Biomechanics of Space Closure

Biomechanics
of
Space
Closure
DEPARTMENT OF ORTHODONTICS AND
DENTOFACIAL ORTHOPAEDICS.
SEMINAR PRESENTATION
Presented by: Guided by:
Dr. Deeksha Bhanotia Dr. Mridula Trehan
M.D.S. Third year Professor & Head
Department of Orthodontics
and Dentofacial Orthopaedics

Biomechanics
of
Space
Closure
 Introduction.
 Relevance of center of resistance.
 Statistically determinate and indeterminate
system.
 Orthodontic space closure.
 Determinants of space closure.
 Fundamental concepts and clinical method of
anchorage control.
 Anchorage from a biomechanical perspective.

Biomechanics
of
Space
Closure
 Biomechanical strategies for differential space
closure.
 Center of resistance of anterior teeth during
retraction.
 Methods of canine retraction.
 Controlled space closure with a pre adjusted
appliance.
 Effects of overly rapid space closure.
 Inhibitors to sliding mechanics.
 Friction in sliding mechanics.
 Segmented approach to space closure
 T-loop
 Opus loop

Biomechanics
of
Space
Closure Introduction
Every object or free body has one point on which it can be perfectly
balanced. This point is known as the center of gravity
In a restrained body, such as a tooth, a point analogous to the center of
gravity is used; this is called the center of resistance.
By definition, a force with a line of action passing through the center of
resistance produces translation.
The center of resistance of a single-rooted tooth is on the long axis of the
tooth, probably between one third and one half of the root length apical to the
alveolar crest.
For a multirooted tooth, the center of resistance is probably between the
roots, 1 or 2 mm apical to the furcation.

Biomechanics
of
Space
Closure
Relevance of the center of resistance
First, the position of the center of resistance varies with root length
The tooth movement resulting from a force delivered at the bracket depends
upon the distance of the line of action of the force from the center of
resistance;
Identical forces applied to teeth with different root lengths can have different
effects.
A second important point is that the center of resistance varies with
alveolar bone height.
The movement of teeth in adults with alveolar bone loss will be different than
in adolescents.
Smith RJ, Burstone CJ.Mechanics of tooth movement.AJODO1984;85(4):294-307.

Biomechanics
of
Space
Closure
The M/F ratio is the relationship between the applied force and the counterbalancing
couple
The type of movement is dictated by the moment to force ratio (M/F) generated by
the appliance at the attachments.
Typically, M/F ratios of approximately 7:1 millimeters result in controlled tipping,
10:1 millimeters result in translational movements, and values of 12:1 millimeters
or greater accomplish root movement.
This has important implications.
It is the ratio between the applied couple and force that determines the type of
tooth movement, not the absolute magnitudes.
Smith RJ, Burstone CJ.Mechanics of tooth movement.AJODO1984;85(4):294-
307.

Biomechanics
of
Space
Closure
These ratios are based on the assumptions that
the root lengths are 12 millimeters,
the distance from the bracket slot to the alveolar crest is five millimeters,
the alveolar bone condition is normal,
the axial inclination of the teeth is normal,
and the center of resistance is located apically a distance .40 times the root
length when measured from the alveolar crest to the apex.
Manhartsberger C, Morton JY, Burstone CJ.Space closure in adult patients using
the segmented arch technique. Angle Orthodontist1989;59(3):205-210.

Biomechanics
of
Space
Closure
Force systems can be defined as statically determinate when the
moments and forces can be readily determined, measured and evaluated
.
Statically indeterminate systems are too complex for precisely
determining all the forces and moments in the equilibrium.
Usually only the direction of the net moment and the appropriate net
force levels can be determined.
Determinate systems in orthodontics are those in which a couple is
created in one end of an attachment with only a force and not a couple at
the other end .e.g. a spring which is inserted to a tube or bracket at one
end and tied at the other end to only one point.
STATICALLY DETERMINATE AND INDETERMINATE
SYSTEMS
Proffit WR, Sarver DM.Contemporary Orthodontics elsevier.2013(5);530-555

Biomechanics
of
Space
Closure
Orthodontic space closure
should be individually tailored
based on the diagnosis and
treatment plan.
The selection of any treatment
whether a particular technique,
stage spring or appliance
designs should be based on the
desired tooth movement.
Orthodontic space closure
Braun S, Marcotte M.Rationale of the segmented approach to orthodontic
treatment. A JODO 1995;108:31-8.

