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In the past 20 years there has been increasing
awareness of growth modifications produced by
functional appliances among orthodontists.
Major reasons for their popularity includes
Increasing recognition of FORM & FUNCTION
Realization that NEUROMUSCULAR
INVOLVEMENT is vital in treatment.
Recognizing the IMPORTANCE OF AIRWAY in
Growing understanding of HEAD POSTURE AND
GROWTH MODIFICATION as far as possible
is the IDEAL APPROACH. The "envelope of
discrepancy" graphically illustrates the current
concepts of how much change can be brought
about by orthodontic tooth movement that is
camouflage alone (Inner Circle). Orthodontic
tooth movement combined with growth
modification (Middle Circle) and surgical
correction (outer circle).
The "envelope of discrepancy” for maxillary
and mandibular arches. The middle circle for
the lower arch indicates that the mandible and
mandibular teeth can be brought forward
10mm by a combination of growth changes and
tooth movement but can be brought back
(restrained) by only 5mm. Growth modification
is more effective in treating MANDIBULAR
The idea of any functional appliance is to
influence the magnitude and direction of
dentofacial growth. Moffet classified
articulation in the craniofacial region as
The Articulation between the upper and lower
teeth as first order of articulation.
The Periodontal ligament between the teeth
and bone the second level of articulation.
The various craniofacial sutures and TMJ as the
third level of articulation.
The first two levels are routinely influenced by
With the functional appliance we are taking
our zone of influence to the third order of
Fox (1803) advocated application of extra oral force
to control the growth of maxilla.
KINGSLEY introduced "Jumping of the bite": in
1879 to correct sagittal relationship between Upper
and lower jaws.
HOTZ modified the kingsley's plate into a
vorbissplate (used it for deep bite and
From Kingsley's concept, VIGGO ANDRESEN
1908 developed a loose fitting appliance on his
daughter as a retainer during summer vacations
which gave remarkable results. He called it
Some yrs before this, PIERRE ROBIN created
monobloc to position the mandible forward to
prevent occluding the airway in patients of
Andresen moved to Oslo University, Norway
where he met KARL HAUPL (a periodontist
and histologist) who became convinced that
appliance induced growth changes in a
physiological manner. Then the name
ACTIVATOR or Norwegian system was coined
Tooth Borne - Passive (MYOTONIC) eg.
(Depends on Muscle Mass for their Action) Balter's
Tooth Borne - Active (MYODYNAMIC) eg. Elastic
(Depends of Muscle activity for their function)
Tissue Borne – Passive eg. Oral Screen, Lip Bumper
Tissue Borne – Active eg. Frankel
Actively growing individual with favorable
(horizontal) growth pattern.
Well aligned maxillary and mandibular teeth
Mandibular incisors should be upright over the
Class II Div 1
Class II Div 2 after aligning the incisors
Class I open bite
Class I deep bite
For cross bite correction (Trimming done in such a
way that maxillary molars are moved laterally and
mandibular molars lingually).
Preliminary before Fixed appliance to improve
skeletal jaw relationship.
For post- treatment retention
Class I crowding, due to tooth size jaw
Increased lower facial height.
Extreme vertical mandibular growth
Severely procumbent lower incisors
Non growing individuals
According to Andresen & Haupl (1955)
Activator is effective in exploiting the
interrelationship between FUNCTION and
changes in INTERNAL BONE STRUCTURE.
During GROWTH, there is also interrelationship
between FUNCTION and EXTERNAL BONE
The CONDYLAR ADAPTATION to the anterior
positioning of the mandible consists of growth in
an upward and backward direction to maintain the
integrity of TMJ. This adaptational process in
induced by the loose fitting appliance.
: Views of various authors are classified into 3
Myotatic reflex activity and isometric
Viscoelastic property of muscle and stretching
of soft tissues
This was the concept given initially by Andresen and Haupl in
It was based on ‘shaking of bone ‘hypothesis of Roux 1883.
