Files of Greater Taper (GT) are rotary nickel-titanium files of three tapers (0.06, 0.08, 0.10) with file tips of sizes 20, 30, and 40. The purpose of this study was to compare in an in situ model the efficacy of root canal debridement in the apical 3 mm when instrumenting to a GT size 20 or a GT size 40 at working length. Twenty matched human cadaver teeth with 32 canals were decoronated at the cementoenamel junction and instrumented with rotary Files of GT to either GT size 20 or GT size 40. Sodium hypochlorite, EDTA, and RC Prep were chemical aids for debridement. The teeth were extracted; decalcified; sectioned at 0.5 mm, 1.5 mm, and 2.5 mm from the apex; and prepared for histologic examination and quantification of remaining debris. No differences were found between each level within each apex size group; however, the GT size 20 group left significantly more debris in the apical third compared with the GT size 40 group. A regression analysis showed that the apical third cleanliness could be predicted mainly by instrument size and to a lesser extent by the canal length. Irrigant volume, number of instrument changes, and depth of penetration of irrigation needle were not likely to explain differences in debridement.
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