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Characterization of New Rotary Endodontic Instruments Fabricated from Special Thermomechanically Processed NiTi Wire

Liu, Jie
http://rave.ohiolink.edu/etdc/view?acc_num=osu1244643081

Abstract Details

2009, Doctor of Philosophy, Ohio State University, Oral Biology.
Although NiTi rotary instruments are very popular for endodontic treatment, instrument separation is still a challenge in clinic. A new NiTi rotary instrument has recently been marketed that is machined from M-Wire that has been subjected to a proprietary novel thermomechanical processing procedure. The manufacturer has claimed that this new M-Wire instrument has considerably improved flexibility and resistance to cyclic fatigue, compared to conventional rotary instruments that are machined from superelastic (SE) austenitic NiTi wire. Clinical use has confirmed that these new M-Wire rotary instruments have outstanding clinical fatigue resistance. However, the mechanism for the improved clinical performance of these instruments is unknown.The objective of this study was to employ a variety of metallurgical laboratory techniques to determine the origin of these improved mechanical properties for the new rotary instruments. Specimens from as-received M-Wire instruments, clinically used M-Wire instruments, and conventional instruments were prepared for evaluation. The temperature range for phase transformation was examined by differential scanning calorimetry (DSC). Vickers hardness measurements were made since hardness variations for the same type of alloy has been found to correlate with variations in mechanical properties. The microstructures of the NiTi alloys were revealed by acid etching and examined with an optical microscope and a scanning electron microscope. Wear resistance of clinically used M-Wire instruments was investigated by examining their surfaces with an SEM. In a complementary study, bright-field images of M-Wire blanks were obtained by scanning transmission electron microscopy (STEM).DSC study showed that M-Wire instruments have much higher Af (austenite-finish) temperatures (over 40°C) than conventional superelastic rotary instruments (below room temperature), and are a mixture of martensite, R-phase and austenite at room temperature. The Vickers hardness of M-Wire instruments is significantly higher than that of conventional rotary NiTi instruments. Mean Vickers hardness number for the tip, intermediate region and shank region of size 30/.04 taper M-Wire instruments were about 374, 380 and 392 each.Better wear resistance was observed with the SEM on clinically used M-Wire instruments, which presented less microcracks and evidence of permanent deformation on the surface compared with surfaces of clinically used conventional NiTi instruments. This improved wear resistance is attributed to increased hardness for surface region of the M-Wire instrument. Acid-etched M-Wire instruments presented a classical lenticular martensite structure when observed with the optical microscope and SEM. EDS analyses of the microstructures of the M-Wire instruments revealed titanium-rich precipitates. STEM examinations of M-Wire blanks revealed much coarser grains, twinning, and a high density of dislocations, which were not observed in starting superelastic NiTi wire blanks for conventional instruments.In summary, increased hardness was found for M-Wire instruments, compared with conventional superelastic NiTi rotary instruments, which served as a control for this study. The STEM observations show that the improved mechanical properties of the starting M-Wire (and the rotary instruments manufactured from this special NiTi wire) arise from strengthening mechanisms in the martensitic structure, which were induced by extensive thermomechanical processing.
William Brantley (Advisor)
William Johnston (Committee Member)
Sarandeep Huja (Committee Member)
John Nusstein (Committee Member)
Dental Care; Materials Science
NiTi rotary instruments; M-Wire instrument; thermomechanical processing procedure; microstructure; phase transformation; DSC; Vickers Hardness measurement; SEM; STEM; twinning microstructure; wear resistance

Recommended Citations

Citations

  • Liu, J. (2009). Characterization of New Rotary Endodontic Instruments Fabricated from Special Thermomechanically Processed NiTi Wire [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1244643081

    APA Style (7th edition)

  • Liu, Jie. Characterization of New Rotary Endodontic Instruments Fabricated from Special Thermomechanically Processed NiTi Wire. 2009. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1244643081.

    MLA Style (8th edition)

  • Liu, Jie. "Characterization of New Rotary Endodontic Instruments Fabricated from Special Thermomechanically Processed NiTi Wire." Doctoral dissertation, Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1244643081

    Chicago Manual of Style (17th edition)

osu1244643081
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© 2009, some rights reserved.Creative Commons License Characterization of New Rotary Endodontic Instruments Fabricated from Special Thermomechanically Processed NiTi Wire by Jie Liu is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by The Ohio State University and OhioLINK.