Current Directions in Biomedical Engineering 2016; 2(1): 101–104 Open Access Johannes Gattinger*, Christian N Bullemer and Ola L A Harrysson Patient specific root-analogue dental implants – additive manufacturing and finite element analysis DOI 10.1515/cdbme-2016-0025 Abstract: Aim of this study was to prove the possibility of manufacturing patient specific root analogue twopart (implant and abutment) implants by direct metal laser sintering The two-part implant design enables covered healing of the implant Therefore, CT-scans of three patients are used for reverse engineering of the implants, abutments and crowns Patient specific implants are manufactured and measured concerning dimensional accuracy and surface roughness Impacts of occlusal forces are simulated via FEA and compared to those of standard implants Keywords: additive manufacturing; biomechanics; dental implant; direct metal laser sintering (DMLS); 3D-printing; finite element analysis (FEA); patient specific; rapid prototyping; root analogue; stress shielding Introduction Dental implants are the most integral part of modern dentistry to provide a permanent and effective solution for a wide range of dental complications and diseases Since the first development of implants for edentulous jaw modern dental implants have been considered a safe and reliable solution for replacing missing teeth [1] In the last 10 years, the application of digital engineering in implant dentistry has become widespread with the introduction of cone beam computed tomography (CBCT), and *Corresponding author: Johannes Gattinger, Institute of Medical and Polymer Engineering, Technische Universität München, Boltzmannstr 15, 85748 Garching, E-mail: johannes.gattinger@tum.de Christian N Bullemer: Institute of Medical and Polymer Engineering, Technische Universität München, Boltzmannstr 15, 85748 Garching, E-mail: christian.bullemer@mytum.de Ola L A Harrysson: Center for Additive Manufacturing and Logistics, Fitts Department of Industrial and Systems Engineering, North Carolina State University, Raleigh, NC 27695-7906, E-mail: harrysson@ncsu.edu progress has been made in the development of computer aided design (CAD) techniques With the availability of high quality CT scans and the development of segmentation software, reverse engineering of dental implants has become a possible solution Therefore, patient specific root analogue dental implants can be designed by the segmentation of patients’ CT scans where anatomical features, like a tooth, can be modelled and turned into a computer-generated model to use it for manufacturing Regarding additive manufacturing methods, direct metal laser sintering can be used to directly turn this model into a patient-specific implant that can achieve a faster and more patient-friendly treatment than the conventional procedure (Figure 1) [2] Material and methods To prove the possibility of patient specific implantation as introduced, CT-scans of patients are evaluated The Scans are segmented with Mimics® and edited with 3Matic® (both products of Materialise, Belgium) for FEA simulation and direct metal laser sintering Models of maxillary bone, implants, abutments and crowns are simulated with finite element analysis (ANSYS® ) Implants, abutments and screws are fabricated via direct metal laser sintering (EOSINT M280) from Ti-6Al-4V The fabricated parts are examined concerning dimensional accuracy by 3D-Scanning (FARO® Edge ScanArm ES) and surface roughness by tactile and optical measurement (Mitutoyo SJ-210 and Hirox KH-7700) 2.1 Geometry The geometry for the root analogue implants and crowns is extracted from CT-scans with Mimics and 3-Matic as shown in Figure Abutments and screws are designed in SolidWorks The resulting geometries are exported as STL files for manufacturing by direct metal laser sintering and finite element analysis © 2016 Johannes Gattinger et al., licensee De Gruyter This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 License Unauthenticated Download Date | 1/31/17 2:29 PM 102 | J Gattinger et al.: Patient specific root-analogue dental implants Conventional procedure Patient specific procedure st Visit CT-Scan, modeling and 3D-Printing of implant 1st Visit Extraction, grafting socket Months nd Visit Gum incision, jawbone drilling, implant insertion 3–6 Months Few days nd Visit Tooth extraction, implant insertion 3–6 Months 3rd visit Installation of abutement and crown 3rd visit Installation of abutement and crown Figure 1: Surgical procedures of total tooth replacement State of the art replacement procedure vs patient specific procedure of 0.65 between implant and cortical bone and 0.77 between implant and cancellous bone [6, 7] Two forces of 