Biomechanics
of
Space
Closure
A well-designed appliance should exhibit three general
characteristics:
(1) It should deliver a known, relatively constant moment-to-force
ratio over a long range of activation;
(2) the resultant motion of the active unit (teeth being moved)
occurs about a predictable center of rotation; and
(3) the force system at the reactive unit (anchor teeth) should be
known and controllable.
Braun S, Marcotte M.Rationale of the segmented approach to orthodontic
treatment. A JODO 1995;108:31-8.

Biomechanics
of
Space
Closure
(1) Differential space closure..
(2) Minimum patient cooperation.
(3) Axial inclination control
(4) Control of rotations and arch width.
(5) Optimum biologic response.
(6) Operator convenience.
The six goals to be considered for
any universal method of space closure:
To achieve controlled extraction site closure, the appliance used must deliver
definable force systems regulated by the clinician and not produce closure in
some ambiguous, indeterminate way. Only when force systems are definable
are the dental movements predictable and treatment outcomes forecast able
with confidence.
Burstone CJ.The Segmented arch approach to space closure. AJODO 1982;82(5):361-378.

Biomechanics
of
Space
Closure
Space closure should result in upright well aligned teeth with parallel
roots and parallel occlusal plane.
Therefore some degree of bodily or even root movement is required.
Idealized objective of space closure:
Burstone CJ.The Segmented arch approach to space closure. AJODO
1982;82(5):361-3

Biomechanics
of
Space
Closure
Amount of crowding:
in cases of severe crowding, anchorage
control is very important to
maintain the extraction space for
relieving the anterior crowding
Anchorage
using the same mechanics for different
anchorage needs is very important.
Traditional anchorage methods like
lip bumpers, headgears,
transpalatal arches may be utilized
but non compliance methods for
anchorage control based on
biomechanics can also be used.
DETERMINANTS OF SPACE CLOSURE
Nanda R.Biomechanics and esthetic strategies in clinical orthodontics. elsevier.2008(5);1-16
The main factors which determine the tooth movement during space closure are:

Biomechanics
of
Space
Closure
Axial inclination of canines
the same force /and or moment applied to teeth with different axial
inclinations will result in different types of tooth movement.
Nanda R.Biomechanics and esthetic strategies in clinical orthodontics.
elsevier.2008(5);1-16

Biomechanics
of
Space
Closure
Midline discrepancies and left right symmetry.
Midline discrepancies should be corrected as early as
possible in treatment as it allows the remaining space closure to be
completed symmetrically. Using asymmetric mechanics can cause in
unilateral anchorage loss, skewing of the dental arches, or unilateral
vertical forces.
Vertical dimension
Control of vertical dimension is essential in space closure.
Undesired vertical extrusive forces on the posterior teeth can result
in increased LAFH, increased interlabial gap, and excessive gingival
display. Class II elastics may potentate this problem.
elsevier.2008(5);1-16

Biomechanics
of
Space
Closure
It is the ability to prevent tooth movement of one group of teeth while
moving another group of teeth.
The problem of anchorage is rooted in Newton’s third law:
For every action there is an equal and opposite reaction.
Several anchorage control methods have been developed over the last
century.
The contributions of Angle, Begg , Case, Tweed and others have provided
a foundation for modern orthodontic mechano therapy.
Although each of them advocated different methods and philosophies, a
review of their work shows a lot of similarities.
FUNDAMENTAL CONCEPTS AND CLINICAL METHODS
OF ANCHORAGE CONTROL
Kulberg AJ, Priebe DN.Space Closure and anchorage control.Semin Orthod .2001;7:42-49.

Biomechanics
of
Space
Closure
In 1907, EH Angle advocated 5 types of anchorage control.
Occipital anchorage depended on the use of extra oral anchorage
Intermaxillary anchorage included the use of elastics.
The remaining three were dental anchorage:
Simple, reciprocal and stationary methods for dental anchorage.
Calvin S Case also advocated stationary anchorage methods despite his
differences with Angle’s school of thought.
He also described the use of extra oral and intermaxillary anchorage as well
as the prerequisite that resistance to tipping movements was requisite for
intra arch control.
Case advocated the use of soldered firm attachment of anchorage teeth to one
another to maintain their upright positions.

