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The purpose of this study was to evaluate the effect of preparation taper using size #20 or size #40 ProFile GT files on the ability to introduce irrigant and remove debris from root canals. Forty-eight bilaterally matched pairs of extracted teeth were instrumented using .04-. 06-. 08-, and .10-tapered files with one tooth of each pair enlarged to size #20 and the other to size #40. The teeth were sectioned at 1 mm and 3 mm from the apex, and the amount of remaining debris was calculated as a percentage of the total lumen area. The following variables were evaluated: apical preparation size, preparation taper, total volume of irrigation, depth of irrigation needle penetration, and number of instrument changes needed to reach working length. Compared with the size #40 preparations, a significantly greater percentage of remaining debris was observed in the size #20 preparations at the 1-mm level for all tapers except the .10 taper group in which there was no significant difference (p = 0.982). There were no significant differences between any groups at 3 mm. Results suggest that debris is more effectively removed using .04. 06, and .08 ProFile GT instruments when the apical preparation size is larger (size #40) compared with size #20 apical preparations. When a taper of .10 can be produced at the apical extent of the canal, there is no difference in debris removal between the two preparations sizes.