Other authors substantiated this; namely Petrik-1957 McNamera-
According to this concept myotatic reflex activity and isometric
contractions induce musculoskeletal adaptation to new mandibular
closing pattern. The receptors in the periodontal ligament and the
lateral pterygoid muscle play an important role in the skeletal
adaptation. These receptors send signals to the masticator nucleus.
sensory signals via the afferent fibers reach the trigeminal nucleus
and send efferent signals to the muscle, which causes the
contraction of muscle fibers. Hence there is no change in the length
of the muscle (isometric). The is the myotatic reflex, which causes
adaptation in musculoskeletal pattern. For this kind of mechanism
to act the side should be within the free way space with minimal
The hypothesis that the activator works according to
the myotatic reflex activity had resistance from the
beginning. Grude in 1952 said that there was a
mismatch between bite suggested by Andersen and the
mechanism of action.
According to this theory whenever any muscle is
stretched beyond its limit isometric contraction does
not take place but the muscle stretches. Further no
myotatic reflex activity was seen in the perioral
musculature. The proponents of this theory suggested
that whenever the bite is opened beyond freeway space
it is the clasp knife reflex that comes into action.
the negative sensory are carried by the fibers to the
ganglion, which inhibits the muscular contraction
leading to stretching of the muscle.
the activator acts by viscoelastic property of muscle
and stretching of soft tissues. That is the basis of
activator action is potential energy. Depending on
the amount of stretch the following effects where
Emptying of vessels
Pressing out of interstitial fluid
Stretching of fibers
Elastic deformation of bone
Bioplastic adaptation of bone
Woodside (1973) and Harvold (1974) suggested 10-15 mm
of vertical opening
This is a mechanism of action between the two
extremes. Here the bite is opened beyond the
freeway space but not an extreme opening as
suggested by Woodside, Herren and Harvold.
Eschler (1952) Suggested that when bite is
opened beyond freeway space muscle
stretching occurs, but there are cycle of isotonic
and isometric contractions. Ahlgren’s
electromyographic research in 1970 also
supported this theory.
Functional Appliances creates following types of
forces by activating the muscles
1) Static: These are permanent forces and can
vary in magnitude and direction. They do not
appear simultaneously with movements of
mandible. Eg. Forces of gravity, posture and
elasticity of soft tissues and muscles.
2) Dynamic: These are interrupted forces and
appear simultaneously with movements of head
and body and have higher magnitude than static
forces. It depends on design and construction of
appliance and patient’s reaction. Eg. Forces
produced during swallowing.
3) Rhythmic forces:
These are associated with respiration and
circulation, and are synchronous with
breathing and their amplitude varies with
The mandible transmits rythmic vibrations to
the maxilla. They are important in
stimulating cellular activity. These are
intermittent and interrupted forces i.e.
Force application to teeth and mandible is
Removal of activator from mouth interrupts
According to original Andersen - Haupl Concept
The only forces acting in activator therapy are
natural ones, however recent modifications with
different designs and incorporation of additional
elements (springs, jackscrews, magnets) have
allowed use of active forces along with natural
The appliance can also interfere with natural forces.
Hence two principles are employed in
Force Application [Source is usually
Force Elimination [Dentition shielded from
normal and abnormal functional and tissue
pressures by pads, shields and wire
Employment of forces in Activator
The growth potential including eruption and
migration of teeth produces natural forces which
can be guided, promoted and inhibited by
Muscle forces and stretching of soft tissues initiate
forces which are functional (muscular) in origin but
their activation is artificial. These artificially
functioning forces are effective in 3 planes:
Sagittal Plane: Mandible is propelled down
and forward and muscle force is delivered to
condyles and strain is produced in Condylar
region. A slight reciprocal force can be transmitted
Vertical Plane: Teeth and alveolar processes are
either loaded with or relieved of normal forces. If
construction bite is high, a greater strain is
produced which if transmitted to maxilla can
inhibit growth increment and direction and can
also influence the inclination of maxillary base.
Transverse plane: Forces also can be created
with midline corrections.
Various active elements (springs,
screws etc.) can be incorporated to
produce an active biomechanic type
of force application.
In a study by NORO et al (AJO - 94 Feb) magnitude of
forces generated by passive tension of soft tissues
increased from 80 - 160 gms in class II patients and 130
- 200 gms in class III patients when the construction
bite heights changed from 2 to 8mm.
