title: SEM observations of nickel-titanium rotary endodontic instruments that fractured during clinical Use.
abstract: Numerous discarded ProFile GT, ProFile, and ProTaper nickel-titanium rotary instruments obtained from two graduate endodontic clinics were examined by scanning electron microscopy. These instruments had an unknown history of clinical use and had fractured or experienced considerable permanent torsional deformation without complete separation. The failure processes generally exhibited substantial ductile character, evidenced by a dimpled rupture fracture surface. Crack propagation at grain boundaries and cleavage surfaces indicative of transgranular fracture were observed for some specimens. It appeared that oxide particles from the manufacturing process served as nucleating sites for the microvoids, leading to dimpled rupture. A previously unreported fracture mode also was observed, in which crack propagation, approximately parallel to the local flute orientation, connected pitted regions on the surface. Combining present and previous scanning electron microscopy observations of clinically failed instruments, suggestions are offered for improving their fracture resistance.
authors.affiliation: Section of Oral Biology, College of Dentistry, The Ohio State University, Columbus, OH 43218-2357, USA.
authors.forename: Satish B
authors.initials: SB
authors.lastname: Alapati
authors.forename: William A
authors.initials: WA
authors.lastname: Brantley
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Svec
authors.forename: John M
authors.initials: JM
authors.lastname: Powers
authors.forename: John M
authors.initials: JM
authors.lastname: Nusstein
authors.forename: Glenn S
authors.initials: GS
authors.lastname: Daehn
mesh_terms: D003722:Dental Alloys; D003762:Dental Instruments; D003799:Dental Stress Analysis; D004548:Elasticity; D004868:Equipment Failure; D019544:Equipment Failure Analysis; D008855:Microscopy, Electron, Scanning; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation*; D013499:Surface Properties; D014025:Titanium
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium