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Class II, Division 1 malocclusion has been called "the most
frequent treatment problem in the orthodontic practice."
The solution to the problem can involve the use of
functional and/or fixed orthodontic appliances. Functional
appliances alter a Class II relationship through
transmission of muscular force to the dentition and
alveolus by positioning the mandible anterior to its usual
position. Doing so a stimuli for further growth is induced
at the condyles leading to progressive class II correction by
condylar growth. This seminar is an attempt to summarize
the events that lead to class II correction and the
controversies surrounding it.
INTRO..
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CONCEPT OF FUNCTIONAL STIMULATION
Bone may one of the hardest tissues in human body but it
is the most responsive to environmental stimuli. Theories
of bone plasticity were traced to WOLF and ROUX who
believed that form and function were intimately related.
Changes in functional stress produced changes in internal
bone architecture and external shape. Influences of natural
forces and functional stimulation on form were first
reported by Roux in 1883 as a result of studies he
performed on tail fins of dolphins.He described the
characteristics of functional stimuli as they build, mould,
remold and preserve tissues.Recent research has supported
Roux 's concept of functional "shaking of bone"and the
anabolic stimulus applied to achieve the optimum
mophogenetic pattern.

Kingsley devised an inclined bite plane in 1879 to ''jump the bite''
forward in cases of "excessively retreating lower jaw." Angle devised
his ''plane and spur retention appliance'' for the very same purpose. In
1902 Pierre Robin published an article describing the monobloc which
was used primarily for bimaxillary expansion as well as jumping the
bite forward. Six years later Andresen developed an appliance very
similar to Robin's monobloc, although Andresen's work was totally
independent of Robin's. Andresen's appliance appears to have been
adapted from Kingsley's, and it was designed also to prevent mouth
breathing. Andresen's appliance was the first one to be freely movable
within the oral cavity. It was intended to use muscle forces to correct
malocclusions.
BIRTH OF FUNCTIONAL APPLIANCES

Originally, he termed his appliance the biomechanical appliance, but
later, with the collaboration of Häupl, the term activator was
introduced because of the proposed activation of the muscles.
Andresen was certainly a major force in the development of FJO, as
he wrote the first textbook during the 1920's. Rogers introduced a
detailed set of myofunctional exercises in 1918. These exercises
were used to correct the cause and, therefore, effect a correction of
the problem.
In 1936 Andresen and Häupl introduced the term functional jaw
orthopedics, which is still used today. Andresen, Häupl, and
Petrovik published an excellent report on FJO in 1957, but it still
remains unpublished in English.

In 1949 Bimler introduced his appliance, which at first was criticized,
but almost all of the more recent appliances appear to incorporate one or
more of his innovations. Bimler's appliance was much less bulky and
incorporated wires and elastics to elicit more muscle response than
previous appliances. Stockfisch a disciple of Bimler, designed the
kinetor, or elastic bite former, which also uses the principle of attempting
to improve the muscle response of the patient. Balters took the activator
and removed the bulk of acrylic from the palate so that the patient could
tolerate the appliance better. He terms his appliance the bionator.
Klammt introduced the elastic open activator, which is another attempt
to reduce the bulk of the appliance and, therefore, encourage better
patient cooperation. Certainly, the trend of FJO has been to make the
appliance more tolerable to the patient, thereby increasing patient
acceptance and wearing time. The goal has been toward appliances
which can be worn essentially full time.

Perhaps the most complete of all the FJO appliances is the
functional regulator of Rolf Fränkel. Fränkel drew from the
concept of mandibular forward posturing plus the oral screen of
Kraus. By reducing the size of the oral screen, Fränkel designed
the appliance to be worn full time. Fränkel's approach differs from
all others because he intends the oral vestibule to be his basis for
treatment, whereas all other appliances operate inside the dental
arches. The vestibular shields add another dimension to FJO.
Treatment in the transverse plane, as well as the traditional
sagittal plane, is a realistic goal. Other than palate-expansion
appliances, lateral expansion using fixed appliances has been
shown by several investigators to be futile, particularly in the
mandibular canine region.

