Post on 11-Mar-2020
Outlinethesignificanceofthepre-adjustedEdgewiseappliance
systemandusefulbracketvariationsinorthodontics
DrMJRowland-WarmannBScBDS(Manc)MScAes.Med.(Lond)MJDFRCS(Eng)
GDC:178642
WordCount(excludingreferences):1680
Module4:FundamentalsofOrthodonticTreatmentofSkeletalProblemsinPreadolescence
andAdolescence
SubmissionDecember2017
StudentIDBP0150715
Contents
Page
Introduction 3
Modernbracketprescriptionsandtheirevolution 3
Andrews 4
Roth 4
MBT 4
Bracketvariationsfordifferentscenarios 6
Palatallyplacedlateralincisors 7
Absentlateralincisors 8
Class3canineangulation 8
Labialmovementofpalatalcanine 9
Caninegingivalrecession 9
Absentuppercentralincisor 9
Incisorsinclass3 10
Upperpremolarsubstitutingcanine 10
Casefinishing 10
Doestheprescriptionmatter? 11
Conclusion 13
References 14
Outlinethesignificanceofthepre-adjustedEdgewiseappliancesystemand
usefulbracketvariations(suchaschangingbracketposition,orientationor
locationinthearch)
________________________________________________
Introduction
Andrewsintroducedthepre-adjustededgewiseapplianceinthe1970sandrevolutionised
orthodontics(Andrews,1979).Thisreplacedtheedgewiseappliancewhereallbrackets
wereidenticalandtherewasgreatneedforwirebending(Johnson,2013).Andrews
introducedtipthroughslotangulationandtorquethroughslotinclination,alongwith“in-
out”throughbracketbasevariation(Thickett,Taylor,&Hodge,2007).
Modernbracketprescriptionsandtheirevolution
Theinceptionofthepre-adjustededgewiseappliancewashailedassignificant,reducing
wirebending,allowingforthemovementofgroupsofteethandthusshortertreatment
times,yetmoreconsistenttreatmentoutcomes(Thickettetal.,2007).Thisincreasedfocus
onprecisebracketplacement,andstraightwiresplacedmorestrainonanchorage(Singh,
2017).
Therehavebeenmanymodificationsintipandtorqueinpre-adjustededgewisesince
Andrews(Mittal,Thiruvenkatachari,Sandler,&Benson,2015).MBTandRotharethemost
commonlyusedtoday.
Andrews
Theoriginalstraightwireapplianceusedsiamesebracketsplacedonthefacialaxisofthe
clinicalcrownwithheavyforcestocontroltoothmovementinthreedimensions
(McLaughlin,Bennett,&Trevisi,2002;Mohammadi&Moslemzadeh,2011).
Prescriptionvaluestookaveragevaluesfrom120models(Andrews,1972,1979).Andrews’
prescriptionhaddifferentsetsforvariousmalocclusions,degreeofcrowdingand
extraction/non-extractioncases(Singh,2017),incorporatinganti-rotationandanti-tipinto
extractioncases(Andrews,1979).Thisresultedinalargenumberofbrackettypes.
Roth
Tominimiseheplethoraofbrackettypesandnecessaryinventory,Rothdevisedonesetof
bracketsapplicableformostcases,combiningAndrews’setCupperincisor,setSlower
incisors,minimumtranslationupperposteriorandlowercaninebrackets,andmaximum
translationuppercanineandlowerposterior(Thickettetal.,2007).Healsoincreasedtipto
assistcanineguidance,anddistalcrowntiptolowerbuccalsegmentsashisprescriptionwas
moreanchoragedemanding.Furthermore,uppermolartorqueincreasedtopreventpalatal
cuspdrop(McLaughlinetal.,2002;Singh,2017;Thickettetal.,2007).
MBT
DevisedbyMcLaughlin,BennettandTrevisiinthe1990s,thisprescriptionisbasedarounda
numberofprinciples.Bracketversatility,lightcontinuousforces,anchoragecontrol,group
movementofteethandasinglefinishingwirearekeyelementsoftheMBTtheory.
Accuratebracketplacementissignificant,andbracketplacementchartsweredevised
(Figure1)(McLaughlinetal.,2002).
