Biomechanics of torque control

1. 1
BIO-MECHANICS OFBIO-MECHANICS OF
TORQUETORQUE
A Finite Element InvestigationA Finite Element Investigation
Dr. Vijay P. JayadeDr. Vijay P. Jayade
Prof. And Head,Prof. And Head,
Department Of Orthodontics,Department Of Orthodontics,
S.D.M. College of DentalS.D.M. College of Dental
Sciences,Sciences,
Dharwad.Dharwad.

2. 2
Salutations to Dr. AngleSalutations to Dr. Angle

3. 3
 Angle’s achieved a quantum leap in orthodonticAngle’s achieved a quantum leap in orthodontic
mechanics by introducingmechanics by introducing root controlroot control in hisin 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”).
 ThisThis “twist“twist in the tale” has dramatically changedin the tale” has dramatically changed
the script of orthodontic mechanics.the script of orthodontic mechanics.

4. 4
TorqueTorque
 Torque control isTorque control is essentialessential forfor
1. Esthetic, functional and health outcome of1. 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 manipulatingIt is commonly attained by manipulating thirdthird
order relationship of a rectangular archwire -order relationship of a rectangular archwire -
rectangular slotrectangular slot..

5. 5
What prompted the presentWhat prompted the present
studystudy
Writings ofWritings of
 IsaacsonIsaacson et al, -et al, - mechanicsmechanics of torque usingof torque using
rectangular wires, more specifically therectangular wires, more specifically the
complex reactions on thecomplex reactions on the adjacentadjacent teeth,teeth,
 DeAngelis and DavidovitchDeAngelis and Davidovitch -- biologicbiologic
considerations of torque application.considerations of torque application.

6. 6
Reciprocal reactionsReciprocal reactions on adjacenton adjacent
teethteeth during torque application withduring torque application with
rectangular wiresrectangular wires
 These were mentioned byThese were mentioned by Brodie (1931)Brodie (1931)
and subsequently byand subsequently by othersothers like Strang,like Strang,
Thurow and Andreasen.Thurow and Andreasen.
 However, theirHowever, their complexitycomplexity was not givenwas not given
due attention till recently.due attention till recently.

7. 7
Theory V/s Practice of TorqueTheory V/s Practice of Torque
Isaacson et al (1993)Isaacson et al (1993)
““The equal and opposite reciprocal reactionsThe equal and opposite reciprocal reactions
(which generally cause(which generally cause undesirable oppositeundesirable opposite
movementsmovements of adjacent teeth) are commonlyof adjacent teeth) are commonly
disregarded”.disregarded”.
““On the basis of theoretical mechanics, thisOn the basis of theoretical mechanics, this
approach is conceptually flawed”.approach is conceptually flawed”.

8. 8
What happens with incrementalWhat happens with incremental
torque?torque?
1,2,3 progressively
torqued more and
more?
Some other
response?
All torqued
equally?

9. 9
Isaacson’s hypothesisIsaacson’s hypothesis

10. 10
Relevant Clinical situationRelevant Clinical situation
 IncrementalIncremental
twisting bendstwisting bends
between 13, 12,between 13, 12,
11 also 21, 22, 23.11 also 21, 22, 23.
XX
XX

11. 11
Ineffectiveness of ProgressiveIneffectiveness of Progressive
Torque inTorque in Clinical PracticeClinical Practice??
 This situation for torquing the incisors, isThis situation for torquing the incisors, is
analogousanalogous 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?

12. 12
PossiblePossible explanationexplanation
 What Isaacson mentioned are theWhat Isaacson mentioned are the initial effectsinitial effects
and not all the actions and reactions, whichand not all the actions and reactions, which
keep on fluctuating till thekeep on fluctuating till the twist in the wiretwist in the wire
expresses itself completely.expresses itself completely.

