Removable functional appliance 2

Part 2
dr Maher FOUDA
Faculty of Dentistry
Mansoura Egypt
Professor of orthodontics
Removable
functional appliance

Andresen Activator
Synonyms: Monobloc, Andresen and Häupl appliance, Andresen appliance
and Norwegian appliance.
History of Activator
In 1909, Viggo Andresen, a Danish dentist (1870–1950) removed his daughter’s
fixed appliances and replaced with a Hawley type maxillary retainer when she
left for her summer vacation. He placed a lingual horseshoe-shaped flange on
the mandibular teeth that guided the mandible forward about 3–4 mm in
occlusion. Andresen was not specializing in orthodontics until 1919. When his
daughter returned, he was surprised to notice that the night time wearing of the
appliance had eradicated her Class II malocclusion and was stable too. Applying
this technique to other patients resulted in significant sagittal corrections that he
could not produce with conventional fixed appliances.

The original Andresen activator was tooth-borne passive (loose fitting)
appliance, consisting of plastic covering of the palate and the teeth in both
arches. This was designed to advance the mandible in Class II correction
by several millimeters and opening the bite by 3–4 mm.
Andresen’s novel device was not initially well received. In 1925, Andresen,
then director of the
orthodontic department at the University of Oslo, began developing for the
government a simple method of treating
Norwegian children.

He modified his retainer into an orthodontic appliance, using a wax bite to
register the mandible in an advanced position. At the university, Karl H‫ن‬upl
(1893–1960), an Austrian pathologist and periodontist, saw the possibilities
of the appliance and became an enthusiastic advocate of what he and
Andresen called the ‘Norwegian system. H‫ن‬upl’s theories were inadvertently
strengthened by the findings of Oppenheim, who showed the potential tissue
damage caused by the heavy orthodontic forces of fixed appliances.4 At that
time, there was no mention of ‘growth stimulation’.

The original name Andresen used for this type of treatment was
biomechanical orthodontics and the appliance was called
biomechanical working retainer. Only later, after teaming up with
Karl Häupl and doing further work on concepts and technique
refinements, was the name changed to functional jaw orthopedics,
which was more descriptive.

Andresen and the Andresen–
H‫ن‬upl appliance. This device
has no tooth-moving parts.
The appliance was made to
treat Class II division 1
malocclusion. Instead of
palatal coverage, a heavy
Coffin spring has been used
to ensure stability, yet allow
tongue contact with the
mucosa. The loops in the
canine region stand away
from the teeth, allowing
maxillary intercanine
development. These loops
are the forerunners of the
Balters’ bionator screening
loops, which extend to the
distal of the deciduous
second molar, and also of
the Frankel buccal shields,
also meant to hold off cheek
pressure

Advantages of the Activator Include:
1. It is possible to treat primary and early or late mixed dentition.
2. Appointments can be extended to 2 months or more.
3. Tissues are not injured easily.
4. Since it is worn only at night-time, it is acceptable from anesthetic
and hygienic standpoint.
5. Eliminates pressure habits, like mouth breathing and tongue
thrusting.

Its Disadvantages Include:
1. Patient compliance is depended for success.
2. Patients must be chosen properly because activator has
no value in relieving marked crowding.
3. Does not have a good response in older adults.
4. Forces on individual teeth cannot be controlled with the
same accuracy as in fixed appliances.

Indications:
• Class I malocclusion with deep bite.
• Class I malocclusion with open bite.
• Class II division 1 malocclusion.
• Class II division 2 malocclusion after aligning the incisors.
• Class III malocclusion (appliance is called reverse
activator).
A, Schematic of functional appliance; B and C, activator demonstrating potential for arch
leveling and anchorage even with unilateral Class I elastics to close extraction site.

