OPUS LOOP

Presented by-DR. PARAG DESHMUKH

Introductin:• Closing loops are used in orthodontics with both segmental

and continuous archwires to generate the desired forces and moments to move teeth in a predictable manner.

• Many closing loop shapes are being used, such as vertical or teardrop loops, T-loops, L-loops, Gjessing springs, and others.

• In the literature, moment-toforce ratios of approximately 10/1 and 7/1 mm are indicated for translation and controlled tipping, respectively.

• At these relatively high moment-to-force ratio levels, stresses reportedly distribute more evenly through the entire root with minimal changes in the mechanical properties during activation; this reduces injuries to teeth and surrounding tissues.

OPUS LOOP :

• Developed by Raymond E. Siatkowski in 1997.

• He designed a new spring which delivers a non varying target M/F ratio

within the range of 8.0-9.0 mm inherently, without adding residual

moments by twist or bends anywhere in the arch wire or loop before

insertion.

Raymond E, Siatkowski , Am J Orthod Dentofac Orthop 1997;112:393-402.)

Physical properties:

• During loop activation, an external load application causes its deformation. The deformed spring produces a force during deactivation as it tries to regain its original form, based on its springback ability.

• When the loop is activated it absorbs and store energy and gets deformed, as it tries to regain its original form during deactivation, it will release the same energy by generating an equivalent force that gradually reduces,

F/D :

During activation:

• Refers to amount of load needed for unit deflection of spring.

• Numerically calculated as amount of load divided by amount of deflection.

During deactivation:

• It will loose the same amount of force per unit deactivation.

• While deactivating, it will generate force of 500 gm, which will be felt at both ends.

• If we were to use another loop which requires a force of 100 gm for 5 mm activation, its load deflection rate would be 20 gm/mm.

• During deactivation, it will initially generate a force of 100 gm and its force will drop by 20 gm for every 1 mm movement of cuspid.

From clinical point of view orthodontic spring should have :

• A large range of activation so that frequent activations are not needed.

• A large allowable working load.

• A low load deflection rate.

Moment to force ratio

• If a force is applied to a body & the force does not act through the center of resistance, it causes the body to rotate.

• Rotation is the movement of a body where no two points on the body move the same amount in same direction.

• Moment: The tendency to rotate is called a moment.

force

Moment

d

Mf = F x d

M

The direction of moment is found by following the line Of action around the centre of rotation toward the point of origin.

F

Siatkowski RE. Force system analysis of V-bend sliding mechanics. J Clin Orthod 28(9):543, 1994.

Siatkowski RE. Force system analysis of V-bend sliding mechanics. J Clin Orthod 28(9):543, 1994.

• No closing loop design previously has been capable of delivering M/F at these levels, most having inherent M/F of 4-5 mm or less.

• To achieve net translation, orthodontists have had to add residual moments to the closing loop arch wire with angulation bends (gable bends) anterior and posterior to the loop.

Disadvantages of adding residual moments:1. The teeth must cycle through controlled tipping to

translation to root movement to achieve net translation (lower Young's Modulus materials go through fewer of these cycles for a given distance of space closure).

2. The correct residual moments are difficult to achieve.

3. The resulting ever-changing PDL stress distributions may not yield the most rapid, least traumatic method of space closure.

• If a closing loop design capable of achieving inherent, constant M/F of 8.0 to 9.1 mm without residual moments were available, en masse space closure with uniform PDL stress distributions could be achieved.

• Such a mechanism would be less demanding of operator skill to apply clinically and might provide more rapid tooth movement with less chance of traumatic side effects.

• Evidence from animal studies shows that intermittent force systems may produce more efficient tooth movement, perhaps 1 hour of force system application followed by 7 hours of rest.

Gibson JM, King GJ, Keeling SD. Long-term orthodontic tooth movement response to short-term force in the rat. Angle Orthod 1992.

• A mechanism based on micromotor technology could be designed in the future to activate/deactivate closing loops on a time schedule, but it would require loops without residual moments to produce a true rest period.

Design

Raymond E, Siatkowski Am J Orthod Dentofac Orthop 1997;112:393-402.)

• The loop can be fabricated from .016X.022 or .018x.025 SS or .017x.025 inch TMA or SS wire.

