Friction less mechanics in orthodontics /certified fixed orthodontic courses by Indian dental academy

FRICTIONLESS
MECHANICS

www.indiandentalacademy.com

INDIAN DENTAL ACADEMY
Leader in continuing dental education








Friction, in general, is the resisting force on the
relative lateral motion of solid surfaces, fluid
layers or material elements in contact.
In orthodontics, friction is the state of drift
between archwire and the bracket slot.
It is a factor which causes the loss of forces
provided during retraction.


Important definitions


FORCE is defined as an act upon a body that
changes or tends to change the state of rest or
motion of the body. Force is a vector it has
both magnitude and direction. Direction
consists of two properties – a line of action and
a sense. In case of understanding of tooth
movement along with magnitude and direction,
point of application of force is important. The
forces are indicated by straight arrows.



A MOMENT is defined as the product of the
force times the perpendicular distance from the
point of force application to the center of
resistance, and thus is measured in units of gmmm (or equivalent). If the line of action of an
applied force does not pass through the center
of resistance, a moment is necessarily created.




MOMENT OF FORCE: When a force is
applied at any point other than through the
center of resistance in addition of moving the
center of resistance in direction of the force, a
moment is created.
In case of tooth, since it is embedded in the
alveolar bone, we cannot apply force directly on
CRES, but can apply force on the exposed part of
the tooth, which is at a distance from CRES.
Therefore with a single force we invariably
create a moment called as moment of force. A
moment may be referred as, Rotation, Tipping
or Torquing.

Contents






Introduction to frictionless mechanics
Anchorage classification
Biomechanics of looped archwire retraction
1. Design of loop
2. Biomechanical considerations
Advantages & disadvantages of loop mechanics








Advantages of a loop
Various types of loop designs
Methods of frictionless mechanics other than the
use of loops
Conclusion


WHAT IS FRICTIONLESS
MECHANICS


Retraction is accomplished with the help of loops or
springs.
Loops

{TEARDROP LOOP}


ADVANTAGES OF A LOOP:
1. The inconsistency of the force system developed by a
SWA can be avoided by using loops.
2. The addition of wire length into the appliance while
maintaining the wire size reduces the load.
3. Greater constancy of force.
4. Since the distribution of the wire with respect to the
bracket determines the moment-to-force ratio, and
tooth movement is produced by the deactivation of the
loop itself, friction is not an issue.
5. It is possible to design a loop in such ways that forces
and moments are dissociated to generate many
combinations of moment and force.


A

A

6.
7.

B

C

B

C

The desired combination of moments and forces can be reached by
choosing different points of force application, controlling the horizontal
dimension of the loop or by angulating the horizontal arm of the loop.
Combining wires of different dimension can produce composite loops.
For correcting major rotations or tipping, the combination loops are
advantageous as their working range is large.


VARIOUS LOOP DESIGNS THAT
HAVE BEEN TRIED FOR
FRICTIONLESS SPACE CLOSURE





Ray D. Robinson (1915) was
the first to document the
use of loops in orthodontics
Dr. Harry Bull advocated a
squashed vertical loop with
an
.0125”/.025”edgewise
wire opened the distance of
a ‘thin dime’.




Since that time various loop designs have been
advocated –
1. Rickett’s canine retractor
2. PG (Paul Gjessing) retraction spring
3. Delta loop
4. Closed vertical loop
5. Bull loop
6. Open vertical loop
7. The R (Rectangular) loop
8. Vertical loop with helix
9. Omega loop
10. T-Loop
11. Opus loop

12. T-loop retraction archwire (continuous and
segmental)
13. Double keyhole
14. Box loop
15. Double delta


RICKETT’S CANINE
RETRACTOR




This is a combination of a double closed helix and an Extended
crossed T made with blue Elgiloy wire.
It delivered 30-50gms per mm of activation.







ACTIVATION
Activated by pulling 3-4mm each adjustment by
pulling the wire through the tube and locking it
with a simple bend.
There should be 90 degree of Gable bend in the
canine region



1.
2.


