title: Structural analysis of HyFlex EDM instruments.
abstract: OBJECTIVE
  To compare the phase transformation behaviour, the microstructure, the nano-hardness and the surface chemistry of electro-discharge machined HyFlex EDM instruments with conventionally manufactured HyFlex CM.
  
  
  METHODS
  New and laboratory used HyFlex EDM were examined by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Nano-hardness and modulus of elasticity were also investigated using a maximum load of 20 mN with a minimum of 40 significant indentations for each sample. Raman spectroscopy and field emission-scanning electron microscope (FE-SEM) were used to assess the surface chemistry of HyFlex EDM. HyFlex CM were subjected to the same investigations and used as a comparison. Nano-indentation data were statistically analysed using the Student's t-test.
  
  
  RESULTS
  XRD analysis on HyFlex EDM revealed the presence of martensite and rhombohedral R-phase, while a mixture of martensite and austenite structure was identified in HyFlex CM. DSC analysis also disclosed higher austenite finish (Af) temperatures for electro-discharge machining (EDM) instruments. Significant differences in nano-hardness and modulus of elasticity were found between EDM and CM files (P < 0.05). FE-SEM and EDS analyses confirmed that both new EDM and CM files were covered by an oxide layer. Micro-Raman spectroscopy assessed the presence of rutile-TiO2.
  
  
  CONCLUSIONS
  HyFlex EDM revealed peculiar structural properties, such as increased phase transformation temperatures and hardness. Present results corroborated previous findings and shed light on the enhanced mechanical behaviour of these instruments.
authors: Endodontic Clinical Section, Department of Biomedical and Neuromotor Sciences (DIBINEM), University of Bologna, Bologna, Italy.
authors: F
authors: F
authors: Iacono
authors: Endodontic Clinical Section, Department of Biomedical and Neuromotor Sciences (DIBINEM), University of Bologna, Bologna, Italy.
authors: C
authors: C
authors: Pirani
authors: Endodontic Section, Department of Surgery, Medicine, Dentistry and Morphological Sciences with Transplant Surgery, Oncology and Regenerative Medicine Relevance (CHIMOMO), School of Dentistry, University of Modena and Reggio Emilia, Modena, Italy.
authors: L
authors: L
authors: Generali
authors: Department of Engineering "Enzo Ferrari" (DIEF), University of Modena and Reggio Emilia, Modena, Italy.
authors: G
authors: G
authors: Bolelli
authors: Department of Engineering "Enzo Ferrari" (DIEF), University of Modena and Reggio Emilia, Modena, Italy.
authors: P
authors: P
authors: Sassatelli
authors: Department of Engineering "Enzo Ferrari" (DIEF), University of Modena and Reggio Emilia, Modena, Italy.
authors: L
authors: L
authors: Lusvarghi
authors: Endodontic Clinical Section, Department of Biomedical and Neuromotor Sciences (DIBINEM), University of Bologna, Bologna, Italy.
authors: M G
authors: MG
authors: Gandolfi
authors: Department of Industrial Chemistry "Toso Montanari" and INSTM UdR-Bologna, University of Bologna, Bologna, Italy.
authors: L
authors: L
authors: Giorgini
authors: Endodontic Clinical Section, Department of Biomedical and Neuromotor Sciences (DIBINEM), University of Bologna, Bologna, Italy.
authors: C
authors: C
authors: Prati
mesh_terms: D002152:Calorimetry, Differential Scanning; D003722:Dental Alloys / Q000737:chemistry; D003762:Dental Instruments; D004548:Elasticity; D006244:Hardness; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
keywords: CM wire; NiTi endodontic instruments; differential scanning calorimetry; electro-discharge machining; metallurgical properties; microstructure