Investigators report various types of orthopedic and dentoalveolar
changes while using FJO appliances. The various changes include
maxillary orthopedic retraction, maxillary dental retraction,
mandibular forward orthopedic growth, mandibular dental
proclination, and occlusal plane changes with differential eruption.
One of the reasons American orthodontists have been reluctant to
accept the FJO concept has been that these various morphologic
changes appear to be in conflict. An attempt will be offered to explain
the reasons some of these changes occur.

CLASS II DIV. I MALOCCLUSIONS
(HYPODIVERGENT CASES)
CLINICAL FEATURES:
convex profile- improves in V.T.O.
posterior facial divergence
low FMA angle
everted lower lip, deep mento labial sulcus
proclined upper anteriors
molar and canines in class II relation
increased overjet and over bite

FUNCTIONAL CRITERIA:
1.Assessment of relation between rest position and
occlusion.
2.Examination of relation between overjet and function of
lips
3.Posture and function of tongue.
4.mode of breathing.
CEPHALOMETRIC CRITERIA
1.relation of max. to cranial base
2.position and size of mandible
3.axial inclination and position of incisors
4.growth pattern to be considered.

CONDYLAR POSITION AND PATH OF CLOSURE
NORMAL POSITION: Ideally the condyle is situated in the
anterio-superior part of the fossa when the mandible is in the most
retruded position. In the case of horizontal growth pattern the
condyle is situated along the anterior curvature of the fossa.
PATH OF CLOSURE:
Treatment prognosis for FJO depends onanalysis of
relationship and determination of the path of closure of the
mandible.
1.TRUE CLASS II- no deviation in path of closure
2.CL II M.O. With functional disturbance-up & back movt.
3. CL II M.O. With functional disturbance-up & forward
movt

The tremendous interest in the mandibular condyle is due to the
similarity between the condylar cartilage and the epiphyseal
cartilage of long bones. There is some evidence that the
proliferative zone of the condylar cartilage is under external or
environmental control. There is also evidence that seems to
suggest that the condyle operates independently of external
factors. When the condyle acts independently, it is said to be a
primary growth site. When it grows in response to its
environment, it is said to be a secondary growth site. Those
investigators who report a stimulation of condyle growth in
response to mandibular hyperpropulsion include Häupl, Hausser,
Korkhaus, Herren, Balters,Fränkel, Gresham, Moss, Demisch,
May, Enlow, Ahlgren, McNamara, and others. Those
investigators who could not find any evidence of condylar growth
increases include Björk, Jacobsson, Harvold and Vargervik,
Hasund, Woodside, Wieslander, Softley, Meach, Trayfoot, and
others.
INDUCING CONDYLAR GROWTH

Histologic studies on laboratory animals have consistently
shown a significant increase in cellular activity when the
mandible is hyperpropulsed. Stöckli and Willert, Petrovic and
associates, McNamara, Elgoyhen and co-authors, and many
others have adequately documented a multifold increase in
cellular activity in experimental animals. There appears to be
no question that, at least histologically, the mandibular
condyle in laboratory animals can be stimulated by extrinsic
factors. The question arises as to whether this growth can be
expected clinically in our patients

It is important to develop a concept of normal growth of the
mandible. By understanding the evolution of different concepts
concerning mandibular growth, and placing them in light of
current research, it is possible to more clearly define both the
reasons for temporomandibular joint disturbance as well as to
dictate an effective therapy to restore a normal growth posture.
For many years, orthodontists have lived with the concept of
upward/backward growth of the condyle as the norm in
mandibular development. We used the supposedly stable
mandibular plane and points on the symphysis as
superimpositional references to delineate an upward and slightly
backward eruption of the teeth
MANDIBULAR GROWTH CONCEPTS

Early research by Hunter, using the pig mandible and a wire
circumferential to the ramus, indicated that there was
resorption on the anterior portion of the ramus and apposition
on the posterior aspect of the ramus. Later Brash, repeating
Hunter's investigations and, using the same type of
experimental animal, came to a similar conclusion about
growth of the mandible. Brodie referred to cartilaginous
proliferation on the superior-posterior aspect of the condyles
giving the mandible the same downward and forward growth
exhibited by the maxilla. This all seemed to make good sense.
The mandible was pushed downward and forward as the back
side of the condyle filled the fossa.

