A novel three-dimensionally printed model to assess biofilm removal by ultrasonically activated irrigation

Aim: To apply an innovative three-dimensionally printed tooth model to investigate the efficacy of three ultrasonically activated irrigation (UAI) systems in removing multispecies biofilms from dentine samples. Methodology: Three-dimensionally printed teeth with a curved root canal were fabricated with a standardized slot in the apical third of the root to achieve precision fit of human root dentine specimens. Multispecies biofilms including Enterococcus faecalis, Streptococcus mitis and Campylobacter rectus were developed in the root canal for 21 days. The canals were allocated to be irrigated with 1% sodium hypochlorite (NaOCl) using a syringe and needle or ultrasonically activated NaOCl with a stainless-steel file (Irrisafe), a conventional nickel-titanium (Ni-Ti) file (CK) or a blue heat-treated Ni-Ti file (Endosonic Blue). Infected root canals irrigated with distilled water served as controls. Bacterial reduction was determined by colony-forming unit (CFU) counting (n = 20), whilst biofilms were analysed using confocal laser scanning microscopy (n = 7) and field emission scanning electron microscopy. For CFU counting, the independent two-sample t-test (Welch's t-test) was examined to compare overall bacterial reduction amongst groups. For CLSM analysis, the data were analysed using one-way analysis of variance (ANOVA), followed by the Scheffé post hoc test. The p-values <.05 were considered to indicate statistical significance. Results: All groups in which NaOCl was ultrasonically activated had significantly lower CFU values than the syringe-and-needle irrigation and control groups (p <.05). Ultrasonic activation with the stainless-steel file and blue heat-treated Ni-Ti file significantly reduced the biofilm volume compared with other groups (p <.05). Overall, UAI with the blue heat-treated file resulted in the highest antibacterial and biofilm removal efficacy. Conclusions: UAI with different inserts had differential antibiofilm effects. The blue heat-treated Ni-Ti ultrasonic insert resulted in the greatest antibacterial and biofilm removal from dentine in this standardized root canal model.