the effect of a transpalatal or nance palatal arch on...

TheeffectofatranspalatalorNancepalatalarchonslidingmechanicswith

varyingdegreesofmolarrotations

By

EmileHabibBDSMJDFMOrthRCS(Eng)

AthesissubmittedtotheUniversityofBirminghamforthedegreeof

MasterofScience(byResearch)

SchoolofDentistryBirminghamDentalHospital

MillPoolWayBirmingham

B57EG

January2017

University of Birmingham Research Archive

e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.

2

Abstract

Aims:Todetermineiftheuseofatranspalatal(TPA)orNancepalatalarchwith

varying degrees of molar rotations significantly affects resistance to sliding

during sliding mechanics. Also, to establish if there is reduced resistance to

slidingusing the extraoral tube (EOT)onmolarbandsopposed to the straight

wiretubewhenusingaTPAorNancepalatalarchwithrotatedmolars.

Materialsandmethod:Acustommadeexperimentalapparatusapproximating

the transpalatal arch, allowing for 1-degree incremental changes to molar

rotationwasdesigned.A0.019x0.025” stainless steel archwirewasdisplaced

throughthemolartubestodeterminetheeffectofmolarrotationonresistance

to sliding, determined as work. Unilateral and bilateral palatal rotations were

evaluatedaswellascomparisonoftheextraoralandstraightwiretube.

Results: Thework required to achieve a constant archwire displacementwas

significantly increased forbilaterally,palatallyrotatedmolarscomparedwitha

unilateral rotation (p<0.05 for displacement of both0.5 and0.1mm). Pearson

correlationanalysis identifiedasignificantassociationbetweenextentofmolar

rotationanddifferenceinworkbetweenunilateralandbilateralrotatedmolars

(p-value 0.002 and 0.01 for displacement of 0.5 and 0.1 mm respectively).

Placementof thearchwire in theextraoral tubesignificantly reduced thework

required for a fixed displacement compared with the straight wire tube. The

magnitudeoftheeffectwasgreatestforbilateralpalatalrotatedmolarsandwas

highly significant (p <0.001 for 0.5 mm) compared with a unilateral palatal

rotatedmolar.

Conclusion:Therelationshipbetweenworkandmolarrotationwasfoundtobe

non-linear, with an exponential increase in work with increasing palatal

rotations. Bilaterally, palatally rotated molars resulted in a significantly

increased amount of work for all amounts of displacement of the archwire

compared with a unilateral rotation. Use of the EOT significantly reduced the

workrequiredtodisplacethearchwirecomparedwiththestraightwiretube.

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Acknowledgements

IwouldliketodedicatethisresearchprojecttomyGrandmother,whosadlypassedawayOctober2016

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Contents

Abstract………………………………………………………………………………………………………….2

Acknowledgements…………………………………………………………………………………………3

Contents………………………………………………………………………………….................................4

DetailedContents……………………………………………………………………………………………5

ChapterOne:Literaturereviewandaimsofstudy…………………………………………..13

ChapterTwo:MaterialsandMethod………………………………………………………………43

ChapterThree:Results………………………………………………………………………………….57

ChapterFour:Discussion………………………………………………………………………………70

ChapterFive:Conclusion………………………………………………………………………………91

References……………………………………………………………………………………………………93

Appendices…………………………………………………………………………….............................102

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DetailedcontentsChapterone:Literaturereviewandaimsofstudy 13

1.1 Introduction 141.2 Rotatedfirstpermanentmolars 14

1.2.1 Quantifyingdegreeofmolarrotation 151.3 Orthodonticfixedappliances 201.4 Friction 22

1.4.1 Thelawsoffriction 231.4.2 Typesoffriction 231.4.3 Resistancetosliding 241.4.4 Frictionandanchorage 261.4.5 Factorsaffectingfriction 281.4.6 Archwirematerial 291.4.7 Archwirecrosssectionalshapeandstiffness 291.4.8 Bracketmaterial 301.4.9 Bracketwidthandinter-bracketdistance 301.4.10 Bracketprescription 301.4.11 Ligation 321.4.12 Biologicalfactors–salivaandocclusalforces 33

1.5 Anchorage 341.5.1 Principles 341.5.2 Sourcesandtypes 351.5.3 Intraoralanchorage–Teeth 351.5.4 Intraoralanchorage–Softtissue/Bone 361.5.5 TranspalatalandNancepalatalarch 371.5.6 EvidencetosupportuseoftranspalatalorNancepalatal

arch 391.6 Aimsandobjectivesofstudy 42

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ChapterTwo:MaterialsandMethods 432.1Estimatingparameterrangesbasedonex-vivodata 442.2Designofexperimentalapparatus 472.3Pilotstudies 522.4Definitivestudies 54

2.5Comparisonofstraightwireandextraoraltube 56

7

ChapterThree:Results 57 3.1Molarrotations 58 3.2Pilotstudies 59 3.3Definitivestudies 62 3.4Comparisonofthestraightwireandextraoraltube 69

8

ChapterFour:Discussion 70 4.1Molarrotations 71 4.2Impactofrotatedmolarsonresistancetosliding 72 4.3Impactofunilateralpalatalrotation 77 4.4Impactofbilateralpalatalrotation 78 4.5Comparisonofunilateralandbilateralpalatalrotation 80 4.6Validationofresults 81 4.7Comparisonofthestraightwireandextraoraltube 82 4.8Limitationsofinterpretingresults 86

4.9Additionalfactorsthataffectfriction 87 4.10Futureresearch 89

9

ChapterFive:Conclusion 91

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LegendtoIllustrationsFigure1.1: Graphicalrepresentationoftherelationshipbetweentooth

movementandappliedorthodonticforce 28

Figure1.2: TheGoshgariantranspalatalarch 37

Figure1.3: TheNancepalatalarch 38

Figure2.1: Exampleofscannedstudymodelandillustrationoftheanglesof

FrielandHenry 45

Figure2.2: Testapparatus–overview 48

Figure2.3: Testapparatus–rotationalstages 49

Figure2.4: Testapparatus–verticalalignmentofarchwire 50

Figure3.1: Typicaldisplacementvs.timeplotobtainedforconstantarchwire

displacement 59

Figure3.2: Plotofdisplacementvs.workfortheleftbuccalrotation–right

palatalrotationdataset 60

Figure3.3: Plotofdisplacementvs.workfortheleftpalatalrotation–right

buccalrotationdataset 61

Figure3.4: Plotofdisplacementvs.workforpalatal-palatalrotationdataset

61

Figure4.1: Plotofloadvs.displacementforrightandleftmolarsinanideal

alignment(zerodegrees) 73

Figure4.2: Plotofloadvs.displacementforrightandleftboth12degrees

palatallyrotated 74

Figure4.3: Plotoftherelationshipbetweendegreeofrotationandworkforan

archwiredisplacementof0.5mmand2mmforaunilateralpalatal

rotation 77

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Figure4.4: Plotoftherelationshipbetweendegreeofrotationandworkforan

archwiredisplacementof0.5mmand2mmforbilateralpalatal

rotations 79

Figure4.5: Plotoftheconvergenceofworkinvolvedforhigherrotationswith

aunilateralorbilateralmolarrotation 81

Figure4.6: Plottocompareworkinvolvedindisplacingthearchwire2mm

betweentheEOTandstraightwiretubeforbilateralpalatal

rotations 83

Figure4.7: Plottocompareworkinvolvedindisplacingthearchwire0.5mm

betweentheEOTandstraightwiretubeforbilateralpalatal

rotations 83

Figure4.8: Plottocompareworkinvolvedindisplacingthearchwire2mm

betweentheEOTandstraightwiretubeforunilateralpalatal

rotations 84

Figure4.9: Plottocompareworkinvolvedindisplacingthearchwire0.5mm

betweentheEOTandstraightwiretubeforunilateralpalatal

rotations 84

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LegendtoTablesTable2.1: Anatomical points, reference lines and angles measured from

dentalstudymodels 46

Table3.1: Mean,SDand95%normalrangeforanglesofFrielandHenry 58

Table3.2: ICCofmeasurementsforangleofFrielandHenry 58

Table3.3: Summaryofpilotstudyresultsofhigherordertermsfor

displacement 60

Table3.4: Meanworkresultsandp-valueformatcheddatafromleftbuccal–

rightpalatalandleftpalatal–rightbuccal 62

Table3.5: Meanworkvaluesforgivendisplacementaccordingtodegreeof

molarrotation 63

Table3.6: ICCresultsfordisplacementsof5mm,0.5mmand0.1mm 64

Table3.7: Squaredandcubictermsfordisplacement 64

Table3.8: Mean,SDandp-valuecomparingrightpassiveandrightpalatal

datasets 65

Table3.9: Correlationanalysestoexamineifthedifferencebetweenboth

groupsvarieddependingonrotation 66

Table3.10: Comparisonofswitchedandun-switchedmeanwork

measurementstovalidateaccuracyofresultsandp-value 66

Table3.11: ComparisonofthemeandifferenceinworkbetweentheEOT

versusthestraightwiretube 68

Table3.12: PearsoncorrelationanalysestocomparetheEOTwiththe

straightwiretube 69

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ChapterOne

Literaturereviewandaimsofstudy

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Chapterone:Literaturereviewandaimsofstudy

1.1Introduction

Orthodontic tooth movement is based on the principal that when a force is

appliedtoatooth,itstimulatesareactionwithintheperiodontium.Remodeling

of the periodontal ligament and alveolar bone occurs and results in tooth

movement. The first stage of orthodontic treatment is to level and align the

dental arches. Leveling and alignment includes derotation of any teeth. The

maxillary first permanent molars are commonly rotated. During derotation,

mesialtoothmovementisoftenundesirable,especiallyinaclassIImalocclusion.

Shouldauxiliaryappliancesbeused toprevent anymesialmovement, thepre-

treatment position of the maxillary first permanent molar is fixed and any

rotationsmaintainedduringthisphaseoforthodontictreatment.

1.2RotatedFirstpermanentmolars(FPMs)

Themandibularandmaxillaryfirstpermanentmolarseruptaround6.5yearsof

age (Berkovitzetal., 2009), signifying the startof themixeddentition stageof

dentaldevelopment.Malpositionof firstpermanentmolarscanbeasignificant

aetiological factor in malocclusion, as molar relationship is considered a key

factor in achieving an ideal and stable occlusion. Angle (1899) based his

classification of occlusion onmolar relationship and upon examining the ideal

occlusion,hedeterminedthatthemesiobuccalcuspoftheupperfirstpermanent

molarshouldoccludewiththesulcusbetweenthebuccalcuspsofthelowerfirst

permanentmolar(Angle,1899).Withthemolarsinthisposition,it isclassified

as a class I molar relationship. A Class II molar relationship occurs when the

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mesiobuccalcuspoftheupperfirstpermanentmolaroccludesanteriorlytothis

position.

With the first permanent molars in the ideal position, it results in good

intercuspation of the upper and lower buccal dentition, adequate space

anteriorly for overjet and overbite correction and creates a stable occlusion.

Andrews (1972) described six key factors required in order to have an ideal

staticocclusion.Oneofthereportedsixkeysofocclusionwasmolarrelationship;

“thedistalsurfaceofthedistalmarginalridgeoftheupperfirstpermanentmolar

occludeswiththemesialsurfaceofthemesialmarginalridgeofthelowersecond

molar.Themesiobuccalcuspoftheupperfirstpermanentmolarfallswithinthe

groove between the mesial and middle cusps of the lower first permanent

molar”.Anotherkey thatAndrews (1972)described in the idealocclusionwas

theabsenceofanyrotationswithinthearches.

1.2.1Quantifyingdegreeofmolarrotation

Palatal rotation of themaxillary first permanentmolars has beendescribed in

the literature, especially in class II malocclusions (Friel, 1959;Hellman,

1920;Lamons and Holmes, 1961). Hellman (1920) reported a very high

prevalenceofmesio-palatalrotationofthemaxillaryfirstpermanentmolar.The

palatalrootofthemaxillaryfirstpermanentmolarismuchlargerthanthetwo

buccal roots. This longitudinal axis forms a pivotal point that can result in a

rotation of the molar (Hellman, 1920). Several studies (Foresman, 1964;Friel,

1959;Hellman,1920;Henry,1956)havebeenconductedinordertoevaluatethe

prevalence,directionandextentofmolarrotation.Allofthestudieshavefound

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thatthemaxillaryfirstpermanentmolarrotates inapalataldirection,withthe

mesiobuccalcuspdisplacedpalatally.