Direction of forces changed from vertical to posterior
and from vertical to anterior in class II and class III
Forces exerted by passive tension remained
significantly longer than that exerted by active
contractions irrespective of construction bite heights.
Study concluded that forces produced by PASSIVE
STRETCH REFLEX plays an important role inducing
Any skeletal effect from activator depends on
growth potential. Two divergent growth
vectors propel the jaw bases in an anterior
Sphenooccipital Synchondrosis moves the
cranial base and nasomaxilary complex
upward and forwards.
Jhonston (1976) attributes this response to
“UNLOADING THE CONDYLE”
If the mandible is positioned anteriorly,
growth direction is more important than
growth increments. Only the upward and
backward growth of condyle is capable of
moving the mandible anteriorly.
Phylogenetic and ontogenetic
peculiarities of Condylar cartilages
affect Condylar growth with
functional orthodontic appliances.
Condylar growth is regulated to a
high degree by local exogenous
According to Moss, Petrovic,Woodside the
condylar growth is an expression of a locally based
homeostasis for establishment and maintenance of
a functionally co-ordinated stomatognathic system.
Petrovic has shown LPM plays a decisive role in
growth because forward posturing of condyles
activate its superior head of the LMP which
induces cell-proliferation in condyle and a growth
response in young people.
Up to a limited degree activator can control
the upper growth vector supplied by
sphenooccipital synchondrosis which moves
the maxillary base forward.
Activators with special constructions can
influence growth and translation of
masomaxillary complex and can also alter the
vertical skeletal relationship.
Changing maxillary base inclination can
compensate for rotations of mandibular
If activator is constructed with a vertical
opening of bite with no or minimal saggital
change the effects are mainly on mid facial
development in subnasal area.
According to Woodside
Small vertical opening Restricts
only horizontal mid facial
Wide vertical opening
Downward displacement of
midface area and decrease in S.N.A.
Extreme vertical opening
Maxillary plane is tipped upwards
and point A moves forwards and
increase in S.N.A. angle.www.indiandentalacademy.com
Serves as a "Night Guard" preventing deleterious
nocturnal parafunctional activity and stimulating
normal muscle activity. (Mandibular protraction
enhances metabolic pump activity of the
retrodiscal pad thereby increases blood flow.
Catabolic byproducts were forced out on
Protracted, unloaded condyle enhances condylar
growth increments and favourable upward and
backward growth direction.
HOTZ, PETROVIC, OUDET, STUZMANN stated
that growth increments were greater at night due
to increased growth hormone secretion.
Electromyographic study of temporalis and
masseter with and without activators (AJO - Aug
It is observed that there was
1. Similar postural activity for both muscles with
or without activator.
2. During swallowing of saliva, muscle activity
was higher with the activator.
3. During maximal clenching similar activity in
anterior temporalis with or without activator.
Higher activity in masseter muscle with the
Increased interrupted electromyographic
(IEMG) activity with activators during
swallowing of saliva supports a
recommendation for DIURNAL WEAR OF
ACTIVATOR because the frequency of saliva
swallowing during sleep is very low.
The higher activity during saliva swallowing
with the activators is particularly important
because it is a functional activity repeated
between 600 and 2400 times each day.
When the patient is upright-
muscle tension, muscle tonus
and atmospheric pressure
equals the weight of the
mandible, associated tissues
and the activator. They act in
opposite directions so the
forces get balanced.
During sleep - activator,
gravity, muscle tension,
muscle tonus all act in the
same direction. However
during sleep, lips drop open,
mouth breathing ensues and
function is minimal.
HARVOLD & WOODSIDE wanted to exceed
the free - way space limits to keep the
appliance in place at night during sleep so as to
maintain the corrective stimulus.
The treatment with the activator or the
activator therapy will be discussed under the
Management of the appliance
Trimming of activator
History: Apart from the routine information one
has to stress more on
Growth status: Since the skeletal correction with the
activator is possible on during growing years.
The first permanent molar relationship in habitual
Nature of midline discrepancy - if present,
functional analysis done to determine the path of
closure from postural rest to occlusion. If midline
changes, functional problem is likely which can be
corrected by the functional appliance. If the
dentoalveolar midlines are not coinciding
functional appliance cannot correct
Symmetry of dental arches evaluated.