Biomechanics
of
Space
Closure
20 years later Charles Tweed advocated similar techniques. His method
of anchorage preparation against unwanted tipping and extrusive side
effects were a series of tip back bends to anchor the teeth like tent stakes
to resist vertical and anterior posterior displacement during intermaxillary
traction.
Although Tweed said his methods of anchorage preparation were more
mechanical than biological, the tip back bends were a further refinement
of Angle’s stationary anchorage methods.
Despite his adherence to the differential force theory, PR Begg
also used a similar technique for anchorage control. His tip back bend to
maintain the anteroposterior position of teeth to effect preferential
movement of teeth was also supplemented by initially tipping the teeth to
be retracted followed by up righting them.

Biomechanics
of
Space
Closure
A ANCHORAGE
This category describes the critical maintenance of the posterior tooth
position.
75% or more of the extraction space is needed for anterior retraction.
Group A arches tend to be of two types:
B ANCHORAGE
This category describes relatively symmetric space closure with
equal movement of the anterior and posterior teeth to close the space.
This is the least difficult of the space closures.
C ANCHORAGE
This category describes non critical anchorage, where 75% or more
of the space closure is achieved through mesial movement of the posterior
segment; this could also be described as critical anterior anchorage.
Anchorage can be classified as:

Biomechanics
of
Space
Closure
Dividing the extraction space into quarters aids in visualizing the anchorage
classification
elsevier.2008(5);1-16

Biomechanics
of
Space
Closure
The basic techniques for anchorage control basically rely on three fundamental
similarities:
extra oral forces on the anchorage unit
intermaxillary elastics
Tipping tooth movement while simultaneously discouraging tipping
of anchorage teeth.
Patient compliance is mandatory for the first two techniques.
Without co operation control of tooth movement is lost and the results may be
compromised.
The way a tooth moves is dependent on the nature of the force systems that act
on it. This includes the actual force and moments at the bracket, the force
distribution around the periodontal ligament,.
The force distribution is a function of the centre of rotation.
ANCHORAGE FROM A BIOMECHANICAL PERSPECTIVE:
elsevier.2008(5);1-16

Biomechanics
of
Space
Closure CONTROLLED TIPPING:
Is tooth movement with the center of rotation at the root
apex. The resultant forces are distributed at the marginal
portion of the periodontal ligament
The M/F ratio is approx. 7/1
TRANSLATION or bodily movement maintains the axial
inclination of the tooth and the centre of rotation is at
infinity. The resultant force on the PDL is equally
distributed along the pressure side of the alveolar
structures.
The M/F ratio is approx. 10/1
ROOT MOVEMENT or displacement of the tooth apex
while the crown remains stationary occurs with a M/F
ratio of approx. 12/1 here forces tend to be concentrated
on the apical third of the root.
Within these basics lie the fundamental
principles of anchorage control.

Biomechanics
of
Space
Closure
What happens when a high M/F ratio is applied to the anchor teeth?
An applied force causes uncontrolled tipping while the applied
moment counteracts the tipping effect of the force. This applied
moment acts in the opposite direction and moves the roots to the
extraction site and if the magnitude further increases, tips the crown
distally
A low M/F ratio produces tipping with the crown moment
noticeably greater
How can these forces be produced clinically?
If M/F ratio of posteriors> M/F ratio of the anteriors there must be
either unequal forces or unequal moments
Unequal forces can be produced by headgear, J hook headgear, and
intermaxillary elastics. Unfortunately this is co operation dependant

Biomechanics
of
Space
Closure
The ideal for system for a group A space closure would have only a force
system resulting in anterior translation and no forces acting on the
posterior teeth thereby maintaining perfect anchorage control.
This is possible only with extraoral anchorage or if the opposite arch is used
as anchorage.
Two approaches:
differential forces
differential moment to force ratios
group A requires the posterior segment to have higher M/F ratios (when the
force is reduced M/F is increased) and the anterior segment to have a
decrease in M/F ratios.
BIOMECHANICAL STRATEGIES FOR
DIFFERENTIAL SPACE CLOSURE:
elsevier.2008(5);1-16

Biomechanics
of
Space
Closure Center of resistance of anterior teeth during retraction
The location of the center of resistance of various consolidated units of the
maxillary anterior dentition was studied using a dry human skull when
subject to retrusive forces.
The units studied consisted of
(a) two central incisors,
(b) four incisors, and
(c) six anterior teeth.
The laser reflection technique and the holographic interferometric
technique were employed to measure the displacement of the dentition
to the applied forces.

