approximatelymv222.com

ONLINEONLYInuenceofthermoplasticappliancethicknessonthemagnitudeofforcedeliveredtoamaxillarycentralincisorduringtippingWolframHahn,aHenningDathe,bJuliaFialka-Fricke,bSusanneFricke-Zech,bAntoniaZapf,cDietmarKubein-Meesenburg,dandRezaSadat-KhonsariaGo¨tingen,GermanyIntroduction:Theaimofthestudywastoquantifytheforcesdeliveredbythermoplasticappliancesmadeof2materialswith2thicknessestoamaxillarycentralincisorduringtipping.
Methods:Twomaterialsweretested,eachin2thicknesses:Erkodur(ErkodentErichKoppGmbH,Pfalzgrafenweiler,Germany)1.
0and0.
8mm,andBiolon(DreveDentamidGmbH,Unna,Germany),1.
0and0.
75mm.
Foreachmaterial,5applianceswerepro-duced.
Tomeasuretheforcesapplied,anisolatedmeasuringtooth,partofastandardizedresinmodel,wasdeectedin0.
05stepsfrom0to0.
42inthevestibularandpalatinedirections,afterplacingtherespectiveapplianceonthemodel.
Forstatisticalanalysis,theforcecomponentsFx/tippingandFz/intrusionatadis-placementof60.
151mmfromtheincisoredgewereselected.
Meansandstandarddeviationswerecalcu-lated.
TheWilcoxon2-sampletestforgrouppairingswasused.
Results:ThenormsforthemeanFxforcesrangedfrom1.
62(SD,0.
41)to5.
35N(SD,0.
63).
ThemeanFzforceswerebetween0.
07(SD,0.
13)and2.
47N(SD,0.
34).
Thehighestintrusiveforcesweremeasuredduringvestibulardisplacementofthemeasur-ingtooth.
Theforcesdeliveredbythethickapplianceswereoverallsignicantlyhigher(P\0.
0001)thanthoseofthethinmaterials.
TheforcesdeliveredbytheBiolonappliancesweregenerallysignicantlyhigher(P\0.
0001)thanthosefortheErkodurmaterials.
Conclusions:Theforcesappliedweremostlytoohighwhencomparedwiththosestatedintheliteratureasideal.
Inadditiontothickness,thethermoformingprocessinuencesthemagnitudeoftheforcedeliveredbyathermoformedappliance.
(AmJOrthodDentofacialOrthop2009;136:12.
e1-12.
e7)Asaresultofincreasedinterestinadultorthodon-tictreatment,estheticalternativestoconven-tionalxedappliancesareoftenrequested.
Therefore,varioustypesofthermoplasticapplianceshavebeenintroducedinorthodontics.
ThetechniquewasoriginallyintroducedbyKes-ling1andsubsequentlyimprovedasanalternativeorasupplementtoxedappliances.
2,3ForthecommercialClearSmilesystem(ClearSmilePtyLtd,Keiraville,Australia),adentaltechnicianresetstheteethonaplastermodelbyhandandformsanover-layapplianceforeverydesiredstepoftoothmovement.
4AlignTechnology(SantaClara,Calif)usesaseriesofcomputer-generatedthermoplasticappliancescon-structedonstereolithographicmodels.
5,6Despitedocu-mentationofsuccessfultreatments,theforcedeliverypropertiesofvariousapplianceshavestillnotbeensys-tematicallyinvestigated,andonlyafewstudieshavebeenpublishedonthistopic.
7-9TheforcesimpartedbyathermoplasticappliancetoamaxillaryrstpremolarinvivoweremeasuredbyBar-bagalloetal4usingapressure-lmapproach.
Onestudywaspublishedrecentlyconcerningtheinuenceofthicknessoftheappliancesonforcedelivery.
10Inthisstudy,3-pointbendingandrecoverytestswereperformedonstandardized,atspecimens.
Theaimofourstudywastoquantifytheforcecom-ponentswithfocusonthetippingandintrusiveforcesgeneratedbyremovablethermoplasticappliancesmadeof2hardthermoplasticmaterialswith2thick-nessesonamaxillarycentralincisorduringtipping.
MATERIALANDMETHODSWerecentlydevelopedamodularforce-torquedeviceformeasuringforcesinorthodonticresearch.
