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RETRACTION MECHANICSGood morning
DR TONY PIOUS
CONTENTS Introduction Definitions & Concepts -force -Center of resistance -Moment -Center of rotation -moment to force Anchorage -Defination -Classification -Anchorage control
Bends -V-bend -step bend
Retraction in Beggs Mechanotherepy
Retraction in Fixed Mechano therepy
Frictional mechanics- friction
a) mechanism of action in friction mechanics b) force delivery system c) variables affecting frictional resistance during sliding tooth movement
Frictionless mechanics-loop
Open vertical loop Closed vertical loop Bull loop Vertical open loop with helix Omega loop Delta loop Opus loop T loop Asymmetrical T loop Mashroom loop
Canine retraction springs
Ricketts maxillary canine retraction
Poul gjessing spring NiTi canine retraction
spring Canine retraction with J
hook headgear Rapid canine distraction
K sir arch Statically
determinate retraction system
Retraction utility arch
Three piece intrusion arch
Translation arch
Retraction by Magnets
The Hycon Device
Retraction by implants Conlcusion
INTRODUCTION
Antero-posterior therapy procedures to close spaces correct procumbency, reduce overjet, and eliminate extraction sites is generally categorized as Retraction mechanics
It involves carefully designed treatment strategy as to lose or not to lose the anchorage.
Whether anterior retraction or posterior protraction or a
combination of both is used the same basic principles of retraction mechanics apply.
FORCE
Defined - An act upon a body that changes or tends to change the state of rest or the motion of that body.
Measured in NewtonForce is a vectors quantity thus has a – magnitude,
point of application, line of action, and sense.
CENTER OF RESISTANCE
Center of mass is a point through which an applied force must pass for a free object to move linearly without any
rotation. The center of a mass is for a generic free body.Tooth – not generic free- periodontal support.
The analogous to center of mass for a restrained body is CENTER OF RESISTANCE
Burstone C.J in AJO 1980 stated that
The center of resistance for a tooth is approximately the 1/3 to ½ apical to CEJ in single rooted teeth along the long axis
For multi rooted teeth it lies 1 to 2 mm apical to furcation
MOMENT
Defined- as the rotational tendency when force is applied away from the center of resistance
Mathematically given as M = f x dWhere M -is the moment
f -is the force d -is the perpendicular
distance from the line of action to the center of resistance
CENTER OF ROTATION
It is the point around which the body seems to have rotated.
The center of rotation is not a fixed point and can be changed by the manner of force application
Translation - infinity Controlled tipping - apex Uncontrolled tipping - slightly
apical to center of resistance.
Root movement - incisal edge
COUPLE
Two equal and opposite non-collinear forces are called a couple
MOMENT OF A COUPLE
The two forces since they are equal and opposite cancel out but
Moments created by the two forces do not cancel out and a pure rotation is produced.
Measured as F x d F=magnitude of one of the forces d=distance b/w the forces
MOMENT TO FORCE RATIO FOR VARIOUS TOOTH MOVEMENTS
M/F 5 : 1 Uncontrolled tipping M/F 8 : 1 Controlled tipping M/F 10 : 1 Translation M/F >10 : 1 Root movement
FACTORS DETERMINING THE TOOTHMOVEMENT REQUIRED DURING SPACE CLOSURE
Amount of crowding Anchorage Axial inclination Midline discrepancies and left or right asymmetries Vertical dimension
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.
NANDA& KULHBERG
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.
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.
ANCHORAGE
Anchorage is an important aspect of orthodontic space closure
Definition “Refers to the nature and degree of resistance to displacement offered by an anatomic unit when used for the purpose of effecting tooth movement”
By: T.M.Graber “amount of movement of the posterior
teeth(molars,Premolars) to close the extraction space in order to achieve selected treatment goal”
By: Ravindra Nanda
ANCHORAGE CLASSIFICATION
According to Ravindra Nanda
GROUP A
GROUP B
GROUP C
BIOMECHANICS IN CLINICAL ORTHODONTICS -RAVINDRA NANDA
GROUP A ANCHORAGE
GROUP B ANCHORAGE
GROUP C ANCHORAGE
Maximum anchorage cases
retractive forces to the anterior teeth and no forces to the posteriors.
Two ways of achieving this-altering the forcesaltering the moments
both the above ways aiming to increase the m/f ratio of the post and decreasing the m/f of the ant
1. Altering the forces -a. ant segment.
moment should be a constant- the only option increase in force should not be associated with a reactionary increase
a.class II elasticsb.j-hook from headgear
b.Post segment.moment should be constant- the only option force opposite to that acting on the post segments
headgear-distal
2. Altering the moments
force constant- increasing the post moment- and decreasing the ant moment-
3. Position of the loopmesio distal positioning- importantmidway-equal and opp activation moments
off centered to distal- tip back moment and intrusive force-maximum anchorage cases. mesially off centered- increases the ant moment- minimum anchorage cases
ANCHORAGE CONTROL
Anchorage control is done in three planes 1.Horizontal 2.Vertical 3.Transverse
HORIZONTAL ANCHORAGE CONTROL(ANTERIO POSTERIOR )
Limiting the mesial movement of the posterior segment while encouraging distal movement of the anterior segment or vice- versa.
