title: Fracture resistance of dental nickel-titanium rotary instruments with novel surface treatment: Thin film metallic glass coating.
abstract: OBJECTIVE
  Dental nickel-titanium (NiTi) rotary instruments are widely used in endodontic therapy because they are efficient with a higher success rate. However, an unpredictable fracture of instruments may happen due to the surface characteristics of imperfection (or irregularity). This study assessed whether a novel surface treatment could increase fatigue fracture resistance of dental NiTi rotary instruments.
  
  
  METHODS
  A 200- or 500-nm thick Ti-zirconium-boron (Ti-Zr-B) thin film metallic glass was deposited on ProTaper Universal F2 files using a physical vapor deposition process. The characteristics of coating were analyzed by scanning electron microscopy, transmission electron microscopy, and X-ray diffractometry. In cyclic fatigue tests, the files were performed in a simulated root canal (radius=5 mm, angulation=60°) under a rotating speed of 300rpm. The fatigue fractured cross sections of the files were analyzed with their fractographic performances through scanning electron microscopy images.
  
  
  RESULTS
  The amorphous structure of the Ti-Zr-B coating was confirmed by transmission electron microscopy and X-ray diffractometry. The surface of treated files presented smooth morphologies without grinding irregularity. For the 200- and 500-nm surface treatment groups, the coated files exhibited higher resistance of cyclic fatigue than untreated files. In fractographic analysis, treated files showed significantly larger crack-initiation zone; however, no significant differences in the areas of fatigue propagation and catastrophic fracture were found compared to untreated files.
  
  
  CONCLUSIONS
  The novel surface treatment of Ti-Zr-B thin film metallic glass on dental NiTi rotary files can effectively improve the fatigue fracture resistance by offering a smooth coated surface with amorphous microstructure.
authors: Graduate Institute of Clinical Dentistry, School of Dentistry, National Taiwan University, Taipei City, Taiwan; National Taiwan University Hospital Hsin-Chu Branch, College of Medicine, National Taiwan University, Hsin-Chu, Taiwan.
authors: Chih-Wen
authors: CW
authors: Chi
authors: Department of Materials Engineering, Ming Chi University of Technology, New Taipei City, Taiwan.
authors: Yu-Lun
authors: YL
authors: Deng
authors: Department of Materials Engineering, Ming Chi University of Technology, New Taipei City, Taiwan; Center for Thin Films Technologies and Applications, Ming Chi University of Technology, New Taipei, Taiwan; College of Engineering, Chang Gung University, Taoyuan, Taiwan. Electronic address: jefflee@mail.mcut.edu.tw.
authors: Jyh-Wei
authors: JW
authors: Lee
authors: Graduate Institute of Clinical Dentistry, School of Dentistry, National Taiwan University, Taipei City, Taiwan; National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan; School of Dentistry, China Medical University and China Medical University Hospital, Taichung, Taiwan. Electronic address: chunpinlin@gmail.com.
authors: Chun-Pin
authors: CP
authors: Lin
mesh_terms: D000497:Alloys; D001895:Boron / Q000008:administration & dosage; D003722:Dental Alloys / Q000627:therapeutic use*; D003762:Dental Instruments / Q000009:adverse effects*; D004868:Equipment Failure; D005898:Glass; D006801:Humans; D008422:Materials Testing; D018915:Root Canal Preparation / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D013499:Surface Properties; D014025:Titanium / Q000008:administration & dosage; D014082:Tooth Fractures / Q000209:etiology / Q000517:prevention & control*; D014131:Trace Elements / Q000008:administration & dosage; D015040:Zirconium / Q000008:administration & dosage
chemical_list: D000497:Alloys; D003722:Dental Alloys; D014131:Trace Elements; C013616:nitinol; D015040:Zirconium; D014025:Titanium; D001895:Boron
keywords: NiTi endodontic instrument; cyclic fatigue life; surface treatment; thin film metallic glass