Optimising the Surface of Co-Cr-Mo-Ni-W Alloys for Dental Implants

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Co-Cr-based alloys are the basis of most dental implant systems. They are used due to their excellent mechanical properties such as stiffness and strength. Moreover, they offer high corrosion and wear resistance. Corrosion of metallic biomaterials is mainly caused by local acidification, which can result from mechanical abrasion of the protective passivated surface and/or by microbial colonization with bacteria such as Streptococcus mutans (Sm).

To prevent these phenomena, it is important to develop coatings to protect the alloy surfaces. In addition, new surface treatments improve the tribological performance of these alloys. One such treatment is the Kolsterising(A) process from Bodycote Hardiff GmbH. The aim of this study was to optimize the surface of a Co-Cr-Mo-Ni-W alloy by applying the K(A) treatment and characterize the result.

For the first time, we compared the tribological performance of a standard Co-Cr-Mo-Ni-W implant with an implant characterized by the K(A) treatment. We also investigated the effects of the surface treatment on the osteoblastic differentiation induced by BMP peptide in vitro and on the osteogenic activity measurable by alkaline phosphatase in vivo. We found that the K(A) treated implant showed a significantly better osteogenic activity compared to the untreated implant.

Furthermore, we evaluated the cytotoxicity of different Co-Cr alloys by using mouse fibroblasts and human bronchial epithelial cells (BEAS-2B). We found that all tested alloys were within the limits of cell viability. Furthermore, we found that the surface roughness and ions release of the alloys did not influence the cytotoxicity tested. These results confirm that the K(A) treatment is a suitable surface modification to enhance the biocompatibility of Co-Cr alloys. However, we must not forget that after 2025 only a well-founded justification with sufficient evidence can lead to the granting of a CE mark for a device containing Co as CMR substance.