1.
2.

Advantages of Rickett’s Retractor
Rapid space closure
Only a few weeks of wearing
Disadvantages of Rickett’s Retractor
Bulky and irritating to soft tissues
Difficult to use in the lower arch because it
extends into chewing area


PG { PAULGJESSING }
RETRACTION SPRING




Paul Gjessing (Denmark) introduced this
spring in 1985.
Design: -


1.

2.

3.

4.

5.

The canine retraction spring was
constructed in 0.016”/0.022” SS
wire
The principle element is a
double helix 10mm
in height
It was introduced to reduce the
load deflection rate of the
spring
The mesial and distal extensions
of the looped
archwire are
angulated in both horizontal and
vertical plane
The posterior curvature is
adjusted to deliver
the force
magnitude of 15-25gms per side.


1.
2.
3.

Advantages
Reduced load deflection rate
Reduced vertical height
The rounded form avoids load concentration


BEFORE RETRACTION

AFTER RETRACTION


DELTA LOOP




The design similar to that of opening loop
William R. Proffit (1993)
0.016”/0.022” SS wire used in .018” slot and
0.018”/0.025” SS wire in .022” slot


VERTICAL LOOP


Vertical loop with HELIX

The advantage of Helix in a vertical loop is that it
increases the working range
Closed Helix


Open Helix

Bull loop


OPEN VERTICAL LOOP




Morris & Bruce
It is used to open the spaces
It is activated by closing the
legs


OMEGA LOOP


THE ASYMMETRIC T LOOP





James J. Hilgers (1992)
This
loop
allows
simultaneous
bite
opening
and
space
closure.
The anterior portion is
smaller and engages the
lateral incisor bracket.


THE OPUS LOOP/STANDARD OPUS



Dr. Raymond E. Siatkoski
This specialized spring can deliver sufficiently
high “inherent M/F ratio” within the range of 89 to produce en masse translation without giving
the pre-activation bends.




Groups of teeth can be
moved more accurately to
achieve
predetermined
anteroposterior treatment
goals for esthetics and
stability



The distinct advantage of
Opus loop is that it is free
of residual moments and
produces the periods of
“true
rest”
when
deactivated.


OPUS LOOP


THE RECTANGULAR LOOP
CHARACTERISTICS:
1. Can be used for first, second and third order
corrections
2. Since the loop is inserted in at least two brackets, it
represents a static force system.
3. The clinician can determine the moment-to-force
ratio delivered to the active unit.
4. All combination of moments and forces can be
produced. The direction of moment generated at the
loop depends on the point of force application in
relation to the horizontal dimension of the box.


FABRICATION OF ‘R’ LOOP:

Fabrication of R loop for the 2nd premolar correction:
Step 1: Measure the distance between mesial of molar tube and the distal of 2nd
premolar bracket (D)
Step 2: The ‘R’ loop is fabricated using the formula A = B = C each being equal
to half of D.
Note: Distance D for any tooth is measured from the distal of the bracket (of the
tooth to be corrected) to the mesial of the bracket (of the tooth distal to it).
A

B

C

A = B = C www.indiandentalacademy.com

VARIOUS ACTIVATIONS:

‘R’ loop can be effectively used for the correction of :
Rotation
First order discrepancies
Second order discrepancies


COMPOSITE LOOPS:

Differences between the stiffness of the active and
reactive units can be varied producing Composite loops.
E.g., Combining 0.017 x 0.025” and a 0.018” TMA wires
Depending on the point of welding, this will displace
the point of dissociation from the geometrical center of
the loop. When correcting major rotations or tipping, the
composite loops are advantageous as their working
range is large. They can also be designed for a correct
moment-to-force combination.

‘T’ LOOP
Characteristics:
1.
2.

3.