It is done by:CONTROL OF POSTERIOR SEGMENT Upper arch a) Headgear b) Palatal bar(trancepalatal arch) c) Nance holding arch Lingual arch a) Lip bumper b) Class III elastics and headgear
VERTICAL ANCHORAGE CONTROL
MOLAR CONTROL a) Upper scond molar banding should avoided initially (in high angle case) b) Expansion if required should be achieved by bodily moment of the posterior teeth(in high angle case) c) Transpalatal arch should be 2-3mm away from the palate and with the U loop facing forward d) High pull or combi pull headgear to be used e) Posterior bite planes or bite blocks
TRANSVERSE PLANE OR LATERAL
b) Correction of molar cross bite1. Rapid palatal expansion2. Quad helix3. Transpalatal arch
BENDS
An infinite number of shapes or bends can be placed on the wire. Two commonly used basic bends are:
1) V-bend 2) step bend
Creative wire bending –The force system from step bends & V-bends, Burstone & Koening, AJODO 1988, 93:59-67
V-bend principle
The force & moments from a V-bend change according to the position of the bend.
α moment –produced anteriorly
Β moment - produced at molar
Centre bend
Also called as symmetric bend
Equal & opposite moments are created
No forces are produced
Off centre bend or asymmetric bend
OFF CENTRE BEND Position b/w 1/2 to 1/3 of distance
Greater moment is generated in the bracket closer to the V-bend.
Opposite moments are generated at both ends. Opposite vertical forces
OFF CENTRE BEND At 1/3
Greater moments at shorter arm.
No moment at longer arm.
Equal & Opposite vertical forces
Represents cantilever system.
OFF CENTRE BEND
At < 1/3 of distance
Opposite vertical forces of greater magnitude
Moments in same direction.
Greater moment on shorter arm.
Step bend
Equal & opposite vertical forces
Equal unidirectional couple
As the height of the step increases the vertical forces & moments increase
RETRACTION
STAGEDENMASSE
FRICTIONLESS SLIDING
TIP AND UPRIGHT
SIMULTANEOUSINTRUSIONAND RETRACTION
STAGE 1 STAGE 2
CANINE ANTERIORS
FRICTIONLESS SLIDING
FRICTIONLESS SLIDING
RETRACTION IN BEGGS The Begg technique advocates a two-stage retraction
and it is not the only technique that uses this kind of two-stage retraction
the first stage involving distal tipping of the anterior crowns with elastomerics and/or interarch elastics.
Begg brackets permit only a point contact between bracket and archwire, no moment is produced by wire bracket interaction.
As a result, only uncontrolled tipping of the anterior teeth (center of rotation between the apex and the center of resistance) occurs during the first stage of retraction.
The second stage involves lingual torquing of the anterior roots, usually by means of a torquing auxiliary.
A moment-to-force ratio of about 12:1 is required for such movement and such a high ratio is technically difficult to achieve. For this reason, two-stage retraction with initially uncontrolled tipping is not the most efficient retraction method.
(JCO 1991 Jun(364 - 369): Clinical Considerations in the Use of Retraction Mechanics - JULIE ANN STAGGERS, & NICHOLAS GERMANE)
RETRACTION MECHANICS IN EDGEWISE
Friction mechanics or sliding mechanics
Friction less or loop mechanics
FRICTION
Friction-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.
Resolved in 2 components –
Frictional component - parallel but opposing the motion
Normal component – perpendicular to contacting surfaces and to frictional component
F = µ N
F is frictional force µ is coefficient of friction. N is normal force
Friction is of two types-
Static friction – is the smallest force needed to start the motion of solid surfaces that were previously at rest.
F = µs N where µs is coefficient of static friction
Kinetic friction- is the force that resist the sliding motion of one solid object over another at constant speed (acts during the period of motion itself)
F= µk N where µk is coefficient of kinetic friction
Static friction is considered to have a greater effect on preadjusted mechanics than dynamic friction
Friction mechanics or sliding mechanics
sliding mechanics involves either moving the bracket along an arch wire or sliding the archwire though brackets and tubes
Advantages Minimal wire bending time More efficient sliding of arch wire through post. Bracket slots No running out of space for activation Patient comfort Less time consumption for placement
Disadvantages Confusion regarding ideal force level Tendency of overactive elastic & spring force initial
tipping & inadequate rebound time for uprighting if forces are activated too frequently
Generally slower than loop mechanics due to friction
MECHANISM OF ACTION OF FRICTION MECHANICS
MECHANISM OF ACTION OF FRICTION MECHANICS
To move a tooth bodily, the force should pass through centre of resistance of tooth.
When force is applied on crown, tooth experiences both moment (in 2 planes) & force
One moment tends to rotate the tooth mesial- out & other distal tipping.
Mesial out rotation is undesirable side effect
Distal tipping retraction, by binding the arch wire which in turn produces moment results in distal root movement hence uprighting of tooth.
As tooth uprights moment ↓es until wire no longer binds.
Again canine retracts along arch wire till tipping again causes binding
ROLE OF FRICTION IN ELICITING BIOLOGICAL RESPONSE Both static and kinetic sliding friction arise in an arch wire through a bracket
or a bracket along an arch wire. Initially, upon appliance activation, the delivered force is sufficient to
''overcome" friction (to exceed the maximum static frictional force in magnitude) and the tooth/teeth are displaced.
This movement continues until the resistance of the deformed periodontal support structure builds to a value which, when added to the kinetic frictional force, offsets the delivered force and tooth motion temporarily ceases.
As time proceeds, periodontal remodeling affects resistance potential, and occlusion, wire resiliency, and masticatory action alter the mean resultant normal force between bracket and wire, so that the "friction lock" is broken and reset over and over again.
