biomechanics of torque control

1

BIO-MECHANICS OF BIO-MECHANICS OF TORQUETORQUE

A Finite Element InvestigationA Finite Element Investigation

Dr. Vijay P. JayadeDr. Vijay P. JayadeProf. And Head,Prof. And Head,

Department Of Orthodontics,Department Of Orthodontics,S.D.M. College of Dental S.D.M. College of Dental

Sciences,Sciences,Dharwad.Dharwad.

2

Salutations to Dr. AngleSalutations to Dr. Angle

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Angle’s achieved a quantum leap in orthodontic Angle’s achieved a quantum leap in orthodontic

mechanics by introducing mechanics by introducing root controlroot control in his in his

appliances. appliances.

( “All that one can do is to push, pull or twist”). ( “All that one can do is to push, pull or twist”).

This This “twist“twist in the tale” has dramatically changed in the tale” has dramatically changed

the script of orthodontic mechanics. the script of orthodontic mechanics.

4

TorqueTorque Torque control is Torque control is essentialessential for for

1. Esthetic, functional and health outcome of 1. Esthetic, functional and health outcome of the treatment, the treatment,

2. Stability of the results.2. Stability of the results.

It is commonly attained by manipulating It is commonly attained by manipulating third third

order relationship of a rectangular archwire - order relationship of a rectangular archwire -

rectangular slotrectangular slot..

5

What prompted the present What prompted the present study study

Writings ofWritings of

IsaacsonIsaacson et al, - et al, - mechanicsmechanics of torque using of torque using

rectangular wires, more specifically the rectangular wires, more specifically the

complex reactions on the complex reactions on the adjacent adjacent teeth, teeth,

DeAngelis and DavidovitchDeAngelis and Davidovitch - - biologic biologic

considerations of torque application.considerations of torque application.

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Reciprocal reactionsReciprocal reactions on adjacent on adjacent teethteeth during torque application with during torque application with

rectangular wiresrectangular wires

These were mentioned by These were mentioned by Brodie (1931)Brodie (1931)

and subsequently by and subsequently by othersothers like Strang, like Strang,

Thurow and Andreasen. Thurow and Andreasen.

However, their However, their complexity complexity was not given was not given

due attention till recently.due attention till recently.

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Theory V/s Practice of TorqueTheory V/s Practice of Torque Isaacson et al (1993)Isaacson et al (1993)

“ “The equal and opposite reciprocal reactions The equal and opposite reciprocal reactions (which generally cause (which generally cause undesirable opposite undesirable opposite movementsmovements of adjacent teeth) are commonly of adjacent teeth) are commonly disregarded”.disregarded”.

““On the basis of theoretical mechanics, this On the basis of theoretical mechanics, this approach is conceptually flawed”. approach is conceptually flawed”.

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What happens with incremental What happens with incremental torque?torque?

1,2,3 progressively torqued more and more?

Some other response?

All torqued equally?

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Isaacson’s hypothesisIsaacson’s hypothesis

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Relevant Clinical situationRelevant Clinical situation

Incremental Incremental

twisting bends twisting bends

between 13, 12, between 13, 12,

11 also 21, 22, 23.11 also 21, 22, 23.

XXXX

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Ineffectiveness of Progressive Ineffectiveness of Progressive Torque in Torque in Clinical PracticeClinical Practice??

This situation for torquing the incisors, is This situation for torquing the incisors, is

analogous analogous to the one discussed by Isaacson. to the one discussed by Isaacson.

It does appear to work clinically. It does appear to work clinically.

HOW DOES IT HAPPEN? HOW DOES IT HAPPEN?

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Possible Possible explanationexplanation

What Isaacson mentioned are the What Isaacson mentioned are the initial effectsinitial effects

and not all the actions and reactions, which and not all the actions and reactions, which

keep on fluctuating till the keep on fluctuating till the twist in the wire twist in the wire

expresses itself completely.expresses itself completely.

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Possible Possible explanationexplanation

Perhaps,Perhaps, as the end teeth start moving, the as the end teeth start moving, the torquing moments on them gradually diminish, torquing moments on them gradually diminish, and so also the reactionary moments on the and so also the reactionary moments on the middle teeth. The twist in the wire would then middle teeth. The twist in the wire would then start acting on the middle teeth. start acting on the middle teeth.

