title: Geometric optimization for development of glide path preparation nickel-titanium rotary instrument.
abstract: BACKGROUND
  This study was done to develop a glide path preparation nickel-titanium rotary instrument by size optimization procedures and evaluate the properties of the prototype.
  
  
  METHODS
  G-1 and G-2 files were tested for cyclic fatigue, torsional resistance, and screw-in force. The cyclic fatigue resistance was compared by measuring the number of cycles to failure by using a 90° curved metal canal (n = 10). The torsional resistance was evaluated at 3 levels (2, 4, and 6 mm from the file tip) by measuring the ultimate torsional load (n = 10 each level). The screw-in forces (n = 5) were measured during sequential pecking in a simulated resin block to the end of foramen by using the customized shaping device (AEndoS). Meanwhile, finite element models of G-1 and G-2 files were made by reverse engineering, and their bending stiffness and torsional properties were calculated. By analyzing the results from mechanical tests and finite element analysis, a universal G (uG) file was designed to have intermediary mechanical properties, and then the prototype was fabricated by the manufacturer. Cyclic fatigue and torsional resistance tests and screw-in force with the uG were compared with G-1 and G-2 files.
  
  
  RESULTS
  The prototype of uG file showed higher cyclic fatigue resistance than the G-2 file and intermediary torsional strength and screw-in forces between the G-1 and G-2 files.
  
  
  CONCLUSIONS
  The prototype production from a size optimization procedure produced appropriate mechanical properties for the purpose of development.
authors.affiliation: Department of Conservative Dentistry, School of Dentistry, Kyungpook National University, Daegu, Korea.
authors.forename: Jung-Hong
authors.initials: JH
authors.lastname: Ha
authors.affiliation: Dongnam Regional Division, Korea Institute of Industrial Technology, Jinju, Korea.
authors.forename: Chan-Joo
authors.initials: CJ
authors.lastname: Lee
authors.affiliation: Department of Conservative Dentistry, School of Dentistry, Dental Research Institute, Pusan National University, Yangsan, Korea.
authors.forename: Sang-Won
authors.initials: SW
authors.lastname: Kwak
authors.affiliation: Endodontic Unit, Dental Services, Dubai Health Authority, Dubai, United Arab Emirates.
authors.forename: Rashid
authors.initials: R
authors.lastname: El Abed
authors.affiliation: Department of Conservative Dentistry, School of Dentistry, Dental Research Institute, Pusan National University, Yangsan, Korea.
authors.forename: Dongseok
authors.initials: D
authors.lastname: Ha
authors.affiliation: Department of Conservative Dentistry, School of Dentistry, Dental Research Institute, Pusan National University, Yangsan, Korea. Electronic address: golddent@pusan.ac.kr.
authors.forename: Hyeon-Cheol
authors.initials: HC
authors.lastname: Kim
mesh_terms: D003722:Dental Alloys; D003799:Dental Stress Analysis / Q000379:methods*; D020342:Finite Element Analysis; D006801:Humans; D008422:Materials Testing; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation*; D013314:Stress, Mechanical; D014025:Titanium; D054159:Torsion, Mechanical
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
keywords: Cyclic fatigue; G file; glide path; nickel-titanium rotary file; screw-in effect; torsional resistance