Study of the Sealing and Antibacterial Properties of Bioceramic Root Canal Sealers Modified With Quaternary Ammonium Salt

Objective  To modify the non-antibacterial bioceramic root canal sealant iRoot SP with the quaternary ammonium salt dimethylaminododecyl methacrylate (DMADDM) and to develop a new type of sealant.

Methods  The cytotoxicity of the modified root canal sealant was evaluated using the cell counting kit-8 (CCK-8). The solubility and flowability of the sealant were tested according to International Organization for Standardization (ISO) methods. The sealing ability and penetrability of the sealant were assessed by micro-computed tomography (micro-CT) and confocal laser scanning microscope (CLSM). The antibacterial activity of the sealant against Enterococcus faecalis biofilm was evaluated by colony-forming unit (CFU) counting, crystal violet staining, scanning electron microscope (SEM), and live/dead staining.

Results  When the DMADDM mass fraction was 0.625%, the modified sealant demonstrated good biocompatibility (P > 0.0125). The flowability (> 17 mm) and solubility (< 3%) of the sealant modified with 0.625% DMADDM met ISO standards and showed no significant difference compared with iRoot SP. DMADDM modification did not affect the sealing ability or penetrability of the sealant at different positions of the tooth root (P > 0.05). Antibacterial experiments showed that the modified sealant reduced the CFU count (0.518 ± 0.333 vs. 8.156 ± 0.011, P < 0.001) and the amount of biofilm (mean difference of 86.94%, 95% confidence interval: 74.82%-99.07%, P < 0.0001) of Enterococcus faecalis biofilm at the unaged stage. However, after 1 week of aging (7.327 ± 0.068 vs. 7.422 ± 0.035) or 4 weeks of aging (7.479 ± 0.065 vs. 7.581 ± 0.071), the CFU count of the modified sealant showed no significant difference from the iRoot SP group (P > 0.05). Live/dead staining and SEM also showed that the modified sealant could inhibit the formation of Enterococcus faecalis biofilm.

Conclusion  iRoot SP modified with 0.625% DMADDM exhibited good biocompatibility, sealing ability, and penetrability, and significantly improved resistance to Enterococcus faecalis biofilm, providing a new approach for the antibacterial modification of bioceramic root canal sealants.