Sicher and DeBrul, in their text The Adaptive Chin, demonstrated that,
from an anthropological standpoint, protuberance menti
(suprapogonion) is a stable landmark upon which superimpositional
registration could be made. This later was verified with bone implant
studies.
Only later did thinking in terms of resorptive changes at B point with
the movement of the dentition begin. Initial references for mandibular
growth and eruption of the dentition were based upon early research,
limited by our ability to study the growth problem .
Concepts of mandibular growth began to change when Bjork, with
bone implants, demonstrated that the mandibular plane was, in fact,
resorbing during normal growth. His work also indicated that in many
cases the condyles were not growing upward and backward as initially
thought, but were proceeding to grow in either a straight upward or an
upward/forward direction.

Although at that point overall concepts of growth of the mandible
were not clear, it was realized that the mandibular plane was no longer
a stable reference mark by which normal eruption of the dentition
could accurately be defined.
Later, Moffett at the University of Washington, using tetracycline
staining techniques on human mandibles, showed that there is a
preponderance of appositional cartilaginous growth on the
upward/forward portion of the condyle. A large body of knowledge
began to accumulate that was beginning to undermine the long-term
understanding that we had maintained about growth of the mandible.,
Moss began to refer to mandibular growth as a logarithmic spiral and
Ricketts proposed that growth of the mandible could be closely
predicted by projecting average growth increments to anatomical
structures as defined by an arc. Research continues to define more
specifically not only the way that the mandible itself is growing, but
also the way in which this bone fits into the overall growth of the facial
complex www.indiandentalacademy.com

SERVO SYSTEM THEORY OF FACIAL GROWTH
Charlier, Petrovic, Strutzmann detected in organ culture following
dissimilarities regarding condylar cartilage growth:
if growth occurs from condroblasts(epiphyseal cartilage) it appears to
be subject to general extrinsic factors and the effect of local epigenetic
factors is restricted to modulation of direction of growth with no effect
on amount of growth.
If growth results from precondroblastic proliferation (condyle) it is
subject to local extrinsic factor influences- here growth may be
modulated by appropriate orthopedic devices.
They state that the variation in the direction of condylart growth 9is
partly a quantative response to changes effected in the lengtheniung
of the maxillae. www.indiandentalacademy.com

The operation of confrontation between the upper and lower dental
arches elicits a deviation signal that modifies the activity of thr
lateral pterygoid muscle.(LPM),allowing the mandible to adjust to
the optimal occlusal position. This change in the LPM activity
favorably influences the growth rate at the condyle.the elicited
signal not only causes an improvement in the masticatory function
but also brings about synchronized growth between the maxilla and
the mandible during the entire developmental period of the facial
skeleton.

The posterior edge of the ramus is a main site of growth, which
appears to occur as the body of the mandible is shifted downward
and forward by the growth of the oral capsule. Growth at the
condyle appears to take place as a secondary phenomenon, to fill
the space left by the mandible as it is displaced downward and
forward by the surrounding tissues; it is compensatory in nature
rather than a primary process.
This displacement of the mandible can be simulated in orthopedic
therapy by having the patient hold the mandible in an artificially
induced downward and forward position. Stöckli and Willert
investigated the reaction of the temporomandibular joint in
growing Macaca irus monkeys, following the placement of splints
which forced the animals to protrude their jaws forward in order
to occlude the posterior teeth.
ENHANCING MANDIBULAR GROWTH