100 N are applied on the occlusal area One force (F1 ) pointing in axial direction and the other (F2 ) with a buccallingual orientation and a tilt angle of 45° as shown in Figure [8, 9] Principal boundary conditions are summarized in Table FEA simulations are done for different patient specific root analogue implants and standard dental implants on first molars from CT-scans of three patients at University of North Carolina dental school 2.2 Material properties Results Material properties used for the finite element analysis are summarized in Table Young’s Modulus and Poisson’s Ratio of cortical and cancellous bone are determined in respect to previous FEA studies [3–5] 3.1 Finite element analysis (FEA) 2.3 Boundary conditions In the structural mechanical FEA simulation the material behavior of all bodies are set to linear elastic, homogenous and isotropic For the contact between implant and bone complete osseointegration is assumed resulting in a contact without gap The model is fixed in all degrees of freedom at the intersecting planes of the maxilla Interfaces between crown, abutment and implant are modeled as bonded contact The interface between bone and implant is modeled as frictional contact with a friction coefficient Figure 2: Geometry generation of implant abutment and crown from CT-Scan data Results for total deformation, resulting stresses (van Mises, maximum principal and frictional stresses in the contact region of implant and bone) and the sliding distance in the implant bone interface are evaluated and compared between patient specific implants and standard implants 3.1.1 Deformation/sliding distance Figure shows an example for the total deformation of the implant system, maxillary bone, implant, abutment Figure 3: Boundary conditions applied in finite element analysis Table 2: Boundary conditions used in finite element analysis Table 1: Material properties of bone and implant used in finite element analysis Material Young’s modulus Cortical bone Cancellous bone Ti-6Al-4V sintered Porcelain (Crown) 13,800 MPa 345 MPa 13,8000 MPa 70,000 MPa Poisson’s ratio 0.26 0.31 0.342 0.19 Forces and contact regions Force F1 (axial) F2 (45° buccal-lingual) Implant – Cortical Bone Implant – Cancellous Bone Implant – Abutment Abutment – Crown 100 N 100 N Friction coeflcient 0.65 0.77 Bonded Bonded Unauthenticated Download Date | 1/31/17 2:29 PM J Gattinger et al.: Patient specific root-analogue dental implants | and crown under occlusal loading In this example the root analogue system shows less deformation than the standard implant version In Figure the results of the deformation of nine simulations are summarized to compare the results of all calculations done with root analogue and standard implants The sliding distance between implant and bone does not differ in a significant way between root analogue and standard implant but is in the same range of about 5–14 µm 103 3.2 Additive manufacturing Modeled root analogue and standard implants (Figure 7) are manufactured through direct metal laser fabrication Investigation of dimensional accuracy via 3DLaserscanning showed average deviation between the CAD model and the fabricated implants of 50 µm and a maximum deviation of 90 µm The arithmetic average of the absolute values of surface roughness Ra of the printed parts turned out to be at about 15 µm 3.1.2 Stresses Resulting stresses from occlusal loading are compared in Figure It turned out that stresses are a bit lower with root analogue implants but not statistically significant However the resulting stresses are at least in a similar range Discussion Figure 4: Total deformation of crown, abutment, implant and bone for the first right molar of one patient Comparison of patient specific implant and standard implant under equal loading conditions Direct metal laser sintering has been proven to be a valid manufacturing method for the production of patient specific dental implants [2, 3, 10] In this study the possibility of two-part (implant and abutment) root-analogue implantation is proven considering the potential of direct metal laser sintering for the fabrication of the implants and finite element analysis to estimate the expectable deformations, stresses and micro-motions in respect to a standard implant Despite the small sample of only three patients, the upcoming results from the FEA simulations of the patient specific implants are at least as good as the results for the standard implants Nevertheless, the measured surface roughness of the manufactured implants might be too high for suitable osseointegration [11, 12] The dimensional accuracy is marginal, which means that in this cases finishing is necessary to grant the fitting