillary
molars.
• Graber(1994)estimated that it corresponds to
approximately 1.5 mm of a total of 6 mm Class II
relationship correction.
• Correction of overjet and molar relationship occurs as a
consequense of other dentoskeletal changes.

TWIN BLOCK APPLIANCE
• Kevin O Brien etal in AJO 2003 in his study
showed that early intervention with a TwinBlock
appliance successfully reduced dental overjet,
molar discrepencies, and severity of malocclusion
by a combination of dental and skeletal changes.
• The amount of overjet and molar change that were
attributable to skeletal change were 27% and 41%
respectively,by growth modification of both the
mandible and the maxilla.
• Even the skeletal changes was statistically
significant,it amounted to only 1.9 mm,which might
not be considered to be clinically significant or
useful.
• Most important changes resulting from treatment
were dentoalveolar.

• Small restraining effect on maxillary growth might
have occured because of the labial bow in the
TwinBlock used in the study.
• The labial bow might have retroclined the maxillary
incisors,and the position of A point might have been
influenced.
• Clark,however,suggests that a labial bow should not
be used because by retroclining the maxillary
incisors,the amount of potential skeletal change is
reduced.
• In the study at the end of TwinBlock treatment the
incisor angulation was normal and not over
retroclined.
• The study concluded that early treatment with a
functional appliance does not ,on average, change
the Class II skeletal pattern of a child to a clinically
significant degree.

• Christine Mills in AJO 98 in their study with
TwinBlock in patients in the mixed dentition stage
showed mandibular length(measured from
condylion to gnathion)increased by 6.5 mm in
TwinBlock group as compared with only 2.3 mm
increase in control group.
• Approximately two-third of the overall mandibular
length increase could be attributed to an increase
in ramus height (measured from condylion to
gonion).
• The remaining one third was the result of an
increase in mandibular body length (measured
from gonion to gnathion).

• Some headgear effect was observed with TwinBlock
group experiencing a slight inhibition of forward
maxillary growth as evidenced by 0.9 degree decrease
in angle SNA during treatment phase.
• Headgear effect was also observed dentally as 1 mm
distalisation effect on upper molars.
• A slight uprighting effect(2.5 degree) was observed for
upper incisors .
• The lower incisors tipped labially 5.2 degree in
TwinBlock group as opposed to 1.4 degree in
control.Lower molars moved mesially 1.4 mm.
• Molar correction or overcorrection was achieved in all
cases.
• Incisor overjet decreased 5.6 mm ,Two third of which
accounted for by forward growth of mandible

TONGUE
• According to Balters, the equilibrium between the
tongue and circum oral muscles is responsible for
the shape of the dental arches and
intercuspation.
• The functional space for the tongue is essential to
the normal development of the orofacial system.
• For Balters, tongue was the most important factor
in treatment.
• A discoordination of its function could lead to
abnormal growth and actual deformation.
• The purpose of Bionator was to establish good
functional coordination and eliminate these
deforming,growth restricting aberrations .

• Posterior displacement of the tongue could lead to Class
II malocclusion and low anterior displacement could
cause Class III malocclusion;narrowing of the arches
with resultant crowding was the result of diminished
outward pressure during both postural rest and
function,as opposed to the forces from the buccinator
mechanism on the outside and open bite was the
consequence of hyperactivity and forward posturing of
the tongue.
• The labial bow and palatal bar of the Bionator directly
influence the behavior of the lips and tongue.
• The appliance can create sagittal and vertical
dentoalveolar changes with certain sucking habits.
• The main consideration still is to influence the function
of the tongue.
• In standard Bionator the palatal bar which is posteriorly
directed,stabilises the appliance and simultaneously
orients the tongue and mandible anteriorly to achieve a
Class I relationship

• In case of open bite appliance ,to inhibit tongue
movements,the acrylic portion of the lower lingual
part extends into the upper incisor region as a
lingual shield,closing the anterior space without
touching the upper teeth.
• In case of Class III or reverse bionator ,the palatal
bar configuration runs forward instead of
posteriorly,with the loops extending as far as the
deciduous first molars or premolars.
• The tongue is supposedly stimulated to remain in a
retruded position in its proper functional space.
• It should contact the anterior portion of the
palate,encouraging the forward growth of this area.
• Researchers now know that abnormal tongue
function can be secondary,adaptive or
compensatory because of skeletal maldevelopment