ItFromtheGeorg-August-UniversityofGo¨ttingen,Go¨ttingen,Germany.
aAssistantprofessor,DepartmentofOrthodontics.
bStaffmember,DepartmentofOrthodontics.
cStaffmember,DepartmentofMedicalStatistics.
dHead,DepartmentofOrthodontics.
Theauthorsreportnocommercial,proprietary,ornancialinterestintheprod-uctsorcompaniesdescribedinthisarticle.
Reprintrequeststo:WolframHahn,DepartmentofOrthodontics,Georg-August-UniversityGo¨ttingen,Robert-Koch-Strasse40,D-37099Go¨ttingen,Germany;e-mail,weahahn@aol.
com.
Submitted,October2008;revisedandaccepted,December2008.
0889-5406/$36.
00Copyright2009bytheAmericanAssociationofOrthodontists.
doi:10.
1016/j.
ajodo.
2008.
12.
01512.
e1consistsofaquadrangularframexedonabaseplateby4columns.
Theseunitsareallmadeofhardaluminum.
Aresinbowlcanbexedintheframeandreversedinthesamepositionandxedwithalockingscrew.
Intheresinbowl,astandardizedresinmodel(FrasacoGmbH,Tettnang,Germany)withtheseparatedmeasur-ingtoothwasxedwithplaster.
Themeasuringtoothwasxedreversiblyonthesensor.
Forreproducibleposi-tioningofthetooth,aplasterkeywasused(Fig1).
Thesensorwasxedonamanualpositioningsys-tem.
Tosimulatetippingmotionsequences,agoniome-ter(GO90-W30,OWISGmbH,Staufen,Germany)wasused.
Tosimulatepuretippingdisplacement,themea-suringtoothoftheresinmodelwasorientatedperpen-dicularwithitsincisoredgetothedirectionofmotion.
Therotationalaxisofthemeasuringtoothwasadjustedatthecalculatedapex.
Themanualposi-tioningsystemwasoncemorexedbyanaluminumframeonthebaseplate(Figs1and2).
Theentiremeasuringdevicecouldbeplacedunderadryingchamber,whichhadaholeinitsbottom,tosimulate37Ctemperature(Fig3).
ThesensorwasaNano17(ATIIndustrialAutoma-tion,Apex,NC)thatmeasuredall6componentsofforceandtorque(Fx,Fy,Fz,Tx,Ty,andTz)(Fig4).
Weusedthecalibrationprovidedbythemanufacturerwith1%full-scaleaccuracy.
Thiscalibrationofferssens-ingrangesintheoptimalmeasuringrangesof612NforFxandFy,617NforFz,and6120NmmforTx,Ty,andTz,respectively.
TheNano17transducerhashardwaretemperaturecompensationtostabilizeitssensitivitytoapproximately625Cinrelationtoroomtemperature.
Afterinstallationofthemeasuringdevice,anim-pression(Tetrachrom,Kanidenta,Herford,Germany)ofthemodelwiththemeasuringtoothintheneutralpo-sitionwastaken,andthenaplastermodelwasmadebyusingGCFujirockEP(GCGermanyGmbH,Munich,Germany).
Theplastermodelwastrimmedtoaheightof20mmparalleltotheocclusalplane,and20identicalplastercopies(withGCFujirockEP)weremadebyusingAdisilblue9:1(Siladent,DrBo¨hme&Scho¨psGmbH,Goslar,Germany).
Fromeachmaterialtobeevaluated,5appliancesextendingtothegingivalmarginweremadefromthesemodels.
ThematerialswereEr-kodur1.
0and0.
8mm(ErkodentErichKoppGmbH,Pfalzgrafenweiler,Germany)andBiolon1.
0and0.
75mm(DreveDentamidGmbH,Unna,Germany).
TheEr-kodurblankswereformedwithErkoformRVE(Erko-dentErichKoppGmbH),andDrufomat-TE(DreveDentamidGmbH)wasusedfortheBiolonblanks.
Mea-surementsweremadeat37Cinthedryingchamber.
Theinnersurfaceoftheappliancewasmoistenedwitharticialsaliva(University-Pharmacy,Go¨ttingen,Ger-many).
Beforestartingtheactualmeasuringcycle,theforcesandmomentsweresettozero.