Henry(1956)aimedtoidentifytheoptimumangleatwhichthemolarswouldbe

ideallyalignedwithin thedentalarch.Thedegreeof rotationof themolarwas

measuredbytheangleformedbetweenthemedianrapheandalinethroughthe

buccal cuspsof themolar.Thestudy found that theoptimumangleof the first

permanentmolar(angleofHenry)hadameanvalueof11.20.Henryalsoagreed

with previouswork byHellman (1920), reporting that the longitudinal axis of

rotation was directed through the palatal root and mesiopalatal cusp. He

concluded that mesiopalatally rotated maxillary first permanent molars were

frequently observed, occurring in83%ofmalocclusions (Henry, 1956).Due to

this high prevalence rate, the rotation of the maxillary first permanent molar

needstobeexaminedandaccountedforduringorthodontictreatment.

Friel (1959) carried out a similar study to Henry (1956) but used a different

methodology.Using themedianrapheasareferenceplane,Frielmeasured the

angle formed between this plane and a line through the mesiobuccal and

mesiopalatalcuspsofthemaxillaryfirstmolars.Measurementsweretakenfrom

studymodelswithaclassIbuccalocclusionandaclassIIbuccalocclusion.The

mean angle in the class I group was 600 on the right and 570 on the left,

comparedwith520ontherightand510ontheleft.Thepost-normalgrouphad

onaverage7degreesmoremesiopalatalrotationcomparedwithnormalgroup

(Friel,1959).

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Whilst the studiesbyHenry (1956)andFriel (1959)werewell conducted, the

sample size was small. Due to natural shape of the maxillary arch, a small

anteroposterior change in the position of the molar could have a significant

effectonthedegreeofrotationmeasured.Nostatisticalanalysiswaspresented.

Lamons and Holmes (1961), using the angle of Friel, found mesiopalatal

rotationsofthemaxillaryfirstpermanentmolaroccurin95%ofcases.Thestudy

concludedthattheoptimumangleofFrielwas610withastandarddeviationof

40.AsimilarstudybyForesman(1964)aimedtodeterminetheamountofspace

gained(asrotatedteethoccupyawidermesio-distalwidth)withinthearchfrom

correctionoftherotationofthemaxillaryfirstpermanentmolar.Thestudyalso

validatedthepreviousliteratureontheoptimumangleofFrielandreportedthe

optimumanglewas600,whichwasinagreementtotheresultsfromthestudies

byFriel(1959)andLamonsandHolmes(1961).Themaxillaryfirstpermanent

molarsinuntreatedcases,onaverage,were10-110moremesiopalatallyrotated

(Foresman,1964).

Limaetal(2015)aimedtoevaluatethecorrelationbetweentheseverityofclass

II division 1malocclusions and the degree of themesiopalatal rotation of the

maxillary first permanent molar. The results showed that the mean angle of

Henryforthesampleswas14.50,whichishigherthantheoptimumangleforthe

maxillary first permanent molar suggested by Henry as their sample did not

examine anymolarswith a class Imolar relationship. Themean angle of Friel

was580,whichwascomparablewithpreviousstudies.Statisticalanalysisfound

arelationshipbetweentheanglesofHenryandFrielandtheseverityoftheclass

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II molar relationship (Lima et al., 2015). This suggests that the degree of

mesiopalatalrotationof themolar isproportional totheseverityof theclass II

molarrelationship.Theresultswerenotstatisticallysignificantforall4groups,

suggesting that it isonlyapplicable tomoresevereclass IImolarrelationships

(Limaetal.,2015).InclinicalscenarioswithasevereclassIImolarrelationship

wherepreventionoffurthermesialmovementofthemolarteethisneeded,the

molars are likely to be rotated with an unknown effect on the sliding of the

archwirethroughthemolartubeifatranspalatalarchisused.

Limeetal(2015)presentedasamplesizecalculationusing5%alphaerrorand

a power calculation with a correlation coefficient of 0.20. This differed from

previous literature regarding quantifying molar rotations as no statistical

analysishasbeenpresented,ifanywereperformedatall.Asaresult,thislimits

thequalityofevidenceprovidedbythesestudies.Themainlimitationofallthe

available literature is the small sample sizes. The angles and the differences

betweentheanglesevaluatedweresmall,requiringalargesamplesizetohave

anystatisticalweightingandprovideconclusiveepidemiologicalresults.Another

limitation of the previous literature is some results were reported to two

decimalplaces,anaccuracythatcouldnothavebeenreliablyachieved.

Inconclusion,rotatedmaxillaryfirstpermanentmolarsarefrequentlyobserved

inclassIImalocclusions.Themolarrotatesinapalataldirectionaroundthelong

axisofthepalatalrootandmesiopalatalcusp(Hellman,1920;Henry,1956).Friel

suggested molars in a class II relationship were, on average, 70 more

mesiopalatally rotated (Friel, 1959). Other studies have found comparable

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results, with Foresman (1964) reporting molars of class II malocclusion on

average 10-110 more mesiopalatally rotated. A recent study has identified a

proportionalrelationshipbetweenthedegreeofmolarrotationandtheseverity

of the class IImolar relationship (Lima etal., 2015). In cases deemed to be of

high anchorage demand, due to the molars already being in a class II molar

relationship, itcanbeassumedthatthemolarswill frequentlybemesioplatally

rotated.Useofanchoragereinforcementintheformofatrans-palatalorNance

palatal arch without prior de-rotation of the molars, could have detrimental

effects on the mechanics of the orthodontic fixed appliance and, as a result,

preventorthodontictoothmovement.

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1.3Orthodonticfixedappliances

With the development and evolution of enamel bonding and machine milled

brackets,mostorthodontictreatmentisnowcarriedoutusingfixedappliances.

EdwardAnglefirstdescribedtheedgewiseappliancein1928(Angle,1928).He

introducedamachine-milledbracket,which in combinationwitha rectangular

archwire andwirebendingallowed for control of toothmovement in all three

planes; in/out, tip and torque. In 1976, Andrews introduced the pre-adjusted

edgewiseappliance,calledtheStraightWireAppliance(Andrews,1976;1979).

The brackets were precisely milled to incorporate a specific in/out, tip and

torque value per tooth, reducing the amount of wire bending required. The

prescription of the bracket was based on the scientific study of 120 non-

orthodonticpatientsdeemedtohaveanidealocclusion(Andrews,1972).

Since the introduction of the pre-adjusted edgewise appliance, numerous

different prescriptions have become available. Andrews originally introduced

different bracket prescriptions for extraction and non-extraction cases to

account for the different treatment mechanics required, as well as different

prescriptions depending on the amount of crowdingpresent (Andrews, 1979).

To simplify the inventory of brackets, orthodontists have suggested a single

bracketprescriptionthatcouldbeusedandmodifiedformostcases.McLaughlin,

BennettandTrevisi(1990)introducedthemostcommonlyusedprescriptionin

the UK, the “MBT” prescription. Several modifications to the prescription

originallydescribedbyAndrewsweremade.Theprescriptionreducedthetipin

the maxillary buccal segments, in order to reduce the anchorage demands

(MclaughlinandBennett,1990).Increasedmesialtipwouldputmorestrainon

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the anchor teethwhen trying to bodily retract the labial segment, resulting in

anchoragelosswiththeanchorteethmovingmesially.

The pre-adjusted edgewise appliance has revolutionized modern day

orthodontics. The appliance system has reduced chair-side time due to the

reduced need forwire bending. It allows for control of toothmovement in all

threeplanesandprovidesprecise,detailedfinishingofcases.Thesystemutilizes

slidingmechanics(Andrews,1976)whichallowsthecliniciantouseavarietyof

different biomechanics to achieve the desired tooth movements. Sliding

mechanicsmeansabracketcanslidealonganarchwireoranarchwirecanslide

through the bracket ormolar tube. Although it has created a larger variety of

mechanics that can be used, it has the disadvantage of the inherent issue of

friction.Thisisthemaindisadvantageofthepre-adjustededgewiseappliance.

Toothmovement is resisted as a result of the friction that occursbetween the

brackets,archwireandligatureinterface.Asaresultofthis increasedfrictional

force, thepre-adjustededgewiseappliance ismoreanchoragedemanding than

otherappliancesystemsthatdonotuseslidingmechanics,forexample,theBegg

appliance (Begg,1956).These increasedanchoragedemands create aneed for

anchoragereinforcementtolimitanchorageloss,whichmanifestsintheformof

undesired toothmovement. Inaclass IImalocclusion this isusually themesial

movementofthemaxillarybuccalsegment.

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1.4Friction

By sliding an orthodontic bracket along an archwire, the sliding movement

resultsinafrictionalresistancethatcanhinderorevenpreventtoothmovement.

With the widespread adoption of the pre-adjusted edgewise appliance,

understandingof frictional resistance, itsmagnitudeandclinical significance is

critical(Tidy,1989).

Frictionistheforcethatresiststherelativemotionoftwoobjectsincontactwith

oneanother.Thedirectionoftheforceistangentialtothetwosurfacesincontact

(Drescher et al., 1989). Stoner (1960) first documented the significance of

friction in orthodontics when he recognized that orthodontic appliance

inefficiencyresultedinanappliedforcebeingdissipatedbyfrictionorimproper

application. Clinically, this creates difficulty in controlling the amount of force

delivered to individual teeth (Stoner, 1960). The direction of the force from

frictional resistance occurs in the opposite direction to the moving object.

Thereforeitisessentialthatfrictionalforcesshouldbeminimisedorcompletely

eliminatedwhen toothmovement is desired (Drescher etal., 1989), otherwise

frictional resistance can prevent tooth movement and/or result in anchorage

loss (undesired toothmovement) (Edwardsetal., 1995).Using appliances and

mechanicsthathavelowfrictionalresistancehastheaddedpotentialbenefitof

reducingtheoveralltreatmenttime.

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1.4.1Thelawsoffriction

To comprehend the relevance and implications of frictional resistance with

orthodontictoothmovement,itisimportanttounderstandtheso-calledclassical

lawsoffriction(Amontons,1699):

1. Frictional force is proportional to the applied load, that is the force

normally acting on the object. In orthodontics this law is obeyed by all

forcecouples.

2. Thecoefficientoffrictionisindependentofthesurfaceareaincontact.

3. The coefficient of friction is independent of the sliding velocity. With

materials that move with a repeated stop-start motion, as occurs with

orthodontic tooth movement, this law would only be obeyed if the

optimal sliding velocity and its implementationwere known. Therefore

thislawisnotobeyedduringtheclinicalpracticeoforthodontics.

(Amontons,1699;Jastrzebski,1976;KusyandWhitley,1997)

1.4.2Typesoffriction

Therearetwotypesoffrictionalresistanceforcesthatoccurduringtherelative

motion of two solid surfaces in contact. These two frictional forces can be

definedastwoseparateentities(Omanaetal.,1992):

1. Static friction–Thesmallest forcerequiredto initiatemovementof two

solidsurfacesincontactthatwerepreviouslyatrest.

2. Kinetic friction – The force that resists the slidingmotion of two solid

surfacesincontactoncemovementhasstarted.

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Static friction is generally greater thankinetic friction as it ismoredifficult to

change an object from a state of inertia than to maintain its movement once

initiated (Kapila et al., 1990;Nanda and Ghosh, 1997;E. P. Rossouw, 2003). In

orthodontic toothmovementboth static andkinetic frictionare importantand

aredynamicallyrelated(P.E.Rossouwetal.,2003).Foragivennormalforce(N),

thedrawingforce(F)buildsuptoamaximumpoint(Fmax)beforeasuddendrop

inthedrawingforceoccurs.Thedrawingforcedropstoarelativeplateau.The

maximum drawing force equates to the coefficient of static friction and the

coefficientofkineticfrictionisdefinedbytheplateauphase(KusyandWhitley,

1997).Accordingtothelawsofphysics,theareaundertheplateauisthework

involvedtomaintainmotion(kineticfriction).

1.4.3Resistancetosliding

Orthodontic tooth movement does not occur in a smooth, continuous motion

along the archwire but in a sequence of short steps (Frank and Nikolai,

1980;Prashantetal.,2015).The toothalternatesbetween tippingof thecrown

and subsequent uprighting of the root. The application of force to the tooth

creates amomenton the tooth crown, resulting in tippingof the crown in the

directionoftheforce.Asthetoothtipsthearchwirebindsagainsttheedgeofthe

bracket(binding).Thisbindingresultsinanincreaseinthefrictionalresistance

and restricts toothmovement (Chimentietal., 2005;Drescheretal., 1989;Kusy

andWhitley,1997;Read-Wardetal., 1997).Consequently, static frictionaffects

space closuremore than kinetic friction (Omana etal., 1992) but is inherently

moredifficulttosimulateandconsistentlymeasure.

