Activators/certified fixed orthodontic courses by Indian dental academy

ACTIVATOR
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INDIAN DENTAL ACADEMY
Leader in continuing dental education

HISTORY
 Kingsley in 1880 introduced the term- jumping the bite for
patients with mandible retrusion. He inserted a vulcanite
palatal plate consisting of an anterior incline that guided the
mandible in a forward position when the pt closed on it. This
corrected the sagittal relationship without tipping the lower
incisors forward.
 Hotz Vorbissplate was a modification of Kingsley plate. He
used it in case of deep bite retrognathism, when the overbite
was likely to cause a functional retrusion and the lower
incisors were lingually inclined by the hyperactivity of the
mentalis muscle and lower lip.

 The activator was originally used by Andresen with
vertical extensions to contact the lingual surfaces of
mandibular teeth. He developed a mobile loose-fitting
appliance that transferred functioning muscle stimuli
to the jaws, teeth and supporting tissues.
 The progenitor of the appliance was a modified
Kingsley plate that Andersen used as a retainer over
summer vacation for his daughter after he removed
fixed appliance used to correct distocclusion. Seeing
the improvement with this retainer, he called it
biomechanical working retainer.

 Pierre Robin – developed monobloc prior to Andersen
appliance.
 Andersen became associated with Haupl at the university of
Oslo. Both termed the appliance as Activator because of its
ability to stimulate muscle forces.
 Haulp concept of individual optimum. The limitation of the
appliance is that it cannot create a large mandible from a small
one, but can help pt achieve optimal size consistent with
morphogenetic pattern.
 The original appliance combined an upper and a lower plate at
the occlusal plane. Only one wire element was used- a labial
arch for the upper ant. teeth. To achieve expansion, the
appliance was split in the centre and a flexible coffin spring
was incorporated.

DRAWBACK OF ACTIVATOR
THERAPY
1. Dual bite can be a late consequence of activator
treatment with a false indication.
Indicated in retroposition of the condyle in the fossa
as a result of dominant retrusive activity of the
posterior temporalis, deep masseter and the hyoid
musculature associated with deep bite.
2. Jumping the bite should be performed without
proclination of the lower incisors. Failure of activator
therapy occurred as a result of overjet reduction due
to proclination of teeth instead of bodily anterior
positioning of the mandible.

EVOLUTION OF APPLIANCE
 Eschler – developed modification of the labial
bow that improved intermaxillary
effectiveness. One part was active, moving the
teeth, the other was passive, holding the soft
tissue of the lower lip away and thus
enhancing the tooth movement desired.

 The initial appliance was worn at night and hence its bulk
was not critical. Subsequent modifications made to reduce
the bulk allowed an increase in wearing time. They were two
types of modifications-
1. Some appliance consist of one rigid acrylic mass for the
maxillary and mandibular arches but with reduced
volume/bulk.
a. Appliance were reduced in the anterior palatal region- open
activator. Their goal is to restore exteroceptive contact
between the tongue and palate, which is prevented in the
classical activator. Pt prefer it as they are reduced in the
linguoincisal area and do not obstruct the oral cavity.

disadvantages- construction bite cannot be opened too far
vertically because it impairs the tongue function. The tongue
may thrust into the anterior interincisal gap, creating a postural
and functional abnormality.
elastic open activator ( Klammt)- lack of support in the cutaway
area of the appliance, especially if guidance of erupting teeth
or expansion is necessary.
b. Appliance with reduced alveolar region and with cross palatal
wires instead of full acrylic plate. They are supported/anchored
dentally. Hence due to their tooth borne anchorage their use is
limited and management can be difficult. The labial bow
eliminates abnormal muscle pressure by extending into the
buccal vestibule area.

2. Appliance consist of two parts joined with wire bows. The
muscle impulse are reinforced by the wire elements
incorporated in the design. The flexibility of the appliance
permits mandibular movements in all directions.
a. Schwartz double plate
b. Stockfish- elastic activator
Difference in the mode of action of rigid one piece activator
(long lasting tonic phase reflex contraction) and flexible two
piece joined by intermaxillary wiring (transient phase reflex
contraction)

SKELETAL AND
DENTOALVEOLAR EFFECT

FORCE ANALYSIS
 When activator activates the muscles, various types of forces are
created-
a. Static force- permanent and vary in magnitude and direction. They do
not appear simultaneously with the movement of mandible. Eg- forces of
gravity, posture and elasticity of soft tissue and muscle.
a. Dynamic force- interrupted, appear simultaneously with the movements
of the head and body and have a higher magnitude than static force. Eg-
swallowing
a. Rhythmic force- associated with respiration and circulation. They are
synchronous with breathing and their amplitude varies with the pulse.
Imp. In stimulating cellular activity. Mandible transmits rhythmic
vibrations to the maxilla. The applied forces are intermittent and
interrupted. Force application to the teeth are intermittent. Removal of
activator from mouth interrupts these forces.