The The changing sequence of actions and changing sequence of actions and reactionsreactions needs to be worked out. needs to be worked out.

IS THERE ANY ROUND TRIPPING? IS THERE ANY ROUND TRIPPING?

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Biologic implicationsBiologic implications(DeAngelis and Davidovitch)(DeAngelis and Davidovitch)

Root resorption possibility increases due to : Root resorption possibility increases due to :

a) a) “round tripping”“round tripping” and “jiggling” of roots, and “jiggling” of roots,

b) b) excessive torquing forces / moments. excessive torquing forces / moments.

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Optimum Torquing momentsOptimum Torquing moments

10 to 20 N mm10 to 20 N mm for rectangular wire torque for rectangular wire torque

(Burstone(Burstone, , Nikolai,Nikolai, andand Meiling and Odegaad) Meiling and Odegaad)

forfor bodily translation bodily translation (M/F ratio 10:1)(M/F ratio 10:1)

Are the moments, which are generated in clinical Are the moments, which are generated in clinical

practice, within this range?.practice, within this range?.

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Aims and objectivesAims and objectives

1. To verify the hypothesis of Isaacson 1. To verify the hypothesis of Isaacson regarding the regarding the initial effectsinitial effects of progressive of progressive root torque.root torque.

2. To work out how the effects of root 2. To work out how the effects of root torque in various situations might torque in various situations might gradually be altering gradually be altering over a period of over a period of timetime..

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3. To explore the effects of different amounts of 3. To explore the effects of different amounts of

built-in torquebuilt-in torque on adjacent teeth in the PAE on adjacent teeth in the PAE

appliances.appliances.

4. To estimate the 4. To estimate the quantum of momentsquantum of moments

generated by different archwires. generated by different archwires.

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MethodologyMethodology

Finite Element Method (Finite Element Method (FEMFEM) – Excellent tool in ) – Excellent tool in

analyzing problems of analyzing problems of mechanical mechanical nature (in nature (in

this instance, this instance, moments and displacementmoments and displacement

behavior).behavior).

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The FEM software employed was The FEM software employed was Nastran- Nastran-

Patran. Patran.

A rectangular wire in edgewise mode was A rectangular wire in edgewise mode was

modeled initially as straight length and later as modeled initially as straight length and later as

anterior part of an archwire on anterior part of an archwire on Autocad Autocad

softwaresoftware

175 175 nodesnodes in the anterior curvature in the anterior curvature

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Appropriate Appropriate torquing momentstorquing moments were applied at were applied at the the correct locations :correct locations :

a) from presumed twists in the archwire OR a) from presumed twists in the archwire OR b) from in-built torque in the brackets.b) from in-built torque in the brackets. Then Then reciprocal reactions were derivedreciprocal reactions were derived from from

the software (both the software (both initial, as also over timeinitial, as also over time from from wire relaxation).wire relaxation).

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Some AssumptionsSome Assumptions

The software assumes that the archwire The software assumes that the archwire

fits precisely in the bracket slot fits precisely in the bracket slot without any without any

playplay (e.g., a slot height of 0.019” was (e.g., a slot height of 0.019” was

assumed for the archwire having the assumed for the archwire having the

dimension of 19x25).dimension of 19x25).

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Will this affect its reliability in application to the Will this affect its reliability in application to the clinical practice? clinical practice?

No, because what it depicts is the No, because what it depicts is the clinically clinically effective torqueeffective torque that acts on the teeth that acts on the teeth after the after the archwire-bracket play has been overcomearchwire-bracket play has been overcome. .

The play is The play is uniformuniform for all the brackets for any for all the brackets for any given archwire. given archwire.

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Validation of force valuesValidation of force values

Any numerical study must be validated by Any numerical study must be validated by

comparing with a laboratory study.comparing with a laboratory study.

A A laboratory set uplaboratory set up, as used by Meling, , as used by Meling,

Odegaard and Meling, was simulated on FEM, Odegaard and Meling, was simulated on FEM,

and moments generated were compared. and moments generated were compared.

