# commonly used retraction loops in edgewise /certified fixed orthodontic courses by indian

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• A COMPARATIVE ANALYSIS OF COMMONLY USED RETRACTION LOOPS IN EDGEWISE SYSTEMS- A FINITE ELEMENT STUDY

• Ideal Loop Characteristics

1) Sufficiently high Moment/Force (M/F) ratio to bring about desired tooth movement.2) Low Load Deflection (F/D) rate to maintain a low rate of force decay.www.indiandentalacademy.com

• Aims and Objectivesa) Compare the Moment Force ratio and Load deflection rates from the FEM with those of Burstones findings.b) To seek an explanation for different findings, if any.www.indiandentalacademy.com

• Aims and Objectives

c) Provided FEM was validated, to apply it to different loop configurations, which are routinely used.www.indiandentalacademy.com

• Materials and MethodsEMRC NISA Ver. 7.0 Finite element software.2-D beam elements used. Elements ranged from 67 to 107.Boundary conditions applied to restrain one end of the wire; force of known magnitude applied at the other end in an increment of 0.5 N.www.indiandentalacademy.com

• Materials and MethodsLarge deflection Non-Linear Static Analysis carried out.Resultant moment and displacement values obtained from the computer analysis.M/F and F/D ratios calculated from this data.www.indiandentalacademy.com

• DISPLACED SHAPE OF THE LOOPwww.indiandentalacademy.com

• PHASE I - VALIDATION WITH BURSTONES FINDINGSwww.indiandentalacademy.com

• Stage I - Validation with Burstones findingsThe same parameters as employed by Burstone were used, namelyWire dimensions of 0.016 with properties of E = 2.1 x 10 4 N/mm2 Yield strength = 40,000 psi

• Stage I- Validation of FEM with Burstones study (Contd) Variations in Moments and displacements calculated due to alteration in loop parameters like Loop Height & Diameter Horizontal Loop length Centred loop or Eccentric placement www.indiandentalacademy.com

• LOOP OF HEIGHT4mm

F M D

6.84 12.94 .7

6.84 8.96 .7 LOOP OF HEIGHT6 mm

F M D

4.85 16.02 1.44

4.85 10.60 1.38LOOP OF HEIGHT10 mm

F M D

3.11 19.47 3.62

3.11 12.60 3.32

RESULTS

FEM

• LOOP OF DIAMETER0.5 mm

F M D

4.69 13.99 1.2

4.69 9.70 1.3LOOP OF DIAMETER1 mm

F M D

4.85 16.02 1.44

4.85 10.60 1.38LOOP OF DIAMETER2 mm

F M D

5.17 20.22 2.01

5.17 12.48 1.90

RESULTS

FEM

• VARIATION IN LOOP LENGTHHORIZONTAL LOOP LENGTH 7mm

F M D

4.85 16.02 1.44

4.85 10.60 1.38

HORIZONTAL LOOP LENGTH14 mm

F M D

4.15 8.04 1.40

4.15 6.99 1.56HORIZONTAL LOOP LENGTH 21 mm

F M D

3.83 4.62 1.34

3.83 5.31 1.68

RESULTS

FEM

• Stage I- Validation with Burstones findings INFERENCESI) The trends in the variations of the moments and displacement values obtained from the FEM and the findings of Burstone are similar.Hence, there is a valid place for using FEM in understanding Loop mechanics.www.indiandentalacademy.com

• Stage I- Validation with Burstones findings INFERENCESII) The numerical values for displacements are very close to the ones observed by Burstone.III) The values for moments from the FEM are, in general, on the higher side. This is probably on account of the boundary conditions in the FEM and other material properties like elasticity.www.indiandentalacademy.com

• Stage I- Validation with Burstones findings INFERENCESIV) The numerical values for the moments , though higher initially , showed a rapid drop when the horizontal loop length was increased from 7-14 and then 14-21 mm.www.indiandentalacademy.com

• STAGE II - COMPARATIVE ANALYSIS OF COMMON LOOPSwww.indiandentalacademy.com

• Stage II - Comparative analysis of Common loopsKeeping in mind these differences between the FEM and the Experimental approach, the second stage was carried out.Material was modelled as a rectangular stainless steel wire of dimensions 0.018 X 0.025.www.indiandentalacademy.com

• Stage II - Comparative analysis of Common loopsThe other material properties were as defined by Siatowsky, namely E = 3 X 10 4 N/mm2 Poissons ratio= 0.3Forces ranging from 0.5 - 5N were applied at one end of the wire of horizontal loop length of 17.25 mm.www.indiandentalacademy.com

• Stage II - Comparative analysis of Common loops

The Moment, Displacement, M/F and F/D values were calculated for the following configurations :

• i) Standard vertical loop with varying height and diameter.www.indiandentalacademy.com

• ii) Vertical loop with arms crossing each other in two designs a) Flattened top b) Curved top

• Iii)Vertical loop with difference in height iv) Curettons loopof the two legs

• vii) T loop

• ix) L loop with angulated legswww.indiandentalacademy.com

• LOOP BY TYPE T LOOP ASYMMETRIC T LOOP L LOOP WITH ANGULATION L LOOP VERTICAL LOOP TEAR DROP LOOP BOX LOOP REVERSE LOOP M/F 5.0988 4.850

4.946

3.914 3.618 3.548 3.330 3.163 F/D 6.642 6.793

8.216

8.092 11.006 10.678 9.432 10.295

• LOOP TYPE

VERTICAL LOOP

CURETTONS LOOP

VERTICAL LOOP WITH A SHORT LEG M/F

3.618

3.650

2.833 F/D

11.006

10.909

• INFERENCESI) Of all the loops studied, T loop has the most ideal properties in terms of M/F and F/D.www.indiandentalacademy.com

• INFERENCESII) The L loop with angulated legs and the Asymmetric T loop come close to the T loop in terms of M/F alone in certain conditions. However, their F/D rate is considerably higher.III) The tear drop loop and the box loop with differing tops are not very different to the standard vertical loop in terms of M/F or the F/D.www.indiandentalacademy.com

• INFERENCESIV) A change in the height of one loop leg does alter the M/F ratio considerably; however the Curettons modification does not significantly alter the M/F ratio or the F/D rate.

• LOOP HEIGHT 8 8 8 8 8 4 6 10

LOOPDIAMETER

2 3 4 5 6 2 2 2 M/F

3.618 3.928 4.108 4.340 4.570 1.217 2.383 4.954 F/D 11.006 10.420 9.820 9.440 9.147 64.400 22.970 6.190