 Two principles are applied in modern activator
therapy-
force application- muscle
force elimination- the dentition is shielded
away from normal and abnormal functional
and tissue pressure by pads, shields and wire
configuration.

 Types of forces employed in activator therapy-
a. Natural force- growth potential, eruption and migration of teeth. These can be
guided, promoted or inhibited by the activator.
a. Artificially functioning forces- muscle contraction and stretching of soft tissues
initiate forces when the mandible is relocated from its postural rest position by
the appliance. The activator stimulates and transforms the contractions. Whereas
the forces may be muscular in origin, their activation is artificial.
sagittal plane- effect on the condyle
vertical plane- teeth and the alveolar process are loaded with or relieved of
normal forces. If the construction bite is high it will inhibit the growth of maxilla
and influence the inclination of the maxillary base.
transverse plane- midline correction
c. Various active elements (springs, screws) can be built into the activator to
produce an active biomechanical type of force application.

CONSTRUCTION BITE
Horizontal H activator- low construction bite
with marked forward mandibular positioning
a. Class II functional retrusion
b. Class II Div 1 malocclusion with sufficient
overjet
c. Class II Div 1 malocclusion with posterior
positioning of the mandible caused by
growth deficiency but with the likelihood of
a future horizontal growth pattern

 Vertical V activator- high construction bite
with slightly anterior mandibular positioning
a. Class II Div 1 malocclusion with vertical
growth direction

FABRICATION OF ACTIVATOR

TRIMMING OF ACTIVATOR
 PRINCIPLES-
The movement and eruption of selected teeth
can be achieved by grinding away areas of
acrylic that contact the tooth surface.
Carefully planned grinding and trimming of the
activator in the tooth contact area improves its
effectiveness in the dentoalveolar region by
stimulating or restricting selective eruption and
movement of anterior and posterior teeth.

 The principles of force application in the trimming process
are determined by the typa, direction and magnitude of force
created by the loosely fitting appliance
a. Intermittent force- isotonic and isometric muscle contractions
enabling the appliance to work by utilizing kinetic energy.
b. The direction of the desired force is determined by selective
grinding of the acrylic surface that contact the u & l teeth.
After proper grinding the desired force acts on predetermined
areas of the teeth and applies pressure in the direction of
needed tooth movement.
.

c. The magnitude of force can be estimated by determining the
amount of acrylic contact with the tooth surface. If the force is
delivered to smaller portion of tooth surface, it is greater than
if broader contact occurs between the acrylic and broader tooth
surface. Acrylic surface that transmit the desired force and
contact the teeth are called guide planes.
d. Approximate trimming can be done on the plaster cast but the
final trimming is done in the mouth. Any undercut acrylic
surface that might interfere with planned tooth guidance must
be removed. Need for trimming can be assessed by-
explorer
observing the shadows created on the acrylic by the undercut

FOR VERTICAL CONTROL
 Intrusion
 Prevention of teeth from eruption
 Teeth are free to erupt and are stimulated to do
so by acrylic planes

INTRUSION OF TEETH
 Incisors-
Performed by loading the incisor edges
Indicated in deep overbite case

 Molars-
Performed by loading the cusps of teeth
Acrylic detail is ground away from the fissures
and fossas to eliminate any possible inclined
plane stimulation to molar movement
Indicated in open bite cases

EXTRUSION OF TEETH
 Incisor-
Loading the lingual surfaces above the area of
greatest concavity in the maxilla and below
this area in the mandible
Enhanced by placing the labial bow above the
area of greatest convexity
Indicated for open bite cases

 Molars-
Loading the lingual surfaces of teeth above the
area of greatest convexity in the maxilla or
below this area in the mandible
Indicated in deep bite cases

SELECTIVE TRIMMING OF THE
ACTIVATOR
 By this only the u & l molars are extruded
 Path of eruption of molars should be
considered
 In case of Class II malocclusion- eruption of
maxillary molar is inhibited while that of the
mandibular molars is stimulated
 In case of Class III malocclusion- eruption of
mandibular molar is inhibited while that of the
maxillary molars is stimulated

FOR SAGITTAL CONTROL
 By this protrusion or retrusion of incisors and
change in molar sagittal relationship mesially
or distally can be achieved.

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Activators/certified fixed orthodontic courses by Indian dental academy

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