• For mild crossbite correction (trimming modified to move
maxillary molars laterally and screws can be incorporated).
• Phase I treatment before fixed appliance treatment.
• As habit breaking appliance.
• As retention appliance.
• Serves as space maintainer in mixed dentition, where
acrylic is extended into the space of missing tooth.
• Used for treating patients who snore during sleep.
• Used in obstructive sleep apnea.
Indications:

• Crowded arch.
• Increased lower facial height.
• Extreme vertical mandibular growth.
• Severely proclined lower incisors.
• Subjects with nasal stenosis.
• Non-growing patients.
• Retroclined upper incisors.
• Crossbite tendency.
• Gross intra-arch irregularities.
Andreasen’s modified Activator
with a lower lip
Contraindications
Activator is not used in the following conditions:

Design and Rationale of Activator
The muscular forces generated by the forward mandibular positioning
were transferred to the maxillary and mandibular teeth through the
acrylic body and the labial bow, which contacted the maxillary incisors.
In theory, these forces were transmitted through the teeth on to the
periosteum and bone, where they produced a restraining effect on the
forward growth of the maxilla, while stimulating mandibular growth
and causing maxillomandibular dentoalveolar adaptations.
Post functional intraoral picture.

Interocclusal acrylic guide planes were given to modify the
dentoalveolar adaptations in a desirable direction. For a Class II
correction, the posterior mandibular segments were directed to
erupt mesially and vertically while the posterior maxillary
segments were directed to erupt distally and buccally. The vertical
eruption of the maxillary teeth was prevented by the acrylic
occlusal stops and the intrusive forces of the appliance.

The incisal acrylic coverage was to inhibit the teeth
eruption of the anteriors of maxilla and mandible while
reducing the flaring of the mandibular anteriors.
Uncontrolled incisal flaring could result in rapid correction
of overjet that would minimize the orthopedic effects of the
appliance on the jaws. Most present day activators are a
modification of the Andresen–H‫ن‬upl appliance which was
originally designed for night time wear..

• Preparation of models: working and study
models.
• Registration of construction bite: horizontal
or vertical bites.
• Articulation of models.
• Wax up and wire bending.
• Processing of appliance.
• Trimming of activator.
S T E P S I N C ONS T RUC T I ON O F A C T I VAT O R

Construction Bite Controversies
Concept 1
The original Andresen–Häupl concept stated that the myotatic reflex
activity that arises and the isometric contraction (kinetic energy)
induce musculoskeletal adaptation by introducing a new mandibular
closing pattern. The stimuli from the activator, muscle receptor, and
periodontal mechanoreceptor promote displacement of the
mandible. The superior heads of the lateral pterygoid muscle have
the most important role in this adaptation, because they assist in
the skeletal adaptation.
activator developed in Norway by Andresen in the
1920s

Petrovic and McNamara20 came to similar conclusion based on
his important and extreme study of the condylar cartilage.
Fundamental requirement for condylar growth stimulation is the
ability to activate the lateral pterygoids. According to this
concept, sagittal advancement is more with minimal vertical
opening; hence, they are called H activator.
The monobloc
developed by Robin in the early 1900s is generally considered
the forerunner of all functional appliances, but the
activator developed in Norway by Andresen in the 1920s
was the first functional appliance to be widely
accepted.

Concept 2
Selmer–Olsen, Herren, Harvold and Woodside21–23 did not accept the above
theory and formulated their own concept. According to their views,
viscoelastic properties of muscle and stretching of soft tissues are decisive for
activator action. Each application of force induces secondary forces in tissues,
which in turn introduces a bioelastic process and that is important in
stimulating skeletal adaptation. The stages of viscoelastic reaction (depends
on magnitude and duration of applied force) include emptying of vessels,
pressing out of interstitial fluid, stretching of fibers, elastic deformation of
bone, and bioplastic adaptation. Thus, not only the muscle contraction but
also the viscoelastic properties of the soft tissues are important in stimulating
the skeletal adaptation.

Harvold and Woodside opened the mandible with
construction bite much as 10–18 mm beyond postural rest
vertical dimensions. Overextended activator stretching the
soft tissue like a splint induces no myotatic reflex activity
but instead applies a rigid stretch and buildup in potential
energy.
According to this concept, sagittal advancement is less with
increased vertical opening; hence, they are called V
activators.
Harvold activator.

Concept 3
There are a number of other authors who take a higher
construction bite without the extreme extension
advocated by Harvold. The mode of action preceding is called
transitional type of activator action, which alternatively uses muscle
contraction and viscoelastic properties of soft tissues (both kinetic and
potential energies are utilized). The appliances in this group have great
bite opening than recommended by Andresen and Häupl. Eschler
defined the technique that opens the vertical dimension beyond 4 mm
construction bite as ‘muscle stretching method’ working alternatively
with isotonic and isometric muscle contraction.

