Retrievability of Intracanal Separated Rotary NiTi Instruments Having Different Metallurgy: An In-Vitro Study

Aim: To evaluate the percentage change in mesial dentin thickness of mesiobuccal canal of mandibular ‎molars during retrieval of apically separated instruments, of different metallurgy, using ultrasonic technique. ‎Furthermore, to evaluate success rate and time in retrieval or bypass. ‎ Materials and methods: Forty-eight separated segments (#25/.06) of different rotary NiTi instruments were induced in ‎the apical third of mesiobuccal canals of mandibular molars with moderate curvature. Samples were divided ‎into three groups (n=16); Group A (AF F-ONE), Group B (ProTaper Next), and Group C (Revo-S SU). Either ‎Retrieval procedure was conducted using Ruddle's technique or bypass in non-retrieved samples. Percentage ‎change in Mesial dentin thickness was evaluated using CBCT at 3 and 6 mm length from the apex. Retrieval ‎Time was calculated. Intergroup comparison was performed using one-way ANOVA followed by Tukey’s post ‎hoc test and intragroup comparison was performed using paired t-test. Success rate was compared using ‎Fisher’s Exact test between groups. ‎ Results: At 3 mm level, a statistically significant difference was recorded in mean mesial dentin thickness ‎percentage change between all groups. At 6 mm; there was no statistically significant difference between ‎groups A and C, while group B was statistically significant compared with groups A and C. There was no ‎statistically significant difference in success rate nor retrieval time between groups. Bypass was only ‎successful in group A (75%).‎ Conclusion: Metallurgy and design of NiTi rotary instruments affect percentage change in mesial dentin ‎thickness.‎