Hence, in the presence of appliance friction, tooth movement apparently occurs as a sequence of very short steps or jumps rather than as a smooth, continuous motion.
Frictional resistances between orthodontic bracket and arch wire - Frank AJO-DO Volume 1980 Dec (593 - 609):
FORCE DELIVERY SYSTEM :
1. ELASTOMERICS 1. ELASTIC MODULES WITH LIGATURE : ( Active tie backs) This method was popularized by BENETT & MCLAUGHLIN
(controlled space closure with preadjusted appliance system) JCO 1990 April.
An elastic module is stretched by 2-3mm(ie) twice its normal length
it usually delivers 0.5 - 1.5mm of space closure per month.
Tie backs are replaced every 4-6 weeks. Modules generate 50-100 gm of force if module was pre stretched before use.
If used directly from manufacture without pre-stretching force delivered is greater.
Alternate systems found to be disadv. to this in following aspects Power chain- variable force, difficult to keep
clean, some times falls off Elastic bands- Applied by patient,
inconsistent results due to cooperation factor Stainless steel coil spring- deliver excessive
force, unhygenic
Elastomeric Chains Introduce in 1960’s Can be used for canine retraction, diastema closure,
rotation correction. Advantages.
Inexpansive Relatively hygienic Easily applied without arch wire removal Not depend on pt. cooperation
Disadvantages Absorb water & saliva Permanent staining after few days in oral cavity Stretching - breakdown of internal bonds –permanent
deformation Force degradation- variable force levels-↓effectiveness Can untie or break if not placed with care
Configurations Closed loop chain Short filament chain Long filament chain
Clinical considerations M/F is lowest at initial placement of E-chain distal crown
tipping of canine As tooth retracted M/F ↑es due to dissipation of E force & by
binding the arch wire produces moment results in uprighting of tooth.
For optimize tooth movement sufficient time should be allowed for distal root movement
A common mistake to change elastic chain too often- maintaining high force & M/F which produce distal tipping only
Even if extraction spaces are closed by tipping canines distally, maintaining the space closure will be difficult without also moving the roots distally.
Hyalinization around canine & direct resorption of pos. anchor loss
E-chain or module should be changed at interval of 4-6 weeks.
Maxillary canine retraction with retraction spring and sliding mechanics - Ziegler and Ingervall
AJO-DO Volume 1989 Feb (99 - 106):
The efficiency of maxillary canine retraction by means of sliding mechanics along an 0.018-inch labial arch and an AlastiK chain was compared with that using the canine retraction spring designed by Gjessing.
The canine was retracted faster and with less distal tipping with the spring than with the sliding mechanics. The canine retraction spring was not Superior to the sliding mechanics in controlling canine rotation during the retraction.
the correction of rotation after the retraction is less time-consuming than the uprighting of a tipped canine and places much less demand on the anchorage.
Closed coil springs
Coil springs were introduced to the orthodontic world as early as 1931.
Nagamoto suggested that the "pulling action" delivered by closed coil springs is more delicate, and such a force is desirable during the course of orthodontic treatment.
The various materials that have been used for making springs are
Stainless steel NiTi Co-Cr Ni alloy
Stainless steel coil spring Apply more predictable level of force than force elastics Easy to apply But have high LDR as compare to NiTi, so as space closes,
some force degradation due to lessening activation
NiTi close coil spring The concept of Nickel titanium coil springs was introduced in
1979. The force degradation is very less due to the low load
deflection rate. Produce more consistent space closure than elastics
Indicated if large spaces need to close or infrequent adjustment opportunities
Two sizes avaliable – 9 mm & 12 mm
Springs should not be extending beyond manufacture Recommend (22mm for 9 mm spring, 36 mm for 12 mm springs)
advantages of NiTi coil springs Can be easily placed and removed without
archwire removal Do not need to be reactivated at each
appointment Patient co-ordination not required.
Nickel-titanium spring properties in a simulated oral environment
Sangkyu Han, Donald C. Quick. Angle Orthodontist 1993 No. 1, 67 - 72:
A study of nickel-titanium springs was undertaken to determine whether their mechanical properties are affected by prolonged exposure to a static, simulated oral environment. Stainless steel springs and polyurethane elastic chains were also studied for comparison
Nickel-titanium springs suffered no degradation of their spring properties in the simulated oral environment. In contrast, stainless steel springs became slightly more compliant to stretching, and polyurethane elastics lost a large portion of their force-generating capacity.
Force degradation of closed coil springs - Angolkar,
Arnold, Nanda, and Duncanson AJO-DO Volume 1992 Aug
examines the force degradation coil spring of SS Co-Cr-Ni and NiTi coil springs they concluded that All springs showed force loss over time The major force loss was found to occur in the first
24 hours for most springs.
coil springs showed a 8% to 20% force loss at the end of 28 days, which is relatively lower than the force loss shown by latex elastics and synthetic elastic modules.
A clinical study of space closure with nickel-titanium closed coil springs and an elastic module R. H. A. Samuels, AJO-DO 1998 Jul (73 – 79)
1.Sentalloy nickel-titanium closed coil springs produce more consistent space closure than an elastic module.
2. 150- and 200-gram springs produce a faster rate of space closure than either the elastic module or the 100-gram spring.