Force Analysis in Activator Therapy
When functional appliance activates the muscles, various types of forces, like
static, dynamic and rhythmic forces, are created.
• Static forces are permanent (e.g. force of gravity, posture, elasticity of soft
tissues and muscles).
• Dynamic forces are interrupted (e.g. movements of head and body,
swallowing).
• Rhythmic forces are associated with respiration and circulation. Mandible
transmits rhythmic vibrations to the maxilla.
Andresen activator

Harvold activator (a–e). The inter‐maxillary force should theoretically be concentrated on both the maxillary dentition and palate, while the
forces are transmitted to the lingual aspect of the mandible rather than the lower teeth. Consequently, well‐extended lower impressions with adequate
lingual depth, in particular, are required. The postured bite is taken 8–10 mm beyond the freeway space with near maximal protrusion, this degree of
vertical opening allows the inclusion of an anterior breathing hole. During fabrication, extensive plaster relief is important in the lower posterior region
to promote full eruption and lower arch levelling, while restricting unwanted lower incisor proclination with extension of the lower anterior acrylic onto
the labial aspect of the mandibular incisors (c). The molars are afforded space to erupt, particularly in the lower arch to facilitate arch levelling and
overbite reduction. An upper labial bow in 0.8 mm spring hard stainless steel may be added to facilitate retention, although more flexible wire may be
used where space closure in the upper anterior region is planned. The labial bow should permit eruption and distal movement of the maxillary canines
where required. The relief for the upper posteriors is such that it provides cusp tip contact with the upper acrylic plate with no interference, which might
inhibit distal movement of the upper posteriors (d, e). These elements are usually introduced during the fabrication stage, with chairside trimming not
usually required. The upper anterior aspect of the acrylic plate should extend to the incisal edges of the maxillary incisors to facilitate three‐dimensional
control, and a relief chamber is provided palatal to the incisors to facilitate intrusion without retraction.

C L INI C A L S I GNI F I C ANC E
Construction Bite
Construction bite is the process by which the position in which
the functional appliance has to be processed is registered
Andresen activator

Guidelines for Bite Registration
Early Mixed Dentition
The mandible should be moved forward until the upper primary canine relates
directly above the interproximal between the lower primary canine and the first
primary molars . On an average, it will be 4–5 mm.
Typical construction bite for activator in Class II correction. (A) Before
bite registration and (B) is after bite registration.

Late Mixed Dentition
The mandible should be moved forward until the upper canine relates
directly above the interproximal between the lower cuspid and first
bicuspid. On an average, it will be 6–8 mm.
Anterior Midline
When the bite registration is taken, the upper and lower midlines
should coincide. If there is skeletal midline deviation, bite registration
is done with midlines coinciding. If there is dental midline shift, no
attempt should be made to correct the midlines.
.

GU I D E L INE S F OR C ONST RUCTION OF BITE FOR ACT I VAT R
Horizontal bite (H activator)
• Mandible advanced by 6–7 mm.
• Vertical opening by 3–4 mm.
Vertical bite (V activator) (high-angle cases)
• Mandible advanced by 2–3 mm.
• Vertical opening by 7–8 mm.
.
Andresen activator appliance.
Faceting in the buccal segments encourages
differential eruption of the teeth and
correction of a class II buccal segment
relationship. The lower buccal segments erupt
mesially and the upper distally.

• Only vertical opening: In deep-bite cases.
Retrusive bite
• In Class III cases.
The maximum amount of sagittal advancement and
vertical opening should be 10 mm in construction bite
for activators. It is called rule of ten

Fabrication of Appliance
After recording of construction bite, the bite with models are reverse
articulated. This helps in providing good access during acrylization
of the appliance, if processed with self-cure resins. A 0.9 mm wire is
used to make a passive labial bow. The ends of the bow cross
between the canine and first premolar or deciduous first molar
through the center of interocclusal wax.
A number of activators (i.e., the Woodside, Herren, and Harvold
models) require a larger vertical opening, which exceeds the freeway
space at postural rest position; this need elicits the viscoelastic properties
of the associated tissues. This illustration shows an 8-mm
opening between the first molars. The lower incisors are capped
to provide more stability and offset the tendency of these teeth to
procline.

