Canine retraction by frictionless mechanics

CANINE RETRACTION BY
FRICTIONLESS MECHANICS
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INTRODUCTION
• OVER THE YEARS ORTHODONTISTS
HAVE INCREASINGLY SHOWN MORE
INTEREST IN RETRACTING
PERMANENT CUSPIDS. THIS DENTAL
MOVEMENT IS NECESSARY IN SPACE
CLOSURE OF THE ARCH FOR
RESOLVING DIFFERENT
ORTHODONTIC PROBLEMS

METHODS OF CANINE
RETRACTION
• FRICTIONAL MECHANICS
• FRICTIONLESS MECHANICS

FRICTIONLESS MECHANICS
• TEETH ARE MOVED WITHOUT THE
BRACKETS SLIDING ALONG THE
ARCH WIRE. RETRACTION IS
ACCOMPLISHED WITH LOOPS OR
SPRINGS,WHICH OFFER MORE
CONTROLLED TOOTH MOVEMENT
THAN SLIDING MECHANICS.THIS
TECHNIQUE PROVIDES EFFICIENT
SPACE CLOSURE WITH EXCELLENT
FORCE CHARACTERISTICS

ADVANTAGES:
• ABSENCE OF FRICTION BETWEEN
THE BRACKET AND THE WIRE
• THE FORCE LEVELS ARE EASIER TO
EVALUATE CLINICALLY
• THE MOMENT/FORCE RATIO OF THE
CUSPID AND THE POSTERIOR
SEGMENT IS PREDICTABLE AND
CONTROLLABLE DURING
RETRACTION

PRINCIPAL CHARACTERISTICS OF
A CANINE RETRACTION SPRING
• MOMENT TO FORCE RATIO (M/F)
APPLIED AT THE BRACKET WHOSE
VALUE DETERMINES THE POSITION
OF THE CENTER OF ROTATION
DURING THE ORTHODONTIC
MOVEMENT
(WHICH CONTROLS THE CENTER OF
ROTATION )

• . LOAD/DEFLECTION RATIO (F/D) OF
THE SPRING (THE LEVEL OF FORCE
PRODUCED BY THE SPRING PER
ACTIVATION)
(WHICH HELP TO MAINTAIN IDEAL
FORCE LEVEL DURING
ORTHODONTIC TOOTH MOVEMENT )

• MAXIMUM STRENGTH (FMAX) -THE
SPRING IS ABLE TO RELEASE
WITHOUT PERMANENT
DEFORMATION.

FORCES
• HORIZONTAL FORCES
• VERTICAL FORCES

HORIZONTAL FORCES
• IT IS THE FORCE APPLIED FOR THE
RETRACTION OF THE CANINE .
• THE DISTAL FORCES ACTING ON THE
ANTERIOR TEETH ALWAYS EQUAL TO
THE MESIAL FORCES ACTING ON THE
POSTERIOR TEETH

VERTICAL FORCES
• THESE ARE INTRUSIVE/EXTRUSIVE FORCES
ACTING ON THE ANTERIOR OR POSTERIOR TEETH
• THESE FORCES ARE GENERATED FROM UNEQUAL
ALPHA AND BETA MOMENTS OR BY PLACING THE
THE LOOP OFFCENTER

• PLACING THE LOOP OFFCENTER TOWARDS THE
CANINE WITH EQUAL ALPHA AND BETA MOMENT
EXTRUDES ANTERIOR AND INTRUDES THE
POSTERIORS.
• IF THE LOOP IS TOWARDS THE POSTERIORS THEY
EXTRUDE POSTERIOR S AND INTRUDE THE
ANTERIORS

MOMENT
• WHEN A RETRACTION SPRING IS
USED TWO MOMENTS ARE CREATED .
• THE ALPHA MOMENT –PRODUCES
DISTAL ROOT MOVEMENT OF THE
ANTERIOR TEETH
• THE BETA MOMENT -PRODUCES
MESIAL ROOT MOMENT OF THE
POSTERIOR TEETH

• IF ALPHA AND BETA MOMENT ARE
UNEQUAL VERTICAL FORCES ARE
GENERATED
• IN CASE OF CENTRAL BEND ALPHA
AND BETA MOMENT ARE
EQUAL,THEN BOTH ANTERIOR AND
POSTERIOR SEGMENTS MOVE TO THE
SAME EXTEND

• WHEN ALPHA MOMENT IS GREATER
THAN BETA MOMENT, POSTERIOR
PROTRACTION IS ACHIEVED .
• IF THE BETA MOMENT IS GREATER
ANTERIORS ARE RETRACTED

