E Kosti1, S Zinelis, I Molyvdas, T Lambrianidis. 1. Department of Endodontics, School of Dentistry, University of Thessaloniki, Thessaloniki, Greece. elkosti@dent.auth.gr
Abstract
AIM: To investigate the effect of root canal curvature on the failure incidence and fracture mechanism of ProFile rotary Ni-Ti endodontic instruments. METHODOLOGY: Three hundred mesial root canals of mandibular molars were instrumented using the ProFile system in a crown-down technique up to size 25 0.06 taper. Root canals were classified according to the angle and radius of curvature to: straight (group A: 0 + 10°, radius 0 mm), moderately curved (group B: 30 ± 10°, radius 2 ± 1 mm) and severely curved (group C: 60 ± 10°, radius 2 ± 1 mm). After each use, instruments were cleaned ultrasonically and autoclaved. Instruments that prepared 20 root canals, fractured or were plastically deformed without fracture were retrieved and substituted. Kaplan-Meier estimator was used for survival analysis and post hoc test for determination of significant differences (a=0.05). All fractured instruments were subjected to fractographic analysis under SEM, and all used instruments were viewed under the metallographic microscope. RESULTS: Regardless of the size of instrument, fracture and overall failure were significantly more frequent (P<0.05) in group C. SEM examination of the fracture surfaces revealed mainly the characteristic pattern of ductile failure, whereas examination under the metallographic microscope revealed no sign of cracks. CONCLUSIONS: The abruptness of root canal curvature negatively affected the failure rate of ProFile rotary Ni-Ti instruments. The fractographic results confirmed that failure of Ni-Ti files was caused by a single overload during chemomechanical preparation.
AIM: To investigate the effect of root canal curvature on the failure incidence and fracture mechanism of ProFile rotary Ni-Ti endodontic instruments. METHODOLOGY: Three hundred mesial root canals of mandibular molars were instrumented using the ProFile system in a crown-down technique up to size 25 0.06 taper. Root canals were classified according to the angle and radius of curvature to: straight (group A: 0 + 10°, radius 0 mm), moderately curved (group B: 30 ± 10°, radius 2 ± 1 mm) and severely curved (group C: 60 ± 10°, radius 2 ± 1 mm). After each use, instruments were cleaned ultrasonically and autoclaved. Instruments that prepared 20 root canals, fractured or were plastically deformed without fracture were retrieved and substituted. Kaplan-Meier estimator was used for survival analysis and post hoc test for determination of significant differences (a=0.05). All fractured instruments were subjected to fractographic analysis under SEM, and all used instruments were viewed under the metallographic microscope. RESULTS: Regardless of the size of instrument, fracture and overall failure were significantly more frequent (P<0.05) in group C. SEM examination of the fracture surfaces revealed mainly the characteristic pattern of ductile failure, whereas examination under the metallographic microscope revealed no sign of cracks. CONCLUSIONS: The abruptness of root canal curvature negatively affected the failure rate of ProFile rotary Ni-Ti instruments. The fractographic results confirmed that failure of Ni-Ti files was caused by a single overload during chemomechanical preparation.
Authors: Arash Azizi; Carlo Prati; Riccardo Schiavon; Raquel Michelle Fitzgibbon; Chiara Pirani; Francesco Iacono; Gian Andrea Pelliccioni; Andrea Spinelli; Fausto Zamparini; Pietro Puddu; Giovanni Bolelli; Luigi Generali Journal: Eur Endod J Date: 2021-03-23