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UBC Theses and Dissertations

Dynamic dissolution and inhibition of biofilm development by endodontic disinfecting agents Wang, Zhejun


Many disinfecting solutions have been developed to disrupt the biofilm and to kill biofilm bacteria. However, there is little data so far showing dynamic dissolution on biofilm. The present study aims to establish a standardized model that makes it possible to evaluate the dynamic dissolution of biofilm and inhibition of growth of multispecies biofilm by endodontic irrigation solutions. Biofilm was grown from plaque bacteria on collagen coated hydroxyapatite (HA) disks in brain-heart infusion broth for 3 days or 3 weeks under anaerobic conditions. Biofilms were stained by the LIVE/DEAD viability stain and subjected to sterile water, 2% sodium hypochlorite (NaOCl), 6% NaOCl, or 2% chlorhexidine (CHX) for 32 minutes. Dynamic change in fluorescence from each biofilm sample after treatment was analyzed using a live-cell imaging confocal laser scanning microscopy (LC-CLSM). Biovolume and proportion of dead bacteria were calculated. The biofilm structures after treatments were visualized by scanning electron microscopy (SEM). The treated biofilms on HA disks were collected and cultured on blood agar plates for the colony forming unit (CFU) test. Another set of sterile HA disks were immersed in 2%, 0.2% or 0.02% CHX solutions for 3 minutes. Plaque biofilm growth on these disks was monitored by LC-CLSM for 12 hours. For 3-day-old biofilms, 2% and 6% NaOCl reduced the biovolume by 63% and 94% in 32 minutes respectively. For 3-week-old biofilms, 75% and 86% of the biofilm was dissolved by 2% and 6% NaOCl respectively in 32 minutes. Six percent NaOCl was the most effective in dissolving and killing bacteria followed by 2% NaOCl and CHX. CFU results indicated difference in bacterial reduction between biofilm and planktonic culturing after disinfection. SEM showed biofilm bacteria disruption after CHX and NaOCl treatments. The use of 2% CHX and sterile water did not result in biofilm dissolution. However, prior exposure of HA disks to 2% and 0.2% CHX for 3 minutes prevented biofilm from growing on HA disk surfaces for at least 12 hours. In conclusion, NaOCl dissolved biofilm effectively, more with higher concentration and longer time of exposure. CHX does not dissolve biofilm but inhibits biofilm growth on HA surface.

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