EFFECTS OF FIXED
FUNCTIONAL APPLIANCE
• Fixed functional appliances are designed to
use 24 hours a day,with a continuous
stimulus for mandibular growth.
• With respect to the maximum mandibular
growth stimulation and long term stability of
the treatment, the ideal period for FFA is in
the permanent dentition at or just after the
pubertal peak of growth corresponding to the
skeletal maturity stages FG to H of the
MP3(implying to the precapping and preunion
stages of the epiphysis and metaphysis)

CONDYLE AND GLENOID FOSSA
• Woodside et al in AJO 87 in his study on
cynomolgus monkeys with Herbst appliance
showed that cephalometric and histologic
examinations of the adolescent and adult
animals did not demonstrate any useful
increase in mandibular length or increase
proliferation of the cellular elements in the
cartilaginous zones of the mandibular condyle.
• The prechondroblastic and chondroblastic
zones were thin and no evidence was found of
matrix calcification or remodeling of the osseous
trabeculae.

• A large volume of new bone had formed in the
glenoid fossa,especially along the anterior border
of the post glenoid spine.With this bone formation
and resorption along the posterior border of post
glenoid spine, the glenoid fossa appeared to be
remodelling anteriorly.
• The new bone formation appeared to be localised
in the primary attachment area of the posterior
fibrous tissue of the articular disk.
• The deposition of the finger like woven bone
seemed to correspond to the direction of tension
exerted by the stretched fibres of the posterior
part of the disk.

• The posterior part of the articular disk, between the
post glenoid spine and posterior part of
condyle,increased in thickness and showed active
cellular and connective tissue response associated
with numerous enlarged fibroblasts in active stage.
• The increased fibrous tissue of the disk posterior to
the condyle, associated with the bone apposition in
the glenoid fossa, appeared to stabilise the anterior
condylar displacement.
• Thus temperomandibular joint changes following
continuous functional appliance therapy may assist
in the correction of disproportionate jaw
relationships.
• Remodelling such as that may create the
appearance of an increased mandibular length with
or without a true increase.

• Ruf and Pancherz in AJO 99 in MRI and
cephalometric study using Herbst appliance on
young adult at the end of the postpubertal growth
period with either minimal or no residual growth and
early adolescent patients in the acceleration phase
of pubertal growth spurt.
• Even though condylar cartilage matures woth age
to an adult nonhypertrophic form,zones of
unminrealised growth cartilage and undifferentiated
mesenchyme are seen in the adult mandibular
condyle.
• Adult human TMJ is capable of remodelling is
derived from observations in connection with
condylar fracture therapy, mandibular osteotomies
and anterior mandibular repositioning in disc
displacement therapy.www.indiandentalacademy.com

• The increase in MRI signal intensity on the
posterosuperior aspect of the condyle found in the
MRI's of patients treated with Herbst appliance
taken at 6 to 12 weeks of treatment could possibly
resemble the histologically proven hyperplasia of
the prechondroblastic-chondroblastic area.
• In adult patients treated with Herbst appliance this
would be the result of a reactivation of cells of the
prechondroblastic zone.
• Thus representing an area of active condylar
growth.
• This interpretation is supported by studies that
demonstrated increased cell proliferation and
increased cyclic nucleotide concentrations in the
prechondroblastic zone of adult rats,as a reaction
to occlusal alterations.www.indiandentalacademy.com

• In contrast to adolescents,the area of
condylar remodelling in young adults was
located between 2 signal poor zone. One
surrounding the condyle and the other just
above the area of intermediate signal
intensity of the bone marrow.
• This inner demarcation line most probably
resembles the continuous bony plate at the
cartilage-bone interface characteristic of adult
condylar morphologic condition.
• Thus a marked condylar growth response
was seen in all adult Herbst subjects.