If curve of spee - leveling needed is severe -
activator cannot perform it.
Crowding and any dental discrepancies are noted.
Precise registration of postural rest position.
Path of closure determined.
Clicking or crepitus in the TMJ palpated.
Interocclusal clearence or free way space
Respiration (if disturbed nasal respiration
present - choice will be an open activator)
Size of tonsil and adenoids recorded.
Helps to identify the craniofacial
morphogenetic pattern to be treated.
Direction of growth determined (average,
horizontal or vertical)
Differentiation between position and size of
Axial inclination and position of maxillary and
Is the method of predicting what the end result of treatment would
Patient is asked to close the mouth in habitual occlusion and relax
the lips - PROFILE is carefully studied. It can be photographed.
Next the patient is asked to posture the mandible forward into a
correct sagittal relationship, reducing the overjet. A photograph
can be taken again.
According to one of the methods, if profile improves with
1/2 protrusion FRANKEL recommended
Full protrusion ACTIVATOR or BIONATOR
If the profile still does not Improve ACTIVATOR with HEAD
Considerable controversy exists over the
cephalometric growth forecasting technique.
Rickets short term prediction is widely used
because it is easily employed in software. But
it makes no attempt to predict post growth
positions of major land marks such as sella.
Hold away growth prediction has 12 stages of
VTO. It provides a dynamic assessment of
After the diagnosis of the kind of problem
depending on the type of correction desired the
type of appliance is planned. The main step
instrumental in bring about the desired
correction is the type of construction bite. The
various types of construction bites areas
Anterior Positioning of Mandible:
The usual intermaxillary relationship for
average class II problem is end to end incisal.
However, it should not exceed 7-8 mm 'OR'
three quarter of M-D dimension of Ist
permanent molar 'OR' half the individual's
1) If it is more than half the maximum
range, it become more uncomfortable
for patient and he may not keep
appliance in mouth and patient may
become less cooperative.
2) The distance between points of
buccal cusps of Ist molars is the amount
of distance necessary to change a class
II malocclusion into class I occlusion.
It is claimed that one of the best position for
obtaining desired histological transformation
of TMJ from class II Malocclusion to class I
occlusion is approximately half the distance
that the condyles can move forward along the
anterior wall of fossa to articulator tubercle.
If it is greater than half it might prevent any
favourable anatomical rebuilding of TMJ
If overjet is too large (18mm eg in
(Anterior positioning is done in stepwise
progression in 2 or 3 phases.)
Severe labial tipping of Maxillary
[First upright incisors by prefunctional
Difficulty of wearing the appliance and
adapting to new relationship.
Muscle spasms often occur and
appliance tends to fall out of mouth.
Difficult to achieve lip seal.
Vertical considerations are as important as to
saggittal determination and are intimately linked
to it. Maintaining a proper horizontal-vertical
relationship and determining the height of bite
are guided by following principles.
Mandible must be dislocated from postural
resting position in at least one direction
Saggittaly or vertically to active the associated
musculature and induce strain in the tissues.
2) If magnitude of forward positioning is
great ( 7-8mm ) the vertical opening should
be minimal so as not to overstretch the
It leads to increased force component in
According to Witt Saggittal force 315-
Vertical force 70-175g
Primary neuromuscular activation is in elevator
muscles of mandible.
3) If extensive vertical opening is needed,
mandible must not be anteriorly positioned i.e. if
bite opening exceeds 6mm, protraction must be
very slight. It is done in functionally true deep
bite cases and cases with vertical growth pattern.
Both muscles and viscoelastic properties of
soft tissue are involved.
If forward positioning is 7-8 m then vertical
opening should be 2-4mm.
If forward positioning is not more than 3-
5mm then vertical opening should be 4-6mm.
Activator can correct lower midline shifts if
actual lateral translation of mandible itself
If midline abnormality is due to tooth
migration no asymmetry exists between
treatment and medicine. An attempt to correct
this type of problem may lead to iatrogenic
Functional cross bite can be corrected by
taking proper construction bite.