• DIFFERENTIAL MOMENT OF THE
ANTERIOR AND POSTERIOR
SEGMENTS CAN BE ACHIEVED BY
OFFCENTERING THE BENDS

• IF THE OFFCENTER IS TOWARDS THE
ANTERIOR IT ENHANCES ANTERIOR
ANCHORAGE
• IF THE OFFCENTER IS TOWARDS THE
POSTERIOR THEN POSTERIOR
ANCHORAGE IS ENHANCED

• FOR ANTERIOR RETRACTION,THE
RETRACTION LOOP SHOULD BE
PLACED CLOSER TO THE CANINE TO
DELIVER GREATER MOMENT TO
FORCE RATIO CONSTANTLY
• A GABLE BEND ADDED NEAR THE
MOLAR WILL PRODUCE A LARGE
BETA MOMENT THUS INCREASING
THE POSTERIOR ANCHORAGE

• AS THE BETA MOMENT BECOMES
RELATIVELY GREATER THERE IS
GREATER INTRUSIVE FORCE ON THE
ANTERIOR TEETH AND EXTRUSIVE
FORCE ON THE POSTERIOR TEETH
• THE M/F RATIO INCREASES AS THE
SPRING DEACTIVATES IT SHOULD
NOT BE REACTIVATED TOO OFTEN

MOMENT TO FORCE RATIO
• CONTROLLED ROOT POSITION
DURING MOVEMENT REQUIRES
BOTH,FORCE TO MOVE THE TOOTH
AND A COUPLE TO PRODUCE THE
NECESSARY COUNTERBALANCING
MOMENT

THE TYPE OF MOVEMENT
• DICTATED BY THE MOMENT TO
FORCE RATIO GENERATED BY THE
APPLIANCE AT THE ATTACHMENTS.
• MOMENT TO FORCE RATIO OF 7:1
RESULTS IN CONTROLLED TIPPING
• 10:1 RESULTS IN BODILY MOVEMENT
• 13:1 RESULTS IN ROOT TORQUE

METHODS TO INCREASE
MOMENT TO FORCE RATIO
• THE LOOP CAN BE MADE AS LONG AS
POSSIBLE IN APICAL DIRECTION
• INCREASE THE AMOUNT OF WIRE
PLACED GINGIVALLY AT THE TOP OF
THE LOOP

LOAD DEFLECTION RATE
• IT REPRESENTS THE RATE OF FORCE
DECAY
• THE LOW LOAD DEFLECTION RATE IS
IMPORTANT IN A SPRING SINCE IT
ENABLES TO DELIVER OPTIMAL
MAGNITUDE OF FORCE FOR A LARGE
ACTIVATION
• LOAD DEFLECTION OF A SPRING DEPENDS
ON ITS MODULUS OF ELASTICITY ,CROSS
SECTION OF THE WIRE USED AND THE
DESIGN OF THE SPRING

OPTIMAL LEVELS OF FORCE
• NIKOLAI HAS DEFINED OPTIMUM
ORTHODONTIC FORCE AS THAT
WHICH PRODUCES A MAXIMUM OF
DESIRABLE BIOLOGIC RESPONSE
WITH MINIMUM TISSUE
DAMAGE,RESULTING IN RAPID TOOTH
MOVEMENT WITH LITTLE OR NO
CLINICAL DISCOMFORT

• SMITH SUGGESTS A FORCE OF 150-
200GMS
• REITAN-250GMS
• PROFIT -100GMS

SPRINGS BEST SUITED FOR
CANINE RETRACTION
• T-LOOP
• PG SPRING
• DRUM SPRING

PG CANINE RETRACTION
SPRING

• INTRODUCED IN 1985 BY POUL
GJESSING
• IT IS CONSTRUCTED IN THE READILY
AVAILABLE 0.016"X0.022" STAINLESS
STEEL WIRE AND CAN BE EASILY
PLACED IN THE ROUTINELY USED
0.018" BRACKETS

CONSTRUCTION :
• THE PG SPRING IS
MADE IN0.016"X.022"
STAINLESS STEEL
RECTANGULAR WIRE.
• IT HAS GINGIVALLY
DIRECTED
OVERLAPPING
DOUBLE HELICES,
OVOID IN SHAPE,10MM
IN HEIGHT AND 5.5MM
AT ITS WIDEST PART
• IT HAS A SMALL
OCCLUSAL HELIX 2MM
IN DIAMETER.

• THE SMALLER END OFTHE WIRE IS
CONTINUOUS WITH THE OCCLUSAL
HELIX.
• THIS PORTION IS THE CANINE PART
AND WOULD FIT INTO THE CANINE
BRACKET. AS IT COMES OUT OF THE
OCCLUSAL HELIX, IT IS GIVEN A 15°
GINGIVAL TURN.

