title: Stress distribution of three NiTi rotary files under bending and torsional conditions using a mathematic analysis.
abstract: OBJECTIVE
  To compare and evaluate the stress distribution of three NiTi instruments of various cross-sectional configurations under bending or torsional condition using a finite-element analysis model.
  
  
  METHODS
  Three NiTi files (ProFile, ProTaper and ProTaper Universal) were scanned using Micro-CT to produce a three-dimensional digital model. The behaviour of the instrument under bending or torsional loads was analysed mathematically in software (ABAQUS V6.5-1), taking into consideration the nonlinear mechanical characteristic of NiTi material.
  
  
  RESULTS
  ProFile showed the greatest flexibility, followed by ProTaper Universal and ProTaper. The highest stress was observed at the surface near the cutting edge and the base of (opposing) flutes during cantilever bending. Concentration of stresses was observed at the bottom of the flutes in ProFile and ProTaper Universal instruments in torsion. The stress was more evenly distributed over the surface of ProTaper initially, which then concentrated at the middle of the convex sides when the amount of angular deflection was increased.
  
  
  CONCLUSIONS
  Incorporating a U-shaped groove in the middle of each side of the convex-triangular design lowers the flexural rigidity of the origin ProTaper design. Bending leads to the highest surface stress at or near the cutting edge of the instrument. Stress concentration occurs at the bottom of the flute when the instrument is subjected to torsion.
authors.affiliation: Department of Conservative Dentistry, School of Dentistry, Pusan National University, Busan, Korea.
authors.forename: T O
authors.initials: TO
authors.lastname: Kim
authors.forename: G S P
authors.initials: GS
authors.lastname: Cheung
authors.forename: J M
authors.initials: JM
authors.lastname: Lee
authors.forename: B M
authors.initials: BM
authors.lastname: Kim
authors.forename: B
authors.initials: B
authors.lastname: Hur
authors.forename: H C
authors.initials: HC
authors.lastname: Kim
mesh_terms: D003722:Dental Alloys / Q000737:chemistry*; D055119:Elastic Modulus; D004548:Elasticity; D004867:Equipment Design; D020342:Finite Element Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional; D008422:Materials Testing; D008962:Models, Theoretical; D009532:Nickel / Q000737:chemistry*; D017711:Nonlinear Dynamics; D018583:Pliability; D018915:Root Canal Preparation / Q000295:instrumentation*; D012984:Software; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*; D054159:Torsion, Mechanical
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; C093824:Martensite; C093826:Austenite; D009532:Nickel; D014025:Titanium