According to Sander (1983)-
Frequency of Maximal
c) 0.8% [Harvold]
Mark the mildlines, molar relation & desired
mesial shift on the cast
Train the patient after seating him in an
upright & relaxed posture
Soften a sheet of bees wax and roll it in to 1cm
Shape it and press it on the lower cast and
mark the midline
Transfer the wax to the patient’s mouth and fit
it on the mandible
Move the mandible as previously practicedwww.indiandentalacademy.com
Remove the wax chill it and remove the excess
Place the bite on the cast and check if the
desired correction has been achieved
Replace the hard wax in patient’s mouth and
check after asking him to bite hard
During bite registration the vertical dimension
can be checked using the two reference points
On the tip of the nose
On the soft tissue chin
Vertical opening is within the limits of free way
space ( 2 to 4 mm).
Mandibular advancement being 3 to 5 mm.
Used for less severe class II MO with deep bite
and upright or lingually inclined lower incisor.
The appliance induces activation of
MYOTACTIC REFLEX & ISOMETRIC
CONTRACTIONS. These muscle forces are
transmitted by the appliance to move the teeth.
Thus the appliance uses KINETIC ENERGY.
REFLEX CONTROL OF SKELETAL MUSCLE
MECHANISM OF STRETCH OR MYOTACTIC
Stretch reflex when elicited causes contraction of
the stretched muscle. Muscle stretch receptors are
proprioceptive nerve endings called muscle
spindles situated within the muscle.
MUSCLE SPINDLES Contain
THIN INTRAFUSAL MUSCLE FIBERS NUCLEAR BAG REGION
MUSCLE FIBRE (non contractile)
(Striated & contractile) Impulses arise
Group I A sensory fibre
supply the extra fusal muscle fibre
CONTRACTION OF STRETCHED MUSCLE.
Therefore called "monosynaptic reflex arc"
Functional significance of stretch reflex serves as a mechanism for upright
posture or standing.
Similarly stretch reflex acts in the mandibular musculature to maintain
postural rest position in relation to maxillawww.indiandentalacademy.com
The mandible is placed approximately 3mm
distal to the most protrusive position sagitally
and vertically an extreme separation of 10 to
15mm beyond the free way space.
Here the mandible is opened beyond 4mm
so it does not work in the same manner as
Anderson's activator but by stretching of soft
tissue - THE VISCO ELASTIC EFFECT. In such
cases CLASP - KNIFE REFLEX plays a role.
MECHANISM OF CLASP KNIFE REFLEX OR
Example: Spastic limb Resistance encountered
Hyperactive reflex contraction
If carried out forcibly
Limb collapses readily
This phenomena is called CLASP KNIFE
RIGIDITY (i.e. muscle first resists and then relaxes
Stimulus is EXCESS STRETCH when elicited leads
to muscle relaxation. Receptors are Golgi tendon
organs situated in the muscle. Impulses conducted
by group I B sensory nerve fibre act on motor
neuron or '' efferent supplying the stretched
muscle . It is a DISYNAPTIC REFLEX ARC
because an INTER NEURON is interposed
between sensory and motor neuron.
Functional significance :- is to protect overload by
preventing damaging contractions against strong
Activator constructed with LOW VERTICAL
OPENING and a markedly forward
mandibular positioning is designated as
horizontal or 'H' activator.
Class II Div 1 with sufficient overjet
Class II Div 1 MO where there is mandibular
overclosure that results in a functional retrusion of the
mandible. In such cases activator can act in the sense
of "Jumping the bite"
Class II Div 1 MO with posteriorly positioned
mandible due to growth deficiency with horizontal
As a mandible moves mesially to engage the appliance,
elevator muscle of mastication get activated.
When teeth engage the appliance MYOTACTIC REFLEX is
In addition muscle force arising during biting and
swallowing causes stimulation of muscle spindles
which elicits reflex muscle activi
Mandible can be postured forward without
tipping the lower incisors labially.
LIP TRAP got eliminated
Maxillary incisors can be positioned upright or
Anterior growth vector of maxilla is slightly
Class II Div 1 MO with vertical growth pattern
when treated with H activator results in DUAL
Activator with large vertical opening and
minimal anterior positioning is designated as V
activator. Mandible is positioned anteriorily
only 3-5mm ahead of habitual occlusion.
