Nanobubble-Enhanced Antimicrobial Agents: A Promising Approach for Regenerative Endodontics

In this study, we investigated the properties of nanobubble (NB) water and its effect on smear layer removal and strengthening the efficiency of disinfecting agents used in regenerative endodontic treatment.

NB water was generated in a NB Generator. The NB size, concentration, and pH were measured. Porcine teeth were enlarged to size 60 by using hand-files and irrigated with either NB water or 17% EDTA or received no further irrigation. The ability of irrigants to remove the smear layer was evaluated by using a scanning electron microscope (9 roots/group). Other samples (6 roots/group) were subjected to Vickers hardness test to determine the dentin microhardness. Autofluorescent tetracycline mixed with distilled water or NB water was placed inside the root canal space of porcine teeth, and the depth of medicament penetration into the dentinal tubules was visualized by using fluorescent stereomicroscope (5 roots/group). For the disinfection experiment, human roots were prepared, autoclaved, and inoculated with Enterococcus faecalis for 3 weeks. Canals were then disinfected by (1) standard needle irrigation (SNI) with 5.25% NaOCl, (2) 5.25% NaOCl with ultrasonication (US), (3) 5.25% NaOCl + XP finisher (XP), (4) SNI with 1.5% NaOCl, or (5) SNI with 1.5% NaOCl in NB water (5 roots/group). Teeth were split open and stained with LIVE/DEAD BackLight and visualized by using confocal laser scanning microscope (CLSM) at the coronal, middle, and apical thirds of the canal. The ratio of dead/total bacteria in the dentinal tubules at various depth levels (50, 100, and 150 μm) was calculated.

NB water was more effective in removing smear layer than 17% EDTA and could allow infiltration of tetracycline into the dentinal tubule more than 1 mm. NB water did not alter the dentin microhardness compared with 17% EDTA (P < .05). At 50-μm depth, CLSM analysis showed no statistically significant difference between 1.5% NaOCl in NB water and 5.25% NaOCl with or without irrigation activation at the coronal, middle, and apical root segments (P > .05), ie, these groups had stronger bacterial killing than 1.5% NaOCl (P < .05). At deeper levels (100 and 150 μm), higher concentrations of NaOCl were more effective than 1.5% NaOCl with or without NB water. No statistically significant difference was noted between 5.25% NaOCl with and without irrigation activation at most depth levels (P > .05).

NB water can allow smear layer removal and enhance tubular penetration of medicaments without changing dentin microhardness. In large canal models, NB water appears to improve the tubular disinfection capacity of lower concentration of NaOCl up to 50 μm. On the other hand, the use of irrigation activation (US or XP) did not provide any added disinfection into the dentinal tubules compared with SNI. These results suggest that NB water may be a promising adjunct to endodontic irrigants and medicaments.