Biomechanics
of
Space
Closure
1. For an anterior segment comprising two central incisors,
the center of resistance was located on a projection line parallel to the
midsagittal plane on a point situated at the distal half of the
canines.
2. For an anterior segment that included the four incisors, the center of
resistance was situated on a projection line perpendicular to the
occlusal plane between the canines and first premolars.
3. For a rigid anterior segment that included the six anterior teeth, the
center of resistance was situated on a projection line perpendicular
to the occlusal plane distal to the first premolar.
Results:
Bulcke MMV, Burstone CJ,Sachdeva RL,Dermaut LR.Location of the centres
of resistance for anterior teeth during retraction using laser reflection
technique.AJODO;1987;91:375-84.

Biomechanics
of
Space
Closure
4. The centers of resistance of the anterior segments incorporating
two or four anterior teeth were within ± 2 mm of each other.
However, inclusion of the canines in the anterior segment resulted in
the center of resistance moving distally by approximately one
premolar width (7 mm). This effect may have been the result of the
resistance of bony structures at the level of the canines and some
bending of the maxillary complex as was observed on the
holograms.
5. No appreciable shift in the location of the centers of resistance of
the various segments studied was detected as varying magnitudes of
retractive force were applied.
Bulcke MMV, Burstone CJ,Sachdeva RL,Dermaut LR.Location of the centres
of resistance for anterior teeth during retraction using laser reflection

Biomechanics
of
Space
Closure METHODS OF CANINE RETRACTION:
Friction
Frictionless ( PG spring, Burstone T loop, Ricketts)
METHODS OF ENMASSE RETRACTION:
OF FOUR INCISORS
Friction
Frictionless
PG retraction spring,
Utility arch, Omega Loop archwire
Extraoral
Headgears
OF SIX ANTERIORS
Closing loop archwire
Burstone T loop continuous archwire
Opus loop
INTRUSION AND RERACTION OF FOUR INCISORS
Burstone’s three piece intrusion arch
Rickets retraction and intrusion utility arch
SIMULTANEOUS INTRUSION AND RETRACTION OF SIX ANTERIORS
K-sir arch

Biomechanics
of
Space
Closure
The most significant distinction between the mechanics of
standard edgewise and preadjusted appliances was observed
during space closure.
With standard edgewise appliances, rectangular archwires did not
effectively slide through the posterior bracket slots because of the
1st-, 2nd-, and 3rd-order bends.
The orthodontist normally used a closing loop arch, which was
activated in the office by opening the closing loop and moving the
archwire through the posterior bracket slots
- Mclaughlin, Bennet, Trevisi.Systematized orthodontic treatment mechanics.Mosby
2001(1)

Biomechanics
of
Space
Closure
The level bracket slot alignment of the new appliances allowed
archwires, for the first time, to move more effectively through the
posterior slots when the patient was not in the office.
As a result, many orthodontists discontinued use of closing loops and
began using various forms of sliding mechanics— for example, placing
hooks in the anterior sections of straight archwires and tying elastics or
springs to them from molar brackets
Mclaughlin, Bennet, Trevisi.Systematized orthodontic treatment
mechanics.Mosby 2001(1)

Biomechanics
of
Space
Closure
Closing loop arches had several
disadvantages:
1. Extra wire-bending time
2. Poor sliding mechanics
3. Tendency to run out of space for activation
(after two or three activations, the omega loop
contacted the molar bracket and the archwire
had to be adjusted or remade)
4. High initial force levels
They also had advantages:
1. Precise control of the amount of loop
activation (often as little as 1mm), limiting
the amount of initial tipping
2. Adequate rebound time for uprighting
between appointments (with minimal
activations, loops closed quickly with little
tipping)