PG CANINE RETRACTION SPRING
Anti rotation bend35º
Anti tip bend
Beta bend
15º 12º
30º
Occlusal loop
Apical loop
2 mm
10 mm5.5 mm
16″X22″ STAINLESS STEEL
60°

• THE LONGER ARM OF THE WIRE IS THE
ONE WHICH IS MEANT FOR ENGAGING THE
PREMOLAR BRACKET AND THE MOLAR
TUBE;
• THIS POSTERIOR MOLAR ARM AS IT EXITS
FROM THE DOUBLE OVOID LOOPS IS
TURNED GINGIVALLY SUCH THAT THE
WIRE MAKES AN ANGLE OF 12° TILL
APPROXIMATELY THE SECOND PREMOLAR
BRACKET AND THEN TURNED UP AT AN
INCREASED TOTAL ANGULATION OF 30°

• THIS PORTION IS ALSO GIVEN AN
ANTI-ROTATION BEND OF 60°
TOWARDS THE CANINE TOOTH AND
THEN THIS BEND AFTER TRAVERSING
THE WIDTH OF THE SPRING IS
CURVED BACK IN AN EXACTLY
OPPOSITE DIRECTION OF THE INITIAL
BEND DECREASING THIS TO A FINAL
35°

PLACEMENT
• THE ANTERIOR END EMERGING OUT
FROM THE SMALLER HELIX IS
PLACED AS CLOSE AS POSSIBLE TO
THE CANINE BRACKET AND THE
FRONT END IS CHINCHED.
• THE POSTERIOR END IS PLACED INTO
THE SECOND PREMOLAR BRACKET
AND THEN INTO THE 1ST MOLAR
TUBE.

ACTIVATION
• THE SPRING IS PULLED BACK TILL
THE DOUBLE OVOID GINGIVAL LOOPS
OPEN BY 1MM AND CHINCHED BACK.
• THIS GIVES AN APPROXIMATE FORCE
OF 160 GRAMS.

SPACE CLOSURE
• ON AVERAGE, 1.2 MM OF SPACE
CLOSURE IS OBTAINED WITH THIS
ACTIVATION IN FOUR WEEKS.
• DURING THIS PERIOD THE
HORIZONTAL FORCE DECREASES
FROM 100 GMS TO 40 GMS
• THE INTRUSIVE VERTICAL FORCE ON
THE CANINE INCREASES UP TO 12
GMS.

• AN INITIAL HORIZONTAL FORCE OF
100 GM GENERATES AN M/F RATIO OF
9 MM AT THE POINT OF THE APPLIED
FORCE.
• THE INITIAL CANINE MOVEMENT IS
THEREFORE A CONTROLLED TIPPING.

AFTER ONLY 0.3 MM OF
DEACTIVATION OF THE SPRING
• THE M/F RATIO INCREASES TO 10-11 ,
THUS PRODUCING TRANSLATION.

WHEN THE SPRING IS
COMPLETELY DEACTIVATED
• THE M/F RATIO IS 18 MM. THIS VALUE
PRODUCES UPRIGHTING OF THE
CANINE ROOT THAT COMPENSATES
FOR THE INITIAL CONTROLLED
TIPPING..

• BODILY MOVEMENT OF THE CANINE
IS THEREFORE OBTAINED BY A
COMBINATION OF CONTROLLED
TIPPING, FOLLOWED BY
TRANSLATION AND UPRIGHTING

DRUM SPRINGS

• Introduced by-
Dr M.Ali Darendeliler
Mr Halux
Darendeliler
Developed in 1992
First published in E.J.O-1997

APPLIANCE DESIGN
• It consists of 4 parts
-Constant force
spring(CFS) with a
hook
-Drum
-Spring box(SB)
-Central pin
soldered to molar
band(CW)

PLACEMENT AND
ACTIVATION
• Assembled and mounted on the
molar band
• Activated by pulling the end of the
spring and engaging the hook on
canine bracket

• The amount of activation does not
influence the amount of force
applied
• The force is constant and
contineous
• Usually 50 gms

RATE OF CANINE
RETRACTION
• 1.975+/- 0.615 mm of distal
movement of canine is obtained in
4 weeks
• Due to the mild force the M/F ratio
is always constant at 10-11
,which results in translation of
canine

ADVANTAGE OF DRUM
SPRING
• No reactivation is necessary
• It doesn’t require patient co-
operation
• Less chair side time
• It produces constant and
contineus force

REFERENCE

Canine retraction by frictionless mechanics

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Editor's Notes