Fig1.
Basiccomponentsofthemeasuringdevice.
Fig2.
Themeasuringtoothistipped3vestibularlybythegoniometer.
Theaxisofrotationislocatedatthevir-tualapex.
12.
e2HahnetalAmericanJournalofOrthodonticsandDentofacialOrthopedicsJuly2009Forthemeasurements,thetoothwastippedinthevestibularandpalatinedirectionsfrom0to0.
42(24.
9arcmin)andbackto0in0.
05(2.
7arcminutes)steps.
Themeasurementswererecorded5timesaftereachstepmovement.
Angulardegreeswereconvertedintomovementrangeinmillimetersfromtheinicisoredge.
Becauseofoverloadprotectionofthesensor,theinci-soredgecouldbemaximallydeectedupto0.
151and–0.
151mminallcases.
Thisactivationrangeisequivalenttothelowestvalueoftheactivationrangedocumentedintheliteratureforathermoplasticappliancesystem(Invis-align,AlignTechnology).
11StatisticalanalysiswasdonewithSASsoftware(SASInstitute,Cary,NC).
TheforcecomponentsFx(horizontalforcecomponent/tipping)andFz(verticalforcecomponent/intrusion)foranactiva-tionrangeof60.
151mmwereusedforfurtheranalysis.
Meansandstandarddeviationswerecalculated.
ThecorrespondingsampleswerecomparedbyusingtheWilcoxon2-sampletest.
Whenatestagainstzerowasapplied,weusedthesigned-ranktest.
RESULTSTypicalmeasuredforcesforFxandFzareshowninFigure5for1material(Biolon,1.
0mm).
Hysteresiseffectswereobserved,butthesewereexcludedfromthisdiscussion,becausethemaximumdeectionof60.
151mm,inwhichhysteresiseffectsarenegligible,wasusedforfurtheranalysis.
ThemeansandstandarddeviationsforFxandFzforcesatdeectionsof60.
151mmaregiveninTableIforeachmaterial.
ThecomparisonsofthecorrespondingsampleswiththeWilcoxon2-sampletestareshowninTableII.
ThecorrespondingboxplotsareshowninFigure6.
Becauseoftheoverloadprotectionofthesensor,somevaluesfortheBiolonappliancesaremissing.
Thus,itcanbeassumedthatthemeanforcevaluesinthesegroupswouldtendtobeevenhigherthanthoseshowninTableI.
Moreoftenthannot,thethicknessofthematerialhadahighlysignicantinuenceontheforcesdeliveredbyaparticularappliance.
OnlyforFxandFzpalatine,whenBiolon1.
0and0.
8mmwerecompared,wasthisinuencenotobserved.
Inallcases(exceptforFzpalatinal,Biolon1.
0mmvsErkodur1.
0mm;P50.
3961),theBiolonappliancesproducedstrongerforcesthatwerehighlysignicantcomparedwiththeErkodurappliances,irrespectiveofthethicknessofthematerial.
Moreover,eventhethinBiolonapplianceproducedmeanhigherFxandFzforces,exceptforFzpalatine,thanthethickErkodurap-pliances,irrespectiveofthedirectionofthedisplace-ment(TablesIandII).
ThevaluesforFzwerehighlyFig3.
Theentiremeasuringdeviceisplacedunderadryingchamber,whichhasaholeinitsbottom.
Fig4.
Thez-axisrunsthroughthecenteroftheincisoredgeandtheapex.
Thex-axisisorientatedperpendicu-larlytotheincisoredgeandparalleltothedirectionofmotionofthegoniometer.
AmericanJournalofOrthodonticsandDentofacialOrthopedicsHahnetal12.
e3Volume136,Number1signicantlydifferentfromzerofortheBiolon1.
0and0.
8mmandtheErkodur1.
0mmappliances,butnotfortheErkodur0.
75mmappliance,duringpalataldis-placement.
Thisshowsanintrusiveforcethatisstrongerinthevestibulardisplacementdirectionofthetooththaninthepalatinedirection(Fig6).
DISCUSSIONOurmeasuringdeviceiscomparabletomanyothersusedinorthodonticresearch.
Theshortcomingofthiskindofforcemeasurementisthelackofsimulationoftheperiodontalligament(PDL).