Biomechanics
of
Space
Closure Sliding mechanics had these advantages:
1. Minimal wire-bending time
2. More efficient sliding of archwires through posterior bracket slots
3. Sufficient space for activations
But sliding mechanics at first also had disadvantages:
1. No established guidelines on amounts of force to be used during
space closure
2. Tendency for initial overactivation of elastic and spring forces,
causing initial tipping and inadequate rebound time for uprighting
2001(1)

Biomechanics
of
Space
Closure
To maximize the advantages and minimize the disadvantages of
sliding mechanics
• force levels are reduced during space closure.
• Instead of springs or over activated elastics (which
can produce 500g of force), single elastic modules are attached
to anterior archwire hooks with ligature wires extended
forward from the molars
These "elastic tiebacks", when activated 2-3mm, generate
about 100-150g of force.
If the arches have been properly leveled, such light force allows
for effective space closure; there is little tipping with
subsequent binding of the archwires, and leveling is maintained
.
2001(1)

Biomechanics
of
Space
Closure
019" × .025" archwires with .022" slots provide optimum
rigidity, but adequate freedom for the wires to slide through the
slots.
Round wires and smaller rectangular wires provided less
precise control of torque, curve of Spee, and overbite.
Hooks of .024 " stainless steel or .028 " brass are soldered to
the upper and lower archwires
2001(1)

Biomechanics
of
Space
Closure
Space closure typically occurs
more easily in high-angle patterns
with weak musculature than in
low-angle patterns with stronger
musculature. The rate of closure
can be increased, particularly in
high-angle cases, by slightly
raising the force level or using
thinner archwires. However, more
rapid space closure can lead to
loss of control of torque, rotation,
and tip.
Effects of Overly Rapid Space Closure

Biomechanics
of
Space
Closure
Loss of torque control results in upper
incisors being too upright at the end of
space closure with spaces distal to the
canines and a consequent unaesthetic
appearance. The lost torque is difficult
to regain. Also, rapid mesial movement
of the upper molars can allow the
palatal cusps to hang down, resulting in
functional interferences, and rapid
movement of the lower molars causes
"rolling in"

Biomechanics
of
Space
Closure
Reduced rotation control can be
seen mainly in the teeth adjacent to
extraction sites, which also tend to
roll in if spaces are closed too
rapidly
Reduced tip control produces
unwanted movement of canines,
premolars, and molars, along with a
tendency for lateral open bite. In
high-angle cases, where lower
molars tip most freely, the elevated
distal cusps create the possibility of
a molar fulcrum effect

Biomechanics
of
Space
Closure
In some instances, excessive
soft-tissue hyperplasia
occurs at the extraction sites
,this is not only unhygienic,
but it can prevent full space
closure or allow spaces to
reopen after treatment. Local
gingival surgery may be
necessary in such cases.

Biomechanics
of
Space
Closure
Proper alignment of bracket slots is essential to eliminate
frictional resistance to sliding mechanics. The common
procedure is to use .018" or .020 " round wire for at least one
month before placing .019"´.025" rectangular wires. Leveling
and aligning continues for at least a month after insertion of the
rectangular wires, and that space closure cannot proceed during
that period.
Inhibitors to Sliding Mechanics
2001(1)

Biomechanics
of
Space
Closure
Therefore the rectangular wires are tied passively for at
least the first month, until leveling and aligning is complete
and the archwires are passively engaged in all brackets and
tubes
Conventional elastic tiebacks are than placed ,In some cases,
this phase takes three months.
2001(1)

Biomechanics
of
Space
Closure
First-order or rotational
resistance
at the mesiobuccal and
distolingual aspects of the posterior
bracket slots is produced by
rotational forces on the buccal
aspects of the posterior teeth.
The most effective way to
counteract this resistance is to
apply intermittent lingual elastic
forces—
one month from cuspid to first
molar, the next month from cuspid
to second molar.
There are three primary sources of friction during space closure
2001(1)

