Calaon, M.

Häfner, B.

Kain, M.

May, M. C.

Miqueo, A.

Nadimpalli, V. K.

Pedersen, D. B.

Tosello, G.

Yagüe-Fabra, J. A.

The demand for high flexibility and mass customization within medical implants has resulted in the early adoption of additive manufacturing technologies in the medical sector. Apart from offering unique customization opportunities, metal additive manufacturing of implants also enables the generation of functionally structured surfaces showing increased biocompatibility. The need for improving properties like biocompatibility is essential since many patients suffer from dental implant failures such as screw loosening, integration failure or implant breakage. The high requirements for implant materials depending on the specific implant environment and function complicates the implant design and results in multi-component implants. This could be overcome by the use of multi-material metal additive manufacturing that enables functionally graded part production. However, current commercial laser powder-bed fusion systems are limited to a single material at a time. By utilizing an open-architecture laser powder-bed fusion system by Aurora Labs it was possible in a controlled way to mix AISI 316L Stainless Steel with AISI 440C Stainless Steel during the fabrication of a dental strut-like geometry thereby functionally grading the properties of the material to have a low hardness near the gums and a higher hardness around the crown. The material distribution was evaluated by cutting and etching and the hardness was measured at various locations. The current work demonstrates the technical viability of manufacturing functionally graded dental strut implants by leveraging multi-material metal additive manufacturing

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Metal Additive Manufacturing of Multi-Material Dental Strut Implants

