Disinfection effects of MTAD on apical isthmus of the root canal system: a scanning electron microscopic evaluation

Abstract

OBJECTIVE: To evaluate the disinfection efficacy of MTAD on Enterococcus faecalis biofilm and smear layer colonization in apical isthums of the root canal system. METHODS: Fifteen extracted human maxillary first premolars with isthmus anatomic structure which confirmed by stereo-microscope were contaminated with E. faecalis in vitro and randomly divided into 5 groups: the first group was not treated serving as a baseline control, the second group was treated by normal saline (NS) serving as negative control, the third group was treated by MTAD , the forth group by 5.25% NaOCl, and the fifth group by 5.25% NaOCl + EDTA. All roots in the latter four groups were instrumented by Protaper rotary files and irrigated with respective irrigant, then the roots were split longitudinally and a scanning electron microscope was used to evaluate the antibacterial activity and smear layer cleaning ability of irrigants on isthmus. RESULTS: In the first group, E. faecalis colonized on the isthmus surface and aggregated together to form biofilm-like microorganism community, some bacteria also colonized in the dentinal tubules. When treated with NS, both smear layer and bacteria remained (median of smear layer score was 5). MTAD can remove partial smear layer, and have limited antibacterial activity, some bacteria embedded in smear layer (the median was 3) and were destroyed; In 5.25% NaOCl treatmentgroup, the smear layer was not removed (median of smear layer score was also 5), but all bacteria on the surface were extinguished. The combined use of 5.25% NaOCl and EDTA produced a cleaner isthmus surface and had marked antimicrobial effect, with the median of smear layer score being only 1. CONCLUSION: MTAD may permeate into the isthmus area of apical root canal system, but only performed a partial effect of disinfection and limited antibacterial activity. Sodium hypochlorite cooperated with EDTA can remove infection effectively in the isthmus area.