Nanosized Bioactive Glass: A High Potential Material for Root Canal Treatments

Bioactive glasses are potentially interesting materials in dentistry not only because of their ability to mineralize dentine [1] but also due to their antimicrobial effect in closed systems [2]. We investigated nanometric bioactive glasses because of their higher surface area and their faster mode of action. We tested the hypothesis whether nano-sized bioactive glasses can kill microbiota via mineralization or the release of ions other than sodium [3]. Flame-spray synthesis was applied to produce nanometric glasses (Figure) with different sodium content. Standardized bovine dentine disks with adherent Enterococcus faecalis bacteria were exposed to test and control suspensions. Furthermore, we tested the antimicrobial effectiveness of nanosized vs. microsized bioactive glass in extracted human premolars mono-infected with E. faecalis bacteria [4]. Sodium containing glasses induced pH levels above 12, compared to less than pH 9 with sodium-free glasses. Calcium hydroxide and the sodium containing glasses killed all bacteria after 1 d. The study revealed that bioactive glasses have both, a non- and a directly pH-related antibacterial effect. The former is due to ion release rather than mineralization. However, when using bioactive glass in the entombed environment of a root canal, both alkaline induction and alkaline capacity are important. Nanometric material had a 12-fold higher specific surface area and high alkaline induction but the micrometric counterpart had a considerably higher alkaline capacity and thus disinfected significantly better. Our study shows that nanoparticulate biomaterial can have a strong combined antimicrobial action but can lack of alkaline capacity when applied as slurry in an entombed environment. Figure: Transmission electron microscopy image of bioactive glass nanoparticles (left). Scannning electron microscopy image of a dentine surface after treatment for 1 week with ultrafine bioactive glass showing no viable bacteria (right). References [1] M. Vollenweider, T.J. Brunner, S. Knecht, R.N. Grass, M. Zehnder, T. Imfeld, W.J. Stark, Acta Biomater., 2007, 3(6), 936-43. [2] P. Stoor, E. Soderling and J.I. Salonen, Acta Odontol. Scand., 1998, 56(3), 161-5. [3] M. Gubler, T.J. Brunner, M. Zehnder, T. Waltimo, B. Sener and W.J. Stark, Int. Endod. J., 2008, 41, 670-8. [4] T. Waltimo, D. Mohn, F. Paqué, T.J. Brunner, W.J. Stark, T. Imfeld, M. Schätzle and M. Zehnder, J. Dent. Res., 2009, 88(3), 235-8.