Comparison between Single-file Rotary Systems: Part 2-The Effect of Length of the Instrument Subjected to Cyclic Loading on Cyclic Fatigue Resistance.

INTRODUCTION: The aim of this study was to compare the cyclic fatigue resistance of XP Shaper (XP), HyFlex EDM One File (EDM), and WaveOne Gold Primary (WOG) when operated according to their manufacturers' recommendations at different lengths and to investigate the cyclic fatigue limit of XP Shaper when operated at 3000 rpm. METHODS: One hundred fifty instruments from 4 different rotary systems (F2 Protaper Universal [PTU], WOG, EDM, and XP) were tested for their cyclic fatigue resistance in a simulated 90° curved canal at a 37°C water bath temperature at 3 different working lengths (15 mm, 17 mm, and 19 mm). The time taken for instruments to fracture was recorded, and the number of cycles to failure was calculated. Statistical analyses were performed by using Levene's test, Kruskal-Wallis test to identify specific groups with statistically significantly higher cyclic fatigue resistance at 5% significance level. Weibull analysis was performed to determine the predictability of survival for each instrument. RESULTS: XP Shaper had the highest cyclic fatigue resistance compared with all other instruments, followed by EDM, WOG, and then PTU. There was no statistically significant difference in the number of cycles to failure between the XP operated at 3000 or 1000 rpm in any of the tested working lengths. There was a reduction in the number of cycles to failure when the working length increased from 15 to 19 mm in EDM, WOG, and PTU. Scanning electron microscopy showed ductile fractures with classic dimpled features in all samples. CONCLUSIONS: XP has a very high resistance to cyclic fatigue compared with WOG, EDM, and F2 PTU. The time to fracture will decrease by almost one third when XP is operated at 3000 rpm. The results of both parts of this study suggest that XP appears to be safe to operate at 3000 rpm in endodontic retreatment.

Comparison between Single-file Rotary Systems: Part 1-Efficiency, Effectiveness, and Adverse Effects in Endodontic Retreatment.

INTRODUCTION: The aim of this study was to evaluate in vitro the performance of 3 single-file systems: WaveOne Gold Primary (WOG; Dentsply Sirona, Ballaigues, Switzerland), Hyflex EDM "one file" (EDM; Coltene/Whaledent, Alstatten, Switzerland), and XP Shaper (XP; FKG, La Chaux de Fonds, Switzerland), for nonsurgical endodontic retreatment on mandibular anterior teeth in regard to the amount of remaining filling material inside the canal, debris extrusion, and operation time. METHODS: Sixty extracted standardized mandibular incisors presenting with a single oval canal were prepared to size 30.04 and obturated using warm vertical condensation. After 30 days (37°C, 100% humidity), teeth were randomly divided into 3 groups (n = 20) according to the file used for retreatment (WOG, EDM, or XP operated at 3000 rpm). During the retreatment procedures, preweighed vials were used to collect apically extruded debris, and the time required to remove the filling material was recorded in seconds. Cone-beam computed tomographic scans were taken before and after the retreatment to determine the amount of remaining filling material inside the root canal space. Statistical analysis was performed using the Kruskal-Wallis test, 1-way analysis of variance, and the Pearson test at a 5% significance level. RESULTS: There was a statistically significant difference among the groups regarding the instrumentation time (P < .05). XP was the fastest to remove gutta-percha from the canals (40.54 ± 28.03 seconds) followed by EDM (55.77 ± 19.76 seconds) and WOG (105.92 ± 53.92 seconds). The percentage of remaining filling was significantly greater for WOG (26.65% ± 14.63%) (P < .05). No difference was found between EDM (13.51% ± 9.53%) and XP (8.60% ± 7.28%). No difference was found regarding the amount of extruded debris among the 3 groups (P > .05). CONCLUSIONS: XP was the most efficient in gutta-percha removal from the canals when operated at a higher speed (3000 rpm) followed by EDM and WOG.