Modus operandi of functional appliances mallik /prosthodontic courses

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INDIAN DENTAL ACADEMY
Leader in continuing Dental Education

• Introduction.
• History.
• Premise on which modus operandi of functional appliance
was built.
• Modus operandi of functional appliance – schools of
thought.
• Research findings.
- Cellular and bio molecular findings.
- Jaw muscle activity and and muscle fiber recruitment.
- Skeletal and dental changes.
• Conclusion.
Contents

“Working with growth” has had been a term
which has been in for quite sometime now.
Its presence has not only given orthodontics
a huge credit but also promised a greater
working range for orthodontist. This
seminar would present claims and counter
claims on the working principles of
functional appliance and at present what to
expect out of it.
Introduction

History

• European orthodontists have long been
aware of the role of peri-oral musculature in
orthodontic problems. They also recognized
the potential use of deforming forces to
eliminate these problems. These ideas have
been borrowed latter by the Americans.

1912
• The spark arose by Lischer’s theory, which
states that if compensatory, adaptive lip and
tongue function could exacerbate excessive
overjet in class-II type of malocclusion and
if abnormal swallowing and prolonged
finger sucking habits could create anterior
open bite and narrow arches, could not the
same muscles be used to correct these and
other problems.

1936 :
Andresen: working hypothesis
• Though Andresen working hypothesis was
not intended for “guiding growth" at that
time ,but only to eliminate the adverse
effects of abnormal function.
• Andresen was surprised to see that night
time wearing of the appliance not only had
eliminated the abnormal neuro-muscular
compensation but also produced a complete
saggital correction and significantly
improved the facial profile.

1967
• Findings concerning the biological peculiarities of
mammalian condyle cartilage, role of respiration on
craniofacial morphology and popular theories on
functional matrix hypothesis and epigenitics at that
time have helped fuel this understanding
• Petrovic and coworkers produced the first rigorous
demonstrations that the condylar cartilage’s growth
rate and amount can be modified using appropriate
functional and orthopedic appliances.
• Since then, many other clinicians and researchers
have inquired about possibility of modifying the
condylar cartilage’s growth ratewww.indiandentalacademy.com

Premise on which modus
operandi of functional appliances
was built

Peculiarity of condylar cartilage:
• Unlike the primary cartilage found at other growth
sites, i.e. Epiphysis of long bones, Speno-occipital
syncondrosis, which are embryonic in origin, the
condylar cartilage originates separately during the
development and further more Stutzmann 1967
emphasized that in primary cartilage the dividing
cells, differentiated condroblasts, are surrounded by
cartilaginous matrix that isolates them from local
factors able to restrain or stimulate cartilage growth
whereas the secondary cartilage ;the dividing cells,
precondroblasts, are not surrounded by a
cartilaginous matrix and thus are not isolated from
local factor influence.

Fig primary vs secondry

Popularity of epigenetic theory
• The genome as providing a set of formal, prior,
intrinsic, and necessary causal factors which, when
combined with efficient, proximate, extrinsic, and
necessary casual factors, together are sufficient to
account for the regulation of development.
• The genetic theory views that the diploid genome, at
the moment of fertilization, contains all the
information necessary, “a blue print,” to regulate
skeletal size, Shape, and location – a blue print,
moreover, that merely requires a permissive
environment in which to express itself.www.indiandentalacademy.com

Various hypothesis on the modus
operandi of functional appliances

• Five hypotheses based on neuromuscular
mechanisms have evolved to account for the
skeletal changes associated with functional
appliance therapy.
• In three of these concepts an increase in postural
and functional muscle activity is fundamental to
the proposed mode of action of the appliances and
thereby their design and the degree of vertical
opening used in the bite registration. This
increased activity is thought to result from either
an enhanced stretch (myotonic) reflex of the
masticatory muscle,

or from "conditioning" of the patient that produces
an enhanced higher-brain-center drive of the
motor neurons supplying the muscles, even during
sleep (Myodynamic).
• Fourth view proposes that increased lip strength is
the prime force in alveolar bone remodeling
during functional appliance therapy.
• Fifth emphasizes the importance of viscoelastic
elements in the stretched masticatory muscles and
other orofacial tissue; these elements produce an
increase in "passive" muscle tension, which
provides the major force elicited by the appliance.