• The design of the loop calls for an off centre positioning with the loop 1.5 mm from the canine bracket.

Activation: • It can be activated by tightening it distally behind the molar tube and

can be adjusted to produce maximal ,moderate and minimal incisor

retraction, but like all closing mechanisms long range of action, must be

monitored carefully.

Raymond E, Siatkowski Am J Orthod Dentofac Orthop 1997;112:393-402.)

• Opus loop is capable of delivering a non-varying 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.

• The resulting precise force systems delivered with non varying M/F can

move groups of teeth more accurately to achieve predetermined position.

Continues arch wire closing loop

ADVANTAGES OF OPUS LOOP

• Only the opus loop has a range of 8.0 to 9.1mm without gable bends, no loop generates this M/F ratio.

• The opus loop maintains the desired M/F range when positioned off-center.

• The posterior and anterior moments are in opposite direction ,decreasing the tendency to change occlusal plane.

RELATED ARTICLES

Continuous arch wire closing and verification loop design, optimization. Part I.Raymond E. Siatkowski, DMD (Am J Orthod Dentofac Orthop 1997)

AIM:

• To systematically derive and verify a closing loop design capable of delivering the required M/F inherently, without adding residual moments, so that more precise force systems with non varying translatory M/F can be delivered by dosing loops in a continuous arch.

Introduction :

• The design process uses Castigliano's theorem to derive equations for moment-to-force ratio (M/F) in terms of loop geometry.

• Further refinements are performed with finite element simulations of designs.

• Experimental data are presented illustrating the improved performance of the new design over standard available designs.

• Two approaches can be used in space-closing movement

I. supplying the appropriate moments to the teeth via a continuous arch wire that passes through orthodontic brackets.

• As tooth move forces decreases applied moment can increase or decrease, dependent on the arch wire configuration.

• Therefore, the M/F changes as the tooth moves, and the tooth responds, typically progressing from controlled tipping (center of rotation at the root apex) to translation to root movement.

• second approach involves bending arch wire loops of various configurations,in a arch wire (to deliver the desired M/F to several teeth).

• Brackets are not sliding along the arch wire during the process.

MATERIAL AND METHODS:

• Theoretical investigations using Castigliano's theorem were undertaken for vertical loops, T-loops, and L-loops.

• Detailed use of the mathematical trends suggested a new design, the "Opus loop."

• Specific vertical loops and Opus loops were then simulated by use of FEM software.

Result:• Equations were independently derived for M/F for vertical

loop with apical helix, T-loops and L-loops using the Castigliano's theorem.

• Greatest effect on raising M/F is to increase loop height. Increasing the number of apical helices has a lesser effect.

• For equal loop heights, theory predicts increased inherent M/F for a T-loop configuration and even more for an L-loop configuration.

• This trend suggested placing a helix somewhere in the apical portion of the "L" to increase M/F further.

• The position choosen is practical in bending the loop in a continuous arch.

• The anterior end was fixed and the posterior end 13 mm distal.

• When centered in the interbracket distance, the M/F at the bracket connected to the helix end of the loop always exhibited at least three times the M/F of the other end.

• Angulation of the vertical legs was then varied in 5-degree increments until M/F was equal at both ends.

• This occurred when the legs were angled at 70 degrees to the plane of the brackets.

• The M/F increased as the loop was positioned closer to one bracket than the other and more when the helix end was closer.

• An activated symmetric closing loop acts as a V-bend located at the loop's center.

• The systematic theoretical derivation of the new closing loop design requires verification.

• True verification requires load, deflection, and moment measurements of actual samples of the loop.

Continuous arch wire closing loop design, optimization and verification. Part II

MATERIAL AND METHODS:

• Test runs of the various loops were performed on the experimental apparatus including load cells and moment transducer

• The load cell measures pure force and is insensitive to moments.

• The moment transducer measures pure moment.

• Activation is performed by the digital micrometer transmitted to the load cell end with no vertical play.

• The moment transducer can twist horizontally, but its center is constrained from moving vertically.

• Closing loops made in stainless steel and TMA wire were tested

• Wire sizes were 0.017 × 0.025 inch in TMA and primarily 0.016 × 0.022 inch in stainless steel, although some tests were performed with 0.018 × 0.025 inch s.s. wire.

