Biomechanics and Use of Loops in Orthodontics.pptx

Biomechanics and Use of Loops in Orthodontics

overview  Introduction  Advantages of loops  Loop principle

 Types of loops  Force system of loops  Clinical application of loops  Conclusion

Introduction  Concept of loops given by Dr.Ray Day Robinson In1915 in

International journal of Orthodontia  Dr.P.R.Begg extensively used vertical loop for rotation

control; space opening & closing  Dr.R.H.W Strang introduced Vertical loop  Stoner (1962) introduced a horizontal loop

Advantages of loops  Increases resiliency of wire  Reduces force  Increase In range by adding wire In between

interbracket span

 Closing loop mechanics  Absence of friction between the bracket and the wire  Force levels are easier to evaluate clinically  Moment/force ratio of the cuspid and the posterior

segment is predictable and controllable during retraction

Loop principles

1)

Function better when activation „closes them‟ instead of „opening them‟

2)

Loops function better when their form is perpendicular to the movement they must perform

3)

The more wire a loop has, less force it will exert

Loop principles

 No loop produce continuous force  Stiffness of loop may be reduced by helix incorporation or

by reducing the cross-sectional dimension of the wire  Elastic range of the loop can be increased by activating in

the loop In the same direction it is fabricated

TYPES OF LOOPS  1.Simple loop loops without helix  2.Springs with helix

Based on shape  1.Vertical loops- movement In horizontal direction  2.Horizontal –vertical axis movements  3.Combination -Vertical loop+ Horizontal loop –deflected In all

three planes  Open or closed types

Vertical loop  Legs of the loop are directed vertically  Activated In any direction

perpendicular to these component  Can be single or double  Contoured In open or closed loops

 Activation is done by compressing legs

CLINICAL USES  Space closure -Single closed vertical loop  Opening space -Single Open vertical loop  Derotation of tooth- Single Open vertical loop 

-Double vertical loop

 Move labially or lingually displaced tooth into line- Double vertical loop  Move teeth bodily In mesial or distal direction -Double vertical loop

MODIFICATION OF VERTICAL LOOPS  Twin helical loop

 Omega loop

 BULL Loop

Ω

Horizontal loop

 Legs of the loop are directed horizontally

 Used for occluso-gingival tooth movements  Leveling the plane of occlusion is readily accomplished

by horizontal loops

 Uses

1.Intrusion of ant. teeth that are in supraversion and for extrusion of post. teeth that are in infraversion.(bite opening) 2.Class II div 2 malocclussion Horizontal helical loops place added intrusive and tipping forces on central incisors

3.) Extrude maxillary canines delayed in

eruption 4. Elevation or depression of individual

teeth-Double horizontal loop 5. Axial paralleling of teeth

6. Correction of rotation with a light continuous force

Combined horizontal & vertical loops

Box loop

 Two loops with horizontal

segments of wire at the gingival level functioning as the working bases.  It is capable of moving teeth

in any direction

 Width is equal to the width of single teeth  This lies in the same plane as that of the arch wire  In occlusogingival plane-deflection is related to the amount

of the wire In the horizontal plane& bending at the corner of the loops  Deflection in the labiolingual plane is related to the total

amount of wire contained in the box loop

 When employed as root tipping device  Rectangular wire should be used to avoid

buccolingual displacement of the apex & to develop rigidity In anchor area  The anterior leg of the box should be shorter than

the posterior leg when uprightening the teeth

 The crown of the tooth to be moved should be tied

directly to the tooth behind it in order to prevent its tipping in an opposite direction to the root .

Bent in Stop loop

 Molar stop- mesial to it  Maintain arch length  Increase In arch length by slight opening loop

Transverse loop  In case of helical loops, when the plane of

the helix is perpendicular to the arch wire, it is referred as transverse loop.

 Used -correct axial inclinations or

mediolateral displacements so as to reduce crossbite.

Characteristics of the force system with loop design  Force & magnitude  Low load deflection rate  Proper moment to force ratio  Force constancy w.r.t deflection

Burstone CJ & Koening (1976)  Described three characteristics feature of retraction

spring  1.Moment-to force ratio  2. Force to deflection rate  3. Maximum strength (Fmax) that the spring is able to

release without permanent deformation.

