Tissue response to functional appliance treatment

TISSUE RESPONSE TOTISSUE RESPONSE TO
FUNCTIONAL APPLIANCEFUNCTIONAL APPLIANCE
TREATMENTTREATMENT
www.indiandentalacademy.com

INTRODUCTIONINTRODUCTION
 Functional appliance is a device that changes theFunctional appliance is a device that changes the
posture of the mandible,holding it open or open andposture of the mandible,holding it open or open and
forward to alter the growth of the mandible byforward to alter the growth of the mandible by
transmitting muscle forces to the teeth andtransmitting muscle forces to the teeth and
dentoalveolar structures in the predetermineddentoalveolar structures in the predetermined
direction.direction.
 An increasing recognition of the interrelationship ofAn increasing recognition of the interrelationship of
form and function,the realisation that neuromuscularform and function,the realisation that neuromuscular
involvement is vital in treatment and a growinginvolvement is vital in treatment and a growing
understanding of head posture and the accomplishmentunderstanding of head posture and the accomplishment
of dentofacial pattern changes are all factors producingof dentofacial pattern changes are all factors producing
growth in the use of functional appliance.growth in the use of functional appliance.

Functional appliances can beFunctional appliances can be
classified asclassified as
 REMOVABLE FUNCTIONAL APPLIANCESREMOVABLE FUNCTIONAL APPLIANCES
 FIXED FUNCTIONAL APPLIANCESFIXED FUNCTIONAL APPLIANCES

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

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

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

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

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

EFFECTS OF REMOVABLE FUNCTIONALEFFECTS OF REMOVABLE FUNCTIONAL
APPLIANCEAPPLIANCE
MUSCLEMUSCLE
 Graber suggested that one of the basicGraber suggested that one of the basic
objectives of a functional appliance is "to trainobjectives of a functional appliance is "to train
the perioral musculature to assist in optimalthe perioral musculature to assist in optimal
dentofacial development by the elimination ofdentofacial development by the elimination of
abnormal perioral muscle function, theabnormal perioral muscle function, the
stimulation of normal functional patterns, andstimulation of normal functional patterns, and
the relief of abnormal muscle forces on thethe relief of abnormal muscle forces on the
developing dentition and basal structures.developing dentition and basal structures.
 When the functional appliance is placed in theWhen the functional appliance is placed in the
mouth, the elevator muscles become elongatedmouth, the elevator muscles become elongated
and the amount of elongation is proportional toand the amount of elongation is proportional to
the amount of bite raising and mandibularthe amount of bite raising and mandibular
protrusion caused by the applianceprotrusion caused by the appliance

 Ahlgren and Bendéus postulated that theAhlgren and Bendéus postulated that the
temporal muscles were stretched more than thetemporal muscles were stretched more than the
masseter muscles when the mandible wasmasseter muscles when the mandible was
repositioned anteriorly by jumping the bite withrepositioned anteriorly by jumping the bite with
an activator.an activator.
 If it is assumed that the muscles respondIf it is assumed that the muscles respond
according to the amount and direction ofaccording to the amount and direction of
repositioning, then one would expect lessrepositioning, then one would expect less
elongation of the temporal muscle when theelongation of the temporal muscle when the
mandible is repositioned posteriorly to an edge-mandible is repositioned posteriorly to an edge-
to-edge bite by approximately 3 mm.to-edge bite by approximately 3 mm.
 Thus the temporal muscles are affected moreThus the temporal muscles are affected more
when the mandible is positioned forward, butwhen the mandible is positioned forward, but
less when the mandible is positioned backward.less when the mandible is positioned backward.www.indiandentalacademy.com

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

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

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

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

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

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

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

V - ActivatorV - Activator
 Harvold and Woodside opens the mandible as muchHarvold and Woodside opens the mandible as much
as 10 to 15 mm beyond postural rest verticalas 10 to 15 mm beyond postural rest vertical
dimension.dimension.
 According to them the viscoelastic properties ofAccording to them the viscoelastic properties of
muscles and the stretching of soft tissues are decisivemuscles and the stretching of soft tissues are decisive
for activator action.The viscoelastic reaction can befor activator action.The viscoelastic reaction can be
divided intodivided into
» Emptying of vesselsEmptying of vessels
» Pressing out of interstitial fluidPressing out of interstitial fluid
» Stretching of fibresStretching of fibres
» Elastic deformation of boneElastic deformation of bone
» Bioplastic adaptationBioplastic adaptation
 According to them ,eliciting a stretch of soft tissuesAccording to them ,eliciting a stretch of soft tissues
primarily requires dislocating the mandible anteriorlyprimarily requires dislocating the mandible anteriorly
or opening beyond the postural rest vertical dimensionor opening beyond the postural rest vertical dimensionwww.indiandentalacademy.com

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

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

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

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

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

Twin block technique - ClarkTwin block technique - Clark
 Within a few days of fitting the appliances, theWithin a few days of fitting the appliances, the
position of muscle balance is altered so that itposition of muscle balance is altered so that it
becomes painful for the patient to retract thebecomes painful for the patient to retract the
mandible.mandible.
 This has been described as the "pterygoid response"This has been described as the "pterygoid response"
(McNamara) or the formation of a "tension zone"(McNamara) or the formation of a "tension zone"
distal to the condyle.distal to the condyle.
 It is rare for such a response to be observed withIt is rare for such a response to be observed with
functional appliances that are not worn full-time.functional appliances that are not worn full-time.
 The rapid clinical response confirms the summary ofThe rapid clinical response confirms the summary of
adaptive responses in functional protrusionadaptive responses in functional protrusion
experiments with fixed inclined planes by McNamara.experiments with fixed inclined planes by McNamara.