3. No significant difference was found in the rates of space closure caused by the 150-gram and 200-gram springs.
EFFECT OF ENVIRONMENTAL FACTORS ON E- CHAIN & NITI-COIL SPRINGS. Claire Nattrass (EJO-1998-vol20/169-176)
Temp variations affected both E-chain and NITI coil springs
E-chains – Effect of temp was more profound. Force loss greater at higher temp.
NITI springs- overall effect of temp was smaller. Force loss greater at lower temp.
This is due to modifications in the crystal structure of the alloy
E-Chains are also affected by other environmental factors such as food. The gross colour change is a common clinical finding in patients who consume spicy foods.
Force decay of E-chain was more in carbonated drinks than in water which may be due to low PH
Dixon et al (JO 2002) compared the rates of orthodontic space closure using active ligatures, polyurethane power chains and NiTi springs.
Mean rates of space closure were 0.35 mm with active ligatures, 0.58 mm with powerchains and 0.81 mm with Ni Ti springs.
The difference between the rate of closure between NiTi spring and active ligatures was significant.
The authors concluded that NiTi springs are the most rapid, and are the treatment of choice, but power chains offer a cheaper option.
Problems During Space Closure 4. DIRECT HEADGEAR RETRACTION
J hook headgear, either of the straight pull or high pull type is clipped on the archwire mesial to the canines to slide them distally.
Straight pull headgear allows swifter canine retraction than the high pull type. However, this may cause anterior extrusion (Perej et al 1980; Hickham 1974) and unfavourable occlusal plane rotations (Bowden 1978). This might specially be a problem in high maxillomandibular angle cases.
High pull headgear may cause more bodily retraction. However, it is not as efficient for distal movement, needing prolonged periods of wear for modest results.
Mulligan’s V bend sliding mechanics
V bend is placed towards the molars thus more moment for anchorage
Canine is at long segment initially tips as less moment But as the space closes moment increases and cause its
translation Finally V bend will become centre bend and root paralleling takes
place
Employing tip edge bracket on canines
In case of upright or distally tipped canine (deepening of bite & lateral open bite) Tip edge bracket
Prevent binding between AW & slot during initial stages when major movements
After retraction is comp.- uprighting spring to correct angulation without ant. Extrusion
Full size rectangular wire can be placed for desired tip/torque specifications.
Effects of Overly Rapid 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.
• 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"
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
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.
Inhibitors to Sliding Mechanics
• 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.
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.
VARIABLES AFFECTING FRICTIONAL RESISTANCE DURING TOOTH MOVEMENT
PHYSICAL ARCHWIRE LIGATION BRACKET ORTHODONTIC
APPLIANCE
BIOLOGICAL SALIVA PLAQUE ACQUIRED PELLICLE CORROSSION
NANDA& KULHBERG
PHYSICAL HYSICAL
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
Saliva Plaque Acquired pellicle Corrosion
BIOLOGICAL
Clinical Considerations in the Use of Retraction Mechanics - JULIE ANN STAGGERS, DDS, MS, NICHOLAS GERMANE, DMD, JCO Volume 1991 Jun(364 - 369)
Wire selection Cobalt chromium, beta titanium, and nickel
titanium wires produce more friction than stainless steel wires.
Rectangular wires produce more friction than round wires
larger wires more than smaller wires
0.016” s.s lowest friction not ideal wire (not offer control) in three planes
0.016X 0.022ss for 0.018 slot 0.017x 0.022 or .019x .025 for 0.022 slot
a. Wire material: Most studies have found stainless steel wires to be
associated with the least amount of friction. This is further backed up by specular reflectance
studies which show that stainless steel wires have the smoothest surface, followed by Co-Cr, -Ti, and NiTi in order of increasing surface roughness.
Kusy & Whitney (1990) found Stainless steel to have least coefficient of friction & the smoothest surface. However B titanium showed greater friction compared to Ni Ti
B. Wire Size: - Several studies have found an increase in wire size
to be associated with increased bracket-wire friction. In general, at non-binding angulations, rectangular
wires produce more friction than round wires. However, at binding angulations, the bracket slot can bite into the wire at one point, causing an indentation in the wire.
C. Wire stiffness: Drescher et al (AJO-DO 1989) stated that friction depends primarily on the vertical dimension of the wire.
An 016” stainless steel round wire and an 016 x 022” stainless steel rectangular wire showed virtually the same amount of friction. This was however lower than that for 018 X 025” wires.
The authors stated however, that for mesiodistal tooth movement, rectangular wire is preferred because of its additional feature of buccolingual root control.
2. Ligation method
Various methods of ligation are available: - stainless steel ligatures, elastomeric modules, polymeric coated modules and finally the self ligating brackets, which may be having a spring clip (Hanson SPEED and Adenta Time) which pushes the wire into place, or it may have a passive clip which does not press on the wire (Activa and Danson II brackets.)
Elastomeric ligatures are adversely affected by the oral environment, and demonstrate stress relaxation with time and great individual variation in properties.
Stainless steel ligatures can be tied too tight or too loose depending on the clinicians technique.
Self ligating brackets with a passive clip have been shown to generate negligible friction.
Henao & Kusy (Angle Orthod. 2004) compared the frictional resistance of conventional & self ligating brackets using various archwire sizes.
They reported that self ligating brackets exhibited superior performance when coupled with smaller wires used in early stages of orthodontic treatment.
However when larger 016 x 022” and 019 x 025” AW were tested, the differences between self-ligating & conventional brackets were not so evident.