Vertical opening 4 to 6mm beyond the postural
Indicated in vertical growth pattern.
Induces myotactic reflex activity. The
greater vertical opening thus allows the
myotactic reflex to remain operative even when
the musculature is more relaxed ( that is when
the patient is sleeping).
Stretching of muscles and soft tissue elicits
an additional force - the viscoelastic force. This
stretch reflex influences inclination of maxillary
May be dentoalveolar or skeletal .
In dentoalveolar problems, the deep
overbite may be due to infra-occlusion of buccal
segments or supra - occlusion of anterior segments.
Construction bite may be moderate or high
depending on the free way space. If it is due to
supra - occlusion of anterior segments,
interocclusal space is usually small and should
resort to high construction bite. Intrusion of
incisors is possible to only a limited extent when
an activator in being used.
Skeletal deep bite MO's have a horizontal
growth pattern, for which forward inclination
of maxillary base can compensate. Loading the
incisors can achieve a slight forward inclination
of the maxillary base as well as frees the molars
to erupt. Here the construction bite is high (5 to
6mm beyond the free way space ). A dento
alveolar compensation is possible by extrusion
of lower molars and distal driving of upper
molars with stabilizing wires.
Anterior positioning of mandible is necessary if
the skeletal relationship is orthognathic. Bite is
opened 4 to 5mm to develop a sufficient elastic
depressing force and load the molars that are in
MO with crowding can sometimes be treated
with the activator and can accomplish the
desired expansion because it is anchored
intermaxillarly. The appliance works in a
manner similar to that of two active plates
with jackscrews in upper and lower parts.
Construction bite should be low.
Goal is posterior positioning of mandible or maxillary
protraction. The construction bite taken by retruding the
lower jaw. Extent of vertical opening depends on the
In PSEUDO CLASS III, functional deviation is present
where the forced bite is easily achieved. The mandibular
incisors hit prematurely in an end to end contact and
mandible slides anteriorly to complete the occlusal
In these cases vertical opening is for enough to clear the
incisal guidance for construction bite. Here it is possible to
achieve edge to edge bite relationship with posterior teeth still
out of contact.
In SKELETAL CLASS III MO with normal path of closure
from postural rest to habitual occlusion, treatment not
possible with functional appliance.
In short lab procedures include
Mounting the casts to a fixator
Preparation of wire elements. Which include labial
bow made of 0.9 mm wire and Additional wire
elements, like the stabilizing wire and active
Fixation of jackscrews and wire elements.
Fabrication of acrylic portion.
Finishing and polishing. This is different from
trimming of the activator. Here only the rough
edges are smoothened to prevent injury to the
Fabrication of the acrylic parts consist of UPPER ,
LOWER AND INTER OCCLUSAL PARTS. Upper
and lower parts consist of DENTAL AND
GINGIVAL PORTIONS. Flanges of upper part
extends 8 to 12 mm high in gingival area and
covers the alveolar crest. Flanges of lower part
extends 5 to 12mm in gingival area. Flange
extention is greater in V activators as the patients
of this category have open mouth postures.
Can be prepared with cold acrylic directly on
models or wax pattern done and invested in a flask
to be prepared in heat cure.
On the first visit insert the appliance and give
Initially it is worn for 2-3 hours in a day for the 1st
Followed by night time wear and 1-3 hours of day time
wear for 2nd week.
The patient is recalled for check up on 3rd week
Followed by check up appointments every 6 weeks
Trimming according to the plan is started from second
visit once the patient gets used to the appliance.
Activation of wire elements are also done if necessary
The patient activates Jackscrew at 2 weeks interval if
In order to stimulate the functional activity
of the perioral musculature with the loose
appliances so that the movement and eruption
of selected teeth can be guided, certain areas of
the acrylic which contact the teeth should be
Intrusion:- Only limited intrusion is possible.
Relative intrusion is one of the objectives.
Incisor intrusion: brought about by
Loading the incisal edge.
Labial bow placed in the incisal third.
Molar intrusion brought about by
Acrylic plate touching only the cusps.
Acrylic plate ground away from fissures and
If larger occlusal surfaces are loaded, reflex
opening occurs frequently resulting in less
depressing action by the appliance
Extrusion: indicated in OPEN BITE problems.