• The prechondroblastic-chondroblastic layer of the
condyle has been shown in animals to correspond to
the inner osteogenic layer of the condylar neck and
mandibular ramus.
• Thus the prechondroblastic cells are homologous to
the preosteoblasts of the periosteum of the mandible
and react in a similar way to mechanical stimuli.
• According to Petrovic and Stutsmann the retrodiscal
pad affects mandibular growth by means of a
biomechanic and a vascular component.
• The biomechanic component of the retrodiscal pad
is probably responsible for the posterior condylar
growth direction and the supplementary
lenghthening of the mandible during functional
appliance treatment.www.indiandentalacademy.com

• Fossa remodeling in the young adult subjects
and adolescents occured at a later treatment
stage than condylar remodelling.Fossa
remodeling in both skeletal maturity groups was
most intensive at the inferior part of the anterior
border of the postglenoid spine leading to an
anteclination of the spine.
• The new bone formation seems to be induced by
tensile forces of the posterior fibrous tissue of the
articular disc transmitted to the periosteum.
• The fossa adaptations in the patients treated with
Herbst appliance was less extensive than in
animals,whichmay be due to the fact that the
size of the postglenoid spine in humans is
reduced compared with that of monkeys.

• The effective TMJ changes in both skeletal maturity
groups could be significantly increased during Herbst
treatment period of approximately 8 months.
• The amount was larger in adolescent than in young adult
group.This is most likely due to the basically larger
mandibular growth rate in adolescents.
• Furthermore,the effective TMJ changes were more
horizontally(posterior) than vertically (superior) directed.
• Earlier MRI studies with Herbst appliance have shown that
condylar position was unchanged and the TMJ changes
are as a result of condylar and glenoid fossa remodelling.
• Substantial improvement in facial profile convexity through
Herbst appliance have been shown for both adolescent
and young adults.

• Investigations using magnetic resonance
imaging(MRI) for patients who were receiving
Herbst appliance therapy show that there is a
combination of condylar growth and remodeling of
glenoid fossa whereas certain researchers believe
that the changes are primarly dentoalveolar.
• It was hypothesised that the mandibular
protrusion triggered by functional appliances could
arouse enhanced upward and backward growth of
the condyle that causes a subsequent
displacement of entire mandible forward and
downward.

• Rabie et al in 2001 in his experiments on sprague
dawley rats with bite jumping appliance showed that
there was significantly more bone formation in the
anterior,middle,and posterior regions of the glenoid
fossa in the experimental animals than in the control
groups,with more bone formation in the posterior region
than in the anterior region.
• This is because primary attachment area for the
posterior fibrous tissue of articular disc is in the
posterior zone.
• The deposition of bone seemed to correspond to the
direction of tension exerted by the stretched fibres of
the posterior part of the disc.
• The highest level of osteogenesis was found on day 21.
• The highest levelof expression of type X collagen,a
marker for endochondral ossification,also occured at
day 21

• In clinical studies with the use of Herbst
appliance glenoid fossa remodeling was
measured by MRI and temporal adaptive
responses were found to occur later than the
condylar adaptive responses due to difference
between the periosteal ossification of the
temporal bone and endochondral ossification of
the condyle.

• Cellular response to mandibular protrusion was
most evident in the posterior aspect of the glenoid
fossa.
• In the fibrous layer ,the fibroblasts were found to
be packed parallel to the articular surface on day 3
and became increasingly oriented towards the
direction of pull by disc fibres from day 7 onwards.
• The fibroblasts were round at the begining and
were stretched and flattened by mandibular
protrusion.
• The mesenchymal cells beneath the fibrous layer
were arranged in line with the articular surface on
day 3.
• With the mandibular protrusion ,however the axis
of the mesenchymal cells became increasingly
aligned with the presumed direction of pull.