• Interbracket distance (IBD) was varied in 2 mm steps between 13 and 7 mm, simulating space closure.

• Each loop was tested at the center of the IBD and then off-centered with one vertical leg 1.5 mm from the moment transducer bracket.

• A test run consisted of incremental activations, measuring displacements (loop activations) for applied loads of 50, 100, 150, and 200 gm; simultaneous measurements of activation force were made via the load cell at its end and moment at the other end.

• The loop was then reversed and all test runs were repeated to measure the moment at the loop's other end so that M/F could be determined at both brackets for each test.

• Each test run was repeated at least once. If values differed, that run was repeated yet again and calculated mean values were used.

Result:

• Neither the 8 mm vertical loop with one 3.5 mm diameter helix nor the 10 mm high, 10 mm long T-loop can achieve the desired M/F range in any position without inducing residual moments

• The gabled T and vertical loops generate posterior moments that are in the same direction as the moments at the anterior ends, whereas the Opus 70 loop's posterior moment is in the opposite direction.

• Therefore, the sum of the moments have the potential to express as occlusal plane change of the entire arch

• If gabled loops are left tied in for a very long time, the anterior and posterior segments will eventually begin to form two occlusal planes at an angle approaching the total of the gable bends' angles.

• Opus 70 loop total moment is the difference between the moments at the two ends they being in opposite directions, decreasing the tendency to change occlusal plane.

• sum of the moments are additive for the T and vertical loops, increasing the total moment attempting to change occlusal plane, whereas the Opus 70 loop total moment is the difference between the moments at the two ends they being in opposite directions, decreasing the tendency to change occlusal plane.

• The Opus 70 loop exceeds the "safe" maximum beyond 170 gm activation whereas the gabled T-loop exceeds it beyond 110 gm.

• T-loop exceeds the desired M/F range at less than 80 gm activation; the gabled T-loop has a very narrow range of acceptable performance (80-110 gm in s.s. at 13 mm IBD) when used in a continuous arch.

M/F at each bracket as a function of activation force while varying IBD (13, 11,9, 7 mm) for off-centered 0.016 x 0.022 inch s.s. Opus 70 (without residual moments, by definition).

Activation (mm) necessary to achieve various activation forces for the Opus 70 loop formed in 0.016 × 0.022 s.s., 0.018 x 0.025 s.s., and 0.017 × 0.025 inch TMA wires

CASE REPORT• A 20-year old Japanese woman transfer patient previously

had impacted maxillary canines extracted near the final stage of treatment with zero overjet but with 3 mm spacing distal to the maxillary lateral incisors bilaterally and the buccal teeth in Class III relationships.

• The maxillary spaces needed to be closed by protraction of the maxillary posterior teeth with no anterior retraction allowed.

• The Opus 90 option was chosen, protracting four premolars and four molars without retracting four incisors.

• The loop was activated 1 mm every 5 weeks, and the protraction was completed in three visits.

• Superimposition of a cephalometric radiograph taken at the time of transfer (the beginning of protraction mechanics) with that at the end of treatment revealed no change in incisor position or inclination or any other structures other than protracted maxillary posterior teeth.

RELATED ARTICLESMechanical properties of Opus closing loops, L-loops, and T-loops investigated with finite element analysisPaiboon Techalertpaisarna and Antheunis Versluisb Bangkok, Thailand, and Memphis, TennAm J Orthod Dentofacial Orthop 2013;143:675-83)

• The objective of this research was to investigate the mechanical properties at both sides of Opus closing loops by analyzing the effects of loop shape, loop position, coil position, and tipping of the vertical legs.

Methods: • Opus loops were compared with L-loops (with and without a coil) and a T-

loop by using finite element analysis.

• Both upright and tipped vertical loop legs (70) were tested.

• Loop response to loop pulling was simulated at 5 loop positions for a 12-mm interbracket distance and 10-mm loop lengths and heights.

• Three-dimensional models of the closing loops were created by using beam elements with stainless steel properties.

• The L-loops and Opus loops were directed toward the anterior side. Loop properties (horizontal load/deflection, vertical force, and moment-to-force ratio) at both loop ends were recorded at activation forces of 100 and 200 g.

Results:

Conclusions:

• Similarities in the mechanical properties between Opus70 and T-loops were demonstrated.

