Activator

A Seminar on
ACTIVATOR
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The term "functional appliance" refers to a
variety of removable appliances designed
to alter the arrangement of various muscle
groups that influence the function and
position of the mandible in order to
transmit forces to the dentition and the
basal bone. Typically these muscular forces
are generated by altering the mandibular
position sagittally and vertically, resulting
in orthodontic and orthopedic changes.
INTRODUCTION:

Functional appliances have been used since
the 1930s. Despite this relatively long
history, there continues to be much
controversy relating to their use, method of
action, and effectiveness. Although there are
a number of functional appliances used by
clinicians, the activator is used to correct
Class II malocclusions.

In 1880, Kingsley introduced the term
and concept of "jumping the bite" for
patients with mandibular retrusion.
He inserted a vulcanite palatal plate
consisting of an anterior incline that
guided the mandible to a forward position
when the patient closed on it.
This maneuver corrected the sagittal
relationship without tipping the lower
incisors forward.
HISTORY OF ACTIVATOR:

Vorbissplatte was a modified
Kingsley plate. Hotz used the appliance in
cases of deep bite retrognathism when
overbite was likely to cause a functional
retrusion deep bite retrognathism, and
the lower incisors were lingually inclined
by hyperactivity of the mentalis muscle
and lower lip.
History:

Robin in 1902had created an appliance quite
similar in its objectives. The monobloc, as he
called it (because it was a single block of
vulcanite), positioned the mandible forward
in patients with glossoptosis and severe
mandibular retrognathism who risked
occluding their airways with their tongues.
Robin noted that forward mandibular
posture reduced this hazard and also led to
significant improvement in the jaw
relationship. The problem, usually
associated with cleft palate, became known
as the Pierre Robin syndrome.
HISTORY:

Impressed by Kingsley's concepts and appliances,
Viggow Andresen in 1908 developed a mobile,
loose fitting appliance modification that
transferred functioning muscle stimuli to the jaws,
teeth, and supporting tissues.
The progenitor of the appliance was a modified
Kingsley plate that Andresen used as a retainer
over summer vacation for his daughter after he
removed fixed appliances used to correct a
distocclusion.
Seeing the continued improvement with this
retainer, he called it a biomechanic working
retainer.
HISTORY:

Familiar with the work of Roux, who subscribed
to the shaking-the-bonding-substance-of-bone
hypothesis, the time Andresen and Haupl in 1955
teamed up to write about their appliance, they
called it an Activator, because of its ability to
activate the muscle forces
HISTORY:

- Biomechanic working retainer
- Andersen appliance
- Nocturnal airway patency appliance.
- Norwegian appliance.
- Monobloc
- kingsley or bite jumping appliance
SYNONYMS:

NOMENCLATURE:
The first removable functional
appliance, developed by
V.Andresen.
Historically, the term "activator"
was introduced to describe the
"activation of mandibular
growth," to which the achieved
correction of a Class II
malocclusion was attributed
The acrylic body of the Andresen
activator covers part of the palate
and the lingual aspect of the
mandibular alveolar ridge.

A labial bow fits anterior to the
maxillary incisors and carries U-
loops for adjustment.
On the palatal aspects of the
maxillary incisors, the acrylic is
relieved to allow their retraction

I. ANDRESEN & HAUPL CONCEPT
According to Andresen & Haupl, the bite is not opened
beyond the postural rest position (i.e. no more than 4mms)
Forward positioning of mandible induces
Myotactic reflex actively and
Isometric muscle contraction.
These muscle contraction forces Stimulate the LPM & retro-
are transmitted by the appliance discalpad thus bring about
to move the teeth. Bone remodeling &
condylar adaptation.
Thus activator rely mainly on the muscle activity during
biting & swallowing & thus works by using KINETIC
ENERGY.

MYOTACTIC REFLEX ACTIVITY:
Lateral pterygoid muscle insertion
Myotactic reflex activity in
the muscle

CRITICISM ABOUT ANDRESEN & HAUPL CONCEPT
Activator is mainly a night time wear appliance. During
sleep the frequency of biting & Swallowing decreases and also
the freeway space is almost double what it is when the patient is
awake. This reduces the myotactic reflex activity & muscle
contraction. So some authors argue that the efficiency of the
activator is questionable.

II. HEREN, HARVOLD & WOODSIDE CONCEPT
Bite is opened approximately 12-15mm beyond the postural
rest position
It induces stretching of soft tissues & the viscoelastic
pull of the soft tissues are responsible for the appliance
action. The power to produce alveolar remodeling is obtained
from inherent elasticity of muscle, tendinous tissues & skin.
Thus the appliance works by POTENTIAL ENERGY rather
than kinetic energy (i.e. Myotactic reflex activity).
III. The third concept is a combination of above 2.