Labial bow is placed in the gingival 1/3
Loading the gingival 1/3 on the lingual surface.
Enhancing eruption by grinding the acrylic
plate from the occlusal surface.
Acrylic contacting the gingival 1/3 on the
Loading the lingual surface with acrylic
Screening away lip strains with passive labial
bow or lip pards. Auxiliaries used are
Protrusion springs (0.8mm)
Guttapercha may be added to the lingual
Acrylic trimmed away from behind the incisors.
Active labial bow.
FOR DISTAL MOVEMENT OF THE POSTERIORS
Guide planes should be on the mesio lingual
Stabilizing wires or spurs can be used
Active open springs.
In class II div 1 MO with deep bite, acrylic
contacts the mesio gingival surfaces of upper
posterior and distogingival surface of lower
posteriors. The upper teeth are hence guided in
downward and backward directions and lower
teeth in an upward and forward directions to
establish the proper sagittal and vertical relations.
Acrylic on the lingual surface of the upper incisors
is ground away and labial bow made active if
they are to be retracted .
To achieve transverse movement lingual acrylic
surface opposite the posterior should be in
contact with the teeth. Higher level of force
can be obtained by adding a thin layer of self
cure soft acrylic. More effective expansion can
be achieved with use of jack screws.
During selective trimming only the upper or lower
molars are extruded. After erupting, eruption of
antagonist can be controlled. Thus both sagittal and
vertical relationship can be influenced.
Eruption pathway of the molars should be
considered. "CONTROLLED DIFFERENTIAL
ERUPTION GUIDANCE" must be employed for the
best interdental and occlusal plane relationship,
particularly in case of flush terminal plane
relationships, proper selective grinding can convert
an impending class II or class III MO into class I
1 EFFECTS ON THE MANDIBLE, (AJO 1989 March - functional
review - Bishara and Ziaji)
Birkebaek, Melsen, and Terp, in an implant study that featured
laminographs of the temporomandibular joint, concluded that the major
effects of activator treatment were an increased amount of condylar
growth and a remodeling of the articular fossa. The combination of these
effects resulted in the PERMANENT ANTERIOR DISPLACEMENT OF
THE MANDIBLE. Using the implants for cephalometric
superimpositions, they determined that the appliance did not inhibit the
growth of the maxilla, but that it did cause the maxilla and mandible to
rotate in a downward and backward direction. Condylar growth during
the 10-month period of activator treatment increased 1.1 mm and was
redirected 12o in a more posterior direction compared with untreated
control. They also found that treatment resulted in a slightly forward
displacement of the glenoid fossa as compared with the slightly backward
displacement in the controls. In addition, the anterior facial height
increased by 1.1mm and the mandibular plane angle was increased by
2.5o. The mandibular plane angle slightly decreased in the controls.
Other investigators also found 1.0 to 2.0 mm incremental increases in
the growth of the mandible after the use of activators.www.indiandentalacademy.com
EFFECTIVE CONDYLAR GROWTH CHANGES AND
CHIN POSITION CHANGES IN ACTIVATOR
TREATMENT (AO 2001: 71: 4 - 11) (SABINE RUF,
SANDRA BALTROMEJUS, HANS PANCHERZ)
According to this study, activator patients exhibited.
Increase in the amount of vertical effective condylar
Decrease in the amount of sagittal effective condylar
Increase in the amount of vertical development of the
Anterior rotation of the mandible.
It was concluded that effective condylar
growth can be increased and chin position can be
changed by activator treatment. Thus it induces
skeletal changes although not always in desired
(SAGITAL) therapeutic directions.
Effects on soft tissue. Forsberg and Odenrick
observed that upper lip retrusion was
significantly more prevalent in the treated class
II group than the control group. The nose
showed equal forward growth in both groups,
but the soft-tissue pogonion was significantly
further anteriorly in the treated group.
Furthermore in the treated group lip balance
was not achieved in patients with relatively
retrognathic profiles or those with steep
Effect of early activator treatment in patients with class II
Evaluated by thin plate spline analysis - (AO 2001: 71;
120-126) Christopher J. Lux ; Jan Rubel, Komposch .