13. 13
PossiblePossible explanationexplanation
 Perhaps,Perhaps, as the end teeth start moving, theas 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 theand so also the reactionary moments on the
middle teeth. The twist in the wire would thenmiddle teeth. The twist in the wire would then
start acting on the middle teeth.start acting on the middle teeth.
 TheThe changing sequence of actions andchanging 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?

14. 14
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.

15. 15
Optimum Torquing momentsOptimum Torquing moments
10 to 20 N mm10 to 20 N mm for rectangular wire torquefor rectangular wire torque
(Burstone(Burstone,, Nikolai,Nikolai, andand Meiling and Odegaad)Meiling and Odegaad)
forfor bodily translationbodily translation (M/F ratio 10:1)(M/F ratio 10:1)
Are the moments, which are generated in clinicalAre the moments, which are generated in clinical
practice, within this range?.practice, within this range?.

16. 16
Aims and objectivesAims and objectives
1. To verify the hypothesis of Isaacson1. To verify the hypothesis of Isaacson
regarding theregarding the initial effectsinitial effects of progressiveof progressive
root torque.root torque.
2. To work out how the effects of root2. To work out how the effects of root
torque in various situations mighttorque in various situations might
gradually be alteringgradually be altering over a period ofover a period of
timetime..

17. 17
Aims and objectivesAims and objectives
3. To explore the effects of different amounts of3. To explore the effects of different amounts of
built-in torquebuilt-in torque on adjacent teeth in the PAEon adjacent teeth in the PAE
appliances.appliances.
4. To estimate the4. To estimate the quantum of momentsquantum of moments
generated by different archwires.generated by different archwires.

18. 18
MethodologyMethodology
 Finite Element Method (Finite Element Method (FEMFEM) – Excellent tool in) – Excellent tool in
analyzing problems ofanalyzing problems of mechanicalmechanical nature (innature (in
this instance,this instance, moments and displacementmoments and displacement
behavior).behavior).

19. 19
MethodologyMethodology
 The FEM software employed wasThe FEM software employed was Nastran-Nastran-
Patran.Patran.
 A rectangular wire in edgewise mode wasA rectangular wire in edgewise mode was
modeled initially as straight length and later asmodeled initially as straight length and later as
anterior part of an archwire onanterior part of an archwire on AutocadAutocad
softwaresoftware
 175175 nodesnodes in the anterior curvaturein the anterior curvature

20. 20

21. 21
MethodologyMethodology
 AppropriateAppropriate torquing momentstorquing moments were applied atwere applied at
thethe correct locations :correct locations :
 a) from presumed twists in the archwire ORa) from presumed twists in the archwire OR
 b) from in-built torque in the brackets.b) from in-built torque in the brackets.
 ThenThen reciprocal reactions were derivedreciprocal reactions were derived fromfrom
the software (boththe software (both initial, as also over timeinitial, as also over time fromfrom
wire relaxation).wire relaxation).

22. 22

23. 23
Some AssumptionsSome Assumptions
 The software assumes that the archwireThe software assumes that the archwire
fits precisely in the bracket slotfits precisely in the bracket slot without anywithout 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 theassumed for the archwire having the
dimension of 19x25).dimension of 19x25).

24. 24
Some AssumptionsSome Assumptions
 Will this affect its reliability in application to theWill this affect its reliability in application to the
clinical practice?clinical practice?
 No, because what it depicts is theNo, because what it depicts is the clinicallyclinically
effective torqueeffective torque that acts on the teeththat acts on the teeth after theafter the
archwire-bracket play has been overcomearchwire-bracket play has been overcome..
 The play isThe play is uniformuniform for all the brackets for anyfor all the brackets for any
given archwire.given archwire.

25. 25
Validation of force valuesValidation of force values
 Any numerical study must be validated byAny numerical study must be validated by
comparing with a laboratory study.comparing with a laboratory study.
 AA 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.

