Advancing dental implants: Bioactive and therapeutic modifications of zirconia

Abstract

Zirconium-based implants have gained popularity in the dental implant field owing to their corrosion resistance and biocompatibility, attributed to the formation of a native zirconia (ZrO₂) film. However, enhanced bioactivity and local therapy from such implants are desirable to enable the earlier establishment and improved long-term maintenance of implant integration, especially in compromised patient conditions. As a result, surface modification of zirconium-based implants have been performed using various physical, chemical and biological techniques at the macro-, micro-, and nano-scales. In this extensive review, we discuss and detail the development of Zr implants covering the spectrum from past and present advancements to future perspectives, arriving at the next generation of highly bioactive and therapeutic nano-engineered Zr-based implants. The review provides in-depth knowledge of the bioactive/therapeutic value of surface modification of Zr implants in dental implant applications focusing on clinical translation.

Keywords: Bioactivity; Implants; Local therapy; Osseointegration; Surface modification; Zirconia; Zirconium.

Graphical abstract

Fig. 1

Surface modification of Zirconia implants. Schematic representation of various surface topographical, bioactive and chemical modifications and the nano-engineered topographies.

Fig. 2

ZrTi alloy implant modified with hydroxyapatite and silver. Histology of bone tissue at implant surfaces post-implantation in pig tibiae after one month. Bone tissue around ZrTi alloys coated with a composite of hydroxyapatite-zirconia-silver layer (HAP-ZrO₂-Ag; A-F) and uncoated ZrTi alloys (control group; G, H). (A, C, E, G) Bone area adjacent to the implant (<2500 μm); (B, D, F, H) bone area 2500–6000 μm to the implant surfaces. For all coated ZrTi implants, the newly generated bone (yellow arrows) was evident after one-month healing with numerous cuboid-shaped osteoblasts infiltration (red arrows and green arrows). Less bone formation was observed around non-coated ZrTi surface, with numerous macrophages infiltration (black arrows). Adapted with permission from Ref. [5].

Fig. 3

Protein incorporated zirconia implants. Zr-1/Zr-3: Non-coated Zr surface; Zr-4/Zr-5: Bone morphogenetic protein-2 (BMP-2) coated Zr; Zr-6/Zr-7: Growth differentiation factor-5 (GDF-5) coated Zr surface. (A) BMP-2 and GDF-5 coatings augmented in vitro alkaline phosphatase (ALP) activity levels of MG-63 osteoblasts at day 7 and 14 on Zr surface. (B) Alizarin red staining showing enhanced calcium deposition from MG-63 osteoblasts on BMP-2 and GDF-5 coated Zr surfaces. (C) Increased mRNA expression of ALP and osteopontin (OPN) from MG-63 cells on BMP-2 and GDF-5 coated Zr surface. Adapted with permission from Ref. [4].

Fig. 4

Ultraviolet (UV) irradiated ZrO₂ surfaces. (A) Photograph of water droplet on untreated and UV treated ZrO₂ surface indicating a shift from hydrophobic to hydrophilic upon UV exposure. (B) Water contact angle of ZrO₂ surface at various treatment times. (C) Initial spread and cytoskeleton of osteoblasts (3 h post cell seeding on treated and untreated surface). (D) ALP activity. (E) Osteogenic marker gene expression. Adapted with permission from Ref. [1].