SKELETAL AND DENTOALVEOLAR EFFECTS OF THE
ACTIVATOR:
1.Any skeletal effect from the activator depends on the growth
potential.
Two divergent growth vectors propel the jaw bases in an
anterior direction
a. The sphenoccipital synchondrosis moves the cranial base
and nasomaxillary complex up & forward.
b. The condyle translates the mandible in a downward and
forward direction.
The activator is most effective in controlling the lower vector
or the downward and forward growth of the mandible.

Two divergent growth vectors

Johnston (1976) attributes this response to "unloading the
condyle."
 Only the upward and backward growth of the condyle is
capable of moving the mandible anteriorly
 As the research by Petrovic has shown, the LPM plays a
decisive role in this growth.
 Forward posturing of the condyle activates the superior
head of the LPM
 The activator can, to a limited degree control the upper
growth vector, supplied by the sphenoccipital
synchondrosis, which moves the maxillary base forward
2. The dentoalveolar efficiency of the activator helps achieve,
a primary treatment objective.
Teeth and bones fill in the space between the two divergent
growth vectors.

Static – Permanent & vary in magnitude and direction
Dynamic – Interrupted, appear simultaneously with
movements of body and head; higher magnitude
Rhythmic – associated with Respiration and circulation,
amplitude varies with pulse
Efficacy of activator during sleep depends
frequency of the movements
kind of construction bite
alteration of interocclusal space
Muscle tone
Restlessness
FORCE ANALYSIS IN ACTIVATOR THERAPY:

Force application - Usually muscular source
Force elimination – dentition is shielded from normal and
abnormal functional & tissue pressures

The types of force employed in activator therapy may
be categorized as follows:
1. The growth potential, including the eruption and migration
of teeth, produces natural forces. These can be guided
promoted, and inhibited by the activator.
2. Muscle contractions and stretching of the soft tissues
initiate force when the mandible is relocated from its
position by the appliance. The activator stimulates and
transforms the contractions. Whereas forces may be
functional (muscular) in origin, their activation is artificial.

These artificially functioning forces be effective in all
three planes:
Sagittal plane: the mandible is propelled down and
forward, so that muscle force is delivered to the condyle
and a strain is produced in the condylar region.
Vertical plane: The and alveolar process are either
loaded or relieved of normal forces. If transmitted to
maxilla these forces can inhibit growth and direction and
influence the inclination of maxillary base
Transverse plane: forces also can be created with midline
corrections.

CONSTRUCTION BITE:
The purpose of this mandibular manipulation is to relocate the
jaw in the direction of treatment objectives. This creates
artificial functional forces and allows assessment of the
appliance's mode of action. Before taking the construction bite,
the clinician must prepare by making a detailed study of the
plaster casts, cephalometric and panoral head films, and the
patient's functional pattern.
Diagnostic Preparation:
Creating an "instant correction"—moving the
mandible forward into an anterior more normal
sagittal relationship—may help motivate patients
with Class II malocclusions.

Study model analysis:
Before constructing the activator, the
clinician must consider the following
factors, based on the cast analysis:
1. First permanent molar relationship in
habitual occlusion
2. Nature of the midline discrepancy, if any:
3. Symmetry of the dental arches:
4. Curve of Spee:
5. Crowding and any dental discrepancies:

Functional analysis.
1. Precise registration of the postural rest
position in natural head posture
2. Path of closure from postural rest to habitual
occlusion 3. Pre-maturities, point of initial
contact, occlusal
interferences, and resultant mandibular
displacement 4. Sounds such as clicking and
crepitus in the TMJ
5. Interocclusal clearance or freeway space
6. Respiration

Cephalometric analysis:
Enables clinicians to identify the craniofacial
morphogenetic pattern
direction of growth
Differentiation between position and size of jaw
bases
Morphologic peculiarities
Axial inclination & position of the maxillary and
mandibular incisors

TREATMENT PLANNING :
The extent of anterior positioning for Class II malocclusion
and posterior positioning for Class III malocclusions should
be determined.
Anterior positioning of the mandible.
The usual intermaxillary relationship for the average
Class II problem is end-to-end incisal. However, it
should not exceed 7 to 8 mm, or three quarters of the
mesiodistal dimension of the first permanent molar, in
most instances.
1.The overjet is too large
2.Labial tipping of the maxillary incisors is severe:
3.An incisor (usually a lateral) has erupted markedly to
the lingual: The mandible must be postured anteriorly
to an edge-to-edge relationship with the lingually
malposed tooth; otherwise, labial movement of this
tooth will be impossible. www.indiandentalacademy.comwww.indiandentalacademy.com

Eschler (1952) termed the condition a pathologic
construction bite. As with severely proclined upper incisors,
use of a short prefunctional appliance to improve alignment
of lingually malposed teeth is advisable before starting
activator treatment, thereby eliminating the need for the
pathologic construction bite.