They found that mechanical stimuli during growth induced stable
adaptive changes and concluded: "During the growth period the
temporomandibular joint has a high potential for compensatory
tissue adaptation by basically physiologic processes. Further
investigations by McNamara with similar protrusion-inducing
splints on growing Macaca mulatta monkeys, with particular
emphasis on the electromyographic changes in the orofacial
musculature, have indicated that muscle activity, histologic
change at the condyle, and increased mandibular growth appear
to be very closely connected. In a growing person it would seem
that an increase in function of the superior head of the lateral
pterygoid muscle is followed by an adaptive response at the
condyle.
A similar conclusion has been reached by other workers in this
field investigating the response in rats to mandibular
hyperpropulsion. www.indiandentalacademy.com

The phenomenon of the neuromuscular feedback mechanism
controlling mandibular growth can be applied in the clinical
sphere, and an appliance system has been developed to use this
effect to advantage in the treatment of the skeletal Class II
malocclusion in growing patients. Treatment involves three
main considerations: (1) The mandible is held forward by the
patient in response to the appliance by continuous contraction
of the lateral pterygoid muscle. (2) The activation must be
increased at 6- to 8-week intervals to prevent adaptation of the
musculature and hence cessation of condylar growth. (3) The
patient must be growing sufficiently fast, with effective levels
of somatotrophic hormone and intermediary growth hormones
circulating, in order for the influence on the condylar growth
cartilage to be significant.

After many investigations, it is now recognized that functional
appliances such as the Fränkel and the activator are effective
devices for the correction of certain types of Class II
malocclusions. There is, however, no general agreement on
how correction of the Class II occlusal relationship takes
place. The following concepts have been advanced:
(1) Hotz6 believes that the retractive mandibular muscle pull
is transmitted from the mandible through the appliance to
orthopedically hold the upper jaw in position which, as growth
occurs, effectively reduces the SNA angle while leaving SNB
relatively unchanged.
(2) Björk and Softley state that dentoalveolar changes account
for the occlusal correction.
CONCEPTS PROPOSED-FOR AND AGAINST
FUNCTIONAL THERAPY:

(3) Fränkel, and Haupl and associates, and others believe that the
correction is due mainly to occlusal plane changes with differential
eruption.
Most of the functional appliance studies reported in the literature
have these common findings regarding the Class II correction: (a)
reduced forward growth of the maxilla, (b) retraction of the
maxillary anterior teeth, (c) increase in height of the mandibular
alveolar process, (d) no change or protraction of the mandibular
teeth (depending on the design of the appliance), and (e) increase in
lower face height. The one observation that is not consistently
found is an increase in the amount of forward growth of the
mandible. This is due partly to the lack of controlled human studies
with their inherent difficulties in experimental designs, treatment
procedures, and measuring methods. As a result, there have been
many conflicting and contradictory findings.

In 1971 Harvold and Vargervik found no effect on mandibular
growth along with an increase in lower face height. Other
investigators have supported these findings. However, a number of
clinical cephalometric studies have shown significant increases in
growth of mandibular length with corresponding forward
movements of pogonion and point B in activator treatment.
Baumrind and his co-authors compared samples of subjects treated
with cervical face-bow, high-pull face-bow, and activator-type
intraoral appliances as well as a control group of untreated Class II
subjects. As compared to the control group, a statistically significant
rate of increase in condyle-pogonion distance was found in the
intraoral group. "To our considerable surprise, the cervical group
exhibited a similar statistically significant rate of increase in
condyle-pogonion distance which is yet unexplained."