25

Friction is only one of the factors that can affect the resistance of sliding of a

bracket along awire or awirewithin amolar tube. Kusy andWhitley (1999)

definedthreefactorsthataffectresistancetosliding:

1. Friction – As a result of contact between thewire and bracket surface.

Thiscanbestaticorkineticfriction.

2. Binding –This occurswhen the tooth tips or the archwire flexes under

loading and contact occurs between the wire and the corners of the

bracket.

3. Notching – This is the permanent deformation of the wire that occurs

when thewire contacts thebracket corner above the critical angle.The

notching deforms the wire by gouging out microscopic areas on its

surface.Notchingpreventstoothmovementcompletelyuntilthenotchis

released. (KusyandWhitley,1999)

Burrow (2009) defined how friction, binding and notching affected the

resistance to sliding by considering the three phases that occur during

orthodontictoothmovement:

1. Firstphase–Resistancetosliding=Frictionalresistance+Binding

During the initial phase of toothmovement, the crown of

the tooth tips and contact between the wire and bracket

corner begins. Both friction and binding are factors that

affecttheresistancetoslidinginthisphase.

26

2. Secondphase–Resistancetosliding=Binding

During this phase binding is the main factor that affects

resistance to slidingbecauseas the tooth continues to tip,

the contact angle between thewire and bracket increases

furtherresultingingreaterbinding.Frictionisnotamajor

factorduringthisphase.

3. Thirdphase–Resistancetosliding=Notching

As the contact angle between the bracket and wire

continues to increase, notchingwill occur above a certain

angulation.Thesenotchesonthewirelockintothebracket

corner and prevent tooth movement until released. The

affectoffrictionandbindinginthisphaseareminor.

(Burrow,2009)

1.4.4FrictionandAnchorage

The literatureonfriction inorthodontics indicatesthat inordertoovercomeit

and achieve toothmovement higher forces are required. There is a belief that

thesegreater force levels increase the strainon theanchor teethandhave the

potential for anchorage loss. As a result, orthodontists consider anchorage

reinforcementwith auxiliary appliances ormechanicswith reduced friction to

minimisethisrisk.

One method for anchorage control would be to concentrate the applied

orthodonticforcetotheteeththatrequiremovement,anddissipatetheresultant

reactionaryforcesoverasmanyteethaspossible.Thismayresultintheapplied

forcebeingdissipatedoveralarger,cumulativerootsurfaceareaandreducethe

27

potentialformovementoftheanchorteeth.Profittetal(2012)hasproposeda

theoretical relationship of tooth movement to the pressure within the

periodontalligament.Astheorthodonticforceisappliedtothedesiredteethto

bemoved,pressureintheperiodontiumresultsinabiologicalresponseeliciting

remodelingoftheperiodontal ligamentandalveolarbone.Thisresults intooth

movement.Pressureintheperiodontalligamentequatestotheforceappliedtoa

tooth divided by the surface area of the periodontal ligament that the force is

dissipatedover.Astheforcelevelsincrease,thepressurewithintheperiodontal

ligament increasesandtoothmovementoccurs.Athreshold levelexists forthe

optimum force required to maximise tooth movement. Below this threshold

there are minimal reactionary forces on the anchor teeth and although the

amountofdesiredtoothmovementisnotoptimal,toothmovementdoesoccur.

Abovethisthresholdarelativeplateauexistswherehigherforcesdonotresult

in increasedtoothmovement(QuinnandYoshikawa,1985).Astheforce levels

andresultingpressureintheperiodontalligamentincreasesfurther,theamount

ofdesiredtoothmovementdecreasesandthereisanincreaseinthereactionary

forces on the anchor teeth.With these high force levels the anchor teethmay

movemorethanthedesiredteeth,astheforcesaretoohightomovethedesired

teethbutareintheoptimumrangefortheanchorteeth(Figure1.1).(Proffitet

al.,2012;QuinnandYoshikawa,1985)

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29

Although these factors are not tested in this study, their complex interaction

needstobeconsidered.Clinicallythesevariableswillaffectfrictionsignificantly

andwillvarybetweenpatients.Laboratorybasedstudiescanthereforeprovide

anapproximationof in-vivobehaviororbeusedtostudyanarrowselectionof

potentialvariablestocontributetoourmechanisticunderstandingofappliance

behavior.

1.4.6Archwirematerial

Orthodontic archwires are fabricated from different substrates and may be

presented with different surface coatings. Differences in frictional resistance

betweenarchwirematerialsincludingNickelTitanium(NiTi),Elgiloywiresand

stainless steel (SS)wireshavebeendemonstrated (Drescheretal., 1989;Frank

and Nikolai, 1980;Kusy and Whitley, 1999). Frictional resistance may be

modified by changing the surface finish of the archwire through machining,

coatingorionimplantation(Kapilaetal.,1990;Kusyetal.,2004).

1.4.7Archwirecross-sectionalshapeandstiffness

Orthodonticarchwirescanberound,squareorrectangularincross-sectionand

cliniciansusethevaryingcross-sectionalshapesaccordingtotherequiredtooth

movementsanddesiredthree-dimensionalcontrol.Thereisevidencetosupport

that rectangular archwires producemore friction than round archwires (Tidy,

1989)butresearchhassuggestedthatitistheoccluso-gingivaldimensionofthe

archwire that is the most important factor (Drescher et al., 1989;Frank and

Nikolai,1980).

30

1.4.8Bracketmaterial

Stainlesssteelbracketsandmolartubesarethemostpopularchoiceofbracket

materialinorthodonticsandhavebeenfoundtopermitsignificantlymoretooth

movementthanceramicbrackets(Tanneetal.,1991).Themeanfrictionalforces

withstainlesssteelbracketsandfourdifferentwirealloys(SS,cobalt-chromium,

NiTiandβ-titanium)havebeenfoundtorangebetween40and336g(Kapilaet

al.,1990).

1.4.9Bracketwidthandinter-bracketdistance

Thebracketwidth isdefinedas themesio-distalwidthof thebracket slot.The

differentcriticalangles formedbetweennarrowandwidebracketsexplain the

differentlevelsoffrictionexperienced(Tidy,1989).Narrowbracketsallowmore

tipping before the critical angle is reached at the bracket/archwire interface

(Drescher etal., 1989). The greater the critical angle the greater the frictional

resistance(AndreasenandQuevedo,1970).

There is limited published literature available on the effect of inter-bracket

distance on friction. Some studies have reported no effect from inter-bracket

distanceson friction (FrankandNikolai, 1980),whilst othershave shown that

reducedinter-bracketdistanceincreasesbinding(KusyandWhitley,2000).

1.4.10Bracketprescription

The pre-adjusted edgewise appliance revolutionised orthodontics by

incorporatingfirst,secondandthirdorderadjustmentsspecifictoeachtooth,as

well as permitting sliding mechanics. First order adjustments account for the

varying in-out requirements per tooth to achieve alignment. Second order

31

adjustmentsvarythetip(angulation)andthirdorderaccountsforthedifferent

torque(inclination)requiredforeachtooth.Thevariousprescriptionsavailable

incorporatedifferentamountsoffirst,secondandthirdorderadjustments,with

eachadjustmenthavingarelativelyunknowneffectonfrictionalresistance.

With mild second order adjustments, the slope of the archwire within the

bracketslotresultsinminimalcontactatthemesialordistaledgeofthebracket

corner. For brackets with increased tip, the archwire contacts the opposing

edgesofthebracketslotdiagonally.Thisresultsinagreateramountofbinding

and therefore an increase in the frictional resistance (Frank and Nikolai,

1980;Kusy and O'Grady, 2000;Loftus et al., 1999;Peterson et al., 1982;Tidy,

1989;Tselepsis et al., 1994). Sims et al (1994) reported a linear relationship

between increasing the tip and torque of the bracket prescription and the

associatedincreaseinfriction.

Third order adjustments allow three-dimensional control of the tooth root

position.Numerous studieshave investigated theeffectof tip (angulation)and

torque (inclination) on frictional resistance with the pre-adjusted edgewise

appliance. All of the studies have concluded that increases in bracket tip

produced a significant increase in friction, as did torquebut to a lesser extent

(FrankandNikolai,1980;KusyandO'Grady,2000;Loftusetal.,1999;Petersonet

al.,1982;Tidy,1989;Tselepsisetal.,1994).

To date there have been no previous studies investigating the relationship of

rotatedteethanditseffectonresistancetosliding.Correctionofrotatedteethis

32

carried out during the leveling and aligning stage at the start of treatment. A

unique scenario arises when the maxillary first permanent molars position is

fixedat thestartof treatmentwhenusinga transpalatalorNancepalatalarch.

Theaimofthisproposedstudyistoinvestigatetheeffectmolarrotationhason

resistancetosliding.

Studies investigatingtheeffectof tipandtorqueon frictionalresistanceuseda

specially constructed jig that allowed for 1-degree variations in the tip and

torquebetweenthebracketandarchwire.Thejigsvariedfromasinglebracket

toafullarchmodel,mountedsecurelyinanInstrontension-testingmachine.The

differentmethodologiesbetweenthestudiesallowsonlyforrelativecomparison

(FrankandNikolai,1980,KusyandO'Grady,2000,Loftusetal.,1999,Peterson

etal.,1982,Tidy,1989,Tselepsisetal.,1994).

1.4.11Ligation

The frictional force exerted by a ligature is dependent upon its coefficient of

frictionandtheforceitexertsonthearchwiretoengageitintothebracketslot

(Francoetal., 1995). Iwasakietal(2003) concluded that 31-54%of the total

intra-oral frictional force was due to ligation when a premolar bracket was

movedalonga0.019x0.025”SSarchwire.

As the archwire is enclosed within a molar tube, no method of ligation is

required. The behavior of the tube can be expected to perform in a similar

manner to self-ligating brackets, as it is a stainless steel archwire within a

stainlesssteeltube.Interestingly,asfarastheauthorisaware,nostudieshave

33

beenpublishedevaluating theeffectof tube lengthon frictional resistanceand

bindingofthearchwire.

1.4.12Biologicalfactors–Salivaandocclusalforces

Theeffectoftheoralenvironmentonslidingmechanicshasbeenwidelydebated

with literature providing contrasting evidence. Clinically, biological variation

betweenpatientseffectsfrictiondifferentlyandisasignificantfactorthatcannot

beeasilyreplicated in laboratorystudies.Thetwomainfactorsthathavetobe

considered are saliva and occlusal forces. Occlusal forces, especially during

mastication,varysignificantlybetweenpatientsandaresignificantlylargerthan

those applied to the teeth by the orthodontic appliance. Its effect varies

significantly between patients and is difficult to replicate in laboratory-based

studies.

34

1.5Anchorage

Inorthodonticsanchorage isdefinedas theresistance toreactionary forces,or

the prevention of unwanted tooth movement. Newton’s third law of motion

statesthatallforcesactingbetweentwoobjectsareofthesamemagnitudebut

areopposite indirection.Orthodontic toothmovement isachievedbyapplying

forcetoteethviaanorthodonticappliance.Whenaforceisappliedtomoveteeth

inaparticulardirection,itresultsinanequalforcebeingexertedintheopposite

direction.Thiscreatesthepotentialforundesiredtoothmovement,alsoreferred

to as anchorage loss (Proffit et al., 2012). These reciprocal forces must be

considered during treatment planning and adequate methods used to control

these forces during treatment so that the occlusal objectives at the end of

treatmentcanbeachieved.

1.5.1Principlesofanchorage

According to the differential force theory (Begg, 1956), orthodontic tooth

movementisrelatedtotheforceperunitrootsurfacearea.Researchhasshown

that teethwith a greater root surface area have increased resistance to tooth

movement, or increased anchorage value (Hixon, 1970). However, the

relationship thatexistsbetweenrootsurfaceareaand toothmovement isnon-

linear, suggesting other factors also have a significant contribution to tooth

movement (Pilon et al., 1996). As previously discussed, tooth movement

increases with an increased applied force until the optimum force is reached.

Thereafter an increase in force does not result in a greater amount of tooth

movement,onlyanincreasedstrainontheanchorunits(QuinnandYoshikawa,

1985).

35

Clinically,theorthodontistaimstodissipatethereactionaryforcesoverasmany

teeth as possible to limit the potential for unwanted tooth movement. Heavy

forcesshouldbeavoidedandideallyforceskeptaslowaspossibletoavoidany

anchorage loss and movement of the anchor teeth. Restricting these teeth to

bodilymovementcanincreasetheanchoragevalueoftheanchorteethfurther,

aslargerforcesarerequiredtomoveteethbodily.