• When the subperiosteal Extracellular matrix is stretched
because of mandibular advancement,its matrix density
will increase because of transverse compression caused
by Poisson effect.
• The increase in the Extracellular matrix density may
attract more cells from adjacent Extracellular matrix.
• Another source of mesenchymal cells could be the
perivascular connective tissue that surrounds the new
blood vessels that are recruited in response to the
stretching effect .
• The decrease of new bone formation after day 21 might
be due to some backward movement of the mandibular
base as a result of dental compensation manifested in
the forward movement of lower teeth.
• Thus,a reduction of elastic stretch of the disc ligament
and subsequent less pull on the periosteum causes a
decline in osteogenesis in the glenoid fossa.

MUSCLE (Hiyama Angle 2000)
• The condylar growth was facilitated by an increased
activity in the lateral pterygoid muscle induced by
insertion of a Fixed functional appliance that forced
the mandible into an anterior position.
• The activity of the lateral pterygoid muscle was
increased significantly during treatment, and the
growth of the mandible was facilitated.
• This indicates that a similar relation could exist
between the human neuromuscular and skeletal
responsiveness to mandibular forward positioning to
that reported in previous animal experiments
[Mcnamara,Petrovic].
• At stage III (4 to 6 months into treatment), lateral
pterygoid muscle activity was decreased to the level
observed at stage I (before treatment).

• The condyles were still located slightly
forward from their original positions
documented at stage I.
• This observation supports the concepts that
the adaptive change in muscle function
preceded the compensatory morphological
change in the anatomical relationship
between the condyle and the glenoid fossa.
• Pancherz and Anehus-Pancherz studied the
changes in the temporalis and masseter
muscle activities during 6 months of
treatment with the Herbst appliance.

• At the insertion of the appliance, the EMG
activity from the 2 muscles was reduced
markedly during maximal biting and chewing
because of the disclusion of the posterior
teeth.
• However, after 3 months, the level of muscle
activity was similar to that observed before
treatment and, at the conclusion of 6 months
of Herbst appliance treatment, the activity of
both muscles exceeded pre-treatment values.
Although we must be careful in comparing the
Pancherz study the results of the study seem
to imply that orofacial muscle function has the
potential to adapt within a relatively short
period to the new conditions created by the
bite-jumping appliance.

DENTOALVEOLAR
• Herbst appliance restrains maxillary growth and
stimulates mandibular growth.
• Sagittal condylar growth increases whereas vertical
condylar growth is relatively unaffected.
• Experimental evidence indicate that articular fossa
is repositioned anteriorly.
• Mandibular teeth are moved anteriorly.
• Mandibular incisors are proclined.
• Maxillary teeth are moved posteriorly.
• Maxillary teeth are distalised as well as intruded.
• Deep overbite may be reduced significantly.
• Overbite reduction is mainly by intrusion of lower
incisors and enhanced eruption of lower molars.
• Maxillary and mandibular occlusal planes tip down.

• Cope in his study showed that the Jasper
Jumper displaced maxilla posteriorly.
• Failed to stimulate mandibular growth and was
rotated backwards.
• Jasper Jumper tipped the maxillary molars
posteriorly and intruded them.
• Also tipped the maxillary incisors posteriorly and
extruded them.
• The mandibular molars were significantly tipped,
extruded and moved bodily in an anterior
direction.
• The mandibular incisors were intruded and
significantly tipped anteriorly .

GROWTH FACTORS
• Rabie et al in AJO 2002 in his study on 35 day old
female sprague-dawley rats showed that mandibular
advancement caused a significant increase in
neovascularisation and osteogenesis in the glenoid
fossa during earlier stages of advancement followed by
a gradual decrease to levels that were insignificantly
different from those of the late stages of natural growth.
• The temporal pattern of neovascularisation and new
bone formation showed a gradual decrease as a
function of age.
• Haynesworth et al suggested that there is a dimunition in
the number of mesenchymal cells as a function of
age,eventually the number of osteoblasts involved in
growth will also diminish decreasing the amount of bone
formation with time.