Figure1:MBTbracketplacementcharts;from(McLaughlinetal.,2002)
MBTreducedanteriortipcomparedwithRothandAndrews.Itsaimwastoreducestrainon
molaranchorageandavoidin-treatmentarchlengthincrease(Thickettetal.,2007);
undertorquingteethrequiresspace,soforevery5°ofanteriorinclination,1mmofarch
lengthisgenerated,resultinginlackofstability(Badawi,Toogood,Carey,Heo,&Major,
2008;Fleming,DiBiase,Sarri,&Lee,2009).Increasedpalatalroottorquecounteracts
torquelossduringoverjetreductionandspaceclosureandlabialroottorqueincreasedto
limitlowerincisorproclineonlevelling.Furthermore,caninetipwasreducedtoupright
rootsandpreventcanineandpremolarrootproximity(Moesi,Dyer,&Benson,2013;
Thickettetal.,2007).
ThetipandtorquevaluesofAndrews,RothandMBTareillustratedinFigures2and3.
Figure2:Andrews/Roth/MBTtorquevalues;from(Thickettetal.,2007)
Figure3:Andrews/Roth/MBTtipvalues;from("Erratum,"2014)
Bracketvariationsfordifferentscenarios
Astheprescriptiononanindividualbracketisknown,variationscanbeemployedwhen
thereisalocaltoothpositioningproblemormissingtoothbychangingtheorientationor
usingabracketonatoothotherthantheoneforwhichitwasintended(Singh,2017;
Thickettetal.,2007).Inversionresultsinatorquechangebutnottip.Swappingtheright
andleftbracketschangesthetipvaluewithoutchangingtorque(Thickettetal.,2007).
Palatallyplacedlateralincisors
Thelateralincisorbracketwillnotsupplyenoughlabialroottorque.Inversionofthelateral
incisorbracketreversesslotinclination,graduallyintroducingtorquewiththewire
sequence,improvingcomfortovertheuseoftorqueingpliers(Singh,2017;Thickettetal.,
2007)
Appliedinpractice,ananAndrewsbrackethasa6°difference,Roth16°andMBT20°
(Figure4-6).
Figure4&5:Managementofpalatallyplacedlateralincisors;from(McLaughlinetal.,2002)
Figure6:clinicalpresentationofbracketforpalatallateralincisors;from(McLaughlinetal.,
2002)
Absentlateralincisors
Thecaninebracketisunsuitablewhenreplacingalateral,asitgivesgraterlabialroottorque
whenpalatalroottorqueisrequiredforlateralincisors–thecrownanatomiesofthetwo
teetharevastlydifferent.Alateralbracketwouldpositionthetoothpalatallyandthefitis
poor;afurtheroptionwouldbetorecontourthecanine,thenplacethebracket,although
thismayresultinpoortoothangulation.Asimplemeasureisinversionofthecanine
bracket,maintainingthebracketfitandin-out(Figure7).MBTandAndrewsgivespalatal
roottorquechangesby14degrees;tipvaluesforlateralsandcaninesinMBTareidentical,
withRoththereisasmalldifference(McLaughlinetal.,2002;Thickettetal.,2007).
Figure7:Positioningcaninebracketforabsentlateralincisor;from(McLaughlinetal.,2002)
Class3canineangulation
Whencamouflaging,theunderlyingmalocclusionisacceptedandincisorsarecompensated.
Toanglelowercaninesfavourably,thecontralateralcaninebracketscanbeswitchedto
encouragedistaltipandreduceanchoragerequirements(Figure8)(Singh,2017;Thickettet
al.,2007).Someclinicianspreferusingthecorrectbracket,angulatingitforcrowntipto
leavethepowerarmavailablebutthismaycauseapoorfittothetooth(Arun&Kallur,
2008).
Figure8:contralateralcaninebracketforclass3;from(Thickettetal.,2007)
Labialmovementofpalatalcanine
Palatalcaninemovementresultsincrownmovementwithouttheroot,causingunattractive
tip.Inordertoincreaselabialroottorque,thelowercontra-lateralcaninebracketcanbe
invertedtotheupper.ThisisrelevantinRothwherethereis9°change;inMBTthereare
similartorquevalues(Thickettetal.,2007).
Caninegingivalrecession
Incaseswherethegingivaehasrecededorthecanineisveryprominent,invertingthe
bracketgivespalatalroottorque,whichcanhelpreducefurtherrecession(McLaughlinet
al.,2002).
