Fatigue properties of a dental implant produced by electron beam melting® (EBM)

doi:10.1016/j.jmatprotec.2015.07.013

Journal of Materials Processing Technology

Volume 226, December 2015, Pages 255-263

https://doi.org/10.1016/j.jmatprotec.2015.07.013 Get rights and content

Highlights

•
The fatigue properties of a dental implant with lattice abutment were investigated.
•
Fatigue crack could be initiated from the partially sintered powder particles.
•
Sharp corners in the design showed the highest risk of failure under cyclic loads.
•
An equation was developed to predict the fatigue life of the designed dental implant.

Abstract

Fatigue properties of a dental abutment with a lattice structure were investigated. Electron Beam Melting® (EBM) was used to produce the dental abutments, made of Ti-6Al-4 V. Four levels of cyclic loads including 100 N, 200 N, 300 N, and 500 N were applied at 15 Hz by using a sinusoidal wave form, and the loading ratio of 10%. According to the experimental results of fatigue test, the dental abutment tolerated the five million cycles of loading at 100 N. Results of fractography suggested that the fatigue crack can be initiated from the partially sintered powder particles that were attached to the truss surface. The numerical results revealed the deleterious influence of sharp corners on lowering the fatigue life of the structure. The high level of surface roughness and the lower relative density of a lattice structure could affect its strain rate sensitivity and consequently lower the endurance limit of the lattice structure. The comparison of the experimental data and numerical modeling suggested that the more conservative Soderbrg relationship for the mean stress correction could be used for numerical modeling of fatigue in lattice structures produced by EBM®. Finally, a regression equation was developed from the experimental results that can be used to predict the fatigue life of the designed dental abutment.

Graphical abstract

Introduction

The ability of additive manufacturing (AM) processes to produce components with very complex designs is one of the unique advantages of the AM technologies that can be applied in biomedical applications. However, an understanding of the effect of implant design on its mechanical performance is required for any further improvement. Some studies have been performed to investigate the influence of a dental implant design on its mechanical properties. Baggi et al. (2008) showed that a change in the length of the dental implant can affect the stress distribution in the cancellous bone, while the implant diameter can change the level of stress in the cortical bone. According to Chun et al. (2002), the most effective results of stress distribution in the jawbone were achieved when a square-shaped design was used for the threads.

Other than the design of a dental implant, the interaction between biting force and the tooth bone is another parameter that needs to be considered. Any natural tooth is surrounded by a thin layer of periodontal ligament (Misch and Carl Contemporary, 2007). The elastic properties of the periodontal ligament provide the natural tooth with three-dimensional (3D) micro-displacements in response to the applied biting force. By extracting a natural tooth, the surrounding periodontal ligament is destroyed as well. As a result, the biting force can be directly transferred to the jaw bone.

Another important factor in the design of an implant is the considerable difference between the mechanical properties of the bone and the implant. This difference can result in an issue known as stress shield. Stress shield is the main cause for bone atrophy that is defined as the reduction in the ability of the bone to be load bearing (Agrawal Mauli, 1998).

According to the above, development of an implant that can mimic the elastic properties and micro-displacement of a natural tooth is highly desirable. Some studies have been performed to develop a dental implant with elastic properties. A conical implant with a shock-absorbing unit made of three silicon rings was introduced by Gaggl and Schultes (2001). The silicon rings were responsible for absorbing the biting force. Wagher (1995) designed a dental implant with a spherical elastic media embedded at the bottom of the implant. Several metallic shafts with a limited vertical displacement were responsible for transferring the biting force to the elastic media. The mentioned of implants were constrained by two major issues including complexities in both production and maintenance. Therefore, finding a new design that satisfies the need for both simplicity and performance would be desirable. Chahine et al. (2008) studied on the development of a single-component dental implant. For this purpose, the geometry of the root in the natural tooth was captured by a Computed Tomography (CT) scanner. Then the CT data was transformed to a .stl format and was used to manufacture an implant of the same geometry as the natural tooth. In the next step, a bio-compatible dental implant could be developed by the combination of a root that mimics the natural tooth and a dental abutment with elastic micro-displacement. Jamshidinia et al. (2014) extended the mentioned study and used the EBM® process to investigate the application of non-stochastic lattice structures for building a bio-compatible dental abutment. Three different lattice structures including cross, honeycomb, and octahedral structures with different unit cell sizes were employed to produce a lattice abutment made of Ti-6Al-4 V by EBM®. According to the results, the octahedral lattice structure with a 2-mm unit cell size showed the best mechanical behavior under a 400-N normal biting force. Also, a numerical model was developed to study the influence of the biting force angle on the stress distribution developed in the lattice abutment. Numerical analysis showed that α = 30° is a critical biting force angle, at which the maximum equivalent stress increased noticeably (Jamshidinia, 2014).