Opening the bite.
Vertical considerations are as important as the sagittal
determination and are intimately linked to it
1. The mandible must be dislocated from the postural
resting position in at least one direction—sagittally or
vertically. This dislocation is essential to activate the
associated musculature and induce a strain in the
tissues.
2.If the magnitude of the forward position is great (7 or 8
mm), the vertical opening should be minimal so as not
to overstretch the muscles. This type of construction
bite produces an increased force component in the
sagittal plane, allowing a forward positioning of the
mandible.
3. If extensive vertical opening is needed, the mandible
must not be anteriorly positioned.

Disadvantages of a wide-open construction bite
Difficulty of wearing the appliance and adapting to the
a new Relationship
Muscle spasms often occur
appliance tends to fall out of the mouth.
The high construction bite also makes lip seal difficult
if not impossible

Vertical force component during
opening of mandible
Opening below rest position Sagittal force arising during
anterior positioning

In a forward position of 7 – 8 mm the opening must be
slight
If forward position id not more than 3 – 5 mm the vertical
opening should be 4 – 6 mm.
If there is midline shift due to translation of mandible then
it can be corrected
GENERAL RULES FOR CONSTRUCTION BITE:

EXECUTION OF CONSTRUCTION BITE:
 Horse shoe shaped wax rim is made in the proper arch
form; should be 2-3mm thicker than the planned
construction bite for guiding the mandible. Wax is placed
is placed in lower for treatment of class II and in the upper
for treatment of class III
 Make the patient sit upright in the relaxed posture, guide
the mandible into desired position without exerting force
 Wax is placed in mouth after the operator is sure the
patient can replicate
 Edge to edge incisal relation is maintained
 Midline is observed for coincidence
 Wax bite is carefully removed

Wax placed over the cast
Casts mounted on wax after obtaining bite registration

• It may not fit.
• Asymmetric biting may have occurred on it.
• The patient may not be really comfortable and may be
disturbed more frequently during sleep.
• The likelihood of unwanted lower incisor procumbency
may be greater, because the appliance exerts undue stress
on these teeth.
Why Construction Bite Cannot be taken in Casts ?

MINIMAL VERTICAL OPENING :
Commonly the bite is registered with the mandible in a
slightly protruded position of 3mm, whereas the vertical
bite is registered within the limits of patients freeway
space. This increases the frequency of the reflex
contractions in the muscle of mastication. When the
mandible is moved mesially to engage the appliance the
elevator muscles are activated. Thus Myotactic reflex is
produced.

VOLITIONAL CONTROL:
The neural pathway for the Volitional control of the
masticatory muscles is explained as follows.
The propioceptive fibers the PDL, muscles and TMJ ascend
via the trigeminal nerve to the brain stem. The cell body is in
the Mesencephalic nucleus. from there the tract descends to
the masticatory nucleus on the ipsilateral side and synapses
with the lower motor neurons. This carries motor impulses
to the masticatory muscles via the third division of trigeminal
nerve. The voluntary control of the muscle arises from the
pyramidal cells of Betz in the cortex and descends via the
upper motor neurons.

VOLITIONAL CONTROL:

MODERATE VERTICAL OPENING:
The mandible is protruded 3mm and the vertical bite is
registered at 4mm beyond the rest position of the mandible.
This activates the myotactic reflex and this increases the
frequency of the swallowing and biting during the first few
days of therapy. This is maintained by the force through
increased active action of stretched muscle. This is needed
when the appliance is worn mostly in the night and the rest
position is altered during sleep. The extreme opening
insures that the reflex will act when the musculature is more
relaxed while sleeping. Since the activator does not permit
muscle shortening the contractions are isometric than
isotonic. Hence the muscle fiber develop more tension
which is sustained during the periods of contraction.

MYOTACTIC REFLEX:
It is the reflex action of skeletal muscle contraction. The
stimuli is the stretch of the muscle which causes the
contraction of stretched muscle. Muscle stretch receptors are
proprioceptive muscle endings called muscle spindles. These
are located within the muscle and contain 2-15 intrafusal
fibers. The long slender ones are striated and contractile but
the center or nuclear bag part is non contractile. The impulses
arising from the spindles are conducted by the Group IA
sensory fibers. They synapse with the motor neurons called
Alfa efferent that supply extra fusal fibers. the myotactic or the
stretch reflex is therefore a Monosynaptic reflex arc.

MYOTACTIC REFLEX:

Construction Bite with Opening and Posterior
Positioning of the Mandible
1) Used in class III cases
2) Prognosis is good for
Pseudo class III

FABRICATION OF ACTIVATOR:
Preparation of wire elements:
the labial bow are the principal elements. Consists of a
middle horizontal section and two vertical loops made of 0.9
mm for active and 0.8 mm for passive labial bow.