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euspen’s 20th International Conference &Exhibition, Geneva, CH, June 2020www.euspen.euMetal Additive Manufacturing of Multi-Material Dental Strut ImplantsM. Kain1*, V. K. Nadimpalli1*, A. Miqueo2, M. C. May3, J. A. Yagüe-Fabra2, B. Häfner3, D. B. Pedersen1, M.Calaon1, G. Tosello11Department of Mechanical Engineering, Technical University of Denmark, Building 427A, Produktionstorvet, 2800 Kgs. Lyngby, Denmark2Escuela de Ingeniería y Arquitectura, Universidad de Zaragoza, Calle María de Luna, 50018 Zaragoza, Spain3wbk Institute of Production Science, Karlsruhe Institute of Technology, Kaiserstraße 12, 76131 Karlsruhe, Germany*mkain@mek.dtu.dk, vkna@mek.dtu.dkAbstractThe demand for high flexibility and mass customization within medical implants has resulted in the early adoption of additivemanufacturing technologies in the medical sector. Apart from offering unique customization opportunities, metal additivemanufacturing of implants also enables the generation of functionally structured surfaces showing increased biocompatibility. Theneed for improving properties like biocompatibility is essential since many patients suffer from dental implant failures such as screwloosening, integration failure or implant breakage. The high requirements for implant materials depending on the specific implantenvironment and function complicates the implant design and results in multi-component implants. This could be overcome by theuse of multi-material metal additive manufacturing that enables functionally graded part production. However, current commerciallaser powder-bed fusion systems are limited to a single material at a time. By utilizing an open-architecture laser powder-bed fusionsystem by Aurora Labs it was possible in a controlled way to mix AISI 316L Stainless Steel with AISI 440C Stainless Steel during thefabrication of a dental strut-like geometry thereby functionally grading the properties of the material to have a low hardness nearthe gums and a higher hardness around the crown. The material distribution was evaluated by cutting and etching and the hardnesswasmeasured at various locations. The current work demonstrates the technical viability ofmanufacturing functionally graded dentalstrut implants by leveraging multi-material metal additive manufacturing.Multi-material, Metal Additive Manufacturing, Dental Implant1. IntroductionDuring recent years the development and improvement ofmetal additive manufacturing (MAM) technologies haveexpanded the domain of application significantly. Previously, themost common areas of applications where foundwithin the fieldof complex part geometries at low volume application or for highvalue customized parts. However, as the technology improvesand becomes more economically efficient it becomes feasible tomanufacture cheaper highly customized low volume parts. Suchparts can be found within the domain of medical implants,where patient specific customization offers an advantagecompared to conventionally mass-produced implants [1].The manufacturing of dental implants is a known area when itcomes to integration of additive manufacturing, whereadditively manufactured dental crowns are already beingoffered on a wider scale [2]. However the remaining part of theimplant, which is assembled from several part components, iscurrently mass-produced using conventional manufacturingmethods. One of the reasons for assembling severalcomponents is the different functional requirements in theenvironment around the implant. Another aspect of AM inimplant manufacturing is the possibility to apply functionalstructuring to a surface or the full implant in order to enhancethe biocompatibility, which also acts as the main motivation forthe investigation undertaken in this study [3].Most current MAM systems are limited to the use of a singlematerial in a build which restricts the capability of functionallygrading the manufactured parts. Hence, a modified L-PBFsystem has been utilized in the present work that is capable ofcontrolling the mixing of material powders thereby creatingcontinuous interfaces between two different materials [4]. Thispreliminary research investigates the potential application ofmulti-material MAM technology for the manufacturing offunctionally graded dental implants.2. Implant Design for Multi-Material Additive ManufacturingThe environmental change in the mouth significantlyinfluences the functional requirements of the implantcomponents. The implants crown, as shown in figure 1, isexposed and needs a cosmetic finish that matches the patient’steeth.Figure 1. Left: Schematic picture of components in a simple dentalimplant consisting of (from the top): Crown, Abutment, Strut [5]. Right:CAD drawing of simplified combined strut and abutment.The crown is frequentlymade from a ceramicmaterial that canbe coloured in custom shades of white, whereas the abutmentand the strut, as shown in figure 1, is frequently made fromeither titanium or stainless steel [2].2.1. Functional gradationIt is important that the functional requirements of the implantmatches the surrounding environment. Whereas the top of theimplant must be strong and yet gum compatible, the lower partshould have bone-compatible capabilities such that a strongbond between the overall implant and the jaw is ensured. Bycombining the abutment and the strut, as schematically shownin figure 1, it is possible to reduce the assembly into a single part.Due to the different functional requirements of this part it canbe manufactured using multi-material MAM where the lowerpart, originally the strut, is manufactured in one material whilethe top part, originally the abutment, is manufactured in asecond material. A strong bonding of the two materials isensured due to the gradual change of the interface materialcomposition during the build. The possibility to introducegeometrical structures on the surfacewhenmanufacturing usingMAM is of large interest, however in this preliminary study, nofunctional structuring has been introduced in the design.2.2. Implant design for additive manufacturingIn order to manufacture the implant component a few designalterations must be considered to optimize manufacturabilityand minimize the need for post processing. A minimum angle ofinclination of 45 degrees has been ensured across the fullspecimen to avoid the need for support structures.2.3. ManufacturingThe implant specimen was manufactured on an Aurora Labs S-Titanium Pro laser powder bed fusion (L-PBF) system whichsimultaneously combines two 150 W CO2-laser sources. Thesystems have been adapted to enable specific ratio mixing oftwo different metal powders for individual layers throughoutthe build job. The two powder materials used in this work areAISI 316L Stainless steel and AISI 440C Stainless steel with aconcentration of 316L of 100% in the lower part of the specimenand a 50/50 concentration of 316L and 440C in the upper part ofthe specimen, as shown in figure 2. The operating processparameters are thoroughly described in Nadimpalli et al. [4].Figure 2. Sample shown as cut, embedded, polished and etched.Different material compositions visible for the lower and top part.2.4. Specimen analysis methodologyIn order to characterize the specimens, the samples were cutand embedded before polishing until 4000 grit SiC paper andsubsequent 3 μm and 1 μm diamond pasted polishing. Thesamples were analysed by light optical microscopy (LOM, ZeissAxio A1). The hardness of the samples were evaluated using aFutureTech FM-700 Vickers microhardness tester with a 2 Nload and 10 s load time. The average and standard deviation ofthe microhardness were based on five repeated measurements.The dimensional part deviation has been evaluated using aNikon 225 X-ray CT system with an acceleration voltage of 200keV and a power of 15 W to achieve a voxel size of 11.5 µm. Thepower and acceleration voltage were optimized to obtain a goodtransmission through the dental strut component.3. Results and Analysis3.1. Hardness evaluationFrom the hardness measurement a hardness of HV0.2 234 witha STD of 9 was measured for the lower part of the specimenconsisting of 100 % concentration of stainless steel 316L. Theupper part of the specimen with a concentration of 50 % 316Land 50 % 440C a hardness of HV0.2 280 with a STD of 11 wasmeasured. Both hardness’s have been evaluated according tothe DIN 50150 standard.3.2. Part deviationFrom figure 3, it can be seen that a part deviation in the rangeof ±0.5 mm is to be found. This deviation may be present due tothe rough surfaces of the as printed part. For this particularstudy, no surface treatment, such as abrasive blasting, has beenapplied however; such a process step would significantly alterthe surface topography and deviation and would be essentialbefore implanting the dental strut in a patient.Figure 3. X-Ray CT scan of the implant specimen showing X, Y and Z crosssection projections and part deviation plot from the nominal CADmodel.4. ConclusionA multi-component implant was analysed and combined intoa single component before being manufactured using multi-material MAM. Thereafter, an analysis of mechanical propertiessuch as material hardness was evaluated for different areas. Thefunctional gradation of both material and geometry possiblethrough Multi-material MAM shows promise in themanufacturing of specimens that are subject to differentfunctional requirements potentially within the field of patient-specific dental implants.AcknowledgementsThis study was undertaken in the context of DIGIMAN4.0Project (“Digital Manufacturing Technologies for Zero-defectIndustry 4.0 Production”, www.digiman4-0.mek.dtu.dk)supported by the European Commission (project no. 814225)and Manufacturing Academy of Denmark (www.made.dk)“MADE Digital” supported by Innovations Fund Denmark(project no. 6151-00006B).References[1] Lowther M et al 2019 Clinical, industrial, and research perspectiveson PBF AMmetal implants Additive Manufacturing 28 565-584[2] Noort R V 2012 The future of dental devices is digital DentalMaterials 28 3-12[3] Wally Z et al, 2019, Selective laser melting processed Ti6Al4Vlattices with graded porosities for dental applicationsMechanicalBehavior of Biomedical Materials 90 20-29[4] Nadimpalli V K et al 2019 Multi-material additive manufacturing ofsteels using laser powder bed fusion Euspen Int. Conf. & Exh. 19[5] https://arialdent.com/servicii/ (visited 11/12/2019)View publication stats

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Metal additive manufacturing of multi-material dental strut implants

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Metal Additive Manufacturing of Multi-Material Dental Strut Implants

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