An in vitro comparison of torsional stress properties of three different rotary nickel-titanium files with a similar cross-sectional design.
BACKGROUND
The purpose of this study was to compare the in vitro torsional stress characteristics of Twisted Files (TFs; SybronEndo, Orange, CA) with 2 milled files of a similar cross-section: EndoSequence (Brasseler USA, Savannah, GA) and ProFile Vortex (DENTSPLY Tulsa Dental, Tulsa, OK).


METHODS
File sizes of 25/.06 and 30/.06 from the 3 file types were compared (n = 20/group). Torsional stress resistance was evaluated by measuring the torque in grams per centimeters and the angle of rotation (°) required for instrument separation with the use of a torsiometer instrument. The fractured files were examined using a scanning electron microscope to look at deformation and fracture surface characteristics. The data were analyzed with analysis of variance to determine statistical differences.


RESULTS
The 3 file types showed a statistically significant difference in both the maximum torsional stress and the angle of rotation before failure. TFs displayed the least amount of torsional stress resistance and the highest angle of rotation. The 30/.06 size files of all 3 types withstood more torsional stress than the size 25/06 files of the same type. Within each file design, there was not a statistically significant difference in angular rotation between the 25/.06 and 30/.06 groups. The scanning electron microscopic analysis of all 3 file types revealed dimpling near the center of rotation on the fractured surface indicative of torsional stress.


CONCLUSIONS
The novel techniques used in manufacturing TFs do not make them more resistant to torsional stress as compared with milled nickel-titanium endodontic files of a similar cross-sectional design.
Department of Surgical Sciences-Endodontics, Marquette University School of Dentistry, 1801 West Wisconsin Avenue, Milwaukee, WI 53233, USA. reid.wycoff@marquette.edu
Reid C
RC
Wycoff
David W
DW
Berzins
D003722:Dental Alloys / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D009532:Nickel / Q000737:chemistry*; D018915:Root Canal Preparation / Q000295:instrumentation*; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*; D019415:Torque; D054159:Torsion, Mechanical
D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium