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Failure mechanism of ProTaper Ni–Ti rotary instruments during clinical use: fractographic analysis
Author(s) -
SpanakiVoreadi A. P.,
Kerezoudis N. P.,
Zinelis S.
Publication year - 2006
Publication title -
international endodontic journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.988
H-Index - 119
eISSN - 1365-2591
pISSN - 0143-2885
DOI - 10.1111/j.1365-2591.2006.01065.x
Subject(s) - dimple , materials science , fracture (geology) , deformation (meteorology) , failure mechanism , composite material
Aim To evaluate the failure mechanism of ProTaper Ni–Ti rotary instruments fractured under clinical conditions. Methodology A total of 46 ProTaper instruments that failed (fractured and/or plastically deformed) during the clinical use were collected from various dental clinics, whereas a new set of ProTaper instruments served as control. After inspection under stereomicroscopy the instruments were classified into three categories: (i) plastically deformed but not fractured, (ii) fractured with plastic deformation and (iii) fractured without plastic deformation. Three instruments from each group were analysed with computerized X‐ray microtomography (micro‐XCT) to detect surface and internal defects, whilst all the fracture surfaces were investigated under SEM. Results Stereomicroscopic inspection showed that 17.4% of the discarded instruments were only plastically deformed, 8.7% were fractured with plastic deformation and 73.9% were fractured without plastic deformation. Micro‐XCT revealed instruments without any surface or bulk defects along with a few files with crack development below the fracture surface. No defects were identified in the unused instruments. SEM examination of fractured surfaces demonstrated the presence of dimples and cones, a typical pattern of dimple rupture developed because of ductile failure. Conclusions The results suggest that a single overloading event causing ductile fracture of ProTaper instruments is the most common fracture mechanism encountered under the clinical conditions.