Cytotoxicity of a novel nano-silver particle endodontic irrigant.

PURPOSE: 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. MATERIALS AND 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. CONCLUSION: Our results showed that the nano-silver irrigant was non-cytotoxic to both NIH 3T3 and hPDLSCs.

Cyclic fatigue resistance tests of Nickel-Titanium rotary files using simulated canal and weight loading conditions.

OBJECTIVES: This study compared the cyclic fatigue resistance of nickel-titanium (NiTi) files obtained in a conventional test using a simulated canal with a newly developed method that allows the application of constant fatigue load conditions. MATERIALS AND METHODS: ProFile and K3 files of #25/.06, #30/.06, and #40/.04 were selected. Two types of testing devices were built to test their fatigue performance. The first (conventional) device prescribed curvature inside a simulated canal (C-test), the second new device exerted a constant load (L-test) whilst allowing any resulting curvature. Ten new instruments of each size and brand were tested with each device. The files were rotated until fracture and the number of cycles to failure (NCF) was determined. The NCF were subjected to one-way ANOVA and Duncan's post-hoc test for each method. Spearman's rank correlation coefficient was computed to examine any association between methods. RESULTS: Spearman's rank correlation coefficient (ρ = -0.905) showed a significant negative correlation between methods. Groups with significant difference after the L-test divided into 4 clusters, whilst the C-test gave just 2 clusters. From the L-test, considering the negative correlation of NCF, K3 gave a significantly lower fatigue resistance than ProFile as in the C-test. K3 #30/.06 showed a lower fatigue resistance than K3 #25/.06, which was not found by the C-test. Variation in fatigue test methodology resulted in different cyclic fatigue resistance rankings for various NiTi files. CONCLUSIONS: The new methodology standardized the load during fatigue testing, allowing determination fatigue behavior under constant load conditions.

Study of the progressive changes in canal shape after using different instruments by hand in simulated S-shaped canals.

This study analyzed the progressive changes in canal shape after the use of different instruments by hand in simulated S-shaped canals. Forty simulated canals with double curvatures, 30 degrees coronally and 20 degrees apically, were randomly divided into four groups and prepared with stainless steel K-files, the ProTaper for hand use (PHU) system, NiTi K-files, and the combination of PHU and NiTi K-files, respectively, by hand. All canals were scanned pre-and postoperatively. Each postinstrumentation image was superimposed with the preoperative one in a computer. The amount of material removed after every instrument was measured at 14 points. Statistical analysis was performed using an analysis of variance (ANOVA) test at alpha=0.05. All four instruments straightened the S-shaped canals, except the combination of PHU (S1, Sx, and S2) and NiTi K-files, which created a continuous funnel shape. There was a significant difference in the amount of material removed between S2 and F1 of the PHU system (p<0.05), and the finishing files of PHU created the same transportation as the stainless steel instruments with the same tip size (p>0.05).