Thin plate spline analysis turned out to be a
useful morphometric supplement to conventional
cephalometrics because the complex patterns of shape could
be suggestively visualized by means of grid deformations.
In the age group of 9.5 – 11.5 male class II patients treated
with activator the grid deformations of total spline analysis
pointed a STRONG ACTIVATOR INDUCED REDUCTION
OF THE OVER JET caused mainly by tipping of the incisors
and to a minor degree by a moderation of sagittal
discrepancy, particularly by slight advancement of the
There are several possible structural mechanisms
through which activator obtains the class II correction.
Optimizing mandibular growth (as a secondary
response to its anterior dislocation from the articular
Redirection of mesial and vertical growth of maxilla
Lingual tipping of maxillary incisors
Labial tipping of mandibular incisors
Mesial and vertical eruption of mandibular molars
Inhibition of mesial movement of the maxillary molars.
Remodeling changes in TMJ
A combination of orthodontic (60% to 70%) and
orthopedic (30% to 40%) movements prov
1. DUAL BITE (JCO 1983 May – Robert Shaye)
is commonly seen in cases treated with
activator. Initially, positional adaptation indeed
takes place during class II treatment. This
Robert Shaye calls it as PHANTOM
ACTIVATOR PHENOMENA. However the
tendency to function in a forward mandibular
position does not guarantee that
STRUCTURAL ADAPTATION will follow
Severe centric relation – habitual occlusion
discrepancies may be observed in the form of dual
bite succinctly termed as "SUNDAY BITE".
It seen mostly in
POST PUBERTAL FEMALES treated with
VERTICALLY GROWING PATIENTS treated
with 'H' activator.
If dual bite is present at the termination of
treatment – it cannot be considered successful.
DUAL BITE CASES ARE FAILURES
Activator produces LABIAL TIPPING OF LOWER
In correcting class II MO, appliance contacts the
lingual of the lower incisors, then as the muscles
pull the mandible back toward CR position, incisor
flaring easily occurs.
This can be overcome by ACTIVATOR / HEAD
GEAR combination (AJO 1996 July)
Activator cannot produce detailed PRECISE
FINISHING OF OCCLUSION. It should be
followed by short phase of fixed appliance therapy
(or) require refinement of occlusion through tooth
Various operators based on their treatment
philosophy have suggested various
modifications in the appliance design. These
modifications of the activator are as follows:
Broadly categorized into 2 types
Appliances with ONE RIGID ACRYLIC MASS
for maxillary and mandible arches but with
reduced volume or bulk.
Reduced volume in anterior palatal region to restore
contact between tongue and palate eg. ELASTIC
Disadvantages : construction bite cannot be
opened too much vertically
Reduction in alveolar region and with a cross-palatal
wire instead of full acrylic plate. Eg. BIONATOR
Appliance consisting of 2 parts joined by wire
bows. Muscle impulse are reinforced by wire
elements in the design. Eg. SCHWARZ
Herren's activator (1953)
Herren's shage activator – LSU activator
The bow activator of Schwarz
Reduced activator of Cybernator of Schmuth
The Karwetsky appliance
The cutout (or) palate free activator
Elastic open activator of Klammt
Hamilton expansion activator system. (or) Bonded
Combined activator /HG Orthopaedics.
MAD – Magnetic Activator Device.
T.M.Graber, Thomas Rakosi, A.G.Petrovic;
Dentofacial orthopedics with functional
appliances: 2nd Edition, Mosby Co. 1997; Page
T.M.Graber,Bedrich Neumann; removable
orthodontic appliances : 2nd edition
W.B.Saunders Co. ; Page no 198- 310
T.M.Graber, Brainerd F. Swain ; orthodontics
current principles and techniques : 1st edition
;Jaypee Brothers 1991 Page no 369- 405
Activator and electromyographic activity -
Miralles, Berger, Bull, Manns, and Carvajal
AJO-DO, Volume 1988 Aug (97 - 103):
REVIEW ARTICLE - Bishara and Ziaja AJO-
DO, Volume 1989 Mar (250 - 258)
Orthodontic and orthopedic effects of
Activator, Activator-HG combination, and Bass
appliances: A comparative study AJO-DO,
Volume 1996 Jul (36 - 45):