After the development of a design for a dental implant, its functionality has to be verified under the cyclic loads as well. According to ISO 14801, any dental implant must tolerate at least 5 million cycles of loading at the loading frequency of 2–15 Hz (ISO 14801, 2007).

In this paper, the fatigue properties of a bio-compatible dental implant produced by a non-stochastic lattice structure were investigated. Four levels of biting forces were applied on the structure at a 30° angle to the abutment axis at the loading frequency of 15 Hz and loading ratio of 10%. Also, a numerical model was developed to investigate the influence of the biting load on the development of stress and strain and the resultant failure risk in the dental abutment with a lattice structure.

Section snippets

Material

In this study, Ti-6Al-4 V was used for the manufacturing of dental implants by the EBM® process. The mechanical properties of Ti-6Al-4 V applied in the numerical modeling of fatigue test could be found in (Jamshidinia, 2014). Also, a detailed description of the EBM® process can be found in literature such as (Jamshidinia et al., 2012, Jamshidinia et al., 2013a).

Design

In the previous study, three different types of lattice structures with different sizes were used for the fabrication of the lattice

Design

It was assumed that the specific geometry of the root did not have a major influence on the mechanical response of the lattice abutment under the cyclic load. Therefore, the complex structure of the root was replaced by a cubic structure. Fig. 3a shows the 3D view of the design used to build the dental abutment by EBM®. The hemispherical member had a radius of 4.65 mm, while the length, width, and height of the cubic structure were 10, 12, and 12.1 mm, respectively (Jamshidinia, 2013b).

Meshing

Experimental testing

Fig. 5 shows an image of the coupons that experienced the cyclic loads in the present study. As shown, only the coupons that were under the 100-N load were able to tolerate the five million cycles. At the other three load levels including 200 N, 300 N and 500 N, the lifetime of the designed abutment was less than the minimum requirement of the ISO 14801 standard.

Experimental results of the load-cycles and displacement-cycles for one of the coupons under the 500-N load were plotted in Fig. 6. It

Conclusion

The fatigue properties of a dental implant made of Ti-6Al-4 V were investigated. A previously optimized design including an octahedral lattice structure with 2-mm unit cell size was used to manufacture the dental implant by the Electron Beam Melting® (EBM) process. Four different levels of cyclic loads including 100 N, 200 N, 300 N, and 500 N were applied at a 30° angle on the implant, at the loading ratio of 10% and the loading frequency of 15 Hz. According to the results, the following could be

Acknowledgments

This work was financially supported by the U.S. Department of Education, GAANN Grant No. P200A090344 and by the NSF Grant No. IIP-1034652.

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Fatigue properties of a dental implant produced by electron beam melting® (EBM)

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Material

Design

Design

Meshing

Experimental testing

Conclusion

Acknowledgments

J. Pros. Dent.

Mater. Des.

Biomaterials

Int. J. Fatigue

J. Mater. Process. Technol.

Dent. Mater.

Adv. Eng. Software

Int. J. Fatigue

Dent. Mater.

Acta Mater.

Int. J. Fatigue

Int. J. Fatigue

Reconstructing the human body using biomaterials

JOM

The design and production of Ti-6Al-4V ELI customized dental implants

JOM

Fatigue life of titanium alloys fabricated by additive layer manufacturing techniques for dental implants

Metall. Mater. Trans. A

Fatigue properties of a dental implant produced by electron beam melting^® (EBM)