 Ideally these three factors should be able to determine

respectively:  1. control of the center of rotation;  2. maintenance of ideal force levels during orthodontic

tooth movement;  3. use of ideal levels of strength for orthodontic tooth

movement.

1.Moment to force ratio

 Most important to determine In manner tooth will move  The M/F ratio determines the center of rotation of a tooth or

segment of teeth, thus allowing translation, tipping or root movement  When force is applied at a distance from Cres Mf causes

tipping- undesirable

1.Moment to force ratio  In order to achieve translation counter moment Mc

should be applied  The ratio of counter moment to force applied is

called as M/F ratio (expressed in mm)

 M/F ratio Uncontrolled tipping < Controlled tipping

< Translation < root movement  M/F ratio remains constant with increased

activation for simple springs but varies with complex springs

Factors affecting Moment to force ratio 1.

Height of the loop

2.

Horizontal loop length

3.

Diameter of loop

4.

Apical length of loop

5.

Helix incorporation

6.

Angulations of loop legs

7.

Placement of loop

Load /deflection  Thus it represents load needed to produce unit deflection

Or



 Force dissipated by the spring when it deactivates by unit

distance  Thus spring with low L/D ratio is preferred  1.Maintain constant force levels during retraction.  2.Less force change from 1mm activation to the next

Relationship of force and deflection  Hooks law

 Within proportional limit of an object deflection is directly proportional

to load  R= F/D (Units=gm/mm)  R= load deflection rate or spring gradient or spring constant is constant

which is the quotient of applied force (F) divided by deflection(D)

Maximum elastic force (Fmax) which the spring exerts

 Must be higher than

the force applied during

activation.  Prevents permanent deformation of the spring

during accidental overloads such as with mastication

or following an aggressive activation

Biomechanics of closing loop springs  Burstone and Koenig investigated the basic configuration of a

closing loop spring in 1976  It consists of .016" steel wire bent into a vertical loop of

varying length.  The closing loop spring lies halfway between the cuspid and

the second premolar and is then activated with varying strengths

1.Loop design  Accommodate a large activation,  Deliver relatively low and nearly constant forces (i.e.

Exhibit low load/deflection characteristics),  Comfortable to the patient,

 Easily fabricated.

A. Height of the vertical loop  Increased - greatest effect on reducing F/D ratio and

simultaneously increasing the moment  Anatomic constraints such as the depth of the vestibule  Overcome this problem is by adding wire horizontally to

increase

Horizontal loop length  Moment-to-force ratio was not as greatly effected by horizontal

changes compared to vertical changes

B. Diameter of the vertical loop

Minimal influence on the system.  An increase in the diameter increases the M/F ratio and decreases the

F/D ratio  C.Incorporating helix  Decreases the F/D ratio but it doesn't affect the M/F ratio

2.Increasing the inter-bracket distance

 Increase in the M/F ratio (less effect, however,

than increasing the height of the loop) and also

increases the F/D ratio

3.Loop Position

 Traditionally,closing loops are

typically placed immediately distal to the lateral incisors or canines.  Allows for repeated activation

of the loop as the space closes.

T-loop positioned midway between the first molar and the canine.

The preactivation bends provide equal and opposite moments in this

position. Encourage reciprocal space closure,

OFF CENTERING -V-bend principle

6.Loop Preactivation OR Gable bends Gable bends increase root control and, thus, avoid “dumping” of the teeth as the space closes. Increase the moments delivered to the teeth & augment the moments that occur during

activation of the closing loop (residual moment.) Promote anchorage control

How works??  When Gable bends are placed in the occlusal portion of a vertical

loop configuration, an unintended mesiodistal force is introduced  This force will alter the desired mesiodistal force originally intended

because of the cross over of the vertical legs  This cross over wire shortens the horizontal wire length between the

brackets  Functions as a V-bend in the archwire

Disadvantages  The teeth must cycle through controlled tipping to translation

to root movement to achieve net translation .  loop's neutral position (zero activation position) becomes ill

defined. making it difficult to achieve proper activations.  The resulting ever-changing periodontal stress distributions

may not yield the most rapid, least traumatic method of space closure

Clinical application of loops

 Alignment & leveling  Space closure  Finishing

1.Individual tooth movement  REQIURED MOVEMENT

Labial  Lingual 

 Double vertical loop –Open  Double vertical loop –Open

 Depression  Elevation  Double Horizontal loop or Box

 Rotation  Root tipping

 Double Horizontal loop or Box  Double vertical loop –Open or

Box  Box or double horizontal (rectangular wire only)