Modus operandi of functional
appliances
• Melvin Moss school of thought (1962)
• Petrovic school of thought. (1972)
• Voudoris school of thought.(2000)

Functional matrix hypothesis
• Claims that the origin, growth (i.e., changes in
size, shape, and location), and maintenance in
being of all skeletal tissues and organs (i.e.,
skeletal units) are always secondary,
compensatory, mechanically obligatory
responses to temporally and operationally
prior events or processes occurring in
specifically related non skeletal tissues,
organs, or functioning spaces (i.e., in
functional matrices, either capsular or
periosteal).

Functional cranial component
Skeletal unit Functional matrices
Micro-
skeletal
unit
Macro
Skeletal
unit
Periosteal
matrices
Capsular
matrices

• Moss stresses the dominance of non osseous
structures of the Cranio-facial complex over the
bony parts. He claims that the growth of the
skeletal components ,whether endocondrial or
intra membranous in origin is largely dependent
on the growth of functional matrices

Petrovic school of thought
• Role of lateral pterigoid muscle (LMP) to
regulate in the control of the condylar cartilage
growth as shown by Petrovic, Stutzmann in
1972,1974,1975 was further confirmed by
McNamara in 1980’s
• Stutzmann et al in 1976 discovered that the
reterodiscal pad apparently has a mediator role
in the efforts of the LPM to control condylar
growth www.indiandentalacademy.com

Functional appliances
Increased contractile activity of lateral pterygoid
Intensification in reterodiscal pad iterative activity
Supplementation in growth stimulating factors
Enhancement of local mediators
Reduction of local regulators
Additional growth of the condylar cartilage
Additional subperiosteal ossification
Supplementary lengthening of the mandible

Cybernetic model
• It is based on communication and information
theory.
• Petrovic 1977 was the first to promulgate a
cybernetic model to account for physiological
phenomenon involved in facial growth and the
method of operation of orthodontic and functional
appliance.
• Claims that the upper arch is the constantly changing
reference input and the lower arch is the controlled variable.
Servosystem
theory

• STH or Testosterone blood level increases, the
supplementary lengthening of the mandible is greater than
that of the maxilla.
STH or Testosterone
Optimum occlusion Suboptimum occlusion.
No positional change Growth
or growth represented
Servo
system
Servo
system

Condylar growth with STH , HP

RDP
LPM
Septal
cartilage
Mandible
Maxilla
Growth
hormones
Functional
appliances
Peripheral
comparator
CO
Central
comparator
Deviation
signal
Detectors
PDL
CNS

Working hypothesis of different
functional appliance.

• Functional appliances that position the mandible
forward increase the condylar growth rate and
amount
• Wearing the postural hyperpropulsor everything
occurs as if the upper dental arch were in a more
anterior position than normal.
• The “operation of confrontation” of the two dental
arches then gives a deviation signal.
• During the growth period the saggital deviation
produced by the postural hyperpropulsor decreases
through the supplementary forward growth of the
mandible.
Postural hyperpropulsor
(Herbst, Frankle)

• Periodic increase in thickness of the postural hyperpropulsor
produce increase in LPM activity and in the activity of the
retrodiscal pad as recorded electromyographically; these,
consequently, bring about increase in the rate and amount of
condylar cartilage growth.
• If the appliance is removed after the growth is completed, little or
no relapse is observed. If the appliance is removed before the
growth is completed, no significant relapse is detected if good
intercuspation is maintained however if good intercuspation is not
achieved, the comparator of the servosystem imposes an increase or
decrease condylar growth rate until a state of intercuspal stability is
established.
• Functional maxipropulsion involving periodic forward
repositioning appears to be the best procedure for eliciting a
supplementary lengthening of mandible.