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Validation of force valuesValidation of force values

Wire Size

Range of

play

Mean play

Expt. Range

Mean value

FEM

18 x25 mil

2.98o - 6.31o 4.6o

3.24-4.79 Nmm

3.86 Nmm

3.39Nmm

Wire twisted by 1 degree -

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I. Verification of Isaacson’s hypothesis I. Verification of Isaacson’s hypothesis for for Straight length of wire

Tooth 1Tooth 1 Tooth 2Tooth 2 Tooth 3Tooth 3 Tooth 4Tooth 4Tooth 1 : 0 Tooth 1 : 0 Tooth 2 : 10Tooth 2 : 10Tooth 3 : 20Tooth 3 : 20Tooth 4 : 30Tooth 4 : 30

-19.5-19.5 00 00 19.519.5

Tooth 1 : -2 Tooth 1 : -2 Tooth 2 : 10Tooth 2 : 10Tooth 3 : 20Tooth 3 : 20Tooth 4 : 28Tooth 4 : 28

-15.3-15.3 -3.8-3.8 44 15.115.1

Torque on teeth (N mm)Torque on teeth (N mm)

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ActivationActivation Torque on teeth (N mm)Torque on teeth (N mm)LeftLeft

LateraLaterall

LeftLeftCentralCentral

RightRightCentralCentral

RightRightLateralLateral

R. Lateral : 0 R. Lateral : 0 R. Central : 10R. Central : 10L. Central : 20L. Central : 20L. Lateral : 10L. Lateral : 10

33.133.1 -1.68-1.68 8.978.97 -19.46-19.46

Verification of Isaacson’s Verification of Isaacson’s hypothesis -for hypothesis -for curvedcurved anterior anterior

segmentsegment

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Verification of Isaacson’s Verification of Isaacson’s hypothesishypothesis

Thus the clinical picture may be slightly Thus the clinical picture may be slightly

different because of different because of curvaturecurvature in the in the

archwire and archwire and different inter-bracket different inter-bracket

distances.distances.

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II. Stepwise resolution of anterior II. Stepwise resolution of anterior TorqueTorque

Incremental Incremental

twisting bends twisting bends

between 13, 12, between 13, 12,

11 also 21, 22, 23.11 also 21, 22, 23.

XXXX

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Amount of torque

(Degrees)

Torque on each tooth (Nmm)

Central Lateral Canine

Central : 20 Lateral : 10

30.74 -6.53-13.76

Central : 18 Lateral : 12 Canine : -2

22.53 -0.23 -8.11

Central : 16 Lateral : 12 Canine : -4

17.62 -0.14 -0.08

Central :14 Lateral :12 Canine :-4

12.91 3.69 -0.06


8.11 7.58 -0.08


6.8 4.97 2.64

Stepwise resolution of anterior progressive torque

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Other situations studiedOther situations studied

Torquing Torquing twotwo incisors incisors in the same direction in the same direction

XX

XX

Torquing Torquing fourfour incisors, incisors, with twists only with twists only between 13 & 12 and between 13 & 12 and 22 & 23. 22 & 23.

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Lingual Root Torque for Central Incisors

Amount of torque

(Degrees)



10 23.94 -19.46

8 15.8 -9.15 -2.76

6.5 9.49 -1.22 -4.8

5 3.4 6.43 -6.9

cent-5 latr-3.5 5.8 1.71 -4.84

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Lingual Root Torque on Four Incisors

Amount of torque

(Degrees)



cent and lat – 10 canine 0

6.81 12.93 -13.76

cent and lat - 8

canine -25.51 6.26 -2.64

cent and lat - 6

canine -24.1 3.6 0.17

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Individual Root Torque – Right central Individual Root Torque – Right central incisorincisor

Wire Wire size/ size/ al loyalloy

Act.Act.

Torque on each tooth (Nmm)Torque on each tooth (Nmm)

L. L. LateralLateral

L. L. CentralCentral

R. R. CentralCentral

R. R. LateralLateral

R. R. CanineCanine

19x25/19x25/ssss

1010 -15.37-15.37 39.1939.19 -19.29-19.29

19x25/19x25/ssss

88 -3.81-3.81 --4.14.1 24.6824.68 --9.149.14 -2.82-2.82

17x25/17x25/ssss

1010 -11.97-11.97 30.2130.21 -14.96-14.96

17x25/17x25/ssss

88 -2.96-2.96 -3.24-3.24 1919 --7.117.11 -2.2-2.2

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III. The effect of built-in torque using III. The effect of built-in torque using MBT MBT prescription prescription

The results are different depending on the The results are different depending on the torque in cuspid bracket torque in cuspid bracket (-7, 0 or +7)(-7, 0 or +7)

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MBT Actual Clinical moment MBT Actual Clinical moment valuesvalues

The high FEM values do not apply (for The high FEM values do not apply (for untorqued arch wire) in clinical practice untorqued arch wire) in clinical practice because of about 10 degrees of wire-slot because of about 10 degrees of wire-slot play. But the play. But the trends seen are importanttrends seen are important. .

