The purpose of the present study was to investigate and compare the effect of different reciprocating movements and angles on the shaping ability of the WaveOne and the single-fle ProTaper F2 using cone beam computed tomography (CBCT). The mesiobuccal canals of 40 extracted maxillary molars, with curvatures of 20 to 45° were coded and randomly divided into 4 equal experimental groups according to the instrument used (ProTaper F2 fle and Wa-veOne) and the reciprocation range, for both instruments, a 150° angle was used for cutting and a 30° angle was used for release. Group 1 - WaveOne primary 150° CCW rotation angle and 30° CW rotation angle; Group 2 - WaveOne 90° CCW rotation angle and 30° CW rotation angle; Group 3 - ProTaper F2 150° CW rotation angle and 30° CCW rotation angle; Group 4 - ProTaper F2 90° CW rotation angle and 30° CCW rotation angle. Canals were scanned before and after preparation using CBCT to evaluate the volumetric change, canal transportation and the canal centering ability at 2.6, 5.2 and 7.8 mm from the apex. The mean ± standard deviation (SD) values were analyzed, and the significance level was set at p ≤ 0.05. There was no significant difference in the amount of dentin removed among the experimental groups, except that WaveOne 150°CCW 30°CW significantly showed the least volume of dentin removed (0.40 ± 0.9) at 7.8 mm. All rotary systems tested in the different groups resulted in canal transportation in different directions at all examined levels. WaveOne 150°CCW 30°CW, demonstrated the lowest mean value of root canal transportation in both the mesial and furcal directions and in both the coronal and apical directions compared to the other groups. At the 7.8 level, WaveOne 150°CCW 30°CW yielded the highest mean centering ratio, whereas ProTaper F2 CW 150° CCW 30° yielded the lowest, statistically significant at p ≤ 0.05. The results of the present study demonstrated that differences among various reciprocating motions and angles could affect the shaping ability of a single-fle Nickel-titanium (NiTi) instrument.

The multiple uses of HyFlex® controlled memory (CM) rotary instruments (Coltene-Whaledent, Allstetten, Switzerland) have been recommended after sterilization. The purpose of this study was to analyze the surface defects on HyFlex® instruments after use and to determine their ability to return to their original shape after autoclaving. Twenty-four new HyFlex® files were scanned using micro-computed tomography before the initial use, after use until defects were visible and after autoclaving. Surface analysis was performed on each file to determine the changes in the files after deformation; defects were recorded as unwinding and curving. These changes were categorized according to the severity, and the initial and final scans of the files were superimposed to illustrate the recovery of the files to their original shape. The data were analyzed using Chi-square and t-test. The t-test of Student’s Newman–Keuls revealed a significant difference (P < 0.05) between unused and used files, almost all files exhibited visible defects without fractures, including unwinding and curving associated with unwinding. The most frequently observed defect was unwinding of the spirals (100%), whereas curving associated with unwinding was infrequently observed. A Chi-square test showed that the deformation (curve: P = 0.000, and unwinding: P = 0.011, incidence depended on the size of the files. The greatest frequency of curving occurred in the small files #20/0.04 and #20/0.06, the difference was statistically significant from all file sizes (P < 0.05). The majority of the files (79%) were able to restore the unwinding and regain their original shape after autoclaving. The highest rate of unrestored files was observed on #20/0.04 and #20/0.06 instruments, and the difference was statistically significant from all file sizes (P < 0.05). HyFlex® CM nickel-titanium files appear to regain their original shape after sterilization.