26. 26
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
3.39
Nmm
Wire twisted by 1 degree -

27. 27
I. Verification of Isaacson’s hypothesisI. Verification of Isaacson’s hypothesis
forfor Straight length of wire
Tooth 1Tooth 1 Tooth 2Tooth 2 Tooth 3Tooth 3 Tooth 4Tooth 4
Tooth 1 : 0Tooth 1 : 0
Tooth 2 : 10Tooth 2 : 10
Tooth 3 : 20Tooth 3 : 20
Tooth 4 : 30Tooth 4 : 30
-19.5-19.5 00 00 19.519.5
Tooth 1 : -2Tooth 1 : -2
Tooth 2 : 10Tooth 2 : 10
Tooth 3 : 20Tooth 3 : 20
Tooth 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)

28. 28
ActivationActivation Torque on teeth (N mm)Torque on teeth (N mm)
LeftLeft
LateraLatera
ll
LeftLeft
CentralCentral
RightRight
CentralCentral
RightRight
LateralLateral
R. Lateral : 0R. Lateral : 0
R. Central : 10R. Central : 10
L. Central : 20L. Central : 20
L. Lateral : 10L. Lateral : 10
33.133.1 -1.68-1.68 8.978.97 -19.46-19.46
Verification of Isaacson’sVerification of Isaacson’s
hypothesis -forhypothesis -for curvedcurved anterioranterior
segmentsegment

29. 29
Verification of Isaacson’sVerification of Isaacson’s
hypothesishypothesis
 Thus the clinical picture may be slightlyThus the clinical picture may be slightly
different because ofdifferent because of curvaturecurvature in thein the
archwire andarchwire and different inter-bracketdifferent inter-bracket
distances.distances.

30. 30
II. Stepwise resolution of anteriorII. Stepwise resolution of anterior
TorqueTorque
 IncrementalIncremental
twisting bendstwisting bends
between 13, 12,between 13, 12,
11 also 21, 22, 23.11 also 21, 22, 23.
XX
XX

31. 31
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
Central :12
Lateral :12
Canine :-4
8.11 7.58 -0.08
Central :10
Lateral :10
Canine :-4
6.8 4.97 2.64
Stepwise resolution of anterior
progressive torque

32. 32
Other situations studiedOther situations studied
 TorquingTorquing twotwo incisorsincisors
in the same directionin the same direction
XX
XX
TorquingTorquing fourfour incisors,incisors,
with twists onlywith twists only
between 13 & 12 andbetween 13 & 12 and
22 & 23.22 & 23.

33. 33
Lingual Root Torque for Central Incisors
Amount of
torque
(Degrees)
Torque on each tooth
(Nmm)
Central Lateral Canine
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

34. 34
Lingual Root Torque on Four Incisors
Amount of
torque
(Degrees)
Torque on each tooth
(Nmm)
Central Lateral Canine
cent and
lat – 10
canine 0
6.81 12.93 -13.76
cent and
lat - 8
canine -2
5.51 6.26 -2.64
cent and
lat - 6
canine -2
4.1 3.6 0.17

35. 35
Individual Root Torque – Right centralIndividual Root Torque – Right central
incisorincisor
WireWire
size/size/
alloyalloy
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

36. 36
III. The effect of built-in torque usingIII. The effect of built-in torque using
MBTMBT prescriptionprescription
 The results are different depending on theThe results are different depending on the
torque in cuspid brackettorque in cuspid bracket (-7, 0 or +7)(-7, 0 or +7)

37. 37
MBT Actual Clinical momentMBT Actual Clinical moment
valuesvalues
 The high FEM values do not apply (forThe high FEM values do not apply (for
untorqued arch wire) in clinical practiceuntorqued arch wire) in clinical practice
because of about 10 degrees of wire-slotbecause of about 10 degrees of wire-slot
play. But theplay. But the trends seen are importanttrends seen are important..
 However, if the 19x25 SS wire is givenHowever, 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 thethen the FEM values would be close to the
Clinical.Clinical.