The labial bow should contact the middle third of the labial surface of
the upper anterior teeth. The labial bow should not be adjusted to exert
any mechanical pressure on the upper anterior teeth. It acts as a
passive medium for the transmission of muscular forces to the
maxillary teeth and arch.
Processing of the appliance is done using either heat-cure or cold-cure.
Appliance consists of: (1) maxillary part—gingival, dental; (2)
interocclusal part; and (3) mandibular part—dental, gingival .
Acrylic parts of activator

Trimming of Activator
After processing of the appliance, an interocclusal block of acrylic is present
between the upper and lower posterior teeth. Guiding grooves are placed in the
interocclusal block to facilitate tooth movement. Appropriate flame-shaped burs
are used to create guiding grooves.
Activator trimming procedure for movement of teeth in vertical plane. (A) Intrusion of
incisors; (B) Intrusion of molars; (C) Extrusion of incisors; (D) Extrusion of molars; (E)
Selective eruption of molars

Trimming for Vertical Movement
Two movements occur in the vertical plane with activator treatment—
intrusion and extrusion.
1. Intrusion of the incisors teeth can be achieved by loading the
incisal edges of teeth. Intrusion is recommended in deep bite case.
Intrusion of molars can be achieved by loading the cusps alone of the
molars. The acrylic is ground from fossae and fissures. Molar
intrusion is indicated in open bite cases .
Activator trimming procedure for movement of teeth in vertical
plane. (A) Intrusion of incisors; (B) Intrusion of molars;

2. Extrusion of the incisor teeth can be achieved by loading the lingual
surfaces above the area of greatest convexity. Extrusion of incisors can
be enhanced by placing the labial bow also above the area of convexity.
This is indicated in open bite cases . Extrusion of molars is achieved by
loading the lingual surfaces above the area of greatest convexity in
maxilla and below in mandible. Molar extrusion is indicated in deep bite
cases .
(C) Extrusion of incisors; (D) Extrusion of molars; (E)
Selective eruption of molars.

During supraeruption of molars, selective trimming is
done. In this, either upper or lower molars are allowed
to erupt individually or both together .
(E) Selective eruption of molars.

Trimming for anteroposterior or sagittal movements. The following
movements can be achieved in the anteroposterior plane.
1. Protrusion of incisors can be produced by loading the entire lingual
surface of the incisors with acrylic . Protrusion can be achieved with
accessory elements, like protrusion springs, wooden pegs or gutta-percha.
Trimming for sagittal movements in activator. (A) Protrusion of incisors;

2. Retrusion of incisors is achieved by trimming away the
acrylic from behind the incisors and alveolar process. If
the labial bow touches the teeth, it also
causes tipping of incisors and is called ‘active bow’ .
(B) Retrusion of incisors;

3. Distal movement of molars: For distalizing movements, the guide
planes load the molars on the mesiolingual surfaces . The guide plane
extends to the area of greatest convexity. Distal movement of upper
molars is indicated in Class II malocclusion. Distal movement of lower
molars is indicated in Class III malocclusion. Distal movement can also
be achieved by active springs.
(C) Distal movement of posterior teeth; (A) loaded areas and (B) guide
planes. Arrow indicates distal movement of molars;

4. Mesial movement of molars: Mesial movement is achieved by the
guide planes contacting the teeth on the distolingual surfaces .
Guide planes extend to the greatest lingual circumference in the
mesiodistal plane. Mesial movement of posterior teeth in upper
arch is indicated in Class III malocclusion.
(D) Mesial movement of posterior teeth; (A) Loaded areas and (B)
guide planes. Arrow indicates mesial movement of molars.

5. Transverse movements with activator: If the construction bite is
shifted to one side, asymmetric action is created in the transverse plane.
Activator may also be trimmed to achieve lateral movements. But this is
not highly effective. For lateral movements, the lingual acrylic surfaces
opposite the molar teeth should be in contact. More effective expansion
can be achieved by incorporating jackscrews.
The activator (lingual view) showing the jack
screw
Activator with jack screw, for transverse
control

Guidelines for Clinical Control
It is important to ensure during treatment that the grooves maintain
their contact. Grinding of grooves should be done to facilitate
mesial and vertical eruption of lower teeth. Proper monitoring of
deep bite should be done. Reshaping of grooves and padding with
fast-setting self-cure acrylic in contact areas should be carried out.
Trimming of the activator for Class II
correction. Note the lower posterior segment is free
to erupt vertically and mesially, thus helping in the
correction of deep overbite and Class II relation