3. Bracketa. Bracket Material: For most wire sizes, sintered stainless steel brackets
produce significantly lower friction than cast SS brackets. (upto 38-44% less friction.) This difference in frictional forces could be attributed to smoother surface texture of sintered SS material.
Ceramic brackets, in spite of their superior esthetics, have frictional properties far inferior to stainless steel. Highly magnified views have revealed numerous generalized small indentations in the ceramic bracket slot, while SS brackets appear relatively smooth
Since ceramic brackets on anterior teeth are often used in combination with stainless steel brackets and tubes on premolar and molar teeth, retracting canines along an archwire may result in greater loss of anchorage because of higher frictional force associated with ceramic than steel brackets. Greater caution in preserving anchorage must be exerted in such situation.
Titanium brackets are comparable to SS brackets in the active configuration & are a suitable substitute for SS in sliding mechanics.
EFFECTS OF SALIVA ON KINETIC FRICTION
SALIVA or saliva substitute serves as an excellent lubricant in sliding of the bracket along the archwire.
Kusy found that saliva had a lubricous as well as an adhesive behaviour depending behaviour on the archwire bracket combination.
SS showed an adhesive behaviour with saliva and there was a resultant increases in coefficient of friction in the wet state
FRICTIONLESS MECHANICSCANNE RETRACTION SPRINGS
EN MASS RETRACTION SPRINGS
frictionless mechanics
In frictionless mechanics, teeth are moved without the brackets sliding along the archwire.
Retraction is accomplished with loops or springs, which offer more controlled tooth movement than sliding mechanics
frictionless system Disadvantages the complexity of loop forming the presence of unknown factors minor errors can result in major differences in
tooth movement some patients find the loop uncomfortable
EVOLUTION OF LOOPS
As early as 1915 (in first issue of I.J.O), Ray.D.Robinson demonstrated about Efficiency of loop arch wire
Dr.Robert H.W Strang (1933) pioneered the loop design for edgewise mechanics
On the other hand Dr.P.R.Begg (1952) advocated their usage in the initial phase of Begg treatment
With advancement in techniques of scientific testing and better understanding of physiological principles of tooth movement improvisation of loop design continued through 60’s and 70’s
Eminent orthodontist like Dr.Joseph Jarabak,Dr.Charles Burstone, Dr.Robert Ricketts must be credited for their single contributions
In the last decade some other contributors are: Dr.Poul Gjessing – P.G.RETRACTION SPRING/AJO/1985,92 Dr.Raymond Siatkowski- OPUS LOOP/AJO/1997
General properties of the loops: David lane (Angle orthodontist 1980)
No loop exerts a truly continous force. Loops may be contoured to open or close up on
activation. The use of any loop will result in reduced stiffness and
greater range of activation because of increased length of wire between brackets.
Loop stiffness may be decreased by incorporating helices in the loop or reducing cross sectional dimensions of the wire of the loop.
Elastic range of loop is increased if the loop is activated in the same direction as it is formed. (Bauschinger effect)
SPACE CLOSING LOOPS Closing loop arch wires should be fabricated from rectangular wire to prevent wire from rollingin the bracket slot
The performance of the loop,from the perspective of engineering theory,is determined by 4 major Characteristics
1. Spring properties2. Moment it generates3. Its location4. Additional design principle
(WILLIAM.R.PROFFIT,II EDITION)
1. SPRING PROPERTIES
It is determined almost totally by the A. wire material B. size of the wire C. distance between point of attachment
Changing the size of the wire produce largest change in its characteristics,but the amount of wire incorporated in the loop is also important
FROMWILLIAM.R.PROFFIT
II edition
2.Moment it generates
To close an extraction space while producing bodily tooth movement closing loop must generate not only closing force but also approximate MOMENT
Bends placed on the mesial and distal legs of loop are called as ALPHA and BETA respectively
These bends produce ALPHA and BETA moments when wire is placed into bracket
• The ALPHA MOMENT produces distal root movement of anterior teeth,
•while the BETA MOMENT produces mesial root movement of posterior teeth.
• If ALPHA = BETA NO VERTICAL FORCE
•If ALPHA not BETA ,VERTICAL FORCE
If BETA moment is >ALPHA posterior anchorageis enhanced by the mesial root movement of posterior teeth and net extrusive effect on posteriors
and intrusive force on anterior teeth.
If ALPHA moment is > BETA anchorage of anterior segment is increased by distal root movement and net extrusive effect on anterior teeth and intrusive effect on posterior.
3.Its location
Its location is very important for its performance in closing space.
As gable bends are incorporated,the closing loops functions as the V bend in the arch wire.effect of V bend is very sensitive to its location
There can be 3 locations of V bend
1.Equal distance
2.Closure to anterior
3.Closure to Posterior
4.Additional design principle
FAIL SAFE this means that ,although a reasonable range of action is desired from each activation tooth movement should stop after that.If patient does not come for scheduled appointment
Controlled force designed to produce desire tooth movement at the rate of appr. 1mm per month should not exceed 2mm per month
So movement would stop if patient missed appointment
Design should be as simple as possible
During activation of loop it is considered more effective when it is closed rather than opened
OPEN VERTICAL LOOP
Dr.Robert.W.Strang(1933).
It was used for retraction of anterior teeth.
Height of the loop was 8mm.
