In vivo evaluation of microbial reduction after chemo-mechanical preparation of human root canals containing necrotic pulp tissue.

AIM To determine in vivo, the degree of microbial reduction after chemo-mechanical preparation of human root canals containing necrotic pulp tissue when using two endodontic irrigating reagents, sodium hypochlorite (NaOCl) or chlorhexidine gel (CHX). METHODOLOGY Thirty-two single rooted teeth with necrotic pulp were divided into two groups. One group (n=16) was irrigated with 2.5% NaOCl, whilst the other group (n=16) was irrigated with 2% CHX gel. Assessment of the bacterial load was accomplished by use of real-time quantitative-polymerase chain reaction (RTQ-PCR) directed against the small subunit ribosomal DNA using the SYBRGreen and TaqMan formats. Statistical analysis was performed using the Mann-Whitney test. For contrast, bacterial load was also determined by traditional culture techniques. RESULTS The bacterial load was reduced substantially in both groups (over 96%). However, using RTQ-PCR the bacterial load before and after chemo-mechanical preparation was greater when compared with evaluation using colony forming units (CFU). Furthermore, as measured by RTQ-PCR, the bacterial reduction in the NaOCl-group (SYBRGreen 99.99%; TaqMan: 99.63%) was significantly greater (P<0.01) than in the CHX-group (SYBRGreen 96.62%; TaqMan: 96.60%). According to culture technique 75% of cases were free of bacteria after chemo-mechanical preparation in the NaOCl-group, whilst 50% of cases were bacteria free in the CHX-group. CONCLUSION NaOCl has not only a higher capacity to kill microorganisms but is also more able to remove cells from the root canal.