• The mechanical strain caused by forward
mandibular positioning stimulated the cells of the
chondroid layer to secrete vascular endothelial
growth factor.
• VEGF enhances neovascularisation and the
perivascular connective tissues surrounding the
new blood vessels are repository sites of
mesenchymal cells.
• These cells could inturn replenish the population
size of osteoprogenitor mesenchymal cells.
• VEGF also stimulates the vascular endothelial cells
to secrete growth factors and cytokines that
influence the differentiation of mesenchymal cells to
enter the osteogenic pathway and engage in
osteogenesis. www.indiandentalacademy.com

• Rabie et al in AJO 2004 showed that stepwise
advancement of the mandible with functional
appliances,such as Bass and the Herbst,led to an
improvement of the jaw base relationship when
compared with a single advancement.
• Mechanical stress plays a fundamental role in
regulating cellular activities during tissue
morphogenesis.
• Many developmental processes depend on external
mechanical cues or internal molecules that sense
mechanical signals.
• The significant increase in vascularisation during
mandibular advancement might have resulted from
the pull of the fibrous tissue of the articular disc.www.indiandentalacademy.com

• Everytime the mandible is advanced,such a
vascular and tissue response should be elicited.
• Stepwise advancement of themandiblefor sagittal
correction of Class II Div 1 malocclusion leads to
greater skeletal changes compared with one step
advancement.
• In the study a mandibular advancement of 3.5 mm
was given in one step group and a 2 mm
advancement in Stepwise group.
• Another 1.5 mm advancement was given for
stepwise group after 30 days.
• The VEGF expression and bone formation was
more in one step group initially,but after day 30
there was significant reduction.

• Stepwise group elicited yet another cycle of VEGF
expression, vascularisation,mesenchymal cell
differentiation,osteoblast production and finally
osteogenesis after day 30.
• The maximum increase in bone formation was
preceded by peak VEGF expression, demonstrating
a correlation between vascularisation and bone
formation.
• Since 3.5 mm advancement of one step group
produced more new bone formation than 2 mm
initial advancement of stepwise group,it is possible
that different magnitudes of advancement would
deliver different levels of mechanical stimulation
with different amounts of tissue response and there
is a minimum threshold of mandibular advancement
required to trigger such tissue responses.www.indiandentalacademy.com

• Work by Kim et al and Turner showed that cyclic
mechanical stress stimulated bone formation,
whereasthe lack of it leads to bone resorption.
• Mechanical stresses are transduced to the cells
from the extracellularenvironment through
deformation of the Extracellular matrix.
• The repeated stretch of the posterior
attachment of the articular disc caused by
stepwise advancement could have elicited a
cellular response leading to increased VEGF
expression and subsequent increase in bone
formation.

FIBROBLAST
• Biomechanical responses of collagen in
functional matrices cause ligaments, tendons,
and fascial sheaths to lengthen during growth.
• The stimulus is presumably the continuous
stretching force provided by the longitudinal
growth of tissues such as the bones and
muscles to which these collagenous fibers are
attached.
• The response of fibroblasts to a low-
magnitude, continuous, tensile force on the
fibers is increased collagen formation and/or
collagen remodeling and cellular division, in a
manner involving interstitial growth.

• This stimulus-response relationship which
carries out the connective tissue growth
mechanism can also be used volitionally to
increase the range of articular motion, as in any
athletic training.
• However, the large amount of time which must be
spent on such physical conditioning and the
reversal which occurs during a period of disuse
show that the cumulative duration of the
stretching force must meet a certain time
threshold; a relatively sustained (either
continuous or intermittent force over a period of
time is required.

• Fibroblast
» Elastic fiber
» Collagen fiber
• Mechanical force plays a role in connective tissue
biology for the differentiation of elastic tissue.
• What stimulus causes a fibroblast to form either
collagenous or elastic fibers?
Elastic fibers:
• A variety of descriptive and experimental evidence
indicates that rhythmic, fluctuating, or pulsating
forces can induce the differentiation of elastic
fibers.
• Thus, we see elastic tissue developing in specific
sites, such as vocal cords, walls of arteries,
trachea and bronchi, and articular capsules of ear
ossicles.

Collagenous Fibers:
• When collagenous tissue is exposed to
intermittent, physiologic, compressive forces,
the fibroblasts can differentiate
metaplastically into chondrocytes surrounded
by a small amount of cartilaginous matrix.
• This change is seen in the articular tissue of
the adult temporomandibular joint in those
areas subjected to functional loading.
• The same stimulus-response relationship
causes the formation of adventitial cartilage,
as described in chick embryos, and in various
cranial and facial sutures in experimental
animals.