Despite the fact that McNamara, Petrovic, and others have
shown that hyperpropulsion of the mandible in laboratory
animals has induced increased cellular activity of the condyle,
there are still some researchers who suggest that these represent
only temporary remodeling changes rather than stimulation of
condylar growth. With no general agreement among clinicians
and researchers alike, the question of whether or not we can
stimulate human mandibular growth remains unanswered.
Clinically, mandibular growth appears to be changed in
response to the appliance, with rapid improvement in the spatial
relationship of the mandibular dental base in both horizontal and
vertical dimensions frequently evident. The mandible appears to
undergo the type of growth often seen during a rapid growth
spurt, but as the maxilla is not undergoing the same downward
and forward growth that it would normally experience in a true
growth spurt, an improvement in the pre-existing skeletal
imbalance becomes apparent.www.indiandentalacademy.com

ACTIVATOR
Woodside investigated the problem of change in mandibular length
19 children undergoing Andresen (monobloc) therapy in which the
appliance was constructed with a greatly increased vertical dimensi
The findings were compared with a group of 30 untreated control
children. It was concluded that a relative increase occurred in the
treatment group, but this was not quantified or stated to be of
statistical significance.
In contrast, Björk was unable to show that treatment by the Andres
appliance increased mandibular growth. In a cephalometric
investigation of the changes following treatment in one Class II,
Division 1 malocclusion and one Class II deep bite (Deckbiss
condition), Björk concluded that although treatment favorably
influenced dentoalveolar development, it did not affect mandibular
growth.

The clinical response was attributed to changes within
the dentoalveolar tissues combined with the patient's
normal (that is, unaffected) maxillary and mandibular
development.
Similar conclusions relating to the use of the Andresen
appliance were also reported by Evald and Harvold in a
comparison of the cephalometric changes in ten Class II,
Division 1 malocclusions and 112 unclassified, untreated
control subjects. Treatment was found to have no effect
on mandibular growth, and it was also shown that in
successfully treated patients, at least an average
increment of mandibular growth was essential during
the treatment period

Although the treatment of Class II, Division 1 malocclusions by the
function regulator (FR) appliance is not strictly comparable with
other methods of FJO, all such appliances incorporate a
"construction" bite in their design, and the various treatment
philosophies share the view that additional mandibular development
(that is, growth that exceeds the anticipated incremental change for
the individual) is experienced in growing children, thus improving
the underlying skeletal features of a malocclusion.
Many of the clinical investigations of functional appliance therapy
already reported are not detailed studies of mandibular dimensional
changes.
FR

Comparisons are also difficult because of the differences in
the composition of the treatment and control groups, and the
variations in the duration of treatment or period of
observation. Fränkel Has frequently inferred that the
function regulator increases mandibular growth in Class II,
Division 1 malocclusions, but this has never been quantified
in a controlled study. He also states that the therapeutic
decision can be made that one might attempt to stimulate
mandibular development from an analysis of the
cephalometric changes observed using the occipital reference
base.

According to Fränkel, a very close form-function interrelationship of
the jaw exists and his function regulator acts by changing the
biomechanical environment of the developing dentition. Fränkel also
believes that abnormal jaw relationships and associated
oromandibular dysfunction are corrected in a more physiologic
manner with functional appliances as compared with purely
mechanical forms of intermaxillary traction. Moreover, he believes
that FR treatment does not move the mandibular molars and
premolars mesially relative to skeletal landmarks in the mandible,
and that bite shifting is also a practical possibility. Creekmore and
Radney compared the cephalometric changes of 50 edgewise cases
(25 Class I and 25 Class II malocclusions) with 62 control cases (50
Class I and 12 Class II malocclusions) and 20 FR treatments (11
Class II, Division 1, and nine unspecified Class I malocclusions).

The method of cephalometric analysis was not specifically designed
to determine mandibular dimensional changes, but nonetheless it
was concluded that all patients receiving FR treatment showed a
significant increase (1.1 mm) in mandibular length when compared
with the untreated sample. These authors also stated that the
increase was caused by additional posterior condylar growth and
that treatment produced elongation of the face rather than a more
prognathic mandible.