Thesecircumstancesdonottotallyallow,forexample,theinvestigatortode-ducetheforcedecayfromthemeasuredvaluesaswouldhappenunderin-vivoconditionsafterloadingasacon-sequenceoftoothmovement.
Hence,thisrestrictsthevalueoftheresultsasrelevantforforces,sincetheyappearimmediatelyafterloadingwhen,becauseoftheviscoelasticpropertyofthePDL,nopronouncedrapidtoothmovementcanbeexpected.
12,13Unfortunately,becauseofthecomplexmulti-phasicpropertiesofaPDLafterloading,acoherentconceptforrelatingtheforcesystemtotoothmovementandthere-actionofthedifferentpartsofthePDLhavenotyetbeenpresented.
14,15Nevertheless,theload-deectioncharacteristicswiththeobservedhysteresis,showninFigure5,espe-ciallyforFz,mightprovideanapproximationforpossi-bleforcedecayinrelationtothedistancemovedbythetoothafterapplicationofaload.
But,becausetheamountoftoothdisplacementisoftenhigherinaclinicalsituation,itisdifculttoassesswhetherhysteresiswillbecomparablewiththeclinicalsituation.
TheblanksforthermoplasticappliancesdescribedintheliteraturearemainlypolyethyleneorpolypropyleneFig5.
TypicalforcesmeasuredforFxandFzasafunctionofthedisplacementofthemeasuringtoothrecordedfor1material(Biolon,1.
0mm).
ForFx,asmallhysteresisphenomenon(reductionintheforcedeliveredduringremovalofaloadcomparedwiththeloadingphasewiththesametoothdisplacement)wasobserved.
ThiseffectwasmorepronouncedforFz.
TableI.
MeansandstandarddeviationsforFxandFzatdeectionrangesof60.
151mmforthemeasuredmaterialsMovementrangeMaterialthickness(mm)MaterialNVariableMeanSD0.
151mmpalatinaltippingofthemeasuringtooth0.
75Biolon10Fx3.
960.
110.
75Biolon10Fz0.
450.
110.
8Erkodur50Fx1.
620.
420.
8Erkodur50Fz0.
070.
121Biolon25Fx3.
880.
411Biolon25Fz0.
400.
381Erkodur50Fx2.
380.
531Erkodur50Fz0.
330.
4110.
151mmvestibulartippingofthemeasuringtooth0.
75Biolon50Fx4.
100.
620.
75Biolon50Fz1.
690.
870.
8Erkodur50Fx2.
480.
480.
8Erkodur50Fz0.
810.
211Biolon45Fx5.
350.
631Biolon45Fz2.
470.
341Erkodur50Fx3.
140.
221Erkodur50Fz1.
160.
2212.
e4HahnetalAmericanJournalofOrthodonticsandDentofacialOrthopedicsJuly2009andhavethicknessesof0.
762and1.
016mm,respec-tively.
5,10,16Therefore,wechosethoseblanksforthisinvestigation.
Themeasuredforcesfortippingareapproximately3to11timeshigherthantheidealforces(0.
35-0.
60N)statedbyProft17irrespectiveofthethicknessofthematerial.
Eventheforcesdeliveredbythethinnerfoilsare3to8timestoostrong.
Itwaspreviouslydemonstratedthattheamountofrootresorptionisdirectlyproportionaltothemagnitudeofforceapplied,butthisisnotthecasewhenremovableandthermoplasticappliances,inparticular,areused.
4,18-20ItisalsoquestionablewhethertheresultsofBarbagalloetal20regardingrootresorptionwiththermo-plasticappliancescanbetransferredtocentralincisors,becausetheyaremoresusceptibletorootresorption.
21,22Thisaspectneedsfurtherresearchwhenusingthermo-plasticappliancesfordifferentkindsoftoothmovement.
Barbagalloetal4measuredmeaninitialforcesof5.
12Natanactivationrangeof0.
5mm.
ThematerialusedinthatstudywasanErkodur0.
8mmblank.
Inourstudy,forthatmaterial,forcenormsbetween1.
62TableII.
SignicancevaluescalculatedforcomparisonoftheforcesdeliveredbytheappliancesinbothdirectionsofdisplacementPalatineVestibularMaterialsTestusedFx(Pvalue)Fz(Pvalue)Fx(Pvalue)Fz(Pvalue)Biolon1.
