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Current Directions in Biomedical Engineering

Joint Journal of the German Society for Biomedical Engineering in VDE and the Austrian and Swiss Societies for Biomedical Engineering

Editor-in-Chief: Dössel, Olaf

Editorial Board: Augat, Peter / Buzug, Thorsten M. / Haueisen, Jens / Jockenhoevel, Stefan / Knaup-Gregori, Petra / Kraft, Marc / Lenarz, Thomas / Leonhardt, Steffen / Malberg, Hagen / Penzel, Thomas / Plank, Gernot / Radermacher, Klaus M. / Schkommodau, Erik / Stieglitz, Thomas / Urban, Gerald A.

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Patient specific root-analogue dental implants – additive manufacturing and finite element analysis

Johannes Gattinger
  • Corresponding author
  • Institute of Medical and Polymer Engineering, Technische Universität München, Boltzmannstr. 15, 85748 Garching
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/ Christian N. Bullemer / 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
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Published Online: 2016-09-30 | DOI: https://doi.org/10.1515/cdbme-2016-0025

Abstract

Aim of this study was to prove the possibility of manufacturing patient specific root analogue two-part (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

1 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 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].

Surgical procedures of total tooth replacement. State of the art replacement procedure vs. patient specific procedure.
Figure 1:

Surgical procedures of total tooth replacement. State of the art replacement procedure vs. patient specific procedure.

2 Material and methods

To prove the possibility of patient specific implantation as introduced, CT-scans of 3 patients are evaluated. The Scans are segmented with Mimics® and edited with 3-Matic® (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 2. 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.

Geometry generation of implant abutment and crown from CT-Scan data.
Figure 2:

Geometry generation of implant abutment and crown from CT-Scan data.

2.2 Material properties

Material properties used for the finite element analysis are summarized in Table 1. Young’s Modulus and Poisson’s Ratio of cortical and cancellous bone are determined in respect to previous FEA studies [3], [4], [5].

Table 1:

Material properties of bone and implant used in finite element analysis.

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 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 buccal-lingual orientation and a tilt angle of 45° as shown in Figure 3 [8], [9]. Principal boundary conditions are summarized in Table 2. 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.

Boundary conditions applied in finite element analysis.
Figure 3:

Boundary conditions applied in finite element analysis.

Table 2:

Boundary conditions used in finite element analysis.

3 Results

3.1 Finite element analysis (FEA)

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 4 shows an example for the total deformation of the implant system, maxillary bone, implant, abutment and crown under occlusal loading. In this example the root analogue system shows less deformation than the standard implant version. In Figure 5 the results of the deformation of nine simulations are summarized to compare the results of all calculations done with root analogue and standard implants.

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.
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.

Comparison of total deformation and maximum sliding distance between implant and maxillary bone of the implant system with root analogue and standard implant.
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.

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.

3.1.2 Stresses

Resulting stresses from occlusal loading are compared in Figure 6. 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.

Comparison of different stresses resulting through occlusal loading 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.

3.2 Additive manufacturing

Modeled root analogue and standard implants (Figure 7) are manufactured through direct metal laser fabrication. Investigation of dimensional accuracy via 3D-Laserscanning showed average deviation between the CAD model and the fabricated implants of 50 μm and a maximum deviation of 90 μm.

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.
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.

The arithmetic average of the absolute values of surface roughness Ra of the printed parts turned out to be at about 15 μm.

4 Discussion

Direct metal laser sintering has been proven to be a valid manufacturing method for the production of patient specific dental implants [3], [2], [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.

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.

5 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.

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About the article

Published Online: 2016-09-30

Published in Print: 2016-09-01


Citation Information: Current Directions in Biomedical Engineering, Volume 2, Issue 1, Pages 101–104, ISSN (Online) 2364-5504, DOI: https://doi.org/10.1515/cdbme-2016-0025.

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©2016 Johannes Gattinger et al., licensee De Gruyter.. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. BY-NC-ND 4.0

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