Fabrication of Acrylic portion:
This consists of upper and lower and the inter occlusal
parts. In a ‘v’ activator the flanges are higher than the ‘H’
activator due to enhanced retention required in ‘V’
activator. The flanges in the upper part are 8-12mm high in
the gingival area covering the alveolar crest while the palate
is free. The Acrylic plate is thin so it does not encroach the
activity. To increase the rigidity palatal bar may be given
which is 1.2mm thick. The lower acrylic plate is 5-10mm
wide or 10-15mm in some cases.

The stimulation of the functional activity of the peri-
oral musculature with loose appliances to guide the
movement and eruption of selected teeth can best be
achieved by grinding away areas of acrylic that contact the
teeth.
Principles of trimming:
The force is intermittent. This allows dynamic and
rhythmic muscle forces to act in such a manner that the
appliance acts by kinetic energy.
The direction of the desired force is determined by
selective grinding of the acrylic surfaces that contact the
teeth.
The magnitude of force is determined by the amount pf
acrylic that contact the teeth.
The acrylic surface that transmit the force and contact
the teeth are called guiding planes

EVALUVATING ACTIVATOR TRIMMING:
Evaluation with explorer
Undercut surface in acrylic;
And after trimming
Shadow test for Trimming

TRIMMING THE ACTIVATOR FOR VERTICAL CONTROL:
INTRUSION OF TEETH:
Incisors:
Can be achieved by loading the
incisal edges of teeth, the labial bow
should be below the area of greatest
convexity or on incisal third.
Molars:
Performed by loading only the
cusps. The pits and fossas are cleared
to eliminate any possible incline plane
effect

Extrusion of teeth :
Incisors:
Requires loading the acrylic above the
area of greatest concavity in the maxilla
and below this area in the mandible.
Although not effective can be enhanced by
placing the labial bow above the area of
greatest convexity.
Indicated in Open bite problems
Molars:
Done by loading the lingual surface of
these teeth above the area of greatest
convexity in maxilla and below this area
for mandible.
Indicated in deep bite cases

SELECTIVE TRIMMING OF THE ACTIVATOR:
During selective trimming either the upper or the lower
molar is extruded.
The path of eruption must be considered

TRIMMING THE ACTIVATOR FOR SAGITTAL CONTROL:
Can be achieved through
PROTRUSION / RETRUSION of Incisors
MESIAL / DISTAL movement of Molars
Protrusion or retrusion is possible through
Acrylic guide planes
Labial bow Active
Passive
Position of Labial bow
Gingival – Extrusion, Decreases
Tipping
Incisal – Inhibit extrusion,
increase Tippingwww.indiandentalacademy.comwww.indiandentalacademy.com

In class III activator lip pads are
used instead of a labial bow

PROTRUSION OF INCISSORS:
Incisors can be protruded by loading their lingual surface and
screening lip strain by passive labial bow.
1) Entire lingual surface loaded
2) Incisal third of lingual surface is loaded.

Protrusion by means of Auxiliary elements
Protrusion springs
Wooden pegs
Guttapercha

Retrusion of Incisors:
Acrylic is trimmed from the back of incisor
Active Labial bow is incorporated

MOVEMENT OF POSTERIORS IN SAGITAL PLANE:
Distalisation:
the Guiding planes are loaded in
the mesio lingual surfaces.
Indicated in class II non extraction cases.
Additional elements such as stabilizing
wires or active open springs can be used.

Mesial movement:
Can be achieved by loading the
disto - lingual surfaces.
Indicated for the upper arch in
class III cases.

Movement in transverse plane:
To achieve transverse movement the
lingual acrylic surfaces opposite to the
posterior teeth must be in contact with
teeth.
More effective expansion can be
achieved using Jack screws.

MANAGEMENT OF THE APPLIANCE:
Checkup appointments should be scheduled every 6 weeks.
During these office visits the clinician should maintain rapport
with the patient, reinforce motivation, and perform the
following procedures
1. All guide planes that have been ground and all areas in
contact with the teeth should be observed for shiny surfaces
that indicate whether the appliance is being worn correctly and
is working properly.
2. Reshaping of acrylic guide areas may be required after initial
trimming to improve function; it also may be needed during the
course of treatment to ensure continued tooth movement
(particularly in the upper arch) if retrusion or distalization is
desired.

3. Acrylic contact guide planes often must be resealed or recon
toured to maintain the proper functional activation on the
desired teeth by adding self-curing soft acrylic in a thin layer.
Clinical examination of the acrylic inclined planes for shiny
spots helps determine the amount of sealing to be done.
4. The labial bows and any additional wire elements must be
checked for action and possible deformation. The active bow
should touch the teeth. The passive bow should position away
from the teeth but remain in contact with the soft tissues.
5. Lip pads should be checked for irritation in the sulcus area
6. Jack screws are activated every 2 weeks.