Frankel
• Fränkel's functional regulator is worn primarily in
the lingual and dental regions, and uses the vestibule
as the operational base in contrast to other
functional appliances. It is claimed that the system
of labial, lingual, and buccal pads and shields
directly affects the level of postural activity in the
facial and masticatory muscles by means of a
training effect. The buccal and labial shields placed
highly in the vestibule would also indirectly put
traction onto the periosteum. This traction would
stimulate bone growth in the apical subperiosteal
areas and provide a guidance of eruption for the
teeth. www.indiandentalacademy.com

• The basic components are
- Equilibrium theory.
- Bone deposition secondary to periosteal pull.
- Training of muscles (hypotonic or
hypertonic)

Class II elastics
• Intermaxillary intra-oral elastics, placed bilaterally
for 14 hours daily, in rats between upper first molar
and lower third molar, are not only orthodontic
devices but also functional appliances capable of
stimulating the growth rate and amount of the
condylar cartilage
• Class II elastics don’t increase the contractile activity
of LPM as the hyperpropulsor .The stimulating effect
of class II elastics is primarily mediated through the
retrodiscal pad (metabolic pump)

Herren (L.S.U.) Ativator
• The Herren activator, or the Louisiana state university
modification of it,is different form of postural
hyperpropulsor; it opens the construction bite well
beyond the postural rest position, similar to that
achieved by the Harvold – Woodside activator.
• Such construction bite do not bring about any increase
activity of the LPM. instead it has a two step effect.
when the appliance is worn ,it creates a new sensory
engram which stimulates reterodiscal pad. But the most
important action of this appliances is seen when the
appliance is not worn. This happen due to decreased
length of LPM which stimulates the condyle when the
appliance is not wornwww.indiandentalacademy.com

• Amidst the claims on the working
hypothesis of functional appliances as put
forward by Petrovec et al, John Voudouris
in 2000 proposed the concept of growth
relativity.
• He attributes the failure of earlier research
on the working hypothesis of functional
appliances due to earlier EMG methods,
which were transcutaneous, short term and
removable as described in 2003.

Voudouris school of thought
• The theory of relatively essentially states that
bone growth modification occurs relative to 2
elements:
1. The reterodiscal tissues
are stretched reciprocally,
similar to a large elastic
band, between the fossa
and the displaced condyle
during the expansion of the
growing facial complexwww.indiandentalacademy.com

2.This is followed by the
stretch of nonmuscular
viscoelastic tissues.
3.The transduction of these
nonmuscular forces has
been shown to be
effective at a significant
distance from the actual
physical soft tissue

• The growth relativity concept describes a specific
set of reciprocal soft tissue forces that operate
during herbst treatment, when muscle
hyperactivity does not appear to to be the primary
cause of skeletal change. The displaced condyle
modifies in a radiating manner relative to the
fossa, and the fossa grows in a radiating fashion
relative to the condyle. The reterodiskal streached
between the displaced condyle and the fossa
contributes to the the formation of new bone in
each region. Further more, force referral or
transduction from the posterior retero discal
attachment to the condyle radiating along condylar
fibrocartilage has been implicated in causing
growth modification.

Fixed vs. Removable functional
appliance
• There are innumerable number of advantages of fixed functional or
full time wear appliance over removable appliances .
• Previous EMG studies on removable functional appliances by
petrovic et al has been discredited because of the decrease in EMG
activity after appliance wear.
• Where as fixed functional appliances The mode of action of
functional appliance therapy has been linked to neuromuscular and
skeletal adaptations to altered function in the orofacial region. The
EMG studies as shown by Pancherz ,kharbanda showed that though
there was decrease in the EMG activity during the initial phase of the
treatment because the muscles were in the stage of adaptation and
from 3 months to 6 months there has been a continuous increase in
EMG activity due the continuous forward posturing unlike removable
functional appliances which do not allow the muscles to stabilize and
adapt. www.indiandentalacademy.com

• 1987 Linden et al.
• During the first phase of functional treatment,
reflexes in jaw muscles are transiently brought
into a state of imbalance. This phase of
imbalance could act as a trigger for the mandible
to attain a new functional position, which
subsequently leads to morphologic changes.

