Cation-doped bioactive ceramics: In vitro bioactivity and effect against bacteria of the oral cavity

We synthesized, using a solid-state reaction, bioactive ceramics of the SiO2-CaO-Na2O-P2O5 system doped with up to 3 mol% of Ag, Mg, Sr, Zn, and Ga, elements that were used as therapeutic agents. On evaluating the in vitro bioactivity of our crystalline samples using the ICG-TC04 method (so far only tested for glassy materials), we observed that those ceramics containing up to 0.5 mol% dopant exhibited hydroxycarbonate apatite (HCA) layer formation on their surfaces in a 24-h in vitro assay - the same time observed for Bioglass*, the material considered to be "gold standard" in terms of bioactivity. The antibacterial activity of these ceramics was confirmed against 23 oral bacteria, related to caries and endodontic infections, by employing three different methods. For the agar dilution method, using a concentration range of 0.5-24 mg/mL, various bacteria were found to be susceptible to the materials - the lowest minimum inhibitory concentration (MIC) values were achieved for the doped samples, particularly those containing Ag. In the biofilm-forming capability assay, we did not observe any viable cells after 24 h incubation. Finally, the direct contact assay confirmed that all the samples showed a stronger antibacterial effect, promoting a significant reduction in the number of viable cells after only 10 min in contact with the microorganisms. This result indicates that the tested materials have an intrinsic antibacterial activity, and do not need to be doped, except for some specific bacteria or depending on how they will be used (extracts or in direct contact). Therefore, besides easy production and in vitro bioactivity, all tested materials demonstrated a considerable antibacterial effect against representative bacteria, stimulating future studies involving their application as topical endodontic disinfectants or in dental prophylaxis procedures.