Finished appliance.
Note deep extension of flanges.

Herren Shaye activator:
Herren modified the activator in two ways :
1. By over-compensating the ventral position of the mandible
in the construction wax bite.
2. By seating the appliance firmly against the maxillary dental
arch by means of clasps (arrowhead, triangular or
Jackson's).

The Bow activator of A.M Schwarz
The bow activator is a horizontally split
activator having a maxillary portion
and a mandibular portion connected
together by an elastic bow. This kind of
modification allows step wise sagittal
advancement of the mandible by
adjustment of the bow.

Wunderers modification:
This is an activator modification that is mostly
used in treatment of Class III malocclusion

Reduced activator or cybernator of Shmuth :
This modification of the activator is proposed by Professor
G.P.F. Schmuth. This appliance resembles a bionator with the
acrylic portion of the activator reduced from the maxillary
anterior area leaving a small flange of acrylic on the palatal
slopes.
The two halves may be connected by an omega shaped palatal
wire similar to bionator.

The Karwetzky modification:
This consists of maxillary and mandibular plates joined by a
'U' bow in the region of the first permanent molar.
Type I: This is used in the treatment of Class II, Division 1. In
this modification, the larger lower leg is placed posteriorly.
Thus when the two arms of the U bow are squeezed the lower
plate moves sagittally forwards
Type II : This is used for the treatment of Class III
malocclusion. In this appliance the larger lower leg is placed
anteriorly. Thus when the U bow is squeezed the mandibular
plate moves distally.
Type III: They are used in bringing about asymmetric
advancements of the mandible. The U bow is attached
anteriorly on one side and posteriorly on the other side to
allow asymmetric sagittal movement of the mandible

Bimler appliance (Bite former, Bimler stimulator)
A modification of the activator by H.P. Bimler. There are three
main kinds of Bimler appliance:
type A for patients with Class II Division 1 malocclusions,
type B for those with Class II Division 2 and
type C for patients with a Class III malocclusion.

Cut out or Palate free activator:
This is a modification proposed by
Metzelder to combine the
advantages of bionator and the
Andresen's activator.
The mandibular portion of
the appliance resembles an
activator while the maxillary
portion has acrylic covering only
the palatal aspect of the buccal
teeth and a small part of the
adjoining gingiva.
The palate thus remains free
of acrylic thereby making the
appliance more convenient for
patients to wear the appliance for
longer hours.
Due to the greater amount of
wearing time, success should be
greater with the palate free
activator. www.indiandentalacademy.comwww.indiandentalacademy.com

Elastic open activator
A modification of the activator
developed by G. Klammt. The
appliance has reduced acrylic
bulk, facilitating increased
appliance wear. The acrylic is
replaced by wires which increase
the flexibility of the appliance.
The flexible design allows
isotonic muscular contractions
(in contrast to rigid appliances,
which only allow isometric
contractions).

Herren activator (L.S.U. activator):
A modification of the activator developed by P. Herren
(also known as the Louisiana State University modification of
the same appliance). It is essentially an activator made to a
construction bite that positions the mandible forward and
downward to a significant degree.
According to P. Herren, the wearing of this appliance is
not supposed to increase the activity of the lateral
pterygoidmuscle

PROPULSOR:
Conceived by Muhlemann and refined by Hotz. Features with
both the Monobloc and a simple oral screen.
Advantage over other activator is the ability to cover and
effect changes in the alveolar process. Useful in cases of
maxillary dentoalveolar protrusion.
No wire elements, needs frequent reactivation or
modification with soft acrylic.

Lehman appliance (Lehman activator)
A combination activator-headgear appliance developed by
R.Lehman. It consists of a maxillary acrylic plate that carries
two rigidly fixed outer bows and a mandibular lingual shield.
The acrylic plate covers the palate and it extends over the
occlusal and incisal surfaces of the maxillary teeth, up to the
occlusal third of their buccal and labial surfaces.
Selective expansion of the maxillary arch is possible by
appropriately activating the two transverse expansion screws
(one anterior and one posterior) that are embedded in the
plate.
Occipital traction is applied through a head strap attached on
the outer bows, which are fixed at the anterior aspect of the
appliance. The mandibular lingual shield is connected to the
maxillary plate by means of two heavy S-shaped wires.

