Evaluation of the lengths and angles of the tips of rotatory files in root canal preparations

purpose: to detect changes in the angles and lengths of the tips of rotary nickel-titanium files after use. methods: forty human teeth were prepared with eight sets of rotary protaper？ universal nickel-titanium files with a length of 25 mm and rotation of 350 rpm. the files were evaluated in a scanning electron microscope (sem) at three different times: group a - before use; group b - after using each file in the preparation of three molars; and group c - after using each file in the preparation of five molars. the length of the tip was determined by measuring the length of a straight line drawn parallel to the file axis, from the apex of the tip to its posterior border. the sem software provided the angle measurements. data were analyzed by using paired t-tests and wilcoxon tests. results: there were no differences between the groups for the s1 file. there was a decrease in length when the f2 file was used to prepare three and five molars, whereas decreases in length were seen when f5 files were used to prepare three or five molars. conclusion: the results suggest that the tips of the rotary instruments showed significant changes in length and angle even with relatively low use.