Differential Cytotoxic Effects Elicited by Three Commonly Used Endodontic Irrigants

Objectives: Success of endodontic treatment greatly depends on the elimination of bacteria, necrotic tissue and other contents from instrumented pulp canals. Aside from instrumentation, this is achieved using canal irrigating solutions. However, the beneficial actions of canal irrigants may be offset by cytotoxicity, occurring when irrigants contact periapical tissues. The acute cytotoxicity of the following irrigants was evaluated: sodium hypochlorite (NaOCl, Javex Fibreguard, Colgate-Palmolive), ethylenediaminetetraacetic acid (EDTA, Pulpdent) and BioPure MTAD (DENTSPLY Tulsa Dental).

Methods: UMR-106 osteoblast-like cells were incubated for 5 or 15 min in medium containing 17% EDTA, 100% MTAD or 4% NaOCl, four 2-fold serial dilutions of each irrigant or medium alone (control). Irrigants were removed and cell survival evaluated using the MTT-tetrazolium assay. Cell survival was compared to control, and the half-maximal inhibitory concentration (IC₅₀) was determined for each irrigant.

Results: All EDTA concentrations (1-17%) and low concentrations of NaOCl (0.25-1%) had no significant toxicity at either exposure time. Similarly, the lowest concentration of MTAD (6.25%) was not toxic at 5 min; however, it reduced cell viability at 15 min (P<0.05). NaOCl (2-4%) and all other MTAD concentrations (12.5-100%) were cytotoxic at both exposure times (P<0.05). IC₅₀s for NaOCl (1.6% at 5 min, 1.4% at 15 min) fell within the range of concentrations used clinically (0.5-5.25%). IC₅₀s for MTAD (7.5% at 5 min, 6.7% at 15 min) were markedly lower than the concentration used clinically (100%).

Conclusions: EDTA and low concentrations of NaOCl and MTAD did not inhibit cell survival indicating adequate short-term tolerability. In contrast, higher concentrations of NaOCl and MTAD (at levels used clinically) induced significant cytotoxicity.

These studies were funded in part by the Canadian Institutes of Health Research (Grant # 10854).