CLOSED VERTICAL LOOP
Only being difference is horizontal overlapping
BULL LOOP
Dr. Harry bull (1951)
variation of standard vertical loop
Loops legs were in contact with each other
.021x .025stainless steel
VERTICAL OPEN LOOP WITH HELIX
Dr Morris Stones Main purpose is to
increase the working range
1975
OMEGA LOOP
As mentioned by Dr Morris Steiner this loop is named so because of the resemblance to the
Greek letter omega.
The loop is believed to distribute the stresses
more evenly
CLOSED VERTICAL LOOP WITHHELIX (MORRIS STONER/1975)
DELTA LOOP
It was described by Dr Proffit.
16 x 22-0.018 slot 18 x 25-0.022 slot Approximately 20
degree angulation on either side
OPUS LOOP RAYMOND.E.SIATOWSKI AJODO 1997
Opus loop, capable of delivering a nonvarying target M/F within the range of 8.0 to 9.1 mm inherently, without adding residual moments via twist or bends (commonly gable bends) anywhere in the arch wire or loop before insertion
As the tooth moves the appld force decreases- moment can or
M/f changes as tooth moves and the tooth responds –
Controlled tipping-translation-root movement
Factors affecting the m/f of the opus loop
1. Wire size and young's modulus have little effect on inherent m/f.[but a major impact on LDR]
2. The greatest effect on m/f-height of the loop
3. Increasing the number of apical helixes-lesser effect on m/f
4. Varying the loop diameter does not significantly affect the m/f. It is maximized –loop dia 3.5mm
Position of the opus loop
it is always placed close to the ant end-1.5mm
Angulation of the vertical le-70 degrees to the plane of the bracket
The experimental results with the opus loop show that the opus loop has to be bent with great accuracy to achieve the design potential
Opus loop can be fabricated from 16×22, 18×25, or 17×25 TMA wire. The design of the loops calls for an off center positioning with the loop 1.5 mm from the mesial canine bracket. It is activated by tightening it distally behind the molar tube and can be adjusted to produce maximal, moderate or minimal incisor retraction. (Siatkowski 2001).
T-LOOP T-LOOP is one of the most versatile space
closure devices available. This was developed by Charles Burstone in 1962. USES: 1. Segmental space closure: a. Anterior retraction b.Symmetric space closure c.Posterior protraction 2. En-masse space closure
ADVANTAGES: The advantages of T-Loop over a vertical loop : 1. Produces higher M/F ratio 2.Lower load deflection rate 3.Delivers more constant forces
Differential force system: The force system produced by a segmented T-
loop consist of several components: 1. Alpha moment 2.Beta moment 3.Horizontal forces 4.Vertical forces
Alpha moment : Produced by placing a bend on the mesial leg of T-loop.It produces distal root movement of anterior teeth.
Beta moment : This is the moment acting on the posterior teeth.It produces mesial root movement of posterior teeth.
Horizontal forces: These are the mesio-distal forces acting on the teeth. The distal forces acting on the anterior teeth always equal the mesial forces acting on the posterior teeth.
Vertical forces :These are intrusive-extrusive forces acting on the anterior or posterior teeth. These forces results from unequal alpha and beta moments.
10 mm
5 mm2 mm
4 mm
ALPHA(ANTERIOR) SEGMENT
BETA(POSTERIOR) SEGMENT
Fabrication: - Made by .017 .025” TMA wire(Titanium-
molybdenum alloy). Advantages of TMA over S.S wire -Low modulus of elasticity -Generate low force -High range of action
Preactivation Bends:
-To increase the moment- force ratio by decreasing the force.
1
2
3 4
65
The center position of the spring can be found by:distance = (interbracket distance –activation)/ 2
where distance = length of the anterior and posterior arms (distance from the center of the T loop to either the anterior or posterior tubes)
interbracket distance =distance between the canine and molar brackets.
Activation = millimeters of activation of the spring
Passive position Neutral position Spring activated
T-loop position and anchorage control AJODO 1997
Phases of tooth movement
Space closure should be monitored periodically. To check the remaining activation, the spring is removed from the canine bracket and the remaining activation at the neutral position is measured
Control of side effects:
Tipping of the anterior and posterior segments into extraction spaces.
Flaring of the anterior teeth. Mesial in rotation of the buccal segments Excessive lingual tipping of anterior teeth.
MUSHROOM LOOP
In this loop -apical addition of the wire in archial configuration decreases the load deflection rate and there for produces more lower and continuous forces
Archial shape has added adv-increases the added moment when the spring is activated
0.017xo.o25 TMA
Bypass premolars and directly engaged the molar auxillary tube –allows force/moment delivery to the active and reactive teeth directly
Increase interbracket distance has the effect of reducing the errors in the loop placement and Maintains force cosistency
Stabilize the posterior teeth with a transpalatal arch and buccal segment
Care taken –make a trial activation ,correct any distortion that may occur under initial loading
Loop activated up to 5 mm
Reactivation done approximately every 6-8 weeks
Ricketts maxillary canine retraction
Combination of double closed helix and an extended crossed T
In critical anchorage case, 45° gable bends and 0-5g/mm of activation (Ricketts 1974)
Rapid canine retraction through Distraction of PDL Eric JW Liou, DDS, MS, and C. Shing Huang, D..AJODO .1998 oct
procesure At the time of first premolar extraction, the interseptal
bone distal to the canine was undermined with a bone bur, grooving vertically inside the extraction socket along the buccal and lingual sides and extending obliquely toward the socket base.
Then, a tooth-borne, custom-made, intraoral distraction device was placed to distract the canine distally into the extraction space.
It was activated 0.5 to 1.0 mm/day immediately after the extraction. The anchor units were the second premolar and first molar
With this technique, anchorage teeth can withstand the retraction forces with no anchorage loss and without clinical or radiographic evidence of complications, such as root fracture, root resorption, ankylosis, periodontal problems, and soft tissue dehiscence.
technique reduces orthodontic treatment duration by 6 to 9 months in patients who need extraction, with no need for an extraoral or intraoral anchorage devices and with not unfavorable short-term effects in the periodontal tissues and surrounding structures
NITI CANINE RETRACTION SPRING JCO/JULY 2002
YASOO WATANABE, DDS, PHDKEISUKE MIYAMOTO, DDS, PHD
Simple closing vertical loop with antitip &antirotation bend.
The major advantage of the spring is the ability to use it without a preliminary leveling stage ,because it can
simultaneously retract the canine and level the posterior teeth.
.016 * .022 titanal wire .10 mm loop is made
the vertical closing loop and the antitip and antirotationbends were memorized by heat-treating the wire in an electric oven.
•Light continous force produced even large activationWithout the need for reactivation of the closing loops, patient discomfort, chairtime, and appointment frequency can all be reduced.
•A 2 × 4 appliance and a lingual arch and/ortranspalatal arch were used for-anchorage reinfocement
.
Retraction utility arch
The retrusion arch originates in the auxiliary tube on the molar, and 5-8mm of wire should protrude anteriorly before a posterior vertical step of 3-4mm is placed.
The vestibular segment extends anteriorly to the interproximal region between the lateral incisor and the canine. At this point, a 90° bend is placed
Activation
Gable bend for intrusion
The wire is pulled 2-3mm posteriorly and then bent upward at a 90° angle for retraction .
Canine retraction with j hook headgear
By Ayala AJO-DO 1980 Nov (538-547):
The hook is attach mesial to the canines Head gear exert a force over them so that they will
slide along the wire Since this incorporates extraoral anchorage in canine
retraction, it should be effective in maximum anchorage cases.
Three different vectors of force, representing high, medium, and low pull headgear, were applied.
The high-pull force vector was placed at an angle of 40 degrees above the occlusal plane, the medium-pull at 20 degrees above, and the low-pull parallel to the occlusal plane
high-pull headgear produced the least tipping effect during maxillary canine retraction
PG retraction spring Poul Gjessing of denmark 1985
Spring design
made from 0.016 by 0.022 inch stainless steel wire.
The predominant active element is the ovoid double helix loop extending 10 mm apically.
It is included in order to reduce the load/deflection of the spring and is placed gingivally so that activation will cause a tipping of the short horizontal arm (attached to the canine) in a direction
that will increase the couple acting on the tooth. The smaller loop occlusally is incorporated to lower levels of
activation on insertion in the brackets in the short arm (couple)
Clinical Application
1. Alignment of the buccal teeth. The spring is constructed to resist tendencies for tipping and rotation during canine retraction
.2 Adjustment of faciolingual loop inclination. The correct faciolingual position of the spring
3. Bracket engagement. The anterior extension of the spring is engaged in the canine bracket. The posterior extension must be engaged in both the premolar and the molar
4. Activation. The spring is activated by pulling distal to the molar tube until the two loops separate. The wire is secured with a gingival bend in the posterior extension. Reactivation to the initial spring configuration should be done every four to six weeks.
1.2mm of space closer takes place in 4 weeks
A study was conducted (Divakar Karanth and V. Surendra Shetty. JIOS 2002) to analyze the horizontal force exerted and the load deflection characteristics of the T-loop retraction spring and PG retraction spring which were fabricated from different dimensions of stainless steel, cobalt chromium, beta titanium and titanium niobium wires and to compare them.
The springs were fabricated on a template for standardization purpose and horizontal forces exerted by these springs were measured for every millimeter of activation till 6 mm.
The results of the study revealed that PG springs exerted relatively low magnitude of force and relatively constant load deflection rate when compared to T spring.
Beta titanium and titanium niobium springs showed force values closer to the optimum force required for translation of canines.
K-SIR ARCH
By Dr VARUN KALARA (JCO 98)
Fabrication 19x25 TMA wire Closed 2x7 mm loop at the extraction site
Indication Retraction of anterior teeth in the first PM extraction
with deep overbite and excessive overjet-require both intrusion and maximum anchorage
A 90 bend is placed on the arch wire at the level of loop that creates two equal and opposite moments that counters tipping moments produced by activation forces.
An additional 60˚ v bend is placed at 2mm distal to u loop. This is a off centered bend that creates greater moments at molars to- Increase molar anchorage To intrude anterior teeth
A 20 anti rotational bend is placed distal to u loop to prevent buccal segment rolling mesio -lingually
A trail activation is performed outside mouthIt releases stresses build up in wire bendingarch wire after trail activation with reduction in severity of bends
Neutral position is determined with legs extended horizontallyIn neutral position loops are 3.5mm apart than 2 mm
Arch wire is placed and activated by 3mm and cinched back2nd premolar is bypassed to increase inter bracket distance
Initially there is tipping but as loop starts deactivating it produces bodily movement than root movement
Thus arch wire not to be reactivated at short intervals but after 8 weeks.
It produces 125 gm of intrusive force on the anteriors.