However, if the 19x25 SS wire is given However, if the 19x25 SS wire is given additional torqueadditional torque that overcomes the play, that overcomes the play, then the FEM values would be close to the then the FEM values would be close to the Clinical.Clinical.

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MBT Cuspid -7MBT Cuspid -7

Amount of Amount of torque torque

(Degrees)(Degrees)


CentralCentral LateralLateral CanineCanine PremolarPremolar

Central: Central: 17 17

Lateral: Lateral: 10 10

Canine:-7Canine:-7

23.4223.42 13.413.4 -42.56-42.56 (13.93)(13.93)

Central: Central: 15 15

Lateral: 8 Lateral: 8 Canine:-5Canine:-5

22.1222.12 6.896.89 --31.7931.79 (10.4)(10.4)

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MBT Cuspid 0 and +7MBT Cuspid 0 and +7


(Degrees)(Degrees)


CentralCentral LateralLateral CanineCanine PremolarPremolar

Central: 17 Central: 17 Lateral: 10 Lateral: 10 Canine: 0Canine: 0

23.4223.42 -0.58-0.58 -13.76-13.76

Central: 17 Central: 17 Lateral: Lateral:

10 10 Canine:7Canine:7

23.4223.42 10.2210.22 15.0515.05 (-13.93)(-13.93)

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MBT Inverted lateral bracketMBT Inverted lateral bracket


(Degrees)(Degrees)

Torque on each tooth Torque on each tooth (Nmm)(Nmm)

CentralCentral LateralLateral CanineCanine PremolaPremolarr


-10 -10 Canine: 7Canine: 7

57.6757.67 -79.35-79.35 42.5642.56 (-13.93)(-13.93)


-10 -10 Canine: 0Canine: 0

57.6757.67 -65.37-65.37 13.7613.76 ------


-10 -10 Canine: -7Canine: -7

57.6757.67 -51.39-51.39 -15.05-15.05 (13.93)(13.93)

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IS IT A GOOD IDEA TO INVERT THE IS IT A GOOD IDEA TO INVERT THE LATERAL BRACKETLATERAL BRACKET ( especially ( especially alongside a cuspid bracket with +7 alongside a cuspid bracket with +7 torque)?torque)?

Even after discounting 40 N mm moment Even after discounting 40 N mm moment due to 10 degrees play, the moments due to 10 degrees play, the moments generated are high.generated are high.

Use Use NitiNiti rectangular wires before SS rectangular wires before SS wires.wires.

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IV. Torquing Moments from various IV. Torquing Moments from various wireswires

The torsional stiffness ratio of SS : TMA : The torsional stiffness ratio of SS : TMA :

NiTi is NiTi is 10 : 3 : 1.10 : 3 : 1.

Torquing moments from heavy SS wires Torquing moments from heavy SS wires

are high and often above, those from TMA are high and often above, those from TMA

generally within and those from NiTi below generally within and those from NiTi below

the the physiologic limitphysiologic limit..

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Clinical recommendationsClinical recommendations Twists in the rectangular archwireTwists in the rectangular archwire seem to be seem to be

appropriate appropriate only when reciprocal torque is only when reciprocal torque is requiredrequired on the adjacent teeth, but beware of on the adjacent teeth, but beware of high moments. (‘Use high moments. (‘Use undersizeundersize wires’- Thurow) wires’- Thurow)

In other situations, this method to cause active In other situations, this method to cause active root torque appears mechanically and root torque appears mechanically and biologically unsound biologically unsound (often high moments (often high moments which drop suddenly, also round tripping)which drop suddenly, also round tripping)

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Clinical recommendationsClinical recommendations

For For active torquingactive torquing with twists in the rectangular with twists in the rectangular

wires, wires, TMATMA wires should be considered. wires should be considered.