Unlike many activator type appliances which are constructed
with the mandible in a protruded position, this appliance is
made from a bite registration taken in centric occlusion.
According to R.Lehman, the S-shaped wires are activated by
approximately 2 mm every 4 to 6 weeks, to achieve a gradual
advancement of the mandible

Teuscher-Stockli activator/headgear combination
appliance
A modified activator used in combination with a high-pull
headgear.
The appliance was introduced by U.M. Teuscher and P.W.
Stockli as a means to avoid the detrimental profile effects of
cervical traction when treating Class II malocclusions in
growing individuals. Buccal headgear tubes are incorporated
in the interocclusal acrylic at the level of the maxillary second
premolar or first molar

Patient with Teuscher-Stockli appliance with headgear

Nocturnal airway patency appliance:
By Peter T George (JCO)1987
NAPA was designed to keep the airway open during
sleep by Posturing the tongue more anteriorly. inhibiting
wide jaw opening. assuring adequate air intake through the
mouth when ever nasal obstruction exists.
The mandible was postured forward to advance the
tongue relative to the posterior pharyngeal wall. Because the
genioglossus originates at the inner surface of the
mandibular symphysis and inserts into the tongue, the
mandibular protrusion brings the tongue forwards.

Indications of activator :
The following are some of the indications for the use ofThe following are some of the indications for the use of
activator :activator :
 1. Class II, Division 1 malocclusion1. Class II, Division 1 malocclusion
 2. Class II, Division 2 malocclusion2. Class II, Division 2 malocclusion
 3. Class III malocclusion3. Class III malocclusion
 4. Class I open bite malocclusion4. Class I open bite malocclusion
 5. Class I deep bite malocclusion5. Class I deep bite malocclusion
 6. As a preliminary treatment before major fixed6. As a preliminary treatment before major fixed
appliance therapy to improve skeletal jaw relationsappliance therapy to improve skeletal jaw relations
 7. For post-treatment retention7. For post-treatment retention
 8. Children with lack of vertical development in lower facial8. Children with lack of vertical development in lower facial
height.height.

Contra-indications of activator therapy
1. The appliance is not used in correction of Class I problems
of crowded teeth caused by disharmony between tooth size
and jaw size,
2. The appliance is contraindicated in children with excess
lower facial height and extreme vertical mandibular growth.
3. The appliance is not used in children whose lower incisors
are severely procumbent.
4. The appliance cannot be used in children with nasal
stenosis caused by structural problems within the nose or
chronic untreated allergy.
5. The appliance has limited application in non-growing
individuals.

Advantages of activator therapy
1. It uses existing growth of the jaws.
2. During treatment the patient experiences minimal oral
hygiene problems.
3 .The intervals between appointments is long.
4. The appointments are usually short due to need for minimal
adjustments.
5. Due to the above reasons they are more economical

Disadvantages of activator therapy
1. Requires very good patient cooperation.
2. The activator cannot produce a precise detailing and
finishing of the occlusion. Thus post-treatment fixed
appliance therapy maybe needed for detailing of the
occlusion.
3. It may produce moderate mandibular rotation (anteriorly
downwards). Thus activators are not used in cases of
excessive lower face height.

Tongue function during activatorTongue function during activator
treatment.treatment.
A cephalometric and dynamometric study byA cephalometric and dynamometric study by
Johan AhlgrenJohan Ahlgren EJO (1979) 251-257EJO (1979) 251-257
The results seem to verify Andresen'sThe results seem to verify Andresen's
hypothesis that tongue activity is stimulated byhypothesis that tongue activity is stimulated by
activators but they do not support his view thatactivators but they do not support his view that
wearing an activator would result in permanentwearing an activator would result in permanent
hypertrophy of the tongue muscles.hypertrophy of the tongue muscles.

How effective is the combined activator-headgearHow effective is the combined activator-headgear
treatment?treatment?
By Olav BondevikBy Olav Bondevik (EJO 1991)(EJO 1991)
The frequency and possible causes of failure andThe frequency and possible causes of failure and
success with the combination activator-headgear as thesuccess with the combination activator-headgear as the
sole appliance was analyzed retrospectively in 32 girls andsole appliance was analyzed retrospectively in 32 girls and
46 boys. The subjects comprised all the patients who46 boys. The subjects comprised all the patients who
started treatment with this combination in thestarted treatment with this combination in the
postgraduate courses in 1972-82 at the Orthodonticpostgraduate courses in 1972-82 at the Orthodontic
Department of the University of Oslo, and where fixedDepartment of the University of Oslo, and where fixed
appliances were not included in the initial treatment plan.appliances were not included in the initial treatment plan.
Only 14 subjects completed the treatment with entirelyOnly 14 subjects completed the treatment with entirely
satisfactory results according to strict criteria set for ansatisfactory results according to strict criteria set for an
acceptable standard. Among the most co-operativeacceptable standard. Among the most co-operative
patients less than 50 per cent ended with entirelypatients less than 50 per cent ended with entirely
satisfactory results, and no one with decreasing or poorsatisfactory results, and no one with decreasing or poor
co-operation had a satisfactory result.co-operation had a satisfactory result.. .. .