The limited nature of the mandibular response to the
prolonged mesial displacement of the mandible that is
inherent in the design of all functional appliances has been
described by McNamara and Carlson in 1979. In this
investigation, the cellular reaction of the condylar cartilage in
monkeys (having a dental age corresponding to a child of
approximately 6 years), following permanent forward
displacement of the mandible by cemented functional splints,
was studied. The initial increase in cellular activity reached
maximal intensity after approximately 4 to 6 weeks, but after
a period of 24 weeks, there were no marked histologic
differences between experimental and control animals.

In contrast, Elgoyen and associates, Petrovic, Stutzmann, and
Gasson, and Petrovic, Stutzmann, and Lavergne concluded that
significant increases in the absolute length of the mandible
occurred following functional appliance wear in laboratory rats.
These findings are also supported by the craniofacial studies of
Moss, and the microbiologic studies of Petrovic and associates
who contend that genetic factors do not exert complete control
over the absolute length (growth) of the mandible.
Hence, it can be seen that the findings of previous investigations
into the effects of FJO are controversial and also that there is
insufficient evidence available that specifically relates to the
mandibular dimensional changes associated with FR treatment.

The treatment of Class II, Division 1 malocclusions by functional
appliances is often considered in anticipation of an early and
continuing improvement in the patient's facial appearance that is
associated with the relatively low demand on operator time. Both
factors tend to encourage an optimistic prognosis, especially since
many clinicians believe that functional appliances have the ability to
promote or enhance skeletal growth in a selective manner and thus
change the unsatisfactory skeletal basis of the more severe
malocclusions. However, whatever method of treatment is adopted,
experience shows that children vary considerably, both in their
ability to cooperate by wearing orthodontic appliances and in their
individual growth characteristics. Moreover, there is also
considerable controversy and confusion with respect to both the
theoretical basis and the nature of the clinical response resulting
from functional appliance treatment or functional jaw orthopedics
(FJO).
SUMMARY

One problem that requires further clinical investigation is the extent
of the change in mandibular dimensions that is said to result from
the use of functional methods. Consequently, it is still not known
whether the microanatomic response demonstrated to occur in the
articular tissues of the temporomandibular joint of experimental
animals (which is also postulated to occur in children undergoing
FJO) contributes significantly to the clinical result. Thus, although it
is reasonable to infer that the tissues of laboratory animals and
actual orthodontic patients will react in a similar manner to the
same physiologic stimuli, the practical validity of relating the
findings observed in strictly controlled experimental conditions to
the more varied environments of home, school, and leisure activity
of most children is doubtful.

Hence, it must be recognized that most children undergoing FJO
do not wear their appliances continuously throughout each 24-
hour cycle as they may be consciously removed during school, at
mealtimes, and frequently during sleep. Moreover, the appliances
described in many experimental studies are usually of a "fixed"
functional design and more directly comparable with the Herbst
appliance ; therefore, they differ considerably from the removable
"loose'' functional appliances that constitute the majority of those
used in clinical practice

Facial beauty is arguably the most powerful generator of
human emotion. In addition to serving the obvious
function of attracting the sexes to each other, it has also
served to inspire great works of art, prompt sadistic acts,
initiate ferocious wars, and reputedly launch 1000 ships.
It might be expected that beautiful faces would display
some common features, but in reality, acknowledged
beauties are often as different from each other as they are
from the rest of us. It would seem that we differ in our
individual preferences, and it is widely accepted that
"Beauty is in the eye of the beholder.”
CONCLUSION !!

Those investigators who report a stimulation of
condyle growth in response to mandibular
hyperpropulsion include Häupl, Hausser, Korkhaus,
Herren, Balters, Fränkel, Gresham,35 Moss,36,37
Demisch, May, Enlow, Ahlgren, McNamara, and
others.
Those investigators who could not find any
evidence of condylar growth increases include Björk,
Jacobsson, Harvold and Vargervik, Hasund,
Woodside, Wieslander, Softley, Meach, Trayfoot,
and others.

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