The rectangular near The rectangular near full size SS wiresfull size SS wires can be can be

used thereafter used thereafter for holding the teethfor holding the teeth in their in their

corrected torque positions. corrected torque positions.

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The The moments generated by the NiTimoments generated by the NiTi archwires even in 19x25 are archwires even in 19x25 are too lowtoo low to to bring about active torquing of teeth bring about active torquing of teeth over over long periodslong periods..

However, they may prove However, they may prove beneficialbeneficial when when reciprocal torquereciprocal torque is needed on adjacent is needed on adjacent teeth.teeth.

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Alternate methodsAlternate methods proposed by authors like proposed by authors like

Thurow, DeAngelis and Burstone/Isaacson Thurow, DeAngelis and Burstone/Isaacson

deserve a serious attentiondeserve a serious attention when when reciprocal reciprocal

torque on adjacent teeth is not neededtorque on adjacent teeth is not needed, and , and

round tripping is to be avoided. round tripping is to be avoided.

The reciprocal The reciprocal reactionsreactions of these are spread of these are spread

on many (often distant) teethon many (often distant) teeth, and are , and are

controlled more easily. controlled more easily.

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Alternate torquing methods Alternate torquing methods (Thurow)(Thurow)

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Alternate torquing methods Alternate torquing methods (DeAngelis)(DeAngelis)

Warren Spring

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Alternate torquing methods Alternate torquing methods (Burstone, Isaacson)(Burstone, Isaacson)

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Twist Twist in the wirein the wire v/s v/s Torque Torque of teethof teeth

Angle’s Angle’s torque control concepttorque control concept is inseparable is inseparable

from good orthodontic practice.from good orthodontic practice.

However, his However, his “twists” in the rectangular wire“twists” in the rectangular wire

for attaining torque should be employed for attaining torque should be employed

judiciously, and not indiscriminately.judiciously, and not indiscriminately.

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THANKS TOTHANKS TO

Co-Authors:Co-Authors:

Prof. Satish Annigeri (B.V.B. Engineering Prof. Satish Annigeri (B.V.B. Engineering

College, Hubli),College, Hubli),

Dr. Chetan V. Jayade,Dr. Chetan V. Jayade,

Dr. Punit Thawani.Dr. Punit Thawani.

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THANK YOUTHANK YOU

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Young’s modulus and Poisson’s Young’s modulus and Poisson’s ratio ratio

Young’s Young’s ModulusModulus

Poisson’s Poisson’s RatioRatio

Stainess Stainess SteelSteel

179000 N/mm179000 N/mm22 0.30.3

TMATMA 71700 N/mm71700 N/mm22 0.30.3

NitinolNit inol 41400 N/mm41400 N/mm22 0.30.3

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Moments generated by SS Moments generated by SS WiresWires

Clinical SituationClinical SituationAmount of Amount of

torque torque (Degrees)(Degrees)


CentralCentral LateralLateral CanineCanine

Lingual root Lingual root torque on two torque on two

central incisorscentral incisors1010 23.9423.94 -19.46-19.46

Lingual root Lingual root torque on two al l 4 torque on two al l 4

incisors - incisors - progressive root progressive root

torque - l ike torque - l ike Isaacson'sIsaacson's

Central : Central : 20 20

Lateral : Lateral : 10 10

30.7430.74 -6.53-6.53 -13.76-13.76

Pre adjusted Pre adjusted Edgewise Edgewise

Prescript ion - MBTPrescript ion - MBT


-10 -10 Canine:7Canine:7

57.6757.67 -99.17-99.17 83.4383.43

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Individual Root Torque – Right central Individual Root Torque – Right central incisorincisor

Wire Wire size/ size/ alloyalloy

Act.Act.


L. L. LateralLateral

L. L. CentralCentral

R. R. CentralCentral

R. R. LateralLateral

R. R. CanineCanine

19x25/19x25/TMATMA

1010 -6.16 -6.16 15.7115.71 -7.73-7.73

19x25/19x25/TMATMA

88 -1.53-1.53 -1.64-1.64 9.899.89 -3.66-3.66 -1.13-1.13

17x25/17x25/TMATMA

1010 -4.79 -4.79 12.112.1 -6-6

17x25/17x25/TMATMA

88 -1.19-1.19 -1.31-1.31 7.617.61 -2.85-2.85 -0.88-0.88

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Ineffectiveness of Ineffectiveness of Progressive Progressive IncrementalIncremental Torque (Isaacson) Torque (Isaacson)

60

Some AssumptionsSome Assumptions The differences in the The differences in the sizes and shapes of sizes and shapes of

rootsroots of various teeth were generally of various teeth were generally disregarded. Also, the disregarded. Also, the periodontal and periodontal and alveolar bone supportalveolar bone support to all the teeth were to all the teeth were considered as uniform.considered as uniform.