• Full-time wearing of the appliance is of
importance in this respect since a continuous
anterior functioning might elicit the muscle
response more rapidly than a discontinuous one.
In view of these considerations, functional
appliances that are worn full-time (Herbst
appliance) or nearly full-time (eg, Fränkel's
functional regulator, Bionator) could be
expected to have a greater net result than those
worn only part-time (eg, activator)

Behind the Screen

• The mechanism of action of functional
appliance in growth modification has been
basically targeted toward the changes at the
condyle and the gleniod fossa but there are
other effects . It wouldn't be justified and
the M.O.A would be in complete without
bringing them to light

• Effect on palatal plane
• Restraining effect on the maxilla Vargervik and
Harvold found that the activator inhibited the
horizontal growth of the maxilla by 2 mm;
Pancherz found it was restricted by 1.7 mm.
• Relative intrusion of the dentoalveolar segment
Do you know how much teeth erupt from age of 8
years to 15 years of age?

• Maxillary teeth at the molars erupt by 6.3
mm and incisors erupt 6mm Mandibular
incisors erupt by 5 mm and molar erupts by
5.7 mm in boys and 3.7 mm and 4.4 mm in
girls.
• If u can relatively intrude or hold on the
teeth vertically and prevent eruption by 5
mm the mandible will auto rotate by 12
degrees and net A-P gain would be helpful
in converting a borderline vertical
malocclusion case with in the domain of
orthodontics

Petrovic vs. Voudoris
• Petr : EMG studies showed hyperactivity of
LPM
• Voud : EMG studies were short term and
transcutaneous
• Voud : Most of the EMGs on a long term
showed in contrary reduced activity of LPM
• .

• Petr : It was believed that upper lateral pterygoid
muscle was attached to the articular disk and the
condyle
• Voud : It has been shown that only few fibers
from the upper lateral pterygoid are attached to the
fibrocarilage of the condyle through lateral
pterygoid tendon
• Petr : Condylar cartilage cell failed to proliferate
in homoautotransplant due to absence of LPM
activation
• Voud : It was thought that resection of LPM
compromised the blood supply and there fore cell
proliferation

Research findings

Cell and molecular biological
findings

• Electromyography of the condylar cartilage
show that cell to cell cytoplasmic junctions
between skeletoblasts become quantitatively
reduced. Consequently, possibilities of
inhibitory inter cellular communications are
cut down; i.e., the cell division rate increases.
Simultaneously, the rate of differentiation of
the skeletoblasts into precondroblasts also
increases Petrovic (1982).

• Characteristic and consistent transmembrane ion flux
variations can be detected : intra cellular Na++
concentration is raised, intracellular K+
concentration is very slightly lowered, and discharge
of H+ from both skeletoblast and precondroblast is
increased, leading to a rise of intracytoplasmic PH.
Intracytoplasmic Ca++ concentration decreases.
• Calmodulin as well as [Ca++ ,Mg++ ] – ATPase and
[H] – ATPase activities are promoted,where as
cAMP, fibronectin, [Na/K] – ATPase activity,cell
trans glutaminase are reduced. The cell division
process is initiated through the momentry surge of
cytoplasmic Ca++ and endogenous cAMP

• The local coupling mechanism include:
a) An open loop part of the control system having a
stimulating effect on the cell multiplication and comprised
of growth hormone ,testosterone, estrogen, insulin,,
glucagon, parathormone, calcitonin, prostaglandin F2, as
well as other mitogenic peptides that corresponds to,
operationally, to fibroblast growth factor which convert
the cell from quiescent to a new cycle stage
b) A feed back part of the control system having an
inhibiting effect on the cell multiplication and comprising
regulators of local origin: a skeletoblast or precondroblast-
multiplication restraining signal of un known nature.
• The intensification in meniscotemporocondylar ligament
activity is associated with an increase in blood and lymph
flow and decrease in cell catabolite concentration and in
negative feed back factors.www.indiandentalacademy.com