Made of 0.017”x 0.025” TMA wire
No side determination be made, however, the alpha leg (anterior leg) of
the T loop is longer than beta leg (posterior leg) by 1mm to compensate
for the difference of height between the bracket of the canine and the
auxillary tube of the molar.
The central position of the loop can be calculated by the formula

D=L-A
2
Where, D = distance from either the molar auxillary tube or
the canine to the center of the loop
L =
distance from the molar auxillary tube to the
canine vertical tube (or center of the bracket)
A=
activation of the spring

10 mm
2 mm
4 mm
BETA
(POSTERIOR) SEGMENT

β

5 mm
ALPHA
(ANTERIOR) SEGMENT

α


PREACTIVATION CHECK LIST:
1.   Check the neutral position of the loop (0 mm).
2.   Determine the amount of activation.
3.   From the center of the T, mark distance D on both arms
of the spring. Place a vertical bend gingivally 5mm
anterior to the mark on the anterior leg.
4.   Check for comfort and passivity and necessary
adjustments are made to achieve the same.
5.   Placement of Alpha and Beta preactivation bends:
Preactivation bends are placed at six points in the
spring


Continuous T loop archwire






Given by Stoner, thus also called as Stoner Tloop archwire
This loop is used when retraction and intrusion
of the upper incisors is desired.
Archwire used is of .016x.022 inch stainless steel
and comprises of a T-loop between upper lateral
and canines.


Construction
 The mesial leg of the T- loop should lie 1 mm
posterior to the loop bracket of the lateral incisor.
 The loops are activated by to 1mm by sliding the
archwire to the posterior brackets and buccal
tubes and bending them up.
 If we need anterior bite opening tooo then a
reverse curve of spee can be formed in the
archwire.
 With every visit only 1 mm of activation can be
done and the visits can be repeated in the
intervals of 3 weeks

Double keyhole loop






Introduced by John Parker of Almeda, California.
When spaces are present anterior as ell as posterior to
canines and need to be closed by front backward or
back forward then this loop is incorporated in
continuous archwire.
The archwires generally used are .019”x.025”
The double keyhole loop archwire also doesn’t allow
the canine to rotate during the space closure i.r.t.
extraction site.

Box loop





Generally used in cases of molar protraction as
well as anterior retraction.
The loop bypasses the tooth anterior to molar.
The mesial leg of the loop is adjacent to canine
while the distal leg is mesial to the molar tube.


METHODS OF FRICTIONLESS RETRACTION
OTHER THAN CONTINUOUS LOOP MECHANICS
1.
2.

3.
4.

Drum spring retractor for canine retraction
Separate canine retraction with cuspid to
cuspid bypass.
Retraction with utility arches
The three piece intrusion and retraction arch.


DRUM SPRING RETRACTOR
FOR CANINE RETRACTION


Constant force without
the need for reactivation
through an intraoral
appliance










Force spring with a hook
fabricated to deliver force of
50gms
Other parts are a drum, a
spring box and a central pin
soldered o molar band
Assembled and soldered to
molar band and activated by
pulling the end of the spring
The force level is always at
50gms and there is no need
for reactivation.

SEPARATE CANINE TO CANINE
RETRACTION WITH CUSPID TO CUSPID
BYPASS




Cuspid to cuspid bypass
is used to prevent
1. Prevent rotation
2. Actively derotate teeth
when there is space
3. alter arch-width
4. eliminate side effect of
vertical forces



1.

2.
3.

The indications for cuspid to cuspid bypass are
Cases requiring bilateral symmetrical canine
retraction where distal-in rotation must be
prevented
Cases with canines with different vertical levels
Cases with bilateral or unilateral canine
rotation






A rigid wire at least 0.017”/0.025” is stepped
down 3 to 4mm mesial to canines and around the
incisors
This allows for the simultaneous bracketing of the
incisors






The arch form is made longer and wider than
the initial 3-3 distance in order to counteract any
constrictive forces caused by the force of
retraction.
The T-loop is then engaged in Burstone Cuspid
bracket and the retraction is started


RETRACTION WITH UTILITY ARCHES


In 1950s Robert Rickett’s developed the lower
step down arch, also popularly known as
Rickett’s Utility arch, to hold the buccal segment
upright during retraction and also for lower
incisor intrusion with light continuous forces.