38. 38
MBT Cuspid -7MBT Cuspid -7
Amount ofAmount of
torquetorque
(Degrees)(Degrees)
Torque on each tooth (Nmm)Torque on each tooth (Nmm)
CentralCentral LateralLateral CanineCanine PremolarPremolar
Central:Central:
1717
Lateral:Lateral:
1010
Canine:-7Canine:-7
23.4223.42 13.413.4 -42.56-42.56 (13.93)(13.93)
Central:Central:
1515 22.1222.12 6.896.89 --31.7931.79 (10.4)(10.4)

39. 39
MBT Cuspid 0 and +7MBT Cuspid 0 and +7
Amount ofAmount of
torquetorque
(Degrees)(Degrees)
Torque on each tooth (Nmm)Torque on each tooth (Nmm)
CentralCentral LateralLateral CanineCanine PremolarPremolar
Central: 17Central: 17
Lateral: 10Lateral: 10
Canine: 0Canine: 0
23.4223.42 -0.58-0.58 -13.76-13.76
Central: 17Central: 17
Lateral:Lateral:
1010
Canine:7Canine:7
23.4223.42 10.2210.22 15.0515.05 (-13.93)(-13.93)

40. 40
MBT Inverted lateral bracketMBT Inverted lateral bracket
Amount ofAmount of
torquetorque
(Degrees)(Degrees)
Torque on each toothTorque on each tooth
(Nmm)(Nmm)
CentralCentral LateralLateral CanineCanine
PremolaPremola
rr
Central: 17Central: 17
Lateral:Lateral:
-10-10
Canine: 7Canine: 7
57.6757.67 -79.35-79.35 42.5642.56 (-13.93)(-13.93)
Central: 17Central: 17
Lateral:Lateral:
-10-10
Canine: 0Canine: 0
57.6757.67 -65.37-65.37 13.7613.76 ------

41. 41
 IS IT A GOOD IDEA TO INVERT THEIS IT A GOOD IDEA TO INVERT THE
LATERAL BRACKETLATERAL BRACKET ( especially( especially
alongside a cuspid bracket with +7alongside a cuspid bracket with +7
torque)?torque)?
 Even after discounting 40 N mm momentEven after discounting 40 N mm moment
due to 10 degrees play, the momentsdue to 10 degrees play, the moments
generated are high.generated are high.
 UseUse NitiNiti rectangular wires before SSrectangular wires before SS

42. 42
IV. Torquing Moments from variousIV. Torquing Moments from various
wireswires
 The torsional stiffness ratio of SS : TMA :The torsional stiffness ratio of SS : TMA :
NiTi isNiTi is 10 : 3 : 1.10 : 3 : 1.
 Torquing moments from heavy SS wiresTorquing moments from heavy SS wires
are high and often above, those from TMAare high and often above, those from TMA
generally within and those from NiTi belowgenerally within and those from NiTi below
thethe physiologic limitphysiologic limit..

43. 43
Clinical recommendationsClinical recommendations
 Twists in the rectangular archwireTwists in the rectangular archwire seem to beseem to be
appropriateappropriate only when reciprocal torque isonly when reciprocal torque is
requiredrequired on the adjacent teeth, but beware ofon the adjacent teeth, but beware of
high moments. (‘Usehigh moments. (‘Use undersizeundersize wires’- Thurow)wires’- Thurow)
 In other situations, this method to cause activeIn other situations, this method to cause active
root torque appears mechanically androot torque appears mechanically and
biologically unsoundbiologically unsound (often high moments(often high moments
which drop suddenly, also round tripping)which drop suddenly, also round tripping)

44. 44
Clinical recommendationsClinical recommendations
ForFor active torquingactive torquing with twists in the rectangularwith twists in the rectangular
wires,wires, TMATMA wires should be considered.wires should be considered.
The rectangular nearThe rectangular near full size SS wiresfull size SS wires can becan be
used thereafterused thereafter for holding the teethfor holding the teeth in theirin their
corrected torque positions.corrected torque positions.

