RESIDUAL ANTIMICROBIAL ACTIVITY AFTER CANAL IRRIGATION WITH CHLORHEXIDINE

We previously reported that the in vitro antimicrobial activity of a 2 .0% chlorhexidine endodontic irrigant was equivalent to that of 5.25% sodium hypochlorite. The purpose of this study was to determine if chl orhexidine irrigants could instill substantive antimicrobial activity in instrumented root canals in vitro, Human teeth were instrumented us ing 2.0% or 0.12% chlorhexidine as irrigants. After instrumentation, t he root canals were filled with sterile water, and samples of the root canal fluid were absorbed with paper points at 6, 12, 24, 48, and 72 h after treatment, The paper points were assayed for antimicrobial act ivity by placing them on agar plate surfaces inoculated with Streptoco ccus mutans and measuring zones of inhibition, Antimicrobial activity was present in all 2.0% chlorhexidine-treated teeth throughout the 72- h testing period and in most teeth, in relatively lower concentrations , for 6 to 24 h after irrigation with 0.12% chlorhexidine. These resul ts indicate that chlorhexidine instills substantive antimicrobial acti vity when used as an endodontic irrigant.