All the archwire materials viz. stainless All the archwire materials viz. stainless steel, T.M.A. and Niti were considered to steel, T.M.A. and Niti were considered to have have linear elastic propertieslinear elastic properties (hence, (hence, applicable only to work hardened NiTi). applicable only to work hardened NiTi).

61

Basic Premise of the Edgewise Basic Premise of the Edgewise ApplianceAppliance

An ideally shaped rectangular archwire, An ideally shaped rectangular archwire, would move the teeth to the desired final would move the teeth to the desired final positions because of its close fit in the positions because of its close fit in the rectangular bracket slots. rectangular bracket slots.

Is this movement a direct translation of the Is this movement a direct translation of the teeth along the shortest route, or does it teeth along the shortest route, or does it involve “round tripping” of some of the involve “round tripping” of some of the teeth, if not all?teeth, if not all?

62

P.A.E. AppliancesP.A.E. Appliances

Same implicit understanding of P.A.E. Same implicit understanding of P.A.E. appliances also (which use continuous appliances also (which use continuous archwires) : the archwire bracket archwires) : the archwire bracket relationship would cause the teeth to relationship would cause the teeth to move from their malaligned positions to move from their malaligned positions to the correct positions. the correct positions.

Again, is there a possibility of some Again, is there a possibility of some amount of round tripping?amount of round tripping?

63


6. To study the possible actions and 6. To study the possible actions and

reactions generated by reactions generated by alternative alternative

torquing mechanismtorquing mechanism such as a Warren such as a Warren

spring, and compare these with those from spring, and compare these with those from

the conventional archwire twist.the conventional archwire twist.

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All brackets perfectly leveled and aligned.All brackets perfectly leveled and aligned.

Root apices of teeth undergoing torque Root apices of teeth undergoing torque

move by move by 1.5 to 2 degrees per month1.5 to 2 degrees per month

(based on what is commonly observed in (based on what is commonly observed in

the clinical practice, and also from the clinical practice, and also from

Creekmore’s interview).Creekmore’s interview).

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Isaacson - Kesling DebateIsaacson - Kesling Debate

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Isaacson Kesling DebateIsaacson Kesling Debate

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Isaacson - Kesling DebateIsaacson - Kesling Debate

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““Orthodontic practice is nothing but push, pull and Orthodontic practice is nothing but push, pull and

twist”. twist”.

Angle introduced the Angle introduced the “twist”“twist” in the tale in the tale thatthat dramatically changed the script of orthodontic dramatically changed the script of orthodontic

mechanics. mechanics.

69

Isaacson’s hypothesisIsaacson’s hypothesis

1R

70

Advantages of FEMAdvantages of FEM

When properly appliedWhen properly applied It could It could obviate the needobviate the need for the use of for the use of

elaborate laboratory (often invasive) elaborate laboratory (often invasive) procedures.procedures.

Its Its accuracyaccuracy is very high. is very high. It can It can segregatesegregate the effects of bending from the effects of bending from

those of twisting in curved members (e.g., those of twisting in curved members (e.g., Archwire). Archwire).

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Appropriate values for Young’s Modulus and Appropriate values for Young’s Modulus and

Poisson’s ratio were given.Poisson’s ratio were given.

As per the expert advice, As per the expert advice, it was not necessary it was not necessary

to model the bracketsto model the brackets, since applying , since applying

appropriate boundary conditions at the location appropriate boundary conditions at the location

of the brackets simulates wire-bracket inter-of the brackets simulates wire-bracket inter-

face. face.

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Optimum Torquing momentsOptimum Torquing moments

A light torquing spring with 3 to 4 N mm moment A light torquing spring with 3 to 4 N mm moment was shown to cause no tissue damage by was shown to cause no tissue damage by ReitanReitan..

biomechanics of torque control

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