Wearing time of the appliance should be monitored. Appliance is to be
worn for 2–3 h during the first 2 weeks and then increased to full night-
time wear. Any trauma or sore spots should be grinded. possible.
changes that can be achieved with activator therapy

Retention Period
Retention period begins when the bicuspid exchange has been
completed and an adult Class I occlusion established. Average length
of retention period is 6–8 months following active treatment. Following
6 to 8 months of retention period, wearing of the appliance is gradually
tapered off over a period of 2–3 months.
A, B. Pre-treatment. Notice the anterior
crossbite. C. Class III activator was used. D,
E. Post-treatment. Notice normal overjet and
overbite. F. Superimposition of pre-and
posttreatment
shows extrusion of upper molar and
labioversion of upper incisors. (red: before
treatment, blue: after treatment)

activator. It permits day and night wear except as it is less bulky when compared
to conventional activator. The principle of treatment with bionator is not to activate
the muscles but to modulate muscle activity. This enhances normal development.
The palatal arch in the appliance serves to stabilize the appliance and also to
encourage the tongue and mandible to adopt a normal posture. The buccinator
loop prevents the cheek pressures from acting
Bionator
Bionator is an activator-derived device. It was introduced by Professor Wilhelm
Balters of Germany. Balters bionator is also referred to as ‘skeletonized
activator’. It is less bulky and elastic when compared to conventional
on the buccal segments, which cause passive expansion of the arch .

Philosophy of Bionator Appliance
According to Balters, the equilibrium between the tongue and circumoral
muscles is responsible for the shape of the dental arches and intercuspation
. The role of the tongue is considered decisive. This hypothesis supports the
early form and function concepts of van der Klaauw and the later functional
matrix hypothesis of Moss.
According to Balters, the
position of teeth is
determined by the
equilibrium between
tongue and circumoral
muscles
Bionator and its parts.

.
The purpose of the bionator is to establish good muscle
coordination and eliminate potentially deforming growth
restrictions, while unloading the condyle through a
protrusive mandibular position. The upper and lower
incisors usually are in contact during wear.

According to Balters’ philosophy, Class II malocclusions are the result
of a backward position of the tongue, which, in turn, generates faulty
deglutition and mouth breathing. The main objective of Class II
treatment with the bionator is to bring the tongue forward. This is
achieved partly by stimulation of the distal aspect of the dorsum of the
tongue by the posteriorly directed palatal archwire and partly by
anterior development of the mandible induced by the edge-to-edge
construction bite.

Class III malocclusions, conversely, are ascribed to
a forward position of the tongue and, therefore, in
the Class III bionator, the palatal arch is inverted,
with the round bend directed anteriorly. The
rationale of this is to train the tongue by
proprioceptive stimuli to remain in a more retracted
position.

The principle of treatment with bionator is not to activate the muscles but to
modulate muscle activity. This enhances normal development. Bite registration
is done only with sagittal advancement with minimal vertical opening.
The objectives of treatment with bionator are:
• Elimination of lip trap and abnormal relationship between the lips and incisor
teeth.
• Elimination of mucosal damage due to traumatic deep bite.
• Correction of tongue malposition and associated mandibular retrusion.
• Attainment of correct occlusal plane.
Standard Bionator.

There are three types of bionator:
1. Standard appliance—used to correct Class II division 1
malocclusion.
2. Screening appliance—used for the elimination of abnormal
tongue activity in open bite cases.
3. Reverse appliance—used for treatment of Class III malocclusion.
Lingual crib and lip bumper.
Standard Bionator.
Functional maxillary orthopedics in early
treatment of class II
malocclusions due to mandibular
retrusion: Case report
Revista Mexicana de Ortodoncia 2017;5 (3): e165-e169

Standard Appliance
Standard appliance (Eirew, 1981) consists of (1) acrylic component and
(2) wire components.
Construction Bite
This is taken in edge-to-edge incisor contact, if possible. In severe
overjet, phased or incremental advancement is advised.
Labial bow for the standard appliance
Construction Bite

Acrylic Component
The standard appliance consists of a flange of acrylic
covering the lingual aspects of the mandibular dental arch
but only small palatal areas of the maxillary molars and
bicuspids. The acrylic block is of minimal extent and
thickness so as not to encroach in the tongue space.