1.5.2Sources/types

There are numerous potential sources for anchorage reinforcement, either

intraoralorextraoral.Theextraoralsourceofanchorageisachievedwiththeuse

ofheadgear,whetherconventionalorprotractionheadgear.Anchorageisgained

by using the cranial vault or the basal bones to oppose the orthodontic forces

appliedtoteeth. Intraoralsourcesofanchoragecanbegainedfromteeth,soft-

tissuesorbone.

1.5.3Intraoralanchorage–teeth

Teetharethemostcommonlyusedformofintra-oralanchorage.Whenapplying

force toa toothagainstanother tooth inorder to induce toothmovement, it is

classifiedassimpleanchorage.Whenthereismorethanonetoothintheanchor

unit(Moyers,1973),itisclassifiedascompoundanchorage.Thiscanbeachieved

from an intra- or inter-maxillary (with the use of elastics between opposing

arches)source(QuinnandYoshikawa,1985).

36

1.5.4Intraoralanchorage–Softtissue/Bone

The soft tissues, in terms of the oralmusculature, also provide anchorage and

resistancetounwantedtoothmovement,orevenexertactiveforcestoproduce

toothmovement(CetlinandHoeve,1983).

Corticalanchorageresultsbecausecorticalboneismoreresistanttoresorption

thanmedullarybone,providinggreater resistance to toothmovementwhen in

contactwiththerootsofteeth(Hixon,1970;Ricketts,1979).Corticalanchorage

canbeutilizedclinicallywiththeuseofcertainmechanics.However,thereisno

scientific evidence available to support the concept of cortical anchorage

(Stivaros et al., 2010) and is based on clinical experience. For example, by

applyingbuccalroottorquetoposteriorteethtobringtherootsoftheteethinto

contactwiththecorticalplates,itisbelievedthatthemesialmovementofthese

teeth is reduced but there is an increased risk of root resorption. It has been

suggested that a transpalatal arch is a form of cortical anchorage. The

reactionary forces onmolar teeth result inmesially directed toothmovement,

butbyfixingthemolarwidththerootscontactthecorticalplatesasthedental

archnarrowsanteriorlyandinhibitsfurthermesialmovement.

Anchoragemaybegainedfromalveolarboneviatheuseoftemporaryanchorage

devices (TADs), osseointegrated dental implants or bone anchors to provide

absoluteanchorage(IsmailandJohal,2002;Youngetal.,2007)andoccasionally,

evenfromankylosedteeth(Kokichetal.,1985).

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39

The currently available literature is limited with a few clinical trials and

laboratory-basedstudiesonthebiomechanicalaspectsandclinicalmanagement

oftranspalatalarches.

1.5.6EvidencetosupportTPAorNancepalatalarch

A randomised clinical trial comparing the effectiveness of a Goshgarian and

Nance palatal arch in preventing mesial drift, distal tipping, mesio-palatal

rotationandpatientcomfortfoundnooverallstatisticalorclinicaladvantageto

provide scientific evidence for the use of one over the other (Stivaros et al.,

2010). Forty-nine that were treated with upper and lower fixed appliances,

upperpremolarextractionsandeitheraGoshgarianorNancepalatalarchwere

included in the data analyses. Study models were digitally scanned and

comparedbetweenpre-treatmentandsix-monthsintotreatmentfollowingonly

levelingandaligning.Nostatisticallysignificantdifferenceintheaveragemesial

movementoftheupperfirstmolarwasfound,withthemeanfortheGoshgarian

andNance palatal arch being 0.98mmand0.72mm respectively. Statistically,

theGoshgarianpalatalarchwassignificantlybetteratpreventingmesio-palatal

rotation of the upper first permanent molars. The Nance palatal arch was

reported to be significantly more uncomfortable by patients (Stivaros et al.,

2010). The trial may have benefitted from a control group, who received no

palatal arch, in order to evaluate the effectiveness of each appliance in

preventingmesialmovementofthemolarsandreinforcinganchorage.

Zablocki et al (2008) undertook a cephalometric study to evaluate the

effectiveness of a transpalatal arch in reinforcing anteroposterior and vertical

40

anchorage. Using two non-randomised, matched groups they found that a

transpalatal arch had no significant effect during extraction treatment. The

transpalatal arch group had on average 0.4 mm less mesial and vertical

movement of the maxillary first permanent molar, which was not clinically

significant.Intermsofhealtheconomics,theuseofonlyatranspalatalarchfor

anchorage reinforcement is difficult to justify. This was in agreement with

another investigation that reported loss of anchorage with the use of a

transpalatalarch(Radkowski,2007).Themajorlimitationofthisstudywasthat

lateralcephalogramradiographswereusedtoevaluatemesialmovementofthe

uppermolars.Linearmeasurements fromtheseradiographswerevariableand

thestudyreportedfindingsto1-decimalplace.

Mini-screwimplantsortemporaryanchoragedevices(TADs)areanincreasingly

popular method of anchorage reinforcement, despite a lack of conclusive,

scientificevidencewithregardstotheireffectiveness.Themini-titaniumscrews

donotosseointergratebutrelyonmechanicalretentiononcein-situtoprovide

anchorage from the jaw bones. A recent Cochrane review has reported some

moderate evidence is available to suggest TADs are effective in reinforcing

anchoragecomparedwithmoreconventionalmethods(Jambietal.,2014).

A multicenter, randomised clinical trial evaluated the effectiveness of three

methodsofanchoragereinforcement;aNancepalatalarch,headgearandTADs.

Seventy-eight patients participated in the study, which found no difference

betweenthemethodsintermsofanchoragereinforcement.ANancepalatalarch

wasperceived tobe as equally comfortable asTADsbut occlusal outcomes, as

41

measuredby thePeerAssessmentRating (PAR),were significantlybetterwith

TADs(Sandleretal.,2014).Itcouldbearguedthattheocclusaloutcomeismore

dependentontheorthodontists’clinicalskillsandexperiencethanthemethodof

anchorage reinforcement. Currently, this is the most robust clinical research

availablewithregardstomethodofanchoragereinforcement.However,itisnot

inagreementwithotherresearch.Apreviousrandomisedclinicaltrialreported

significantlygreatermesialmovementof themaxillary firstmolarswithaTPA

thanwithTADs(Sharmaetal.,2012).

In summary, Goshgarian and Nance palatal arches are equally effective in

reinforcing anchorage. There is a lack of evidence to support the use of these

appliances for anchorage reinforcement, but no clinical trials have included a

control group without any anchorage support to evaluate the overall

effectivenessofthesepalatalarches.Arecentrandomisedclinicaltrial(Sandler

etal.,2014)hasfoundthataNancepalatalarchisasequallyeffectiveasTADs,

and currently, TADs are perceived to be the best method of anchorage

reinforcement,otherthanosseointergratedimplantsorboneanchors.

42

1.6Aimsandobjectivesofstudy

Aims:

• Determine if the use of a transpalatal (TPA) orNancepalatal archwith

varying degrees of molar rotations significantly effects resistance to

slidingduringslidingmechanics

• Establishifthereisreducedresistancetoslidingusingtheextraoraltube

(EOT)onmolarbandsasopposedtothestraightwiretubewhenusinga

TPAorNancepalatalarchwithrotatedmolars

Objectives:

1. Establish the range of molar rotations encountered from a randomly

selectedsampleofpatientstudymodels

2. Identifywhethervaryingdegreesofmolarrotation increases thekinetic

frictionrequiredtoallowthearchwiretoslidethroughthestraight-wire

tubeonthemolarbands

3. Examine whether using the extraoral tube on molar bands alters the

frictional force when using sliding mechanics in comparison to the

straight-wiretube

4. Establish how the varying degrees of molar rotation would affect the

efficiency of the sliding mechanics used in the pre-adjusted edgewise

appliance

43

ChapterTwo

MaterialsandMethods

44

ChapterTwo:MaterialsandMethods

2.1Estimatingrangeofaveragemolarrotationsbaseduponex-vivodata

StudiesexaminingthedegreeofmolarrotationspresentinclassIImalocclusions

have concluded that the maxillary first permanent molar is mesio-palatally

rotatedonaverageby7to110(Foresman,1964;Hellman,1920).Theparameters

usedinpreviousstudiestoexaminetheeffectofangulation(mesio-distalangle)

or inclinations (bucco-palatal angle) have ranged from0 to 130 for angulation

and 0 to 120 for inclination (Articolo and Kusy, 1999;Hamdan and Rock,

2008;Moore et al., 2004). Although the parameters used in these studies can

serveasaguidetotheparametersforthepresentstudy,theyareinsufficientin

order to form the parameters for this study, because the studies had small

samplesizesandtheircohortofmalocclusionsmaybesignificantlydifferent.No

literature is available regarding the effect of rotated teeth on the resistance to

slidinginthepre-adjustededgewiseappliance.

Therangeofaveragemolarrotationsforthisstudywereestimatedbymeasuring

theangleofFrielandtheangleofHenryon50randomlyselectedstudymodels

(Figure2.1)fromtheBirminghamDentalHospitalmodelboxstorageroom.No

previous studieswereavailable toguide sample size calculations.However,by

examiningtheleftandrightmolarindependently,50studymodelswouldgivea

largesamplesizeof100modelswhichwasfelttobesufficient.Thepurposeof

this exploratory study was to identify a range of clinically relevant first

permanent molar angulations for subsequent in-vitro simulations and not

specificallytoallowgeneralizationofepidemiologicaldatatoalargerpopulation.

Arandomnumbergenerator(www.randomizer.org)wasusedtoselectthestudy

45

models from the database. The studymodels were scanned at a resolution of

9600 x 4800 dpi, using an Epson flatbed scanner and subsequently printed at

300dpi(figure2.1).

Figure2.1:ExampleofscannedstudymodelandillustrationoftheanglesofFriel

andHenry

From the printed images, anatomical points (Table 2.1) were identified and

clearlymarkedwitha0.1mmfibre-tippedpentoserveasreferenceforthelines

and angles to be measured. These angles were measured by hand using a

protractorandusedtoevaluatethedegreeofmolarrotation.Thevariouspoints,

linesandanglesmeasuredarelistedinTable2.1.

46

Table2.1:Anatomicalpoints,referencelinesandanglesmeasuredfromstudymodels

PointsR1 MostanteriorpointofthepalatalrapheR2 MostposteriorpointofthepalatalrapheMP Tipofthemesio-palatal(MP)cuspofthemaxillaryfirst

permanentmolarMB Tipofthemesio-buccal(MB)cuspofthemaxillaryfirst

permanentmolarDB Tipofthedisto-buccal(DB)cuspofthemaxillaryfirst

permanentmolarLines

R1-R2 LineconnectingpointsR1toR2MB-DB LineconnectingpointsMBtoDBMB-MP LineconnectingpointsMBtoMP

AnglesAngleofFriel AnglebetweenthepalatalrapheandthelineMBtoMPAngleofHenry AnglebetweenthepalatalrapheandthelineMBtoDBA single examiner (EmileHabib)measured the angles proposed byHenry and

Friel tocalculate thedegreeofrotationof themaxillary firstpermanentmolar.

Toevaluateintra-examinererror,20%ofthesamplesizewasrandomlyselected

and measurements repeated 120 days after the first measurements and

comparedwiththeoriginalmeasurements.Theanglesobtainedwereexamined

by calculating the mean and standard deviation for the left and right molars,

alongwitha95%normalrange.

Theresultsobtainedfromtheassessmentofarandomsampleoftheorthodontic

population at Birmingham Dental Hospital were then used to define in-vitro

simulationstoevaluatetheeffectofrotatedmolarsonresistancetoslidinginthe

transpalatalandNancepalatalarchset-ups.

47

2.2Designofexperimentalapparatus

Aspeciallydesignedapparatus (Figure2.2)wasused tomeasure resistance to

sliding between a 0.019 x 0.025” inch stainless steel archwire (Resilient

Orthoform III Ovid, 3M Unitek) and two stainless steel molar tubes fixed in

position to replicate the effect of a transpalatal arch. This archwire size was

selected,asit isthemostcommonlyusedworkingarchwireinclinicalpractice.

The apparatus allowed for themolar tubes to be precisely rotated buccally or

palatallyin1-degreeincrements.Thedesignoftheexperimentaljigwasadapted

frompreviousstudies(HamdanandRock,2008;Mooreetal.,2004).