45. 45
Clinical recommendationsClinical recommendations
 TheThe moments generated by the NiTimoments generated by the NiTi
archwires even in 19x25 arearchwires even in 19x25 are too lowtoo low toto
bring about active torquing of teethbring about active torquing of teeth overover
long periodslong periods..
 However, they may proveHowever, they may prove beneficialbeneficial whenwhen
reciprocal torquereciprocal torque is needed on adjacentis needed on adjacent
teeth.teeth.

46. 46
Clinical recommendationsClinical recommendations
Alternate methodsAlternate methods proposed by authors likeproposed by authors like
Thurow, DeAngelis and Burstone/IsaacsonThurow, DeAngelis and Burstone/Isaacson
deserve a serious attentiondeserve a serious attention whenwhen reciprocalreciprocal
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 reciprocalThe reciprocal reactionsreactions of these are spreadof these are spread
on many (often distant) teethon many (often distant) teeth, and are, and are
controlled more easily.controlled more easily.

47. 47
Alternate torquing methodsAlternate torquing methods
(Thurow)(Thurow)

48. 48
Alternate torquing methodsAlternate torquing methods
(DeAngelis)(DeAngelis)
Warren Spring

49. 49
Alternate torquing methodsAlternate torquing methods
(Burstone, Isaacson)(Burstone, Isaacson)

50. 50
TwistTwist in the wirein the wire v/sv/s TorqueTorque of teethof teeth
 Angle’sAngle’s torque control concepttorque control concept is inseparableis inseparable
from good orthodontic practice.from good orthodontic practice.
 However, hisHowever, his “twists” in the rectangular wire“twists” in the rectangular wire
for attaining torque should be employedfor attaining torque should be employed
judiciously, and not indiscriminately.judiciously, and not indiscriminately.

51. 51
THANKS TOTHANKS TO
Co-Authors:Co-Authors:
Prof. Satish Annigeri (B.V.B. EngineeringProf. Satish Annigeri (B.V.B. Engineering
College, Hubli),College, Hubli),
 Dr. Chetan V. Jayade,Dr. Chetan V. Jayade,
 Dr. Punit Thawani.Dr. Punit Thawani.

52. 52
THANK YOUTHANK YOU

53. 53

54. 54

55. 55

56. 56
Young’s modulus and Poisson’sYoung’s modulus and Poisson’s
ratioratio
Young’sYoung’s
ModulusModulus
Poisson’sPoisson’s
RatioRatio
StainessStainess
SteelSteel
179000 N/mm179000 N/mm22
0.30.3
TMATMA 71700 N/mm71700 N/mm22
0.30.3
NitinolNitinol 41400 N/mm41400 N/mm22
0.30.3

57. 57
Moments generated by SSMoments generated by SS
WiresWires
Clinical SituationClinical Situation
Amount ofAmount of
torquetorque
(Degrees)(Degrees)
Torque on each tooth (Nmm)Torque on each tooth (Nmm)
CentralCentral LateralLateral CanineCanine
Lingual rootLingual root
torque on twotorque on two
central incisorscentral incisors
1010 23.9423.94 -19.46-19.46
Lingual rootLingual root
torque on two all 4torque on two all 4
incisors -incisors -
progressive rootprogressive root
torque - liketorque - like
Isaacson'sIsaacson's
Central :Central :
2020
Lateral :Lateral :
1010
30.7430.74 -6.53-6.53 -13.76-13.76
Pre adjustedPre adjusted
EdgewiseEdgewise
Prescription - MBTPrescription - MBT
Central: 17Central: 17
Lateral:Lateral:
-10-10
57.6757.67 -99.17-99.17 83.4383.43

58. 58
Individual Root Torque – Right centralIndividual Root Torque – Right central
incisorincisor
WireWire
size/size/
alloyalloy
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/
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

59. 59
Ineffectiveness ofIneffectiveness of ProgressiveProgressive
IncrementalIncremental Torque (Isaacson)Torque (Isaacson)

60. 60
Some AssumptionsSome Assumptions
 The differences in theThe differences in the sizes and shapes ofsizes and shapes of
rootsroots of various teeth were generallyof various teeth were generally
disregarded. Also, thedisregarded. Also, the periodontal andperiodontal and
alveolar bone supportalveolar bone support to all the teeth wereto all the teeth were
considered as uniform.considered as uniform.
 All the archwire materials viz. stainlessAll the archwire materials viz. stainless
steel, T.M.A. and Niti were considered tosteel, T.M.A. and Niti were considered to
havehave linear elastic propertieslinear elastic properties (hence,(hence,
applicable only to work hardened NiTi).applicable only to work hardened NiTi).