Proliferative cells
SOX 9
Differentiation Condroblasts
Cartilage matrix/
condrocytes
SOX 9Regulates type
II collagen synthesis
Hypertrophic cartilage
Precedes on set of EO
Secretes
Type x
collagen
express
VEGF
New blood
vesselsRecruits
Osteoprogenator
Mesenchymal cells
Osteoblasts
osteocytes
Endocondrial
ossification
Condylar growth
Differentiation
osteogenisis

Effect of hyperpropulsor on the precondroblastic cells count
• The following data are from the study of periodic forward
repositioning of the mandible (12 male rats in each
experimental group, sacrificed at day 48 )
• Number of H- methyl-thymidine- labelled cells in condylar
cartilage for various thickness of postural hyperpropulsor.
• Group 1 (control) at 0 mm thickness - 876 cells – 13.5 mm
• Group 2 at 0.5 mm thickness - 1049 cells – 14.9 mm
• Group 3 at 1.0 mm thickness - 1316 cells - 15.2 mm

Effect of various functional appliances on the growth
of the rat mandible
• H- methyl-thymidine- labeled cells in condylar cartilage for
various appliances
• Bionator and frankel
• No appliance – 859 cells – 14.2 mm
• Bionator (end to end) – 988 cells – 14.6 mm
• Bionator (1mm) - 1199 cells – 15.2 mm
• Frankel (lip pad) - 1236 cells – 15.2 mm
• Postural hyperpropulsor and intra oral elastics
• No appliance - 878 cells – 13.9 mm
• P H (0.5 mm) - 1049 cells – 14.8 mm
• PH (1mm) - 1316 cells – 15.25 mm
• Elastics - 1336 cells – 15.26 mmwww.indiandentalacademy.com

Study to identify and quantify the temporal Sequence of,
replicating mesenchymal cells during natural growth and
mandibular advancement in the condyle and the
glenoidfossa . Rabie et.al., (Ajo 2003.)

• The number of mesenchymal cells in anyone is
genetically controlled. Heritable influences were
found to contribute up to 90%. Nongenetic
factors were still appreciable and account for
approximately 3.6%.
• A most interesting finding in the present study is
that resident mesenchymal cells in the condyle
contributed to bone formation in response to
forward mandibular positioning, whereas
resident mesenchymal cells in the glenoid fossa
contributed less to growth modification.

•Human mesenchymal cells can be harvested, purified, and
grown in vitro to increase their numbers and, when
reimplanted, they can still differentiate into bone-making cells
and lead to a significant increase in bone formation — a
principle that should be seriously considered for managing
patients with hemifacial microsomia and other craniofacial
anomalies requiring growth modification.
•The number of replicating mesenchymal cells, which is
genetically controlled, influences the growth potential of the
condyle and the glenoid fossa. Mandibular protrusion leads to
an increase in the number of replicating cells in the
temporomandibular joint. Individual variations in the
response to growth modification therapy could be a result of
the close correlation between mesenchymal cell numbers and
growth. www.indiandentalacademy.com

• BMP-2 is characterized by an ability to induce
ectopic cartilage and bone in soft tissues.
• A recent report showed that the lack of
expression of Sox 9 leads to campomelic
displasia in humans, a disease affecting all
cartilage-derived skeletal structures, resulting in
bowing and angulation of long bones, vertebral
abnormalities, small thoracic cages, craniofacial
defects with macrocephaly, micrognathism, and
cleft palate. Rabie, Urban Hagg (Am J Orthod
Dentofacial Orthop 2003;123:40-8)

Photomicrograph showing positive immunostaining of VEGF
expression (®) in the posterior (P) and middle (M) regions of
the mandibular condyle with forward mandibular positioning
on Day 14. During normal growth on Day 14.
Photomicrograph showing positive PAS
staining of new bone formation (B) in
the posterior region of the mandibular
condyle during forward mandibular
positioning on Day 30..www.indiandentalacademy.com

