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UBC Theses and Dissertations

Characterization of deformed or separated XP instruments after clinical retreatment of molar teeth - a multicenter experience Shabehpour, Kiarash


Objectives: The present study examined the defect characteristics of clinically used, discarded nickel titanium rotary retreatment instruments, and analyzed the impact of clinical use on their metallurgical properties. Materials and methods: 92 XP Endo Shaper (XPS; FKG Dentaire) and 20 XP Endo Finisher-R (XPFR; FKG Dentaire) instruments with structural deformation or separation were collected from four specialty endodontic offices over a 20-month period. The types of defects and their relative locations were recorded. The lateral and fractured surfaces of the separated instruments were examined with scanning electron microscopy. Differential scanning calorimetry was used to investigate the thermal behavior of new, as well as deformed and/or fractured instruments. Results: 77 (84%) XP Endo Shapers and 4 (20%) XP Endo Finisher-Rs had an area with structural deformation while 15 (16%) XP Endo Shapers and 16 (80%) XP Endo Finisher-Rs were fractured. All unfractured, deformed XP Endo Finisher-Rs showed unwinding close to the coronal end of the flute. Fractures in the XP Endo Shapers and XP Endo Finisher-Rs were often close to the coronal end of the flutes or the expanding segments of the instruments. Most of the XP Endo Shaper fractures were because of torsional failure (67%), while XP Endo Finisher-Rs failed predominantly by cyclic fatigue (81%). The austenite finishing temperature of XP Endo Finisher-R (40°C) was higher than that of XP Endo Shaper (35°C). Both XP Endo Shaper and XP Endo Finisher-R exhibited 2-stage phase transformation. Conclusion: Torsional failure was more prevalent in XP Endo Shaper instruments and fatigue failure was more prevalent in XP Endo Finisher-R instruments. Among the investigated instruments, XP Endo Finisher-Rs were more likely to separate without warning whereas XP Endo Shapers frequently exhibited plastic deformation. The latter may be used as a pre-separation forewarning sign during clinical retreatment. Clinical significance: The failure mode of XP Endo Shaper and XP Endo Finisher-R used clinically for retreatment, appeared to be different. Plastic deformation, the forewarning sign of instrument separation, occurs when XP Endo instruments are used for retreatment

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