The apparatus was set-up on a 300mm x 300mm solid aluminum base plate

(HighDensityMini-BreadboardMS12B,Thorlabs, Inc).Thebaseplateweighed

2.37 kg to provide stability for mounting of 2 rotational stages (Mini-series

rotationplatformMSRP01,Thorlabs,Inc).Thestagesweremountedandfixedto

thebaseplateonstainlesssteelrodsattheaverageinter-molarwidthof51mm

(Bisharaetal.,1997).Thisrecreatedtheeffectofatranspalatalarchbyfixingthe

molartubesinanantero-posteriordirection.

Totherotationstagealabfabricated,castmetalheadwasfixedinplace.Itwas

grooved toallow for themolarbands (MBT™prescription,Victoryseries™,3M

Unitek)tobechangedandsecuredinanidenticalposition.Themolartubeswere

aligned so thatwhen at 00 rotation the archwire sat passively in both left and

rightmolartubes,followingthenaturalcurvatureofthedentalarch.

48

Testing was performed on a MTS universal test machine (Model 42, MTS

Criterion® Series 40 Electromechanical universal test systems, MTS systems

corporation, Minnesota, USA) using a 250 N load cell, recording the drawing

forceat0.1-secondintervals.Thetestapparatuswasfixedtothelowerclampof

themachineand thearchwire secured to theupper clamp.Theapparatuswas

positionedsothatthearchwirewasmovedonlyinaverticaldirectionrelativeto

themolartubes,thereforeensuringnotiportorquewasintroduced(Figure2.2-

2.4).

Figure2.2:Testapparatus–overview

49

Figure2.3:Testapparatus–rotationalstages

50

Figure2.4:Testapparatus–verticalalignmentofarchwire

The independentvariable for this study is themolarrotationand theeffecton

resistancetosliding.Thiswastestedforthreescenarios:

1. Bothleftandrightmolarsarepreciselyaligned(bothpassive)

2. Onemolarispassiveandonemolarispalatallyrotated(active)

3. Bothmolarsarepalatallyrotated(active)

51

Thereweremultipleconstantvariablesthatneededtobecontrolledtoallowfor

the independentvariabletobetheonly factoraffectingthedependentvariable

(resistancetosliding).Thesecontrolvariableswere:

• Thearchwidthwascontrolledbyfixingthedistancebetweenthemolar

tubesandthewidthofthearchwireused.

• The length of unsupported archwirewas fixed at 18mm. Thiswas the

distance between the upper clamp (replicating the distal surface of the

maxillarycaninebracket)andthemolartube.Thedistancewasbasedon

thepreviousstudyconductedHamdanandRock(2008).Thedistanceof

unsupportedwire reduced the relative stiffness of the archwire so that

bindingdidnotcompletelydominatefrictionalresistanceduringtesting.

• Theangulationandinclinationwasfixedbyincorporatingseatinggrooves

onthecastmetalheadontherotationalstages.Thisallowedforthebands

tobechangedandsecured inan identicalposition inall threeplanes to

ensurethetipandtorqueofthebandwasnotalteredbetweentests.

• Theprescriptionortubelengthofthebandwasnotalteredbetweentests.

TheMBT™prescriptionwith100distaloffset,140buccalroottorqueand

4.6 mm tube length was used for all tests. The tube dimensions were

0.022x0.028”.The tubewasmade fromstainlesssteel.TheroundEOT

was4.6mminlengthandhadadiameterof1.3mm

• Thecrossheadspeedwas2mm/min.Otherstudiesonfrictionwithpre-

adjustededgewiseappliancesusedacrossheadspeedof10mm/minbut

thiswas felt tobe toohigher rate to fully evaluate the effect of binding

(ArticoloandKusy,1999;KusyandO'Grady,2000;Tselepsisetal.,1994).

52

• TheMTS universal testmachinewas recalibrated to zero prior to each

testtoaccountfortheweightoftheapparatusanddriftoftheloadcell.

Althoughthevalueofinterestfororthodontistsismostcommonlystaticfriction,

due to the nature of the study it is anticipated that binding will contribute

significantly to the overall resistance to sliding. Therefore, the value of kinetic

frictionwillbegreaterthanthatofstaticfrictionandmorerelevanttothisstudy.

Kinetic friction is represented by the area under the curve of a displacement

versusforcegraph.RawdatafromtheMTSuniversaltestmachinewasexported

to an excel spreadsheet. Thedatawas analysedusing Sigmaplot 12.0 software

(Systat software, Inc. Hounslow, London, UK) to calculate the work involved

(areaunderthecurve),whichequatestotheresistancetoslidingforce.

2.3Pilotstudies

Pilot studieswere conducted to evaluate the sensitivity and reproducibility of

thetestapparatus.Theaimofthepilotexperimentswere:

1. To evaluate the degradation of the archwire and how often it requires

replacement

2. Toevaluatethedegradationofthemolartubeandhowoftenitrequires

replacement

3. Toestablishifdisplacementisproportionaltowork

4. To evaluate if the left and right molar tube experimental results are

equivalentandcomparable

53

5. To increase thenumberof repeatexperiments toexamine thenatureof

therelationshipbetweenrotationandwork,and identifyanysignificant

rotations.

Thepilot studieswere conducted in three groups andprovided threedatasets

accordingly.Thegroupswere:

1. Leftbuccalrotation–rightpalatalrotation

2. Leftpalatalrotation–rightbuccalrotation

3. Leftpalatalrotation–rightpalatalrotation

Based upon previous studies and the results of the ex-vivo data, both left and

right molars rotation was varied between 160 buccally and palatally rotated.

Buccal rotationswereexamined forcompletenessand to identifyanypotential

errorsintheapparatuspriortothedefinitivestudies.Therotationswerealtered

in4-degreeincrementsandtheexperimentsconductedrandomlytopreventany

systematic errors. Data was recorded from 0.1 mm to 10 mm, the minimum

displacementdetectableby the test apparatusand themaximumdisplacement

thatwouldbeexpectedclinically.

To examine the nature of the relationship between displacement and work,

linear regression was used. For each dataset, work was considered as the

outcomevariableandthedisplacementthekeypredictorvariable.Allindividual

measurements were included in the analysis. Aside from displacement, the

degreeofleftandrightrotationwasalsoincludedaspredictorvariables.Initially

54

linear,squaredandcubictermsfordisplacementwereincludedintheanalysis.If

the cubic termwas not found to be statistically significant, this was removed

fromtheanalysisandonlythelinearandsquaredtermswereincluded.

An additional analysis compared the work values between the first two

experimentaldatasets(leftbuccal–rightpalatal,leftpalatal–rightbuccal).The

datasetswerematchedupbytherotationvalues,withtheleftrotationfromthe

first dataset matched to the right rotation from the second dataset. This was

undertakeninordertoconfirmtheset-upoftheleftandrightrotationalstages

weresimilarandcomparable.Duetothe‘paired’natureofthedata,thepairedt-

testwasusedtocompareworkvaluesbetweenthetwodatasetsusinganalpha

value0.05.

2.4Definitivestudies

Focusingonpalatalrotations,thedefinitivestudiesdividedtheexperimentsinto

twoconceptualgroups:

1. Theeffectofaunilateralmolarrotation–rightpassiveandleftincreasing

palatalrotation

2. Theeffectofabilateralmolarrotation–rightpalatalandleft increasing

palatalrotation

Whentherightmolarwaspassive,itsrotationwasfixedatzerodegrees(i.e.the

idealalignment).Whentherightmolarwasactive,itsrotationwasfixedat100.

This provided sufficient palatal rotation in order to differentiate from when

55

passive but was not significant enough so that the variable of the left molar

rotationcouldbeexamined.Theleftmolarrotationwasexaminedbetweenzero

and160,alteredintwo-degreeincrements.

Tovalidate the accuracyof the results, the left and rightmolar rotationswere

switched.Theleftmolarwasfixedatapassivealignmentofzerodegreesoran

activealignmentof100palatalrotation.Therightmolarrotationwasexamined

at8,12,16and20-degreerotations.Therotationswereextendedto200sothat

theexpectedresult,calculatedfromtheequationoftherelationshipfound,could

becomparedwiththeactualresult.

Toincreasethevalidityoftheresultsandcounteracttheincreasedvariationin

the results for higher rotations, each experimentwas repeated 7 times at the

samerotation.Statisticalanalysiswasconductedonthesummarydata.

The agreement between the repeated measurements was examined by

calculatingtheintra-classcorrelation(ICC).Thepilotstudiesprovidedevidence

thattherewasmorevariationforhigherrotationsthanthatoflowrotations.To

counterthis,theanalysiswasdonewiththeworkvaluesonthelogscale.

The two datasets werematched by rotation value and themean work values

compared.Due to the ‘paired’natureof thedata, thepaired t-testwasused to

compare the mean work values. An additional analysis examined how the

difference inwork betweenmethodswas associatedwith the rotation (that is

whetherthedifferenceswerehigheror lowerforgreaterrotations).Duetothe

56

continuousnatureofbothvariables, theanalysiswasperformedusingPearson

correlation.

2.5Comparisonofstraight-wireandextraoraltube

TheeffectofusingtheEOTonthemolarbandopposedtothestraight-wiretube

was evaluated. The archwire was offset labially immediately below the upper

clampoftheMTSmachineandpassedintotheEOT.Theexperimentswereagain

divided into twogroupsasper thepreviousdefinitivestudies.Therightmolar

rotationfollowedthepreviousmethodology(eitherfixedatzeroor100)andleft

molar rotation was examined between zero and 120, altered in 4-degree

increments.Four-degreeincrementswereusedbecausethepassivenatureofthe

EOTmeant variation in the results for 2-degree increments wasminimal and

wouldresultinanincreasednumberoftestswithlittlevariationintheresults.

Thepairedt-test(matchingmeasurementsbyrotation)wasusedtocomparethe

average difference between the straight-wire and EOT group. Pearson

correlation was used to examine whether the difference between methods

variedbyrotation.

57

ChapterThree

Results

58

ChapterThree:Results3.1Molarrotations

From the sample of 50 study models (100 molars examined), the mean and

standarddeviationfortheanglesofFrielandHenry,alongwiththe95%normal

rangearesummarizedinTable3.1:

Table3.1:Mean,SDand95%normalrangeforanglesofFrielandHenryMeasurement Mean(Degrees) Standard

deviation95%normal

rangeAngleofFriel-Left 57.2 5.7 46.0–68.5-Right 57.5 5.2 47.2–67.7 AngleofHenry-Left 17.1 3.8 9.6–24.6-Right 16.6 3.1 10.5–22.8Asub-sampleofmeasurementsfrom10studymodels(20%oforiginalsample)

was repeated after120days and the repeatabilitywas assessedby calculating

theintra-classcorrelation(ICC).TheresultsaresummarizedinTable3.2:

Table3.2:ICCofmeasurementsforangleofFrielandHenryMeasurement Intra-classcorrelation(95%CI)AngleofFriel-Left 0.91(0.71–0.98)-Right 0.97(0.90–0.99)AngleofHenry-Left 0.85(0.54–0.96)-Right 0.97(0.89–0.99)TheanalysessuggestedfairlyhighICCvaluesforallparameters.ThehighICC

valuessuggestgoodrepeatabilityofthemeasurements,andvalidatedtheresults

forthetwoanglesmeasured.

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62

Table3.4:Meanworkresultsandp-valueformatcheddatafromleftbuccal–rightpalatalandleftpalatal–rightbuccalDisplacement(MM)

LB–RPMean(SD)

LP-RBMean(SD)

Difference(*)Mean(95%CI)

P-value

10mm 69(34) 63(24) -6(-16,4) 0.240.5mm 2.6(1.2) 2.4(0.9) -0.1(-0.5,0.2) 0.450.1mm 0.28(0.10) 0.22(0.08) -0.05(-0.09,-0.01) 0.01(*)Differencescalculatedasvaluesforleftpalatal–rightbuccalminusleftbuccal–rightpalatal

A statistically significant difference was only observed for the 0.1 mm

displacement values. The left palatal – right buccal dataset had lower values,

withworkvalues0.05J(N/m),onaverage,lowerthanthosefortheleftbuccal–

right palatal dataset. The analysis found no significant difference in work for

displacementof10mmand0.5mm.

