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

A COMPARATIVE ANALYSIS OF

COMMONLY USED RETRACTION LOOPS

IN EDGEWISE SYSTEMS- A FINITE

ELEMENT STUDY

www.indiandentalacademy.com

INDIAN DENTAL ACADEMY

Leader in continuing dental education


INTRODUCTION


FEM VS EXPERIMENTAL


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.


Aims and Objectives

a) Compare the Moment Force ratio

and Load deflection rates from the

FEM with those of Burstone’s

findings.

b) To seek an explanation for

different findings, if any.www.indiandentalacademy.com

AIMS AND OBJECTIVES


Aims and Objectives

c) Provided FEM was validated, to

apply it to different loop

configurations, which are routinely

used.


Materials and Methods

EMRC 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 METHOD


A MODELLED STANDARD LOOP

FR


Materials and Methods

• Large 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

BURSTONE’S FINDINGS


Stage I - Validation with Burstone’s

findings

• The same parameters as employed

by Burstone were used, namely

• Wire dimensions of 0.016” with

properties of

E = 2.1 x 10 4 N/mm2

Yield strength = 40,000 psiwww.indiandentalacademy.com

Stage I- Validation of FEM with

Burstone’s 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

placementwww.indiandentalacademy.com

LOOP OF

HEIGHT

4mm

F M D

6.84 12.94 .7

6.84 8.96 .7

LOOP OF

HEIGHT

6 mm

F M D

4.85 16.02 1.44

4.85 10.60 1.38

LOOP OF

HEIGHT

10 mm

F M D

3.11 19.47 3.62

3.11 12.60 3.32

RESULTS

FEM

B

VARIATION IN LOOP HEIGHT


LOOP OF

DIAMETER

0.5 mm

F M D

4.69 13.99 1.2

4.69 9.70 1.3

LOOP OF

DIAMETER

1 mm

F M D

4.85 16.02 1.44

4.85 10.60 1.38

LOOP OF

DIAMETER

2 mm

F M D

5.17 20.22 2.01

5.17 12.48 1.90

RESULTS

FEM

B

VARIATION IN LOOP DIAMETER


VARIATION IN LOOP LENGTH

HORIZONTAL

LOOP LENGTH

7mm

F M D

4.85 16.02 1.44

4.85 10.60 1.38

HORIZONTAL

LOOP LENGTH

14 mm

F M D

4.15 8.04 1.40

4.15 6.99 1.56

HORIZONTAL

LOOP LENGTH

21 mm

F M D

3.83 4.62 1.34

3.83 5.31 1.68

RESULTS

FEM

B


Stage I- Validation with Burstone’s

findings INFERENCES

I) 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


findings INFERENCES

II) 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


findings INFERENCES

IV) 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 LOOPS


Stage II - Comparative analysis of

Common loops

Keeping 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


Common loops

The other material properties were as

defined by Siatowsky, namely

E = 3 X 10 4 N/mm2

Poisson’s ratio= 0.3

Forces ranging from 0.5 - 5N were

applied at one end of the wire of

horizontal loop length of 17.25 mm.www.indiandentalacademy.com


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.


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) Curetton’s loop

of the two legs


v)Tear drop loop


vi) L loop


viii) Asymmetric T loop


vii) T loop


ix) L loop with angulated legs


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

10.295www.indiandentalacademy.com

LOOP TYPE

VERTICAL LOOP

CURETTON’S

LOOP

VERTICAL LOOP

WITH A SHORT

LEG

M/F

3.618

3.650

2.833

F/D

11.006

10.909

15.770


INFERENCES


INFERENCES

I) Of all the loops studied, T loop has

the most ideal properties in terms of

M/F and F/D.


INFERENCES

II) 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

INFERENCES

IV) A change in the height of one loop

leg does alter the M/F ratio

considerably; however the Curetton’s

modification does not significantly

alter the M/F ratio or the F/D rate.


LOOP

HEIGHT

8

8

8

8

8

4

6

10

LOOP

DIAMETER

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


INFERENCES

V) The increase in the M/F of a

standard vertical loop when the height

or the diameter are increased is not

strictly proportionate.

Although a vertical loop with a 10 mm

height or a 6 mm diameter do give high

M/F ratios, the anatomic constraints

come in the way of clinically

employing them.www.indiandentalacademy.com

A NEW FINDING


INFERENCE

A kink like deformation in the Z plane

(1mm) of a tear drop or a vertical loop

showed a drastic rise in the values of

the M/F.

If this could be verified, it could give

us an additional tool to enhance the

M/F of any loop by a very simple

manipulation.www.indiandentalacademy.com

Shortcomings of FEM

1) It is not possible to exactly simulate

the clinical conditions.

2) It is quite difficult to duplicate the

wire bracket relationship.

3) Boundary conditions need to be

altered at times, which is not possible

in the current software.


CONCLUSION

Finite Element Method is a useful tool for

studying Loop mechanics.At the present

juncture it cannot entirely replace

experimental methods.

Software refinements shall help in using

this numerical procedure increasingly more

in Orthodontic research


CONCLUSION SAYING



Thank you

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

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