Biocompatibility of polymer infiltrated ceramic network materials

The development of computer-aided design and manufacturing (CAD-CAM) processes generated the recent emergence of innovative prosthetic materials, especially for the manufacture of transgingival implant components. In particular, Polymer Infiltrated Ceramic Network (PICN) materials look as a promising alternative to ceramics especially because of their good biomechanical properties, which are the consequence of their specific microstructure and innovative polymerization mode. However, the biological properties of these new materials, which are crucial in implant prosthetics, have been little studied.
Therefore, the main objective of this work was to evaluate, in vitro, the biocompatibility of PICNs in comparison with current metallic and ceramic materials used for implant prostheses: titanium, zirconia and lithium disilicate glass-ceramic. The attachment, proliferation and spreading of human gingival fibroblasts (HGFs) and keratinocytes (HGKs) were evaluated. Titanium and zirconia showed the best results and can be considered as the gold standard of materials in terms of HGF and HGK behavior. On the other hand, PICNs presented intermediate and comparable or slightly better results than lithium disilicate glass-ceramics. The favorable behavior of PICNs, which are composite materials, compared to glass-ceramics was notably explained by the hypothesis of the influence of their high temperature and high pressure (HT-HP) innovative polymerization mode. Indeed, the polymerization mode and the degree of monomer conversion were previously reported to affect toxicity and cellular response. Therefore, the secondary objective of this study was to measure the indirect cytotoxicity of PICNs and the free monomer release from the tested samples. The results were found to be negative, reinforcing the idea that HT-HP polymerization mode could promote the biocompatibility of PICNs. On the other hand, many surface properties being reputed to influence cell adhesion and proliferation, so the sample surface was characterized in terms of roughness, contact angle, surface morphology and chemistry. A correlation between cellular behavior and contact angle was established but none could be observed with surface roughness. Glass-ceramics were found to be much too hydrophilic while PICNs were slightly too hydrophobic compared to titanium and zirconia. These results highlight the complexity of the influence of material properties on cell behavior.
The impact of PICN encouraging in vitro results with HGFs and HGKs now needs to be clinically investigated in regards to gingival tissues and implant health before recommending their routine use as transgingival prosthesis components, particularly for bone-level implants.