EEC no JOE oct 2011 - Torsional Resistance of Retreatment Instruments

Torsional Resistance of Retreatment Instruments    

H elio P. Lopes, LD,* Carlos N. Elias, PhD,† Gislaine A.F. Vedovello, DDS,‡ Carlos E.S. Bueno, PhD,‡ Marcelo Mangelli, PhD,§ and Jos e F. Siqueira, Jr, PhD*

Introduction: This study compared the torsional resis- tance of two brands of rotary nickel-titanium (NiTi) instru- ments indicated for endodontic retreatment. Methods: Mtwo retreatment instruments #15 and #25 (VDW, Mu- nich, Germany) and ProTaper Universal retreatment instruments D2 and D3 (Maillefer/Dentsply, Ballaigues, Switzerland) were subjected to a torsional assay in clock- wise rotation. The two parameters evaluated were maximum torque and angular deflection at failure. Frac- tured instruments had their fractured surfaces and helical shafts examined by scanning electron microscopy. Results: The results indicated that the angular deflection at fracture decreased in the following order: Mtwo retreatment file #15 > Mtwo retreatment file #25 > Pro- Taper Universal retreatment file D2 > ProTaper Universal retreatment file D3. As for the maximum torque values, the results revealed the following descending order: Pro- Taper Universal file D2 > Mtwo retreatment file #25 > ProTaper Universal file D3 > Mtwo retreatment file #15. Scanning electron microscopic analysis revealed that plastic deformation occurred along the helical shaft of the fractured instruments. Fractured surfaces were of the ductile type. Conclusions: The instruments tested showed different torsional behavior depending on the parameter evaluated. If one considers that high angular deflection values may serve as a safety factor, then the Mtwo retreatment instruments showed significantly better results. 

(J Endod 2011;37:1442–1445)

Key Words

Angular deflection, endodontic instruments, endodontic retreatment, maximum torque, torsional fracture 


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