BONE LENGTH
• Studies by Mcnamara and Bryan indicate that the
length of the mandible can be increased
significantly (ie 5 to 6 mm) at the end of the
growth period when a functionally protrusive
appliance is used in growing monkeys.
• In a study with Herbst appliance hyperplasia and
hypertrophy of the prechondroblastic and
chondroblastic layers of cartilage was evident in
both the posterio and posterosuperior areas by
three weeks.
• The increase in cartilage thickness was
significant particularly in the posterior
region.Studies show step wise advancement
result in more bone formationwww.indiandentalacademy.com

• During the first advancement,bone formation in the
condyle and glenoid fossa was less than that of 1
step advancement.
• In response to second advancement,new bone
formation in the condyle and glenoid fossa was
significantly greater.
• It confirms the earlier work of Petrovic who
recommended this and stated that periodic
advancement produced increased mandibular
length.
• Woodside and coworkers reported that in older
primates there was a more pronounced response
in the glenoid fossa than the condyle in
mandibular advancement whereas in younger
primates there was a more pronounced response
in the condyle.www.indiandentalacademy.com

• The increase of sagittal condylar growth in
Herbst patients was significantly greater than
in untreated Class II control subjects.
• Irrespective of the growth period,the
difference of mandibular length increase
when comparing Herbst and control subjects
amounted to an average of 1.3 mm.
• Thus,the increased amount of condylar
growth accomplished by the Herbst appliance
seems to be the result of an equal addition of
enhanced growth to normally occuring
condylar growth,irrespective of the somatic or
skeletal maturation stage of the patient.

GROWTH RELATIVITY HYPOTHESIS
• Over the years several theories have emerged on
condylar growth.
• Earliest was the genetic theory which suggests that the
condyle is under strong genetic control like an
epiphysis that causes theentire mandible to grow
downward and forward.
• Several long term investigations actually showed
clinically insignificant condylar growth modifications
after continous mandibular advancement with a
resonable retention period in human beings.
• This leads ta the conclusion that the general growth of
the condyle appears relatively unaltered in long term
studies.
• A second hypothesis based on EMG monitoring
technique suggests that hyperactivity of the lateral
pterygoid muscle(LPM) promotes condylar growth.
• By using LPM myectomy in rats,which may have
disrupted condylar blood supply,

• Whetten and Johnston found little evidence that
LPM traction had any pronounced effect on
condylar growth.
• More recently permanently implanted longitudinal
muscle monitoring techniques have found that the
condylar growth is actually related to decreased
postural and functional LPM activity.
• A third hypothesis,the functional matrix theory
postulates the principal control of bone growth is
not the bone itself,but rather the growth of soft
tissue directly associated with it.
• Endow and Hans presented an excellent overall
perspective suggesting that mandibular growth is
a composite of regional forces and functional
agents of growth control that interact in response
to specific extracondylar activating signalswww.indiandentalacademy.com

• The glenoid fossa promotes condylar growth with the use
of orthopedic mandibular advancement therapy.
• Initially,that displacement affects the fibrocartilaginous
lining in glenoid fossa to induce bone formation locally.

• This is followed by the stretch of nonmuscular
viscoelastic tissues.
• New bone forms some distance from the actual
retrodiscal tissue attachments in the fossa.
• Thus condylar growth is affected by viscoelastic tissue
forces via attachment of the fibrocartilage that blankets
the head of the condyle.