Absentuppercentralincisor
Inordertofacilitaterestorativetreatment,thepreferentialmesialrootmovementoverthe
crownshouldoccur.Bondingthecontralateralcentralincisorbrackettotiltthetooth
allowsthis(Figure9)(Thickettetal.,2007);however,somecliniciansprefercentringthe
lateralincisorinthespaceforrestorativepurposesclaimingthisimprovesforce
transmissionthroughtheroot(Arun&Kallur,2008)
Figure9:managementofmissingcentralincisor;from(Thickettetal.,2007)
Incisorsinclass3
Inclass3cases,thereisaneedforupperincisorproclination.Itispossibletoinvertincisor
bracketsforlabialroottorque,MBTgivingthegreatestchangeat34°(Thickettetal.,2007)
althoughthereareconcernsthatthisamountoftorquerisksrootresorption(Arun&Kallur,
2008).
Upperpremolarsubstitutingcanine
Incaseswherethecanineisabsentorreplacingthelateralincisor,placementofthebracket
moredistallyonthepremolarmovesthepalatalcuspoutoftheway(Singh,2017).
Smoothingthepalatalcuspofthefirstpremolarmayberequiredtofurtherhideitor
improveocclusalinterference.
Casefinishing
InordertoachievegoodfinishingandocclusioninMBTprescription,lowersecondmolar
tubescanbeusedonthecontralateralupperfirstandsecondmolarstoresultinzerotip
andzerorotation,resultinginmesio-palatalrotationofuppermolars,asshowninfigure10
(McLaughlinetal.,2002).
Figure10:casefinishingmolars,from(McLaughlinetal.,2002)
Doestheprescriptionmatter?
MoesietalandMittaletaldemonstratedthattherewasnodifferenceinsubjective
aestheticjudgementoranteriortoothangulationbetweenMBTandRothbracket
prescriptions,andsmallchangesintheprescriptiondonotmakeclinicallydetectableresults
(Kattner&Schneider,1993;Mittaletal.,2015;Moesietal.,2013).
Theconceptoftorsional(slot)playmustbeaddressed.Theengagementanglebetweenthe
bracketandwireisvariable,sosmallchangesinbracketsmaynotfullyexpressasthe
workingwireonlyengagesthebracketatfewpointsandfullprescriptionexpressionmay
neveroccur(Figure11)(Archambaultetal.,2010).
Figure11:theconceptoftorsionalplay;from(Johnson,2013)
Prescriptionexpressionisdependentontheworkingarchwireandthevariationin
engagement.Figure12showsincreasingthethicknessofarchwiresindifferentbracket
slotsdecreasestorsionalplay;achangeinarchwireisasimilardifferencetotheprescription
differenceindegreesbetweenRothandMBT(Archambaultetal.,2010;Badawietal.,2008;
Moesietal.,2013).Usingawiresequencethatgraduallyexpressestheprescriptionand
finishingcasesinthethickestwirepossibleisthereforeessential(Badawietal.,2008;Moesi
etal.,2013).Errorsinprescriptioncanalsostemfromimpropermachining(Cash,Good,
Curtis,&McDonald,2004).Inanattempttoexpressmoreofthedesiredvalues,high
torqueprescriptionshavebeenadvocated(Gioka&Eliades,2004).
Figure12:changeinwiresizeversusslop;from(Johnson,2013)
Conclusion
Cliniciansmustunderstandprescriptionstoachieveidealtoothposition.Evenwithpre-
adjustedappliances,achievingallsixkeysofocclusionisstilldifficult(Davies,Gray,Sandler,
&O'Brien,2001;Kattner&Schneider,1993).Thereisaneedforabracketinventoryto
includeavarietyofprescriptionsandtheknowledgetoapplythemindifferentscenariosfor
individualpatientneeds.Whilstthepre-adjustedapplianceiseconomicalandefficient,and
hasnodoubtrevolutionisedorthodontictreatment,itreliesheavilyonaccuracyofbracket
placement,andnosingleprescriptiontotallyeliminateswirebending.Theoutcomeof
orthodontictreatment,however,doesnotrelyontheprescriptionalone(Kattner&
Schneider,1993;Lotzof,Fine,&Cisneros,1996;Thickettetal.,2007).
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