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  • iMedPub Journalshttp://www.imedpub.com

    2016Vol. 2 No. 1:21

    1 Copyright iMedPub This article is available in http://orthodontics-endodontics.imedpub.com/

    Research Article

    Journal of Orthodontics & Endodontics ISSN 2469-2980

    Ferreira TJ1, Vieira MT1,Costa J2, Silva M3 andGago PT3

    1 CEMUC Centro de Engenharia Mecnica da Universidade de Coimbra, Portugal

    2 IPNInstitutoPedroNunes,Coimbra,Portugal

    3 3DTech Marinha Grande, Portugal

    Corresponding author: Ferreira TJ

    tferreira@student.dem.uc.pt

    CEMUC Centro de Engenharia Mecnica daUniversidadedeCoimbra,Portugal.

    Tel: +351 239 700 967

    Citation: Ferreira TJ, Vieira MT, Costa J, et al. Manufacturing Dental Implants usingPowder InjectionMolding. JOrthodEndod.2016,2:1.

    Manufacturing Dental Implants using Powder Injection Molding

    AbstractDuring the last decennia it is demonstrated that the injection molding usedin polymers could be the solution to decrease the price of parts / devices ofmetallic alloys for large-scale series production. The metal powder injectionmolding (MIM) techniquehasfivemain steps: selectionofpowderandbinder,productionoffeedstock,injectionmolding,debindingandsintering.Thematerialselected was the 316L steel due to its wide use as biomaterial associated to low costofpowdersand itshigh injectability.The feedstockwassuitableoptimizedandproducedby torque rheometry technique.The ideal feedstockhas60:40%vol. of powders:binder andhas low torque value (suitable to injection step). Itisimportanttodecreasethefrictioncoefficient(betweenthemoldingpartsandmoldsurfaces)andto improvesignificantlythewearstrengthofmoldsurfaces.The(micro)moldwasdesignedanddevelopedforproducingdental implantsinlargeseriesthatmeanscoatedwithahighhardnessandnearfrictionlessthinfilmofdichalcogenidessulphides(W-S-C).Theinjectionstepwascarriedoutat10MPaandthebinderwasefficientlyremovedfromgreenimplants.Aftersinteringstep(at 12500C), dental implants have a goodfinishing and the shrinkageof dentalimplants was evaluated. The osseointegrability was promoted by coating thesinteredimplantswithathinfilmofnon-modifiedandSimodifiedhydroxyapatite(HA).Thecoateddentalimplantsweremechanicallyevaluatedduringimplantationusingabovinerib.Thenewstrategicproduction leadscheaper implants,called"implants for crisis", where surface modification assures a similar or superiorbioactivitythancommercialimplants.

    Keywords: Powderinjectionmolding;Dentalimplants;316Lpowders;Micromold;W-S-Ccoating;HAthinfilms

    Received: December09,2015; Accepted: February18,2015; Published: February22,2016

    IntroductionDentalimplantsexistedformanyyearsandtheyincludeartificialteeth to restore the natural dental function [1]. Conventionaldental implants are typically made in metal and metal alloys,where titanium and its alloys have an important role. Besidesthehigh cost of thesematerials, the traditionalmanufacturingsystemsareexpensivehavinginmindthenumberofimplantstobeproducedandtheircomplexshape[2].

    Currently, there isaneedto improvethemethodmanufactureofdentalimplants,makingthemcheaperandfastmanufacturing[1].Inordertoinvestigatealternativecosteffectivemanufacturingmethods for producing dental implants, MIM technique wasevaluated. TheMIM is regardedas verypromisingnet shaping

    technique,duetoitsadvantagesforcomplexgeometry,precisionand production in large-scale series of implants with highperformance,withoutfinishingprocess[3].TheMIMtechniquehavefiveprocessingsteps,namely:rawmaterialcharacteristics(4S's=particlesize,particledistributionsize,shapeandstructure),mixingofpowderandbinderforfeedstockpreparation,injectionmoldingoffeedstocktothedesiredshape,debindingtoremovethe binder and sintering to give the required properties [3-5].The thermalcharacterizationofthebinder isvery importanttoknowthemeltinganddegradationtemperatures, todefinetheprocessing conditions for mixing and injection, as well as fordebindingcycle.Inthefeedstockpreparationisessentialthatallthe metallicpowdersareinvolved/coatedbybinderandsuitableviscosityforoneinjectionstepadequate.Thebindercontentin

    http://www.imedpub.com/search-results.php?keyword=coatedhttp://www.imedpub.com/search-results.php?keyword=implantshttp://www.imedpub.com/search-results.php?keyword=teethhttp://www.imedpub.com/search-results.php?keyword=titaniumhttp://www.imedpub.com/search-results.php?keyword=thermalhttp://www.imedpub.com/search-results.php?keyword=metallic

  • 2

    ARCHIVOS DE MEDICINAISSN 1698-9465

    2016Vol. 2 No. 1:21

    CopyrightiMedPub Thisarticleisavailableinhttp://orthodontics-endodontics.imedpub.com/

    Journal of Orthodontics & Endodontics ISSN 2469-2980

    feedstockmustbeoptimizedinordertohaveasuitableviscosityvalueandafterinjectionanddebinding(necessarytoproduceametallicpart/device)tomaintainthegeometrybeforesintering.

