Finite element analysis of the biomechanical effects of PEEK dental implants on the peri-implant bone

https://doi.org/10.1016/j.jbiomech.2014.11.017Get rights and content

Abstract

Dental implants are mostly fabricated of titanium. Potential problems associated with these implants are discussed in the literature, for example, overloading of the jawbone during mastication due to the significant difference in the elastic moduli of titanium (110 GPa) and bone (≈1–30 GPa). Therefore poly-ether-ether-ketone (PEEK) could represent an alternative biomaterial (elastic modulus 3–4 GPa). Endolign® represents an implantable carbon fiber reinforced (CFR)-PEEK including parallel oriented endless carbon fibers. According to the manufacturer it has an elastic modulus of 150 GPa. PEEK compounds filled with powders show an elastic modulus around 4 GPa.

The aim of the present finite element analysis was to point out the differences in the biomechanical behavior of a dental implant of Endolign® and a commercial powder-filled PEEK. Titanium served as control.

These three materials were used for a platform-switched dental implant-abutment assembly, whereas Type 1 completely consisted of titanium, Type 2 of a powder-filled PEEK and Type 3 of Endolign®. A force of 100 N was applied vertically and of 30° to the implant axis.

All types showed a minimum safety factor regarding the yield strength of cortical bone. However, within the limits of this study the Type 2 implant showed higher stresses within the adjacent cortical bone than Type 1 and Type 3. These implant assemblies showed similar stress distributions.

Endless carbon fibers give PEEK a high stability. Further investigations are necessary to evaluate whether there is a distinct amount of endless carbon fibers causing an optimal stress distribution behavior of CFR-PEEK.

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.

References (27)

  • V. Demenko et al.

    Ultimate masticatory force as a criterion in implant selection

    J. Dent. Res.

    (2011)
  • S.G. Gomes et al.

    Chewing side, bite force symmetry, and occlusal contact area of subjects with different facial vertical patterns

    Braz. Oral Res

    (2011)
  • H. Guan et al.

    Evaluation of multiple implant-bone parameters on stress characteristics in the mandible under traumatic loading conditions

    Int. J. Oral Maxillofac. Implants

    (2010)
  • Cited by (111)

    • Patient-specific mechanical analysis of PCL periodontal membrane: Modeling and simulation

      2024, Journal of the Mechanical Behavior of Biomedical Materials
    View all citing articles on Scopus
    View full text