Adv- simultaneous retraction and intrusion Shortens treatment time
Statically determinate retraction system
This novel system consisted of a single-force cantilever arm
Made of 0.017 x 0.025 TMA wire for active retraction
active component for space closure is a cantilever, it is simple to measure the force system
of the spring with a force gauge
The system consists of passive rigid stabilizing units and active retraction springs. Rigid stainless steel wire is used for the buccal stabilizing units and an anterior stabilizing unit. The buccal stabilizing units are connected with a transpalatalarch to the contralateral side.The anterior stabilizing arch has a distal extension with a hook about six mm superior to the canine bracket slot. The SDRS spring is made with 0.017 3 0.025–inch titanium molybdenum alloy wire. A turn of helix is placed in front of the auxiliary tube for the molar and ended with a hook at the anterior end. A 90 bend is placed in the middle of the spring. The spring is activated 90 at the helix as well. The hook from the SDRS spring and the extension hook of the anterior segment are connected with a ligature.
(A) The statically determinate retraction system (SDRS)before activation.
Activated shape of the SDRSNote the indicatedlocations of the center of resistance for the anterior and posteriorsegments and the line of action
Advantages
SDRS uses frictionless mechanics
The cantilever spring has a low load-deflection rate, thus constant force
The force direction changes minimally and remains constant during space closure
Its force system can easily be visualized & measured and can be modified by the clinician.
Three piece intrusion and retraction
Bhavna Shroff, Won M. Yoon, Steven J. Lindauer Angle Orthodontist 1997 No. 6, 455 - 461
Principle
Applying an intrusive force parallel to the long axis of the incisors and lingual to the center of resistance of the anterior segment of teeth is a more efficient means of achieving simultaneous intrusion and retraction of these teeth
Design
Arch consists ofA rigid anterior segment of wire (0.021" x 0.025" or larger stainless steel) is placed into the brackets of the four incisors and extended distally to the mesial aspect of the canines.
This anterior wire is stepped up around the canines to avoid any interferences with the brackets. Typically, this anterior segment extends 2 or 3 mm distal to the center of resistance of the anterior segment of teeth
Bilateral tipback springs of 0.017" x 0.025" TMA the wire is bent gingivally mesial to the molar tube and the helix is formed .the mesial end of the cantilever is bent in to a hook .the cantilever than activated by making bend mesial to the helix at the molar tube, such that anterior end lies passively in the vestibule
Intrusive force- 60 g at the midline (30 g per side).
Distal force is added by placing an elastomeric chain or elastic extending from the molars to the anterior segment of wire on each side
TRANSLATION ARCH JCO/1997MARTINA
016" × .022" TMA for .018" bracket slots. The anterior segment of the Translation Arch is
inserted into the incisor brackets, and the two buccal segments into the gingival first molar tubes
Two loops, extended as far vertically as possible, connect the anterior and posterior segments. The bends in the TMA wire should be rounded to avoid fracturing the wire.
Translation Arch is easy to manage clinically. The system of forces and moments required for bodily
incisor retraction is quite complex
Magnets
Magnetic force systems in orthodontics - Blechman AJO-DO Volume 1985 Mar (201 - 210)
The use of operator-controlled, small, permanent magnets for inter-maxillary and intra maxillary mechanics.
Upper and lower magnetic poles in attraction must face each other in order to generate the force necessary to move the upper canine distally along the base arch wire and the lower buccal segments mesially along the base wire
The force that is developed is determined solely by the distance that is set between the magnetic poles, that is, the air gap.
F ∞ 1∕distance²
Upper canine retraction can be enhanced, if needed, by the addition of a third magnet attached to the lower sectional arch and positioned mesially to repel the upper magnet.
Anchorage for the lower arch is protected by a full heavy arch wire.
Intramaxillary magnetic forces to close spaces.
The Hycon Device
The Hycon Device for extraction space closure was developed in Germany orthodontist Dr. winfried schutz in 1980s.
This system uses a screw mechanism that is attached posteriorly to the molar tube and anteriorly to the anterior segment to be retracted.
The nut and bolt assembly can be turned by the patient for space closure.
It is compatible with all common fixed appliances.
Use of implants to facilitate retraction mechanics In recent years, with the introduction of miniscrews,
palatal implants and miniplates, absolute anchorage or skeletal anchorage has become a reality.
In case of direct anchorage, a miniscrew or miniplate is inserted near the upper first molar during retraction of anterior segment.
Nickel titanium coil springs or elastics are used to connect this bone anchor with the anterior segment.
In many cases, incisors and canines can be distalized simultaneously with sliding mechanics.
A comparison between friction and frictionlessmechanics with a new typodont simulation systemJoon-No Rhee, DDS, MSD,a Youn-Sic Chun DDS, MSD, PhD,b and Joon Row, DDS, MSD, PhDc (Am J Orthod Dentofacial Orthop 2001;119:292-9)
This study was designed to explore the differences between friction and frictionless mechanics for maxillary canine retraction with the use of a new typodont simulation system, the Calorific machine system.this study concluded that
Friction mechanics were superior to frictionless mechanics for rotational control and arch dimensional
maintenance. Frictionless mechanics were more effective than friction mechanics at reducing the tipping and extrusion.
There was no significant difference in anchorage loss between the 2 methods.
This study could not establish the superiority of 1 of the 2 methods over the other.
conclusion
Today's orthodontist needs a working knowledge of both friction and frictionless mechanics. There are indications for both, and therefore a practitioner should not be limited to one or the other.
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