Movements with edgewise appliance /certified fixed orthodontic courses by Indian dental academy

Moments with the edgewise
appliance: Incisor torque control
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

 Will the crowns move or will the roots move?
 Which direction will they move?
 Will anchorage loss result?
 Will the overbite increase or decrease?
 Will spaces open or changes in arch perimeter
occur?
 Are the inherent reciprocal forces that
develop recognized?
 How are these forces controlled?

 The purpose of this article is to describe the
fundamental mechanics used in developing
incisor torque and to show clinical examples
effectively applying the principle of (1) the
moment of a couple and (2) the moment of a
force.

 Couple
-pair of equal and opposite parallel forces
-capable of rotating the tooth around a
center of rotation coincident with the center of
resistance
-cannot move the center of resistance
-measured as the magnitude of one of the
two equal forces times the distance between the
forces
-expressed in units, such as gram-millimeters.

 To evaluate equilibrium forces- insert wire
component only in the bracket part where
greater moment is placed. The direction of
remaining wire part dictates the direction of
equilibrating forces on the adjacent part.
 The direction and amount of net equilibrium
forces result from the amount of net moment
created at adjacent brackets.

 When the two bracket slot-wire axis angles are
in the same direction, the moments at each
bracket are in the same direction and their
equilibrium forces at each bracket are in the
same direction.
 when the two bracket slot-wire axis angles are
oriented in opposite directions, the resulting
equilibrium forces at each bracket are in
opposite direction and the net equilibrium force
is the difference between the larger and smaller
force at that tooth.
 Point contact at one end

 Length of the molar tube and the depth of
the incisor bracket differ markedly, this
difference will modify the moment- this issue
deserves further investigation.
 It is also possible to activate a torquing arch
upside down.

 Un-cinched
 Cinched - "rowboat" effect

 treatment of an anterior crossbite

Moment of a force
cannot cause a tooth to
rotate around its center
of resistance because a
force always acts to
displace the center of
resistance in the
direction the force

 So has a center of rotation located
somewhere between the center of resistance
and infinity determined by the moment to
force ratio present.
 In this ratio, the moment is the algebraic
combination of all moments arising from the
forces or couples acting to rotate the tooth.

 Point of attachment of basal arch
 Effect of insertion of basal arch in to anterior
brackets

 No work has ever been reported that shows
the extrusive force at the molar results in any
greater molar extrusion than that which is
readily attributable to normal vertical
growth.
 It is also possible to activate a base arch
upside down to produce extrusion of incisors.

 Uncinched
 Cinched- reverse
"rowboat" effect

 In the clinical application, the torquing arch is
used for incisor crown facial/root lingual
movement when open bite tendencies are
present.
 When excessive incisor overbite is present,
the base arch is used for the opposite
equilibrium effects.
 Arch perimeter changes are a function of
cinching or not cinching these systems.

 Inherently present equilibrium forces also
create moments of the force that must be
used or controlled
 Use of TPA

 All orthodontic force systems designed to produce
incisor torque must employ either the moment of a
couple or the moment of a force.
 Moment of a couple -The rotation that a couple
produces has its center of rotation at the center of
resistance. The equilibrium forces of a torquing arch
tend to produce incisor extrusion and molar intrusion.
A torquing arch may also produce molar crown
facial/root lingual rotation, lose posterior anchorage,
and increase arch perimeter depending on how it is
employed. Activating a torquing arch upside down
produces the same force systems, but all of their
directions are reversed.

 moment of a force- rotation occurs with a center
of rotation determined by, the moment to force
ratio present. The equilibrium forces of a base
arch tend to produce incisor intrusion and molar
extrusion. A base arch may also produce molar
crown lingual/root facial rotation, gain posterior
anchorage, and increase arch perimeter
depending on how it is employed. Activating a
base arch upside down produces the same force
systems, but all of their directions are reversed.

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Movements with edgewise appliance /certified fixed orthodontic courses by Indian dental academy

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Movements with edgewise appliance /certified fixed orthodontic courses by Indian dental academy