Acrylic starts from the distal of the upper canine to 2–3 mm
behind the first molars. It covers only 2–3 mm of mucosa
above the gingival margins of the upper and lower cheek
teeth. The upper and lower are joined by the interocclusal
acrylic block. This extends over half the occlusal surface of
the teeth.

Wire Components:
1. Palatal arch : Palatal arch is made rigidly of 1.2 mm wire. This
originates near the maxillary canine/first premolar embrasure. From
there, it rises vertically to the vault of the palate. Roughly on a line
joining the centers of first premolars or first deciduous molars, it turns
distally to form the palatal loop. It extends up to the line joining the distal
aspects of the first permanent molar.

The loop is egg-shaped, horizontal and 1 mm clear of the
mucosa. It is adapted to follow the contours of the palate. The
purpose of the palatal arch is to: (1) stabilize the appliance
and (2) encourage the tongue and mandible to adapt a more
anterior posture. The palatal arch should not be activated.

Wire components of bionator. Palatal arch (A) and vestibular arch showing labial
component and buccinator loop in different views (B, C).

2. Vestibular arch : The vestibular arch is made of
0.9 mm wire. It consists of two parts. The labial
portion of the vestibular arch is ideally shaped
and it should not touch the incisor teeth surface.
At the distal of lateral incisor, the wire bends
downward and distally to form the buccinator
loop.

Buccinator loop runs along the middle of the crowns of
posterior teeth standing 3 mm away from the tooth surface.
Buccinator loop extends as far as the embrasure between
deciduous second molar and first permanent molar of the
maxillary arch. From here, it makes a 90° rounded bend and
runs along the crowns up to the embrasure between canine
and deciduous first molar or premolar. It is anchored to the
acrylic here.

The buccinator bends are intended to
perform functions similar to the vestibular shields of the Frankel
appliances:
1. They prevent the soft tissues of the cheeks from intruding into the
interocclusal space, thereby facilitating eruption and occlusal plane
leveling in the buccal segments.
2. They hold the internal surfaces of the orobuccal capsule laterally,
encouraging transverse expansion of the maxillary dental arch.

Bionator must be worn day and night except while
eating. Time interval between successive appointments
is about 3–5 weeks. Trimming of facets are done as
required.
(A) Standard bionator appliance. (B) Bionator inside patient’s
mouth.

Indications and Contraindications of Bionator
Indications:
1. The bionator is useful in the treatment of Class II division 1 malocclusions in the
mixed dentition, par
ticularly those associated with habits and abnormal tongue function.
2. The bionator has an important role as a retention appliance:
a. Following correction of a Class II malocclusion in the mixed dentition with a bionator,
the same appliance is used for night-time retention.
b. After correction of Class II malocclusions by conventional fixed appliance therapy,
the bionator maintains and protects the dentoalveolar changes against disruption by
post-treatment growth. The bionator has greater patient acceptance in this application
than the activator, which, because of its bulk, looms as a major treatment phase.
c. The bionator is a suitable retention device following Herbst treatment.

3. The bionator is useful in the treatment of open bite due
to functional causes.
4. It is useful in correction of Class III malocclusion due
to retrognathic maxilla.
5. Bionator can also be used to correct TMJ problems.

Contraindications:
1. Labial flaring of lower incisors.
2. Anterior crowding.
3. In vertically growing patient.

Bionator for Open Bite Correction
This appliance is used to inhibit the abnormal posture and
function of the tongue. The construction bite is as low as
possible, but a slight opening in the posteriors will allow the
interposing acrylic to interfere with tooth eruption. Unlike the
standard appliance, the labial bow crosses the interincisal area
and the lingual acrylic extends into the upper incisor region as a
lingual shield to prevent the tongue thrusting.

Class III Reverse Bionator
This appliance is used to encourage the development of the
maxilla. Construction bite is taken in the most retruded position
possible. Lingual shield acrylic is extended behind the upper
incisors to guide them forward. The labial bow runs in front of the
lower incisors instead of the upper. The palatal bar runs forward
instead of posteriorly as in the standard appliance. The reasoning
behind this is to stimulate the tongue to remain in a retracted
position.

Various Modifications of Activator
Herren Shaye Activator
Herren states that the mandible along with the activator will not retain
its position during sleep. A slight unconscious lowering of the
mandible will detach the incisor from the maxillary parts and lessen
the effectiveness.