It is known as 2/4 appliance because it engages
only molars and incisors
It has multiple uses in various stages of
orthodontic treatment.



1.
2.
3.
4.

Types of utility arches
Passive utility arch
Intrusion utility arch
Protrusion utility arch
Retrusion utility arch
The retrusion utility
arch is used in either the
mixed or permanent
dentition to achieve
retraction and intrusion
of
incisors
by
incorporating loops in
the archwire.





THREE PIECE INTRUSION
ARCH

It was given by Burstone for simultaneous
Intrusion and retraction.
The force of application for intrusion is
lingual to centre of resistance so there is no
flaring of anteriors as seen in continuous
arch intrusion


THREE-PIECE INTRUSION ARCH

Parts:
1. The posterior anchorage unit
2. The anterior segment with a posterior extension
3. The intrusion cantilevers
4. An elastic chain.

•The anterior segment is bent gingivally distal to the laterals, then
bent horizontally, creating a step of approximately 3 mm.
• The distal part extends posteriorly to the distal end of the canine
bracket, where it forms a hook.
•This anterior segment should be made of 0.019” x 0.022” / 0.017” x
0.025” SS wire.
•The intrusion cantilevers are fabricated from 0.017” x 0.025” TMA
wire.
•The wire is first bent gingivally mesial to the molar tube (and
then helix is formed if SS wire is used).
•On the mesial end of the cantilever, a hook is bent through which
the intrusive force can be applied to the anterior segment.
• The cantilever is then activated by making a bend mesial to the
helix at the molar tube, and then cinched back.

An elastic chain can be attached to the hook of the
anterior segment to the molar tube to redirect the forces
in a posterior direction.

THREE-PIECE INTRUSION ARCH


CONCLUSION




This is only a simplistic presentation of extremely complex
mechanism
It is impossible to calculate the required force magnitude for
every patient because there are many variables
1. Different tooth sizes and inclinations
2. Different arch sizes which affect the length of wire
spans
3. Change in the arch size as the tooth movement takes
place
4. Individual biomechanical responses
5. Limitations of the material properties.









Although bracket design and proprietary
treatment protocols are broadly used in clinical
circumstances, achieving predictable and stable
orthodontic results requires more than simply
selecting a particular bracket system
The fundamental basis of orthodontic treatment
remains the application of mechanical forces to
produce desirable tooth movement.
Today’s orthodontist needs the knowledge of
both friction and frictionless mechanics
No single technique suits every situation. There
are specific indications for both.



The foremost thing in orthodontics is Discipline
Discipline in diagnosis
Discipline in treatment planning
Discipline in use of appliance system
Discipline in mechanics
Discipline in management of patient’s
orthodontic needs


REFERENCES


CONTEMPORARY ORTHODONTICS: WILLIAM R. PROFFIT



BIOMECHANICS IN CLIICAL ORTHODONTICS RAVINDRA
NANDA
BURSTONE CJ, HANLEY KJ: MODERN EDGEWISE MECHANICS
SEGMENTED ARCH TECHNIQUE.
SMITH RJ, BURSTONE CJ: MECHANICS OF TOOTH MOVEMENT.
AM J ORTHOD 85:294-307, 1984.
KOENIG HA: OPTIMIZING ANTERIOR AND CANINE
RETRACTION. AM J ORTHOD 70:1-19 1976.







:


Thank you
Leader in continuing dental education


Friction less mechanics in orthodontics /certified fixed orthodontic courses by Indian dental academy

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Friction less mechanics in orthodontics /certified fixed orthodontic courses by Indian dental academy

Similar to Friction less mechanics in orthodontics /certified fixed orthodontic courses by Indian dental academy (20)

More from Indian dental academy

More from Indian dental academy (20)

Recently uploaded

Recently uploaded (20)

Friction less mechanics in orthodontics /certified fixed orthodontic courses by Indian dental academy

Editor's Notes