Osteoblast integration of dental implant materials after challenge by sub-gingival pathogens: a co-culture study in vitro

Sub-gingival anaerobic pathogens can colonize an implant surface to compromise osseointegration of dental implants once the soft tissue seal around the neck of an implant is broken. In vitro evaluations of implant materials are usually done in monoculture studies involving either tissue integration or bacterial colonization. Co-culture models, in which tissue cells and bacteria battle simultaneously for estate on an implant surface, have been demonstrated to provide a better in vitro mimic of the clinical situation. Here we aim to compare the surface coverage by U2OS osteoblasts cells prior to and after challenge by two anaerobic sub-gingival pathogens in a co-culture model on differently modified titanium (Ti), titanium-zirconium (TiZr) alloys and zirconia surfaces. Monoculture studies with either U2OS osteoblasts or bacteria were also carried out and indicated significant differences in biofilm formation between the implant materials, but interactions with U2OS osteoblasts were favourable on all materials. Adhering U2OS osteoblasts cells, however, were significantly more displaced from differently modified Ti surfaces by challenging sub-gingival pathogens than from TiZr alloys and zirconia variants. Combined with previous work employing a co-culture model consisting of human gingival fibroblasts and supra-gingival oral bacteria, results point to a different material selection to stimulate the formation of a soft tissue seal as compared to preservation of osseointegration under the unsterile conditions of the oral cavity. The risk of infection may be reduced by constructing dental implants from combinations of materials that resist bacterial growth. Microbes can potentially form antibiotic-resistant biofilms on the surface of implants, particularly if the surrounding tissue does not form a tight seal. Researchers led by Yijin Ren at the University of Groningen in The Netherlands devised a ‘coculture’ model to study how oral bacteria interfere with bone cell growth on different implant materials. Although smooth titanium surfaces work well in gum tissue, the researchers found that oral bacteria readily displaced bone cells from this material. Materials based on zirconium or titanium-zirconium alloys provided a far more hospitable environment for bone cell growth, even amid biofilm-forming pathogens. These results suggest that implants composed of two different materials may facilitate better integration of implants.