Since the correct posture of the mandible during sleep is
essential for the success of the activator therapy, the following
modifications are done:
• Sagittal positioning is overcompensated in the construction
bite advancing the mandible forward 3–4 mm beyond the
neutral relationship.
.

• Triangular arrowhead clasps are used to firmly seat
the appliance on maxillary dentition. Jackson clasp or
Duyzing clasp may be used as well.
• Long lingual flanges are constructed to hold the
appliance in position during sleep.
• In this modification, lower incisors bite on the acrylic
plane, impeding eruption of incisors and allowing the
posterior teeth to erupt occlusally thus leveling the
curve of Spee

Louisiana State University (LSU) or Activator of Shaye
It is essentially a modification of Herren activator. In this
appliance, the lower incisors bite on a plane formed by
the acrylic. Hence, growth in occlusal direction is
impeded. The eruption of premolars and molars is
achieved by selective grinding and the occlusal plane is
leveled.

Herren and LSU activators exert their actions mainly through
sagittal repositioning of the mandible. These appliances have the
following effects.
• During wear, the more forward positioning of the mandible hold
the retractor musculature of the mandible passively stretched. In
contrast the protractors, lateral pterygoid muscle (LPM) are
slackened. Simultaneously, a new sensory engram is registered
for the new positioning of the lower jaw.
.

• Even when the appliance is not worn, the mandible functions in a
more forward position in such a way that the retrodiscal pad is
much more stimulated and as a result of which there is earlier
beginning of condylar chondroblastic hypertrophy—and
consequently an increased growth rate of condylar cartilage takes
place (phantom activator phenomenon). Thus, LPM mediates the
action of the activator but the stimulating effect as condylar
growth appears to be produced almost exclusively during the time
that the appliance is not worn

Bow Activator of AM Schwarz
This is a flexible activator in which the upper and lower halves
of the activator are connected by a simple elastic bow (0.9 mm).
In the anterior area between the halves, a layer of rubber is
attached to act as a shock absorber and to open the incisors in
front. The advantages of this appliance are:
• Stepwise sagittal advancement is possible by periodic
adjustment of the bow.
• Transverse mobility was thought by Schwarz to provide an
additional stimulus.

• It can also be used in subdivision cases by activating
only the bow on the side of a unilateral distoclusion
• Maxillary and mandibular expansions can
independently be attempted by activating the screws
incorporated in the particular half of the appliance.

Reduced Activator or Cybernator of Schmuth
The acrylic part of the activator is reduced similar to the
bionator and the labial bow is used. Lower incisors are
covered by acrylic to hold them in a stable position. The
lower acrylic structure is split to permit expansion,
which prevents the frequent breakage in this region.

A coffin spring in the palatal portion is judiciously used to keep the parts
of the appliance in contact with the lateral teeth without pressure. This
will have a widening effect, especially when inserted during or soon after
the eruption of the lower incisors. Spurs may be used to prevent the
mesial drift of upper first molars. When the appliance is not split, the
appliance is stabilized and made more resistant by a lower labial bow.

Karwetzky Modification
This is similar to Schwarz bow activator. It consists of both upper
and lower active plates united by a ‘U’ bow in the region of the first
permanent molar. The ‘U’ bow has one shorter leg embedded in
the upper appliance and a long leg embedded in the lower plate.
By constricting the bow, i.e. narrowing the U-bend, mandibular
horizontal movements are created.

(A) Modified activator, lateral view. (B) Modifiedactivator, oblique
view. (C) Modified activator, backviewwith the adjustable U-claps. The
U-claps allow an anteriordisplacement of about 6–8 mm

The advantages of this modification are the following:
• It exerts a delicate influence on the dentition and TMJ.
• Mobility of the parts allows various mandibular movements.
• It allows sequential forward positioning.
• This appliance may also be used to supplement the treatment of
certain types of jaw fractures.
• The appliance can also be used in certain types of orthognathic
surgeries, like corticotomies and subapical resection.
U bow activator from Karwetzky.
U bow activation by making
the “U” smaller.

Wunderer Modification for Class III MO
The appliance is split horizontally with the upper and lower
portions connected by a screw (designed by Weisse) that is
embedded in an acrylic extension of the mandibular portion
behind the maxillary incisors..