of abutments and screws to the implant The fitting of the implant to the bone could be problematic because of insufficient resolution of the CT-Scan data Figure 5: Comparison of total deformation and maximum sliding distance between implant and maxillary bone of the implant system with root analogue and standard implant Figure 6: Comparison of different stresses resulting through occlusal loading of the implant system with root analogue and standard implant Unauthenticated Download Date | 1/31/17 2:29 PM 104 | J Gattinger et al.: Patient specific root-analogue dental implants Figure 7: Direct metal laser fabricated root analogue implants A: Patient specific implant for first molar with some left over support structure from direct metal laser sintering B: Patient specific canine implants with and without support structure It is to reflect if it wouldn’t be better to fabricate the root analogue implants by milling than via additive manufacturing, because the geometry is not that complex (e.g no undercuts) that additive manufacturing would be necessary Conclusion Results indicate that it would be possible to manufacture patient specific root analogue two-part implants by reverse engineering and direct metal laser sintering The two-part implant design allows covered healing of the implant Insertion of abutment and crown follows just after proper osseointegration of the implant as with standard dental implant systems Anyhow finishing is to be done because of the insufficient dimensional accuracy and surface quality of the sintered parts Author’s Statement Research funding: The author state no funding involved Conflict of interest: Authors state no conflict of interest Material and Methods: Informed consent: Informed consent has been obtained from all individuals included in this study Ethical approval: The conducted research is not related to either human or animal use References [1] Branemark P-I Osseointegrated implants in the treatment of the edentulous jaw Experience from a 10-year period Scand J Plast Reconstr Surg 1977;16:1–132 [2] Mangano C, Mangano F, Shibli J, Luongo G, De Franco M, Briguglio F, et al Prospective clinical evaluation of 201 direct laser metal forming implants: results from a 1-year multicenter study Lasers Med Sci 2012;27:181–9 [3] Chen J, Zhang Z, Chen X, Zhang C, Zhang G, Xu Z Design and manufacture of customized dental implants by using reverse engineering and selective laser melting technology J Prosthet Dent 2014;112:1088–95.e1 [4] Huang HL, Hsu JT, Fuh LJ, Lin DJ, Chen MY Biomechanical simulation of various surface roughnesses and geometric designs on an immediately loaded dental implant Comput Biol Med 2010;40:525–32 [5] Tang C-B, Liu S-Y, Zhou G-X, Yu JH, Zhang GD, Bao YD, et al Nonlinear finite element analysis of three implant-abutment interface designs In J Oral Sci 2012;4:101–8 [6] Grant J, Bishop N, Götzen N, Sprecher C, Honl M, Morlock MM Artificial composite bone as a model of human trabecular bone: the implant–bone interface J Biomech 2007;40:1158–64 [7] Yu HY, Quan HX, Cai ZB, Gao SS, Zhu MH Radial fretting behavior of cortical bone against titanium Tribol Lett 2008;31:69–76 [8] Eser A, Tonuk E, Akca K, Cehreli MC Predicting timedependent remodeling of bone around immediately loaded dental implants with different designs Med Eng Phys 2010;32:22–31 [9] Saidin S, Abdul Kadir MR, Sulaiman E, Abu Kasim NH Effects of different implant–abutment connections on micromotion and stress distribution: prediction of microgap formation J Dent 2012;40:467–74 [10] Figliuzzi M, Mangano F, Mangano C A novel root analogue dental implant using CT scan and CAD/CAM: selective laser melting technology Int J Oral Maxillofac Surg 2012;41:858–62 [11] Coelho PG, Jimbo R, Tovar N, Bonfante EA Osseointegration: Hierarchical designing encompassing the macrometer, micrometer, and nanometer length scales Dent Mater 2015;31:37–52 [12] Hansson S, Norton M The relation between surface roughness and interfacial shear strength for bone-anchored implants A mathematical model J Biomech 1999;32:829–36 Unauthenticated Download Date | 1/31/17 2:29 PM ... conditions applied in finite element analysis Table 2: Boundary conditions used in finite element analysis Table 1: Material properties of bone and implant used in finite element analysis Material... Gattinger et al.: Patient specific root- analogue dental implants | and crown under occlusal loading In this example the root analogue system shows less deformation than the standard implant version... calculations done with root analogue and standard implants The sliding distance between implant and bone does not differ in a significant way between root analogue and standard implant but is