Neither sex, treatment time, nor ossification of the ulnarNeither sex, treatment time, nor ossification of the ulnar
sesamoid bone seemed to influence the results significantlysesamoid bone seemed to influence the results significantly

Treatment needs following Activator-headgearTreatment needs following Activator-headgear
therapytherapy
By Lav Bondevik, ( Angle orthod 1995)By Lav Bondevik, ( Angle orthod 1995)
 The purpose of this study was to analyze the types andThe purpose of this study was to analyze the types and
prevalence of malocclusions that remain to be correctedprevalence of malocclusions that remain to be corrected
after a period combined activator-headgear treatment.after a period combined activator-headgear treatment.
Study models of all patients who started treatment with anStudy models of all patients who started treatment with an
activator-headgear appliance in the graduate orthodonticactivator-headgear appliance in the graduate orthodontic
clinic at the University of Oslo between 1972 and 1982 wereclinic at the University of Oslo between 1972 and 1982 were
screened.screened.
 Results show that the most frequently remaining problemsResults show that the most frequently remaining problems
following activator-headgear treatment were overbite,following activator-headgear treatment were overbite,
overjet and the presence of interdental spaces. Correctionoverjet and the presence of interdental spaces. Correction
of the Class II skeletal and dental relationship wasof the Class II skeletal and dental relationship was
achieved in the majority of the cases. The only predictorachieved in the majority of the cases. The only predictor
for success was age at the time of treatment.for success was age at the time of treatment.

Combination Headgear-ActivatorCombination Headgear-Activator
DR. HERMAN VAN BEEKDR. HERMAN VAN BEEK
JCO Volume 1984 Mar(185 - 189):JCO Volume 1984 Mar(185 - 189):
Clinical Aspects of Headgear-Activator TreatmentClinical Aspects of Headgear-Activator Treatment
The headgear-activator has the following modes of action:The headgear-activator has the following modes of action:
 1. Intrusion and retraction of upper front teeth1. Intrusion and retraction of upper front teeth
 2. Distalization of upper molars2. Distalization of upper molars
 3. Maxilla retraction3. Maxilla retraction
 4. Mandibular growth stimulation, especially in the4. Mandibular growth stimulation, especially in the
brachyfacial groupbrachyfacial group
 5. Opening of the facial axis in the brachyfacial group5. Opening of the facial axis in the brachyfacial group
 6. Maintenance of the facial axis in the dolichofacial group6. Maintenance of the facial axis in the dolichofacial group
 7. Minor, if any, tilting of lower incisors7. Minor, if any, tilting of lower incisors
 8. Stopping lower incisor eruption8. Stopping lower incisor eruption
 9. Stopping the descent of the palate9. Stopping the descent of the palate

Activator treatmentActivator treatment
Vargervik and HarvoldVargervik and Harvold
Response to activator treatment in Class II malocclusions.Response to activator treatment in Class II malocclusions.
A clinical study was designed to disclose the effects ofA clinical study was designed to disclose the effects of
activator treatment in the correction of Class II malocclusions.activator treatment in the correction of Class II malocclusions.
The rationale for the use of the activator appliance was basedThe rationale for the use of the activator appliance was based
on the premise that correction of distocclusion can beon the premise that correction of distocclusion can be
achieved byachieved by
 (1) inhibition of forward growth of the maxilla,(1) inhibition of forward growth of the maxilla,
 (2) inhibition of mesial migration of maxillary teeth,(2) inhibition of mesial migration of maxillary teeth,
 (3) inhibition of maxillary alveolar height increase and(3) inhibition of maxillary alveolar height increase and
extrusion of mandibular molars,extrusion of mandibular molars,
 (4) increased growth of the mandible,(4) increased growth of the mandible,
 (5) anterior relocation of the glenoid fossa,(5) anterior relocation of the glenoid fossa,
 (6) mesial movement of mandibular teeth,(6) mesial movement of mandibular teeth,
 (7) combinations of these effects.(7) combinations of these effects. www.indiandentalacademy.comwww.indiandentalacademy.com

A cephalometric analysis of skeletal and dental
changes contributing to Class II correction in
activator treatment
Hans Pancherz, (Am J Orthod) 1984
The purpose of this investigation was to evaluate
cephalometrically the mechanism of anteroposterior occlusal
changes in activator treatment.
The following results were found:
(1) The improvement in occlusal relationships in the molar and
incisor segments was about equally a result of skeletal and
dental changes.
(2) Overjet correction averaging 5.0 mm was a result of 2.4 mm
more mandibular growth than maxillary growth, a 2.5 mm distal
movement of the maxillary incisors, and a 0.1 mm mesial
movement of the mandibular incisors.