3.3Definitivestudies

The results for the two data sets examining the effect of a unilateral palatal

rotationandbilateralpalatalrotationofthemolarsareshowninappendix1.The

meanandstandarddeviationoftheresultsaresummarisedinTable3.5:

63

Table3.5MeanworkvaluesforgivendisplacementaccordingtodegreeofmolarrotationRightmolar(passive/active)

Leftmolarrotation(degrees)

Meanworkfordisplacement(standarddeviation)–Joules(N/m)5mm 0.5mm 0.1mm

Passive 0 2.12(0.65) 0.45(0.14)

0.07(0.03)

2 2.01(0.34) 0.41(0.08)

0.07(0.01)

4 2.33(0.33) 0.45(0.08)

0.07(0.02)

6 3.59(0.55) 0.72(0.15)

0.10(0.03)

8 4.24(0.46) 0.85(0.05)

0.13(0.02)

10 5.65(0.96) 1.26(0.28)

0.20(0.05)

12 6.81(1.25) 1.42(0.31)

0.20(0.04)

14 8.49(0.77) 1.93(0.27)

0.26(0.07)

16 12.69(0.90) 2.50(0.31)

0.37(0.05)

Active 0 5.01(0.61) 0.99(0.14)

0.14(0.02)

2 5.61(0.67) 1.09(0.15)

0.16(0.02)

4 6.12(0.49) 1.17(0.10)

0.17(0.02)

6 6.53(1.46) 1.32(0.36)

0.20(0.06)

8 7.07(1.75) 1.36(0.43)

0.20(0.06)

10 7.76(1.39) 1.48(0.34)

0.20(0.04)

12 9.12(0.44) 1.78(0.17)

0.26(0.03)

14 10.23(0.67) 2.03(0.30)

0.28(0.05)

16 12.41(0.84) 2.46(0.23)

0.33(0.04)

TheICCtoassessrepeatabilityofthemeasurementsateachrotationisshownin

table3.6:

64

Table3.6ICCresultsfordisplacementsof5mm,0.5mmand0.1mmData Displacement(mm) ICC(95%CI) Rightpassive 5mm 0.94(0.86,0.98) 0.5mm 0.92(0.82,0.98) 0.1mm 0.86(0.71,0.96) Rightpalatal 5mm 0.82(0.64,0.95) 0.5mm 0.74(0.52,0.92) 0.1mm 0.66(0.42,0.89)The nature of the relationship between rotation andworkwas analysed using

squaredandcubictermsfordisplacement(Table3.7).Thecubictermswerenot

found to be significant for any displacement values in the right passive data.

However, after removalof the cubic terms, the squared termswere significant

for all three displacement values. This suggests evidence that there is a non-

linear relationship between rotation and work for this dataset. For the right

palatal(active)data,thecubictermsweresignificantforthe5mmand0.5mm

data, suggestingevidenceofanon-linearrelationship.As thecubic termswere

significant,thesquaredtermswerenotexaminedfurther.Thecubictermswere

notsignificant for the0.1mmdata,andtheresult for thesquaredtermwasof

borderline statistical significance.This suggests some, althoughnot conclusive,

evidenceofanon-linearrelationshipbetweenrotationandwork.

Table3.7SquaredandcubictermsfordisplacementData Displacement

(mm)Cubicterm-P-value Squaredterm–P-value

(*) Rightpassive 5mm 0.17 0.001 0.5mm 0.82 <0.001 0.1mm 0.67 0.003 Rightpalatal 5mm 0.003 - 0.5mm 0.01 - 0.1mm 0.15 0.06

65

The work values were compared between the right passive and right palatal

datasets and a summary of the results is reported in Table 3.8. The figures

presentedarethemeanandstandarddeviationforeachsetofdata,alongwith

themeandifferencebetweendatasets and corresponding confidence intervals.

The differences are calculated as value for right palatalminus values for right

passive.

Table3.8Mean,SDandp-valuecomparingrightpassiveandrightpalataldatasetsDisplacement(mm)

Rightpalatalmeanwork

(SD)

Rightpassivemeanwork

(SD)

Difference(*)meanwork(95%CI)

P-value

2mm 7.8(2.4) 5.3(3.6) 2.4(1.5,3.4) <0.0010.5mm 1.5(0.5) 1.1(0.7) 0.4(0.2,0.6) 0.0020.1mm 0.21(0.06) 0.16(0.10) 0.05(0.01,0.09) 0.02 (*)DifferencescalculatedasvaluesforrightpalatalminusrightpassiveTherewassignificantdifferenceintheworkvaluesbetweenthetwodatasets,on

average, for all displacement values. In each case thework in the right palatal

dataset was significantly higher than for the right passive data. The results

indicatethatthereisasignificantincreaseinworktoslidethearchwirethrough

the molar tube with bilaterally, palatally rotated molars compared with a

unilateral,palatalrotation.

The difference between the right passive and right palatal datasets was

examined further to see if the differences varied depending on the rotation.

CorrelationanalyseswereperformedandtheresultssummarisedinTable3.9:

66

Table3.9CorrelationanalysestoexamineifthedifferencebetweenbothgroupsvarieddependingonrotationDisplacement(mm) CorrelationCoefficient P-value 2mm -0.83 0.0060.5mm -0.88 0.0020.1mm -0.79 0.01 Theresultssuggestedasignificantassociationbetweenthelevelofrotationand

thedifference inworkbetweenpalatal andpassivedata.All correlationswere

negative,suggestingthatagreaterrotationwasassociatedwithalessdifference

betweentherightpassiveandrightpalataldatasets.

Switching the left and rightmolar tubepositions validated the accuracyof the

results. The results are presented in Appendix 2. The work involved at a

displacementof0.5mmand2mmwascomparedbetweentheswitcheddataset

and the previous dataset (un-switched). The results are summarised in Table

3.10.Thefigurespresentedarethemeanandstandarddeviationforeachsetof

data, alongwith themean difference between datasets and the corresponding

confidence interval. The differences are calculated as the results for the un-

switchedminustheresultsfortheswitched.

Table3.10Comparisonofswitchedandun-switchedmeanworkmeasurementstovalidateaccuracyofresultsandp-valueData-Displacement(mm)

UnswitchedMean(SD)

SwitchedMean(SD)


P-value

Rightfixed–0.5mm 1.6(1.0) 1.5(0.9) -0.1(-1.4,4.1) 0.83Rightfixed–2mm 7.3(4.1) 6.8(3.4) -0.5(-6.4,5.4) 0.76 Rightpalatal–0.5mm

1.9(0.6) 1.8(0.7) 0.0(-0.5,0.4) 0.74

Rightpalatal–2mm 9.5(2.7) 8.6(2.9) -0.9(-2.4,0.6) 0.12 (*)Differencescalculatedasvaluesforswitchedminusunswitched

67

Theresultssuggestednosignificantdifferencesintheworkvaluesbetweenthe

switched and unswitched measurements for either dataset, and for both

displacementsexamined.

68

3.4Comparisonofthestraightwireandextraoraltube

TheeffectofplacingthearchwireintheEOTopposedtothestraightwiretube

was examined using the samemethodology and dividing the experiments into

two groups (right passive and left increasing palatal rotation, right palatal

rotation and left increasing palatal rotation). The results are presented in

Appendix3.Thepairedt-test(matchingmeasurementsbyrotation)wasusedto

comparetheaveragedifferencebetweenthetwomethods(Table3.11):

Table3.11ComparisonofthemeandifferenceinworkbetweentheEOTversusthestraightwiretubeData–Displacement(mm)

StraightWireMean(SD)

EOTMean(SD)


P-value

Passive-2mm 3.9(2.4) 0.9(0.4) -3.0(-5.9,0.0) 0.05Passive–0.5mm

0.79(0.46) 0.18(0.07) -0.61(-1.24,0.01) 0.05

Active-2mm 6.8(1.7) 1.3(0.7) -5.6(-7.2,-3.9) 0.002

Active–0.5mm 1.33(0.33) 0.29(0.23) -1.03(-1.26,-0.81) <0.001

(*)DifferencescalculatedasvaluesforEOTminusstraightwireThe analysis results suggested some evidence of a differencebetween the two

tubes for all analyses.The results for thepassivedatawereonlyofborderline

statistical significance.Allanalyses foundmuch lowerworkvalues for theEOT

comparedwiththestraightwiretube.

ThePearson correlationwasused to examinewhether thedifferencebetween

methodsvariedbyrotation.TheresultsaresummarisedinTable3.12:

69

Table3.12PearsoncorrelationanalysestocomparetheEOTwiththestraightwiretubeData–Displacement(mm)

CorrelationCoefficient P-value

Passive-2mm -0.94 0.06Passive–0.5mm -0.93 0.07 Active-2mm -0.99 0.007Active–0.5mm -0.94 0.06 The results foundsomeevidenceofanassociationbetweendifference inwork

between the two methods and rotation. The results are generally only of

borderline statistical significance. The differences between methods were

negative(thatislowervaluesforEOT),thenegativecorrelationssuggestedthat

thedifferencebetweenmethodswasgreaterforhigherrotations.

70

ChapterFour

Discussion

71

ChapterFour:Discussion

4.1Molarrotation

Thecurrentevidencebaseformeasuringthedegreeoftheupperfirstpermanent

molar rotation suggests the mean angle of Henry to be 11.2 +/- 0.8 degrees

(Henry, 1956) and the angle of Friel to be in the range of 57 to 61 degrees

(Foresman,1964;Friel,1959;LamonsandHolmes,1961). Theuseoftheangles

ofFrielandHenry todetermine thedegreeofmolarrotation in thisstudywas

warrantedbecausethemeasurementshavebeenshowntobereproducibleand

havebeenpreviouslyvalidated(Dahlquistetal.,1996;Friel,1959;Henry,1956).

TheresultsforthemeanangleofHenrywere17.1+/-3.83degreesfortheleft

molarand16.6+/-3.14degreesfortheright.Thissuggestedthatthemolarsin

this samplewere,onaverage,palatally rotated comparedwithmolars that are

fully aligned to the optimum angle. This is to be expected as the sample was

derived from study models at Birmingham Dental Hospital, where patients

would have been assessed as in need of orthodontic treatment. They are

thereforeunlikelytohaveanidealocclusionorwell-alignedarches.Thisfinding

isinagreementwithpreviousstudiesevaluatingrotationofthefirstpermanent

molar rotation in class II malocclusions (Henry, 1956;Lima et al., 2015). The

resultsforthemeanangleofFrieldidnotsupportthisfinding.Themeanangleof

Frielwas57.20fortheleftmolarand57.50fortheright.Thiswasinagreement

with the previous studies on the ideal rotational angle for the upper first

permanentmolar, although on the lower end of the normal range (Foresman,

1964;Friel,1959;LamonsandHolmes,1961).Itisimportanttonotethaterrors

mayhaveresultedduetoanexaminererrorinidentifyingthemesio-palatalcusp

72

tip of the molar, anatomical variations of the first permanent molar or,

alternatively, this result may be correct with the mean angle of Henry being

incorrect.

The repeatability of themeasurementswas examined by calculating the intra-

class correlation (ICC). The analyses suggested fairly high ICC values for all

measurements, andparticularlyhighvalues for theFriel right andHenry right

measurements(ICCof0.97forbothmeasurements).ThehighICCvaluessuggest

goodrepeatabilityofthemeasurements.

4.2Impactofrotatedmolarsonresistancetosliding

The results of this study demonstrated that as the palatal rotation of the

maxillary first permanent molar increased, the work involved in sliding the

archwirethroughthemolartubeincreased,thatistherewasanincreaseinthe

resistance to sliding. For smaller rotations, the displacement-force tracings

obtained were comparable with other studies examining friction with fixed

appliances(ArticoloandKusy,1999;HamdanandRock,2008;Mooreetal.,2004).

Following an initial peak in force as static friction was overcome, the force

dropped to a relative plateau. This plateau represents the kinetic friction

involved in maintaining movement of the archwire through the molar tube

(Figure4.1).

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75

tube,bindingcanrapidlyoccuranddominatesfrictioninrelationtoresistanceto

sliding.Thiscreatesaninabilitytoaccurately identifystaticandkinetic friction

values. Resistance to sliding swiftly enters the second phase as defined by

Burrow (2009),where resistance to sliding is equal to thebinding that occurs

betweenthemolartubeandbracket.

Articolo andKusy (1999) investigated the influenceof the angulationbetween

the archwire and bracket on the resistance to sliding (N), and designed a

mathematical model for understanding the relative impact of binding and

friction to resistance to sliding. The results demonstrated a linear relationship

forall resistance tosliding (N)regression lines.As theangulationbetween the

bracketandarchwirewas increased, the forcerequired tomaintainmovement

increased. Comparison of the regression lines demonstrated that resistance to

slidingincreasedwithincreasingangulationbetweenthearchwireandbracket,

astheregressionlinewasnoticeablyhigher.Interestinglythedistancebetween

the lines was fairly constant and the lines were approximately parallel. They

suggestedtheparallelismofthelinesindicatedthatfrictiondoesnotchangewith

increased angulation but was caused by the increased binding between the

archwire and bracket. The results indicated that binding approximately

accountedfor80%oftheresistancetoslidingforallcoupleswhenthecontact

critical angle was 70. It showed that binding began to dominate frictional

resistanceshortlyafterthearchwirebracketchangedtoanactiveconfiguration.