Biomechanics
of
Space
Closure
Second-order or tipping resistance
at the mesio-occlusal and distogingival
aspects of the posterior bracket slots is
caused by
excessive and overactivated
tieback forces, which lead to
• tipping of the posterior teeth,
• inadequate rebound time to
upright these teeth,
• and a resultant binding of the system.
The importance of light forces (50-
150g) and minimal activation length (to
provide time for uprighting) cannot be
overemphasized.
2001(1)

Biomechanics
of
Space
Closure
Third-order or torsional resistance
occurs at any of the four areas of the
bracket slot where the edges of the
archwire make contact.
Like tipping resistance, this is produced
mainly by
excessive and overactivated
tieback forces, which cause the upper
posterior lingual cusps to drop down
and the lower posterior teeth to roll in
lingually
2001(1)

Biomechanics
of
Space
Closure
1. Inadequate leveling, resulting in archwire binding
2. Posterior torque such that torquing and sliding cannot occur
simultaneously
3. Blockage of the distal end of the main archwire by a ligature wire
4. Damaged or crushed brackets that bind the main archwire
5. Soft tissue resistance from build-up in extraction sites
6. Cortical plate resistance from a narrowing of the alveolar bone in
extraction sites
7. Excessive force, causing tipping and binding
8. Interferences from teeth or the opposing arch
9. Insufficient force
Constant attention is required to prevent any of the
following inhibiting factors:
2001(1)

Biomechanics
of
Space
Closure
Friction is a function of the relative roughness of two surfaces in contact. It is
the force that resists the movement of one surface past another and acts in a
direction opposite the direction of motion.
VARIABLES AFFECTING FRICTIONAL RESISTANCE DURING
TOOTH MOVEMENT
PHYSICAL
ARCHWIRE
LIGATION
BRACKET
ORTHODONTIC APPLIANCE
BIOLOGICAL
SALIVA
PLAQUE
ACQUIRED PELLICLE
CORROSSION
elsevier.2008(5);1-16

Biomechanics
of
Space
Closure PHYSICAL
ARCHWIRE
crossectional size/shape
material
surface texture
stiffness
LIGATION
ligature wires
elastomerics
self ligating brackets
BRACKET
material
manufacturing process
slot width and depth
first/second/third order bends
ORTHODONTIC APPLIANCE
interbracket distance
level of bracket slots between adjacent teeth
forces applied for retraction
BIOLOGICAL
Saliva
Plaque
Acquired pellicle
Corrosion
elsevier.2008(5);1-16

Biomechanics
of
Space
Closure
The segmental arch technique as
developed by Burstone utilizes
T loop space closure springs for
anterior retraction, symmetric
closure or posterior protraction.
The segmental T loop as
described by Burstone is one of
the most versatile space closure
devices available.
One of the main principles of the segmental arch technique is considering
the anterior segment and posterior segment as one large tooth
respectively. The right and left buccal units are connected by a
transpalatal arch forming one big posterior unit.
The basic configuration of the TMA loops consists of a .017X.025” TMA
wire.
Burstone CJ.The Segmented arch approach to space closure. AJODO 1982;82(5):361-378.

Biomechanics
of
Space
Closure
The advantages of the T-loop design over a vertical loop
is that the T-loop produces a higher M/F ratio, a lower load-deflection
rate, and delivers a more constant force and M/F ratio
Often in adult patients, where no growth is anticipated, extraction
therapy is performed. The situation is often complicated through loss
of bone. In order to maintain an assumed stress magnitude and
distribution under the condition of reduced bony support area, force
magnitude must be reduced and the M/F ratio must be increased.
The necessity of producing a lower load deflection rate in such cases
suggests the use of a wire with lower stiffness
SEGMENTED ARCH TECHNIQUE FOR SPACE CLOSURE IN ADULTS:
Manhartsberger C, Morton JY, Burstone CJ.Space closure in adult patients using the segmented
arch technique. Angle Orthodontist1989;59(3):205-210.

Biomechanics
of
Space
Closure
The rate of decay of the force applied by a spring is called
the load-deflection rate, and it averages 33 Gm. per
millimeter in the Burstone’s T loop.
The low load-deflection rate is important in this spring,
since it enables the orthodontist to deliver optimal
magnitudes of force.
Manhartsberger C, Morton JY, Burstone CJ.Space closure in adult patients using
the segmented arch technique. Angle Orthodontist1989;59(3):205-210.

