In vitro investigation of biofunctional response of fibroblasts osteoblasts toward roughened, injection-moulded zirconia implant material

Background

The high strength and exceptional biocompatibility qualified zirconia to be one of the leading bioceramics. Zirconia may outperform titanium as an implant material. This can be attributed to optimum aesthetics, antibacterial properties and periointegration capacity. Achieving a rough zirconia surface is major challenge due to insolubility, high surface hardness and Young's modulus. Injection of molten zirconia in a roughened mould may overcome such problem.

Aim/Hypothesis

The present study aimed to compare the surface characteristics of a SLActive-like titanium surface and an MDS zirconia surface as well as the biofunctional response of fibroblasts and osteoblasts toward these surfaces.

Material and Methods

Confocal laser microscope (CLM) was used to obtain 3D topographic maps and to determine surface roughness parameters for acid-etched, injection-moulded zirconia (MDS-Zr) and sandblasted, acid-etched cpTi (Ti) discs (n = 10 p/g). Scanning electron microscope (SEM) was used to examine surface topography of representative samples of each group.

Human gingival fibroblasts (HGF) and human osteosarcoma cells from G-292 cell line were seeded on three discs from each group with seeding density equals to 5 × 104 cell/well. Tissue culture plastic was used as a control (TCP). The cells were incubated for 24 hours, 1, 2 and 3 weeks periods. Proliferation of both cell types was calculated by means of cell number and doubling time. The percentage of viable, pre-apoptotic, apoptotic and dead cells as a result of necrosis was determined using flow cytometry technique.

SPSS statistics, version 19 (IBM, USA) was used to compare findings among the experimental groups.

Results

Ti surface appeared significantly rougher than MDS-Zr on SEM images. There was no significant difference in the fold increase of surface area, Havg, Ra and Rq values between MDS-Zr and Ti surfaces (ANOVA- P > 0.05). Ti surface demonstrated the higher mean maximum peak height (Rp) and maximum valley depth (Rv) (Kruskal-Wallis- P < 0.05). The mean doubling time of HGF and G-292 cells seeded on TCP and MDS-Zr was significantly lower than that for cells seeded on Ti (ANOVA- P < 0.05). Total cell counts varied according incubation period. HGF and G-292 counts were significantly higher in MDS-Zr TCP compared to Ti at 24 hours and 1 week. After 2 and 3 weeks incubation, difference in total cell counts became statistically insignificant. All studied surfaces exhibited high cytocompatibility after all incubation periods (>87% viability). MDS surface induced the least amount of HGF necrosis. Ti had higher viability percentage compared to MDS-Zr and TCP at 2 weeks (P < 0.05).

Conclusion and Clinical Implications

The MDS-Zr surface exhibited moderate roughness and high biocompatibility when tested with HGF and G-292 cells. The findings of this study indicate that a rough zirconia implant surface can be achieved using injection moulding and acid etching. The short doubling time indicates high osteoconductive capacity. Shorter healing times, faster loading and better osseointegration in compromised surgical sites are all theoretical advantages for such surface that should be further explored and verified.