(3) Class II molar correction averaging 5.1 mm was a result of
2.4 mm more mandibular growth than maxillary growth, a 0.4
mm distal movement of the maxillary molars, and a 2.3 mm
mesial movement of the mandibular molars.
(4) When the findings were compared with longitudinal
records of persons with normal occlusion (Bolton standards),
activator treatment seemed to inhibit maxillary growth, move
the maxillary incisors and molars distally, and move the
mandibular incisors and molars mesially. Mandibular growth
appeared not to be affected by activator treatment

Effects of Activator Treatment on Class II, DivisionEffects of Activator Treatment on Class II, Division
1 Malocclusion1 Malocclusion
DR. CHANG, DR. KAI-MING WU, DR. KUN-CHEE CHEN,DR. CHANG, DR. KAI-MING WU, DR. KUN-CHEE CHEN,
(JCO) Aug 1989(JCO) Aug 1989
This study was undertaken to evaluate the effects of activatorThis study was undertaken to evaluate the effects of activator
treatment on a group of Class II, division 1 patients with skeletaltreatment on a group of Class II, division 1 patients with skeletal
mandibular retrusion.mandibular retrusion.
Activator treatment in this study was successful in girls andActivator treatment in this study was successful in girls and
boys from age 7 to 12. Children from age 7 to 12 are highlyboys from age 7 to 12. Children from age 7 to 12 are highly
responsive to praise and positive reinforcement andresponsive to praise and positive reinforcement and
therefore tend to be cooperative.therefore tend to be cooperative. Early functionalEarly functional
appliance treatment can correct any abnormal muscularappliance treatment can correct any abnormal muscular
habits that might influence later facial development andhabits that might influence later facial development and
form.form.

Temporal muscle activity during the first year of
Class II, Division 1 malocclusion treatment with an
activator
Bengt Ingerval and Urs Thüer
(1991 Apr) Am J Orthod
The activity of the anterior and posterior temporal
muscles in response to treatment with a splint type of activator
was studied in children with distal occlusion.
The activity in the rest position was constant during the
1-year period of observation. During maximal bite the activity
of the posterior temporal muscle decreased significantly in the
group with headgear and the control group and in a subgroup
of children with large protrusions in the construction bite who
had been treated with activators. This decrease was considered
to be an effect of occlusal instability brought about by the
treatment. www.indiandentalacademy.comwww.indiandentalacademy.com

There was no evidence of a decrease in the postural (rest)
activity of the posterior temporal muscle, although such a
decrease has been described as a sign of forward
displacement of the mandible during treatment with a
functional appliance.

Functional treatment of condylar fractures in
adult patients
E. K. Basdra,A. Stellzig, Drmeddent
1998 Jun A J O
Functional treatment of condylar fractures in adult patients
usually follows the closed reduction / maxillomandibular fixation
approach. Some of the problems arising when functional
appliances (i.e., activator) are used have been identified and
presented here, especially in patients where fractured parts are
dispositioned/dislocated.
They conclude that activators are not the best means of
treating condylar fractures with displacements/dislocations in
adult patients. Therefore patients who after the removal of the
intermaxillary fixation show good occlusal relationships should be
only treated with the use of intermaxillary elastics. Patients
exhibiting anterior or lateral open bites after intermaxillary
fixation should be treated with biteplates (half or posterior
bilateral), combined with vertical elastics, to reestablish the initial
occlusal relations www.indiandentalacademy.comwww.indiandentalacademy.com

A small group of patients with condylar fractures treated
by the above functional concept has been shown. They showed
good response and reported no complaints or discomfort 1 year
later. The occlusion recovered to the initial relationship and no
selective grinding was necessary after treatment. This approach
seems promising in the treatment of condylar fractures in adult
patients.

Orthodontic forces exerted by activators with varying
construction bite heights
Takuji Noro, Kazuo Tanne, and Mamoru Sakuda,
A J O 1994 Feb
The present study was conducted to investigate the
nature of forces induced with activators by measuring strains,
electromyogram (EMG) and electroencephalogram (EEG)
during a 2-hour sleep period.
Duration of forces generated by passive tension was
most significantly longer than that of active contraction of the
jaw closing muscles, irrespective of the construction bite
heights. It is concluded that passive tension, derived from
viscoelasticity of soft tissues, plays a more important role in
inducing changes than phasic stretch reflex during jaw
orthopedic therapy with activators

Predicting functional appliance treatment
outcome in Class II malocclusion
Susi Barton, and Paul A
(A J O 1997)
Selecting cases suitable for treatment with a functional
appliance remains a problem as much of the relevant literature
is anecdotal. There are also design and methodologic
differences between the available studies, and most studies are
limited to the Andresen type of appliance. The literature
suggests that functional appliances are most successful in cases
with an over jet of up to 11 mm, an increased overbite, active
facial growth, and good cooperation

CONCLUSION
Catch them young Watch them grow

www.www.iindiandentalacademy.comndiandentalacademy.com

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