Background: Various assays are used to evaluate the cytotoxic effect of chemicals on cultured cells. The sulforhodamine B (SRB) colorimetric assay is based on the ability of the SRB dye to bind basic amino acid residues on proteins. In contrast, the MTT (dimethylthiazol-diphenyltetrazolium bromide) colorimetric assay is based on mitochondrial uptake and succinate dehydrogenase reduction of soluble, yellow, MTT tetrazolium salt to an insoluble blue MTT formazan product. The aim of this study was to evaluate the cytotoxicity of a Thai herb by comparing MTT and SRB assay results. Methods: Mouse fibroblast (L929) cells were exposed to 0.01, 0.1, 0.25, and 0.5% (w/v) of a Thai herb in a 96-cluster well culture plate for 24 h. Cell viability after exposure to the Thai herb was determined by MTT and SRB assays in separate tissue culture plates. The two assays were compared using intra-class correlation coefficient (ICC) analysis. Results: There were no significant differences between the two cytotoxicity assays (p > 0.05). The ICC values showing the agreement of the two assays in the negative and positive control groups and Thai herb concentrations of 0.01, 0.1, 0.25, and 0.5% were 0.93 and 0.99 and 0.53, 0.51, 0.95, and 0.98, respectively. Conclusions: In general, the MTT and SRB assays performed similarly, exhibiting moderate to excellent correlation in the evaluation of the cytotoxicity of a Thai herb.

An evaluation of the accuracy of the "Root ZX" apex locator was conducted on 20 single-rooted teeth that had been extracted because of severe disease or orthodontic treatment. After the pulp chamber had been accessed and the tooth length determined using the Root ZX apparatus, the file was fixed to the tooth with light-cured composite resin. After extraction, the tooth was longitudinally ground with a diamond bur until the file was visible. The distance between the file tip and the apical foramen was measured under a microscope (x 100). The results showed that the tip of the instrument reached the apical foramen in all teeth.

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