Mechanical stimuli
(static or dynamic)
Deform EM & bone cell
Reception Transduction Transmission
Ionic Mechanical
Multicellular
Bone cell response
CCN MMCCytoskeleton
(connectin)
(actin)
Nuclear membraneOsteocytic
genome
Ca++
Frankel

Effect of functional appliances on
the jaw muscle activity and type of
muscle fibers recruited

Muscle fibers
• Muscle fibers can be characterized by type according
to the amount of myoglobin; fibers with higher
concentration of myoglobin are deep red in color and
capable of slow but sustained contraction. They have
well developed aerobic metabolism and there fore
resistant to fatigue
• Fibers with low concentration of myoglobin are
whiter and are called fast muscle fibers; they have
fewer mitochondria and relay more on anaerobic
activity for function. Fast fibers are capable of quick
contraction but fatigue more rapidly
• Type I and Type IIa are slow twitch fibers.
• Type II b is fast twitch fibers

Functional appliance
Muscle
fatigue
Excessive muscle
function
Lateral pterygoid
Type IIb
Type I & IIa
Accumulation
Of
Lactic acid
Lateral pterygoid
Type I & IIa
Type IIb
Excessive muscle
function
Accumulation
Of
Lactic acid
S A D
Continuous
Muscle
activity

• Adaptations of masticatory muscles to a hyperpropulsive
appliance in the rat by Reggiani 1996
• The plasticity of masticatory muscles, i.e., their ability to
change their properties in relation to loading conditions,
represents a potentially important determinant of structure
and function of the mouth and the teeth. The effects of
changes of the masticatory loading conditions have been
described by Kiliaridis by comparing two groups of rats fed
with a hard diet and with a soft diet. In the two muscles
examined (deep masseter and anterior belly of digastric), the
soft diet was associated with a higher proportion of fast and
easily fatiguable IIB fibers.

• A series of studies was carried out by Petrovic and by
other workers to test the hypothesis that protrusion
muscles, and particularly lateral pterygoid, can
influence the growth of condylar cartilage. Interestingly
wearing a protrusive appliance induced fiber
transformation in pterygoideus lateralis and superficial
masseter. The proportions of slow fibers and of fatigue-
resistant type I & IIA fibers increased in pterygoideus
lateralis, whereas only an increase in IIA fibers
occurred in the superficial masseter muscle.

• Adaptation of the lateral pterygoid and superficial masseter
muscles to mandibular protrusion in the rat - Easton and
Carlson 1990
• The experimental rats wore bonded protrusive-type
appliances for 2 weeks. Histochemically, the lateral
pterygoid muscle in the experimental group exhibited a
significantly greater area occupied by type I fibers at the
expense of type llb fibers. The superficial masseter muscle
exhibited a significantly greater percentage of areas for both
type lla and type llb fibers in the experimental group.
Contraction time (TPT) increased in both muscles; that is,
the muscles became slower. The histochemical and
contractile-properties data indicate that the protrusive
appliance caused the lateral pterygoid muscle to become
more active with respect to tonic (postural) activity, whereas
the superficial masseter muscle became more active
phasically. www.indiandentalacademy.com

• 1990 Woodside et. al.
• Effect of functional appliances on jaw muscle activity - The
electromyographic (EMG) activity of masticatory muscles was
monitored longitudinally with chronically implanted EMG electrodes
to determine whether functional appliances produce a change in
postural EMG activity of the muscles. Preappliance and postappliance
EMG levels in four experimentals that had been fitted with functional
appliances were compared against the background of EMG levels in
controls without appliances. The insertion of two types of functional
appliance to induce mandibular protrusion was associated with a
decrease in postural EMG activity of the superior and inferior heads
of the lateral pterygoid, superficial masseter, and anterior digastric
muscles; the decrease in the first three muscles was statistically
significant. This decreased postural EMG activity persisted for
approximately 6 weeks, with a gradual return toward preappliance
levels during a subsequent 6-week period of observation. Progressive
mandibular advancement of 1.5 to 2 mm every 10 to 15 days did
not .prevent the decrease in postural EMG activity.