With further increases in angulation, binding continued to be greatly more

significant than frictional resistance (Articolo and Kusy, 1999). The effect of

rotation is expected to be almost identical to that of angulation, if not more

76

significant.The implications in relation to the results obtained from this study

indicate that the increased resistance to sliding resulted from the increased

bindingthatoccurredandnotasaresultofincreasedfrictionalresistance.

The clinical implications of these results provide significant evidence for

derotationoftheupperfirstpermanentmolarspriortofittingofatranspalatal

or Nance palatal arch. If a transpalatal arch is used, the molars could be

derotatedusingtheappliancepriortothecommencementofoverjetreduction.

Should the molars be significantly rotated, the forces required to slide the

archwire through the molar tube are substantial and may prevent tooth

movementas theappliedorthodontic forcewouldnotbe sufficient inorder to

overcome binding. Should the applied force be increased, it significantly

increases theriskoforthodontic inducedroot resorption,pain,discomfortand

evenanchorageloss.

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78

An exponential relationship between the degree of molar rotation and work

providedthebestfitfortheresultsoftheexperiments.AnR2valueof0.96for0.5

mm displacement and 0.97 for 2 mm displacement suggests it is an accurate

representationoftherelationship.TheICCanalysessuggestedgoodrepeatability

oftheexperimentalmeasurementswithvaluesapproaching,orexceeding0.9.

4.4Impactofbilateralpalatalrotations

Theimpactofbilateralpalatalrotationswasassessedwiththerightmolartube

fixedatanactivepalatalrotationof100andtheleftmolartubewithincreasing

palatal rotation. Thework involved in sliding the archwire through themolar

tube,onaverage,wassignificantlygreater than foraunilateralpalatalrotation

(p-valueof0.002and0.02fordisplacementofthearchwireby0.5and0.1mm

respectively). The results were in agreement with the impact of a unilateral

palatal relationshipandsuggestedanexponential relationshipexistedbetween

increasing palatal rotation andwork. Graphical illustration of the relationship

betweendegreeof rotationandwork for an archwiredisplacementof0.5mm

and2mmisshowninFigure4.4:

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80

mm displacement and 0.98 for 2 mm displacement suggests it is an accurate

representation of the relationship. The ICC analyses suggested agreementwas

poorer between the measurements than the results obtained when the right

molartubewaspassive.TheICCvaluesweremuchlower,withavalueof0.74for

the 0.5mm displacement and 0.66 for the 0.1mm displacement. This can be

explained as having both molars palatally rotated is expected to significantly

increase thebindingbetween thearchwire and thebracket.Theoccurrenceof

the binding varies greatly, resulting in an increased variability and slight

unpredictabilityoftheworkvaluesobtainedbytheexperimentalapparatus.

4.5Comparisonofunilateralandbilateralpalatalrotations

Comparing the data between a unilateral and bilateral palatal rotation, the

analysis results suggested that there was a significant difference in the work

valuesbetweenthetwodatasets,onaverage,foralldisplacementvalues.Ineach

variationtheworkvaluesinthebilateralpalatalrotationgroupwassignificantly

higherthanfortheunilateralgroup.

Whilst therewasanaveragedifferencebetweenthetwogroups, thedifference

between the groups was examined further to see if the differences varied

dependingon the rotation.Pearsoncorrelationanalysis suggesteda significant

associationbetweenthelevelofrotationandthedifferenceinwork(p-valueof

0.002and0.01fordisplacementofthearchwireof0.5and0.1mmrespectively).

Allcorrelationswerenegative,suggestingthatahigherrotationwasassociated

with a less difference between the two groups. This convergence of thework

involved for higher rotations with a unilateral or bilateral molar rotation is

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82

resistancetoslidingthatwasoccurring.Thepilotstudiespreviouslyconducted

hadsuggestedthattheleftandrightmolartubeswerecorrectlyset-upandtheir

rotationscomparable.

Thepairedt-testwasusedtocomparetheworkbetweentheswitchedandun-

switched groups. The results suggested no significant differences in the work

valuesbetween thegroups foreither0.5mmor2mmarchwiredisplacement.

Forbothunilateralandbilateralpalatal rotations thep-valuewasgreater than

0.05.However,theseanalyseswerebasedononly3measurements,thesebeing

therotationsthatwerecommontobothmethods.

4.7Comparisonofthestraightwireandextraoraltube

InsertinganoffsetintothearchwireandpassingitthroughtheEOTsignificantly

reducedtheworkinvolvedindisplacingthearchwirecomparedwithusingthe

straight wire tube. Graphical illustrations comparing the work involved in

displacingthearchwireby2mmand0.5mmbetweentheEOTandstraightwire

tubeareshowninFigures4.6-4.9:

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85

Matchingthemeasurementsbyrotation,thepairedt-testwasusedtocompare

the average difference between the EOT and straight wire tube. The results

suggestedsomeevidenceofadifferencebetweenthetwotubesforallanalyses.

Theresultsforabilateralpalatalrotationfoundasignificantreductioninwork

fortheEOTcomparedwiththestraightwiretube foralldisplacements.Thep-

valuewas0.002and<0.001for2mmand0.5mmrespectively.Theresultsfor

theunilateralpalatal rotation,with therightmolar fixedatzerodegrees,were

onlyofborderlinestatisticalsignificance(p-valueof0.05).However,therewere

larger differences in work values, and the lack of significance is likely to be

mainly attributed to the small number of data points. All analyses confirmed

muchlowerworkvaluesfortheEOTcomparedtothestraightwiretube.

ThedifferencebetweentheEOTandstraightwiretubewasexaminedtoidentify

ifthedifferencesvarieddependingontherotation.Pearsoncorrelationanalyses

suggestedsomeevidenceofanassociationbetweendifferenceinworkbetween

the two tubes and the rotation. The results are generally only of borderline

statisticalsignificance.However, thecorrelationsarevery largeandthe lackof

statistical significance ismainly attributed to the small sample size.Given that

the differences between the two tubes were negative (lower work values for

EOT), thenegativecorrelationssuggestedthat thedifferencebetweenmethods

wasgreaterforhigherrotations.

86

4.8Limitationsofinterpretingresults

Whilst the results of this study provide some strong evidence regarding the

effectonresistancetoslidingthattheuseofapalatalarchwithrotatedmolars

has,therearecertainaspectsthatlimittheinterpretationoftheresults.

Themethodologyof thestudywascomparablewithpreviousstudiesbutthere

weresomekeydifferences.Dueto thenatureof theexperimentalapparatus, it

did not fully replicate a full mouth typodont. Use of full arch typodont, with

bracketsligatedtothearchwiremayhavegivenaclearerpictureofthedynamic

interaction occurring between the bracket and archwire with regards to the

resistancetosliding.Thislab-basedstudycanneverreplicatetheenvironmentof

oralcavityanddoesnotaccountforothersignificant factorsthataffect friction

andresistancetosliding.Mainexamplesincludeocclusalandmasticatoryforces.

Themaindifference in themethodologyof this study comparedwithprevious

literature was that resistance to sliding was examined opposed to static or

kinetic friction.Asbinding rapidlybecame themost significant factor affecting

the resistance to sliding of the archwire, evaluation of the friction involved

wouldhavebeen inappropriate. Itwouldhavebeen impossible toseparate the

binding and friction components of the overall resistance to sliding andmake

any conclusions from the results.The largevariabilityof thenatureofbinding

that occurred affected the results because it significantly affected the

reproducibilityoftheresultsofhigherrotations.

87

Theexperimentalapparatuswasdesignedtoalloweachexperimenttobeset-up

andconductedunderalmostidenticalconditions.Nobracketswereincorporated

mesialtothemolartubetoallowthefulleffectofthevaryingmolarrotationsto

beevaluated.Thisresultedinalongerspanofunsupportedarchwirethenmight

be encountered clinically, thus increasing the flexibility of the rectangular,

stainless steelarchwire.The implicationsofusing thisdesignmean the results

obtainedunderestimatedtheeffectofpalatalrotationsdueto theabilityof the

archwiretoflexinapalataldirection.Thiswouldnotoccurclinically,therefore

conclusionsontherelationshipfoundbetweenmolarrotationsandresistanceto

sliding can be accepted but thework involved in displacing the archwiremay

varyclinically.

The sample sizewith regards to certain statistical analysiswas small.A larger

sample would have given greater power to the statistical analysis in order to

provide more conclusive evidence. The study focused on multiple key areas

regardingmolarrotations,resistancetoslidingandtheuseoftheEOT.Toallow

forbetter interpretationof the results, the studycouldbedivided into smaller

studies and repeatedwith a greater number of repeat experiments andmolar

rotations.

4.9Otherfactorsthataffectfriction

Aspreviouslydiscussed,theaetiologyoffrictionismulti-factorialandtheresults

obtained from a clinical study would vary from the results of this lab-based

study.Multiplevariableswerestandardisedsothat theeffectofmolarrotation

with a trans-palatal arch was evaluated. Biological factors, mainly saliva and

88

occlusal forces, have a significant effect on friction that is very difficult to

replicateinthelaboratory.Researchintotheroleofsalivahasprovidedvarying

andoftenconflictingresults,withevidencetosuggesta lubricatingoradhesive

influence. Baker et al (1987) reported that artificial saliva reduced frictional

resistancewithstainlesssteelarchwiresby15-19%.Thiswas incontrast toa

study by Downing et al (1995) who concluded that artificial saliva increased

frictioncomparedtowhentestedinadrystate.

The effect of occlusal forces has been examined clinically and in lab-based

studies.Aclinicaltrialwithpatientsaskedtochewsoftenedgumtoevaluatethe

effectofmasticatoryfunctiononfrictionfoundnosignificantreduction(Iwasaki

et al., 2003). Braun et al (1999) applied perturbations to the orthodontic

applianceandfoundthatfrictionalresistancewasalmostcompletelyeliminated

everytimetheappliancewastapped.Theyconcludedthatmasticatoryfunction

did reduce friction but its effect was unpredictable and inconsistent. It is

important to remember that occlusal forces can also prevent toothmovement

completelybytheinterlockingnatureofapatient’socclusion.

Variation in the fixed appliances and their set-up has a significant and highly

variable effect on friction. The bracketmaterial, prescription,width and inter-

bracket distance have a significant effect, that varies between patients. These

factorswillalterthefrictionalresistancewithintheappliance.

89

4.10Futureresearch

The study has provided evidence to support the need for a clinical trial to

evaluatetheeffectivenessoftheuseoftheEOTcomparedwiththestraightwire

tubewithaNancepalatalarch,regardlessofthemolarrotation.Theresistance

to sliding is significantly reduced when using the EOT and this method of

anchoragereinforcementmayprovetobeofclinicalbenefit.

TodeveloptheconceptfurtherofusingtheEOTtube,afurtherlab-basedstudy

should be conductedwith a larger sample size (number of experiments). This

wouldgivetheresearchmorestatisticalpowerandtheabilitytoprovidemore

conclusive evidence. This includes the potential for inclusion of a reduced

number ofmolar rotations as a variable, to give amore accurate reflection of

whatwouldbeencounteredclinically.

The design of the experimental apparatus can be adapted for further research

into friction and resistance to sliding. It would be possible to investigate the

effectofdifferentarchwidthsandtheireffectonresistancetosliding.Thewidth

of the archwire can be adapted to investigate the effect of expanded or

contracted archwires. Furthermore, placing torque in the archwire in the

posterior segment and its effect on resistance to sliding would provide some

valuableclinicalinformationregardingthemechanicsoforthodontictreatment.

Thetubedimensionsonthemolarbandwerestandardisedinthisstudybutthis

isavariablethatcouldbeinvestigated,asarangeofmolartubedimensionsare

90

currentlyavailable.Nohighqualityliteratureiscurrentlyavailableontheeffect

ofmolartubelengthonfrictionorresistancetosliding.

Notching of the archwire was not investigated as part of this study but some

valuablescientificknowledgecouldbegainedbyexaminingthearchwireswitha

scanningelectronmicroscope.Followingtestingofvariousmolarrotations, the

archwire could be examine to evaluate the effect rotated molars have on

notching.