Biomechanics
of
Space
Closure
.
The attachment on the posterior tooth (segment) is a 0.018 by 0.025 inch
auxiliary tube on the first molar, and the one on the anterior tooth (segment) is
an auxiliary vertical tube on the canine bracket
Manhartsberger C, Morton JY, Burstone CJ.Space closure in adult patients using the
segmented arch technique. Angle Orthodontist1989;59(3):205-210.

Biomechanics
of
Space
Closure
Differential moments are obtained by the principle of off center V bends
which results in unequal moments. the closer the V bend is to the tooth
the higher the moment. the segmented T loops approximated a V bend.
Clinically the spring needs to be positioned at least 1-2mm closer to one
side than another to obtain a moment differential.
Manhartsberger C, Morton JY, Burstone CJ.Space closure in adult patients using the
segmented arch technique. Angle Orthodontist1989;59(3):205-210.

Biomechanics
of
Space
Closure
This demonstrates another method
that may be used for controlling the forces
and moments produced by segmented
0.017 ´ 0.025-inch TMA T-loop springs or
closing loops in general.
Previously, the approach described for
achieving differential alpha/beta moments
with segmented T-loops used asymmetric
angulations of the preactivation bends.
However, with this method the
moment differential does not remain
constant with spring activation, i.e., the
moment differential is dependent on both
spring activation and the differences in the
preactivation angulations.
OFF CENTERED T LOOPS
Kulberg AJ, Priebe DN.Space Closure and anchorage control.Semin Orthod

Biomechanics
of
Space
Closure
The T loop is positioned closer to the
posterior segment
(1-2 mm off centering) is sufficient .
activation of 4 mm is necessary.
This reduces the horizontal forces
without altering the moment
differential.
The force system acting on the anterior
segment favors tipping. The moment
difference remains as the space closes
and the spring deactivates.
The spring must be re activated when 2
or less mm of activation remains.
MAXIMUM POSTERIOR ANCHORAGE:
(Group A anchorage)
Kulberg AJ, Priebe DN.Space Closure and
anchorage control.Semin Orthod
.2001;7:42-49.

Biomechanics
of
Space
Closure
CONTROL OF THE SIDE EFFECTS OF SPACE CLOSURE:
Careful monitoring is essential during space closure.
A frequently overlooked side effect of space closure is the first order side
effects.
The mesially directed buccally located force of the molar may lead to the
erroneous supposition that there is anchorage loss.
Distalization is not necessary . A mesially out directed force is all that is
needed to regain the original molar position.
A transpalatal arch provides an excellent mean to prevent this or actively
corrects it.
.2001;7:42-49.

Biomechanics
of
Space
Closure
CORRECTION OF THE SIDE EFFECTS
Tipping of the anterior and posterior teeth into the extraction space
Increase the alpha and beta moments
Flaring of the anterior teeth
Reduce the alpha moment or increase the distal activation
Mesial in rotation of the buccal segments
Mesial out rotation of the palatal arch, archwire or lingual arch
Excessive lingual tipping of the anterior teeth
Increase the alpha moment
.2001;7:42-49.

Biomechanics
of
Space
Closure
The OPUS loop was designed to deliver an inherent M/F ratio
sufficient for enmasse space closure via translation of teeth of
average dimensions with no bone loss.
Because its inherent M/F ratio is high enough no preactivation
bends is needed before insertion
The neutral position is the passive position of the spring as it sits
before insertion.
Simple cinch back activations can take care of the tooth movement
thresholds to meet anchorage objectives.
Siatkowski RE.Continuous arch wire closing loop design, optimization and
verification . AJODO 1997;112:487-95.

Biomechanics
of
Space
Closure
The apical horizontal leg is 10mm long,
The ascending legs at an angle of 70 degrees to the plane of the brackets
The apical helix is on the leg ascending from the anterior teeth, (that
ascent must begin within 1.5mm posterior to the most distal bracket of the
anterior teeth being retracted)
The spacing between the ascending legs especially the apical loops legs
must be 1mm or less
All these dimensions are critical to the performance of the loop.
Clinically comfort bends are not necessary.

