1041 Hardness And Microstructure Of Nickel-Titanium Endodontic Instruments

Friday, March 23, 2012: 3:30 p.m. - 4:45 p.m.
Presentation Type: Poster Session
E. NINAN1, A. ZAPF2, and D.W. BERZINS1, 1Marquette University, Milwaukee, WI, 2Dental Materials, Marquette University, Sussex, WI
Hardness is an important property of endodontic files as it influences cutting efficiency. Lately, companies have altered manufacturing and processing variables to introduce nickel-titanium (NiTi) files of different bending and torsion properties with the latest generation of files being characterized as “shape memory” or “controlled memory”.  This implies these files may have a different proportion of phases (austenite/martensite) compared to conventional superelastic NiTi files that are predominantly austenite at room and oral temperature.  As a result, they may possess a different hardness and microstructure.

Objective: The objective was to compare the hardness and microstructure of six NiTi files currently on the market.

Method: The NiTi endodontic files tested were ProFile & GTX (Dentsply Tulsa Dental Specialties), K3 & Twisted File (SybronEndo Corporation), CM wire (DS Dental), and HyFlex (Coltene-Whaledent). The latter two are considered “shape-memory” files.  Files from each brand (n=5/brand) were embedded in resin and underwent metallographic preparations to assess the hardness and microstructure. Vickers microhardness (VHN in kg/mm2) was measured and statistically analyzed by one way ANOVA and Tukey’s HSD test (α=0.05). Microstructure was examined with an optical microscope after etching.


Vickers microhardness values are shown below.



CM wire

255±10     a


264±11     ab

Twisted File

285±4       bc


297±6       cd


309±18     d


359±14     e

Different letters denote significant differences (p<0.05) between files. The “shape-memory” files possessed the lowest hardness values, whereas GTX was the hardest file tested. A martensitic lathe-like structure was a microstructural component in all files.  A slight variation in the proportion and size of the lathes was observed between brands, but this observation did not appear to correlate with microhardness results.


The new “shape memory” endodontic files have lower hardness values compared to superelastic NiTi files.

Keywords: Endodontics, Hardness and Metals