91

ChapterFive

Conclusion

92

ChapterFive:ConclusionsTheuseofatranspalatalorNancepalatalarchwithrotatedmolarsresultsinan

exponentialincreaseinworkinordertoslideanarchwirethroughamolartube.

• Therelationshipbetweenworkanddisplacementwasfoundtobelinearfor

allrotationcouples.

• The relationship between work and molar rotation was found to be non-

linear,withanexponentialincreaseinworkwithincreasingpalatalrotations.

• Bilaterally, palatally rotated molars resulted in a significantly increased

amountofwork for all amountsofdisplacementof thearchwire compared

withaunilateralrotation.

• Pearson correlation analysis found a significant associationbetween extent

of molar rotation and difference in work between unilateral and bilateral

rotatedmolars.

• Useoftheextraoraltubesignificantlyreducedtheworkrequiredtodisplace

thearchwire through the tube comparedwith the straightwire tube.For a

unilateral palatal rotation thiswas of borderline statistical significance but

forbilateralpalatalrotatedmolarsthiswashighlysignificant.

Cliniciansneed toevaluatemolaralignmentprior to fittingofa transpalatalor

Nance palatal arch. For noticeable rotations, consideration should be given to

derotationpriororuseoftheextraoraltubeinordertoreducetheresistanceto

slidinginordertoreducethereactionaryforcesontheanchorteeth.

93

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99

AppendicesAppendix1

Tableofresultsforunilateralpalatallyrotatedmolar(rightispassiveat

zerodegreesandleftisincreasingpalatalrotation)

Rotation(degrees) Testnumber Meanandstandarddeviation(SD)

Workforgivendisplacement(Joules)

2mm 0.5mm 0.1mm

R0L0 1

2.24 0.42 0.06

2

3.26 0.71 0.11

3

1.94 0.38 0.06

4

1.65 0.34 0.05

5

2.59 0.58 0.1

6

1.33 0.3 0.04

7

1.8 0.43 0.07

Mean 2.12 0.45 0.07

SD 0.65 0.14 0.03

ROL2 1

2.06 0.42 0.07

2

1.66 0.32 0.05

3

2.06 0.45 0.07

4

1.52 0.32 0.05

5

2.55 0.53 0.09

6

2.22 0.46 0.07

7

1.97 0.38 0.06

Mean 2.01 0.41 0.07

SD 0.34 0.08 0.01

ROL4 1

2.44 0.52 0.08

2

2.37 0.49 0.08

3

2.1 0.38 0.05

4

1.84 0.33 0.05

5

2.81 0.57 0.09

6

2.15 0.4 0.06

7

2.59 0.47 0.07

Mean 2.33 0.45 0.07

SD 0.33 0.08 0.02

R0L6 1

2.91 0.55 0.08

2

3.96 0.93 0.15

3

3.3 0.67 0.1

4

4.6 0.91 0.13

5

3.46 0.59 0.07

6

3.26 0.75 0.11

100

7

3.65 0.64 0.08

Mean 3.59 0.72 0.10

SD 0.55 0.15 0.03

R0L8 1

4.49 0.94 0.14

2

4.68 0.84 0.11

3

4.86 0.82 0.1

4

3.64 0.8 0.12

5

4.19 0.87 0.14

6

3.93 0.84 0.13

7

3.86 0.84 0.14

Mean 4.24 0.85 0.13

SD 0.46 0.05 0.02

R0L10 1

4.56 0.98 0.16

2

4.55 0.97 0.15

3

6.19 1.68 0.27

4

6.92 1.55 0.25

5

5.06 1.08 0.17

6

5.69 1.19 0.18

7

6.6 1.36 0.21

Mean 5.65 1.26 0.20

SD 0.96 0.28 0.05

1

5.68 1.27 0.19

R0L12 2

5.01 0.91 0.13

3

7.53 1.58 0.22

4

8.51 1.8 0.27

5

6.13 1.2 0.17

6

7.8 1.64 0.23

7

7.01 1.52 0.21

Mean 6.81 1.42 0.20

SD 1.25 0.31 0.04

R0L14 1

8.66 1.86 0.26

2

8.23 1.78 0.29

3

7.56 1.47 0.2

4

9.13 1.93 0.28

5

9.65 2.29 0.12

6

8.63 2.2 0.35

7

7.6 2 0.29

Mean 8.49 1.93 0.26

SD 0.77 0.27 0.07

1

10.86 2.11 0.31

101

R0L16 2

12.37 2.11 0.32

3

13.43 2.8 0.37

4

13.16 2.68 0.4

5

12.51 2.56 0.37

6

13.38 2.87 0.4

7

13.11 2.36 0.44

Mean 12.69 2.50 0.37

SD 0.90 0.31 0.05

Tableofresultsforbilateralpalatallyrotatedmolars(rightisfixedata

palatalrotationof10degreesandleftisincreasingpalatalrotation)

Rotation(degrees) Testnumber

Workforgivendisplacement(Joules)

2mm 0.5mm 0.1mm

R10L0 1

4.54 0.88 0.12

2

5.73 1.16 0.17

3

4.96 1 0.14

4

5.99 1.21 0.17

5

4.51 0.86 0.11

6

4.82 0.93 0.13

7

4.54 0.87 0.13

Mean 5.01 0.99 0.14

STD 0.61 0.14 0.02

R10L2 1

5.86 1.11 0.17

2

6.85 1.39 0.19

4

5.64 1.12 0.16

5

5.47 1.03 0.14

6

5.63 1.07 0.16

7

5.18 1.03 0.16

8

4.66 0.88 0.14

Mean 5.61 1.09 0.16

STD 0.67 0.15 0.02

R10L4 1

6.06 1.11 0.15

2

5.51 1.06 0.17

3

6.93 1.32 0.17

4

6.02 1.12 0.15

5

6.43 1.25 0.19

6

6.3 1.26 0.19

7

5.58 1.09 0.16

Mean 6.12 1.17 0.17

102

STD 0.49 0.10 0.02

R10L6 1

7.88 1.63 0.25

2

9.13 1.95 0.3

3

5.64 1.11 0.16

4

5.39 1.04 0.16

5

5.25 0.97 0.13

6

5.83 1.19 0.2

7

6.61 1.38 0.22

Mean 6.53 1.32 0.20

STD 1.46 0.36 0.06

R10L8 1

7.63 1.5 0.23

2

10.56 2.25 0.33

3

6.56 1.17 0.16

4

7.31 1.33 0.19

5

6.48 1.24 0.18

6

5.59 1.02 0.15

7

5.35 1 0.16

Mean 7.07 1.36 0.20

STD 1.75 0.43 0.06

R10L10 1

8.17 1.59 0.22

2

10.43 2.09 0.27

3

7.19 1.14 0.14

4

6.25 1.16 0.16

5

6.61 1.25 0.19

6

8.22 1.63 0.18

7

7.48 1.49 0.23

Mean 7.76 1.48 0.20

STD 1.39 0.34 0.04

R10L12 1

9.38 1.74 0.26

2

9.41 1.98 0.29

3

8.73 1.52 0.2

4

8.34 1.59 0.26

5

9.35 1.9 0.28

6

9.55 1.9 0.28

7

9.07 1.84 0.23

Mean 9.12 1.78 0.26

STD 0.44 0.17 0.03

R10L14 1

9.61 1.71 0.28

2

9.88 1.95 0.24

3

9.3 1.77 0.22

103

4

11.19 2.54 0.36

5

10.65 1.97 0.26

6

10.31 1.95 0.24

7

10.66 2.31 0.33

Mean 10.23 2.03 0.28

STD 0.67 0.30 0.05

R10L16 1

11.27 2.42 0.35

2

12.35 2.24 0.28

3

12.48 2.21 0.27

4

12.78 2.62 0.39

5

11.51 2.28 0.3

6

13.8 2.72 0.35

7

12.71 2.73 0.34

Mean 12.41 2.46 0.33

STD 0.84 0.23 0.04

104

Appendix2

Tableofresultsforswitchingleftandrightmolartubeposition–Left

passiveandrightincreasingpalatalrotation

Rotation(degrees)

Testnumber

Workforgivendisplacement(Joules)2mm 0.5mm

R8L0 1 3.53 0.75

2 2.28 0.48

3 2.85 0.64

4 3.16 0.52

5 3.38 0.56

6 3.35 0.6

7 2.47 0.47

Mean 3.00 0.57

SD 0.48 0.10

R12L0 1 7.76 1.72

2 7.4 1.58

3 8.37 1.8

4 8.1 1.76

5 8.4 1.85

6 6.48 1.41

7 8.28 1.77

Mean 7.83 1.70

SD 0.70 0.15

R16L0 1 8.36 2.09

2 5.18 1.25

3 9.93 2.18

4 10.47 2.49

5 10.76 2.55

6 11.87 2.87

7 10.64 2.54

Mean 9.60 2.28

SD 2.22 0.52

R20L0 1 17.34 3.84

2 17.6 3.87

3 11.23 2.52

4 9.28 2.06

5 17.51 3.92

105

6 17.42 3.91

7 17.51 3.91

Mean 15.41 3.43 SD 3.57 0.79

Tableofresultsforswitchingleftandrightmolartubeposition–Leftfixed

palatalandrightincreasingpalatalrotation

Rotation(degrees)

Testnumber

WorkforgivendisplacementJoules2mm 0.5mm

R8L10 1 7.47 1.51

2 5.07 0.9

3 5.11 1.03

4 6.28 1.37

5 5.32 1.08

6 4.91 0.98

7 4.84 0.98

Mean 5.57 1.12

STD 0.97 0.23

R12L10 1 7.83 1.46

2 8.51 1.9

3 7.99 1.77

4 9.4 2.11

5 10.03 2.26

6 8.69 1.94

7 9.38 2.1

Mean 8.83 1.93

STD 0.81 0.26

R16L10 1 11.92 2.47

2 12.49 2.61

3 11.27 2.35

4 12.21 2.6

5 10.44 2.26

6 10.48 2.25

7 11.09 2.42

Mean 11.41 2.42

STD 0.82 0.15

R20L10 1 16.05 3.33

2 13.37 2.82

106

5 13.13 2.85

6 14.49 3.12

7 13.22 2.86

9 14.98 3.25

10 14.47 3.17

Mean 14.24 3.06

STD 1.08 0.21

107

Appendix3

Tableofresultsforextraoraltube

Rotation(degrees) Testnumber

Workforgivendisplacement(Joules)2mm 0.5mm 0.1mm

R0L0 1 0.671 0.335 0.148

2 0.392 0.19 0.09

3 0.612 0.276 0.119

4 0.699 0.313 0.136

5 0.631 0.28 0.119

Mean 0.601 0.279 0.122

SD 0.122 0.055 0.022

ROL4 1 0.846 0.412 0.187

2 0.757 0.344 0.15

3 0.687 0.261 0.11

4 0.68 0.296 0.127

5 0.801 0.349 0.153

Mean 0.754 0.332 0.145

SD 0.072 0.057 0.029

R0L8 1 0.81 0.316 0.135

2 0.852 0.384 0.173

3 0.984 0.455 0.21

4 0.904 0.332 0.148

5 0.991 0.516 0.236

Mean 0.908 0.401 0.180

SD 0.080 0.084 0.042

R0L12 1 1.394 0.553 0.289

2 1.448 0.677 0.304

3 1.517 0.637 0.332

4 1.458 0.568 0.211

5 1.302 0.492 0.22

Mean 1.424 0.585 0.271

SD 0.081 0.073 0.053

R10L0 1 0.698 0.323 0.149

2 0.733 0.227 0.099

3 0.672 0.292 0.129

4 0.62 0.278 0.13

108

5 0.704 0.364 0.173

Mean 0.685 0.297 0.136

SD 0.043 0.051 0.027

R10L4 1 0.737 0.328 0.153

2 0.733 0.322 0.176

3 0.944 0.422 0.195

4 0.95 0.424 0.197

5 0.956 0.426 0.198

Mean 0.864 0.384 0.184

SD 0.118 0.054 0.019

R10L8 1 1.259 0.456 0.21

2 1.244 0.45 0.21

3 1.25 0.452 0.211

4 1.289 0.466 0.217

5 1.298 0.467 0.215

Mean 1.268 0.458 0.213

SD 0.024 0.008 0.003

R10L12 1 2.39 1.135 0.555

2 2.592 1.403 0.668

3 2.245 1.376 0.637

4 2.041 1.432 0.669

5 2.052 1.439 0.673

Mean 2.264 1.357 0.640

SD 0.234 0.127 0.050

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