Biomechanics
of
Space
Closure
The advantage of having the opus loop formed in 17X25 TMA is that it
provides a relatively long range of activation;
unfortunately it is difficult to bend the wire with sufficient incisor torque
to reduce the wire play.
It is difficult to contour the loop for comfort on one side without altering
the other side also and a large stock of wires is necessary for preformed
wires.
This can be over come by having:
An anterior wire of Niti alloy with two separate 17X25 TMA posterior
segments, which are attached by a Forestadent cross tube
This bialloy has the following advantages:
Infrequent activations
Ease of comfort bending
Incisor axial inclination control

Biomechanics
of
Space
Closure
Siatkowski
RE.Continuous
arch wire closing
loop design,
optimization and
verification .
AJODO
1997;112:487-95.

Biomechanics
of
Space
Closure
Although less so than with other closing loop designs, Opus loops do
have the potential to steepen the cant of occlusal plane in the maxillary
arch and flatten it in the mandibular arch.
Although steepening occlusal plane can be useful for overtreatment of
Class III relationships (and flattening occlusal plane for Class II
relationships), that potential should be monitored for possible
intervention.
Such intervention could be reducing maximum activation force levels or
using an occipital headgear with short and high outer bows to generate a
moment tending to flatten maxillary occlusal plane.
For the most severe anchorage required to achieve treatment goals,
second molars, if available, could be included with the posteriors and/or a
Combi headgear used.
For less severe or moderate anchorage, the canines could be incorporated
with the anteriors
DISADVANTAGES OF THE OPUS LOOP

Biomechanics
of
Space
Closure
The closing loop arch wire generates the moments required and some of the
protraction force.
Most of the protraction force is generated by the large anterior moment and by
the intermaxillary elastics to a rigid rectangular arch wire in the opposing arch.
Intermaxillary Niti closed coil springs capable of delivering 150 gm force can be
substituted for the elastics. The potential exists for changing occlusal plane in the
opposing arch. Should such cant changes begin to be observed, the
intermaxillary force can be reduced.
The configuration for posterior protraction

Biomechanics
of
Space
Closure
In group C anchorage cases, class III elastics with a force of
150gms/side from the opposite arch which has a rigid rectangular
stainless steel archwire can be used.
Another alternative is to use TP 256 torquing auxiliary which when
overlaid over the closing loop provides an additional protraction force
to the posteriors.
It has the following advantages:
The clinician is free to continue treatment in the lower arch
Undesired vertical forces from the elastics are not a problem
Posterior arch width increases are not a problem when using a
TMA wire

Biomechanics
of
Space
Closure
The clinical discipline of orthodontic space closure requires complete
understanding of its complexities
Just as an orthodontist is provided with innumerable alternatives of
appliance systems, it is imperative to be aware it the merits as well as
the limitations of the techniques involved
Mechanical as well as biologic factors must be considered in selecting
the appliance best suited for the patient
Conclusion

Biomechanics
of
Space
Closure
 Smith RJ, Burstone CJ.Mechanics of tooth
movement.AJODO1984;85(4):294-307.
 Braun S, Marcotte M.Rationale of the segmented
approach to orthodontic treatment. A JODO
1995;108:31-8.
 Manhartsberger C, Morton JY, Burstone CJ.Space
closure in adult patients using the segmented arch
technique. Angle Orthodontist1989;59(3):205-210.
 Nanda R.Biomechanics and esthetic strategies in
clinical orthodontics. elsevier.2008(5);1-16

Biomechanics
of
Space
Closure
 Kulberg AJ, Priebe DN.Space Closure and
anchorage control.Semin Orthod .2001;7:42-49.
 Bulcke MMV, Burstone CJ,Sachdeva RL,Dermaut
LR.Location of the centres of resistance for anterior
teeth during retraction using laser reflection
 Burstone CJ.The Segmented arch approach to space
closure. AJODO 1982;82(5):361-378.

Biomechanics
of
Space
Closure
 Siatkowski RE.Continuous arch wire closing loop
design, optimization and verification . AJODO
1997;112:487-95.
 Proffit WR, Sarver DM.Contemporary Orthodontics
elsevier.2013(5);530-555
 Mclaughlin, Bennet, Trevisi.Systematized
orthodontic treatment mechanics.Mosby 2001(1)

Biomechanics of Space Closure

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