As the screw is opened, the maxillary portion moves
anteriorly with a reciprocal posterior thrust on the
mandibular dentition. Occlusal surfaces of the posterior
teeth are covered with acrylic to enhance retention

Cutout or Palate-free Activator
Metzelder attempted to combine the advantages of the bionator
to the original Andresen–Häupl activator. This
is a modified activator wherein the maxillary acrylic portion covers only
the palatal or lingual aspects of the buccal teeth and a small part of the
adjoining gingival, while the palate remains free. It has a small screw
incorporated in the narrow anterior portion of the appliance and has a
labial bow of 0.9 mm diameter.

• There is no coffin spring in the palate. Stabilization is
provided by carrying the acrylic over occlusal surface over
some of the buccal teeth. Protrusion springs may be added
for lingually tipped upper incisors in Class II division 2
cases. The mandibular portion is the same as regular
activator.

Elastic Open Activator
This modified appliance is reduced in the anterior palatal region and is called
open activator. Its goal is to restore exteroceptive contact between the tongue
and palate. The standard appliance consists of bilateral acrylic parts, an upper
and lower labial wire, a palatal arch and guiding wires for the upper and lower
incisors. These wires will have different designs, depending on the treatment
objectives.

The acrylic parts extend from the canine posteriorly to the
point just behind the first or the second permanent molar.
The acrylic is thin in order to have a larger possible space
for the tongue. Stabilization of the acrylic portion is
accomplished by means of contact with the lingual surface
of the maxillary and mandibular canines.

Elastic Activator for Treatment of Open Bite
The intermaxillary, rigid acrylic of the lateral occlusal zones is replaced
by elastic rubber tubes. By stimulating the orofacial muscular system
by orthopedic gymnastics (chewing gum effect), activators intrude
upper and lower posterior teeth. Cribs can also be incorporated to
eliminate habits.

Combined Labial Bow
Eschler in 1952 developed a modification of the labial
bow with intermaxillary effectiveness. It consists of an
active part that moves the teeth and a passive part that
holds the soft tissue of the lower lip away, thus
enhancing tooth movement as desired.

Removable functional appliance 2

The Propulsor
This is designed by Muhlemann and refined by Hotz; it is a hybrid
appliance, with features of both monobloc and oral screen. A definite
advantage of propulsor over other activator-like appliances is in its
coverage and its ability to effect changes in the alveolar process.
This appliance does not carry any wire components. It is commonly
used in maxillary dentoalveolar protrusion.

Hamilton Expansion Activator
This appliance has a palatal
expansion screw and is bonded to
the maxillary arch. The lingual
flanges guide
the mandible into its correct anterior
construction bite via proprioception.

Petrik’s Modification
The activator modified by Petrik has simple
stiff sections of wire mesial to the permanent
first molars for stabilizing the sagittal and
vertical position of the activator (support bars).
In addition, it also has other stiff wire
constructions that deliver forces, during
occlusion, to specific teeth to promote their
movement.

Akkerman Fixed Appliance
Activator
Akkerman constructed an
activator that can be used as a
retainer after fixed appliance
treatment as well as in a
modified form during the
treatment.

Teuscher Activator
This is an example of an activator with headgear. The
appliance has headgear tubes placed in bite-blocks
in the deciduous molar region and four torquing
springs in the anterior region.

Van Beek Activator
It is another example of headgear–activator combination. The
short and strong outer bow is placed in the acrylic of the
activator between central and lateral incisors. The lower
incisors are covered by acrylic labially and the lingual surface
is let free. The upper incisors are also covered by acrylic.
Position of the mandible is achieved by lingual flanges.

Magnetic Activator Device
This magnetically active functional appliance was developed by Dellinger in the year 1993.
The types of magnetic activator devices are as follows:
• MAD I: Correction of lateral mandibular displacement;
• MAD II: Correction of Class II MO;
• MAD III: Correction of Class III MO;
• MAD IV: Correction of open bite.
Other modifications of activator are kinetor and bionator.
Removable MAD II
appliance with
Smart Clasps on
the molars and
torquing springs
on the upper
incisors used in
the study
evaluating the
dental and skeletal
effects of the
appliance.

(A-G) Magnetic Activator Device II (MAD II) appliance designed for severe Class II problems with
repulsive posterior and attractive anterior magnets (A-D). This design ensures the gradual forward posture of the
mandible between repulsive effects of the posterior and attractive effect of the anterior magnets (E-G).

Removable functional appliance 2

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Removable functional appliance 2