title: Cyclic fatigue resistance of ProTaper Universal instruments when subjected to static and dynamic tests.
abstract: OBJECTIVE
  This study evaluated the number of cycles to fracture of ProTaper Universal S2 instruments when subjected to static and dynamic cyclic fatigue tests.
  
  
  METHODS
  ProTaper Universal S2 instruments were used until fracture in an artificial curved canal under rotational speed of 300 rpm in either a static or a dynamic test model. Afterward, the length of the fractured segments was measured and fractured surfaces and helical shafts analyzed by scanning electron microscopy (SEM).
  
  
  RESULTS
  The number of cycles to fracture was significantly increased when instruments were tested in the dynamic model (P<.001). Instrument separation occurred at the point of maximum flexure within the artificial canals, i.e., the midpoint of the curved canal segment. SEM analysis revealed that fractured surfaces exhibited characteristics of the ductile mode. Plastic deformation was not observed in the helical shaft of fractured instruments.
  
  
  CONCLUSIONS
  The number of cycles to fracture ProTaper Universal S2 instruments significantly increased with the use of instruments in a dynamic cyclic fatigue test compared with a static model. These findings reinforce the need for performing continuous pecking motions during rotary instrumentation of curved root canals.
authors: Department of Endodontics, Faculty of Dentistry, Estácio de Sá University, Rio de Janeiro, Brazil.
authors: Hélio P
authors: HP
authors: Lopes
authors: Izabelle M O
authors: IM
authors: Britto
authors: Carlos N
authors: CN
authors: Elias
authors: Julio C
authors: JC
authors: Machado de Oliveira
authors: Mônica A S
authors: MA
authors: Neves
authors: Edson J L
authors: EJ
authors: Moreira
authors: José F
authors: JF
authors: Siqueira
mesh_terms: D003722:Dental Alloys; D003754:Dental High-Speed Equipment; D003762:Dental Instruments; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D004868:Equipment Failure; D006801:Humans; D008422:Materials Testing; D018915:Root Canal Preparation / Q000295:instrumentation*
chemical_list: D003722:Dental Alloys