2.MIDLINE CORRECTION  Mesial or distal movement :  Double vertical loop

 Combination of open and

closed loops

3.BITE OPENING  T loop mesial to canines.  Arch wire in the anterior section between the two

loops should have a reverse curve to transmit the pressure equally to all four incisor

4.Axial inclination correction

 Double vertical loop –Open or Box

 Box or double horizontal (rectangular wire

only  5.Second molar alignment

Intrusion of anterior segment Horizontal loop can be achieved when it is used to depress the anterior segment.  If a pair of these loops is contoured mesial to the canine, the

reciprocal activity with a long range of action will be very effective.  Asymmetric T loop- Hilger

SPACE opening (Opening loops/ Expansion loops)

 When compressed between adjacent teeth & seated into

their respective brackets, the stored elastic force developed pushes the teeth apart.

To create space for alignment of Single or  a no. of teeth

Various expansion loops made of round stainless steel wire & differing only in no. of turns in the helix

½ Turn helix 1 ½ Turn helix 2 ½ Turn helix 1 ½ Turn helix with 2 moment arms

Molar distalisation-K loop  Made of .017”×.025” TMA wire

 Used for molar distalization along with a

Nance button.  Each loop of K should be 8mm long 7 1.5

mm wide.  The legs of K should be bent down 20˚ &

inserted into molar tube & premolar bracket.

Space closure

Two methods  Friction the teeth slide along the archwire  Frictionless incorporated loops which produce forces

and moment to move the teeth in desired position

 The forces generated In the loop or the arch wire will be

transmitted to tooth through the bracket attachment as a tipping or bodily force depending upon the contour or mode of activation.

Loop designs for retraction  Close vertical loop  I-loop  T-loop or Segmented "T" loop (Burstone;1976)  Bull loop (Henry bull,21x25 ss)  Keyhole loop ( R.Roth) orDouble key or DKL arch

 Mushroom loop (with or without pre-activation bends)

Loop designs for retraction † PG spring (Poul Gjessing, 16x22 ss,1985) † Opus loop (Reymond Siatkowsky,1997) † Rickets retractor (R.Rickets,1979,.16x.16 blue elgiloy) † Drum spring canine retractor † K-sir arch wire (modification of burston and Nanda

segmented loop)

T loop Phases of tooth movement  Tipping

 Translation

 Root movement

Symmetrically centered spring

 M/F ratio of 6/1 to the teeth  2mm of deactivation -- M/F ratio increases 10/1  1-2 more mm of space closure -- M/F increases to

12/1 high (root movement)

Modifications of T- loop

Broussard Loop 5m m

2mm

5mm

Asymmetrical T loop

Opus loop  It is capable of delivering a nonvarying target M/F within the

range of 8.0-9.1 mm inherently, without adding gable bends

Delta loop  It is half of a box loop, distorted so that

it can fit into a single interproximal space.  The range of this loop can be increased

by adding helices at the lower corners.

Keyhole loop

Open "I" loop

Ricketts' maxillary canine retractor

 It is a combination of a double closed helix and an extended crossed

'T'.  The retractor is fabricated using.016" .016" blue elgiloy wire  In critical anchorage cases, 45 gable bends and 30-50 g/mm

activation is recommended .  For lower canine retraction, double closed helix is used. This

delivers50g/mm of activation

THE POUL GJESSING CANINE RETRACTION SPRING 

0.016 X 0.022 inch stainless steel



active element = double helix loop extending 10 mm



genty rounded = avoids effect of sharp bends on load/deflection



use of the greater amount of wire in the vertical direction = minimizing horizontal wire increases rigidity in the vertical plane

Mechanics associated with loops are used improperly

 Loss of anchorage,  Excessive verticalization of incisors,  Increase of overbite,

Mechanics associated with loops are used improperly

 Dental mobility,  Root resorption,  Increase in treatment time may result,  Irreversible damage to the patient

Conclusion  It is important to prevent undesired tooth movement

, ensure optimal tooth movement and effective space closure, frictionless mechanics (loops)must be understood and controlled.