• The action of the types of functional appliances on the
activity of the masticatory muscles Camilo Yamin- ajo
1997
• Three commonly used functional appliances; namely, the
Herbst, Frankel, and a simulation of the Clark twin block
appliances were used to test the lateral pterygoid muscle
hypothesis. The electromyographic (EMG) activity of the
masseter, digastric, superior, and inferior heads of the lateral
pterygoid muscles was monitored with chronically inserted
EMG electrodes, in nonhuman primates. The insertion of
these three appliances was associated with a decrease in
functional EMG activity of the four muscles. This decrease
was statistically significant in all muscles 3 and 6 weeks
after appliance insertion. In view of the fact that the animals
showed large skeletal changes in the temporomandibular
facial area, this study could not support the lateral pterygoid
muscle hypothesis. www.indiandentalacademy.com

• An electromyographic study was performed on 10
young growing girls in the age group of 9 to 12
years with Class II Division 1 malocclusion and
retruded mandible, who were under treatment with
Twin-block appliances. Bilateral EMG activity of
elevator muscles of the mandible (ie, anterior
temporalis and masseter) was monitored
longitudinally with bipolar surface electrodes to
determine changes in postural, swallowing, and
maximal voluntary clenching activity during an
observation period of 6 months.

• The changes were noted at the start of treatment (0 month),
within 1 month of Twin-block insertion, at the end of 3
months, and at the end of 6 months. The results revealed a
significant increase in postural and maximal clenching
EMG activity in masseter and a numeric increase in anterior
temporalis activity during the 6 month period of treatment.
The increased electromyographic activity can be attributed
to an enhanced stretch (myotatic) reflex of the elevator
muscles, contributing to isometric contractions. The main
force for Twin-block treatment appears to be provided
through increased active tension in the stretched muscles
(motor unit stimulation) and from initiation of myotatic
reflex activity and not through passive tension (viscoelastic
properties) of jaw muscles. The results of this study reaffirm
the importance of full-time wear for functional appliances to
exert their maximum therapeutic effect by way of
neuromuscular adaptation. Ajo 1999 Preeti Aggarwal, .
Kharbanda,,

Skeletal and dental effects of
functional appliances

• Kevin O Brien et al conducted a multicentric,
randomized, controlled trial evaluated the
effectiveness of early orthodontic treatment
with the twin block appliance for class II
division 1 malocclusion

Over jet correction
6.93 mm 100%
Dental
5.05mm 73%
Skeletal
1.88mm 27%
MAX
3.03 mm
44%
MAND
1.00mm
14%
MAND
2.03mm
29%
MAX
0.88mm
13%

Molar correction
4.59 mm 100%
Dental
2.71mm 59%
Skeletal
1.88mm 41%
MAX
1.19 mm
26%
MAND
1.00mm
22%
MAND
1.52mm
33%
MAX
0.88mm
19%
Kevin O’ Brien et al ajo-2003

• Most of the studies on the functional
appliances claim that the small changes that
occur in the skeletal relation ship might not
be considered clinically significant or
functional appliances accelerates growth
ahead of time. Hence may be effective in
reducing the skeletal dysplasia earlier and
interception of exacerbation of
malocclusion and has psychological benefit.

Conclusion
• Functional appliances or rather Dentofacial orthopedics
has been a lurking mirage in orthodontic literature and
has had enough victims, disappointments and limited
long term success, but no wonder the quest is still on,
hoping that there are still ways to communicate with
various cell populations of the condylar cartilage with
mechanical stimuli which remain to be learned. The
answer to whether mandible can be grown in excess
beyond the whelms of genetics or it’s a barren field,
lies with time.

Modus operandi of functional appliances mallik /prosthodontic courses

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Modus operandi of functional appliances mallik /prosthodontic courses