In Vitro Study of the Torsional Properties of New and Used ProFile Nickel Titanium Rotary Files

Abstract

The purpose of this study was to investigate torque and angle of rotation at fracture of new and used .06 ProFile instruments. ProFile sizes 15 to 40 were tested according to American National Standards Institute/American Dental Association Specification #28. Thirty new and used instruments were tested for each size. An analysis of variance was used to compare the torque and angle of rotation at fracture between new and used instruments. The relationship between torque at fracture and size of instrument was determined with a regression analysis. The used instruments had significantly lower torque and angle of rotation at fracture values compared with the new instruments (p < 0.0001). A stronger relationship was found between the size of the instrument and the torque at fracture for the new instruments (p < 0.0001) than for the used ones (p < 0.0001). In conclusion, the repeated use of .06 ProFile instruments significantly reduced the torque and angle of rotation at fracture.Instrument separation is a serious concern in endodontic therapy. Several studies have evaluated the influence of various factors on the fracture of nickel titanium (NiTi) endodontic rotary instruments (1-6). It is important for the clinician to have detailed research information to provide a rational basis for instrument selection. According to American National Standards Institute/American Dental Association (ANSI/ADA) Specification #28, the torsional properties of endodontic instruments can be evaluated as torque and angle of rotation required to cause instrument fracture (7). Previous studies have investigated the torsional properties of NiTi endodontic rotary instruments (2, 8 -10).Flexural fatigue (1) is not the major cause of NiTi rotary instrument fracture (10 -13). Instruments can lock into the canal (3) and be subjected to high levels of torsional stress leading to fracture. On the other hand, Sattapan et al. (8) showed that torque at fracture was significantly higher than torque during instrumentation. In their study, each set of instruments was used to prepare only one canal. Questions have been raised about whether repeated use of NiTi rotary instruments adversely alters their torsional properties, thus rendering them more prone to torsional fracture. To date, the influence of repeated use of .06 ProFile instruments (PRI)(Tulsa Dentsply, Tulsa, OK) on the torsional properties has not been evaluated.This study compared torque and angle of rotation at fracture of new and used .06 ProFile instruments and investigated the relation between size of instrument and torque at fracture. MATERIALS AND METHODS Evaluation of New InstrumentsSizes 15 to 40 .06 PRI were evaluated. Thirty new instruments of each size were tested for resistance to fracture by twisting according to ANSI/ADA Specification #28 (7). Two parameters were measured: torque (gcm) and angle of rotation (degrees) at fracture in clockwise rotation. A digital torque meter memocouple (A-Tech Instruments, Scarborough, Ontario, Canada) measured torque with an accuracy of Ϯ1 gcm ...

Numerical Study on the Influence of Material Characteristics on Ni-Ti Endodontic Instrument Performance

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