title: Cytotoxicity of a novel nano-silver particle endodontic irrigant.
abstract: OBJECTIVE
  The aim of this study was to evaluate the cytotoxic effect of a novel nano-silver particle (25.2±6.5 nm) endodontic irrigant (0.2 mM) and compare it with 3% sodium hypochlorite.
  
  
  METHODS
  Two cell types, mouse fibroblast National Institutes of Health 3T3 (NIH 3T3) and primary human periodontal ligament stem cell (hPDLSCs) were used in a test for the effect of direct and indirect (by separating the agent and cell with a layer of agar) exposure to the two solutions. In the direct exposure experiment, ten groups of cell cultures were exposed to one dilution (3:1, 2:1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6 or 1:7) of a nano-silver irrigant for 48 hours; the concentration-response function was estimated by determining the number of viable cells in each group by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The 50% lethal dose of the testing irrigant for NIH3T3 and hPDLSCs were estimated. In the second part of the experiment, a modified agar overlaying technique was applied. Twelve culture wells (6-well plate) were divided into three groups (n=4). The cell lysis zone (cytotoxic range) created by the stock nano-silver solution, 3% sodium hypochlorite, and an isotonic phosphate buffering saline (control) was measured by two double blinded observers (Kappa score =100%). The cytotoxic score of specific irrigant was derived by modified Sjögren's method.
  
  
  RESULTS
  The 50% lethal doses of the testing nano silver irrigant for NIH 3T3 and hPDLSCs after 48 hours of direct exposure were 0.58 and 0.608 dilution of stock solution, respectively. The cytotoxic scores of nano-silver irrigant and control (phosphate buffered saline) on NIH 3T3 were 0.25 (95% confidence interval [CI] =0 to 1.04) and 0 (95% CI =0 to 0); and on hPDLSCs were 0.13 (95% CI =0 to 0.52) and 0.25 (95% CI =0 to 1.04), respectively. Toxicity of the test and control group on both mouse fibroblasts (P>0.05) and hPDLSCs (P=1.00) was not statistically different.
  
  
  CONCLUSIONS
  Our results showed that the nano-silver irrigant was non-cytotoxic to both NIH 3T3 and hPDLSCs.
authors.affiliation: Department of Health, Government of Hong Kong SAR, Hong Kong, Special Administrative Region, People's Republic of China.
authors.forename: Eric Lk
authors.initials: EL
authors.lastname: Chan
authors.affiliation: Comprehensive Dental Care (Endodontics), Faculty of Dentistry, University of Hong Kong, Hong Kong Special Administrative Region of the People's Republic of China.
authors.forename: Chengfei
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Comprehensive Dental Care (Endodontics), Faculty of Dentistry, University of Hong Kong, Hong Kong Special Administrative Region of the People's Republic of China.
authors.forename: Gary Sp
authors.initials: GS
authors.lastname: Cheung
keywords: MTT; agar overlay; biocompatibility; hPDLSC; root canal irrigant