Finite element analysis of the biomechanical effects of PEEK dental implants on the peri-implant bone
Introduction
Polyetheretherketone (PEEK) is a high performance thermoplastic polymer that was first commercially offered as a biomaterial for long-term implants in April 1998 (Invibio Ltd., Thornton-Cleveleys, UK) (Kurtz and Devine, 2007). Today it is well known as an alternative biomaterial to metallic implant materials in the field of orthopedics (Liao, 1994, Maharaj and Jamison, 1993) and traumatology (Corvelli et al., 1997, Kelsey et al., 1997) as it presents many advantages, such as an elastic modulus similar to that of bone avoiding high stress peaks during load transfer at the bone-implant interface on the one hand, and a stress shielding effect on the other. These are just two factors that led to the assumption that PEEK could also represent a viable alternative to titanium and titanium alloys in the field of dental implantology (Cook and Rust-Dawicki, 1995). Finite element analysis (FEA) is a commonly used method for evaluating the biomechanical behavior of dental implants in vitro (Borchers and Reichart, 1983, Cook et al., 1982, Geng et al., 2001, Guan et al., 2010, Lewinstein et al., 1995, Van Staden et al., 2006, Weinstein et al., 1979, Wider et al., 1976). This method was therefore also used to evaluate the stress distribution during load transfer of a PEEK dental implant reinforced with 30% chopped carbon fibers and a titanium dental implant (Sarot et al., 2010). The authors of the latter study concluded that under an oblique loading condition the carbon fiber reinforced (CFR-) PEEK dental implant shows higher stress peaks at the bone-implant interface due to a higher deformation, whereas the titanium implant shows a more homogenous stress distribution. This finding leads to the assumption that a stronger reinforced PEEK dental implant could show reduced stress peaks at the bone-implant interface due to a reduced elastic deformation.
Endolign® (Invibio Ltd., Thornton-Cleveleys, UK) is a CFR-PEEK with 60% parallel oriented endless carbon fibers. It represents the upper limit of PEEK compounds regarding its elastic modulus as per the manufacturer of 150 GPa, which is higher than that of titanium (110 GPa).
The aim of the present FEA was to evaluate the bone’s stresses and deformations during loading of three platform-switched dental implants with a uniform design, each modeled of a distinct material. The materials used for the different implant types were two different PEEK compounds representing new implant materials and titanium, which served as control.
Section snippets
3D model
A 3D section of a left human mandible bone was derived from a computer tomography scan of a 29-year-old male and saved as ⁎.stl data. The solid geometry of the mandible including the cancellous bone and the cortical layer was rebuilt from the ⁎.stl data with Creo Parametric 2.0 (PTC, Needham, MA 02494, USA). The dimensions of the section of the bony mandible are presented in Fig. 1(1.1).
For reasons of simplification, a cylindrical platform-switched implant of 10 mm length and 4.5 mm width was
Results
The maximum values of the two evaluated parameters (Von Mises stress and deformation) occurring within the peri-implant bone caused by loading are summarized in Table 4.
For a better traceability of these values, the pictures resulting from the FEA demonstrate the effects on the peri-implant bone caused by loading (Fig. 4, Cook and Rust-Dawicki, 1995).
In both load cases the titanium and the CFR-PEEK assembly showed similar maximum values for the two evaluated parameters. The pure PEEK assembly
Discussion
For the specific two load cases of the current study, the implant assemblies showed a minimum safety factor regarding the yield strength of cortical bone at 121 MPa (Figs. 4 and 5). This means that no implant material failed due to an overloading of the cortical bone. This outcome may be influenced by various factors underlying the design of the set up and the FEA.
Conclusion
An implant of CFR-PEEK with 60% endless carbon fibers distributes the stresses in a similar manner as a titanium implant. If both properties, minimal deformability and minimal stress distribution during loading are required at once, the optimum amount of endless carbon fibers within the PEEK-matrix can be assumed at somewhere below 60% to obtain the most optimal elasticity.
Further investigations, including a more complex set up with more realistic material properties such as anisotropy, are
Conflict of interest statement
None.
Acknowledgements
This work was supported by the Central Innovation Programme for SMEs (ZIM) of the German Federal Ministry for Economic Affairs and Energy (Project management agency: AiF Projekt GmbH, Berlin; grant number ZIM—2863301KJ1).
The authors would like to thank the dental technicians Mr. Andreas Klar and Mr. Daniel Ellmann from R+K CAD/CAM Technologie GmbH & Co. KG for contributing their know-how to the implant design.
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