• There are posterior,anterior and 2 collateral soft
tissue attachments between the retrodiscal tissues
and the condyle,along with the fibrous capsule and
synovial fluid.
• These distinct attachments to the condylar head
use the articular disk and fibrocartilage to
communicate between the glenoid fossa and the
condyle.
• During orthopedic mandibular advancement,there
is an influx of nutrients and other biodynamic
factors into the region through the engorged blood
vessels of the stretched retrodiscal tissues that
feed into the fibrocartilage of the condyle.
• The expulsion of these factors occurs during
reseating of the displaced condyles in the fossa
during relapse. www.indiandentalacademy.com

• Nitzan used disoccluding appliances in human beings to
demonstrate low subatmospheric intraarticular
pressures within the TMJ in the open position.
• The low intraarticular pressures were significant in
altering the joint fluid dynamics or flow of synovial fluid.
• It was observed surgically that these negative pressures
shift synovial fluid perfusion in a posterior displaced
direction.
• This TMJ pump may initially act similar to a suction cup
placed directly on the displaced condylar head to
activate growth.
• These negative pressures,initially below capillary
perfusion pressure,permit the greater flow of blood into
the condyle-glenoid fossa region.
• This increases the flow to the synovial capillaries near
the condyle and the fossa.www.indiandentalacademy.com

• By the anterior orthopedic displacement the
condyle is affected by the posterior viscoelastic
tissues anchored between the glenoid fossa and
condyle;inserting directly into the condylar
fibrocartilage

• Displacement and viscoelasticity further stimulate
normal condylar growth by the tranduction of forces
over the fibrocartilage cap of the condylar head.
• The ensuing increase in new endochondral bone
formation appears to radiate as multidirectional
finger like processes beneath the condylar
fibrocartilage and significant appositional(periosteal)
bone formation is seen in the fossa.
• Bjork,Popovich and Thompson have found that
glenoid fossa grows in a posterior and inferior
direction.Anterior slope of articular eminence
undergoes extensive resorption in a posterior and
inferior direction and the posterior slope undergoes
compensatory endosteal deposition until 7 years of
age. www.indiandentalacademy.com

• The posteriorly directed forces of the viscoelastic
tissues may affect the advanced condyle and fossa.
• The fossa is reported to grow in the reverse
direction ,relocating anteroinferiorly to restore
normal function during orthopedic treatment and it
contributes to class II correction.
• One key element in using propulsive orthopedic
appliances is to avoid compression of the condyle
against the eminence.
• This compression has been associated with reduced
condylar growth,TMD,and osteoarthritic
changes,including post treatment degenerative
condylar flattening in a number of isolated Herbst
patients of preadolescent age.
• A thin posterior bite block in case of herbst will
prevent the condylar compression.

ARTICULAR DISC
• A slight retrusion of the disc was seen with the
treatment of Herbst appliance.
• This seems at least partly to be the result of a slight
anterior position of the condyle after treatment.
• During the post treatment period the amount of disc
retrusion decreased.
• Disc retrusion can be the result of a change in form
because of the remodeling processes of the condyle
and fossa.
• Furthermore,a remodeling of the disc in the course of
bite jumping might also have contributed to the disc
retrusion,although because of its avascularity the
remodeling capacity of the disc is limited.
• The effect of Herbst appliance on the position of the
articular disc was found to depend on the pretreatment
disc position. www.indiandentalacademy.com

• Partial disc displacement could be repositioned
successfully and remained stable.
• In contrast to normal disc repositioning therapy
,recapturing of the disc during Herbst treatment was
achieved by a retrusion of the disc and not by a
protrusion of the condyle.

• A possible misinterpretation of the disc repositioning in
the MRI because of a fibrosis of the posterior
attachment seems unlikely as disc repositioning was
associated with a disappearance of the clinical
symptoms.

• In case of total disc displacements with reduction, only a
temporary repositioning of the disc could be achieved during
Herbst treatment.
• Thus with an increasing degree of displacement,the retrusive
effect of the the Herbst appliance on the disc position seems to
be insufficient to stabilise the disc.
• Consequently the disc relapsed to a displaced position when
the condyle moved backwards in the fossa during the
posttreatment period.
• In joints with a total disc displacement without reduction,the
displacement of the disc prevailed during the entire observation
period.
• The development of a pseudodisc because of extensive fibrotic
adaptation of the posterior attachment was seen in some joints.
• TMJ function in general improved in subjects with total disc
displacement without reduction.
• Herbst appliance must be considered the only functional
appliance able to improve the position of the articular disc in the
course of treatment.

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