0vsBiolon0.
75Wilcoxon2-sample1.
00.
0706\0.
0001\0.
0001Erkodur1.
0vsErkodur0.
8Wilcoxon2-sample\0.
0001\0.
0001\0.
0001\0.
0001Biolon1.
0vsErkodur1.
0Wilcoxon2-sample\0.
00010.
3961\0.
0001\0.
0001Biolon0.
75vsErkodur0.
8Wilcoxon2-sample\0.
0001\0.
0001\0.
0001\0.
0001Biolon0.
75vsErkodur1.
0Wilcoxon2-sample\0.
0001\0.
3262\0.
0001\0.
0160Fig6.
TheboxplotsshowcomparisonsofdifferentlevelsofforceforFx(left,verticalaxis)andFz(right,verticalaxis)deliveredbytheparticularmaterial(plottedonthehorizontalaxisofbothdia-grams)foradisplacementrangeoftheincisoredgeof–0.
151mm(palatine)and10.
151mm(vestib-ular).
TheplottedforcesforFxarepositiveforvestibulardisplacementandnegativeforpalatinedisplacementoftheincisoredgeand,ingeneral,arehigherthantheforcesmeasuredforFz.
TheforcesmeasuredforFzareclosetozeroorslightlynegativeforpalatinedisplacementandgenerallynegativeforvestibulardisplacementoftheincisoredge.
ThenegativevaluesforFzrepresentintru-siveforcesforbothdirectionsofdisplacementoftheincisor.
Levelsofsignicanceareindicatedbyasterisks:*P#0.
05;****P#0.
0001.
n.
s.
,notsignicant.
AmericanJournalofOrthodonticsandDentofacialOrthopedicsHahnetal12.
e5Volume136,Number1(SD,0.
42)and2.
48N(SD,0.
48)weremeasured.
Theseslightlyhigherforcesmightbeexplainedbythediffer-entmorphologiesofthecrownofapremolarandanin-cisorand,therefore,thedifferentlylocatedandformedcontactareasbetweentheapplianceandthetooth.
Apartfromthemagnitudeoftheforce,therangeinwhichitactsisofgreaterinterestintermsofcompressionofthePDLandadversebiologiceffects.
Anactivationrangeof60.
151mmisadaptedtothewidthofthePDL(0.
1-0.
3mm);thisdiminishestheimportanceoftheforceactinginitiallyinhorizontaltoothmovement.
23,24Togetherwiththetippingforces(Fx),theintrusiveforces(Fz)couldalsobemeasured.
Thismightexplainposttherapeuticintrusion,whichhasbeendescribedpreviously.
25Altogether,theintrusiveforcesduringvestibulardisplacementwerehigherthanthoseforpal-atinedisplacement(Fig6,TableI).
Arationaleforthismightbedifferencesinthevestibularandpalatinemor-phologiesofamaxillarycentralincisor,whichtendstoresultinthegeometricdependenceofdifferentintrusiveforcesasshowninFigure7.
Theintrusiveforcesmeasured,especiallyforvestib-ulardisplacement,independentofthethicknessoftheappliance,areoveralltoohighcomparedwiththeforcesstatedbyProft(0.
1-0.
2N).
17Keepingalowactivationrangeof60.
151mminmind,onecouldassumethattherangeinwhichtheintrusiveforceactsisalsosmall,and,therefore,theamountofforcemightbeirrelevant.
Nev-ertheless,the2displacementdirectionsmustbeconsid-ered,asshowninFigure7.
Therefore,itmightbepossiblethat,despitealowhorizontalactivationrange,amuchhigherverticalactivationrangeresults.
Inthiscontext,itisstillunclearhowthemeasuredforcesaregenerated.
First,theycanbeexplainedasre-activeforcesresultingfromlocaldeformationoftheap-plianceatthecontactpointbetweentheapplianceandthetooth.
Second,thereducedtoftheappliancepro-ducedbythedisplacementofthetoothmightcontrolverticalraisingoftheappliancenearthedisplacedtooth.
Butbecausetheapplianceisstillretainedbyfrictioninthemolarregion,thewholeappliancebecomesde-formedlikeabow.
Thiscouldresultinaforceactingverticallythattendstopresstheappliancebackonthecompleterowofteethagain,evenatthesiteofthedis-placedtooth.