 The placement of appliances results in anThe placement of appliances results in an
immediate change in the neuromuscularimmediate change in the neuromuscular
proprioceptive response.proprioceptive response.
 Provided all phasic and tonic muscle activityProvided all phasic and tonic muscle activity
is affected, the resulting muscular changesis affected, the resulting muscular changes
are very rapid, and can be measured in termsare very rapid, and can be measured in terms
of minutes, hours and days.of minutes, hours and days.
 Structural alterations are more gradual andStructural alterations are more gradual and
are measured in months, whereby the dentoare measured in months, whereby the dento
skeletal structures adapt to restore askeletal structures adapt to restore a
functional equilibrium to support the alteredfunctional equilibrium to support the altered
position of muscle balance.position of muscle balance.

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

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

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

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

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

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

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

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

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

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

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

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

 Hamilton et al in 1987 and Nielsen et al inHamilton et al in 1987 and Nielsen et al in
1984 have found no increase in mandibular1984 have found no increase in mandibular
growth as a consequence of the use of thegrowth as a consequence of the use of the
FR in the treatment of Class II malocclusions.FR in the treatment of Class II malocclusions.
 There was a greater maxillary forward growthThere was a greater maxillary forward growth
restriction and a greater increase in LAFH inrestriction and a greater increase in LAFH in
the fixed appliance/cervical headgear groups.the fixed appliance/cervical headgear groups.
 Nelson et al 1993 and Stuber in1990 showedNelson et al 1993 and Stuber in1990 showed
the FR demonstrated greater mandibularthe FR demonstrated greater mandibular
development,counter clockwise mandibulardevelopment,counter clockwise mandibular
rotation, and greater stability of mandibularrotation, and greater stability of mandibular
incisor position.incisor position.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

EFFECTS OF FIXEDEFFECTS OF FIXED
FUNCTIONAL APPLIANCEFUNCTIONAL APPLIANCE
 Fixed functional appliances are designed toFixed functional appliances are designed to
use 24 hours a day,with a continuoususe 24 hours a day,with a continuous
stimulus for mandibular growth.stimulus for mandibular growth.
 With respect to the maximum mandibularWith respect to the maximum mandibular
growth stimulation and long term stability ofgrowth stimulation and long term stability of
the treatment, the ideal period for FFA is inthe treatment, the ideal period for FFA is in
the permanent dentition at or just after thethe permanent dentition at or just after the
pubertal peak of growth corresponding to thepubertal peak of growth corresponding to the
skeletal maturity stages FG to H of theskeletal maturity stages FG to H of the
MP3(implying to the precapping and preunionMP3(implying to the precapping and preunion
stages of the epiphysis and metaphysis)stages of the epiphysis and metaphysis)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 CopeCope in his study showed that the Jasperin his study showed that the Jasper
Jumper displaced maxilla posteriorly.Jumper displaced maxilla posteriorly.
 Failed to stimulate mandibular growth and wasFailed to stimulate mandibular growth and was
rotated backwards.rotated backwards.
 Jasper Jumper tipped the maxillary molarsJasper Jumper tipped the maxillary molars
posteriorly and intruded them.posteriorly and intruded them.
 Also tipped the maxillary incisors posteriorly andAlso tipped the maxillary incisors posteriorly and
extruded them.extruded them.
 The mandibular molars were significantly tipped,The mandibular molars were significantly tipped,
extruded and moved bodily in an anteriorextruded and moved bodily in an anterior
direction.direction.
 The mandibular incisors were intruded andThe mandibular incisors were intruded and
significantly tipped anteriorly .significantly tipped anteriorly .

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

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

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

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

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

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

FIBROBLASTFIBROBLAST
 Biomechanical responses of collagen inBiomechanical responses of collagen in
functional matrices cause ligaments, tendons,functional matrices cause ligaments, tendons,
and fascial sheaths to lengthen during growth.and fascial sheaths to lengthen during growth.
 The stimulus is presumably the continuousThe stimulus is presumably the continuous
stretching force provided by the longitudinalstretching force provided by the longitudinal
growth of tissues such as the bones andgrowth of tissues such as the bones and
muscles to which these collagenous fibers aremuscles to which these collagenous fibers are
attached.attached.
 The response ofThe response of fibroblastsfibroblasts to a low-to a low-
magnitude, continuous, tensile force on themagnitude, continuous, tensile force on the
fibers is increased collagen formation and/orfibers is increased collagen formation and/or
collagen remodeling and cellular division, in acollagen remodeling and cellular division, in a
manner involving interstitial growth.manner involving interstitial growth.

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

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

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