• Loop properties varied with loop configuration and position.

• Clinicians should understand the specific characteristics of each loop configuration to most effectively exploit them for the desired tooth movements.

Evaluation and comparison of biomechanical properties of snail loop with that of opus loop and teardrop loop for En mass retraction of anterior teeth. – A FEM study.

Rao PR, Shrivastav SS, Joshi RA. J Ind Orthod Soc 2013;47(2):62-67.

Introduction:

• In retraction loop mechanics the only known disadvantage is that, the loop may fail to produce ideal expected results in practice due to the complexity of loop fabrication and some unknown factors.

• Teardrop loop is very simple to fabricate, but the inherent M/F ratio of loop is inadequate for causing translatory motion of the teeth. Opus loop design inherently produces M/F ratio close to 10:1.

• A blend of both the designs is seen to be integrated in snail loop.

• It has got design configuration similar to teardrop loop and additionally has got a helix in its design similar to opus loop.

• For any retraction loop to be made universally acceptable a complete knowledge of its biomechanical properties are very essential.

Aim:

• To evaluate the biomechanical properties of snail loop and compare it with teardrop loop and opus loop.

Materials and methods:• Based on the dimensions prescribed by the respective authors

a total of 13 FEM models were constructed and 14 analyses were conducted in the study.

• The horizontal length of all the loop models (distance between the anterior and the posterior node) were kept 13mm considering the interbracket distance from the second premolar midpoint to the canine midpoint considering a first premolar extraction case.

• Both TMA and SS wires of both 0.017 × 0.025 inch and 0.019 × 0.025 inch wire dimensions were used.

Following 13 FEM models were prepared for the study:

• Three models for snail loop were prepared in 0.017 × 0.025 inch TMA wire with 0°, 10° and 20° preactivation bends.

• Two models for snail loop were prepared in 0.017 × 0.025 inch SS wire with 0° and 10° preactivation bend.

• Four models for snail loop were prepared in 0.019 × 0.025 inch TMA wire with 0°, 5°, 10° and 20° preactivation bends.

• Two models of snail loop were prepared in 0.019 × 0.025 inch SS wire with 0° and 10° preactivation bend.

• One model each of teardrop loop and opus loop was generated in 0.019 × 0.025 inch TMA wire without any preactivation bends.

RESULTS:

Finite element analysis was carried out for different FEM models and MCSPD code was given to different models prepared, where

• M represents material types (TMA or SS)

• C represents configurations of loops (teardrop, Tr, opus, Op and snail, Sn loops)

• S represents size of wire ( 0.017 × 0.025 inch as S1 and 0.019 × 0.025 inch as S2)

• P represents preactivation angle alpha (zero degree as 0°, five degrees as 5°, ten degrees as 10°, twenty degrees as 20°)

• D represents displacement, the amount of activation of the given loop model (1 mm as D1 and 2 mm as D2).

Conclusion:

• Snail loop has a definite advantage over teardrop loop in all respects of biomechanical characters but less advantageous when compared to opus loop.

• Snail loop with incorporation of gable bends is very efficient to deliver M/F ratio similar to that of opus loop. Finer shape morphology of snail loop provides ease of fabrication and prevents tissue impingement which is a drawback of opus loop.

Conclusion:• Opus loop is found to have desirable biomechanical properties

which will provide less traumatic and more desired tooth movement with minimal side effects.

• Though the opus loop is promising to the orthodontist care should be taken while fabrication to avoid undesirable effects.

• Opus loop still needs detailed clinical trials to understand its mechanism more correctly and in future, which will be useful for timely activation of this loop using new technology.

References:• Continuous arch wire closing loop design, optimization, and

verification - Part I Raymond E. Siatkowski, American Journal of Orthodontics and Dentofacial Orthopedics October 1997

• Continuous arch wire closing loop design, optimization and verification. Part – II Raymond E. Siatkowski, American Journal of Orthodontics and Dentofacial Orthopedics November 1997

• Mechanical properties of Opus closing loops, L-loops, and T-loops investigated with finite element analysis, Paiboon Techalertpaisarn American Journal of Orthodontics and Dentofacial Orthopedics May 2013 Vol 143 Issue 5.

• essential of orthodontics biomechanics – by Vijay Jayde andChetan Jayade.

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