61. 61
Basic Premise of the EdgewiseBasic Premise of the Edgewise
ApplianceAppliance
An ideally shaped rectangular archwire,An ideally shaped rectangular archwire,
would move the teeth to the desired finalwould move the teeth to the desired final
positions because of its close fit in thepositions because of its close fit in the
rectangular bracket slots.rectangular bracket slots.
Is this movement a direct translation of theIs this movement a direct translation of the
teeth along the shortest route, or does itteeth along the shortest route, or does it
involve “round tripping” of some of theinvolve “round tripping” of some of the
teeth, if not all?teeth, if not all?

62. 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 continuousappliances also (which use continuous
archwires) : the archwire bracketarchwires) : the archwire bracket
relationship would cause the teeth torelationship would cause the teeth to
move from their malaligned positions tomove from their malaligned positions to
the correct positions.the correct positions.
 Again, is there a possibility of someAgain, is there a possibility of some
amount of round tripping?amount of round tripping?

63. 63
Aims and objectivesAims and objectives
6. To study the possible actions and6. To study the possible actions and
reactions generated byreactions generated by alternativealternative
torquing mechanismtorquing mechanism such as a Warrensuch as a Warren
spring, and compare these with those fromspring, and compare these with those from
the conventional archwire twist.the conventional archwire twist.

64. 64
Some AssumptionsSome Assumptions
 All brackets perfectly leveled and aligned.All brackets perfectly leveled and aligned.
 Root apices of teeth undergoing torqueRoot apices of teeth undergoing torque
move bymove 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 fromthe clinical practice, and also from
Creekmore’s interview).Creekmore’s interview).

65. 65
Isaacson - Kesling DebateIsaacson - Kesling Debate

66. 66
Isaacson Kesling DebateIsaacson Kesling Debate

67. 67
Isaacson - Kesling DebateIsaacson - Kesling Debate

68. 68
 ““Orthodontic practice is nothing but push, pull andOrthodontic practice is nothing but push, pull and
twist”.twist”.
 Angle introduced theAngle introduced the “twist”“twist” in the talein the tale thatthat
dramatically changed the script of orthodonticdramatically changed the script of orthodontic
mechanics.mechanics.

69. 69
Isaacson’s hypothesisIsaacson’s hypothesis
1R

70. 70
Advantages of FEMAdvantages of FEM
When properly appliedWhen properly applied
 It couldIt could obviate the needobviate the need for the use offor the use of
elaborate laboratory (often invasive)elaborate laboratory (often invasive)
procedures.procedures.
 ItsIts accuracyaccuracy is very high.is very high.
 It canIt can segregatesegregate the effects of bending fromthe effects of bending from
those of twisting in curved members (e.g.,those of twisting in curved members (e.g.,
Archwire).Archwire).

71. 71
MethodologyMethodology
 Appropriate values for Young’s Modulus andAppropriate 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 necessaryit was not necessary
to model the bracketsto model the brackets, since applying, since applying
appropriate boundary conditions at the locationappropriate boundary conditions at the location
of the brackets simulates wire-bracket inter-of the brackets simulates wire-bracket inter-
face.face.

72. 72
Optimum Torquing momentsOptimum Torquing moments
 A light torquing spring with 3 to 4 N mm momentA light torquing spring with 3 to 4 N mm moment
was shown to cause no tissue damage bywas shown to cause no tissue damage by ReitanReitan..