    Among the big challenges facing MIM, the (micro) mold isunquestionablyoneofthemostrelevant,becauseofitsqualitydepends on the success or failure of this technology. Themolding blocks for injectionmolding, usually consist in inserts(cavityandcore)micro machined and assembled on a standard structure.Whilethemoldsstructureanditsinjectionsystemsaremanufacturedby conventionalprocesses,other techniquesareusedformanufacturingthemoldingsurfaces.Themanufactureof(micro)moldsusessubtractivemicromachiningtechnologiesthat can create 3D micro geometries, in some cases, with high-precision and aspect ratio, like micro-milling, laser beammachining (LBM), micro electric discharge machining (EDM)and,aspolish/finishtechnology,electronbeammachining(EBM)[6]. All of these techniques,micro-milling is themost versatileandabletoproducecomplex3Dshapes,butquiteproblematicindetailsbelowthan0.1mm.TheEDMand,especiallytheLBM,will produce a thermal affected layer, therefore not ensuringthedesirable textureand integritysurface for thegeneralityofapplications,butthis limitationcanberesolvedwiththeuseofEBM.NotethatfinishingbyEBMpromotessignificantresistanceto oxidation and corrosion,when comparedwith conventionalsurfacetreatmentprocesses[7].

    One of the critical steps of injectionmolding is the extractionof the implant from(micro)cavity.During theextractionsteps,thepartsaremechanicallyforcedtoseparatefromthemoldingsurface and this aspect is more relevant in the case of deepcavities. Thedesignof theejection systemdependson severalfactors:draftangles,surfacefinishing,propertiesofthematerialtoinjectandtemperatureduringtheejectionstep[8].

    Othermain existing problems in themanufacture of the teethimplantsisbasedontheabilitytoprocesshighqualitysurfaceswith minimal roughness values associated to the dimensional precisiontolerances,whicharefundamentaltothemicroscale.Moreover, the injection ofmetallic feedstock ismore abrasivethan the polymeric ones, which difficult the outflow duringinjection and consequently, the extraction process of smallcomponents. In order to overcome this critical issue, coatingsreferredtoasnear-frictionlessasDichalcogenidesSulphidesare an optimal solution [9, 10]. They arewell known for theircrucial role in reduction ofmechanical and abrasivewear andbyexhibit lowfrictioncoefficient,which isrelevanttopromotetheextractionfromthecoatedmoldofimplants.Thesputteringtechnology used on the development of this type of coating,whichbelongstothegroupofadditiveprocessescalledPhysicalVapor Deposition (PVD), is a versatile technology that enablesdeveloping coatings with suitable chemical compositions andhomogeneous growth over surfaces to protect /modify them,responding effectively to the challenges in themanufacture ofmoldsformicro-componentsormoldswithmicrodetails.

    The MIM technology can help to produce cheap dentalimplants, however it can be necessary to improve the rateof osseointegration e.g. through implants coated with nanohydroxyapatite(nanoHA)withorwithoutsiliconaddition.There

    are studies reporting that HA doped with specific elements(titanium)hasadvantageinbiologicalprocess[11,12].Therefore,HAbasedcoatingswereselectedduetotheirgoodperformanceinosseointegrationbehaviour.

    Themainobjectiveofthepresentstudyistoshowthepotentialofinjectiontechnologyforproducingmetallicdentalimplantsfrommetallicpowders,highlightingtheengineeringsolutionsforthemanufactureofmicro-moldscoatedwithW-S-Cto improvetheperformanceofejectionstepandminimizetheforcetoseparatethe parts from the molding surface. Were produced dentalimplantsbyMIMfrompowdersofausteniticstainlesssteel (SS316L).Thesintereddentalimplantswerephysicalandmechanicalcharacterisedandthetorquestrengthofimplantswasevaluatedusingascounterbodyabovinerib.ThedentalimplantsproducedwerecoatedbynanoHAwithvariouscontentsofsilicon.

    Materials and MethodsMaterialsIn thiswork, themetalpowderusedwaswateratomized316Laustenitic stainless steel - SS316L (Epson Atmix Corporation)andthemulti-polymericbinderbasedonpolyolefinwaxes(fromAtect).Thematerialusedforproducingthe(micro)moldwasasteelDINX40CrMoV51(48to52HC).

    Themolding blockswere coatedwithDichalcogenide SulphidecoatingW-S-C.Theyweredepositedbyco-sputtering fromtwoWS2andoneCarbontargetsinanunbalanced-sputteringunity(Teer coating equipment). A fourthChromium target was used as interlayer step, inorder to improve thecoatingadhesion toSSsubstrate.Finally,dentalimplantswerecoatedfromHAtargetusingrfsputtering.

    MethodsThe mixture of metallic powder and binder was optimized bytorquerheometrytechniqueinBrabenderPlastographmixer,forsuitableevaluationofthecriticalpowdervolumeconcentration(CPCV), at programmed temperature and rotational speed [5].Afteroptimization,itwaspossibletoselectthesuitablepowder:binder ratio for produce feedstock and this was evaluated bycontrollingthetorquevalueduringthemixtureprocessandbySEMmicrographs.Finally,thefeedstockwasgranulatedintosmallgranules pro

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