Thiscorrelateswiththeobservationdur-ingthisstudythat,duringprogressivedisplacementofthemeasuringtooth,theapplianceliftsupmorenearthedeectedtooththanfartherawayanddeformspro-gressively.
Also,whenthedeectionofthemeasuringtoothisreducedagain,theappliancetendstorepositionitselfontherowofteeth.
Bothmechanismsareconcor-dantwiththeforcesmeasuredinthisstudy,becausethedifferentthicknessesoftheapplianceshaveadirectin-uenceonthephysicalpropertiesoftheapplianceatthecontactpointandtheentirebodyoftheappliance,respectively.
Inaddition,thevacuum-formedappliances(Erko-dur),whichalsohaveanadditionalspacingfoilwithaninitialthicknessof0.
05mm(accordingtothemanu-facturer'sinformation)thatisremovedafterthermo-forming,deliveredlowerforcesonaveragethantheappliancesformedunderhighpressure(Biolon)(Fig6,TableI).
Potentially,betterttingoftheappliancesformedunderhighpressuremightincreasethefrictionthatreducesthelift-upoftheappliancefarfromthedis-placedtooth.
Thesendingsalsosupporttheforce-gen-erationtheoryinrelationtoreversibledeformationofthecompleteappliance,likeabow,initiatedbyalocalliftingaction.
Consequently,onecouldproposeadifferentiatedtherapeuticconceptinwhichjustafewteethin1partoftherowofteethareintendedtomove,andtheothersprovideretentionfortheappliance.
Underthesecondi-tions,forcescouldbegeneratedthroughlocalandwhole-bodydeformationoftheappliance.
Apartfromthedifferentforcesmeasuredinvitroduetovariousthicknessesofthematerials,inpreviousFig7.
Differentinclinationsofthevestibularandpalatinepartsofthethermoplasticappliancesneartheincisoredgearerepresentedbythe2tangents.
Whentheinci-soredgeisdisplacedinthevestibularandpalatinedirec-tionsoverthesamedistance(jdxvj5jdxpj,dashedarrow),thethermoformedappliancemustbedeformedorliftedalongthez-axismuchmoreduringvestibulardisplacement(dzv,longdottedarrow)thanduringpala-tinedisplacement(dzp,shortdottedarrow).
12.
e6HahnetalAmericanJournalofOrthodonticsandDentofacialOrthopedicsJuly2009studies,itwasshownthatmaterialstiffnesshasnosub-stantialinuenceoncompletingtherapyoronocclusalimprovementsorimprovementsinalignment.
7,8Kwonetal10usedatprobestomeasuretheforcesdeliveredbyathermoformedappliance.
Forprobescomparablewiththethinnerblanksweused,wemea-suredforcesof0.
522N(SD,0.
268)foradeectionrangeof0.
2mm.
Inthisstudy,withacorrespondingma-terialbutataslightlyloweractivationrange(0.
151mm),thenormsoftheforcesweremuchhigherandwerebetween1.
62(SD,0.
42)and4.
10N(SD,0.
62).
Anexplanationforthedifferentmeasuredforcescouldbethat,afterthermoforming,theresultingappliancebe-comesabodythatconsistsofmanyhalfshells,crests,sharpbends,andgeometricelementsthatstimulaterein-forcementofthematerialused.
Thisiscomparabletotheincreasingstiffnessofpaperwhenitisformedascorrugatedcardboard.
Therefore,atprobesarenotuse-fulforsimulatingtheforcedeliverycharacteristicsofthermoplasticappliances.
Thefullclinicalsignicanceofourresultshasyettobeestablished,andunansweredquestions,particularlywithregardtotheoptimalforcefortoothmovementsandcomplexforcedeliverycharacteristics,needtobeinvestigated.
CONCLUSIONSRemovablethermoplasticappliancesdelivercom-plexforcesystems.
Despitethetippingforce,itwasnev-erthelesspossibletoshowandquantifytheintrusivecomponent.
Thethicknessoftheblankcaninuencetheforcedelivered.
Anotherpossibilityisthatthespe-cicthermoformingprocess,combinedwithaparticularblank,hasasignicanteffectonthemagnitudeofforceassociatedwithaparticularappliance.
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